WEB DIRECTORY - see page ELECTRONICS WORLD · 2020. 5. 3. · Recruitment ads start on page 1 70 9 I I 77095 83304. 1 ... 8920A R/F Comms Test (various options) 8922 BGH G.S.M. Test

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Contents

91 COMMENTCopyright, and the right to copy

93 NEWS EMP bullet detects land mines C&W pips BT in broadband race £7m for extreme-uv litho UK flat panels for video Java chips Morphing dashboard Euro dumping damage

98 PLDS/LOGIC ANALYSERIn -system programmable devices and freesoftware have made plds cheap - providedyou have a pc. To illustrate their power,Colin Attenborough describes a five -chiplogic analyser using the simplest pld.

107 LETTERS50W from a 3.6W mains adaptor?Students' lotsDigital audio far from perfectHave you seen a microwave fuse?Wideband fet amplifierWindows commentary

109 HANDS ON INTERNETCyril Batemen reveals three clearinghouses for data sheets and application notes- all accessible via the net, free of charge.And there's design information for thoseinterested in temperature measurement.

Elle Ede View fie peekewes irks gplione Diectocy WidowNab

("naves:lion and radiation lout loss from a printed

rr

circuit board

In last nute't came a method for calculating the theme] conductrety of a puntedwatt hoed (PCB) wet deschhed Now. we look a, mare comphcaled heat hamletprocess, namely the loss of heat h ont the surface of a PCB to the athlete an Thusituation u mare challenge -4 to thumb° mathemahcally moo U involves thesimultaneous processes of heal spreading by conduction and heat extraction over thesurf ace of the board by convection and radiation The fight. below Illustrates thehoe flow patrons for a leadhame package attached to a test PCB. The effmency ofheat It auto ft ore the PCB to air has a significant effect onto temperaturedifference between the chap and the no

!regionIl

tip.l Neel* eattensfera Waken .9.

How can the Internet help you solve yourthermal management problems? Find out onpage 109.

113 NEW LOGICDavid Warren -Smith's rethink of Booleanalgebra fills in the gaps, making it evenmore useful to digital designers.

120 CIRCUIT IDEAS Chopper -stabilised bridge amplifier Set/reset and bistable flip-flops Simple linear sawtooth Lf signal rectifier Medium -power inverting driver Capacitance bridge

127 400HZ 1KW INVERTERPaul Bennett's three-phase power inverteruses high -frequency switching to avoid thebulky, expensive inductive components.

133 KNOW NOISEJoe Carr looks at noise from the viewpointof the receiver designer.

138 SUPER-REGEN ORSUPER -REPLACEMENT?Performance in a receiver usually goeshand -in -hand with complexity.Ian Hickman describes an exception.

145 NEW PRODUCTSNew product outlines,presented by Phil Darrington.

153 SPEAKERS' CORNERThis month, John Watkinson looks intothe basket - the chassis part of anelectromagnetic loudspeaker.

156 IMAGE PORTRAYALTechnologies for image portrayal incomputer graphics, film and televisionwere once very different, but digitalelectronics is causing them to converge, asJohn Watkinson explains.

160 DIGITAL VISIONSDon McLean has new evidence to showthat Baird' s television system was betterthan we were led to believe.

166 DSP VERSUS THEMICROCONTROLLERDSPs at the bottom end of the market arefinding themselves used in ever increasingapplications, but how will they competeagainst the likes of Risc andmicrocontrollers? Steve Bush finds out.

Cover photography: Mark Swallow

On impact, this 30mmbullet blasts a 10MWpulse - making land minesvisible to detectors. Readabout it on page 94.

Did Baird get it so wrong?Evidence that he didn't is theTornado's airbornereconnaissance system. Formore see page 160.

x

0

y

11

xey = xy'+x'yIf this means anything to you,you'll find a good read onpage 113.

March issue on sale 4 February

February 1999 ELECTRONICS WORLD 89

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Wandel & GoltermannPFJ-8 Error & jitter test set(All options fited)PCM4 PCM Channel measurement set

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Hewlett Packard 8642AHigh Performance R/F Synthesiser -0.1 to 1050Mhz £8500

Textronix 2467B400Mhz - 4 channels -high writing speed oscilloscope £8500

OSCILLOSCOPESBeckman 9020 - 20MHz - Dual channel £150Hewlett Packard 54100D - IGHz Digitizing £1500Hewlett Packard 54200A - 50MHZ Digitizing £500Hewlett Packard 54201A - 300MHz Digitizing £1250Hitachi V152N212N222/V302B/V302FN353FN550BN650F from £125Hitachi VI 100A - 100MHZ - 4 channel £1000Intron 2020 - 20MHz. Dual channel D.S.O. (new) £450lwatstu SS 5710/SS 5702 - from £125Kikusui COS 5100 - 100MHz - Dual channel £350Lecroy 9450A - 300MHz/400 MS/s D.S.O. 2 channel £2250Meguro MSO 1270A - 20MHz - D.S.O. (new) £450Philips 3055 - 50MHz .Dual channel £450Philips PM 3335 - 50MHZ - D.S.O. Dual channel £1200Philips 3295A - 400MHz - Dual channel £1750Panasonic VP574 1 A - 100MHZ D.S.O. Dual channel £1750Tektronix 455 - 50MHZ - Dual channel £275Tektronix 465 - 100MHZ - Dual channel £350Tektronix 464/466 - 100MHZ - (with AN. storage) £350Tektronix 475/475A - 200MHz/250MHz - from £450Tektronix 468 - 100MHZ - D.S.O. £650Tektronix 2213/2215 - 60MHz - Dual channel £350Tektronix 2220 - 60MHZ - Dual channel D.S.O £1250Tektronix 2225 - 50MHZ - Dual channel £395Tektronix 2235 - 100MHZ - Dual channel £600Tektronix 2221 - 60MHz - Dual channel D.S.O £1250Tektronix 2245A - 100MHZ - 4 channel £900Tektronix 2440 - 300MHz/500 MS/s D.S.O. £2950Tektronix 2445A - 150MHz - 4 channel £1250Tektronix 2445 - 150MHZ - 4 channel + DMM £1200Tektronix TAS 475 - 100MHZ - 4 channel £995Tektronix 7000 Series (100MHZ to 500MHZ) from £200

SPECTRUM ANALYSERSAndo AC 821 1 - 1.7GHz £2250Avcom PSA-65A - 2 to 1000MHz £850Anritsu MS 62B - 50Hz to 1700MHz £2500Anritsu MS 610B 10KHz - 2GHz £4750Advantest/TAKEDA RIKEN - 4132 - 100KHz - 1000MHz £2500Hewlett Packard 3561A - Dynamic Signal Analyser £4750Hewlett Packard 3562A Dual channel dynamic signal analyser

64pHz - 100KHz £6250Hewlett Packard 3585A - 20Hz to 40MHz £4500Hewlett Packard 8591A - 9KHz - 1.8GHz with tracking generator, option 10 £6500Hewlett Packard 8505A - 1.3GHz - Network Analyser £1995Hewlett Packard 8753A - 3GHz - Network Analyser £4995Hewlett Packard 8753B - Network Analyser £6,500

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EDITORMartin Eccles0181 652 3614

CONSULTANTSIan HickmanPhilip DarringtonFrank Ogden

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es,,rAlk, REED1 .4.10 BUSINESS\lir INFORMATION

Copyright, and the right to copyArecent report in the Daily Telegraph said thattelevision viewers could be stopped from

videoing programmes at home or be forced to paya new tax on blank tapes under a directive beingdrawn up in Brussels to harmonise copyright lawsacross the European Union.

The Government was said to be "not happy"with plans to reduce the right of individuals torecord programmes for personal use and does notwant a return to the situation before 1990. In thosedark days, video recorders were sold with direwarnings printed in their manuals: "The recordingand playback of any material may require consent"and "the user must refer to the provisions of theCopyright Act 1956 and the Dramatic and MusicalPerformers Protection Act 1958" etc etc.

This was clearly a joke. The law wasunenforcable and everyone knew it. Anyway, whatwas wrong recording a programme and watching itlater - even if you skipped over the adverts? But ittook a long time to come up with the words thatwould protect the livelihoods of performers andlegalise the use of videos at home. Let's hope thatwe don't have to go back.

But there is a wider issue here; copyright lawsare difficult to enforce.

There is always a sneaking suspicion amongstthe general public that companies are not being`fair' and are trying to take too much. Thisengenders a culture where people have no qualmsabout copying software because they think thatBill Gates is rich enough already. Or, as anotherexample, photocopying music without regarding itas stealing despite the clear printed warnings.

There are other instances where copyright is feltto be too tightly held. For example the BritishStandards Institution, which is a public service,does not allow any reproduction of its work even ifit is just a quotation. Another example was theschool in the North of England not being able toperform a musical because it happened to be in aLondon West End theatre at the time. This onlyadds to the feeling of unfairness.

They may have the law on their side, butcompanies find that litigation is expensive andrisky. So the response has been to developsophisticated copy protection mechanisms.Programmes can search your hard drive to see ifyou qualify for the new version. Digital`fingerprints' can be put on to cds literally in thenoise, using spread spectrum techniques, to enableauthentication.

There are some clever virus -like software copy

protection methods used in games; if the cd iscopied then the hard drive is completely filled upwith junk. Satellite tv has had VideoCrypt in placefor several years and this will no doubt beenhanced by digital television.

On the photocopying side, there was specialprinting ink patented that could not be photocopied(does anyone know what happened to that?).

There is a school of thought which says that allinformation should be free. And the main vehicleof this freedom is of course the Internet (whocould have predicted it?). The main driver mayhave been the adult web sites but it is certainly avery beneficial institution. And there's freewareand shareware. Maybe "one day all software willbe sold this way"?

This brings us on to the problem of quality.There's lots of useful stuff out there on theInternet. But you have to search very carefully forit to avoid 'info -glut'. The quality of some datacan be poor and often links are missing, referred toby that wonderful expression 'web rot'. And allthat free software. Who supports it? It is alarminghow many companies depend completely on apiece of free software - the web browser.

I believe that the integration of the browser intothe operating system, as in Windows 98, isessential, because then its supported.

But I digress. The point is that you get what youpay for, and you also value what you pay for. Forexample, when all those electronics magazines fallthrough the letter box which one do you read first?The one you pay for. Good information costsmoney in all the sifting, analysis, presentation andmarketing. So we need copyright to protectlivelihoods and to maintain quality, and thatcopyright needs to be protected.

But what happens next? No doubt protectionmechanisms will improve and become easier toimplement in the digital world. Material that iscurrently free could be protected. The argumentgoes like this: if people want something and youcan protect it, you can sell it.

Media companies would see this as anopportunity here to corner the market. Hugetechnical monopolies could be created whichcould control access to and the use of publishedworks.

Perhaps they would eventually decide what isgood or bad for us. Big Brother by the back door.Of course it could never happen here.

Peter Marlow

Electronics World is published monthly. By post, current issue£2.45, back issues (if available £3.00). Orders, payments andgeneral correspondence to L333, Electronics World, QuadrantHouse, The Quadrant, Sutton, Surrey SM2 SAS. Tlx:892984REED BP G. Cheques should be made payable to Reed Business

Information LtdNewstrade: Distributed by Marketforce (UK) Ltd, 247 TottenhamCourt Road London W1P OAU 0171 261-5108.Subscriptions: Quadrant Subscription Services, Oakfield HousePerrymount Road, Haywards Heath, Sussex RH16 3DH. Telephone01444 445566. Please notify change of address.Subscription rates 1 year UK £36.00 2 years £58.00 3 years£72.00. Europe/Eu 1 year £51.00 2 years £82.00 3 years £103.00ROW 1 year E61.00 2 years £98.00 3 years £123

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© Reed Business Information Ltd 1997 ISSN 0959 8332


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UP DATEI

CM pips BT in broadband raceCable and Wireless looks likepipping BT to the post in

providing broadband links to thehome. But the UK's top twotelecom operators will be goingdown different routes - Cable andWireless via cable modem and BTvia asymmetric digital subscriberline, adsl.

The need for a broadband strategyfrom the two companies hassharpened in the wake of CompaqComputer's decision to ship pcswith G.Lite 1.5Mbit/s dsl modems.Purchasers wanting to use theseveral megabits per second data

rates offered by dsl modems will bedisappointed if the operators refuseto support them by providing a dslservice at the exchange end of theirtelephone line.

BT refuses to say when it willallow customers to take advantageof the twenty times plusimprovement in access speeds whichadsl offers.

"We are trialling adsl," said a BTspokesman. The trials will last untilMarch 1999. They are consumertrials - the technology has alreadybeen proven in technical trials.

BT said "it is not appropriate to

speculate" about when, and at whatcost, adsl will be provided. SinceBT's business customers payupwards of £25 000 for broadbandleased lines, it could be put in aquandary when customers startdemanding cheaper dsl access.

Cable and Wireless customerslook luckier. Cable modemsoffering 37Mbit/s downstream, and2 to 10Mbit/s upstream, will beavailable either in television set -topboxes which can also connect to thePC, or as stand-alone items, by theend of 1999.

David Manners Electronics Weekly

£7m Euro money for extreme -UV lithoThe European Commission is toput £7m (10m ECU) into a

programme to develop sub 0.1pmmanufacturing processes based onextreme UV lithography (EUVL).

"This will be the third consortiumto study EUVL, the others are theIntel -backed group in the US and oneformed between the big Japanesesemiconductor companies,"said DrDean Morris of Oxford Instruments,part of the EC consortium.

Extreme UV lithography, usingelectromagnetic radiation betweendeep ultra -violet at 150nm andX-rays at l nm, is one of thecontenders for a future sub 0.1µmlithography process.

The Semiconductor IndustryAssociation roadmap released in1997 calls for the first ICs with0.07pm features to be produced by2009. For this, commercial tools willbe needed by 2008.

Oxford will head group efforts todetermine which type of particleaccelerator will be best -suited toEUV generation. The company hasbuilt and sold two X-ray generatingsynchrotrons, one of which is beingused by IBM for X-ray lithography.

Another programme member isthe Dutch firm ASM Lithograph.ASML is an established maker oflithography equipment, claimingto have over 1000 systems

installed worldwide.The third, final member of the

European consortium is Germany'sCarl Zeiss which will look at theproduction of focusing optics andmasks.

"EUV cannot be focussed byrefraction and is only weaklyreflected. Carl Zeiss is going to makehighly accurate multi -layerreflectors, with over 50 layers, to actas focussing optics and reflectivemasks," said Morris.

The European project is to becalled Euclides, short for ExtremeUV Concept LithographyDevelopment System.

Steve Bush Electronics Weekly

UK group demonstrates video -speed flat panelsA consortium of UK

organisations has produced avideo -rate, limited -colour displayby combining a light -emittingpolymer (LEP) backlight with apassive ferroelectric lcd (FLCD)shutter.

"It has video capability withoutusing expensive thin-filmtransistors or colour filters,"said DrKarl Heeks, technical manager atCDT, supplier of the LEP backlight.

The light source for the display isalternate narrow stripes of green andred -emitting LEPs, laid down tomake a square.

All the red strips are energisedsimultaneously followed by all thegreen strips in a repeating cycle.

By synchronising the timing of the

CRL-supplied ferroelectric LCD,which is a matrix of individuallyaddressable 330 by 330pm pixels,either green, red, or a combinationof the two can be selected per pixel.

"The display is only possiblebecause LEPs and FLCDs are fastenough for time -sequentialoperation," said Heeks.

The University of Cambridgeprovided material characterisationand failure analysis for the project,while funding was supplied by thegovernment.

Currently there is no blue in thebacklight. The development of ablue LEP has lagged red and greentypes. "We will be making someannouncements about blue LEPsvery shortly," said Heeks.

Two display companies, together with the University ofCambridge, have developed a display that combines thestrengths of light emitting polymers and ferroelectric liquidcrystals to make a limited colour display. The technologydemonstrator is 7.5cm square and displays red, green andcolours in between.

February 1 999 ELECTRONICS WORLD 93

UP DATE

Magic bullet... Not anew way of killing

people, but a high-techway of detecting

mines. Kinetic energyis converted to an

electromagnetic pulseas this projectile buries

itself in the ground.The pulse bounces ofnearby mines givingaway their position.

Multi -wavelengthIR imaging

Post scannedantenna array

Accousticsensor array

Detection andneutralisation area

EMP bullet helps detect land minesResearchers at the University ofMissouri, Columbia are

developing a landmine detector basedon a high -power rf source in aprojectile.

The projectile is fired vertically intothe suspected minefield, where itemits a high power electromagneticpulse. Buried metallic objects aredetected when a phased -array antenna

Radial sourceEM and

Accousticwaves

Ground breaking technology... The University of Missouri isaiming to detect landmines by firing electromagnetic pulsegenerators into the soil from a helicopter. The system, says theuniversity, will detect reflections from metallic objects as small as'm13 around a 15m radius from 100m up. In keeping with currentmine detection theory, the system will be multi -sensor. Not onlyare electromagnetic reflections sensed, but acoustic activitycaused by the impact will be analysed as well, then mixed withthermal image data. The work is sponsored by the US Army and iscurrently still in the laboratory.

mounted on the helicopter 'sees' thepulse reflected from them.

Producing the pulse underground,claims the university, couples far moreenergy into the locality than anabove -ground source, which loosesmost of its power in reflections fromthe air -soil boundary.

Key to the project is the projectile.This must be a powerful emitter - thetarget is 10MW - but small enough tobe fired from a gun, in this case30mm in diameter.

The power source that the Missouriteam has chosen is the kinetic energyof the projectile itself. They arelooking at two ways of turning this intoan electromagnetic pulse.

The first is magnetic induction. Theinduction projectile has a ferromagneticslug at its rear which sits inside a short-circuited multi -turn coil.

Just prior to firing, a current isinduced into the coil which continuesto flow during flight.

As the projectile hits the ground,the slug flies forward into a spaceprovided. This leaves the coilcoreless and reduces its inductancequickly and dramatically. Currentrises with the ratio of the inductancechange and the coreless coil acts asan antenna radiating half the energyLfinalifina12-

The other projectile type ispiezoelectric. In this case a mass at therear of the projectile bears down on a

The numbersThe projectile weighs between50-100g and travels at500-1000m/s, giving itbetween 6 and 50Id of energywhen it hits the ground.

Because not all of its mass isinvolved in conversion, andconversion is inefficient, only tenper cent of this is converted toelectrical energy. This meansthat there is a minimum ofaround to be radiated. Thisis converted in around 1 ms,resulting in a 1MW pulse.

piezoelectric block as the collisionoccurs. This produces a high voltagewhich is switched into a coil antennaaround the projectile by a spark gap.

Both types have proved successfuland 100kW pulses are expected fromprototypes before the end of this year.

The next phase of the project callsfor changes, based on findings so far,to create MW pulses from smallerprojectiles. Work will also be done onthe coil antennas to control thefrequency content of the output pulse.

The helicopter part of the system,still in its early stages, may containacoustic and thermal imaging arraysalongside the passive radar array to aidthe differentiation of mines from otherobjects.

Steve Bush

Dumping gone bananasBananas or semiconductors?Although the EU is fighting its

corner on imported bananas, Sir LeonBrittan, v -p of the EU, has succeededin scuppering European anti -dumpingmoves against importedsemiconductors.

While the US government hassupported its local semiconductorindustry by imposing anti -dumpingduties on Hyundai and LG andpursuing anti -dumping actions againstTaiwan, the EU announced itsdecision last week not to fight forEurope's semiconductor industry.

"The US government is aware ofthe importance of semiconductors forits economy. The EU is not," said DrEckhard Runge, director-general ofthe European ElectronicsComponents Association (EECA)."The closure of two fabs in the UKcould have been avoided if pricinghad been normal."

Reckless over -investment by theKorean chaebols flooded the marketand killed prices. EECA asked the EUto take action against low dumping

prices, personally lobbying Brittan,but he refused support.

In the ensuing bloodbath, SiemensSemiconductors lost £400m and isnow being put up for sale by itsparent company Siemens AG. "TheKoreans should have been hit forwhat they have done," said Runge. "Itis very disappointing that the EU doesnot consider the industry important."

The reason given by the EU for nottaking action against the Koreans isthat, because everyone is sellingbelow cost price, action against theKoreans would be discriminatory.

The US government refused to takethat view despite the fact that theirown domestic producer, MicronTechnology of Idaho, has pursuedone of the most aggressive pricingpolicies in the industry.

EECA points out that, between1990 and 1997, Japanese DRAMmarket share in Europe dropped from45.3 per cent to 27.8 per cent, whileKorean market share grew from 14.7per cent to 42 per cent.

David Manners

94 ELECTRONICS WORLD February 1999

hArcru.,ort Internet Explorer

File Edit View Go Favorites Help

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CASearch Favorites History Channels

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Address I ilwww.tiepie.n1

PLUG IN AND MEASURESpectom enaly7e. P111:112

Fie Measure Ch1 Ch2 Ftespency Luszofs Enfemocel aeitino Hob

l'Alf22fI(F,") 4096 samples

2Cneco-

IMO

TiePie introduces the HANDYSCOPE 2A powerful 12 bit virtual measuring instrument for the PC

The HANDYSCOPE 2, connected to theparallel printer port of the PC andcontrolled by very user friendly softwareunder Windows or DOS, gives every-body the possibility to measure within afew minutes. The philosophy of theHANDYSCOPE 2 is:

"PLUG IN AND MEASURE'.

Because of the good hardware specs(two channels, 12 bit, 200 kHz samplingon both channels simultaneously, 32KWord memory, 0.1 to 80 volt full scale,0.2% absolute accuracy, softwarecontrolled AC/DC switch) and the verycomplete software (oscilloscope,voltmeter, transient recorder andspectrum analyzer) the HANDYSCOPE2 is the best PC controlled measuringinstrument in its category.

The four integrated virtual instrumentsgive lots of possibilities for performinggood measurements and making cleardocumentation. The software for theHANDYSCOPE 2 is suitable forWndows 3.1 and Wndows 95. There isalso software available for DOS 3.1 andhigher.

A key point of the Wndows software isthe quick and easy control of theinstruments. This is done by using.- the speed button bar. Gives directaccess to most settings.- the mouse. Place the cursor on anobject and press the right mouse buttonfor the corresponding settings menu.

- menus. All settings can be changedusing the menus.

Some quick examples:The voltage axis can be set using a dragand drop principle. Both the gain and theposition can be changed in an easy way.The time axis is controlled using ascalable scroll bar. Wth this scroll bar themeasured signal (10 to 32K samples)can be zoomed live in and out.

The pre and post trigger moment isdisplayed graphically and can beadjusted by means of the mouse. Fortriggering a graphical WYSIWYG triggersymbol is available. This symbolindicates the trigger mode, slope andlevel. These can be adjusted with themouse.

The oscilloscope has an AUTO DISKfunction with which unexpecteddisturbances can be captured. When theinstrument is set up for the disturbance,the AUTO DISK function can be started.Each time the disturbance occurs, it ismeasured and the measured data isstored on disk. When pre samples areselected, both samples before and afterthe moment of disturbance are stored.

The spectrum analyzer is capable tocalculate an 8K spectrum and disposesof 6 window functions. Because of thishigher harmonics can be measured well(e.g. for power line analysis and audioanalysis).

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The voltmeter has 6 fully configurabledisplays. 11 different values can bemeasured and these values can bedisplayed in 16 different ways. Thisresults in an easy way of reading therequested values. Besides this, for eachdisplay a bar graph is available.

When slowly changing events (liketemperature or pressure) have to bemeasured, the transient recorder is thesolution. The time between two samplescan be set from 0.01 sec to 500 sec, so itis easy to measure events that last up toalmost 200 days.

The extensive possibilities of the cursorsin the oscilloscope, the transientrecorder and the spectrum analyzer canbe used to analyze the measured signal.Besides the standard measurements,also True RMS , Peak- Peak, Mean, Maxand Min values of the measured signalare available.

To document the measured signal threefeatures is provided for_ For commondocumentation three lines of text areavailable. These lines are printed onevery print out. They can be used e.g. forthe company name and address. Formeasurement specific documentation240 characters text can be added to themeasurement. Also "text balloons" areavailable, which can be placed within themeasurement. These balloons can beconfigured to your own demands.

For printing both black and white printersand color printers are supported.Exporting data can be done in ASCII(SCV) so the data can be read in a

spreadsheet program. All instrumentsettings are stored in a SET file. Byreading a SET file, the instument isconfigured completely and measuringcan start at once. Each data file isaccompanied by a settings file. The datafile contains the measured values (ASCIIor binary) and the settings file containsthe settings of the instrument. Thesettings file is in ASCII and can be readeasily by other programs.

Other TiePie measuring instruments are:HS508 (50MHz-8bit), TP112 (1MHz-12bit), TP208 (20MHz-8bit) and TP508(50MHz-8bit).

Convince yourself and download thedemo software from our web page:http://www.tiepie.nl.When you have questions and / orremarks, contact us via e-mail:[email protected]

Total Package:The HANDYSCOPE 2 is delivered withtwo 1:1/1:10 switchable oscilloscopeprobe's, a user manual, Wndows andDOS software. The price of theHANDYSCOPE 2 is £. 299.00 excl. VAT.

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Driver's seat...Ford's

reconfigurableconcept cardashboard.

Java chips on showPrototype Java chips made theirfirst public appearance at the

recent Comdex trade show in LasVegas, writes Tom Foremski.

Sun Microsystems, LG Semicon,NEC and Fujitsu showed evaluationboards that contained Java -basedchips, and Patriot Scientific showedits Javachip.

Sun was keen to arrange suchdemonstrations because of criticismfrom industry analysts that its Javachip program had run out of steamand that there has been little to showsince Sun licensed Java core designsto major chip companies over thepast two years.

"This shows that Java chips are areality and that they have applicationsin different types of systems," said aSun representative. "Although theseare just initial demonstrations of whatour licensees are working on, there isa bright future for Java chips."

The advantage of Java chips is thatthey can be used in applicationswhere there is no overhead for aJava -based operating system and thememory required to run a JavaVirtual Machine. Instead of usingsoftware to interpret the Javainstructions, the chips directlyprocess the Java byte code. Sun says

that with the cross -platformcapabilities of Java, it is possible tobuild a large number of embeddedapplications in areas such asautomotive control systems andfactory production lines, where smallJava applications can be run.

Sun showed an evaluation boardcontaining its prototype MicroJava701 microprocessor, based on itspicoJava core design. This will bereleased to developers in the secondquarter of 1999 along with anoperating system and developmenttools.

NEC demonstrated a picoJavabased evaluation board which it istargeting at embedded systemsdevelopers and said that it is alsoworking on semi -custom chipproducts that are more closelytargeted at specific applications.

Fujitsu demonstrated apicoJava-based board but says thatits main focus is system -on -a -chiptype applications where the picoJavacore is just one part of an overalldesign that includes microprocessorand other cores.

LG Semicon was showing itsprototype MJI chip which isdesigned to be a discrete part to becombined with other chips in various

applications. It also said that anotherJava chip, designated MJ501, isbeing developed and it will offerimproved performance.

Sun admitted that it has changedstrategy with its Java chip program."Instead of separate Java chips, werecognise that the industry is movingmore towards a semi -custom modeland we are encouraging ourlicensees to move in that direction,"said Harlan McGann, head of thearchitectural and technology groupin Sun's Microelectronics division.

Sun has been criticised for its Javachip plans. Jim Turley, seniorindustry analyst at MicroDesignResources says that Java is too slowfor embedded chip applications."Java does have a place but inembedded systems I'm notconvinced that it has theperformance that makes it useful,"Turley said.

McGann notes that Java isbecoming faster and that Java chipswill be found in a wide variety ofembedded applications such as cellphones, set -top tv boxes andindustrial control systems. But it willbe a while before Sun can showactual real -world applications forJava chips.

Dashboard that can change as you driveFord subsidiary Visteon hasdesigned a reconfigurable concept

car dashboard that uses TexasInstruments' Digital MicromirrorDevice (DMD).

The dashboard is 350 by 85mm andcan display traditional mechanicalinstruments, user customisedinstruments and even navigationaldata.

Visteon has selected the TI partdespite strong competition from LCD

colour -shutter technology fromvarious manufacturers.

"We are using the DMD because ofits resolution, fill -factor andtemperature performance. The highfill -factor, which is over 90 per cent,means that there are no difficultissues if we want to increase screensize," said Alex Calton, productmarketeer at Visteon.

Poor yield of the DMD has beenrumoured to be a problem for TI.

Does getting hold of the devicesworry Calton? "No," she said. "If wesell the product concept to acustomer, TI will be able to producethe devices."

Another feature Visteon ispromoting is a "baby -watchfunction" to keep an eye on the kidsin the rear seat - which can only beused when stationary. It is alsodeveloping a 350 by 255mm unit forcentre console use.

Easy PC, Tina, where?rad packages Tina and Easy -PC%....have both had changes of UKaddress recently. The Tina Windowscircuit simulation suite is nowdistributed by Quickroute andcomplements the company'sestablished and successful autorouter.

Easy -PC is now owned bySightmagic in Tewkesbury. "Weintend to make Easy -PC For Windowsby far the best value sub -£500 pcblayout product on the market today,"Sightmagic's Marketing Manager BobWilliams told us.Sightmagic Tel. 01684 773662Quickroute Tel. 0161 476 0202


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DIGITAL DESIGN

There was a timewhen plds werethe domain of thewealthy, but asColin Attenboroughexplains, in -systemprogrammabledevices and freesoftware havebrought themdown to pocket -money level -provided youalready have a pc.To illustrate howmuch digitalprocessing poweryou get from eventhe smallest pld,Colin describes afive -chip logicanalyser capableof capturing 4096byte -wide wordsat sampling ratesto 10MHz. PLDs for all

All too often, a bright idea for a logic -based deviceloses its appeal when you draw up a detaileddesign and find that the circuit is not as simple as

you first thought. There's the added disincentive that whenyou have finished implementing the design, it will notwork as expected and you will have the dubious task ofrewiring it.

For such applications, modern programmable logicdevices, or plds, are an excellent alternative. There aredesign tools that make implementing and simulating thelogic easy, and making a modification is simply a matter ofreprogramming the device.

There was a time when programmable logic was Mac -

`This particular cd has recently become obsolete. The new cdallows you to design an expanded range of parts, but requires you

to register for a six-month licence. Use is still completely freethough. Electronics World is due to obtain around 30 of the originallife-long licence Lattice cds for 1016 and 2023 parts only. These

will distributed free with requests for the author's software until theyrun out. Details later in the article. Ed.

cessible to most because of the high cost of developmentequipment. For devices like the one I use as an example inthis article, the development software is free and the hard-ware is little more than a cable that links your target designto the pc for programming.

All you need is a pc, a free cd and a cableTo illustrate just how accessible plds have become, Idescribe here a logic analyser comprising just five ICs. It isbased on a Lattice Semiconductor's ispLSI1016, a 60MHzversion of which costs under £10.

Given Lattice's software, installed from the company'sfree cd onto a pc*, a design specified at the gate/flip-flop/adder sort of level can be drawn, checked, compiled,and programmed into the device. The only additional hard-ware needed is a simple adaptor that goes between the pc'sprinter port and the device being programmed.

And if the design doesn't work, debug the error, amendthe circuit diagram, and simply reprogram the device. Witha few restrictions you can even reprogram it withoutremoving it from its circuit board.


DIGITAL DESIGN

Design example - 10MHz logic analyserMy logic analyser using the ispLSI1016 has only five icsexcluding the power regulator, yet it can acquire 4096 sam-ples of an eight -bit word at rates up to 10MHz.

Operation of the analyser is controlled via a pc's printerport using a dynamic link library written in Visual C++ V5to access the printer port, and Visual Basic 5 to provide aWindows user interface. But note that you don't need eitherlanguage to use the software; it can be installed on any pcrunning Windows 95 or later.

The analyser's software lets you set the acquisition rate,

Input data Inputbuffers

RAM

Read/'write

Triggerlogic

Addresscounter

Stop4

counter

the trigger word, and an internal or external clock source.You can also search for chosen logic words - zeros, ones ordon't cares - among the acquired data, and bring eachoccurrence of the chosen word to the centre of the screen.The number of samples displayed on screen can be set tobetween 8 and 256.

For use in the logic analyser, the ispLSI1016 incorporatesa 12 -bit counter, an 8 -bit counter and a 21 -bit shift register.It also has sundry gates, latches and flip-flops.

Pre-programmed devices are being made available forthose of you who don't want to do the programming.

Clockrate

select

Trigger word found

Set trigger word

ll

Control

High/low nibble select

Blocks in italics implemented in ispLSI1016PLD

Note: connect a 10n ceramiccapacitor from +5V supplyto ground at each device

Each input connectionis protected by 47k to

ground

7 to 12VDC in

Details of ispLSI1016 supplies andprogramming connections

+5V

10k

SDOUT*ISPenSCLK

MODESDI

+5V

18 D71716151413

19

1817

6

5

3

2

31

18

407

17

28

15

26

Mpx

420MHz

oscillator

-Download clock from pc

Clock and trigger data from pc

-External clock

8-wide data bus

Trace data to pc

HM65764H5

*OE

*WR

*OS

30634

2

+5V

28

26

4

22

16

74HCT157

Fig. 1. Outline of a logicanalyser, whose job it is toread a sequence of logic levelson an eight -bit bus anddisplay the results on thescreen of a pc. Note thatasterisks denote active -lowsignals in this article.

Pins of PC's

470Rprinter port

10

470R12

7 470R--fit 13470R

27

1523121A24A25A3 A4 5 6 7 486 8 41 42 431 441 25116 21

20

9 k1032 19

CLR

'WA

*DLO

SCK

ispLSI1016 DCK

SDATA

EXTCK

STILL COUNTING

29

16

8

15

Fig. 2. Logic analyser details. Usinga pld dramatically reduces thenumber of components needed tolook for a specific trigger word onthe bus being tested, store asequence of bytes after triggering,then send out the information to apc. The pld also handles controlsignals from the pc for setting upthe analyser.

+5V

T2

.4394104-22

37

17

12

14

15

13

2 11

27

+5V20MHzcrystal

oscillatormodule

74HCT541

Pins of PCsprinter port

4

34-4-I-4-47

11910

2 Clr8 Select high nibble/low nibble

6 Not Download

4 S_Ck (serial data entry clock)

3 DownloadClock

5 S_Data (serial data)

9 (Extemal clock)11 Still counting

470R (0 when acquisitioncomplete)

Each input connectionis protected by 47k to

ground


DIGITAL DESIGN

IS_Data>

LS Ck>

Data101 1_61

Datap) 1_62

Datal2f 1.63

Data[3] 1

Data[4] 1_651 I S_Dala1_17

Datai5) 1_66, r

Datal6) 1_67c

S_Cs)--Dk1t1

Data171 13a1,710 71

1)68

I30 0Ixo_

BUSCF

NagErtrEco- ,s Osta N,d. 1143%_2

010 71MPS IPDX 0

March

60

D 0 S 0

1_24

SYNC 8

0000

- To20_1n 03Clr 05

Clk

0607

1,33_01.3

20

a

St SO

Fig. 3. 'Top level' of the pld, giving anoverview of the functions carried out by thedevice at the heart of the logic analyser.

1 29

SO

D 0

18

0 0--4-S0

38

00 -02-0305

Tow13 04Dr 06

06 070908

10

Tao,.

D Q

1 19

D

20

D Q D

1 22

D 0

123

D

124

D

125

D Q

6

D

127

D Q

8

D 0

129

0

One[0:7]

D

NeqExtEclanlet NotExt

MPX_2MPX 1MPX 0

130

Db(0:71

iar[0:71Cf[0:71

-Yor[0:7]

D 0

X(0:7]

131

D Q

18

D

19

D Q

110

D 0 D Q

L12

D

113

D

L14

CI10]Cf[1]CI[2]

> C1131Cf[41Cf151

Ct161

Cf> [71

g

BullerloeCE

ot WS)

Fig. 4. Bus_cf trigger andrate setting details. Thissection compares theinput word with thetrigger word andproduces an output whenthe two are identical.

Match


DIGITAL DESIGN

Togg_in

Clr

Clk

SYNC4

Toggin Q0

Clr 02Clk 03

ToggoutL2

Q1

ooQ2

SYNC4Q1

Toggin Q0

CIr 02Clk 03

Toggout1_1

Q3

01

0002

Q3

Togg Ou

Fig. 6. Clocking counters Sync8 and Sync12 - eight and12 bits respectively - are made up of cascaded four -bitsynchronous counters.

What is a logic analyser?For fault-finding analogue systems, the most useful singletest instrument is the oscilloscope. For digital systemsthough, the oscilloscope has limitations. Triggering isn't justa matter of setting a voltage level and polarity; it's useful totrigger from a combination of zeroes and ones. And ofcourse the oscilloscope's two channels are not sufficient toexamine the relationships between all the lines in, say, aneight -bit wide bus.

What is needed is a logic analyser, where rather than twoanalogue channels you have eight binary channels, andwhere the trigger criteria are set as a word rather than signallevels and polarity. It is also useful to be able to store results,so they may be examined at leisure, and 'this -causes -that'relationships checked.

Logic analyser basic requirementsA logic analyser needs memory to store acquired data. Staticram is cheap and readily available in byte -wide amounts suf-ficient to store an adequate number of samples. It is alsoavailable to work at a speed fast enough to allow 10MHzanalyser clocking.

An analyser also needs a reference oscillator to define theacquisition rate and clock -rate logic to allow data to beacquired at defined rates below that of the reference oscilla-tor. Trigger logic is needed to compare the incoming datawith a trigger word and stop acquisition when a matchoccurs.

An address counter for the ram is clocked by the selectedclock rate, in order to put successive input data bytes intosuccessive locations of the ram. Control logic supervises get-ting data into and out of the system.

All the above elements are shown in Fig. 1. Figure 2 is thedetailed overall circuit; a tri-state input buffer is needed notonly to allow read/write operation of the memory, but, if youconnect an input to an excessive voltage, makes it more like-ly that you'll vapourise something comparatively cheap.

Figure 3 is the top level circuit of the pld, showing that itimplements a large fraction of Fig. 1 ' s circuitry.

How it worksTo prepare for acquisition of data, the pc sets the `Clr' line,clearing the sync8 and syncl2 counters, and all the D typesand latches shown in Fig. 3.

Trigger -word data, acquisition rate selection, internal/exter-nal clock selection and external clock polarity settings arecommunicated as a serial word. This word is sent to the shiftregisters in the BUSCF block. Acquisition -rate selection is

Togg_in

Clr

Clk

SYNC401

Toggin Q0

Clr 02

Clk Q3

Toggout1_1

01

Q0

Q2

SYNC4Toggin Q1

Clr Q0

Clk 0203

Toggout1_3

Q3

Q5

04

06

SYNC401

Toggin 00CIr 02

Clk 03Toggout

L2

07

Q9

08

010Q11

Togg Out

Tip: re -using circuit designsSuppose you copy a top level circuit by usingFile/Save As, intending to use it as the basis of anew design project. You will find that, in theSources window, the sub -circuits are markedwith queries. The system doesn't know where tofind the subcircuits. Tell it where to look byclicking on an unknown subcircuit and then useSource/Import to import it.

carried out via the 8 -to -1 multiplexer.The eight -to -one multiplexer selects one of the outputs of

the sync8 counter; if an internal clock is used, this will beselected by the four -to -one multiplexer and clocks the sync12counter which addresses the ram.

To acquire data, `Clr' is set to logic zero and`Not_Download' to logic one. The input buffers in Fig. 3 areenabled, and input data are written to the ram. TheNot_WR' signal is identical to the clock and provides awrite signal to the ram.

Acquisition starts to end when the 'match' output ofBUS_CF goes to logic one, Fig. 4. This happens when alleight inputs of the and gate - assembled from two four -inputand gates and a two -input and gate - go to logic one.

The logic to detect a match between incoming data and thetrigger word consists of an exclusive -or gate and an or gate,repeated for each of the eight lines of the data bus. It is con-venient to represent the exclusive -or and or gates as iterated(repeated) components, and their input and output connec-tions as busses.

The control input to the exclusive -or gates is the One[0:7]bus; a logic zero in the input word and a logic one in the cor-responding position of the One[0:7] bus gives a logic one atthe output of the exclusive or gate. This feeds the b[0:7] busdriving the or gates, because the gates are fed from a bus andare iterated, the connections between the gates are themselvesa bus.

That's how we detect a logic zero in the incoming data; weset a logic one in the One[0:7 ] bus. (You're right, it isn't awell-chosen name.) To let either state of the incoming data


DIGITAL DESIGN

end acquisition, we set a logic one in the corresponding bit ofthe X[0:71 bus which feeds the or gates.

A logic one at the 'match' output does not stop acquisitionimmediately, Fig. 3. After deglitching by the D type, it isheld by a set:reset latch. It is only when the sync12 counternext reaches its final state, with Togg_out at logic one, that asecond s:r latch clears the syncl2's Togg_in line. Thisinhibits further clocking, and puts a logic zero on the`still_counting' output to tell the pc that acquisition is com-plete.

Applying the pidThis outline covers the sequence of events from circuit dia-gram to programmed device. I'll use the circuits of the logicanalyser as examples to show you how to turn your ideas intoa programmed device.

First, install both ISP Synario and ispDS+ then start a newproject. The top level circuit Fig. 3, contains some simplegates and flip-flops, as well as the blocks bus_cf, sync8 andsync12, which are made up from such simpler elements.

From Lattice's cd, install the ispSynario and ispDS+ pro-grams: both are needed. Start ispSynario and you'll get the`Project navigator' window. Select 'File/New project'; nameand store the `.syn' file.

Double-click 'Virtual device' in the 'Sources' window;select ÌSP Synario starter device' and then, in the lower win-dow, ìspLSI 1016-60 PLCC44'. Click OK and accept theYes option.

Entering circuits. Now you can start entering circuits. Click`Source/New/Schematic/OK'. Name and store the new `.sch'

file. You'll see two windows; a schematic editor where you'lldraw your circuit, and a tools palette with seven rows andthree columns.

Most tool palette functions are also available in menus. Theprompt line at the bottom of the schematic editor is a usefulguide to what to do next in any command. Start by enteringthe sync4 circuit, Fig. 5; this will be used as part of sync12and sync8 counters.

Begin with a toggle flip-flop with clear. Click the 'Addcomponent' icon in the top left of the tools palette. A SymbolLibraries window appears; click on

c:\...\GENERIC\REGS.LIB,

and then scroll down the lower part of the window until yousee `G_TC'.

When you move the mouse onto the circuit diagram, you'llsee a symbol for the flip-flop at the end of the mouse point-er. Click on the circuit diagram to place the symbol. Place theother three flip-flops while you're about it.

Click on

c:\..\GENERIC\GATES.LIB

and import the gates you need. The term 4AND is a four -inputAND gate; less obviously, 4AND1 has one input inverted.

Wiring components. After you have placed all the gates andflip-flops, you need to wire them up. At this point you willprobably realise that you haven't placed them quite correctly.

Two items in the centre row of the tools palette let youmove components. The centre one lets you click on an indi-vidual component and drag it, breaking any connections; the

Software downloadThe ISP Synario Starter software is available fordownloading on www.latticesemi.com. This software includesall the tools that you need for designing with Lattice ispLSI1000, 1000E, 2000, 2000V, and GAL device families. TheISP Synario Starter runs under Windows NT and Windows95, and includes:

Lattice ispDS+(tm) Starter (Part 1)ispDS+ HDL Synthesis -Optimised Logic FitterExplore ToolPin Assignment EditorispTA(tm) Timing AnalyserispDOWNLOAD(tm) and ispATE(tm) UtilitiesVITAL and Non -VITAL VHDL Simulation LibrariesOVI-Compliant Verilog Simulation Library

ISP Synario Software Starter (Part 2)ISP Synario Project Navigator GUIISP Synario ABEL-HDL Entry and CompilerISP Synario Functional SimulatorISP Synario Schematic CaptureGAL Compiler

Minimum System RequirementsThe ISP Synario Starter software for the PC environmenthas the following system requirements: 486/Pentium pc -compatible; mouse; Windows NT or 95; 16 megabytes ofram; SVGA resolution display (800 x 600); 35 megabytes offree hard -disk space.

The full procedure for downloading is given on the site.Note that you will be asked to open an account in order touse the software, but this does not entail any moneychanging hands. Full Acrobat documentation is available fordownloading, as is a copy of the Acrobat reader.

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DIGITAL DESIGN

right hand one lets you lasso a group of components and con-nections, and move them all, preserving connections.

The wiring tool is at the centre of the top row of the toolspalette. Click it to select it, click a component lead end - or anexisting lead -to start a wire, click again to anchor at a bend,and click on the destination wire or component lead end.

Double click to end a wire in the middle of nowhere. Usethe zoom in and out controls, shown as magnifying glassesat the top of the circuit editor, as needed. At some pointyou'll doubtless need the eraser tool at the right hand end ofrow five of the tools palette; it works on wire segments andon components, and on lassoed areas. And -a useful fea-ture - F9 is the 'Undo' button.

Naming i/o. Name the inputs and outputs and give themconnectors. To name an input or output, click the centreicon in the second row of the tools palette.

Enter, for example, CLR and hit return. Then click themouse on the end of the appropriate wire. Note that theremust be a wire; it won't work on device pins themselves.Repeat this for each of the i/os.

To attach an i/o marker, use the right-hand icon of thesecond row of the tools palette. Up pops a window to letyou select input or output; choose the right one and lassothe names you've just added. Lasso several at a time forspeed, but make sure they're all inputs or all outputs.

It is essential to realise that these i/os are merely for thissection of the circuit, they are not pins on the completed pld.

You can name any wire - not just i/os. This is useful, say,when you want to tie an input to one or zero: in this case,you can give the input the more useful name of GND orVcc respectively.

Make a symbol for your circuit block, and check yourwork so far. Use Àdd/New Block Symbol', click 'UseData From This Block', and 'Run'. This will make a sym-bol for the sync4 counter, which can be imported to futurecircuits just like any other gate or flip-flop. It will appear inthe 'local' section of the Symbol Libraries menu.

To check your work, click the tick mark at the top of theschematic editor. A window listing errors will be opened,and if you click on the error description the error will behighlighted on the circuit diagram.

Pins of pc'sprinter port

10

13

15

4

10k

5

+5V

8o12 The +5V supply comes from0 the ispLS11016 board150-0-1AAN-+5V

47R

17

Pins of ispLSI101624

SDOUT

100R 14

=560p

100R 3

560p

100R 36

1560p

18 100R 13

1560p

100R 11

Each buffer is 1/8 74HC244

Pins 1 and 19 are outputenables for groups of 4 gates

in the 74HC244

SDIN

SCLK

MODE

ispEN

RESET (not used)

Building the pldThe logic analyser uses a 12 -bit (sync12) and an 8 -bit (sync8)counter; both are made up from sync4 counters.

To make sync12, start a new circuit diagram as for thesync4. Import three sync4s from the 'local' section of the`Symbol Libraries' menu. Connect them up as shown in Fig.6, add i/os and names, give sync12 a block symbol, check it

ispLSl 1000/E families: overviewThe ispLSl(r) 1000/E families are high -density devices with applications ranging from registers, to counters,to multiplexers, to complex state machines.Densities of the the ispLS1 1000/E families range from 2000 to 8000 gates.Each device contains multiple generic logic blocks. These are designed to maximise system flexibility andperformance. A balanced ratio of registers and i/o cells provides the optimum combination of internal logicand external connections.A global interconnect scheme ties everything together, enabling utilisation of up to 80% of available logic.

1000/E family attributes

Family Member 1016E 1024Density: (PLD Gates) 2000 4000Speed - f,, (MHz) 125 90Speed - tpd (ns) 7.5 12

Macrocells 64 96Registers 96 144Inputs and i/o 36 54Pin/Package 44 -pin PLCC 68 -pin PLCC

44 -pin JLCC 68 -pin JLCC44 -pin TQFP 100 -pin TQFP

1032E 1048E6000 8000125 1257.5 7.5

128 192

192 28872 11084 -pin PLCC 128 -pin TQFP100 -pin TQFP 128 -pin PQFP84 -pin CPGA 133 -pin CPGA

For more ambitious designs, there are five more pld families with progressively higher component counts.For more information, or to register for your free CD, see www.latticesemi.com.

Fig. 7. This is thebuffer circuitryneeded to programan ispLS11016 viayour pc's printerport. Take greatcare withdirections andpower supplieshere - particularlyif your printer portis an integral partof your motherboard. It may bewise to use an add-on i/o card to giveyou LPT2 andprobably two extraCOM ports. Theseare very cheap.Note that thisinterface handles 5and 3.3V devices inan isp or /TAPprogrammingchain, but not amix of isp and/TAG parts. Aready-made cableis available for thistask.

February 1999 ELECTRONICS WORLD 10>

DIGITAL DESIGN

Logic analyser softwareTwo sets of logic analyser driving software are available on disk - one forreaders with Visual Basic 5 and the other for readers without. Note that this issoftware for Windows 95. Notes on how to use the software are included on thetwo -disk set.Free CD. Electronics World has obtained 30 Lattice CDs with life-long licencefor the 1016 and 1024 parts. The first 30 requests for Colin's software willreceive one each. Send a postal order or cheque for f 1 5 payable to ReedBusiness Information to Logic Analyser, Electronics World, Room L333,Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS.Programmed pld. Colin will program your pld for you if you send it to himsealed in its original packaging together with reply -paid return postage andpacking and a cheque or postal order for £8 payable to Colin Attenborough.Send your request clearly marked PLD to Electronics World Editorial, QuadrantHouse, The Quadrant, Sutton, Surrey SM2 5AS.

Fig. 8. With afew minor

sacrifices, thepld can be

programmedin situ. Here,

the topdiagram showsa developmentadaptor usingtwo cables.

chose thisoption, andused one of

theprogramming

cables tocontrol theanalyser in

use.

and save it. Repeat this process for sync8.The bus_cf circuit, Fig. 6 introduces the idea of busses - i.e.

groups of wires - and of iterated components - or componentsrepeated for each line of a bus. Make a bus by drawing a wireand naming it data[0:7] for example. Use the centre icon in thesecond row of the tools palette, just as you did when namingi/os. The wire thickens to show that it is now a bus.

To add eight exclusive -or gates, import one gate from thesymbols library. Now name the instance of the gate, usingthe left-hand icon of the second row of the tools palette, asx[0:7]. Enter the name, hit return, and click the mouse overthe gate. You can now wire the iterated gate to the bus.

Add the iterated Or gate and name it; add the other buses.Note that the connection between the iterated gates mustitself be a bus.

To connect individual signals to a bus, use the icon at thetop right corner of the toolbox palette. Follow the prompts atthe bottom of the schematic editor window, clicking first onthe bus and then on the destination connection.

Name the wire you've added, as you've done before. If you

PCprinter

port

PCprinterport

25 way IDC D plug

Cable A

26 way IDC plug

26 way IDC socket

25 way IDC D plug

try to name a wire to mybus[0:7] as yourbus[3], or asmybus[8], you'll get an error message.

Device i/o padsThe only thing left to explain about the circuit diagram is theaddition of device i/o pads at the top level. These representthe connections on the programmed pld. They are importedin the same way that any other components from thecA.AGENERIC\10PADS.LIB section of the Symbol Librarieswindow are.

Add names and i/o markers as for the lower level circuits.Notice the use of a clock driver to connect the clock input ofsync8 to a device i/o pad.

There are three possibilities when allocating device pins.Before making the `*.jed' file which programs a blank deviceto your specification, you must decide how many restrictionsto impose on the pin allocation process.

The simplest option is to do nothing; the system willchoose pins for you. You're giving the system an easy time,and if your circuit can be connected, it will be. This is thebest route to take for a complex circuit which may stretch thecapacity of the device.

By default, the system may use some of the programmingpins as i/o connections. This means that you may need to dis-connect other devices if you want to reprogram theispLSI1016 in circuit.

To stipulate that the programming pins shall be put to noother use, as I did for this project, go to the project navigatorwindow, click on the top level circuit in the sources window,on 'Compile Schematic' in the processes window, and on`Process/Properties' on the navigator menu bar. Make surethat ISP (in -system programming) is set to 'True', and closethe window.

The last, most restrictive, option is to stipulate which pinnumber shall be associated with each i/o. Select 'SymbolAttribute Editor', which is the centre icon in third row oftools palette. Use the mouse to draw a line around the i/o padand buffer in question.

The left window of the symbol attribute editor contains

16 way IDC socket

16 way IDC socket

26 way IDC plug

Cable BFinalcircuitboard

16 way IDC plug

26 way IDC socket

16 way IDC plug

Cable A

Finalcircuitboard

26 way IDC plug


DIGITAL DESIGN

three entries; the second is named the `Synario Pin'. Enter thepin number you want in the 'Attribute' window, then clickelsewhere in the schematic editor window.

This approach is also useful when you want to make minorchanges to an already -programmed device which has beencommitted to a printed circuit board, where changing thepinout would involve changing the board. You can force thepin numbers to be identical to those of a previous version.

But first I must show you how to find what pin numbersthe system allocates when given a free hand.

Making the programming .jed fileIn the project navigator window, click the device, in thiscase, ispLSI1016-60 PLCC44, in the sources window. Thendouble-click 'Fitter Report' in the processes window. Theprocess may complete successfully with or without warnings,or may fail if there are errors. In any event, the ReportViewer window will open.

If the process completes successfully, you will see a <pro-jectname>.rpt, with, at the end, a list of which i/os have beenallocated to which pins. If errors or warnings arise, they willbe shown in a .log file.

Use F2 - the 'Find' function - to examine descriptions oferrors and warnings in the .log file.

Programming the deviceTo program the device, you need a programming adaptor,Figs 7, to go between the pc's printer port and the devicebeing programmed.

Details of the hardware connecting pc, programming adap-

tor and target ispLSI1016 are left to the you since there aredifferent implementations to choose from. You will have todecide whether you want a separate programming board forthe pld, or whether you will program the device in the finalcircuit board.

Because my final circuit needed to communicate with thepc via its printer port, I used a 25 -way D to 26 -way IDCcable to connect the printer port either to the programmingadaptor or to the final circuit board. I then used a 16 -way1DC cable between programming adaptor and final circuitboard, Fig. 8.

Once the printer port is connected to the programmingadaptor and the cable linking the adaptor to the final circuitboard is in place, and the ispLS11016 is fitted, double click onÌSP Download System'. The download window appears;choose 'Configuration/Scan Board' and check that the sys-tem can find the pld.

Now click Browse, find the <projectname.jed> file andpress OK. Hit the Run icon - the running figure - on thedownload system icon bar. All being well, after a few sec-onds, you'll get a 'programming successful' message.

I haven't touched on the simulation tools available, or onthe graphical tools available under ispDS+. Everything I'vedescribed so far has used the isp Synario program. Theseadditional facilities can be found by looking at the help filesand on-line manuals provided with the software.

I am grateful to my employers, Cambridge Consultants, forpermission to publish this article, and particularly to JulianColes for giving me the idea and to Neil Johnson and KarlSwepson for their enlightenment.

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LETTERSLetters to "Electronics World" Quadrant House, The Quadrant, Sutton, Surrey, 5M2 SAS

E-MAIL [email protected]

Students' lotsIn response to Dr Allen Brown'sopening article in EW October 1998,it is indeed much harder to be astudent than 25 years ago. From1984 till 1990, I studied electronicsat a Netherlands university andmoved abroad in 1992. That wouldseem to underline Dr Brown'sarticle. But nothing is further fromthe truth, as I will try to explain.

The Dutch grant and pay -backsystem is similar to the one recentlyintroduced in the UK. Tuition feeswere introduced in 1986. This metwith opposition, obviously. From metoo. But the numbers of new studentsdid not drop.

By the time I finished my course,my debt had build up to anequivalent of £4000. That meant Icould not buy a house in 1991. Notthat that was a problem, since a lot ofengineers are not totally sure wherethey are going to work for the nextfive years at the start of their career.

On the other hand, the gap betweenmy student lifestyle and the firstsalary was so big - going up fromabout £300 to £800 per month - thatI was able to pay off my debt within18 months. To allude to twice thedebt for couples is unfair since youeither have a double income or youdon't have to start to paying backright away.

The fact that Holland, Germany orFrance still has some engineers leftshould also undermine the validity ofDr Brown's view. And not everyoneis happy to give up their country,friends and family for a good salary.My reasons for moving abroad werecertainly not the money since I work

for the NHS.Dr Brown also forgets to mention

that there is another side to the coin.Governments struggle to eke outtheir available resources. You canbet that if the system remains thesame, future cuts in the grantssystem are inevitable unless othergovernment departments aresacrificed.

I think it is not unfair to askstudents - most of whom will be alot better off later compared toworkers without a degree - to investa little in their own future to avoidbreakdown in other parts of theeducation system.Frank CookOswestryShropshire

Watt exposeI read Lawrence Woolf s article`RMS watt, or not?' with particularinterest. I had just bought a pair ofsmall amplified loudspeakers to usewith my pc and had been enjoying aboggle at the numbers on the box.

The front of the box claimed 50WPMPO, peak music power output.On the back of the box, thespecification claimed 10 watts rms(2x5W). But the plug -top powersupply included was rated at 6V,600mA - i.e. 3.6W.

The amplifiers inside consist ofeight -pin DIL chips of the typeusually rated at 2W into 80 using a12V supply. The speakers are 4in,80 units. Realistically with a 6Vsupply, I would expect about a wattof output.

They work well and sound about asloud as a portable radio. I am not

complaining. They are just what Ineeded, and were remarkably goodvalue at £6 the pair - new and boxed.Some pc loudspeakers on offer arerated at 400W. I settled for the 50Wjobs - fearful of the wrath of myneighbours.

It would be great if we couldbelieve specifications at face valuewithout the chore of trying tounderstand what's watt.Manufacturers take note: I for oneam more impressed by a realisticspecification as opposed an unlikelysensational one. But then I expectyour marketing people know better.John CronkPrestatynClwyd

Digital dog's dinnerDigitised tv sound production andtransmission promised to be thepanacea of sound quality, but has itdelivered?

I can't remember hiss being aproblem recently, but distortion is.Viewing on old-fashioned terrestrialfm in mono, it seems that as studiofacilities are updated to digitalworking, the distortion gets worse.Live sound is quite acceptable, firstgeneration tape is a little distorted,while edited, second generationsound is appaling.

In the summertime, the BBC`Working Lunch' programme wasextolling the virtues of its new OBtruck which had won awards. Yet thevery same truck was, and is,producing horrendous distortionwhen broadcasting edited stories.

What does this distortion soundlike? Usually very sibilant, a

pumping, rough, muddy,intermodulational noise, akin torecordings made without bias. Thesound is dynamically distorted bothin frequency response and amplitude.

News 24' items from America canbe even worse. Presumably thesehave been processed a greaternumber of times.

When combined with a strongaccent, words can be unintelligible.Music seems to be less affected, dueto fewer generations, maybe, qt thefact that music is a more continuoussignal than speech.

If digital should be so transparent,can anyone explain why it is socloudy?M. GentleLondon

HV fuses?A friend recently asked me if I couldobtain a replacement for the high -voltage fuse in his microwavecooker. I tried all my sources to noavail. He tried service shops and wastold they were not available, or thatthey could only be fitted by trainedpersonnel, or was offered a fudge,consisting of replacing the fuse witha diode. The cost was about £50 ineach case. Where can one buy high -voltage fuses? They seem to be madeby only one company in the Far East.M. GentleLondon

There's more toRadio 4...BBC Radio 4 is broadcasting astrange signal which I would like todraw to the attention of readers.Listen to 'Today' on Radio 4 any

Wire into thisImagine you want to make a simple luxmeter in a hurry.You haven't time to order components so you have to usewhat's to hand: an LDRO3 light -dependent resistor, somelinear resistors, a 350µA 2500 galvanometer, a 9V batteryand two bipolar push switches.

As the resistance of the LDRO3 will vary from some 100to 5001(0, you need two scales. For low light levels, youjust put together the ldr, battery, galvanometer, a 24Ic0resistor and a Skil trimmer as in Fig. 1 a). The trimmer isnecessary to adjust full scale, Fig. 1 b). For the strong lightyou adopt the layout of Fig. 1 c).

Here comes the problem. All available items are in Fig.1d). Switch S1 selects the first scale and S2 the second one.Pressing both switches together allows you to adjust fullscale.

Of course there is no current through the battery whenneither S1 or S2 are pressed. Try wiring the circuit up. I willbe surprised if you found the solution in the first half-hour.lean -Marc BrassartSaint Laurent Du MarFrance

(a) 350µA (b)250Q LDRO3

24k

5k

9VF -

5k

24k

9V

350µA (C12)25052

350µA(c) 25011

24k(d)

24k

350µA25011

0ANV\i-ci 11)5k 5k

S1

LDRO3

S2

r011110111111.

LDRO3

9V

-19V

Fig. 1. Luxmeter with two ranges. All you have to do is wire it up so that each switch selectsa range, both switches on allows fsd setting and both switches off disconnects the battery.


LETTERS

time from 6am until 9am weekdays.You'll need an audio system with agood bass response. From time totime, you will hear a rumble, notunlike that from vinyl records. Thebandwidth of the rumble is quitenarrow; a sub -woofer doesn't bring itout much. I have phoned the BBCand e -mailed them. I got an e-mail inreply but it simply said that theywouldn't be replying.Charles CoultasWokingham

Seeing throughWindowsThere have been a few editorialsabout Microsoft, Windoze, etc, inyour journal recently, and being areluctant user of the stuff I thought Iwould throw in my two bob's worth.

Phil Darrington's piece in the Juneissue, bemoaning the poorperformance of '95, indicates somelack of understanding of the beast onhis part. Trying to run it on a 33MHz386 with a minuscule 4Mb of ram is

simply asking for trouble. It reallyneeds a minimum 16Mb of ram, andmore is better. Rod Cooper prettymuch confirms this in the Augustissue. Windows 98 requires abouttwice as much - presumably becauseyou must have Internet Exploderloaded all the time. The entry levelfor a pc these days is 64Mb of ram.

Windows 3.x was much lessforgiving in my experience, and it wasless graceful when it did fall over. Onseveral occasions it has locked up sotight on me that even the DOSconfiguration would hang the pc, andthe only option was completereinstallation of Windows afterdeleting it. If Phil is tired of waitingfor the `disk -scanner' he can surelybypass it with a few quick keystrokes,although why one keystroke is notsufficient is beyond me.

In the August issue Rod Cooperwonders at the value of FAT 32 withits ability to make clusters as smallas 4Kb. My system at work is alowly 586 with a 1.6Gb drive. Withthe current state of research funding I

am unlikely to get it upgraded in thenear future.

My old system at home had a2.6Gb drive, and both of thesesystems are squeezed for hard diskspace. I partitioned both drives tominimise the cluster size but even sothere is some 80 to 100Mb of lost`slack space' in a 1Gb partition dueto the cluster size -a loss of nearly10%. Most of this would bereclaimed with FAT 32.

Win 95 revision B supports FAT32 and a drive can be convertedwithout loss of data with PartitionMagic.

Broadly, however, I agree withPhil. I also think Windows 95 reallyrequires more intervention on thepart of the user or system manager tomake it user friendly. I recommendthat all 95 users obtain and installPower Toys, TweakUl being themost important component. Why it isnot a standard part of the package isa mystery, unless Micro$oft has apolicy of denying its customers theability to be able to set their systems

INPUT

OM

0.01

10k

01

2N5486

1k

GAIN

ADJ

2k 300i1 2 5011

*1k 2470

022N3904

032N3906

A

5.6k 2 3k

- 15V

0 002

100

10M

OUTPUT

15V

-15V

Wide -band fet amplifierI have some commentary regarding the circuit, 'wide -band, variable -gain FET amplifier,' submitted byFrantisek Michele in your August 1998 issue. In particular, because the 2N5486 fet is outside the feedbackloop, the circuit will not follow the gain equation given in the text.

In practice, the fet follower suffers gain loss, although this is correctable by trimming the feedback ratio toachieve the overall desired circuit gain. Also, the feedback path should be returned to Tr3's emitter, asopposed to Tr2's.

This circuit is of special interest to me because it is identical to a circuit that appears in the LinearTechnology Corporation application note 21, 'Composite Amplifiers' dated July 1986. The sole difference isthat our circuit used feedback trimming to avoid the previously mentioned problem.

The circuit also appeared, with LTC's approval, in the January 1987 issue of EDN magazine. Your readersand Mr Michele may wish to reference these publications for expanded discussion of this circuit's operations.

WilliamsStaff ScientistLinear Technology CorporationMilpitasUSA

up the way the user wants it, ratherthan how Microsoft wants it. As fornot supplying manuals, they are anoptional extra these days, a way forto cut costs and boost profits.

By all accounts Windows 98 is noreal improvement on 95. In fact theadvice I have seen is that there islittle or no advantage in changing to98 unless there is a specific featureyou need.

From all I have seen it requiresmore resources than 95, and sinceInternet Explorer is such an integralpart of the system, the system hangswhen Explorer hangs, which couldlead to loss of data. This is not thecase with Netscape. Furthermore,every review and all the advice Ihave seen suggests that IE is inferiorto Netscape.

The issue of Microsoft's nearmonopoly is perhaps more serious.The Internet is becoming moreimportant as a communicationsmedium for news, etc, and I believethat the bun fight over InternetExplorer has more to do with thatthan Microsoft's desire to provide abrowser.

In Australia we already have analliance of Microsoft with one of ourbiggest media groups (PBL, ownedby the Packers), called NineMSN. Afriend recently bought a new pcwhich had '98 loaded, and therewere dozens of shortcuts in menus -up to five deep - to various sites fornews, sports, movie, etc, owned oroperated by PBL, Microsoft, andtheir associates.

We certainly don't want Bill Gatesand Microsoft - or PBL for thatmatter - to be in a position exercisecontrol over the information we haveaccess to, any more than we wantthat other well known US citizen,Rupert Murdoch, to. It is essentialfor democracy that they don't.

For more details on how flakyWindows 95 is, and some usefulinformation that will help, I directyou towww.iarchitect.com/msoft.htm andwww.creativelement.com

To conclude I proffer this smallpiece for your amusement. I don'tknow its origins.

Definition of Windows95:Windows95: /win-doz-nin-te-fiv/ n.32 -bit extensions and a graphical

shell for a16 -bit patch to an8 -bit operating system originally

coded for a4 -bit microprocessor, written by a2 -bit company, that can't stand1 -bit of competition.Phil DennisSchool of PhysicsUniversity of SydneyAustralia

Bang go my chances of a reviewcopy of NT5 - ed.


COMMUNICATIONS

Hands-on InternetC ril Bateman reveals three clearing houses for data sheets andapplication notes here - all accessible via the net, free of charge. Healso focusses on design information for those of you interested inthermal management and temperature measurement.

For many designers, the Internetcan be used to quickly ascertainpotential design options,

reducing time to market. It contains awealth of electronics design data,both data sheets for specificcomponents, application notes anddesign guides. But how best canthese be accessed ?

Assuming that you know thecomponent part number andmanufacturers name, a data sheet iseasily retrieved. You simply visit themanufacturer's web site and searchagainst this part number.

If you do not have enoughinformation to take you directly to asite, you might visit and search eachmaker's site in turn. This can provetime consuming though - particularlyfor readers outside North America.

Especially when Internet is slow, tominimise on-line time, I try,

whenever possible, to download threeor four files concurrently. While eachindividual file transfer rate may thenbe reduced, I find that as one siteslows down, another usually speedsup. My modem then tends to runcontinuously close to maximumspeed and my total download time isminimised.

Searching for applicationsinformationWhen starting a new design, you willknow what the application is, butoften, you will not know thedesignations of parts suitable for thedesign, nor who makes them.

Using a conventional Internetsearch engine, such as Alta Vista, tosearch against the requiredapplication might provide the neededdata. More often that not though, youwill be left with countless hits to sift

through, and even after sifting thereis no guarantee that you will findwhat you are looking for.

Specialist library search sites canbe useful here. In recent issues, Ihave mentioned several specialisttopical magazine -based sites that canprovide useful backgroundinformation and articles. They alsooffer links to other sites, but notusually to specific device orapplication note numbers.

To date I have found only threelarge, specialist data -sheet andapplication -note libraries that can besearched free of charge. These arepopular sites, so again can be veryslow to access.

Questlink.com3 hosts the EEDesign Center community page,which can be electronically searched.You can have free access to this site,but downloading information


COMMUNICATIONS

Where to look...1. IE bug opens users' hard drives. http://www.news.com/News/Item/0,4,27482,00.html2. Cuartango Security WEB Site. http://pages.whowhere.com/computers/cuartangojc/index.html3. EE DESIGN CENTER. http://www.questlink.com4. Electronic Designer Interface. http://www.info-quick.com5. Global Semiconductor Datasheets Library. http://www.semi.com.tw6. Electronics Cooling Magazine. http://www.electronics-cooling.com/Resources/EC_Articles7. Application Note AN -225. http://www.national.com8. Application Note AN28. http://www.linear-tech.com9. Application Note AN -369 http://www.analog.com

As features are added, operating system andapplication software becomes more vulnerableto software bugs and hacker attacks. Accordingto a CINET1 report, on-line Windows or NTusers of Internet Explorer 4 with activescripting enabled, have been exposed.

A malicious VBScript received via HTML e-mail or directly from a Web page could copyor even delete files from your hard disk -without your knowledge.

Details of fixes for these new bugs can befound in the Microsoft bulletin ms98-015.Until these fixes have been applied, Microsoftrecommends you turn off active scripting forExplorer.

Juan Cuartango2 posted on his Web sitedetails of four recent security problems. Hisdemonstration test pages let you confirmwhether your system is vulnerable.

fie k ylew 4o gookma43 Links golionsSelo

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lEnterprise Computing

IE bug opens users'hard drivestarot t+Stall Wren, CNET Nem com0.3.13 1998 1200pm PT

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pitetloi y Window

Hopefully the last of a year long series of'scripting' enabled hacks, which could affectInternet Explorer 4 users.

Wender. III Desipls f eidei Applk alion Hole smash ResoldFile Edit View Cot Bookmarks Links Options Ditedoty WindowHelp

EE DESIGN CENTERsmThe WodetvriA, Dap; Ikerizeeteke ametrungt,

The EE Design Center found 3 Application Notes that contain`therm° couple"Displaying I - 3

Andag Devices

ADDlIcation Note. Thermocouple Signal Conditoning Using the AD594/AD595 (106kb PDF)Steal.

j. Alin Intimated Pied=

Applicatton Note. Design Showcase: Thermocouple Preamp (79kb PDF)Ise almirmiliecromim

APplication N ote 1CTemperature Sensor Provides Thermocouple Cold -JunctionCompensation (124 kb PDF)See aboading

- -

Fig. 1. Result ofsearching theuser friendlyQuestLinkapplication notesdatabase, for'thermocouple'applications.

requires you to first register.One nice feature is that while

QuestLink redirects your downloadto the manufacturer's site, yoursearch result page stays on -screen,facilitating multiple simultaneous filedownloads. My application -notesearch on 'thermocouple' for thisarticle found only three hits. Oneeach from Analog Devices, Maxim

Integrated Products and NationalSemiconductor, Fig. 1.

Info-quick.com4 I find less useful,mainly because I use Netscape 2.With this early version of thebrowser, I experience pull -downmenu bugs. These are listed in Info -quick's help files. On my first visit tothis site, I was unable to access anydata at all until I referred to the helpfiles. Using version three or later ofNetscape is said to overcome thisproblem.

In the March '98 issue, I mentionedthe Icesoft library which can beaccessed at the semi.com.tw Websites based in Taiwan. Although thissite can be slow, it remains my firstport of call when seeking a list ofdatasheets and application notes.

Of the three sites mentioned here,Icesoft regularly returns the mosthits. My search on 'thermocouple'returned 23 hits. It included manyfrom Linear Technology, which theother sites missed. But it failed tofind the Maxim or National hitsfound by QuestLink.

Icesoft provides a listing ofpotentially suitable parts, then routesyour selected item directly to the

manufacturers site files. But in theprocess, it removes your searchresults page. Having commenced adownload, returning to this resultspage can be quick, but thisintermittent page loss inhibits mypractice of concurrent file downloads.

Managing component heatEvery electronic design shares acommon characteristic - itscomponents heat up. Excessiveoperating temperatures dramaticallyreduce the equipment's service life.Frequently, electronic circuit designbecomes a trade-off betweenperformance, cost and componenttemperature.

While specialised circuit -boardthermal -simulation software isavailable, it requires you to inputmany parameters, some of whichmay not be available. Choice ofcircuit -board materials and printedtrack design further complicate thesecalculations Fig. 2.

As a practical alternative,component temperatures on thefinished board can be measured.Heatsinks and other large parts areeasily measured, using sensors madefrom diodes, diode connectedtransistors, thermistors, senseresistors, dedicated integrated circuitsand pre-packaged thermocoupleprobes.

Smaller - and especially surfacemounted components - ideallyrequire use of the non -contacttemperature -measurement methods.Such methods were outlined inHands-on Internet in the January '99issue. But non -contact measuringequipment is costly, and can bedifficult to obtain. This month I lookat lower cost methods.

PTFE-insulated naked beadthermocouples made using 0.2mmdiameter wires are a readily availableand economical alternative. Thethermocouple wires conduct heatfrom the device being measured,particularly when attached to 1206size or smaller components,understating its true temperature. So


COMMUNICATIONS

the thinnest possible thermocouplewires should be used.

In principle, it is feasible to simplymeasure the thermocouple's outputvoltage. Connection of thethermocouple wires to a measuringinstrument imposes a seconddissimilar metal, 'cold' junction. Thedifference voltage generated by thesehot and cold thermocouple junctionsdepends on their temperaturedifference. Published thermocouplecharacteristic tables assume this coldjunction be maintained at exactly0°C.

Thermocouple linearity issuesAll thermocouples have a non-lineartemperature/voltage characteristicwhich requires compensation. Inpractice, most electronic componentsrun at temperatures between 25°Cand 150°C, so the type 'K',Chromel/Alumel thermocouple ispreferred.

Several tutorials on minimisingerrors when using thermocouples canbe found on Internet. The ElectronicsCooling Magazine6 site allows itsback issues to be accessed. Twotutorial articles, 'Notes on using

Netscape - ETkimerics - September 1998 - Calculation CornedFlle Edit View Bo

HelpBookmarks Mrs Dhotis Directory Window

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Convection and radiation beat loss from a printedcircuit hoard

In lest Mlle's column, a method for caladarmg the thermal conductvivi of a printedwant board (PCB) was described. Now, we look ate mote complicated heal transferprocess, namely the loss of heat from the surface of a PCB to the ambient an This;Motion is more diaRenging to describe mathematically once 11 involves thesimultaneous processes of heal spreading by conduction and heat extraction over thesurf ace of the board by =vector, and imitation The figure below Muse ate5 theheat flow patterns for a leadframe package attached to o test PCB The efficiency ofheat transfer from the PCB to air has a significant effect on the tempetarinedifference between the chip and the an.

RegionRegion I

Figrae 1 Ho$63,3 0113rn: for 313 ar arr. pwl we a I Ow 1 to a,31- PCB

_,Ezif Document: tee

TEMPERATURE

SENSORMATED TO

SERVO

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MEASUREMENTTHERMOCOUPLE

1

T1

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V OUTPUT =

V MEASUREMENT -

V COLD JUNCTION

T2

U

Fig. 2. Heatdissipated fromprinted boardmountedcomponents, is acomplexcombination ofheat dissipated bythe component,the pcb and itstracks.

Fig. 3. Anelectronicmethod ofmaintaining atrue zerodegreesCentigrade,reference coldjunction, foraccuratethermocouplemeasurements.

Fig. 4. Electronic voltage compensation methods can be substituted to avoidmaintaining a zero degrees Centigrade, reference cold junction.

V IN

CORRECTS FOR BOW IN COLD JUNCTION.NOT IN PROBE (HOT JUNCTION) GND

thermocouples' by Dr. R J Moffat ofStanford University and 'Heattransfer measurements in electroniccooling applications' by Dr. N RKeltner of Ktech Corporation areespecially relevant. They can befound in its January '97 andSeptember '98 issues.

Many makers producethermocouple meters and DMMadapters, with varying claims foraccuracy. The 40.6µV/°C 'Seebeck'coefficient of type 'K' thermocouplesgenerates some 3mV at typicalcomponent temperatures.

Common -mode noise pickup canbe a problem when measuringcomponent temperatures on 'live'circuits. Using applications datafound on the Internet though, you canquickly understand how to minimiseerrors for 'in -circuit' temperaturemeasurement of components.

Optimised thermocouplemeasurementsFor laboratory use it is possible tomaintain an extremely accurate 0°Creference cold junction for manyhours by simply using melting iceheld in a thermos flask. Butelectronic compensation would bemore portable and practicable, sothermoelectric coolers are used toprovide a 0°C cold junction, Fig. 3.

Temperature is one of the mostcommonly measured physicalparameters. As a result, dedicatedelectronic integrated circuit solutionsfor thermocouple cold -junctioncompensation have been developedby many makers.

This technique adds a voltage intothe thermocouple loop, equal in valuebut opposite in polarity to thatgenerated by the cold junction, Fig.4. One simple method of cold -junction compensation is described inthe twenty-year old NationalSemiconductor application note AN -225.7 It uses their LM335 integratedthermometer circuit to measure the

Fig. 5. Anintegrated circuitmethod whichsupplies a switchselectable coldjunctioncompensationvoltage, suitable foruse with commonthermocouples.


COMMUNICATIONS

Fig. 6. A totallyanalogue,

continuousfunction

linearisationcircuit, which can

correct for allthermocouple

non-linearities.

Fig. 7. A modernintegrated

thermocouplecold junction

compensationcircuit, used with

multiple switchselectable

thermocouples,for rapid multi -

pointtemperature

measurements.

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cold junction temperature. Thiscircuit then applies a 'best straightline' fit correction voltage.

While best straight-line fitcorrection is acceptable for smalltemperature changes, even near roomtemperature, thermocouple outputfollows a curve. Improved cold -junction compensation using a 'bow'correction circuit was provided bydedicated cold junction compensationintegrated circuits. Switch selectionof the appropriate correction pinpermits cold junction compensationfor a variety of thermocouples, Fig. 5.

Twenty pages of thermocoupleinfo...Linear Technology's application note

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AN28, titled 'ThermocoupleMeasurement' is a twenty pagetutorial which includes thermocouplebackground and many practicalmeasurement circuit drawings.8These detail both linear and digitalcorrection methods for thermocouplehot junction non -linearity as well asthe improved cold junctioncompensation techniques, Fig. 6.

Analog Devices' application noteAN -369 describes a singleintegrated circuit which combinesthe required cold junctioncompensation with an 'in -amp' forsignal amplification in the onepackage.9 Thermocouple hot -junction linearisation however is notincluded, so external compensation

CO NSTANTA N(AL UMEL )

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for this needs to be added. Thinthermocouple wires and junctionsare fragile, and this package alsoincludes an on -board brokenthermocouple alarm circuit.

Electronic cold -junctioncompensation requires the coldjunction, correction circuitry andprinted circuit tracks all be at thermalequilibrium. Correct printed boardlayout and thermal shielding or heatsinking, is needed to minimisemeasurement errors.

Having provided an accuratethermocouple compensation circuit,multiple thermocouples may beswitch selected, for near simultaneoustemperature measurement of manycomponent parts, Fig. 7.

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DIGITAL DESIGN

Having foundlimitations whileusing traditionalBoolean algebra,David Warren -Smithset about rethinkingthe concept from anexclusive -OR origin.His new methodgreatly increases thescope of Booleanalgebra, and thus itsusefulness in digitaldesign.

CIhave developed a complete Boolean algebra using theexclusive -OR and AND operators. This article demon-strates that this algebra complements the more familiar

Boolean algebra using the inclusive -OR operator. In doing so,it greatly increases the scope of Boolean algebra for use in thedesign of digital circuits.

Simplification methods are are available for this algebra.The use of conventional Karnaugh maps is described here, butI have also developed a systematic algebraic method thatallows you to equate up to six variable using with just penciland paper. I hope to discuss this in a second article.

The material in this article requires nothing more than abasic understanding of digital design theory.

IntroductionMy first digital project in the late fifties was a plant -speciescounter for a botanist. The counter was constructed fromdecatrons - gas discharge display devices for the youngeramong you. To implement a logic gate that was needed, weused a valve rectifier.

This, and subsequent projects, gave me my introduction todigital design - then called switching -circuit theory. We usedthe mathematical logic invented by George Boole anddescribed in 'An investigation of the Laws of Thought', in1854. I came across this emerging concept on visits to a localtechnical book shop and bought several books about it.

One of these books gave an interesting account of CharlesBabbage' s attempts to invent a mechanical computer out ofgears and levers - i.e. the Difference Engine for compilingtables and later in 1833 the Analytical Engine. This machinewas to be driven by a steam engine. Note that this was some20 years before Boole published his account of his algebra.

The concept of the finite mathematical structure of logicaldesign theory, and the way in which it solved digital designproblems, for me became of great interest. I discovered thatBoolean algebra was a whole new algebra based on a finitenumber system.

Instead of having an infinite number of integers, you onlyhad two numbers or values, one and zero, or 1 and 0. The dig-its 1 and 0 are used for convenience; they could be called any -

David N. Warren -Smith,MSc, CPENG


DIGITAL DESIGN

Fig. 1. The familiarelements of AND, OR

invert algebra. A

A B AB A B A+B

A'

A A'0 00 1

0

0

0

0

0

1

00 1

1 0 0 1 0 A 1 0

1 1 1 1

B

A A

Relay, SPNC

BAB

BA+B A A') >0

NOTAND2 OR2

AB A+B A1

A'1

Fig. 2 . The 16possible binaryoperators andthe 4 possible

unary operators.

A 0011B 0101

000000010010001101000101011001111000100110101011

11001101

11101111

AND2 IEEE

AND operator

Open circuit (stuck low)AND operatorAND operator with B invertedAAND operator with A invertedB

Exclusive OR operatorInclusive OR operatorNOR operatorExclusive NOR operatorInverse of BOR operator with A invertedInverse of AOR operator with B invertedNAND operatorShort circuit (stuck high)

OR2 IEEE

OR operator

A 01

00 Open circuit01 No inversion

\ 10 Inversion11 Short circuit

thing such as `true and false', 'high and low' or 'on and off .The algebra was the same whatever names you used, but

the application of the algebra could vary depending on whatyou wanted to apply it to. You have constants and variablesin this algebra, but they take on only one or the other of thetwo values that you have assigned to the algebra.

Some of the early books that I bought were written by PostOffice engineers and applied to relay circuits. I discoveredthat in a digital design problem, you could separate the log-ical analysis or synthesis of a problem from the implemen-tation of the final hardware solution. The algebra was just asapplicable to logic gates, and diode gates as it was to relaycircuits.

Another thing I discovered was that after the initial bit ofthinking to get used to the new algebra and concepts, it wasquite easy to understand and use for practical problems. Justa little persistence was needed to get used to the new way ofthinking.

Digital design was launched by Claude Shannon in 1938 inhis account of his thesis 'A Symbolic Analysis of Relay andSwitching Circuits', Trans AIEE, Vol. 57, pp. 713-723.Shannon made a good account of relating Boole's mathe-matical logic to switching circuits.

By the way, Shannon is better known for his major con-tributions to communications theory. Logical design is there-fore quite a young subject and has grown with the develop-ment of computers and other digital systems. Furtherdevelopment of logical design theory is possible and ongo-ing.

The incredible and rapid development of personal com-

NOT IEEE

INVERSE operator

puters has been made possible by the invention first of pointcontact transistors by Brattain, Bardeen and Shockley in1948. Soon after, integrated circuits appeared with the devel-opment of planar transistors in about 1959.

First encountersIn the sixties, my first encounter with integrated circuits waswith Fairchild resistor -transistor logic, known as rtl. This wasquickly superseded by diode -transistor logic and then tran-sistor -transistor logic, or ttl, that is still sometimes seen.

These developments were based on a sound understandingof the physics of solid state devices. The design of comput-ers and other digital applications similarly requires a soundunderstanding of logical design theory and the Boolean alge-bra on which it is based.

In this article, I take a look at Boolean algebra as it is pre-sented in popular books on digital design theory. In doing so,I hope to change some of the ways of thinking depicted inthese books.

My aim is that you should discover that the Boolean alge-bra that is usually taught in technical schools or undergrad-uate universities is incomplete and inadequate. I redress thissituation by filling in the missing bits.

My starting point is a detailed look at the exclusive -ORgate - ex -OR for short. This device is an essential part ofBoolean algebra and should be treated as such. In order toreach the objective of being able to deal with these gates eas-ily I will develop basic theorems relating to these gates. Ihave also developed a method of using conventionalKarnaugh maps to deal with them.

You will find that my approach is more decisive than thepattern matching idea given in some digital text books. I alsoexplain why my approach has not been generally recognised,as far as I can tell, from reading books on digital design.

To get the most out of this article you will need to keep inmind my ground rules. I don't feel that I understand some-thing unless I can see how each part of it is arrived at.Consequently you will find that each step in my explanationdepends on earlier steps described, down to the initial con-cepts that I describe first. If you start in the middle, the topicwill look more complicated than it is.

Also, this article would have become too long if I had goneover ground well covered in existing books. Consequently Iassume that you are familiar with basic Boolean algebra, asit is presented in popular books on digital design. Thisincludes concepts such as a canonical expansion, the dualityprinciple, and Karnaugh maps, abbreviated to K-maps.Theway I display K -maps is the way I feel most comfortable


DIGITAL DESIGN

with them. I find that this method makes them easier to drawtoo.

Exclusive -OR algebra is sometimes referred to as a Reed -Muller algebra. If you are familiar with R -M, then you mightlike to compare it with my approach. My approach has notoriginated from R -M, and you don't need to understand thisform of algebra in order to benefit from this article.

You might also have come across the concept of a GaloisField - GF(2) in particular. Exclusive -OR functions have avery wide spectrum of applications - particularly in com-munications and data storage applications, where GF(2) isused. I don't go into this in this article.

If you have done any work with digital circuits, you willhave noticed the rapid emergence of application -specific inte-grated circuits or ASICs. Many digital designers are nowusing programmable -logic devices, or plds. These are ASICsthat offer instant digital designs.

A popular class of these devices are cplds, or complex plds,to distinguish them from the earlier programmable -arraylogic, and similar devices. Some of these cplds are repro-grammable. You can program them directly from your pcthrough a simple cable attached to your computer's parallelport.

The whole process takes seconds. You don't even have toremove the device from the printed circuit board for yourapplication. This significantly speeds up the developmentprocess. The once popular ttl devices have gone into the junkbox and discrete cmos logic is not far behind.

Many complex plds contain an exclusive -OR gate in theirlogic structure. Consequently, an easy way of dealing withthese gates is useful.

This article offers such a way. If you are using a cplddevelopment system such as Altera's MaxPlus II, or one ofthe many other similar systems on the market, then you arebeing spoiled. These systems will do all your logical designdrudgery work for you.

There are Altera systems in use at literally thousands ofuniversities, technical colleges and design laboratoriesthroughout the world. With this system you just have to typein what you want or draw it on the screen, make a few choic-es and press a button.

As an instructor in digital design I believe that you stillbenefit from understanding the theory. You will know whatthe system is doing, why it is doing it, and what the short-comings and limitations in the system are.

Due to the convenience and capacity that these devicesoffer for development and small production run applications,new families of devices and new manufacturers of cplds,eplds, fpgas, etc., are still appearing. Devices keep gettingbigger, faster, more efficient and more of them.

The proper use of these devices demands an understandingof the underlying theory that they all depend on. Think equa-tions rather than circuits. In the context of cplds, circuits areboth unnecessary and clumsy.

I believe that my use of K -maps for exclusive -OR algebraand my simplification method were original when I firstinvestigated the material for this article in 1965. They maystill be.

The derivation of Boolean algebrasTo make the matter a bit more intelligible you need to goback briefly to the AND, OR invert algebra.

Figure 1 shows truth tables for the AND, OR and invertoperators, together with the symbols commonly used forthese operators. If you look at the right-hand columns ofthese truth tables you can see the characteristic patterns offour possible values of two variables for the AND and ORoperators and the characteristic pattern of two possible valuesfor the inverse operator. For example the pattern for theAND operator is 0001 looked at from top to bottom.

I like to call the AND and OR operators binary operators

Basic theorems

A&0 =0A&1 =AA&A =AA&A'=0

A+0 =AA+1 =1A+A =AA+A'=1

Commutative law AB=BA

Associative law A (BC) = (AB) c

Distributive law A ( B+C ) =AB+AC

A+B=B+A

A+(B+C)=(A+B)+C

A+SCHA+B)(A+C)

DeMorgan's theorem:

The inverse of a logic function can be obtained by replacing all +operators with & operators, replacing all & operators with + operators,priming all unprimed variables and unpriming all primed variables.

Simplification relationships:VI3=1 A+A'B=A+B

and the inverter a unary operator due to the number of vari-ables involved in each case. To be more general you couldconstruct 16 possible binary operators by making use of allpossible patterns for the binary operators. And you couldconstruct four possible unary operators. Figure 2 illustratesthe possibilities.

In this diagram, six of the binary operators are identified asnon trivial by a tick along side them. Note that only oneunary operator is non -trivial. The names for the operators areshown.

Trivial operators include such cases as the output stuckhigh or low, the familiar operators with one input invertedand cases where the output reduces to the case of a singleinput or the input inverted.

Looked at in this light, the AND, OR operators can be seento be an arbitrary selection of two of the six possible non-trivial binary operators from which the well known Booleanalgebra has been constructed. The fact that this is a completealgebra, in the sense that any arbitrary function of Booleanvariables can be constructed from it, can be seen from thecanonical expansion for this algebra.

Of course the AND and OR operators appear naturallywhen physical switches are connected together or where theconstruction of logic gates is considered, which has con-tributed to their popularity. This is a bit like the naturaldevelopment of the decimal number system because we haveten fingers. We know we can develop other number systems.By the same token, we can also develop other Boolean alge-bras.

The theorems of AND, OR, inverse Boolean algebra canbe derived by use of the truth tables in Fig. 1. Take the truthtables in Figure 1 as the postulates - i.e. starting point - forthe algebra. From here, you simply plug the results fromthese truth tables into the truth tables constructed for the var-ious theorems to prove the theorems.

This is the truth table method of proof - or proof byexhaustion. It is possible because there are only a finite num-ber of possible combinations of values of Boolean variablesso we can consider all possibilities. This method of proofallows you to derive all the results that we need directly.

Keep in mind that all mathematical structures are abstrac-tions. I won't do the derivation here since the results are wellknown. To refresh your memory the theorems are shown inFig. 3. Note the way that they are arranged.

Considered first is the case of each binary operator withone variable and 0 or 1 as the second variable, then the caseof each binary operator with one variable and the same vari-able uninverted or inverted as the second variable.

Fig. 3. Summaryof AND, OR,Invert Booleanalgebra theorems.


DIGITAL DESIGN

Fig. 4. Truth table andcircuit diagrams for

the exclusive -ORoperator.

Fig. 5. Derivationof the inversiontheorems.

xy00011011

x'

y

x

y

XY+X'y

0

oXy+X'y'

) x0 y

EXOR

xy xey0001

1011

0

0

x0y xy' + x'y

x

=1y

EXOR IEEE

Next the three laws are dealt with - namely the associative,commutative and distributive laws. These allow you to per-form manipulations with parenthesis and with rearrange-ments. Next, inversion is dealt with, given by DeMorgan'stheorem for AND, OR Inverse algebra.

Finally, two simplification results are included with thetheorems. When you derive the exclusive -OR algebra youwould of course expect to find some new or different results.

Exclusive -OR algebra basicsNow you can make another arbitrary choice of binary oper-ators and develop another Boolean algebra. Take the exclu-sive -OR and AND operators. You don't specifically need theinversion operator for this algebra since the exclusive -ORfunction has an inversion property built in. But you will needthe inverse of variables.

Also, there is nothing to stop you using results alreadyobtained for the AND, OR invert algebra, so all the resultsfrom this algebra carry over. You are actually extending thisalgebra.

Other choices of operators are possible. For example Icould have chosen the exclusive -NOR operator with one ofthe AND or OR operators. Out of the six non -trivial binaryoperators, three of them are the same as the other three, butwith outputs inverted. This gives them a degree of related-ness. A complete development of Boolean algebra shouldtherefore include at least the AND, OR, exclusive -OR andInvert operators.

To start the process I will first extend Fig. 1 to show theexclusive -OR function as in Fig. 4. This diagram also showsthe symbol that we will use for the exclusive -OR operator.

The basic theorems can be derived algebraically using theresults from AND, OR, Invert logic. This is simpler thandrawing up the truth tables.

In terms of the inclusive -OR, the exclusive -OR is given by

Ti.

T2.

T3.

T4.

xy'+x'yxx'+x'x =0xx+x'x' =1xl+x'0 =x

= x0+x'1 =x'

where ED represents the exclusive -OR operator.The theorems have been labelled for convenience in ref-

erencing, as will be the following ones.Equation T1 shows that applying the same signal to both

inputs gives an output stuck low, while T2 shows that apply-ing a signal and its inverse to an exclusive -OR gives an out-put stuck high.

In T3, applying a logic low signal to one input gives anoutput that is the same as the other input. Equation T4 shows

(x ED y) (x e y)' x' ®y X ED y'

0 1 1 1

1 0 0 01 0 0 00 1 1 1

T5. (x y). = x' = x y'

xy00011011

x y x' y'

0

0

0

0

T6. x e y = x' y'

that applying a logic high to one input gives an output that isthe inverse of the other input.

Both T3 and T4 show the well known result that the exclu-sive -OR gate can be used as a means of controlling thepolarity of a logic signal under the control of one of itsinputs. This result is frequently used for toggling a bit in amicrocontroller output between high and low by exclusive-ORing the bit with a logic -1 bit.

Inversion theoremsEquations T5 and T6 derived in Fig. 5 are theorems relatingto inversion. In addition, T6 follows from T5 by doubleinversion. These are in addition to T4.

T5. (xey)' = x'ey = xey'T6. xey = x'EDy'

Many of these results can be seen by considering physicalarguments. However, by representing all results in the formof equations you can avoid having to depend on physicalarguments - which can quickly get you in a tangle.

Commutative, associative and distributive lawsThe commutative, associative and distributive laws are sim-ilar to the case of the inclusive OR. Proofs can be made bythe truth table method or by expanding both sides and usingthe results for the inclusive -OR case. The proofs are omittedhere.

These theorems show how to deal with parenthesis andrearrangements.

T7. xey = yexT8. (xey)ez = xe(yE9z)T9. x(yez) = xyexz

Commutative lawAssociative lawDistributive law

Converting AND, OR Invert logicThe next theorem provides a way to convert AND, OR logicto AND, exclusive -OR logic. This will be the starting pointin the development of a systematic approach to findingforms of functions that include an exclusive -OR operator.

Theorem T10 states that if g, h are functions of the sameswitching circuit variables, then if f=gEDh and gh=0, then f=g + h. Disjunction theorem T10 can be proved as follows:

f = gEDh = gh'+g'h

= gh'+g'h+gh

since gh=0,

g(h+h')+h(g'+g)= g+h

which is the required result.

Canonical forms for the exclusive -OR logicTheorem T10 can be used for expressing a function given interms of the + operator in terms of the CD operator. The func-tion in terms of the + operator is expanded to minterm form,so that all terms are disjoint - i.e. the product of any twoterms is 0. The + operators can then be replaced with EDoperators.

This means that any function can be expressed in exclu-sive -OR form directly from its truth table or Karnaugh map.A canonical form for the exclusive -OR operator is thereforewith three variables:

Cl f ( abc) = aoa cea2a'bc 'Elke3a'bc,ED

a4ab ' c' Da5ab' cea6abc 'ea7abc

where a is 1,0 depending on whether the ith term is presentor not. Expressions like this are sometimes referred to asexclusive -OR sum -of -products or ESOPs in the literature.

An alternative canonical form is found by expandingprimed variables with T4 (x' =xel ) multiplying out andcancelling duplicate terms with T3 and Tl. It is:


DIGITAL DESIGN

C2. f (abc)=130$131ael32b$133c$134abe135ac$136bc$137abc

where is 1,0 again depending on whether the ith term ispresent or not.

The canonical expansions imply that any Boolean functioncan be expressed in terms of the AND and exclusive -ORoperators. Exclusive -OR algebra is therefore a completeBoolean algebra.

The majority functionCertain functions are true in both inclusive and exclusive -ORform. Take, for example, the majority - or arithmetic carry -function:

abeacebc=ab+ac+bc

Alternative representation of basic theoremsEquations T1-4 are dual theorems and are frequently labelledto reflect this property.

Alternative expressions for T1 and T3 are:

Tla. x x = 0,

for an even number of x,

T3a. xex... = x,

for an odd number of x,

T1b. xeyez = 0,

if an even number of variables x, y, z... have the value 1

xeyez = 1,

if an odd number of variables x, y, z... have the value 1.

Alternative systemsEquations Ti to T10 are a system of exclusive -OR -ANDlogic. A dual system of Exclusive -OR -OR logic is also pos-sible. In such a system T9 would have to be replaced by thefollowing:

T9' x(yez) = (x'+y)EE)(x'+z)

This follows from applications of the distributive law,DeMorgan's theorem and T6.

The exclusive -OR operator can be thought of as a secondaddition operator, known as modulo -2 addition, givingswitching circuit algebra two addition operators.

Duality in the exclusive -OR theoremsThe duality principle states that "Given any of the basic the-orems of Boolean algebra, changing OR operators to ANDoperators, AND operators to OR operators and changingzeros to ones and ones to zeros where these occur leads toanother of the basic theorems." This applies specifically tothe AND and inclusive OR operators.

However, if you apply the inversion theorems to both sidesof the basic theorems of the exclusive -OR operator you cansee that T1 becomes T2 and vice -versa. The same holds forT3 and T4. This gives a sort of duality to exclusive -OR the-orems.

A useful theoremA theorem that gives exclusive -OR logic an unusual

degree of freedom is T11: If f, g, h are functions of the sameswitching circuit variables and f = g eh, then g = fell andh = gOf.

Theorem T11 can be derived as follows. Given thatf=g eh, then adding 'h' to both sides of the equation gives:

f eh = gehela = gsince hell disappears due to T1 and T3. As a result,

g = fOh. Similarly, h = get'.By means of this theorem any given term or expression

can be made to be a part of any other expression of the samevariables.

For example, let x=ac'ea'bc and suppose that the termh=ac is to be made a part of this expression. Now,

g=xelasac'Ca'bc(Bac=a(c'El)c)ea'bc=aea'bcSo,

x=g@h=aSa'bc(DacAs a check, this could have been obtained in this simple casedirectly from the given expression for x by replacing c' withlec and expanding by T9 the distributive property.

You might want to use this idea if you want to find out if asingle variable, with a single exclusive -OR operator will givean expression with fewer product terms than the originalexpression. Let p be the single variable in function f, thenevaluate g=fep. If this expression or its inverse has fewerproduct terms as required then g is the required result. i.e.

f=-g0p or f=g' P'

You would need to evaluate g =fe p for each variable inturn and take the best result, or you might stop with the firstgood result if any.

Another example of the use of this theorem is to find aGray code to binary code converter circuit, given the circuitfor a binary code to Gray code converter. It is known that theGray code is constructed from the binary code by the exclu-sive -OR of adjacent binary bits. You can see this from Fig.6. For four bits:

go=looebi, g1=b1eb2, g2=b2eb3, g3=b3

The most significant bit, b3, is the same for both the Graycode and the binary code.

If you want a Gray -to -binary code converter you can sim-ply apply Ill to the above equations to get,

bo=goebi, b1=gieb2, b2=g2eb3, b3=g3Or by substitution,

bo=g0@g1Sg2@g3b1=g1Sg2eg3b2-g2eg3b3 -g3

Exclusive -OR operator on a Karnaugh mapTake the problem of expressing the function,

f=ac+b'c+a'bc'in exclusive -OR form.

If you are observant you could solve this problem as fol-lows:

f=ac+b'c+a'bc'=c(a+b')+a'bc=c(a'b)'+a'bc=cea'b

There are many cases like this for functions of three vari-ables. Often though, this approach may not be so easy tocarry out. Fortunately the K -map technique can be readilyadapted for the purpose.

First consider the exclusive OR function plotted on a K-

map as in Fig. 7. The K -map technique for the exclusive -ORfunction depends on T10 and the extended forms of Ti andT3. This leads to the relatively simple and more conclusivemethod I mentioned earlier.

Plotting the variables x and y individually on the mapresults in minterm xy being plotted twice, consequently bythe extended form of Ti, this term will disappear from theexclusive -OR form.

b3b2bibo g3g2gigo0 0 0 0 0 0 0 0

0 0 0 1 0 0 0 1

0 0 1 0 0 0 1 1

0011 0 0 1 0

0 1 0 0 0 1 1 0

0 1 0 1 0 1110 1 1 0 0 1 0 1

0 111 0 1 0 0

1 0 0 0 11001 0 0 1 1 1 0 1

1 0 1 0 1 1 1 1

1011 1 1 1 0

1 1 0 0 1 0 1 0

1101 1 0 1 11 1 1 0 1 0 0 1

1 1 1 1 1 0 0 0

Fig. 6. Binary to Graycode conversion.


DIGITAL DESIGN

y

0 1

x

1

xOy = xy'+x'y

Fig. 7. Exclusive -ORfunction plotted on aKarnaugh map.

Fig. 8.Examples of

exclusive -ORforms of logic

equations.

Fig. 9. Four variableexamples of

exclusive -ORfunctions.

Similarly by the extended form of T3, where the mintermis plotted once or an odd number of times it will be retained.

Generalising this observation for the exclusive -OR formgives the rules: 'any minterm included in the function mustbe plotted an odd number of times,' and 'any minterm that isto be excluded from the function must be plotted an evennumber of times, or zero.'

Two examples of this result are shown in Fig. 8. The firstresult is the example given at the start of this section. Youcan see that one term a'bc has been plotted twice and istherefore excluded from the equation.

The second example is the function that had the same formfor the exclusive -OR operators as it had for the AND, OR,Invert operators. Here, one term has been plotted three timesand is therefore included in the function.

C 0 0 1 1 C 0 0 1 1

AB 0 1 1 0 A B 0 1 1 0

0 11 1 0 1

1 1 111 1

The function:A'BC'+AC+B'C = CEDA'B

D 0 0 1 1

ABC 0 1 1 0

00

01

11

10

1

fl = a'b'c+a'cd+bc'd+ac'd'+abd'= aSb'cebdEBac'd

Fig. 10. Anexample of usinga Karnaugh map

to find anexpression for a

Boolean functionin terms of

exclusive -ORoperators.

Fig. 11. Anotherexample of usinga Karnaugh map

to find anexpression for a

function in termsof the

exclusive -ORfunction.

aCO

b001

1

1

1

0

0 1 1

1 1 1 1

(a)

CO 0 1 1

a b0 1 1 0

0

1

(c)

SIMEitiu

aCO 0b0 1

1

1

1

0

0 1

1

(a)

CO 0 1 1

a b0 1 1 0

01

(c)

IOW

The function:abEeacEtc = ab+ac+bc

CD

AB00

01

11

10

0 0 1

0 1 1

1

0

1 1

1

f2 = (a+b)E0(c+d)= a'b'Oc'd'

a01

(b)

a

0

1

(d)

CO

b001

1

1

1

01 1

11 1 1 1)

CO

b00

1

1

1

1

0

1

1

11

1

111

y = a0c0ab'c

(b)

c0 0 1 1

a b0 1 1 0

0 1 11 1

1 1 11 111 11

(d)

y a0b0c

With a little practice, the exclusive -OR forms can be read-ily found for three variable functions and sometimes for fourvariable functions. Figure 9 shows two examples of fourvariable exclusive -OR functions.

A procedure for using the K -map to find opportunities forsimplification of a logic expression by using exclusive -ORgates, by inspection, is to look for a grouping of ones thatcould be simplified if an extra square or squares betweenthem are filled in with ones to combine the terms. This isapplicable if only one exclusive -OR is needed to representthe function. The following examples show a more generalapproach where more than one exclusive -OR is needed.

To plot a function given in exclusive -OR form, simply plotindividual terms by placing ones in all squares for the termand cancel all squares that have an even number of ones.

Don't care conditions are treated in the K -map approachthe same way as for the inclusive -OR case: the don't careterm is used or not, as required. For the exclusive -OR func-tion, don't care terms can be plotted an even or odd numberof times.

In the case of fl in Fig. 9, the minimal exclusive -OR formof the equation may not be so easily found by inspection.Here it would be useful to have an algebraic simplificationprocedure. I hope that the description of my algebraic sim-plification procedure will appear in a subsequent article.

Using a K -map to find ex -OR representationsTwo more examples are shown in Figs 10 and 11. Here,more than one exclusive -OR is required to represent thefunction. These figures shows the step-by-step procedure tobe followed.

Consider the function plotted on the K -map shown in Fig.10a). You might start by plotting variable a, as in 10b). Thiscovers three of the ones in the map but places an additional1 at position abc. The additional ones in Figs 10 and 11 areshown in lighter text.

Next, you might plot variable c as shown at 10c). Thiscancels the extra one at abc, covers the ones at position a'bcand a'b'c but cancels the one at position ab'c. To regain aone at this position, place an additional one there and mapthat position as shown at 10d). This gives the final result asshown below the K -map at 10d).

From a practical point of view, you might implement theresulting expression as follows, since there is generally onlyone exclusive -OR function available in a complex pldmacrocell:

y=aSc@ab'c=ae,c(1@ab')=a@c(ab')'=a@c(a'+b)=a1g)(a'c+bc)

or,

a'ED(c (ab' ) ' )'

for NAND gate implementation. Remember that a NANDgate has the form (ab)'.

Another example is shown in Fig. 11. The same steps aretaken as for Fig. 10. The function is shown plotted on aKarnaugh map at 11a). As before, you start by plotting vari-able a as in 11b), since this looks like a suitable startingpoint. This covers two of the ones in the function but intro-duces two additional ones.

Next you plot variable b as shown in 11c). This cancelsone of the unwanted ones introduced in 11b) but also cancelsone of the ones that need to be kept and introduces an addi-tional one at a'bc.

Finally, add the plot for variable c. As you can see thisrestores the one at abc covers the one at a'b'c and cancels theunwanted ones at a'bc and ab'c. The final well known resultis shown under the K -map at 11d) as it was in Fig. 10. The


DIGITAL DESIGN

method is somewhat heuristic but at least in general themethod gives the result in a direct way.

The last example show a slightly different way of using theKarnaugh map. Assume that you entered the followingexpression into your complex-pld hardware -description lan-guage software:

y=ac'd' +abci-ab'd+b'c 'd+a'b'cd'

The compiler in your cpld software has came up with the fol-lowing expression for this logic function and you would liketo confirm that it is the same function,

y=a® (D' cd'+abc'd+a'b' c'd)

The Karnaugh map shown in Fig. 12 confirms the identity.Note that you can plot all the terms in parenthesis as a func-tion and use this as a whole with the exclusive -OR approachwith the term a.

A reduction of five product terms to three is achieved withthis function. The use of the Karnaugh map is obviously a lotless work than expanding out the exclusive -OR function.

In summaryFigure 13 is a round up of the theorems for the exclusive -ORoperator. This may be about as far as you need to go with thissubject. But, it is possible to treat the simplification of exclu-sive -OR forms of equations by a systematic algebraic pro-cedure. I hope to bring you my description of this procedurein a later article.

This article has demonstrated that a complete Boolean alge-bra can be developed in terms of the exclusive -OR operator

in place of the inclusive -OR operator. Examples have beengiven that demonstrate the use of this approach to Booleanalgebra. The exclusive -OR algebra adds to and does notreplace inclusive -OR algebra. The algebra is complete withsimplification methods including the use of conventionalKarnaugh maps.

I hope that reading this paper willhave given you a few new ideasabout using Boolean algebra and thatyou will no longer be put off whenyou see exclusive -OR operators inlogic expressions.

Fig. 13. Summary of theorems for theT1 xex= 0

T3. xe0=xT5. (xey) ' =x ' (Dy=x0y

T7. xey=yEDx

T8. (xey)ez=xe (yez

T9. x ( yez ) =xyexz

T9' x(yez)=(x'+y)(1)(x'+z)

T10 . If : f=geh and gh= 0 ,

a b

0001

11

10

d0 0 1

c0 1 1 0

'1 1

,1 U101 1

David is based in Adelaide,South Australia where he

pursues his interest in the

theory and design of digital

circuits. Some of thematerial in this article is

already in use in Technical

and Further Education

institutes in South

Australia.

Fig. 12. Confirming theidentity of thesefunctions with aKarnaugh map.

y=a(131(b'cd'+ abc'd + a'b'c'd)= ac'd' + abc + ab'd + b'c'd + a'b'cd'

exclusive -OR operator.T2 .x(Dx .1

T 4 .xel=x'

T6 .x ' ey ' =xey

Commutative law

Associative law

Distributive law

Distributive law with OR function

then f=g+h

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February 1999 ELECTRONICS WORLDCIRCLE NO.110 ON REPLY CARD

CIRCUIT IDEAS Over £600 for a circuit idea?New awards scheme for circuit ideas Every circuit idea published in Electronics World receives £35.

The pick of the month circuit idea receives a Pico Technology ADC42 - worth over £90 - inaddition to £35.

Once every six months, Pico Technology and Electronics World will select the best circuit idea

published during the period and award the winner a Pico Technology ADC200-50 - worth

How to submityour ideasThe best ideas are theones that save readerstime or money, or thatsolve a problem in abetter or more elegantway than existing circuits.We will also consider theodd solution looking for aproblem - if it has adegree of ingenuity.

Your submission will bejudged on its originality.This means that the ideashould certainly not havebeen published before.Useful modifications toexisting circuits will beconsidered though -provided that they areoriginal.

Don't forget to say whyyou think your idea isworthy. We can acceptanything from clear handwriting and hand -drawncircuits on the back of anenvelope. Type written textis better. But it helps us ifthe idea is on disk in apopular pc or Macformat. Include an asciifile and hard -copydrawing as a safety netand please label the diskwith as much informationas you can.

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Turn your PC into a high-performance virtualinstrument in return for a circuit idea.The ADC200-50 is a dual -channel 50MHz digital storage oscilloscope, a

25MHz spectrum analyser and a multimeter. Interfacing to a pc via its parallel

port, ADC200-50 also offers non-volatile storage and hard -copy facilities.

Windows and DOS virtual instrument software is included.

ADC42 is a low-cost, high -resolution a -to -d converter sampling to 12 bits at

20ksample/s. This single -channel converter benefits from all the

instrumentation features of the ADC200-50.


CIRCUIT IDEAS

Medium -power inverting driverSince the 555 can sink and source up to 200mA, it provides sufficient power todrive small lamps, relays, motors and low -power inverters.

As shown, it can be used as a static or alternating inverting 200mA driver capableof operating at moderately high frequencies. In H -bridge inverters, it replaces thenormal gate and power transistor, with the bonus that it has in-built protection.

Make sure that the input cannot exceed the supply voltage. If there is no risk ofnegative input excursions, the diode can be left out.K SamsonThornton Cleveleys, Lancashire C8

input

Too trivial to publish? Yes, unless you needa very cheap and simple inverting

buffer/driver with 200mA switching.

C1+100µ

R1 25V3k3

D1

1N4148

Vcc 5V to 16V

output

Capacitance bridgeomparing two time constants isthe method used in this bridge.

Two integrators producing triangularwaves are connected to onecomparator to produce a comparisonbetween the unknown and a standard.Balance is indicated by leds.

At balance, RyCy=ltCx and

Cx=RyCy/R, where Cy is constant, Ry

is a calibrated variable resistor and I?),

is the range -selecting resistor. In thebalance condition, both integratorsproduce a triangular wave of the samefrequency. Their outputs A and B arecapacitively coupled to a rectifier andsmoothing capacitor to drivecomparator IC3a.

Output from IC3a drives theindicator amplifier IC3b, whichilluminates 'high' and low' leds. Inthe out -of -balance state, one of theintegrators will have too long a timeconstant and lower amplitude than theother, the leds indicating the fact.

Since only relative values areimportant, the only componentswhose absolute values need care arethe range -selecting resistors and Cy,

ADC42 Winnerwhich may be selected to match aknown calibration capacitor.Frequency of the waveform dependson the setting of Ry and remainswithin 500-5000Hz to keep the errordetection simple.

The zero volts line is obtained froma divider and p -n -p transistor to give avoltage close to the centre of theLF353 comparator; it tracks as batteryvoltage falls and allows the use of asingle on/off switch./D GrayLondonC6

Time constant measurement of two CRcircuits, translated to a voltage outputwith led indication, is the basis of thiscapacitance bridge.

100k Iin. 9k1

Cy 10n-I

56k

IC1a

+ LF353

100R Rx1k -"\N-C.10k 11-"\AAN-4)100ke-\AAA'°44-°11M10Me-Wh-°

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150k

Rectifier

Integrator.100n

4- -V

10n

02"100n150k7

Integrator

10n

11

33k

33k-WA,-mmi 100n

150k 150kT

_T.100nRectifier

---V

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LF353

Error detector

T

51.1

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10k

10k

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511

Comparatorwith

hysteresis

IC3b

LF353

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1k2

1k2

+V

50µ

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CIRCUIT IDEAS

Stabilisedinstrumentation

amplifier using acmos chopper ic

and softwarefiltering.

Chopper -stabilised bridge amplifierThis instrumentation amplifier

with a bridge input is stabilisedagainst input offset voltage drift bymeans of a chopper driven by amicrocontroller and is of the typeused in load cell measurement,pressure sensors and others.`Chopping' is removed in software.

Between points A, B to point C,the circuit is that of a conventionalinstrumentation amplifier, beforewhich comes the 4066 cmos switchic, receiving its switching inputfrom the microcontroller. Duringalternate switching intervals, points

12,13

Lo< 3

HEF4049

5,6

X, Y are connected to point A, Band vice versa. Input voltage plusdrift is amplified in one state of theswitch and amplified in the reversecondition in the other. It is thenconverted to digital form in theICL7135 a -to -d converter and storedin the controller's memory.

Since the resistance from A to Band from both to ground is to closetolerance, any drift and offset driftis cancelled, i.e:

Veven=k(+ Vin+Voffset)

Vodd=k(-Vin+Voffset)

100R

Subtracting,

Vout=klin

The whole thing goes in a thermallyinsulated case, care being taken withthermocouple and leakage currenteffects. The 10012 and 10 resistorsshould be matched pairs of metal -filmtypes.

In the original, all calibration datais held in an eeprom.Popovici Dan lancuBucharestRomaniaC17

Switch -operated set/reset and bistable flip-flopsThe main feature of these two flip-flop circuits is their very low off

current - about 65µA - and theyalways start in the off state.

At (a) is the set/reset type, whichhas separate switches for each stateand which may have a relay insteadof S1 or S2. For lowest off statecurrent, R5 may be 150k11 and R62701a off current being 65µA and

Two flip-flops for manual operationby switches. At (a) is a set/reset type,

which could be modified to take asplit power supply and a centre -

biased toggle switch. The bistable at(b) uses one switch. Both exhibit anoff -state current of as low as 65pA.

current in the on state 4mA -a ratioof more than 60:1.

Circuit (b) is a bistablearrangement, in which the sameswitch triggers both states. Cyclingrate is slow at about 100ms with C1 at0.47µF; contact bounce may causeproblems with lower values.

Current gain spreads cause notrouble, several examples of the

k7

R668k

S1 S2

ON OFF

transistors shown have been triedsuccessfully. Increasing the value ofR1,2 to 10kL2 reduces on -state current;at lkf2, the on voltage across theseresistors is 4V.

For other supply voltages, resistorsmust be scaled accordingly.Peter KenyonAlmancilPortugal, C19

ON/OFF


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CIRCUIT IDEAS+12V +12V

Linear sawtooth from a 555A 555 free -running oscillator provides a

iramp output, but not one sufficientlylinear for measurement purposes. This oneuses a constant -current source to charge thecapacitor C1 in a linear manner. The resultingoutput was used to simulate a chart recorderoutput on a crt display.

Output from pin 3 is a sync., the input to pin2 sync. in for one-shot working and thesawtooth comes from pin 6 and is buffered foruse.M J NicholasBournemouthDorsetC18

Tr,

Constant -currentcharging produces alinear sawtooth fromthis 555 oscillator.

2

3

555

+12V0

6

0 sync out

1C1o sawtooth out

0(C18)

Lf signal rectifierMany signal rectifiers have diodes in the signal path.This one doesn't; instead, there is a variable 'ground'

that is only present during half -cycles of the input, makingit possible to obtain an output with little or no distortion.

Fig. 1. Signal rectifierwithout signal -path

diodes.

+15V

+I15V , V2

-r15V V1

-15V

V3

stimulus = V3

500mV

V(output_gnd)

-500mV1.0V

V(+in)

-1.0V2 OV

V(output)

R7

100k -4.441mV

-197.84mV

output gnd

+15V

R5

68k

output-14.96pV

(C15a)

2 OV0 0.5ms

1.0rns 1.5ms

Time

Fig. 2. Waveforms in the circuit of Fig. 1.

2.0ms 2:5ms 3:0ms

Looking at the circuit diagram in Fig. 1, diode DI doesnot conduct during negative half -cycles and R1,3 form apotential divider, pin 2 of IC2a being held at ground by itsfeedback through D4. Loss of amplitude in the divider iscompensated in /Cia by the addition of R7 to change itfrom a unity -gain follower to a amplifier.

During positive excursions, DI conducts and maintainsthe non -inverting input of /Cia at ground. As the invertinginput is at the same level, the op -amp is now an invertingamplifier, so that the input appears as a negative outputwith the same amplitude. Resistor R7 has no effect at thistime since both connections are at the same level.Waveforms are shown in Fig. 2.

Diode D4 clamps IC2a output at 0.6V to preventsaturation , which would introduce distortion at crossover,since there would be a delay between change in polarityand the start of regulation of the ground level, as shown inFig. 3.

A certain amount of distortion is caused by the level atthe non -inverting input of IC2a being added to the inputsignal when it is working as an inverter, which does nothappen when it is a non -inverter. The distortion is clearlyworse with small signals. There is also a difference ininput impedances in the two half -cycles.Van den Abeele BernardEvergemBelgiumC15

20V

V(output_gnd)

-2V1.0V _

V(+in)

-1 OV2.0V _

V(output)

-2 0V0

(C15c)

4IW 0.5ms 1.0ms 1.5ms

Time2:0ms 2.5ms 3.0ms

Fig. 3. Without the inclusion of D4, crossover distortion wouldoccur, caused by saturation in IC2a.


TELFORD ELECTRONICSOld Officers Mess, Hoo Farm, Humbers Lane

Horton, Telford, Shropshire TF6 6DJ, UKPhone: (00 44) 01952 605451 Fax: (00 44) 01952 677978

e-mail: [email protected]: http://www.telford-electronics.com

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ALL OUR EQUIPMENT HAS A 30 DAY GUARANTEE(EXCEPT CLEARANCE ITEMS WHICH ARE SOLD AS -IS)

MICROWAVE

JFW stepped Attenuators 0-9.8dB in .2dB steps DC-2GHz£65.00JFW Stepped Attenuators 0-10dB in 1dB Steps DC-2GHz.£65.00HP5342A 18GHz Frequency Counter... ....£800.00HP8405 Vector Voltmeter .£250.00HP13502A Transmission/Reflection Test Set 500KHz-1.3GHz........

.£750.00HP8743B Reflection Transmission Test Unit 2-12.4GHz..£600.00Maury Microwave Sliding Termination up to 20GHz........1600.00HP11720A Pulse Modulator 2-18GHz...................£720.00HP11722A Sensor Module.... .£600.00HP11691 D Directional Coupler.HP11692D Directional Coupler. .£700.00HP3351) 120dB Attenuator DC-1GHz .£300.00Wilton 560 Scaler Analyzer 0./w Detectors & SWR Bridge...........

£1500.00Semi Rigid Co -Axial Cable Type: UT141/A 0-20011z. 3 metrelengthsDiscount qty: 100pcs.£500.00......PRICE EACH LENGTH £10.00Continental Microwave Transmitter Control VML-TR240 1/1.......

Digital Microwave 12GHz TX/RX (NEW). £1200.00HP H752A Directional Coupler 3dB.HP X382A Variable Attenuator 0-5008 8.2-12.4GHz £120.00HP11720A Pulse Modulator 2-18GHz...... ............... £720.00HP11722A Sensor Module 160000HP33304A Programmable Anenuator 180Hz 0-1108..... £175.00HP33305A Programmable Anenuator 18GHz 0-110dB... £175.00HP33320A Attenuator 11d8 .£250.00

HP532B Frequency Meter .£200.00HP536A Frequency Meter 3.7-12.4GHz...........................£200.00HP54111A 2GHz S/S Test Set.. £560.00

DATA/TELECOMS

Anritsu MS334A PCM Error Detector. .£120.00

BT (Fulcrum) 71020 Network Transmission PerformanceAnalyzer £500.00Cushman CE24 FX Selection Level Meter ........................£400.00Datalab DL1000 Programmable Transient Recorder........£250.00GN Elmi EPR31 PCM Signalling Recorder .....................£500000

HP3336A Synthesized/Level Generator......................... £1300.00HP3497A Data/Acquisition ControlHP3586B Selective from £850.00HP3717A 70MHz Modulator/Demodulator........................£P0A

HP37204 HP -IN Extender. £300.00

HP3763A Error Detector s800.00HP3764A Digital Transmission Analyzer............HP3770B Telephone Line Analyzer.... £200.00H3780A Pattern Generator/Error Detector 01100.00HP3781A Pattern Generator. £500.00HP3782A Error Detector £500.00HP4935A Transmission Tester £1100.00HP4984A In-service Transmission Impairment Measuring Set....

£P0AHP5005B Signature Tester... £950.00HP5006A Signature Analyzer EstfooHP6942A Multiprogramme, £20000HP8170A Logic Pattern Generator.................................. £60000HP8954A Transceiver Interface...H....H... ....................£600.00Matsu DM2350 Digital Memory 10 bi1/20ns...................£400.00Marconi 2828A Digital SimulatorMarconi 2829 Digital Analyzer.Marconi 2831 Channel Access Switch.. £200.00Marconi 0A2805 PCM Regenerator Test £250.00Marconi TF2019C Noise Generator - many filters available..........

Marconi TF2092C Noise Receiver ..................._...............£250.00Marconi TF2808/2 Pattern Generator andMarconi TF2807A PCM Multiplex Tester 2200.00Marconi TF2830 Multiplex Tester £20000

OSCILLOSCOPES

Tektronix TAS455 60MHz Dual Channel Oscilloscope £60000Gould 051602 Digital Storage Oscilloscope 20MHz.. 250000Gould 00300 20MHz Oscilloscope..................................£120.00Hitachi VC6015 Digital Storage Oscilloscope ...F300.00Hitachi VC222 20MHz Oscilloscope................................ £225.00

Philips PM3325A 60MHz Digital Storage. .£1000.00Philips PM3262 100MHz. ...£250.00Philips PM3352A 50MHz Storage.. £900.00Tek 2215 60MHz £300.00Tek 2225 50MHz £35000Tek 2235 600MHz £500.00Tek 2236 100MHz £500.00

Tek 468 100MHz Digital Storage £500.00

POWER SUPPLIES

HP6634A Systems DC Power Supply 0-1001/ 0-1A 100W£650.00

HP6653A Systems DC Power Supply 0-35V 0-15A,.,.,,.,,£800.00HP62648 0-200 0-200 ..£250.00HP6181C OC Current Source 0-1000 0-250mA.............. £300.00Powerline Electronics 0-700 .£175.00

Farnell Type: 60/25 0-600 0-25A Metered - Brand New..£400.00General Radio 1265A DC Power Supply 0-4001/ 0-50,...1475.00Farnell TSV70 MK2 Stabilised Power Supply......_._.,..,.. £180.00Farnell 30/100 30V 1000...... .£700.00Power Ten Systems Power Supply 0-30V 0-600,,,,,,,,,,,,,£300.00Powerline Type: LAB510 0-30V 0 10A............................ £300.00Powerline Type LAB532 5V -5A + 150-0.5A, -150-0.50,

£20000

SIGNAL ANALYZERS

HP8903B Audio Analyzer £2500.00HP3708A Noise & Interference Test Set. £P0AHP3561A Dynamics Signal Analyzer £4000.00

Takeda Riker TR4172 Spectrum/Network Analyzer 1.8GHz..................................................................... £6500.00HP8901A Modulation Analyzer. £1500.00HP5370A Universal Counter/TImer..................................£850.00Philips PM6680 High Resolution Programmable Counter/Timer option C fitted ...£1350.00Philips PM6666 Timer/CounterPhilips PM6666 Option C fittedTimer;Counter................£650.00Marconi 2955 Test Set... £1600.00Advantest TR4132 Spectrum Analyzer 1GHz.................£1500.00

13&K 2636 Measuring Amplifier....................................£4000.00BOK 5935 Dual Microphone Supply ................................£650.00HP182T HP8558B Spectrum Analyzer 100KHz-1.5GHz..................................................................... . £120000

HP339A Distortion Measuring Set ...£1200.00HP3580A 25KHz Spectrum Analyzer...............................£600.00Marconi 2305 Modulation Meter. ...£2000.00Marconi 2382 + 2380 400MHz Spectrum Analyzer....... £3500.00Marconi 2601 True RMS Voltmeter.................................£500.00Marconi TF2370 110MHz Spectrum Analyzer £600.00

R&S CMS52 Comm. Service Monitor..........................£5000.00Tektronix 0A4084 Programmable Distortion Analyzer....£700.00

SIGNAL GENERATORS

Adret 71008 300KHz-650MHz............................... ...£700.00Cushman CE12 Two Tone Generator £150.00Farrell DSG2 Synthesized 0.1MHz-110KHz.....................£185.00

Fluke 60100 10Hz-11MHz Synthesized. ..£175.00HP11710B Down Convertor (HP8640B).........................1275.00HP2148 Pulse Generator 1000 £1200.00HP3325A Synthesized Generator 1Hz-21MHz...............£1250.00HP4204A Oscillator 10Hz-1MHz ......£125.00HP654A Test Oscillator 10MHz .1225.00HP8005B 0.3Hz-10MHz. .1300.00HP8008A 1005-200MHz...HP8015A 1Hz-50MHz Pulse. .. £450.00HP8165A Programmable Signal Source............... £1200.00HP8620C HP86222B 0.01-24GHz Sweeper...............£1200.00HP8642M 0.1-2100MHz....HP8657A 01-1040MHz. £3500.00HP8684B 5A-12.5GHz.. ...21950.00Marconi 2019A 800Hz-1040MHz £1450.00Marconi 2022 10KHz-1GHz..... £900.00Marconi 6057 Signal Source 5.5-8.5GHz 2200.00Marconi 6059A 12-180110 Signal Source. 2200.00

Systron Donner 1702 Audio-1GHz................ ...£600.00Tektronix 504 0.001-240MHz. ...£350.00Tektronix FG501A 2MHz Function. ...£250.00Wavetek 1080 1-1000MHz Sweeper. £800.00Wavetek 157 Programmable Waveform.. £150.00Wavetek 159 Waveform Generator 1Hz-3MHz................£300.00Wavetek 171 Synthesizer/Function........................ ...£400.00Wavetek 185 Sweeper/Function 0-5MHz. £350 00Wavetek 2001 1-1400MHzWavetek 907A 7-12.4GHz... £900.00Wiltron 6100 «62238 Sweeper 4-12.4GHz £500.00Systron Donner 1720 Signal Source 50MHz-18GHz £2000.00HP8091A « 80928 + 8093A (x2) 1Gliz Pulse Generator System..

£650.00Marconi TF2015 + TF2017 10-520MHz £200.00

MISCELLANEOUS

I. L. X. LIGHTWAVE EQUIPMENTLDT59016 Temperature ControllerPDA6424 Photo Diode AmplifierLDX3742 Laser Diode ControllerLDX320713 Precision Current Source3M Fibre Splice Preparation KitCossor Optical Cable Faun Locator Type: OFL108LLaser Precision Type DB2900 Single Mode Variable AttenuatorSchlumberger Type: S17780 OTDR S177823 Plug-inSolomat MPM4000 Matrix Processor c/w Software. Portablemultichannel, datalogger, alarm monitor Battery/MainsOperated.Kane -May: KM4003 Air Velocity 0-30 in metres/seconds AirTemperature (C) -30 to +200C. Battery Operated,Portaflow MK11: Portable diagonal beam flowmeter. Made by:MicronicsBacharach. Combustion Analyzer/Environmental monitor Type:300NSX.Kane -May: Combustion Analyzer Type: 9004Kane -May: Temperature Sensor Type 1204 c/w 8004Temperature & Humidity Sensor. GGA-26 Thermo -Anemometer+ KM801 IntratraceCasella: Aerosol Monitoring System Type AMS950 Ranges,0-20mg/m 0.200mg/mCEL Instruments: Precision Interpreting Impulse Meter Type:CEL 493 dux CEL 296 Octave 8 third octave scan filter setCEL 284/2 CalibratorHoffmann SWM3 Flow MeterCEL 281 +281 Keypad + Programmable Noise DosemeterNeotronics Exotox 75 Ambilog + Charger. Portable atmospheremonitor.HP4275A Multi -Frequency L.C.R. Meter. .13,250.00HP4193A Vector Impedance £5,000.00HP85688 Spectrum Analyzer High Performance........110,000.00AVO PAT Tester. .£300.00Wayne Kerr Precision Inductance Analyzer Model 3245............

NEW STOCK

HP8753C HP85047A 300KHz-66Hz Network Analyzer System,Option: 002, 006 & 010 fitted £11,000.00HP8672A 2-18GHz Synthesized Signal Generator........£4,850.00HP8756A Scaler/NetworkHP436 Power Meter + HP8481 Sensor .£900.00HP8111A 20MHz Programmable Pulse Generator....... £1,200.00Tek 2465/A/13/CT 300MHz + OscilMscope...........From £1,500.00R&S AFG Function Generator 10MHz-20MHz £2,000.00Philips PM57868 Pulse Generator 1Hz-125MHz rise time:2ns to 0.1s £1,250.00Gould 4072 400Ms/s 100MHz DSO c/w Integral Printer .£750.00HP3326A Two channel Synthesizers...c.c.s.. .....25,000.00


Sharp Toolsfor Embedded Systems

CCS - PIC C CompilersDevelop PIC applications faster than you ever thought possible withCCS PIC C compilers. Generates fast efficient native PIC code. Built inlibrary support for timers, serial comms, PWM, ADC, I2C etc. I/Olibraries use hardware support where available or else use softwaregenerated modules. DOS/Windows Development Environment Write Interrupt service routines in C Supports in line assembly language Automatic linking of multiple code pages Supports BIT and BYTE variables at absolute positions

PCW - Windows IDE for PIC 16C5X, 16CXX, 12CXXX, 14000- IRE270 PCM - DOS IDE & Command line for PIC 16CXX, 12C6XX, 14000 - 1R£95 PCB - DOS IDE & Command line for PIC 16C5X, 12C5XX - 1R£95

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BASIC Stamp ComputersBASIC Stamps are small computers which are programmed in PBASIC,a powerful BASIC dialect that includes many enhancements specificallydesigned for embedded control. PBASIC programs are downloadeddirectly from a PC to the BASIC Stamp where they are executed fromon board EEPIROM. DOS/Windows Development environment. Program directly from PC. Reprogrammable up to 10,000 times. I/O pins can source/sink up to 20mA. Easily interfaced to ADCs, LEDS, motors, relays. Built in functions for Serial, PWM, pulse in/out etc.

BASIC Stamp 1 - 8 I/O, 2400 baud serial. 16 pin SIP Module -18E29 BASIC Stamp 2 - 16 I/O, 50K Baud serial, 24 pin DIP Module - IRC42 Starter Kits from 81E79 (All prices exclude V.A.T. and delivery)

For further information on CCS PIC compilers, BASIC Stamps andother sharp tools, please phone, email or visit to our web site.

gui Paul 0 Neill Designs, Dublin, Ireland.Tel/Fax:+353-1-8215060Email - [email protected] Web - www.pond.ie

Paul 001

CONTROL & fromMilfordROBOTICS InstrumentsBASIC Stamps- Re -Programmable BASIC language RS232 Serial ports 8 or 16 I/O lines SPI/DTMF Fast development

Serial tCDs RS232 Serial interface 2x16 to 4x40 Simple 3 -pin connection Integral Keypad option Large Numerics option Driver chips available for OEM use

3 -Axis Machine Stamp 2 based Drills PCBs 3 -Axis movement Stepper drive 4 thou resolution Win 3.1

software

Scenix Fastest 8 -bit micro 50MIPS Flash Eprom 18/28 pins PIC1 6C5x

pin replacement

Robotics Humanoid 5 -Axis Arm Walking Insect

Servo Controller Control up

to 8 servos RS232

CommandsIR Decoder Uses any remote 7 digital outputs Toggle/momentary Re -Programmable

Milford Instruments 01977 683665 www.milinst.demon.co.uk I

CIRCLE NO.113 ON REPLY CARD CIRCLE NO.114 ON REPLY CARD

Amiga gunlock pcb (encased) for titling videos it has a 23pin Dlead to plug into the computer and pcb pins for composite videoin and out. When no video input is connected the normalcomputer display is shown on the composite video out when thevideo input is added the white areas on the screen are replatedby the video image. The pcb is powered from the computer

.11998WATCH SLIDES ON TV "Liesgang diatu" automatic slide viewerwith built in high quality colour to camera, composite videooutput with a BNC plug In very good condition with few signs ofuse £108.00

Board cameras all with 512x582 pixels 4.4x3.3mm sensor withcomposite video out. Al need to be housed in your ownenclosure and have fragile exposed surface mount parts andrequire 10 to 12vdc power supply 47MIR size 60x36x27mrnwith 6 infra red leds (gives the same illumination as a small torchwould) 1.50.00+vat = E58.75

4.0MP size 39x38x23mm spy camera with a fixed focus pinhole lens for hiding behind a very wall hole.E57+vat - £66.98

40MC size 39x38x28mm camera for 'C' mount lens this givesa much clearer picture than with the small lenses ..........£68.79

standard 'C mount lens F1.6 16mm for 40MC.....£26.431 -vat = E31.06

waterproof camera with stylish tilt & swivel case

....£92.76+ eat = E109.00.or 10+ £89.32 + vat - £104.95

DTA30 Hand held transistor analyser it tells you which lead is thebase, the collector and emitter and if it is NPN or PNP or faulty.HMA20 hand held MOSPET analyser identifies gate drain aridsource and if P or N channel DTA30 & HMA20 ..£38.34 eachDCA50 component analyser with lcd readout identifiestransistors mosfets diodes & LEDs lead connections

£69.95

Speaker cabinets 2 way speaker systems with motorola tweeters

speaker dia 15" 12" 8"power rating 250WRMS 175WRMS 100WRMSimpedance Bohm Bohm 8ohmfrequency range 40hz-20Idu 451.-20khz 60h020khzsensitivity(1W/1M) 97dB 94dB 92dBsize in nun 500020,640 450x640x345 315x460x230weight 21.1kg 16.8kg 7.4kgprice each for blackvinyl coating £139.95 £9999 £5494grey felt coaling £159.97 £119.97" £64.99

(** = not normally in stock allow 1 week for delivery)Power amplifiers 19. rack mount with gain controls

STA150 2x160Wrms (4ohm load) 14kg .................._£202.11STA300 2x190Wrms (4ohm load) I lkg ....................£339.00STA900 2x490Wrms (4ohm load) 15kg £585.00

LEDs 3mm or 5mm red or green 7p each yellow 1 1p each cablehas 1p each .£5.95 per 1000

£49.50 per 10,000

R.harg.ble BatteriesAA(HP7) 500rnAHAA 500mAH with solder tags .£1.55

AA 950mAH...... . El 75CHP11) 1.2AH.....C 2AH with solder tagsD (HP2) 1.2411 .£2.60D 4AH with solder tags .£4.95PP3 8.4V 110mAH .E4.951/2AA with solder tags .£1.55Sub C with solder tags .E2.50AAA (HP16) 180mAH .£1.751/3 AA with tags(philpsCTV) .£1.95

Nickel Metal Hydryde M cells high capacity with no memory.If charged at 100ma and discharged at 250ma or less

1300mAH capacity (lower capacity for high discharge rat.) ....£2.95

Special offers please check for availability stick of 4 42 x 16mmnicad batteries 171mmx16mm dia with red & black leads 4.8v

15.95

5 button cell 6V 280mAh battery with wires (Varta 5x25001{)_.........,..........£2.45

Orbitel 866 battery pack 12v 1.60AH contains 10 sub C cellswith solder tags (the size most commonly used in cordless

screwdrivers and drills 22 dia x 42mm tall it 0 .sy to crackopen and was manufactured in 1994, £8.77 each or £110.50per box of 14 BCI box 190x106x51hnm with slots to house apcb the lid contains an edge connector (12 way 8mm pitch) andscrew terminals to conned in wires' and 5 slide in cable blanks.

.£2.95

7.gment common anode led display 12mm

GaAs PET low leakage current 58873 £12.95 each £9.9540+ £795 100 + BC547A transistor 20 for. '.£1.00

SL952 UHF Limiting amplifier LC 16 surface mountingpackage with data sheet .E1.95

DCDC convertor Reliability model V12P5 12v in 5v 200ma out300v input to output Isolation with data £4.95 each or pack of10 £39.50 Airpax A82903 -C large stepping motor 14v 7.5'step 27ohm 68mm dia body 6.3mm shaft E8.95 or £20000 fora box of 30

Polyester capacitors box type 22.5mm lead pitdh 0.9uf 250vdc18p each 14p 100+ 9p 1000+ luf 250Vdc 20p each,15p100+,10p 1000+ Polypropylene luf 400vdc (Wima MKP10)27.5mm pitch 32x29x17mm case 75p each 60p 100+ Philips123 series solid aluminium axial leads 33uf 10v & 2.2uf 40v40p each, 25p 100+ Solid carbon resistors very low inductanceideal for RF circuits 27ohm 2W,68ohm 2W 25p each 15p each100+ we have a range of 0.25w 0.5w lw and 2w solid carbonresistors please send SAE for list MX180 Digital milometer 17rang. 1000adc 750vac 2Mohm 200mA transistor Hfe 9v and1.5v battery test .£9.95

CV2486 gas relay 30 x lOmm dia with 3 wire terminals willalso work as a neon light 20p each or £8.50 per 100 VarbatirnR300NH Streamer tape commonly used on nc machines andprinting presses etc. it looks like a normal cassette with a slot cutout of the top £4.95 each (E3.75 100+) H.tsink compoundtube £095 HV3-2405-E5 5-24v 50mA, regulator is

18-264vac input 8 pin DIL package £3.49 each (100+ 2:25)

All products advertised em new and unused unless otherwise stated. Wide range of CMOS TTL 74HC 74F Linear Transistors kitsrechargeable batteries, capacitors, tools etc always in stock. Please add £1.95 towards P&P (orders from the Scottish Highlands,

Northern Ireland, Isle of Map Isle of Wight and overseas may be subject to higher P&P for heavy items). VAT included in all prices.

JPG Electronics 276-278 Chatsworth Road Chesterfield S40 2BHMastercard/Visa Orders (01246) 211202 Fax 550959

Callers welcome 9-30am to 5-30pm Monday to Sa.,turday


PHONE0181 684

1166

LANGREX SUPPLIES LTDDISTRIBUTORS OF ELECTRONIC VALVES FAX

TUBES AND SEMICONDUCTORS AND I.C.S. 0181 6841 MAYO ROAD CROYDON SURREY CR0 20P 305624 HOUR EXPRESS MAIL ORDER SERVICE ON STOCK ITEMS

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£ p KT66 China 10.00 5Z4GT 3.00 6V6G 8.00AZ31 6.00 KT88 China 12.00 6AQ5 2.00 6V6GT 5.00CL33 10.00 N78 8.00 6AR5 20.00 6X4 3.00E88CC 8.50 0A2 3.00 6AS7G 7.50 6X5GT 3.00E180F 3.50 052 3.00 6AU5GT 4.00 12AT7 3.00E810F 20.00 003 3.00 6AU6 2.00 12AU7 3.50EABC80 2.00 OD3 3.00 6AW8A 4.00 12AX7 5.00EB91 1.50 PCF80 2.00 6B4G 22.00 12AX7A 7.50EBF80 1.50 PCL82 2.00 6BA6 1.50 12AX7W 6.00EBF89 1.50 PCL85/805 2.50 6BE6 1.50 12BA6 2.00EBL31 15.00 PCL86 2.50 6BH6 2.00 12BE6 2.00ECC33 12.00 PD500 6.00 6BQ7A 2.00 12BH7/1 10.00ECC35 12.00 PL38 3.00 6BR7 4.00 12BY7A 7.00ECC81 3.00 PL81 2.00 6BR8 4.00 12DW7 15.00ECC82 3.50 PL504 3.00 6BW6 4.00 12E1 10.00ECC83 5.00 PL508 3.00 6BW7 3.00 13E1 85.00ECC85 3.50 PL509/519 10.00 6BZ6 3.00 572B 85.00ECC88 6.00 PL802 4.00 6C4 2.00 gm 45.00ECC808 15.00 PY500A 3.00 6CB6A 3.00 807 7.50ECF80 1.50 PY800/801 1.50 6DC6G 5.00 811A 25.00ECH35 3.50 QQV02-6 12.00 6066 3.00 812A 55.00ECH42 3.50 QQV03-10 5.00 6CG7 7.50 813 27.50ECH81 3.00 00V03.20A 10.00 6CH6 3.00 833A 85.00ECL82 3.50 00V06.40A 12.00 6CW4 6.00 866A 20.00ECL86 3.50 U19 8.00 6005 17.50 872A 30.00ECLL800 25.00 UABC80 1.50 6006B 10.00 931A 25.00FE37A 3.50 UCH42 5.50 6F6G 5.00 2050A 12.50EF39 2.75 UCL82 2.00 6F07 7.50 5751 6.00EF40 4.00 UCL83 2.00 6GK6 4.00 5763 6.00EF86 10.00 UF89 4.00 6J5G 6.00 5814A 5.00EF91 2.00 UL41 12.00 6J5M 4.00 5842 12.00EF183/4 2.00 UL84 3.00 6J7 3.00 6072A 6.00EL33 15.00 UY41 4.00 6JB6A 27.50 6080 6.00EL34 8.00 UY85 2.00 6JE6C 27.50 6146B 15.00EL34G 6.00 VR105/30 3.00 6JS6C 27.50 6201 8.50EL36 5.00 VR150/30 3.00 6K6GT 4.00 6336A 35.00EL41 3.50 Z759 10.00 6L6G 15.00 6550A 25.00EL84 2.25 Z803U 15.00 6L6GC 15.00 6883B 15.00EL95 2.00 2021 3.50 6L6WGB 10.00 7025 7.50EL360 15.00 3628 12.00 607 3.00 7027A 25.00EL509/519 12.00 4CX256B 45.00 6SA7 3.00 7199 15.00EM34 15.00 5R4GY 7.50 6507 3.00 7360 25.00EM814/7 4.00 5U4G 10.00 6SG7 3.00 7581A 15.00EN91 7.50 5U4GB 10.00 6SJ7 3.00 7586 15.00EZ80/81 3.50 5V4G 4.00 6SK7 3.00 7587 20.00GZ32 8.50 5Y3GT 2.50 6SL7GT 5.00GZ33/37 6.00 5Z3 5.00 6SN7GT 5.00 Prices correct whenKT61 15.00 5Z4G 6.00 OUBA 1.50 going to press.

OPEN TO CALLERS MON-FRI 9AM-4PM. CLOSED SATURDAYThis is a selection from our stock of over 6,000 types. Please enquire for types notlisted. Obsolete items are our speciality. Valves are new mainly original British or

VISAAmerican brands.Terms CWO/min order £10 for credit cards.

P&P 1-3 valves £2.00 4-5 valves £3.00 SDAdd 17.5% VAT to total including P&P.


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J-EITHRXAdvanced Systems & Technology for PCB Manufacture

(UCIRCLE NO.117 ON REPLY CARD

Paul Bennett'sthree-phase powerinverter useshigh -frequencyswitching to avoid thebulky and expensiveinductive componentsassociated withnon -switching 400Hzinversion.

400Hzinverter

This design is for a three-phase 400Hz inverter for run-ning 200V aircraft equipment from a normal 230Vmains supply. High -frequency techniques are used, i.e.

there are no 400Hz magnetics or other special components.Each phase is separately regulated and isolated from themains, output neutral being connected to earth. Maximumoutput is around lkVA, about 3A per phase.

Input converterThis design divides into two parts - the mains input convert-er and the three phase output bridge.

For the input side, a half -bridge forward converter is used,sometimes called an asymmetric half bridge. This providestwo outputs, t200V either side of ground. Only the positiveside is sensed for regulation. Acceptable regulation isachieved for the negative output by cross coupling thesmoothing inductors.

Mains supply is filtered, rectified and smoothed. A ther-mistor with a negative temperature coefficient providesinrush limiting. Two igbts are used for the switching tran-sistors, type IRGP440U from International Rectifiers. Theseare 500V die -size 4 types but size 3 or above, 500 or 600Vultra -fast types should prove satisfactory. Size 5 mosfetscould also be used.

When igbts are used, a reverse diode across the transistoris needed to clamp any reverse voltage transient. Thedevices are rated for some reverse voltage, but at unrealis-tically low current for most power -switching applications.A fast turn on diode should be used such as a slow or mod-erate reverse recovery speed type.

Generally with low voltage output switch mode powersupplies, diode reverse recovery can be ignored. The result-ing current spike at turn on of the power switches is veryshort and requires little energy.

As the output circuit impedance level increases with high-er output voltages, the diode recovery transient becomes

more significant - even with the latest ultra fast types. Thiscan be tolerated, but it causes higher EMI, extra stress inthe switch and diode, and fast current sensing problems.

The spike can be reduced by slowing the turn on of thepower switch, but this increases losses. The technique I haveused is a current snubber. This device slows down the cur-rent rise by placing an inductor in series with the switch.

At turn off, some energy is returned to the supply by theBYW96C diodes. The igbts now turn on at zero current andthe current wave form is very clean.

Another bonus is that during output short circuits, such aswith the output capacitors uncharged, the snubber lengthensthe pwm duty cycle required. This reduces demands on thecurrent limit speed and propagation delays.

Drive to the igbts is provided by an RM8 size trans-former. The driver IC and IN4148 diode network is effec-tively the same topology as the power converter. Thisarrangement ensures proper reset of the RM8 core everycycle under all conditions, including under current limitwhen the duty cycle may vary rapidly.

The pulse -width modulation IC is the popular voltagemode SG3525A, running at around 30kHz and 50% maxi-mum duty cycle. Digital current limiting is employed whichterminates the pwm on a pulse by pulse basis.

The LM319 provides more accurate limiting than theSG3525A's shut -down pin. An RM6 transformer sensescurrent at the collector of the lower igbt. The current limitsets the inverter's maximum overall power output to around1 kW, giving a peak switch current of about 7A.

Output bridgeDesign of the three-phase output bridge is conventional. Ituses closed -loop pwm at 25.6kHz.

Three reference sine waves are generated by the crystaloscillator, counter/divider, eprom and d -to -a converter circuit.All three phases are identical, apart from a 120° and 240°

WarningIn addition tolive mains, thiscircuit involvesequally lethal dcvoltages. Don'tforget that high -voltagecapacitors canhold lethalcharges whenthe circuit isswitched off too.


CONTROL ELECTRONICS

Packaged inverter

Inverterbreadboard

Mains input converter. Its main task isto produce a ±200V supply from themains. At the bottom is the 3525 pulse -width modulator.

6A IEC filter

E

T1 RM6 AO 3C85 1:50T2 RM8 AO 3C85 18:18:18T3 ETD59 AO 3F3 48:68:68L1 T94-2 33 9µHL2 ETD49 A2 3C85 105+105 (5mH) +12V

0

50

N4148 1k

10Abridge

Artificial horizon and motors

phase shifts encoded in the eproms.The most significant address line is used to swap between

two look up tables which swap the codes around for the A andB phases. This reverses the phase rotation.

The algorithm used, in floating-point decimal, is:

A.INT(128*(1+SIN(2*PI*(X+0.5)74096)))-0.5)

B=INT(128*(1+SIN(2*PI*(X+1365.83)/4096)))-0.5)

C=INT(128*(1+SIN(2*P1*(X+2731.17)/4096)))-0.5)

To check the rounding errors, etc., the resulting sine waveshould look perfect with no flat on the peak or trough. Theresulting code should contain equal numbers of Os and 255sand change from 127 to 128 as the address changes from2047 to 2048 for phase A.

The reference signal is compared to a sample of the outputby an LF347 op -amp. This modifies the reference to the pwmgenerator to remove any distortion in the output. I chose thecompensation to give a good compromise between stabilityand transient response.

1RGP440U

BYW96C

BYW96C

RUR8100

68

68

L2 2000µ200V 250V +200V

HFA8 +TB60 T T OV

RUR8100HFA8TB60 2000µ

200V 250V470k

2k2

15 13

LM319

220R100p

Ok

22R47n

Adjust for1kW

2

10SG3525A

ICL7667CPR5V1

20k 100k 10k 47nii100p

Adjust for200V

T

12 5

20k

7 ICL7667CPR

A 1N4148

T2

18

=1 N4148

-200V


CONTROL ELECTRONICS

An LM319 compares the modified reference to a 25.6kHztriangle wave derived from the crystal. Basic pwm is thenmodified by the monostables to give two outputs includingsome dead time to avoid cross conduction in the bridge.

The modified reference is not bounded to the triangularwave so the pwm could saturate positive or negative. This isundesirable as the bridge current is sensed with transformerswhich cannot pass dc.

To prevent total saturation addition pulses are added to thepwm by the NAND gates. Current limiting is achieved by ter-minating each pwm pulse on detection of over current at eachswitch. The 74HC74 bistable device is set by an over -currentturning off both pwm drives. It is then reset twice each cycleat 51.2kHz.

As with the input converter igbts are used, typeIRGBC2OU. Other ultra -fast igbts, size 2 or 3, 500 or 600V,should prove suitable or size 4 mosfets.

Recovery problemsDiode recovery is potentially a bigger problem in pwm invert-ers, where the duty cycle swings close to 0 or 100%.

The snubber used in the input converter cannot be used as

there is insufficient time for it to properly reset. Instead, aftermuch experimentation, I simply limited the turn on speed byinserting a 10012 gate resistor. A 1N4148 diode across thisresistor makes sure that turn off is still as fast as possible.

Electromagnetic interference is not a significant problem asthe converter is referenced to true ground. Gate drives are pro-vided by high-speed opto couplers and buffer ICs. This meansthat four floating gate drive supplies are needed, provided bya simple dc -to -dc converter.

The low side switches use a common supply. Current sens-ing is by six RM6 size transformers. Each transistor is indi-vidually sensed so that all combinations of phase -to -phase andphase -to -neutral faults are protected against.

A single potentiometer sets the current -limit comparator ref-erences. This determines the overall kVA rating of the invert-er and is set to approximately 5A for 3A rms output.

Output filteringThe output filter inductor and capacitor have to be chosencarefully and an exacting compromise is required.

Too large a value for L will cause droop at the 400Hz out-put frequency necessitating a higher dc supply. Too low a

+5V

74HC4040

D1

D7 D6 R

74HC4040

100p

25.6kHz

51.2kHz

+5V

0Phase

rotation

4k7

01

D2

D3

D4

D5

D6

D7

08D9

D10

D11

D12

27256

To otherphases

AO

AlA2

A3

A4

A5

A6

A7

A8

A9

A10All

D1

D2

D3

D4

05D6

D7Al2 D8

A13 CS

DAC0800

LSB

+REF

MSB

0.1p

REF

4k7

10k

4k7

One phase of theintermediatedriver circuitry.Sine -waves areconstructed by ad -to -a converterfrom informationin eprom. Acrystal -controlledclock feeds the4040 counterthat addresses theepromsequentially.Analogue ICspowered from±12V, power pinsdecoupled with47nF.

4k7

4k7

Outputsense

220k

1 0k 10k4-AAAA.-

Adjust115V rms

10k

1M

4n7 100k1-1AAA

47k*-1 ,-

Currentlimit>-

+5V

1k

LF347

+5V

D PRClr

0

74HC74

Adj. 5Vpk-pk

1k-1AN r-fj.

74HCO2

Current Fruit resetto other phases

1M +5V

47n

LM6361+5V

1k

LM319

47k

74HC04/V

To otherphases

+5V

10k100p

Clr

A

C

/0

+5V

2n22k2

+5V

2k22n2

74HC123A

+5V

+5V

100p

hClr R

A /0

> DC ref toother phases

74HC20

74HC123A

> Output onto pther phases

Minimum duty cycle pulsesto other phases

Highswitch

Lowswitch


CONTROL ELECTRONICS

+200V>

0 V >

-200V>

value will increase the peak transistor current and associatedlosses and output 25.6kHz ripple. Too high a value for C willincrease circulating current inside the bridge legs, and again ifthe value is too low, 25.6kHz ripple will increase.

Further constraints are placed on L by available core sizesand materials. The values chosen just allow 115V output with400V dc bus and give around 1.5V rms 25.6kHz ripple.

Adjust current limitfor 1 kVA (common all phases

Electrolytics shared withinput converter

3Acr\P

18k

18k +=

Output bridge. Atthe top is the final

conditioningcircuit for current

limiting. In themiddle is onepower driver.

Below is powersupply circuitry

for producing theisolated low

voltage needed forthe high -side

driver.

+12Vo

0 V0

+12V +5V

The complete inverter was spread out on an aluminiumsheet ground plane then repackaged in a custom-made box.

A 12V 100ft3/min fan was used for cooling with the ±12Vand +5V supplies derived from 78/79 series regulators and a12VA 50Hz transformer. Both converters have fuses betweenthe converters and electrolytic capacitors.

It is surprising how many commercial power switchingdesigns have inadequate fusing. Without it, all mannerof expensive blow -outs can occur.

Five neons indicate, mains present, intermediate dcvoltage present and output phases on. The output wastested using various 400Hz loads, small fans and blow-ers, an artificial horizon and array of 115V 100Wlamps.

Simplifications and enhancementsVarious simplifications and enhancements appear pos-

I limit sible. Numerous possibilities exist for the sine wavereferences, with perhaps reduced precision. One tech-niques is to have a six -pole filter extract the funda-mental from the 400Hz square wave.

Three 120° -spaced square waves are easy to generatewith logic. PWM signals can be directly encoded ineprom with a simple RC filter to decode the pwm backto a sinewave. A 1.6384MHz clock would allow 64

1k

+12V

Highswitch

OV >

9ICL7667CPA

100R

1N4148 1OR

HCPL2201+12V

1kLow

switc

3Aop

,4k7

T4n7

NE555

22µ25V

47n

-I I

100R

1N4148

0.47u.IRGBC RUR860 400V

20

L

210

ETD49 3C85 41 5mH

A 0.47µRUR860 400V

IRGBC20

Newport1002

BYV27

lOR IRF530AA

2 2

°Output

> Phasesense

1µ

T250V

oN (OV)

+12VA

+12VB

+12VC

+12VD

High sidefloatingsupplies

Low sidefloatingsupplies


CONTROL ELECTRONICS

samples per 400Hz cycle with 65 levels. All six drive signals forthe bridge could be encoded in eprom. This would reduce thecomponent count significantly but would not allow closed loopwaveform or voltage regulation. Only the overall output couldbe regulated by regulating the dc input.

Recently Micro Linear2 has brought out a sine -wave referencegenerator IC series, the ML2037/8/9, and a simple three-phasepwm driver IC including sine reference, the ML4423. The for-mer works well and is very flexible with regard to clock andoutput frequencies. Synchronising three at120° may be tricky oranologue means will be needed for the other phases. TheML4423 proved less satisfactory with various stability and out-put purity problems. It is intended for low cost driving of threephase motors. Linfinity3 has brought out an audio pwm con-troller for class D amplifiers.This is designed to drive two fullbridges for stereo, and features closed loop and current limiting.Fully independent operation of each phase may be a problem butthese should match the precision of the eproms with far fewercomponents.

My prototype included a little extra circuitry to offer 50Hz,variable frequency, variable amplitude and linear voltage -to -fre-quency operation for motor driving. Slightly more logic or dif-ferent clock frequency could give 60Hz.

The output control loop may benefit from refinement for dif-ficult loads. The system may even benefit from open -loop oper-ation in some circumstances.

Various ICs are available for high side driving bridges. Thesewould eliminate the need for the dc -to -dc converter and optocouplers. These may not be able to cope with the split rails about

ground though. The HCPL3120 and HCPL3150 igbt opto-cou-pled gate drivers from Hewlett Packard4 are simpler and cheap-er than the HCPL2201 and ICL7667CPA employed here.

The input converter needs little regulation, so a power -factorcorrection scheme could be added. This would do away with theelectrolytic and surge suppressor. But it would also result inmuch higher peak currents in the input converter.

If the inverter only needs to run at one output frequency, say400Hz, then a transformer could be used at the output. Thiscould be wired delta/star fashion to produce a neutral and pro-vide isolation. The three phase bridge could then work directlyfrom rectified mains or the usual boost power -factor correctioncircuit.

Only one current sense per phase would be needed. The dis-advantage would be getting hold of a suitable transformer.

Thanks to Chris Clarke for programming the eproms and toGraeme Penhorwood for taking the photographs.

References1. International Rectifier, Hurst Green, Oxted, Surrey RH8

9BB, tel. 01883 713215.2. Micro Linear, 2092 Concourse, Drive San Jose, CA 95131.

Tel. 408 433-5200. Distributed in the UK by AmbarComponents Ltd, tel. 01844 261144.

3 Linfinity Microelectronics, 11861 Western Ave, GardenGrove, CA.92841, tel +1 714 898 8121

4. Hewlett Packard Ltd, Amen Corner, Cain Road, Bracknell,Berkshire, RG12 1HN, tel. 01344 360000. Distributed in theUK by Famell Electronic Components, tel. 0113 263 6311.

CHART AUDIO LEVELSIn -vision colour display or hard copy printout

PPM10 In -Vision PPM and Chart Recorder generates a display emu-lating the well known coaxial TWIN movements for monitoring stereoaudio levels and mono compatibility. Also: STEREO TWIN METER BOXcomprising two PPM9 boards, featuring inherent stability with law undermicroprocessor control. A free standing mains powered box frequentlyused for the final stereo monitoring when working to broadcaststandards. Manufactured under licence from the BBC.

* Advanced Active Aerial 4kHz-30MHz * Stabilizer frequency shift unitsfor howl reduction * 10 Outlet Distribution Amplifier * Stereo VariableEmphasis Limiter * PPM9, PPM5 hybrid and PPM8 IEC/DIN -50/+6dBdrives and movements * Broadcast Stereo Coders * Broadcast MonitorReceiver 150kHz-30MHz *

SURREY ELECTRONICS LTDThe Forge, Lucks Green, Cranleigh

Surrey GU6 7BGTelephone: 01483 275997 Fax: 276477

The Stereo Headphone Amplifier Box 'Balanced or unbalanced line inputs to stereo

headphone outputProfessional portable units operating from an internal PP3 battery

or external mains adaptor

*Precision transformerless differential left and right inputs

*Wide range of headphone drive impedances *High common

mode rejection *Low noise and distortion *Low quiescent power

consumption for extended battery life *Extensive RFI protection

The Balance Box (mic/line amplifier) - The PhantomPower Box - The OneStop DIN rail mounting radio frequency

interference filter and voltage transient pretector for voltage and

current loop process signal lines

Conford Electronics Conford Liphook Hants GU30 7QW

Information line 01428 751469 Fax 751223

E-mail [email protected]

Web http://www.confordelec.co.uk/catalogue/



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HP8557A .01Mc/s-350Mc/s - 8558B 0.1-1500Mc/s - 8559A .01-21GHz 180T or 180C -D -T £500 - £2000.TEK492 Spectrum Anz-OPT 2-50Kc/s-21GHz - £2.5k.TEK492P S.A. opt 1-2-3-50 Kc/s - 21GHz £4k.TEK495 S.A. 100Hz - 1.8GHz - £3k.TEKTRONIX - HP Oscilloscopes - 100Mc/s-465-465B-1740-1741 etc - E300 - qty in stock.Phillips 3217 50Mc/s oscilloscopes - £150-£250.Phillips 3296 350Mc/s IR remote oscilloscope - £500.Hitachi VC6041 Dig storage oscilloscope - 4OMc/s - £500.TEKTRONIX 2445 + DMM - 250Mc/s - £800.R&S APN 62 LF S/G 0.1Hz - 260KHz with book - £750.Wavetek-Schlumberger 4031 Radio communication test set -£POALIGHT AND OPTICAL EQUIPMENTAnritsu ML93A & Optical Lead Power Meter.Anritsu ML93B & Optical Lead Power Meter.Power Sensors for above MA96A - MA98A - MA913A -Battery Pack MZ95A.Anritsu MW97A Pulse Echo Tester.PI available - MH914C 1.3 - MH915B 1.3 - MH913B 0.85 -MH925A 1.3 - MH929A 1.55 - MH925A 1.3GI - MH914C1.3SM.Anritsu MW98A Time Domain Reflector.PI available - MH914C 1.3 - MH915B 1.3 - MH913B 0.85 -MH925A 1.3 - MH929A 1.55 - MH925A 1.3GI - MH914C1.3SM.Anritsu MZ100A E/0 Converter.+ MG912B ILD 1.351 Light Source + MG92B ILD 0.85)Light SourceAnritsu MZ118A 0/E Converter.+MH922A 0.8 0/0 unit + MH923 A1.3 0/E unit.Anritsu ML96B Power Meter & Charger.Anritsu MN95B Variable Att. 1300.Barr & Stroud LS10 Light Source.BT Power Unit 850 - 1300 - 1500.Photo Dyne 1950 XR Continuous Att. 1300 - 1500.Photo Dyne 1800 FA. Att.NKT Electronic QAM30 Att Meter (MN3032TX) 1300 out.Electo Optic Developments FO -500 TX Laser.Cossor-Raytheon 108L Optical Cable Fault Locator0-1000M 0-10kM.Intelco 220 Single Mode Att 1532.TEK P6701 Optical Converter 700 MC/S-850.TEK Orionics 7000 Type PI OTDR-103A.HP81512A Head 150MC/S 950-1700.HP84801A Fibre Power Sensor 600-1200.HP8158B ATT OPT 002+011 1300-1550.HP81519A RX DC-400MC/S 550-950.STC OFTX-3 Laser source.STC OFRX-3.STC OFR10 Reflectometer.STC OFSK15 Machine jointing + eye magnifier.Anritsu MS555A2 Radio communication anz - £1500Anritsu MG3601A Syn S/G 0.1 -1040 Mc/S AM -FM - £POAAnritsu ME453L RX Microwave ANZ.Anritsu ME453L TX Microwave ANZ.Anritsu MH370A Jitter Mod Oscillator.Anritsu MG642A Pulse Putt Gen.Anritsu SA MS 2601A 10KHz - 2.2 GHz - £2500.Anritsu SA MS 710F 100KC/S - 23 GHz - £POA.Complete MS65A Error Detector.System MS02A Timer & Digital Printer.Anritsu ML612A Sel Level Meter.Anritsu ML244A Sel Level Meter.Advantest TR98201 Signal Gen.Advantest TR9402 Digital Spectrum ANZ.Siemens D2108 Level Meter.Siemens 02150 Bit Error Meter,W&G PCM3 Auto Measuring Set.W&G SPM14 Sel Level Meter.W&G SPM15 Sel Level Meter.W&G SPM16 Sel Level Meter.W&G PS19 Level Gen -Elk.W&G DA2O+DA1 Data ANZ.W&G PMG3 Transmission Measuring Set.W&G PSS16 Generator.W&G PS14 Level Generator.W&G EPM-1 Plus Head Milliwatt Power Meter - £450.W&G DLM3 Phase Jitter & Noise - £500W&G DLM4 Data Line Test Set - £750.W&G PS10 & PM10 Level Gen.HP5352B Microwave counter Opt 010--005. 46 GHz brandnew £5000.HP8342A+5344A Microwave counter +Syn 18GHz - E1600.HP8112A Pulse Gen SOMc/S - £1400.HP8660C S/G AM/FM - Phase 01-110MC/s - 1300MC/s -2600 MC/s £1-E2k.HP4274A LCR Meter + Adaptor.HP8754A Network ANZ 4-1300MC/s + 8502A + cables.HP8754A Network ANZ H26 - 2600MC/s + 8502A + cables.HP8116A Pulse function Gen f2200.HP3588A S.A. 10Hz - 15OMC/s opt 001-003.HP54100A DIG Oscilloscope 1GHz - P.O.R.HP54501A DIG Oscilloscope 100MC/s - P.O.R.TEK 0F150 Fibre Optic TDR.MAR S/G 2022D 10KC/s - 1GHz - White - E1400.HP1630-1631-1650 Logic ANZs.

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Johns Radio, Whitehall Works, 84 Whitehall Road East, Birkenshaw, Bradford BD11 2ER. Tel: (01274) 684007. Fax: 651160


13L

RF DESIGN

Know noiseJoe Carr looks at noise from the receiver designer's perspective andexplains which elements of the receiving system are the biggestcontributors to it.

If you are in electronics, and you work with signals, thenyou will undoubtedly have to deal with noise. A radioreceiver for example must detect signals in the presence of

noise. Indeed, radio reception - especially at the weak signallevel - is essentially a game of signal-to-noise ratio.

The signal-to-noise or s -to -n ratio is the key here because asignal must be above the noise level before it can be success-fully detected and used.

Noise affects other electronics systems as well as receivers.In medical electronics, for example, the very low electricalpotentials generated by the human brain are displayed by anelectroencephalograph, or EEG, machine. Those signals are ofthe order of 1 to 100µV. Because they exist in a high -impedance source and high 50 or 60Hz electrical mains fields,they are often obscured. But they can also be obscured by noisegenerated in amplifier circuits.

Noise comes in a number of different guises, but for sake ofthis discussion we can divide noise sources into two classes:sources external to the receiver or amplifier and internalsources.

There is little you can do about external noise sources. Theyconsist of natural and man-made electromagnetic signals thatfall within the passband of the receiver. Figure 1 shows anapproximation of the external noise situation from the middleof the amplitude -modulation broadcast band to the low end ofthe vhf region. One has to select a receiver that can cope withexternal noise sources - especially if the noise sources arestrong.

Some natural external noise sources are extraterrestrial.

Joseph J. Carr, MSEE

These signals that form the basis of radio astronomy. Forexample, if you aim a beam antenna at the eastern horizonprior to sunrise, a distinct rise of noise level occurs as the Sunslips above the horizon - especially in the vhf region. Thereverse occurs in the west at sunset, but less dramatically, prob-ably because atmospheric ionisation decays much slower thanit is generated.

During World War II, it is reported that radar operators notedan increase in received noise level any time the Milky Way

Fig. 1. Natural noisemeasured at theterminals connectingan antenna to areceiver.

10

Frequency (MHz)30


RF DESIGN

Ri

(a)

R1

(b)

Fig. 2. Model ofan ideal resistor,

a) and a realresistor - i.e.

pure resistanceplus a noisesource, b).

Fig. 3. Noisevoltage for

bandwidths to10kHz for a 5051

resistor.

was above the horizon, decreasing the range at which theycould detect in -bound German bombers. Radio astronomywas only then in its infancy, so the effect was apparently notanticipated.

There is also some well-known, easily observed noise fromthe planet Jupiter in the 18 to 30MHz band.'

Internal noise sourcesA receiver's internal noise sources are affected by the designof the receiver. Ideal receivers produce no noise of their own,so the output signal from the ideal receiver would containonly the noise that was present at the input along with theradio signal. But real receiver circuits produce a certain levelof internal noise of their own.

Even a simple fixed -value resistor is noisy. Figure 2a)shows the equivalent circuit for an ideal, noise free resistor,while Fig. 2b) shows a practical real -world resistor. Thenoise in the real -world resistor is represented in Fig. 2b) by anoise voltage source, Vn, in series with the ideal, noise freeresistance,

At any temperature above absolute zero - OK or about-273°C - electrons in any material are in constant randommotion. Because of the inherent randomness of that motion,however, there is no detectable current in any one direction.

In other words, electron drift in any single direction is can-celled over even short time periods by equal drift in theopposite direction. Electron motions are therefore statisticallydecorrelated. There is, however, a continuous series of ran-dom current pulses generated in the material, and those puls-es are seen by the outside world as noise signals.

If a shielded 500 resistor is connected across the antennainput terminals of a radio receiver, the noise level at thereceiver output will increase by a predictable amount over theshort-circuit noise level. Noise signals of this type are calledby several names: thermal agitation noise, thermal noise, orJohnson noise. This type of noise is also called 'white noise'because it has a very broadband - near gaussian - spectraldensity.

The thermal noise spectrum is dominated by mid -fre-quencies - 104 to 105Hz - and is essentially flat. The term`white noise' is a metaphor developed from white light,which is composed of all visible colour frequencies. Theexpression for such noise is,

V, = 4KTBR (1)

Where Vn is the noise potential in volts, K is Boltzmann'sconstant (1.38x10-23 J/K), T is the temperature in kelvin, Ris the resistance in ohms and B is bandwidth in hertz.Temperature T is normally set to an average room tempera-ture of 290K by convention.

Table 1 and Fig. 3 show noise values for a 5052 resistor atvarious bandwidths out to 10kHz. Because different band-widths are used for different reception modes, it is commonpractice to delete the bandwidth factor in equation 1 andwrite it as,

VV, = 4KTR (2)

With this equation, you can find the noise voltage for anyparticular bandwidth by taking its square root and multiply-ing it by the equation. It is essentially the solution of the pre-vious equation normalised for a 1Hz bandwidth.

Signal-to-noise ratioReceivers are evaluated for quality on the basis of signal-to-noise ratio, also known as S/N or SNR and sometimes denot-ed Sn. The goal of the designer is to enhance the s -to -n ratioas much as possible.

Ultimately, the minimum signal level detectable at the out-put of an amplifier or radio receiver is that level whichappears just above the noise floor level - usually measured indBm. Therefore, the lower the system noise floor, the small-er the minimum allowable signal. Designers of weak signalreceivers spend a great deal of effort on suppressing the noisefloor as low as possible.

Noise factors, figures and temperaturesThe noise performance of a receiver or amplifier can bedefined in three different, but related, ways: noise factor, orFN, noise figure, or NF, and equivalent noise temperature,Te; these properties are definable as a simple ratio, decibelratio or kelvin temperature, respectively.

Noise factor, FN. For components such as resistors, the noisefactor is the ratio of the noise produced by a real resistor tothe simple thermal noise of an ideal resistor.

The noise factor of a radio receiver - or any system - is theratio of output noise power, P,,, to input noise power, P

100

90

80

70

60

50

40

30

20

10 -

0

0 4 6

Bandwidth (kHz)8 10

Table 1. Noise voltage for bandwidths to10kHz.Bandwidth (kHz) Noisex10-8 (V)1 2.831.5 3.462 4.002.5 4.473 4.93.5 5.294 5.664.5 6.005 6.335.5 6.636 6.936.5 7.217 7.497.5 7.758 8.008.5 8.259 8.499.5 8.7210 8.95


RF DESIGN

Fs, =[Pir 1T = 290K (3)

In order to make comparisons easier, the noisefactor is usually measured at the standard tem-perature To of 290K, i.e. standardised roomtemperature; in some countries though, 299 or 300K arecommonly used, but the differences are negligible.

It is also possible to define noise factor FN in terms of theoutput and input signal-to-noise ratios:

SNIF=SNo

where SNI is the input signal-to-noise ratio, SN0 is the outputsignal-to-noise ratio.

Al

Gain = Gi

Noise factor = F-1

A2

Gain = G2

Noise factor = F2

A3

Gain = G3

Noise factor = F3

AN

100

Gain = GN

Noise factor = FN

(4)

Noise figure, NF. The noise figure is frequently used tomeasure the receiver's 'goodness,' i.e. its departure fromIdealness.' Thus, it is a figure of merit. The noise figure isthe noise factor converted to decibel notation,

NF=10logFN (5)

where NF is the noise figure in decibels and FN is the noisefactor. Note that the log here is base 10.

Noise temperature, Te. The noise 'temperature' is a meansfor specifying noise in terms of an equivalent temperature.That is, the noise level that would be produced by a resistorat that temperature, expressed in kelvin.

Evaluating the noise equations shows that the noise poweris directly proportional to temperature in kelvin, and also thatnoise power collapses to zero at the temperature of absolutezero (OK).

Note that the equivalent noise temperature Te is not thephysical temperature of the amplifier, but rather a theoreticalconstruct that is an equivalent temperature that produces thatamount of noise power in a resistor.

Noise temperature is related to the noise factor by:

Te=(FN-1)Te

and to noise figure by

T, = 290(10""° -1)

(6)

(7)

Noise temperature is often specified for receivers and ampli-fiers in combination with, or in lieu of the noise figure.

Noise in cascade amplifiers and receiversA noise signal is seen by any amplifier following the noisesource as a valid input signal.

Each stage in the cascade chain, Fig. 4, amplifies both thesignals and the noise from previous stages. Each stage alsocontributes some additional noise of its own. Thus, in a cas-cade amplifier the final stage sees an input signal that con-sists of the original signal and noise amplified by each suc-cessive stage plus the noise contributed by earlier stages.

The overall noise factor for a cascade amplifier can be cal-culated from Friis' noise equation,

FF2 -1 F, -1 Fft, -1

N ,= F + -+ ...+G, G2

(8)

where EN is the overall noise factor of N stages in cascade,F1 is the noise factor of stage 1, F2 is the noise factor of stage2, FN is the noise factor of the nth stage, G1 is the gain ofstage 1, G2 is the gain of stage 2 and GN-1 is the gain ofstage n-1.

As you can see from Friis' equation, the noise factor of theentire cascade chain is dominated by the noise contribution ofthe first stage or two. High -gain, low -noise rf amplifierchains, or receivers, typically use a low -noise amplifier cir-cuits for the first stage or two in the cascade chain.

As an example, you will find a low -noise amplifier at thefeedpoint of a satellite receiver's dish antenna, and possiblyanother one at the input of the receiver module itself. Otheramplifiers in the chain might be more modest, although theirnoise contribution cannot be ignored at radio astronomy sig-nal levels.

Receiver noise floorThe noise floor of the receiver is a statement of the amount ofnoise produced by the receiver's internal circuitry, and direct-ly affects the sensitivity of the receiver.

The noise floor is typically expressed in dBm. Its specifi-cation is evaluated as follows: the more negative the better.The best receivers have noise floor numbers of greater than-130dBm, while some very good receivers offer numbers of-115 dBm to -130 dBm.

The noise floor depends directly on the bandwidth used tomake the measurement. Receiver advertisements usuallyspecify the bandwidth, but remember to compare the figuregiven with the bandwidth that you'll need for the mode oftransmission you want to receive. If, for example, you areinterested only in weak 6kHz wide amplitude -modulated sig-nals, and the noise floor is specified for a 250Hz cw filter,then the noise floor might be too high for your use.

Receiving -system exampleFigure 5 shows a receiving system that is common in the vhfthrough microwave regions of the spectrum. An antenna isused to obtain the signal, and a low -noise amplifier, Al inFig. 5, is provided to boost the antenna signal.

It is common practice to place the low -noise amplifier at

Transmission line

Noise calculations for a configuration such as Fig. 5, obtained via Excel from gain and noise figure entered into thespreadsheet in decibels.

Stage Gain/loss (dB) Gain/loss (lin.) Noise figure Noise factor Noise Temp.Preamplifier 15 31.62 2.2 1.66 191

Transmission line -2 0.63 2.00 1.58 170RF amplifier 10 10.00 3 2.00 289Mixer -6 0.25 4.5 2.82 527Overall 17 50.12 2.398 1.737 214

Fig. 4. In a cascadedamplifier chain likethis one, each stagenot only adds its ownnoise, but amplifiesnoise from thepreceding stage.

Receiver

RF amplifierMixer

RF IF

LO

Fig. 5. Typicalreceiver systemfront-end. Low -noiseamplifier Ai is putbefore thetransmission line. If itcame after, it wouldhave to deal with asignal subjected tomore loss.


RF DESIGN

the antenna terminals so that it does not have to overcome the loss of thetransmission line.

The receiver may or may not have an rf amplifier, but in this model oneis used, namely A2. The mixer then converts the rf signal to the inter-mediate frequency used by the receiver.

Loss in the coaxial cable transmission line can be a significant cause ofnoise in the system. The cable loss is usually expressed in decibels, andis taken from the manufacturer's data sheets if no actual measurementsare available.

Typically, the manufacturer will provide a chart that relates loss indecibels per metre (dB/m) to frequency. Find the loss factor appropriateto the desired frequency, and correct for the actual length of the line.

The noise temperature of the transmission line is:

Te(line)=TaL-1) (9)

where Te(line) is the noise temperature of the line and L is the loss ofthe line expressed in linear terms, as a ratio.

Table 1 shows the results of making the noise calculations on a receiv-ing system such as Fig. 5 when the following specifications are used,

Stage Gain (dB)Preamp 15Trans. line -2RF amp 10Mixer -6

Noise figure (dB)2.22.03.04.5

Overall gain for this part of the receiver is the sum of the gains, or 17dB.The results of the Friis equation shows an overall noise figure of 2.398.

If you program a spreadsheet with the noise equations so that you canvary the noise figure parameters, it becomes apparent that the first stagedominates.

Let's do a little ceterus paribust exercise in which one noise figure ischanged by 1dB. If the preamplifier noise figure is increased to 3.2dB,then the overall noise figure rises to 3.36dB.

Increasing the transmission line noise figure to 3dB only raises thenoise figure to 2.47dB. Increasing the rf amplifier noise figure to 4dBincreases the overall noise figure to 2.46dB. This finally increases themixer noise figure to 2.41dB.

For a 1dB increase in noise figure, the overall noise figure changes to:

StageLow -noise amplifierTransmission lineRF amplifierMixer

New NF (dB) Change3.20 +0.8 dB2.47 +0.072dB2.46 +0.062dB2.41 +0.012dB

Note that the increase in overall noise figure is greatest for the first stagein the chain, and that the change for each succeeding stage is less than forthe stage before. The lesson here is to put as much effort as possible intothe first stage in order to reduce the noise figure overall.

Reference1. Carr, J., RadioScience Observing, Vol. 1.

t All else remaining unchanged.

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RF DESIGN

Conventional wisdom has it that highperformance in a receiver goes hand -

in -hand with complexity. Compare acomms receiver with a crystal set. Butthere is a notable exception, as

explains.Ian Hic man

Super-regen orsu er-re lacement?

As a lad, my introduction to wire-less technology was a crystalset, given me by my grand-

mother.Wanting something better, I was

soon building battery sets of my own,and experiencing the thrill of DXing -receiving distant stations - thanks tothe greatly increased sensitivity afford-ed by an expertly wielded reactioncontrol.

Reaction - or in simple terms, posi-tive feedback at rf - is the key toobtaining a receiver with high sensi-tivity while keeping the componentcount low. With reaction as it is nor-mally implemented though, you needto be skillful in using both the tuningand reaction controls, in order toachieve the best performance.

But all this is effectively automatedin the 'super -regenerative' receiver,which dates from well before theSecond World War. It was described -but not explained - in reference 1. Thisdescription left me unclear about howthe super -regenerative receiver worked.The author gives a reference to anotherdescription, reference 2, which I hopeis more illuminating, although I havenot seen it.

While I could find no mention of thesuper-regen' in the Admiralty

Handbook of Wireless Telegraphy of1925, by the 1939 edition it had dulymade its appearance. Army veterans ofthe Second World War may remembera super-regen set used for communica-tion between tanks, and operating inthe uhf range.

The receiver with reactionIn a simple receiver with reaction, sen-sitivity and selectivity both increase asthe degree of positive feedback isincreased. This increase continues untilthe set is on the verge of oscillation, oractually oscillating very weakly. Anyfurther increase in the positive feed-back actually reduces the sensitivity, asthe following explanation shows.

In any oscillator circuit, the gain ofthe active device - at the fundamental,i.e. the resonant frequency of the tunedcircuit around which reaction is applied- falls with increasing amplitude. Thisis the mechanism which stabilises theamplitude of oscillation.

In a circuit suitably designed for useas a receiver with reaction, the way theloop gain changes with amplitude is all


RF DESIGN

important. Several characteristics areshown in Fig. 1.

Characteristic a) - and even more soc) - is ideal for a high -stability low -noise oscillator. The rapid change ofloop gain with amplitude, in the regionof unity loop gain, results in low ampli-tude modulation noise sidebands. Thefm noise sideband performance is gov-erned mainly by other factors.

But for a receiver with reaction, char-acteristic d) is just what is wanted. Theshallow angle at which the characteris-tic cuts the unity gain level makes theoscillator extremely susceptible toinfluence by any outside factor, such asan incoming signal.

Characteristic b), on the other hand isno good to man nor beast. As an oscil-lator, it will usually start, being kickedinto life by the switch -on transient, butmay occasionally fail too. As a reac-tion -aided receiver, as the degree ofreaction is increased, it will suddenlyburst into oscillation. It will not stopuntil the reaction control is wound backdown some way, where the gain is lowagain - an annoying sort of hysteresiseffect.

Many ingenious attempts have beenmade to harness reaction, automating itso as always to be at the optimumlevel. Older readers may remember the`Sobellette' small valve table radiofrom the fifties. This was a superhet,with but one IF transformer and no IFstage! Instead, the usual double -diodetriode detector stage was replaced by apentode leaky grid detector with reac-tion.

The theory was that, at the fixed 1F, afixed degree of reaction could beapplied, achieving gain and selectivityequivalent to a conventional superhetfour -valve -plus -rectifier line-up, butwith one less valve.

So much for the theory: the outputimpedance of the frequency changervaried across the band. This changedthe damping on the IF transformer,severely limiting the degree of factory -preset reaction that could safely beapplied.

The super -regenerative receiverThe super-regen receiver is anotherattempt at harnessing the gain increaseachievable with reaction. Reverse biason an initially cut-off valve or transis-tor rf amplifier with feedback is grad-ually reduced, until the stage begins tooscillate. When the oscillation has builtup to the intended design amplitude,the beyond -cut-off bias is againapplied, and the oscillation dies awayagain.

There are two ways of implementingthe periodic cut-off of the device.

In the externally quenched super-regen, a separate quench oscillator is

x10

2Gain

x1

x0.1

x1

Input signal IevelE

x

x

Fig. 1. Showing various ways the open -loop gain of an oscillator can vary withsignal level.

used, resulting in a fixed quench fre-quency, Fig. 2. This is usually in thesupersonic or low-rf range, typically 50to 100kHz.

Alternatively, the oscillator can beprovided with self biasing, with anover -long time -constant, so that it`squegs'. This results in bursts of class -C operation, each burst cutting off thedevice until the reverse bias dies awayagain sufficiently for oscillation torecommence. The self -quenching fre-quency is again typically in the range50 to 100kHz in the absence of anincoming signal, but will increasesomewhat in the presence of a signal.

The arrangement is usually similar toFig. 2, but with the time -constant CRincreased, and the separate quenchoscillator replaced by a short circuit.

External versus internalquenchingFigure 3 shows the build-up of ampli-tude of rf oscillation, lower trace, insympathy with the quench waveform,middle trace, in the absence or pres-ence of an incoming signal, top trace.The external quench waveform isshown as sinusoidal, but in the case ofa self -quenching circuit, it would be thetypical sawtooth waveform of a squeg-ging oscillator.

In the absence of an incoming signal,the oscillation has to build up from thelevel of the noise floor in the circuit.With an on -tune incoming signal, thebuild-up starts from a higher level.Consequently, the amplitude reachesany given level sooner than would oth-erwise be the case.

Thus in the externally quenched case,the burst of oscillation is longer, as inFig. 3, while in the self quenched case,

Quenchoscillator

Fig. 2. Simplified circuit diagram of a basic super -regenerativereceiver.

Gain

IIIIIuInIIIIIIIIIIIIIIIIIIIII

Iffilithill1111111111111111111RF signal

Quench oscillator

Voltage controlling gain

With signal No signal

AAmplitude of oscillations across tuned circuit

the amplitude reaches the level neededto cut off the circuit sooner, Fig. 4.Either way, the current drawn from thesupply increases, and as in Fig. 2 thismay be taken as the detected signallevel.

Whether self or externally quenched,a super-regenenerative receiver can bedesigned to run in either of two modes.In the linear mode, each newly startedburst of oscillation is quenched beforeever reaching its maximum possiblevalue. The result is a detected signalwhich varies linearly with the incomingsignal level, over a wide range.

Fig. 3. Illustratingthe circuit actionof a basic super-regen receiver.


RF DESIGN

No signal

Signal present

Alternatively, the amplitude of oscil-lation may be designed to reach almostthe maximum possible for the givensupply rail, before being quenched.This 'logarithmic mode' provides thegreatest sensitivity to the smallest sig-nals, giving a kind of limiting or auto-matic -gain control action with largersignals. Thus the dynamic range of theoutput is compressed to a manageablevalue, over a wide range of input lev-els.

Under the floorIt is important to note that, whetherusing linear or log mode, external orself -quenching, the off period must belong enough to allow the amplitude ofoscillation in the tuned circuit to diedown to below the level of the noisefloor in the circuit.

Thus each burst of oscillation startsin a random noise -initiated phase,rather than a phase coherent with theprevious burst of rf. Otherwise, the

Fig. 4. Bursts of rfin a selfquenching super-regen receiver.The no -signalquench frequency- upper trace -isabout 80kHz. Theincreased pulserate - with aconsequentincrease in supplycurrent drawn - isseen in the lowertrace. The raggedappearance of therf pulses is due tosub -sampling ofthe waveform bythe digital storageoscilloscope used.

Fig. 6. Block diagramshowing the internalsof the MICRF001 uhf

superhet receiver.

ANT 0

VDD oVSS o

RF amp

SELO 0

SEL1 0

SWEN 0

receiver will 'hear' itself, as well asany external signal, with resultantreduced sensitivity.

The super-regen circuit, in commonwith the reactive receiver, providesgreat sensitivity with a low componentcount. But it does not enjoy the othervirtue of the receiver with reaction.

The reactive receiver shows enhancedselectivity as well as enhanced sensi-tivity, due to the Q multiplying effect ofreaction. But clearly, the faster build-upof oscillation in the super-regen will becaused by any signal within the band-width of the tuned circuit.

At this early stage in the process,

f if

Af10

A dBm-30.0

-40.0

-50.0

-60.0

-70.0

-80.0

-90 0

-100 0

-110.0

-120 0

-130 0

Atten 0dB 50u

there is as yet no Q enhancement. As aresult, the relevant bandwidth is simplythe natural, unenhanced bandwidth ofthe tuned circuit.

The other main drawback of thesuper-regen receiver, besides its poorselectivity, is its antisocial behaviourtowards other users of the band inwhich it operates. In addition to being areceiver, the super-regen also acts as avery effective broadband jammer.

The narrow pulses of rf, seen in thetime domain in Fig. 4, correspond to aforest of spectral lines, spaced at thereceiver's pulse repetition frequency.These appear in the frequency domain

TG -10.0dBm

I'

V

Ref. 16 700MHz, 200kHz increments Avg B

Fig. 5. Typical spectrum of the stray radiation from a super-regen receiver,actually from that shown in Fig. 4. The broad band of interference makes thesuper-regen a social outcast among receiver architectures.

Programmablesynthesizer

REFOSC ft

I IICeramicresonator

Controllogic

UHF downconverter

1.807MHz

F amp1MHz

IF amp

AGCcontrol

Peakdetector

1

Referenceoscillator

Reference and control

Switched -capresistor

RSC

Programmablelow-pass

filter

DGK demodulator

Comp

<>DO

CTH0

I140 ELECTRONICS WORLD February 1999

RF DESIGN

as in the spectrum analyser display ofFig. 5. The typical appearance shownhas earned the super-regen the fanciful,if not entirely inappropriate, nicknameof the 'hedgehog'.

One ingenious scheme to render thesuper-regen receiver somewhat lessobnoxious appeared in the literature ayear or two ago. In this, an additionalgrounded -gate junction-fet stage pre-ceded the receiver proper, in an attemptto prevent the quench -frequency -mod-ulated rf getting back up the aerial.How effective this was I am unable toreport, but the idea does not seem tohave caught on.

Simple, but not a super-regenImagine your boss comes in onelunchtime, saying that he wants areceiver design for the UK low powerradio 418MHz licence -exempt band toMPT1340, and he wants it on his deskby the following morning.

For a quick solution, a super-regenmight appear to be the answer. Butthey are tricky things to get right, andthere's not enough time for a superhetdesign. The answer - ready by teabreakthat same afternoon - might be a func-tional replacement for the super regen,which has recently appeared. Thisoffers the same low component countcombined with high sensitivity as thesuper-regen circuit, but without any ofthe troublesome stray radiation of thelatter.

The MICRF001 QwikRadio3 is infact a fully functional superhet receiv-er, but the level of integration is sogreat that an absolutely minimal com-ponent count is achieved.

Figure 6 shows the internal workingsof the device, which comes in either a14 -pin plastic DIL package or a 14 pinSOIC. Both options operate over -40to +85°C and draw just 6.3mA from a+5V supply. The claimed sensitivity is-95dBm, making it directly compara-ble with a super-regen receiver.

The design range of receive frequen-cies is 300 to 440MHz, over which thedevice handles on -off keying, datarates of 100 up to 4800bit/s. Talking tothe Micrel rep. on the company's standat the recent Low Power RadioAssociation Exhibition andConference, he boasted that theMICRF001 was the only uhf radio chipyou could build into a working radioon experimenter's plug -board.

A uhf radio on bread board?I obtained a sample for evaluation and,decided to put his boast to the test. Mycircuit was just about the crudest, sim-plest that one could devise, Fig. 7.Built on the well known Experimentorwhite plug -board, testing commencedas soon as a suitable reference fre-

78L05

9VPP3

I

18cm Wire Fig. 7. Circuit diagram of a hastylash-up uhf receiver using theMICRF001 chip.

MICRF001

I

SELO WEN NC*

VssRF REF

VssRF SEL1 NC*

ANT CAGC

VddRF VssBB

VddBB VssBB

CTH DO

10n

F 3.19690MHzCrystal

4.7u

Effectively logic 1, dueto internal pull-ups

quency crystal had been procured. Thiswas at 3.1969MHz, which is effective-ly multiplied by a factor of 130 in thedevice's synthesiser to produce a localoscillator frequency of 415.602MHz.

Given the device's intermediate fre-quency, which is itself a weak functionof the reference frequency, this sets thereceive frequency as 418MHz. There'smore on this in the panel entitled 'Thesingle -chip superhet'.

Being temporarily without a uhf sig-nal generator, I connected 18cm ofwire to the output terminal of a LeaderLSG- 16 100kHz to 100MHz signalgenerator, to act as a quarterwavewhip. The receiver, a metre or so away,was similarly equipped. With internal1kHz AM selected, the signal genera-tor's output frequency was set to83.6MHz.

The MICRF001 receiver picked upthe generator's fifth harmonic, slicingthe envelope cleanly to recover whatlooks like a 010101 data stream run-ning at 2kbit/second, Fig. 8, top trace.This is quite a feat, given the low levelof the fifth harmonic. In addition, thelow modulation depth - barely 20% -hardly resembles on/off keying by along margin, Fig. 8, lower trace.However, it gave no real indication ofthe range that I could expect in prac-tice.

Fortunately, an open -site test rangeon the extensive flat rooftop of a fac-tory, plus a wide range of test equip-ment, was available to me at the time.This permitted a more quantitive mea-surement approach.

A Marconi 2022D 10kHz to 1GHzsignal generator, with its front panelhorizontal and standing on a lm highparapet, was set to 418MHz and 18cmof wire left poking up from its output

Data out (and tocrystal earpiece)

Technical supportMICRF001 - MicrelSemiconductor (UK)Ltd., 21 Old NewtownRoad, Newbury, RG147DP. Tel: 01635524455, fax: 10635524466, e-mail:[email protected],Websitewww.micrel.com

3.1969MHz crystal,Golledge ElectronicsLimited, Ashwell Park,Ilminster, Somerset,TA19 9DX. Tel: 01460256100, fax: 01460256101, e-mail:[email protected],Websitewww.golledge.co.uk.

socket. The output level was set to-33dBm (500nW), with 99% ampli-tude modulation depth at 1kHz.

Range testingI monitored the receiver's data outputat pin 8 with a crystal earpiece.Walking away with the receiver hand-held at about the same 1.5m height, theclear 1kHz tone held out to a range ofabout 20m. Beyond this distance, it dis-appeared in the noise. Clearly, thisbrief test involved no danger of inter-ference with other, off -site users.

The permitted transmitter power inthe 418MHz band, per MPT1340, is250pW, or some 500 times as much asthe signal generator was delivering. Sotaking the optimistic free space lossfigure of -6dB per doubling of rangewould predict a working range of450m. This assumes a transmitterworking within the legal limit ofpower.

The flat earth loss figure of -12dBPDOR is more realistic than the free

Fig. 8. Uppertrace -a 010101data stream at2kbit/s,recovered fromthe fifthharmonic of the83.6MHz outputof a signalgenerator.2V/div. vertical,500ps/divhorizontal. In thelower trace is thesignal generatoroutput, showingjust 20%amplitudemodulationdepth. 50mV/divvertical,500ps/divhorizontal.


RF DESIGN

space loss, and predicts a range of justunder 100m in a clear site.

Clearly, under more cluttered condi-tions, the useful range would be less,but then the circuit of Fig. 7 really doesnot take full advantage of the IC'spotential. The pin 4 antenna inputimpedance at uhf is about 6k52 in par-

allel with 2pF, whereas the impedanceof a quarter wave whip workingagainst a ground plane is 3752 -a hor-rendous mismatch.

The antennaIn the typical application circuit of Fig.

9, some simple antenna tuning is incor-

porated. This provides some selectivityto reduce the possibility of blocking ordesensitisation by large out -of -bandsignals. Matching the antenna into a tapon the inductor would further increasesensitivity.

The arrangement in Fig. 9 providesprotection against response to other

The single chip superhetAn rf amplifier feeds the mixer, the local oscillator for which issupplied by the synthesiser. The mixer output is fed to an IFamplifier stage, followed by the IF filter.

The filter has a 1MHz bandwidth, centred on 2.25MHznominal. But as equation 1 shows, the exact value is a functionof Fret. The IF filter output passes to a final IF amplifier stage, andthence to a peak detector.

A post -detection low-pass filter with programmable cut-offfrequency permits selection of the optimum bandwidth for thedata rate used. The filter output supplies automatic gain controlto the mixer and IF stages, as well as driving the demodulator viaa programmable single -pole low-pass filter.

The time constant of this filter is usually in the range 5 to 50ms,its output forming the comparator reference level. Thecomparator slices the recovered analogue data relative to thereference level, converting it to a 5V logic output. The slicingaction, for typical data, is shown in Fig. 10.

The device is designed primarily as a more sanitaryreplacement for the super-regen receiver. One 'advantage' of thesuper -regenerator is that its selectivity is so poor that it can beused in conjunction with a very cheap transmitter whosefrequency, being determined simply by an LC circuit, is poorlydefined.

To achieve the same broad bandwidth, the MICRF001 uses asignals can be received with the local oscillator

either high or low. Furthermore, two modes of working areavailable, in one of which, namely the sweep mode, the effectivebandwidth is further increased as described later.

The equation relating the the intermediate frequency Fit and thesynthesiser reference frequency Fret is,

-(Fri x(M+a)F,/ 390

x 2.25= (1)

where all frequencies are in megahertz, M=128 and cc=1 forSweep mode or oc=2 for Fixed mode.

Fixed mode. This mode is used with transmitters having a goodfrequency stability. These would have, for example, a SAW orcrystal frequency reference. In this mode the transmitter, receiver

Preamble DataDelimiter

V(2)

V(4)V(3)

Dead timePreamble Data

IF and local oscillator frequencies are related by,

Fy- =

and the synthesiser reference frequency becomes,

F = FI""f (M + 2)

This assumes low -side mixing. From these three equations,

2.25f= Fir x (1+ (4)

So, for a given transmitter frequency, Flo is determined fromequation 4, where Fret is given by equation 3.

As an example, for operation in the UK's 417.9 to 418.1MHzband, as specified by MPT1340, operation at 418.000MHzwould require an Fret of 3.1969MHz. Manufacturers may useother frequencies in the band, which is intended for a variety ofapplications including those requiring a wide bandwidth.

In various European countries, the band 433.050-434.709MHzis available for non-specific SRDs, as per CEPT RecommendationCEPT/ERC/REC 70-03, which may be viewed at www.ero.dk

(2)

(3)

Sweep mode. In sweep mode, the local oscillator sweeps a bandcentred on the nominal transmit frequency, so that the effectivebandwidth is much greater than the IF pass bandwidth Fbp, asshown in Fig. 11.

In this mode,

F,/min) = Fref x M(5)

Floon,,) = x (M+ 2)

thus the sweep range AFsw=2xFret. The resultant coverage is4F,,,,,+(2xF,t)+Fbp. In Sweep mode, Fret is simply given by,

F = "rì (M +1)

So, for example, given Ftx=387MHz ±0.5%, including initialtolerance, temperature and ageing, then from equation 6,

Fret=387/129=3.00MHz - a standard ceramic resonatorfrequency.

tO

11= 5ms slic ng level time constantV 3 = 50ms srcing level time constantV 4 = 0.5ms s icing level time constant

Fig. 10. Comparator action with various reference level filter time constants.

5ms

4- 50ms

4-- 0.5ms

fif + fbp/2 fif + fbp/2

(6)

fmin flo(min) ftx flo(max) fmax14-

Sweep band

4 Coverage band

(Coverage band = Afsw + 2fif +fbp)

Fig. 11. Showing how in Sweep mode, theeffective bandwidth is increased by sweepingthe local oscillator.


RF DESIGN

1/4 wavelengthmonoplole antenna

PCB foilinductor

10nH

Optionalfilter

+5V

7.3"

15p

MICRF001

SELOVSSRFVSSRF

ANTVDDRFVDDBBCTH

Ceramicresonator

SWEN N/C 3.00MHz

REFOSCSEL1 N/C

CAGC

VSSBBVSSBB

DO

mm 470n

Itransmissions, which may appear onthe same channel. It does this by virtueof the coding supplied by the HoltekHTI2D address/data decoder shown,and its companion coder in the trans-mitter.

Data receiptThe receiver only responds to theappropriate one of 64 different codes,providing on receipt up to four differ-ent commands which can be decodedfrom data bits D11 and D12. Note thatin Fig. 8, a 3MHz ceramic resonator isused as the reference frequency. Thisarrangement is possible due to the

6 -bitaddr.

HT -12D

AO

-0-13- Alit -0-1)- A2.-o -o- A3

A4

A6- A7

VSS

+5V

Optional LEDVDD indicates valid

VT p I decode°sot -h-osc2 68k

DIN

D11

D10D9

D8

more generous spectrum allocation andrelaxed frequency accuracy require-ments for srds (short range devices) inNorth America and some other coun-tries.

Even allowing for the additional costof a crystal or surface -acoustic -wavedevice to provide the greater frequencyaccuracy demanded by the Europeanmarket, clearly the device provides aquick and economical answer for any-one needing to design a receiver for the418MHz or 433MHz licence exemptbands.

Note that while srd transmitters andreceivers for these bands are licence

Code Bit 0Code Bit 1

exempt as far as the user is concerned,the manufacture must obtain typeapproval to the relevant specificationsfor any countries in which he intends tosell his products.

References1. The Manual of Modern Radio, J.

Scott -Taggart, The AmalgamatedPress Ltd., London 1933

2. See an article on the super -regener-ative receiver by J. Dent, WirelessWorld, June 16, 1933

3. Produced by Micrel Inc. 1849Fortune Drive, San Jose, CA 95131,USA.

Fig. 9. A typicalapplication circuitfor the MICRF001for North Americanuse.

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144


ELECTRONICS WORLD February 1999

NEW PRODUCTS CLASSIFIED . 0 . . Please quote "Electronics World" when seeking further information

PASSIVE AND ACTIVE

COMPONENTS

Connectors and cablingHeavy-duty connectors. Han Seriesconnectors by Harting are designedfor a hard life, during whichmechanical strength and tolerance ofvibration are needed. They conform toa number of international standardsand come in various hood andhousing sizes. Mixed contacts providefor the connection of optical fibres,pneumatics and electrical cables andsignals in the one connector. Manydifferent termination forms work atdifferent voltage and current ratings.Arrow-Jermyn. Tel., 01234 270027;fax, 01234 214674/791501.Enq no 502

ArraysMemory/logic asics. Samsungnow has available new asicsbased on 0.25pm mergedmemory and logic. Up to 8.2million gates combine to formthree types of device: STD110standard cell; MDL110 mergeddram and logic; and MFL110,which is merged flash memoryand logic, allowing users tobegin with a logic design, addingdram or flash. Libraries areavailable for products such asnotebooks, cellular handsetsand cellular graphicsacceleration, all needing lowpower and high density; asecond library concernsnetworking and desktop systemsneeding high performance andsomewhat higher power.Samsung SemiconductorEurope Ltd. Tel., 0181 3807200;fax, 0181 3807220.Enq no 501

Cable repeater. For connecting 1394cables and products in a largenetwork, DDK's 1394 Cable Repeaterallows a continuous signal strength tobe maintained on all 1394 serial -busnetworks over a cable extension of upto 72m. It conforms to 1394 IEEEstandards, uses an IBM three -i/o portphysical layer chip, may be connectedup to 16 hops and gives automaticdetection of data transfers up to400Mb/s.DDK Electronics (Europe) Ltd. Tel.,01959 561224; fax., 01959 561034Enq no 503

Discrete active devicesH -v p-n-ps. New p -n -p transistorsare able to handle a maximumcollector/emitter voltage of 500V.Two types are available: theFZT560 in SOT223 and theFMMT560 in the smaller SOT23package. Both provide the samehigh -voltage performance, thepower dissipations being 2W and0.5W. Current handling for both is500mA peak pulse and 150mAcontinuously. At 50mA, typical gainis 80 at 500V.Zetex plc. Tel., 0161 622 4422; fax,0161 622 4420; web,www.zetex.com.Enq no 504

Displays12.1in svga tft. A 30000h life, highbrightness tft liquid -crystal displaypanel from Toshiba, theLTM12C289, is meant for industrialapplications and not necessarily forthose involving personalcomputers. It provides wide viewingangles and brightness levels inexcess of 250cd/m2 with a typicalcontrast ratio of 200:1. Since thelighting ccfls are both at the top ofthe screen, size has been kept to278 by 209 by 14mm to provide anactive display of 245 by 184mm toan 800by 600 pixel resolution.Voltage needed is 3.3V and theunit can be supplied with aninverter designed to optimisebacklight life.Toshiba Electronics UK Ltd. Tel.,01276 694730; fax, 01276 694800.Enq no 505

SXGA lcd controller. DigitalView's AC -1280 analogue lcdinterface controller resolves toSXGA (1280 by 1024) at 75Hz,comes in single -board form and willdrive 3.3V and 5V panels from allmajor makers. It provides full -screen image expansion for VGA,SVGA and XGA modes ofoperation, using 24 -bit working togive millions of colours. There isauto -detection for sync -on -greeninputs and the board takesinterlaced and non -interlacedsignal. Various accessories are

offered and there are differenthousings available for desk -top,industrial use and panel mounting.Digital View Ltd. Tel., 01812361112; fax, 0181 2361116; web,www.digitalview.com.Enq no 506

19in monitor. Panasonic's SL90ZenTan crt monitor uses a 100°deflection tube, with the result thatit takes up no more back-to-frontspace than a 15in type. Imagequality is not compromised by thedesign, since the shorter gun -to -screen distance and the use of thecompany's specialised signalprocessor is claimed to actuallyimprove performance. Use of aCrystal Pigment phosphor reducesambient light reflection for bettercontrast, as does the screencoating. The monitor supports anumber of power -saving standards,including Energy Star.Panasonic UK Ltd. Tel., 0500404041; web,www.panasonic.co.uk.Enq no 507

FiltersEmc filters for machines. Steatite'sSentinel filters are designed to reduceconducted noise from electricalmachinery and motors, in compliancewith UL 1283 and EN133200 emcstandards. Operating current is6-180A and voltage ratings up to520V. For currents to 25A, single -stage filtration is used; for currentsbetween 36A and 180A, there aretwo -stage filters. All have versatile

MemoryDirect Ram -bus dram. Toshibaoffers working samples of thenew generation of 64M and 72Mrdrams, which provide a datatransfer speed of 800MHz or1.6Gb/s. Organisation is 4Mwordby 18 bits with a 1kbyte pagesize. Refresh cycle is8kcycle/32ms, voltage supply is2.5V, power 2.2mW, or 260mW instandby and 10mW asleep.Toshiba Electronics UK Ltd. Tel.,01276 694730; fax, 01276694800.Enq no 512

mounting flanges on the aluminiumenclosures and the filters themselvesare relatively small. As a result, theywill often fit inside equipment controlpanels. Transient protection isavailable as an option.Steatite Insulations Ltd. Tel., 0121678 6888; fax, 0121 693 8804.Enq no 508

HardwareSpot cooling fan. Micronel's newfans use vanes within the housing toimpart a "turbo" effect, whichincreases airflow and pressure by20%. The fans are for low -powerworking and localised cooling, theairflow being straighter than is usual.Speed is 13000rev/min and operatingvoltage 12V or 24V.Radiatron Components Ltd. Tel.,01784 439393; fax, 01784 477333.Enq no 509


NEW PRODUCTS CLASSIFIED

Please quote "Electronics World" when seeking further information

Small fan. Designed to cool smallcomponents such as individualsemiconductors, the Model 2008 byShicoh measures 20 by 20 by 8mmand weighs 5.3g.lt uses a linearmotor on ball bearings and is virtuallysilent, although airflow is 0.015m3 perminute. It is designed to work from70mA at 12V dc, but starts working at7V and still turns at 2.5V. It is suitablefor flush mounting on a gasket ormetal and insulation resistance is10M4 at 500V ac.Key Electronic Components. Tel.,0118 9351546; fax, 0118 9660294; e-mail, [email protected]; web,www.keyelectronic.com.Enq no 510

MaterialsConductive paints. IVC has threenew paints for use with its Spraycoatprocess of emi/rfi shielding. They aremade using very mild solvents towithstand the higher built-in stressesfound in some plastics. They havepassed the requirements of theUnderwriters' Laboratory. AG1010contains pure silver particles for thehighest shielding performance,providing sheet resistivity of0.05Q/square in a 10pm thickness.AGCU120 has blended silver andsilver-plated copper particles to give a

Thin-film terminators. PCSterminators are capable of stableworking at up to 10GHz andoffer a vswr between 1.1 and1.3. Stray inductance andcapacitance are negligible andstability with temperature andtime is down to 0.2%±0.50following the cycling and load lifetests. Power ratings in the seriescover 125mW to 80W in 500 or750 versions.Rhopoint Components Ltd. Tel.,01883 717988; fax, 01883712938; e-mail,components@rhopoint co.ukEnq no 520

sheet resistivity of 0.05-0.1Q/squarein a 15pm thickness; and CS725 usessilver-plated copper for plasticsurfaces, for which it has excellentadhesion. The paints may be appliedselectively to plastic surfacesmanually or robotically.IVC Ltd. Tel., 0121 511 1115; fax,0121 544 5253.Enq no 511

Microprocessors andcontrollersMicro supervisor ics. Fivemicroprocessor ics from IMP containpower management circuitry to switchthe power source to a backup batterywhen the main supply fails. They alsohave a watchdog function andinitialisation to reset the system afterfailure or lockup. IMP690A/692A andIMP802L/M/805L are equivalent toMaxim devices with the same namesbut with the addition of thermal andshort-circuit protection. Currentconsumption on the IMP versions is100pA.IMP Inc. Tel., 001 408 432 9100; fax,001 408 434 0335; web,http://www.impweb.comEnq no 513

64 -bit microprocessors. From IDTare two RISController micros forcommunications systems. Available inspeeds of 180, 200 and 250MHz, theyare 3.3V devices tolerating 5V i/o, ajtag interface and an enhanced writemode to simplify support ofsynchronous dram. They are alsocompatible with Windows CE andother op. systems and deliver a330-Dhrystone performance at250MHz. Two-way set -associativecaches have cache locking and theRC64474 has a 33 -bit interface busto provide 64 -bit processing and low-cost 32 -bit memory. The RC64475uses 64 bits throughout to give over1 Gb/s bus bandwidth and 4Gb/ssystem bandwidth.IDT Europe. Tel., 01372 363339; fax,01372 378851.Enq no 514

Optical devicesOptical transceiver. When used withlow-cost optical fibre of up to 100mlong, NEC's NL2100 opticaltransceiver handles data at between1Mb/s and 156Mb/s. It uses a 650nmled, a silicon PIN detector and apreamplifier. Power supply is 5V, theelectrical interface is high-speed andconnectors are of the F07 PN type.The unit is contained in a standard1 -by -9 sip package and the mountingarrangement makes the devicesuitable for network interface cardsand other uses in which it must takehard use. It complies with the ATMForum standard and the path lengthmay be increased from 100m to1000m by the use of plastic -clad fibre.NEC Electronics (UK) Ltd. Tel., 01908691133; fax, 01908 670290.Enq no 515

OscillatorsOvened v -c crystal oscillators. TeleQuartz GmbH has a new range ofoven -controlled, voltage -trimmedcrystal oscillators. 0001000oscillators are stable to within0.03ppm over the 0-70°C range,annual ageing being less than0.1ppm. A cheaper AT -cut type givesa stability of 0.15ppm over thetemperature range and ageing of0.2ppm/year; both types provideHcmos output. Frequencies lie in therange 10-26MHz, with specificfrequencies at 10, 13, 16.384 and26MHz. The company also has aversion designed for use in switchingand transmission systems, operatingfrom 3.3V at 350mA. This type has astability of 0.1ppm at 8.192-26MHz,with voltage trimming. Output isLVHcmos.Webster Electronics Ltd. Tel., 0146057166; fax, 01460 57777; e-mail,[email protected] no 516

Passive componentsChip inductors. Surface -mountedchip inductors from BI Technologiesnow come in three standard sizes of0603, 0805 and 1206, instead of onlythe last. In the 0805 size, theinductors cover a range of 0.047pH to33pH, the same as in the 1206 type,

Photosensor. UZE is a newphotoelectric sensor byMatsushita that operates from12-240V dc or 24-240V ac. Itoffers sensing ranges of 30mfor through -beam applications,7m in the retro-reflective modeand 0.7m with diffused beam.The sensor is only 18 by 62 by35mm in size; retro-reflectiveand diffuse versions haveautomatic cross -talk protectionand may be mounted next toeach other. Its case is IP66sealed. There is also theoption of dark -on or light -onswitching. To ease alignment,some models have a red ledlight source.Matsushita AutomationControls Ltd. Tel., 01908231555; fax, 01908 231599;,mail, info @macuk.co.uk;www.mac-europe.com.Enq no 527

in 34 values; maximum and minimumcurrent ratings are 300mA and 5mA.In 0603, the range is 0.047p1-1-27pHat 50/2mA. All are shielded and arecompatible with vapour -phase and itreflow soldering.BI Technologies Ltd. Tel., 01162781133; fax, 0116 2781199.Enq no 517

Chip attenuators. Kamaya RAC16chip attenuators replace threeresistors with the one chip, whichmeasures 1.6mm square by 0.55mm.They take the form of an unbalancedpi section and exhibit a vswr of lessthan 1.2. Characteristic impedancesare 500, 750 or up to 1000 onrequest, attenuating by 1, 2, 3, 6 or10dB at temperatures between -40°Cand 125°C.Surtech Distribution Ltd. Tel., 01256840055; fax, 01256 479785Enq no 518

Sensing resistors. Sensors withvirtually zero inductance are offeredby VTM. Materials are resistancealloys, allowing values down to R0005to be produced with temperature

1 46ELECTRONICS WORLD February 1999


coefficients down to 4Oppm/°C. Powerratings are 0.6W -6.8W in straight stripsor preformed in 5mm to 25mm steps.Resistance values are 5% or 3%.VTM (UK) Ltd. Tel., 01494 738600;fax, 01494 738610.Enq no 519

Power semiconductorsLow R,, p -channel power mosfet.This SO -8 power mosfet byInternational Rectifier has the loweston resistance of any available in thisoutline. The IRF7210 is a 12V typewith an on resistance of 7m0 at agate/source voltage of 4.5V, which isabout the same as that quoted forn -channel devices and around halfthat previously achieved in SO -8.International Rectifier. Tel., 01883732020; fax, 01883 733410.Enq no 521

Protection devicesSurge protection for Ericsson slics.TISPPBL programmable telecommssurge protectors by PowerInnovations are for use withEricsson's PBL3xxx series ofsubscriber -line interface circuits; theserequire a complex voltage/timeprotection envelope. The devices arerated for the full voltage range of theslic up to 90V. Programming is doneby reference to battery voltage,providing minimum stress to the slic,regardless of the supply. Two modelsare produced: the TISPPBL1 forstandard use; and the TISPPBL2 for

Radio remote control. UsingRF Solutions' GlobemasterPager Decoder, one canoperate systems remotely bymaking a telephone call. Whathappens is that you call a pagerservice, which then transmitsthe relevant command code tothe Globemaster receiver -decoder, activating its four high -current switched outputs. Eachunit has its own identificationcode to validate the caller'sidentification number. Powerneeded is 5V or 12V dc and thestandard outputs at cmos /ttllevel may be replaced by relayoutputs. The device is normallya board -mounted module, but isalso available as a completesystem in a case.RF Solutions Ltd. Tel., 01273488880; fax, 01273480661; e-mail [email protected]; web,www.rfsolutions.co.uk.Enq no 538

Please quote "Electronics World"when seeking further information

line currents over 60mA. Two buffertransistors are used to lower supplyloading and to prevent the slic powersupply being charged.Power Innovations Ltd. Tel., 01234223001; fax, 01234 223000; e-mail,[email protected] no 522

Switches and relaysRubber keypads. Keypads in rubberby Radiatron give a proper responseto touch, choices of keystroke andtravel and a range of actuation forces.there are also printing choices,backlighting and a number of surfacefinishes, including simulated plastickeytops with no tooling cost.Radiatron Components Ltd. Tel.,01784 439393; fax, 01784 477333.Enq no 523

Automotive relay. Matsushita has arange of twin relays designed forvehicle use. CT relays measure 17.4by 7 by 13.5mm for the singlechangeover type, the twin andH -bridge types double the width.Switching capability is 20N14V dc percontact. Three package styles areavailable. There is a singlechangeover with spdt operation, adual changeover with a twin -coil relaywith two spdt operation and anH -bridge version. This last version isfor use where the simultaneousforward and reverse operation of amotor drive must be avoided, as inelectric sunroofs and windows.Matsushita Automation Controls Ltd.Tel., 01908 231555; fax, 01908231599; e-mail, [email protected];web, www.mac-europe.com.Enq no 524

Solid-state relays. Omron's range ofrelays provides output currents in the100mA-40A range. Smallest is theG3VM mosfet type that switches ac/dcloads to 350V in spst-no and dpst-noversions. There are double -throwtypes in 8 -pin packages and single -throw types in 4 -pin or 6 -pin packs, allin through -hole or surface -mountedversions. Also in the range are single -in -line types and i/o relays for usebetween logic and load.ICE Electronics. Tel., 01480 496466;fax, 01480 498335.Enq no 525

Sealed push -buttons. ITW 49-59series of momentary -actionpush-button switches are sealed toIP67. They are available with orwithout led status lighting and can bepanel mounted with a series 16microswitch or with flying leads.Maximum current is 10A and theaction is spdt, double break to providereliable dc switching. They come inround or square bezels in six coloursand are made in PBT thermoplastic.Townsend Coates Ltd.Tel., 0116 274 4488.Enq no 526

Transducers andsensorsSmall load cell. Wherever a verysmall load cell is needed, Control

Transducers' Model ME should fill thebill, being 12mm in diameter and 6mmthick. Ranges are 250g to 5kg in 14steps, errors due to non -linearity,hysteresis and repeatability combinedamounting to less than ±0.15%. Theunits are in the form of a four -armWheatstone bridge using bondedstrain gauges. Overload is 150%full-scale. A 10V ac/dc excitation isneeded, output is 20mV and bridgeresistance 3500.Control Transducers. Tel., 01234217704; fax, 01234 217083.Enq no 528

EQUIPMENT

Production equipmentPower screwdrivers. Mains -poweredModel ET screwdrivers fromToolworld are meant for benchassembly operations, the powersupply being capable of running twosuch tools simultaneously. The rangeincludes six models with torques of0.4kgf cm to 20kgf cm, three of themtaking 4mm or 6.35mm hexagonal bitsand the others 6.35mm or 5mm; theET -7000R is a right-angled version. Acatalogue is on offer.Toolworld Ltd. Tel., 01249 821234;fax, 01249 816723.Enq no 530

Miniature power tool. New fromMinicraft is the MiniMax 230, a small,mains -powered rotary tool turning atspeeds variable from 8000 to21000rev/min and taking all thestandard accessories in thecompany's range in its four -jawkeyless chuck. It fits the standardlathe attachment and drill stand, aswell as those of other makers. Thetool is available on its own or in acase with a 100 -piece set ofaccessories.Minicraft. Tel., 01388 420535; fax,01388 817182.Enq no 531

Power suppliesBattery chargers. Hitec batterychargers by Merlin are flexible enoughto handle a number of different batterytypes, keep them topped up or chargethem quickly. They detectenvironmental variations that wouldresult in incorrect charging regimes insimpler chargers. Switched -modecharging is used to provide bulk,absorption and float characteristics forrapid charge to 80%, followed byabsorption for the other 20% and floatto maintain the charge. High currentscan be supplied to allow the battery topower a heavy load without going flat.The chargers will cope with badlyregulated mains. When batteries areleft on charge for a long period, theHitec analyses battery state and giveswhichever charge is needed. Variousprotection alarms are provided.Merlin Equipment. Tel., 01491824333; fax, 01491 824466.Enq no 532

Universal bench supplies. FromKenwood comes the PDS range of

Microwave bulb. Primarc UVTechnology offers the Primarcelectrodeless bulb for ultravioletcuring in optical -fibre coating, cdmanufacture, etc. It is excited bymagnetron, ignition being bymeans of a low-pressure mercurylamp in the bulb, which irradiatesthe gas and ionises it. Warm-uptakes a few seconds. Standardgas fill is mercury/gas, but halidesmay be added to modify theoutput.Primarc UV Technology.tel., 01753 528678;fax, 01753 811678;e-mail, [email protected] no 529

Data/telemetry transceiver. Asynthesised transceiver for use inportable and hand-held equipmentto provide two-way radiocommunication, the Wood &Douglas SX500 is approved to ETS300 220. The unit mounts on aboard and measures 60 by 40 by17mm, works in the 400-500MHzband and provides up to 100mWoutput power from a 5.5V -15Vsupply. It has 128 frequencies,selected via the serial interface andprogrammed over 5MHz switchingbandwidth without being realigned.Modulation may be digital oranalogue. Other versions will soonbe available to work in the130-185MHz and 860-880MHzbands. A development kit isavailable.Wood and Douglas Ltd. Tel., 0118981 1444; fax, 0118 981 1567email,[email protected];web,www.woodanddouglas.co.uk.Enq no 539




bench dc supplies, providing outputsof 20V at 36A to 120V at 6A. Lightweight and small size have beenachieved by the use of combinedswitching and linear operation.Performance is said to be as goodas as that of large, fully linear types.Line and load regulations are bothbetter than 0.005%, transientresponse time is 100ps andtemperature coefficient 100ppm. Allhave 3.5 -digit displays showingvoltage and current simultaneouslyand there is provision for an internalGPIB, RS232 or analogue interface.Kenwood UK Ltd. Tel., 01923655291; fax, 01923 655297.Enq no 533

Low drop -out regulators. Toko'sTK112xxB linear regulators havebuilt-in switching and provide a 2%output. They are available in 0.1Vsteps from 1.3V to 5V, 5.5V and 8V.Quiescent current is 170pA no loadand 1mA with a 30mA load; standbycurrent is 100nA. The internal p -n -ptransistor gives a dropout of,typically, 80mV at 30mA. Internalswitching is controllable by ttl orcmos levels and there are the usualprotective circuits.Cirkit Distribution Ltd. Tel., 01992444111; fax, 01992 464457; e-mail,enquiries @cirkit.co.ukEnq no 534

150W dc -dc converters. New to theArtesyn Technologies BXB family ofdc -to -dc converters is 150W seriesmeant for use in communicationsand distributed power applications.These come in the industry -standard

half -brick package and have thesame footprint as BXB50/75/100types, being drop -in replacements toprovide increased power. All haveremote sensing and adjustment.Operation is permitted to 100°C,heat -sink mounting increasing thelimit. Isolation input:case andoutput:case is 1500V dc.Artesyn Technologies. Tel., 003532425272; fax, 00353 2493510; e-mail, [email protected] no 535

Multiple -supply controller.Cherry's CS -51313 synchronousbuck controller allows the generationof a number of different supplyvoltages to power computermotherboard core logic with just theone switching regulator. A 1%internal bandgap reference is takento an output pin, where it may beused with external components andpower transistors to supply variousvoltages to a Pentium II processorand its support logic. There is also apair of signals to drive n -channelmosfets supplying the processorcore. Transient response is 200ns.There is a range of protectivemeasures.Cherry Semiconductor. Tel., 001 401885-3600; fax, 001 401 885-5786;web, www.cherry-semi.corn.Enq no 536

Radio systemsDownconverter/mixer ic. TQ5M31by TriQuint is a general-purposemixer and down -converter ic for usein cellular and PCS mobile 'phones,

tal=g1 ar-ns II.10,== arm. otliiraz. i64.6

U444alit a

1.4, LA,

11.1111111.11.1.111.111111111

ga alika I

80 -channel logic analyser. Thurlby Thandar's TA4000 logic analyserseries is capable of asynchronous data capture at 400MHz with amemory depth of 8Kword. There are three versions with 32, 48 or 80channels. An eight -level random branching trigger sequencer providestrace control, each trigger term consisting of up to four words, Or-ed orNot-ed, the latter triggering on the absence of a word. All this goes at50MHz without restriction or at 100MHz if a 2Ons delay between stepscan be tolerated. The instrument works as a timing analyser with aresolution of 2.5ns and the screen displays any 16 channels and amarker. Up to 512Kbyte of data card storage is available and there areRS232 and GPIB interfaces, with a Centronics for printing.Thurlby Thandar Instruments Ltd. Tel., 01480 412451; fax, 01480450409; e-mail, [email protected] no 540

ISM bands, GPS and pagers. Rfinput range is 500-2500MHz and ifoutput 45-500MHz. Very few externalcomponents are needed, althoughthe lo buffer amplifier frequencyresponse and if gain response areexternally trimmable. Conversiongain is 2-3.5dB within ±0.3dB over awide temperature range. Input third -order intercept is 9dB minimum at a

noise figure of 9.5dB. I/o is 500.TriQuint Semiconductor. Tel., 001503 615-9000; fax, 001 503 615-8900; web, www.triquint.com.Enq no 537

Test and measurementVirtual instruments. NationalInstruments has a new family ofcomputer -based instruments, which

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PRODUCTS CLASSIFIED

includes digital oscilloscopes,digital multimeters, arbitrarywaveform generators, Fast Fourieranalysers and serial dataanalysers. Advantages of virtualinstruments in, for example, anoscilloscope, include faster set-up,fast sampling, deep memorybuffering, multiple acquisitionrecords, advanced triggering andsmall size.National Instruments UK. Tel.,01635 572400; fax, 01635 524395;web, www.natinst.com/uk.Enq no 540

COMPUTER AND

DATA HANDLING

Computers233MHz Pentium sbc. ICP'sNOVA -600 is a 233MHz single -boardcomputer that complies with theAmpro/Motorola EBX specification,which is a non-backplane form forembedded boards. The processorsupports MMX and PC/104-Plus(PCI-enhanced PC/104). It offers up


to 128Mb of dram, 72Mb solid-stateflash, four serial ports, an EPP/ECPparallel port, an Ultra DMA/33enhanced PCI IDE interface,10/100Mb/s Ethernet controller,floppy disk interface and muse andkeyboard interfaces. There is also anIcd/crt display controller to handle a36 -bit lcd and 2Mbyte of videomemory.Wordsworth Technology. Tel., 01732861000; fax, 01732 863747; e-mail,sales @wordsworth.co.uk; web,www.wordsworth.co.ukEnq no 541

Data communicationsModem/audio card. Smart hasannounced its internal Data/FaxModern and Audio PCI Combo card,which is said to be the first for oemsand which meets V.90 and K56flexstandards for 56K transmissionspeed. It is Soundblaster Pro -compatible. The card runs underWindows 98/95/NT and has powermanagement for wake -up -on -ringand caller identification.Smart Modular Technologies. Tel.,01908 234030; fax, 01908 234191;e-mail, [email protected] no 541

Development andevaluationMBX 860/821 development. Twodevelopment platforms for use withMBX compact PowerPC 821/860embedded computer boards areavailable from Crellon. One of them,CMS-MBX-SDC, is for softwaredevelopment and the other, theCMS-MBX-HDC, is for hardware. TheSDC unit is based on a 5.25inhalf -height disk -drive chassis, its panelhaving leds to show power in Ethernetactivity, while the rear has connectorsfor one serial port and a 10BaseTEthernet port, further expansion beingpossible from the front panel.Hardware development is the provinceof the HDC, which has a 150W supplyand space for a 3.5in drive and two5.25in peripherals. The MBX is on topof the chassis to provide access to thelinks and connectors and allow abackplane to be fitted.Crellon Microsystems. Tel., 01734776161; fax, 01734 776095.Enq no 542

InterfacesData security. Compblock by Aditalis designed to prevent unauthorised

access to computer data and, indeed,the computer itself. The unit connectsbetween keyboard, screen and pcwith many security screws, disarmingthe keyboard, mouse and screenwhen armed. An electronic key usinga secure code allows access, up toeight keys for each Compblock beingallowed. The keys may not bescanned to obtain the code and theyneed no batteries, although they canbe cancelled and new ones issued.The unit automatically arms atswitch -on and again when the userleaves the pc, so that no passwordsor rebooting are needed.Adital Ltd. Tel., 01803 844455; fax,01803 846032.Enq no 543

Mass storageUSB floppy drive. TEAC has astand-alone 3.5in floppy disk drivethat connects directly to the USB portof notebook or palmtop computers,avoiding the situation where smallcomputers are sometimes without adrive or where the drive must beremoved to allow the insertion of acd-rom. Capacities supported are720KB, 1.25MB and 1.44MB,transferring data at 250kb/s and

Music EngineeringThe Electronics of Playing and Recording

Highly illustrated guideto the technology ofmusic and recording.

Written in anapproachable style usingexamples of well-knownsongs, this book is amust -have guide forsound recordingengineers and electronicengineers.

If you are an electronicsengineer who needs specificinformation about musicreproduction, or if you are asound recording engineer whoneeds to get to grips with theelectronic technology, MusicEngineering is for you.

This handy volume is atechnical guide to electric andelectronic music, including theessential science, butconcentrating on practicalequipment, techniques andcircuitry. It covers not only basicrecording techniques and audioeffects, kit such asmicrophones, amps andinstruments, but also valve

by Richard Brice

technology, stereo and digitalaudio, sequencers and MIDI,and even a glance at videosynchronisation and a review ofelectronic music.

Music Engineering lifts the lidon the techniques andexpertise employed in modernmusic over the last fewdecades. Packed withillustrations, the book alsorefers to well known classicrecordings to describe how aparticular effect is obtainedthanks to the ingenuity of theengineer as well as themusician.

Richard Brice has worked asa senior design engineer inmany of Britain's top broadcastcompanies and has his ownmusic production company. Heis the only writer who canprovide this unique blend ofelectronics and music.Contents: Soul Man - Scienceand sensibility; Good Vibrations- The nature of sound; StandBy Me - Microphones and theirapplications; Message in aBottle - Valve technology; Rollover Beethoven - Electric

BOOKPlus FREE CD

Instruments; Wild Thing -Electronic effects; Pet Sounds- Electronic synthesis; SilverMachine - Sequencers & MIDI;Got to Get You into My Life -Sound recording; Bits 'n'Pieces Digital Audio; SpaceOdyssey - Stereo and spatialsound; Let's Stick Together -Recording consoles; UnchainedMelody - Amplifiers; Shout -Loudspeakers; Synchronicity -Video and synchronisation;Dark Side of the Moon -Electronics and the music ofthe 20th century.

Richard Brice

EngineerlingThe Electronics of Playing

and Recording

Inclusive price: £22.50 UK, £25 Europe, £28 ROW.

To order by post, send a cheque or postal order to Jackie Lowe atElectronics World, Quadrant House, The Quadrant, Sutton, SurreySM2 5AS. Please make your cheque payable to Reed BusinessInformation. Alternatively, fax full credit card details to 0181 6528111, e-mail [email protected]: 0 7506 39032Paperback, 256pp, 150 line illustrations.

Copies of Richard's previous book, Multimedia and VirtualReality Engineering, are still available, inclusive hardbackprice: £27.50 UK, 29.50 Europe, £32 ROW.



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500kb/s. The drive complies withUSB specification Rev.1.0 and maybe used with Win 95, 98 and NT 5.0up. Power is 500mA from 5V.TEAC UK Ltd. Tel., 01923 225235;fax, 01923 236290.Enq no 544

SoftwareTriCore development. TASKINGoffers the first programmingpackage for the Siemens TriCoreprocessor and its derivatives. Itconsists of the Nucleus PLUS real-time kernel, Ansi C and C++compilers, a macro assembler,linker/locator and Crossview Prodebugger. All elements togetherform the Embedded DevelopmentEnvironment, which provides aWindows -based facility for thegeneration of TriCore applicationssoftware. Features includeadditional data types for fractionalnumbers and the automaticgeneration of multiply/divideoperations; the C++ package alsohas a set of dsp classes for fixed-point data types.Tasking Software BV. Tel., 0031 334558584; fax, 0031 33 4550033.Enq no 545

PUBLICATIONS

CataloguesSwitches. Catalogue No 4 from Mecis available, in which are describedprocess-compatible/sealed switchesand surface -mounted types, togetherwith full specifications.Quiller Switches Ltd. Tel., 01202436777; fax, 01202 421255.Enq no 547

Application notesFlexible circuits. Designers' Guide toFlexible Circuit Technology ispublished on a cd-rom by Flextronicand provides technical data on almostevery aspect of flexible circuit design(the word being used here in thesense of 'bendy). There are sectionson materials, applications, markets,sculptured circuits, interference, andeconomical design. A hypertext formof presentation is used to give aneasy path through the information.Flextronic Ltd. Tel., 01243 784515;fax, 01243 774376; e-mail, [email protected] no 548

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Dictionary ofCommunications Technology

dictionary of

communicationtechnology

you didn't know you needed to know

CortiWatch An off -site network monitoring servicemarketedby Ilmeplex,Inc., of Woodcliff -Lake, NJ.

concatenation I. The Baking of transmissionchannels or subnetworks end mend. 2. The linkingof blocks of user data or protocol transmissions.3. In fiber optic technology, the interconnection oftwo or more fibers into one continuous length.

concentation Collection of dem at an intermediatepointrfrom several low- and medium -speed linesfor transmission moss one high-speed line.

concentrator A device used m divide a data channelinto two or more channels of average lower speed,dynamically allocating space according to the

demand in order to mmimice data throughput atcoos

or sod

concurs111101E

condenopence

Conditicva

indite

requeMoot

conditioned circuit A cncuil that has been

electrically altered to obtain the desired charac-rtristics far voice and data transmission. The readeris refmed to the enrnes GI through C-8 and D-I and D-2 for specific information on C -level andThlevel conditioning.

conditioned loop A loop that has conditioningequipment, usually emalirers, attached to obtaina desired line characteristic, to facilitate voice ordata trammioion.

conditioning The "canine or addition of equip-ment to improve Me transmission characteristicsor quality of a leased voice -grade line so that itmeets specifications for data mnsmission. (Seafigure below.)

nottnmodem, multiport A device that combines a

multiplexer and a modem allowing two or moreDTF-s to be connected to the same War Also splitstream modem.

modem, quick turnaround A modem with minimalturnaround time when the line is used in a half -duplex mode. Also Quick Poll (QP), Past Poll (FP).

modem, short haul Dearription of both line driversand limited distance modems.

modem, wideband A modern designed to operateat speeds greater than those used with high-speedmodem, such as 102 or 56 Kbps. Widebandmodems will not operate over voice -grade circuitshart require a Mdeband circuit.

Modems] Communications software program sup-porting the public -domain, X -modem, env,correcting Me transfer protocol. This version of the%modem has multifile transfer capability.

modem connect The name used in DNA for thatclass of communications Mks govemrn by industrystandards for modem connection.

modem eliminator A device used to connectlocal terminal and a computer pm in hell ofhe pair of modems that they would expect toconnect to: allows DIE-to-DTE data and controlsignal connections otherwise not easily achievedby standard cables or connectors. Modified cables(crossover cables) oreonnectors(adapterOcan alsoperform this function.

modem operation characteristics See page 270.

modem pooling A feature of a PABX and othercom-monications products that permits subscribers to bemtomatitally or manually connected. a group ofshared or "pooled" modems.

modem dialing unit A device that splits a signalamong a cluster of terminals and allows them toMarc one modern

modem substitution swikh An external option thatallows you to reroute your data through a hot"spare (a modem that is already powered up) in theevent the original modem fails.

moderator A participant who is in charge of aconference. A moderatoris responsible for keepingthe discussion on track, for alleviating fights, andfor similar functions.

MODES Discrete optical waves that can propagatein optical waveguides. Whereas, in a single -mulefiber. only one mode, the fundamental mode, canpropagate. There are several hundred modes in amultimode fiber which differ in field pamm andpropagation velocity (multimode dispersion). Theupper limit to the number of modes is determinedby the core diameter and numerical aperture of Mewaveguare.

Modified Chemical Vapor Deposition An AT&TBell Laboratoriespateoed process that uses hightemperaMres to speed the manufacture of largequantities of fiber lightguide. The glass is madeby allowing hs vapors to form a coating inside atube of heated silica, which is later drawn Om fiber.

Temperatures teach 4000 degrees F. (The meltingpoint of steel is 2800 degrees F.)

Modified Final Judgment (MEI) The IMThedemlCourt ruling that determined Me rules governingthe divestiture of the Bell Operating Companiesfrom AT&T and other antitrust and deregulationissues. Presided over by Judge Harold Genii, aswas the AT&T Mailing settlement which the MFImodified. Judge Greene continues his involvemeniin enforcing and interpreting the provisions of thissettlement.

modular distribution accessories A term used toreference splitters, modular adapters and modular

With over 9000 entries and 250 illustrations, this book isan invaluable reference work for anyone involved withelectronics and communications. Dictionary ofCommunications Technology provides comprehensivecoverage of data and communications and has entries onPC lans, the Internet, communications testing and client-

server applications - in 500 pages.Over 20 major companies helped prepare the Dictionary

of Communications Technology, including AT&T, IBM andDigital Equipment Corporation.Gilbert Held, author of Dictionary of Communications

Technology, is an internationally author who has used hisenormous expertise to make this work one of the mostcomprehensive sources of telecommunications information.

UK Price: £38.95 Europe £42.95 ROW £46.95

** Price includes delivery and package * *

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111WAV41.:41::,PilCORNER

Fig. 1. Chassislocates surround,

spider andmagnet. It also

protects againstoperational loads

and transitshocks.

This month, John Watkinson looks into the basket - thechassis part of an electromagnetic loudspeaker thatholds everything together - and explains how it canaffect reproduction quality.

Aloudspeaker's chassis or bas-ket is a part which is oftentaken for granted, but it can

have an effect on performance. At abasic level, the chassis providesmounting points, so that the drive unitcan be fixed in an enclosure, and itsupports the cone and the magnetassembly. A little thought shows thatthe chassis material and constructioncan affect the magnetic and thermalproperties of the speaker, as well asbeing a potential source of colouration.

Take the example of a woofer, Fig.1. This shows that the cone is support-ed in two planes. The first is the planeof the surround which serves as a flex-ible pressure seal between the movingcone and the stationary chassis. Thesecond is the plane of the 'spider' orcentring device which supports theneck of the cone.

The cone is located within the spiderplane so that it can only move axially,and a (sometimes) linear restoringforce is provided against cone travel tokeep the cone in the centre of its rangeof travel.

Figure 1 also shows that the magnetassembly is supported by the chassis.Magnets and steel pole pieces areinevitably heavy, and the chassis has tobe rigid enough to ensure that the rela-

Spider

Surround

Magnetassembly

tionship between the spider and thepole pieces is held constant. If this isnot achieved, the coil may rub on thepole pieces.

In many applications it has to beaccepted that the loudspeaker will bedropped or handled roughly. The chas-sis has to withstand very high transientforces from the magnet under theseconditions.

Benefits of rare earthIn addition to the audible advantagesof rare-earth magnets already advancedin this column, we now have a non -audible advantage. This is that thelighter rare earth magnet will place lessstress on the chassis during rough han-dling, giving a distinct reliabilityadvantage in applications such as PA,as well as making the unit easier tomove.

When the cone is driven forwards,the magnet assembly experiences theNewtonian reaction backwards. It isoften heard that the chassis of a loud-speaker has to be incredibly rigid towithstand the reaction of the magnet.This is a myth. If the relative masses ofthe cone and the magnet assembly areconsidered, it is clear that with a ratioof about 1000:1 the magnet isn't goinganywhere.

Figure 2a) shows what really hap-pens when the cone is driven forwards.The pressure in the enclosure goesdown, and atmospheric pressure flexesthe front of the enclosure inwards,actually moving the entire drive unit.

Some designers install the tweeter ina separate enclosure which is mountedon springs so that its position is notmodulated by any enclosure flexingcaused by the woofer. This is a near -plausible argument which justifies ahigh price tag on 'high -end' hi-fiequipment. But if such an approach

results in an audible improvement, thismust be an admission that the wooferenclosure isn't rigid.

Brace itThe solution is properly to engineerthe enclosure for rigidity, a techniquewhich is actively avoided in tradi-tional wooden box speakers. A usefulimprovement can be obtained bybracing the rear of the woofer magnetagainst the opposite wall of the enclo-sure with a suitable strut.

Figure 2b) shows that the atmo-spheric pressure forces cancel at themagnet which stays put.Unfortunately it is difficult to behyperbolic about an invisible block ofwood, and so in certain markets it hasno advantage at all.

Chassis can be made from a widevariety of materials, but the choice isfar from obvious and depends uponthe production volume and powerhandling requirement. Candidatesinclude cast alloys, pressed steel andinjection moulding.

With ferrite magnets, a steel chassiscan increase flux leakage, requiring alarger magnet for the same perfor-mance. Alnico and rare-earth designsdo not have this problem. Aluminiumor plastic chassis avoid flux leakagein ferrite magnets.

The high strength and ductility ofsteel means that chassis can be madein quantity by pressing from a rela-tively thin sheet with a very low mate-rial cost. For rigidity, thin sheet cannotbe left flat over any significant areaand so the pressing will need to becomplex to ensure that every edge isflanged. The press tool also has topunch out holes to allow the pressurefrom the back of the cone to escape.This results in a loss of strength, andmany pressed steel chassis tend to err

153

AUDIO DESIGN

on the side of plenty of metal ratherthan freedom of air movement.

Thermal considerationsFor high -power speakers, thermal con-siderations are usually uppermost. Thecoil dissipates a lot of heat, most ofwhich has to be removed through themagnet.

Mounting the magnet on a substan-tial cast aluminium chassis is a goodway of losing that heat with minimumtemperature rise. Casting allows thecomplex ribbed structures needed forrigidity to be replicated with ease. Forvolume production, die-casting is anatural technique. The die tools maycost thousands of pounds, but the unitcost is very low.

Cast chassis will also be found onlow volume, prototype and special-pur-pose drive units. These may be sandcast because the tooling costs are quitelow, requiring only very basic woodenpatterns which are well within thescope of the home builder. Sand cast-ing is, however, labour intensive andbecomes uneconomic as quantity rises.

Casting may advantageously be

4 Tweeter moves in

1 Cone moves out

2 Internalpressure

goes down

3 Enclosure flexes inwards

Fig. 2. An easy way of preventing 'woofer reaction' is to brace the back of the speakeragainst the back of the cabinet, as in b).

taken further than just the chassis. Inproduction engineered active speakerdesigns, one casting may form theentire front of the speaker, having inte-gral woofer and tweeter chassis,mountings for the power transformerand also acting as the heat sink for theamplifier.

Advances in composite materials

have meant that chassis can practicablybe moulded. It is easy to mould in anyrequired details, and as plastic is non-conducting, the connecting tags can bemounted directly in the plastic, ratherthan on a separate tag strip. Plasticstend to be poor thermal conductorsthough, so their use is limited to driveunits of moderate power.

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HP 8620C/8624IA 3.2-6 5 GHz sweeper 1900 ANRITSU MS65A 2 GHz error detector L500 £500HP 86200862305 I.8 GHz-4.2 GHz sweeper 1900 ANRITSU MSO9C I voiceband monitor (boxed new with manuals) . L400HP 8620C/86220A 101300 MHz sweeper L600HP 8620C sweeper mainframes (as new) L250HP 80055 03 Hz -20 MHz pulse generator L250 BALL EFRATROM MR -PH mbidnim frequency standard 13,500HP 33365 10 Hz -2I MHz syntheosernevel meter L300 BIRD 8329 300W 30d13 attenuatorHP 3320A frequency synthesiser 0.1 Hz -11 MHz 1300 BIRD 8323 100W 3045 wenuator £200 HP 435B/848IA/8484A/11708A 10 MHz -I8 GHz (new/HP case/manteds) LI,0 0HP 3314A 0 001 Hz -19.99 MHz function/waveform monitor £1,250 HP 435A/8482AH 100 KHw4 2 GHz OF power meter 1500HP 3312A 0 1 Hz -11 MHz function generator 1400

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February 1999 ELECTRONICS WORLD 15.5

COMMUNICATIONS

My last article looked at thecharacteristics of the eye andintroduced the concepts of the

optic -flow axis and dynamic resolution.When examined using these concepts,the shortcomings of interlaced videoscanning were revealed.

This article continues the theme byexamining the performance of film andthen looks at how progress can be madeacross all image portrayal systems

Making filmsGood dynamic resolution is essential forrealism, and will only be achieved ifthe motion portrayal is accurate.Accurate motion portrayal requiresthat the optic -flow axis is reproducedwithout distortion.

Figure 1 a) shows how movie film isshot. Originally a frame rate of only18 frames per second was used, foreconomy reasons. The optic flow axis

is correctly preserved on the film formoderate motion. However, 18 framesper second is below the critical flickerfrequency of human vision and isunwatchable.

The traditional palliative was to pre-sent each frame three times. The pro-jector had a three -bladed shutter whichproduced three flashes of light foreach frame pull -down.

Development of the 'talking picture'

John WatkinsonBSc MSc FAES MBCS

Image portrayalTechnologies forimage portrayalin computergraphics, filmand televisionwere once verydifferent, butdigital electronicsis causing themto converge.Some features ofthe oldtechnologies willremain useful.Others - amongthem interlacing- will be ahindrance, asJo n Wat insonexplains in thissecond article.


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meant that an optical soundtrack wasadded to the film. The resolution ofthe sound -head optics was such thatthe film speed at 18 frames a secondwas too low and so the speed wasraised to 24 frames a second toimprove the audio bandwidth. Now atwo -bladed shutter could be used toproduce a flicker frequency of 48Hz.

Figure 1b) shows that this corruptsthe optic flow axis because there can-not be motion between the repeatedframes. The eye tries to track themotion the best it can, but the opticflow axis of the film now oscillateswith respect to the retina as shown inFig. 1c).

Unlike interlace - which is worst onvertical movement - this effect isequally powerful in all directions. To atracking eye, the two identical versionsof a frame appear in different places onthe retina. For slow movements, thisresults in an aperture effect whichdamages dynamic resolution. For rapidmovements, the result is visible as jud-der or multiple images.

Assuming the film has a thousandlines of static resolution, dynamic res-olution will be halved by apertureeffect when a speed of one pictureheight in 40 seconds is reached. This istoo slow to be useable, so the bestdynamic resolution achieved by filmhardly ever reaches half the static res-olution that the film is capable of.

The best that cinematographers cando is to mount cameras on very solidand smooth supports and move themslowly to avoid judder. Rapidly mov-ing objects of interest must be panned.Quality films are shot like this becausethe film makers know the restrictions.

Background strobingIn my last article, the concept of back-ground strobing was described. Whena tracking eye follows a moving objectof interest, the background is presentedin a different place on each frame. Intelevision the background is at 50 or 60different places per second, whereas infilm there can only be 24 backgroundlocations per second. In other wordsthe background strobing is twice asbad.

As a result, good cinematographersuse shallow depth of focus in order toblur the background and disguise theeffect of background strobing.

The damaging effect of picturerepeat in film means that although filmmanufacturers have dramaticallyimproved the static resolution of filmin recent years, the improvement can-not be seen by the movie-goer in thepresence of even very slow motion. AsI have shown, there is more to movingpicture quality than static resolution.

The picture repeating of film projec-

tion is carried over into telecinemachines which convert film into tele-vision signals. To produce 50Hz videoin Europe, the 24Hz film is run at25Hz and two fields are made fromeach frame.

Figure 2a) shows the traditional 'fly-ing -spot' telecine which uses a crt as a

Film frame 1

light source and a photocell behind thefilm to produce the video signal. Thefilm moves at constant speed, drivenby a capstan.

To produce a progressive scan pic-ture the crt would only need to scanfrom side to side in a line. However, toproduce an interlaced scan, the crt

Film frame 2 Film frame 3

With frame repeat in cinema

Relative to tracking eye causes apertureefect and motion judder

Photocell

'Flying spot' telecine -imaging on source side

3

Fig. 1. Frame repeatdamages optic flowaxis.

Fig. 2. Telecine basics. The'flying -spot' telecine, a),uses a crt to develop a two -dimensionally scanned spotwhich is focussed onto thefilm. The vertical scan ofthe crt allows interlacedfields to be created in realtime from steadily -movingfilm. In the more modernline -scan telecine, b),vertical scanning is basedsolely on film motion. Thefilm is focussed onto theline sensor. Interlace isachieved by readingalternate lines from aframe store.

Linescan telecine -imaging on sensor side

2 3

Relative to tracking eye - worse judder and aperture effect

Linearsensorarray

Fig. 3. To obtain 60Hzvideo from 24Hz film,a process called 3:2pull -down is used.Resultant demolitionof the optic flow axiscauses judder.


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requires vertical deflection as well sothat it can scan each film frame twicein succession even though it hasmoved to a different location in eachscan.

Figure 2b) shows the more modernline -scan telecine. The light source illu-minates the whole gate and a ccd linesensor is used. The steady motion ofthe film performs a vertical progressivescan, but the signal is stored in aframe -store. To obtain an interlacedoutput alternate lines of the frame -storeare read out to produce two fields.

Producing 60Hz videoThe production of 60Hz video from24Hz film in USA requires 3:2 pull -down, where one frame is made intothree fields and the next is made intotwo fields. Pull -down with a 3:2 ratiohas a devastating effect on the optic -flow axis, as shown in Fig. 3. Withrespect to a tracking eye, images areportrayed in three places, leading toserious judder.

Figure 3 shows that the action of theinterlaced telecine is to display aframe, sampled at one point in time, asfields at two (or three) separate times.In the presence of motion, the optic -flow axis turns and these fields nolonger superimpose.

The shift of the fields with respect toone another causes an aperture effectwhich reduces the visibility of interlacealiasing. Consequently a motion arti-fact of film has the result of concealingan interlace artifact in video.

Bearing this in mind, using 24/25Hzfilm material to test or demonstratehdtv systems must be a very suspectpractice indeed, and the results aremeaningless. The dynamic resolutionof the television system under testcould be - and often is - quite poor yetthe artifacts due to film judder couldwell conceal the fact.

The damage done to the optic -flowaxis by 3:2 pull -down is bad enough.

MPEGbitstream

Fig. 4. MPEGachieves much of

its compression bysending vectors to

shift a previouspicture so that it

more closelyresembles the

current picture. Aprediction error issent to cancel the

remaining smalldifferences.

Predictionerror

Previouspicture

But there is an even worse option, andthat is to convert 3:2 pull -down 60Hztelecine video to 50Hz video in a stan-dards convertor. This is known in theindustry as the 'Dallas' effect after thetelevision soap opera which first triedit out - briefly.

Film and MPEGMPEG is a set of standards for videocompression, i.e. bit -rate reduction,which will be used for services such asdigital television broadcasting and dig-ital -video disc, or dvd.

Figure 4 reveals that MPEGachieves much of its compression bysending only the differences betweenpictures. In the case of motion, anMPEG coder can send motion vectorstelling the decoder how to shift a pre-vious picture to make it more similar tothe current picture.

In an MPEG environment, the dam-aged optic -flow axis from telecinecauses compressors a lot of trouble.The field repeating means that motionvectors are zero between repeat fieldsbut of doubled amplitude elsewhere.This alternating vector data means thatthe data available for picture differ-ences fluctuates, causing quality loss.

The current approach to MPEG com-pression of telecine video is to use apreprocessor which de -interlaces thefields back to progressively scannedframes. In 3:2 pull -down systems, thethird field is entirely redundant and isdiscarded. The adoption of progressivescan at the same frame rate as the filmmaterial allows MPEG to work at itsmost efficient as the vector data ismore stable from frame to frame.

Set -top boxes receiving MPEG filmframes at 24/2Hz have no trouble accu-rately decoding the frames, but displaythem by reading the output frame -storeat 50Hz using interlace and at 60Hzusing interlace and 3:2 pull -down. Thisinterlacing process recreates the dam-age to the optic -flow axis which took

Horizontaland vertical

Predictedpicture

vectors

Outputpicture

place in the original telecine material.Telecine machines are actually stan-

dards converters because the input andoutput picture rate is different. It isobvious that the only way to overcomethe poor motion portrayal of thetelecine machine is to use motion com-pensation in the conversion process. Inthis way, the optic flow axis is not dis-torted. A telecine which does not dothis cannot be regarded as having highdefinition.

The advantage of the motion com-pensated telecine is that the outputvideo has the same motion character-istics as video from cameras. As aresult, it doesn't need handling differ-ently by MPEG. Motion -compensatedtelecine machines are currently almostunknown, but will come to prominencein due course.

There is an enormous archive of35mm 24Hz film material which willbe heavily used to attract customers tonew television services. The advan-tages of a high quality television sys-tem will be lost if primitive fieldrepeating telecines are used.

High -definition filmTraditionally, film and television werein competition and incompatibility wasoften quite deliberate. With the con-vergence of technologies though, thesetraditional incompatibilities havebecome an obstacle to progress and anholistic solution is required.

The clear solution is to use moderntechnology to remove the compro-mised motion portrayal of both filmand television and to make them trulyinterchangeable and compatible withcomputer imaging.

Anamorphic optics are frequentlyused with film cameras to get wide-screen pictures. Effectively, the mag-nification of the camera lens is differ-ent horizontally and vertically so that awide picture is squeezed into a regular -shaped frame. This is a lossy non -per-ceptive technique which is inefficient.

Resolution of the film - and that ofthe eye - is axisymmetrical. The resulton the screen with anamorphic film isthat the vertical resolution is in excessof the horizontal resolution. The eyejudges quality on the worst axis so thatvertical resolution - and film andmoney - is wasted.

Anamorphic opticsPractical anamorphic optics are notideal and cause further loss of quality.Non-axisymmetrical systems are inef-ficient and sub -optimal as the input toan MPEG compression system.

There is a worse case than that. Passanamorphic film with impaired hori-zontal resolution into an interlacedtelecine machine which has impaired


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vertical resolution. Pay for 35mm film- and get the resolution of 16mm film.

Consequently if film is being used asthe source for an advanced imagingsystem, it should use axisymmetricallenses (note the similarity with the useof square pixels giving the same verti-cal and horizontal resolution in graph-ics). In film this means that the greatestefficiency or the lowest film cost isachieved when the aspect ratio of thefilm frame is the same as that of thescreen, just as in video the number ofhorizontal pixels should be given bythe number of vertical pixels multipliedby the aspect ratio.

The 24/25 frames per second rate ofconventional film corrupts motion por-trayal and is incompatible with televi-sion and computer displays. The use ofanamorphic optics is inefficient. Bothproblems can be solved instantly byadopting 2-perf 35mm film frames run-ning at 50 or 60 frames per second fortelevision filming. This doesn't changethe film speed, so running costs areunchanged.

Judder and aperture effect are elimi-nated by correct motion portrayal sothat the dynamic resolution will beextremely good. A further advantageof 2-perf is that by halving the heightof the frame it is automatically given awider aspect ratio. Now sphericaloptics can be used. Theseand cause less resolution loss.

Technicolour introduced 2-perf yearsago as Techniscope, but running atconventional frame rates for economy.All that is proposed here is to run it ata more appropriate speed. There is notechnical problem whatsoever in using50 or 60Hz as a film frame rate, espe-cially as the pull -down distance ishalved.

Existing telecine machines can easi-ly be adapted to use 2-perf. Existingoptics and transports are suitable.Telecine machines are naturally pro-gressive scanning devices and have togo to great lengths to obtain interlace.Disabling the interlacing processesyields a simpler machine.

OversamplingPeople seem to think that high -definitiontelevision needs lots of lines. But that's amyth. Cameras and displays need lots oflines to overcome aperture effects and torender the raster invisible, but the trans-mission medium between does not.

In the early days of television the cap-ture, transmission and display formatshad to be identical for simplicity, butthat is no longer true or desirable.

A 525 line camera cannot give 525lines of resolution, but a 1050 line cam-era with down -conversion can.Effectively the camera is using over -sampling.

a)

c)

d)

Spatial frequency

No aliasing

Output sampling rate

Although oversampling has totallydominated digital audio because of itsobvious merits, it is harder to use it inconventional television because ofinterlace. Interlace puts half the picturedata at another time and reduces theperformance of spatial resamplers.Once interlace is dispensed with, over -sampling becomes an obvious and

technology.Oversampling overcomes practical

limitations in optical filters. In a ccdcamera, the sensor elements samplethe image spatially. The sensors arelarge for maximum light sensitivityand so a serious aperture effect isexperienced.

Ideally, an optical anti-aliasing filteris needed between the lens and thesensor. Unfortunately it is difficult tomake a filter which has a sharp cut-offand it is usually necessary to compro-mise between visible aliasing and pic-ture softness.

Using oversampling makes this com-promise unnecessary. Figure 5 showsthat in an oversampling camera, thespatial sampling rate must be increasedby using a larger number of pixels inboth dimensions - i.e. use a high -defi-nition camera. The optical anti-aliasingfilter then only needs to prevent alias-ing at the higher sampling rate.

Output of the ccd element is spatial-ly low-pass filtered and decimated toproduce a television signal with the tar-get pixel count. It will contain no spa-tial aliasing, but will not suffer loss atthe band edge.

As a crt is a sampled device, break-ing the picture up into lines, it shouldideally be followed by an optical filter.As before, this is not done because inorder to eliminate the raster it wouldintrude into the passband.

tSpatial sampling rate

4

Removing the rasterOversampling can also be used to ren-der the raster invisible. Once more aform of standards convertor isrequired, but this now increases thenumber of input lines using interpola-tion. The aperture effect of the displayfilters out the raster, leaving the pass -band unaffected.

Oversampling can also be used in thetime domain in order to reduce or elim-inate display flicker and backgroundstrobing. A different type of standardsconvertor is necessary, which increas-es the input picture rate by interpola-tion. Such an oversampling convertormust use motion compensation. If itdoesn't, moving objects will not becorrectly positioned in an interpolatedpicture and the result will be judder.

The adoption of progressive scanallows spatial oversampling to be eas-ily implemented in both camera anddisplay. The number of lines needed inthe channel between is then quite mod-erate.

Progressively -scanned sensors anddisplays having 700 to 1000 lines con-nected by a 480P channel are all that isrequired to deliver a truly high defini-tion television service. The up -con-verter in the display is optional andlower cost receivers could omit it.Equally, large expensive receiverscould incorporate motion vectorsteered frame rate up -conversion toreduce background strobing.

John Watkinson is an independentinternational consultant on audio andvideo technology. He is a Fellow of theAES and a Chartered InformationSystems Practitioner. John is currentlywriting a book on helicopters. His webaddress is www.culinaire.se/JWA.

Fig. 5. Spatialoversampling.Modulationtransferfunction, ormtf, of cameraplus sensor hasgradual roll -off, a). In b),sampling athigh spatialfrequencyavoids aliasing.In the digitaldomain, c), alow-pass filterrestricts thespectrum. Inb), the outputsampling ratehas droppedand the outputhas no aliasingor apertureeffect.

Februaryl 999 ELECTRONICS WORLD 159

HISTORY

Digital visionsIs digital television new? Maybe not, but Baird's televisionsystem was certainly a pig in a poke: wasn't it?Don McLean has some new evidence.

The much -hailed start of digitaltelevision may not be quite thegiant leap you think. Digital tele-

vision broadcasting - converting pro-gramme distribution to a fully digitalenvironment - is just one small step ina steady 'technology refresh'.

This engineering process started overtwenty years ago and will continue formany years yet. Fully digital television,and digital scanning standards, willemerge when the flat -screen tv replacesthe cathode-ray tube in our televisionsets. Then, analogue tv and all its trap-pings, such as PAL (or NTSC) coding,sync pulses, colour bursts and interlace,will be history.

That digital future, with our currentanalogue tv obsolete, will give us anew view of television's engineeringhistory. The early years of mechani-

Donald F McLean BSc(Hons) CEng FIEE

cally-scanned television - viewed fordecades with disdain - will then, Ibelieve, sit alongside electronic ana-logue tv as an equally valid engineer-ing solution to 'television'.

Mechanically -scorned tvToday though, most of us have accept-ed a view originating from the BBCback in the late thirties. We think ofJohn Logie Baird's low -definition tele-vision system of the twenties and earlythirties as somehow 'wrong', and ofelectronic television as being 'right'.

Part of this comes from 'technologyarrogance'. In the sixties, the BBC'seriously questioned Baird's achieve-ments because no part of his technolo-gy was in sixties' television systems.But, today, nothing directly of sixties'technology is in a nineties' consumerdigital video camcorder - with its chipsensor, image stabilisation, digital auto -

focus, lcd, digital data recorder andcomputer interface.

We should neither revere nor ridiculehistoric technologies - they are merelythe best solutions available at the time,Fig. 1.

A new view on the pastTo be objective about early television,what we need - and have not had upuntil now - is evidence. Without it, his-torians have had to rely on written oreyewitness accounts, some of themmade decades after the event and mostof them dismissive and derogatory.

In 19962 and early 1998, hard evi-dence turned up in the form of homevideo recordings made from BBC tvprogramme transmissions in the thir-ties. Until then, the entire mechanical-ly -scanned era of television wasthought to be devoid of any suchrecording. These digitally restored


HISTORY

Fig. 2. One of the many consumer devices that recorded audio onto aluminiumdiscs. On more than one occasion, machines such as this were used by viewers torecord the video signal of the BBC's 30 -line broadcasts.

recordings now challenge the long-established view.

To understand why this is so, let usfast rewind to just after Baird's exper-imental period of the years around1930.

BBC chooses Baird's 30 -line system.In 1932 the BBC chose Baird's 30 -linestandard for its television service,despite higher definition being avail-able. It was chiefly the lack of suitablewide -band transmitter hardware thatforced the BBC into using an existingsolution.

The 30 -line video signal was lowenough in bandwidth to be transmittedon an existing BBC medium wave fre-quency normally used for audio. Thepublic simply used their existing radiofor the audio channel and a secondradio receiver for the video channel.Only the display had to be bought - orin some cases built.

Baird's mature 30 -line system -developed in the late twenties - pro-vided the BBC with an exceptionallylow-cost engineering solution that

exploited their existing broadcastinfrastructure to the full.

No recordings? If the BBC or theBaird Company ever attempted record-ing their programmes, there is today norecord of it. Fortunately for us, a fewenthusiastic viewers made crude videorecordings on their domestic audioequipment, Fig. 2, from BBC broad-casts. They had been inspired byBaird's attempts to make a practicalvideodisc player in the late twenties3and were encouraged by articlesdescribing how to do it.4

Recently, Jon Weller, a collector ofold electronics equipment, retrieved acollection of direct -cut aluminiumdiscs from a house clearance. Thediscs were previously owned andpossibly recorded by Marcus Games,a keen amateur movie enthusiast. Jonlater discovered that several discs inthat collection had unusual materialon them, Fig. 3.5

What are the recordings of?Although the discs were recorded at

Fig. 1. Mechanically -scanned television is in use today by themilitary. In airborne reconnaissance, the high -resolutiontelevision cameras on RAF Tornado GR1A aircraft use mirror -drum scanning. Coincidentally the aspect ratio is similar tothat of Baird's 30 -line standard. (from Crown Copyrightoriginal)

;4 ,.*

'0La<.041

Rfim

different speeds, the starting point wasthat the signal matched Baird's 30 -linevideo standard. Without a date to goby, I had to rely on comparing thevideo content with knowledge of thedevelopment of 30 -line television inorder to determine whether they wereauthentic or recent.

The evidenceOnce restorationstarted, the cluesbegan to appear. In the collection, thereare eleven separate recordings of 30 -line video. Each recording is a frag-ment from a programme and lasts nomore than a minute. There were twotypes of programme - one type featur-ing four individual singers and theother containing what may be materialfrom children's programmes.

Fig. 3. With noclue as to date orauthenticity, oneof the discs has ahand-writtenmessage"Woman. LargeHead". Thisunflatteringmessage

describes themain disc of BettyBolton's BBC tvperformance inthe thirties.


HISTORY

Scanning optionsTwo main types of mechanical scanning were used for 30 -line cameras and displays:Nipkow disc and mirror -drum. The Nipkow disc -a spiral ring of apertures around theouter edge of the disc - created a curved image that was scanned in an arc. The mirrordrum, shown in Fig. 4, however scanned in straight lines with a slight 'bow -tie' distortion.

The BBC transmitted its images from a mirror drum camera system, yet most viewersused receiver -displays based on the Nipkow-disc. They were cheaper and easier to make.Viewers accepted the minor distortion - just as today they surprisingly accept a normaltelevision picture stretched to fit a wide-screen display.

Fig. 4. The mirror -drum camera of the thirties scanned the scene using a projected flying spot. TheNipkow camera disc of Baird's video recording experiments of the twenties used more traditional - butless efficient - lens -based imaging.

Fig. 5. BettyBolton. The photoon the left and itssimulated 30 -lineequivalent show

Betty in 1929. Thetwo pictures on

the right havebeen restored off -

disc. One showsthe glint off

Betty's hair andthe other, her

distinctive profilewith kiss -curl and

hair clasp.

The digitally restored images fromthe set of discs do not show the distor-tion caused by arc -scanning. The onlyalternative camera was one based on amirror -drum.

Mirror -drum cameras for 30 -lineshad a fixed vertical field -of -view ofjust over 20°, excluding blanking.Hence the singers who we see in medi-um shot were around 9-10 feet, i.e. 2.7-3m, from the camera.

With the bottom of the back wall ofthe studio in shot, the images show thatthe studio was large and the camerasystem was sensitive. Showing camerafeatures common with the 1933`Looking In' recording, the quality ofcamera -work appears superior, imply-ing a later date.

Relative to what amateurs todayachieve6 and relative to a genuine 30 -line re -make of a 1930 play7, the inher-ent quality of the vision signal is excel-lent. With no detectable image errors,the mirror drum camera was a preci-sion -built mechanism. Lighting, cam-era -work and production have all beenperfectly matched to the 30 -line sys-tem.

Allowing for the almost `dictaphone'recording quality, the home -recordeddiscs show details that have beentalked about before,8 but not seen .

BBC's first television serviceThese then are undoubtedly recordingsmade from the first BBC television ser-vice of 1932-35. The clues above sug-gest the transmissions came from theBBC tv studio at Portland Placebetween 1934 and '35.

With the 1933 programme, 'LookingIn',9 we now have the total comple-ment of video recordings of broadcasttelevision - at least in the UK - beforethe fifties. Since they were discoveredand restored only in the last two yearssuggests that more material may yetappear.

Singer without the song. Only one ofthe singers is easily recognisable by herdistinctive features and hair -style -Betty Bolton, Fig. 5. As an accom-plished contralto, she recorded manydance -band songs in the late twentiesand early thirties.

Between 1929 and 1935 she per-formed well over a dozen times on 30 -line broadcasts including being the firstperformer on the opening night of theBBC Television Service in August1932.

Betty's performance exudes profes-sionalism. Here is a highly accom-plished performer, perfectly natural infront of a television camera. When Ishowed the images to her, she imme-diately recognised herself from herappearance and actions.

1 62 ELECTRONICS WORLD February 1999

HISTORY

Fig. 6. An unknown male operatic singer. Details ofhis collar, tie and jacket show up well consideringthat the computer -restored sequence originated froma dicta phone quality audio recording.

Fig. 7. An unknown female singer performs in silence through a rain ofhigh disc -surface noise. On the right she is caught part -way throughblowing a kiss at us.

Fig. 8. Captured at120rev/min, thisfemale singer'sperformance is spreadacross three of theeleven separaterecordings. They havebeen brought backtogether digitally asone long sequence.

The glossy shine of her hair, the glintof her tiny silver hair -clasps, her gemnecklace and the pattern on her dressare all remarkably clear. A well-defined dark streak either side of hernose and dark eye shadow seemed tobe the only make-up. Betty confirmedthat only her eyebrows, nose and lipshad been enhanced in dark -blue.

The other recordings of singers, Figs6, 7, 8, are not distinctive enough to beidentified. Hence it is difficult to estab-lish when the recordings were made.

For the first time ever, we can trulyappreciate something close to the orig-inal scene quality from a 30 -line broad-cast. The only surviving Baird

Company engineer described these dig-itally restored pictures as about as badas they got. I°

The first commercial videodisc...In mid -1935 - rather late in the day tobe of much use - the first video discwas offered for sale. It was a double -sided 30 -line vision -only test disc,bearing a 'Major Radiovision' label,Fig. 9. It comprised a series of twentystill cartoon images - ten per side ofthe disc.

These stills are slid in, left for abouttwenty seconds, then pulled out. Theyare transparencies - lantern -slides -

February 1999 ELECTRONICS WORLD

RECORDED

TELEVISIONPROVISIONAL PATENT INN 34

DOUBLE -SIDED record gmney enctunes realenome

a

% for6 mmutet on each side Cbeetent

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bops to be employed. Reversek -up feeds to obtain negabe or a

posture pee< Only one stage ofamp101catebe required. Recorded at

tame sped and number Q4 lanes asbe present B BC If1/11,111104.1 (30

hate) A Boon to the cepenneenter andeemestrator.

MAJOR RADIOVISION CO.a ttLEVISION MANUFACTURERS

Fig. 9. The 30 -linevideo test discmanufactured and soldfor seven shillings bythe 'Major RadiovisionCompany' under F.Plew. The onlyrecording of 30 -lineTelevision in the BBC'sarchives is 12PH69197.Disappointingly, thisturns out to be a poorcopy of this 'MajorRadiovision' disc.

1(3

HISTORY

Fig. 10. Animatedbinary images ofthe mid -twentiespre -dated Baird's

successfuldemonstration in1926. The MajorRadiovision disc

of 1934-5 hasmore in commonwith those early

images than 'true'television.

because one of them is slid in twice,the second time backwards. Therecording shows the characteristic dis-tortion from using a Nipkow disc as acamera - at a time when cameras usedmirror -drums.

Back in the early twenties, peoplelaid down rules to establish what wasand was not 'television'. They decidedthat 'true' television should encompassthe ability to see subjects in reflectedlight.

For many years before Baird's suc-

Fig. 11. The time -base corrected imagedirectly off -disc shown on the leftsuffers from 'ringing' at around .5kliz.On the right, signal processing hasgreatly reduced the distortion and theproper arc -scan pattern has beenrestored.

Fig. 12. A composite of most of thepictures from the 'Major Radio vision'

test disc. The strange pattern atbottom right is a high frequency test

pattern.

cessful demonstration of 'true' televi-sion in 1926, the early pioneers demon-strated video pictures of silhouettes andshadows. Here, an intense light wasshone on the scanning area with thephotocell behind it. Animated silhou-ettes, Fig. 10, a Maltese cross, evenwaggling fingers were all 'subjects'.However this was not 'true' television.Likewise, the 'Major Radiovision' testdisc, made in that way is not 'true'.

Although sold as a test disc, thewhole recording is marred by a 5kHz`ringing' on transitions, Fig. 11. Thefact that these are stills without move-ment means that the full capability ofthe 30 -line system is not realised, Fig.12.

There is a 'sister' disc of stills'',made in the same way as the 'MajorRadiovision' disc but containing dif-ferent subject matter. Strangely, whilstthe recording is clear, none of thelantern -slides are even remotely recog-nisable, Fig. 13.

The new television systemLow definition TV had virtuallynational coverage with at least eightthousand viewing sets. After the last of1,500 programmes was transmitted on11 September 1935, these viewersfound that their 30 -line TV receivershad become obsolete. The new highdefinition service began a year later.

True revolution. Unlike digital televi-sion today, the transition from the 30 -line service to the new high definitionservice was not an enhancement, it wasa total revolution.

Thirty -line tv was designed to useexisting radio channels intended foraudio broadcasting. The BBC had usedmature technology for its 30 -line tele-vision studio. It had also used its exist-ing audio distribution channels andradio frequencies for vision transmis-sion, leaving the public to buy or evenbuild their own receivers.

In sharp contrast, a totally newinfrastructure supported the high defi-nition system. Virtually everything hadto be developed from scratch - cam-eras, cables, distribution amplifiers,routers, transmitters, receivers and dis-plays.

The investment was enormous butthe time was right and the public werecrying out for a full television service.The potential returns for the right solu-tion made the investment appearsecure.

Trial by televisionWhen test transmissions started in 1936from RadioOlympia, the price ofreceivers, full of the latest technology,left the public far behind. Much likethe start of BBC Choice in September


HISTORY

Fig. 13. Identical in every way butcontent to the 'Major Radiovision' 30 -line test disc, a second disc containstest stills that are clear yetunrecognisable.

1998 on the digital service, hardly anyof the public had the new receivers towatch it.

Television coverage shrank frommost of Britain to London and theimmediate vicinity. Initially, televisionsets had to be dual -standard: the choicebetween the Baird Company's totallynew 240 -line progressive scan systemand rival Marconi -EMI's 405 -lineinterlaced system was to be resolvedon -air.

Dual standard reception made thefirst electronic televisions even morecostly. By January 1937, the all -elec-tronic 405 -line system had beenselected.

Viewers outside the London area,who switched off their 30 -linereceivers for the last time in 1935, hadto wait more than fifteen years for tele-vision to return. It took until 195212 forcoverage to reach Scotland and Walesand 1953-54 for prices of receivers tobecome affordable to the averageworking family.

But what of Baird?John Logie Baird, Fig. 14, has easilyearned the acclaim of Britain's fore-most television pioneer. His list ofachievements is legendary. He devel-oped and demonstrated the world's firstpractical solution to television.

Uniquely amongst the tv pioneers,

Fig. 14. John Logie Baird - Britain's foremost television pioneer, 1888-1946.

Baird developed, demonstrated andpatented almost every aspect of televi-sion including colour, infra -red, 3D,and video recording. He introduced andfunded a broadcast television service.His 30 -line system was adopted - andhence sanctioned - by the BBC fortheir first television service.

That he lost the prime competitionfor supplying the BBC's high defini-tion service to Marconi -EMI in 1936 isunfortunate - the all -electronic systemwas simply better. This does not detractfrom his remarkable achievements andinnovations throughout the dawn oftelevision and, indeed, for the rest ofhis life.

Baird received only one honour -honourary Fellowship of the RoyalSociety of Edinburgh." If we recog-nise comedians and retired politiciansand their secretaries through our coun-try's honour system, then the time islong overdue to bestow proper honourson John Logie Baird.

Acknowledgments. I would like tothank Jon Weller, the owner of alu-minium discs described here and toEliot Levin of Symposium Records,who freely gave up his time to transferthe discs expertly and professionally.Final thanks go to Betty Bolton, theearliest video star, who has charmedme both on disc and in person.

ReferencesI. BBC, "The Discovery of Television",

Documentary celebrating 25 years ofTelevision, 1961

2. McLean, D F "First Frames",Electronics World, November 1998

3. McLean, D F "Restoring Baird'sImage", Electronics World, October1998

4. Practical Television, "CannedTelevision", Barton Chapple, November1934

5. Weller, J. Private Communication, Jan -March 1998

6. NBTVA - Narrow Band TelevisionAssociation - uses low definition TV asan alternative amateur radio mode

7. Remake of "The Man With The FlowerIn His Mouth", 1967, ILEA, producedby Lance Sieveking (the original 1930producer) and filmed entirely in 30 -linesby Bill Elliott.

8. Bridgewater, T H "Just a Few Lines",British Vintage Wireless Society, 1992

9. McLean, D F ibid Electronics World,November 1998

10. Herbert R M. Private Communication,June 1998

11. A tape copy of this disc was supplied byDoug Pitt, NBTVA, 1982. The source ofthis tape is unknown.

12. Briggs, A. "The BBC: The First FiftyYears". OUP 1985

13. Baird, Prof M H I, private communica-tion, Sep 1998

Don will be describinghis work in a lectureto be given at theIEE, Savoy Place,London on 11 May1999 at 6pm.Admission is free andopen to non-members. Themultimediapresentation will relyheavily on the videorestorations and willbe entitled "RestoringBaird's Image: therestoration of theworld's earliest -known televisionrecordings."


DIGITAL DESIGN

DSPs at the bottomend of the marketare findingthemselves used inan ever increasingnumber ofapplications. Buthow will theycompete against thelikes of Risc andmicrocontrollers?Steve Bush reports.

With hugely powerfulsuper -scalar digitalsignal processors

grabbing the limelight, it is easy toforget the bottom end of the market- the 16 -bit fixed-point processorsthat sell in increasing numbers intoproducts as unlikely as video babyalarms and fridges.

It is a highly competitive sectorwhich is also the target of Riscprocessors and microcontrollers.

What are chip manufacturersdoing to keep their share - or evenincrease it?

Jean -Marc Darchy is TexasInstruments' European dspspokesman. He said: "There is stilla lot we can do. The first thing isthat dsps will be adopting the latestproduction technology. With an0.18 or 0.151.tm process, you candeliver for $5 three to four timesthe performance compared with adsp from two to three years ago.For instance, our 5402 [due tosample next month] will deliver100Mips for $5. There will be avariety of products on the market atthis performance."

With 100Mips for $5, dsps willbecome more attractive in a marketthat is awash with Risc processors,microcontrollers, and existing dsps.

takes controlIn some cases, fast dsps will have

an inherent advantage. "DSPs willbe better than microprocessors forvoice coding and datatransmission," said Darchy.

According to Darchy, there is asecond factor that will affectforthcoming sales. "To win againstmicrocontrollers, dsps will becomemore specialised and will focus onan application, or a cluster ofapplications, with specific on -chipperipherals. This will need a goodunderstanding of the market andthe products that will use theprocessors."

An example he cites is motorcontrollers, where TI, AnalogDevices and Zilog already havededicated dsp products. "This is asuccess. It was a puremicrocontroller market which isnow switching to mediumperformance dsps because theon -chip peripherals, pulse -widthmodulators and timers, focus theproduct on the application," saidDarchy.

Applications likely to receive theattention of dsp makers in the nearfuture, according to Darchy,include: point of sale terminals,payphones, imaging systems andremote data acquisition. "One dsp

could handle all of the usualfunctions in a sales terminal, plusimplement a modem tocommunicate with the storecomputer. It could perhaps do somevoice recognition as well. For datalogging, you will be able tomeasure parameters, performcalculations and transmit the resultsdown a phone, all with a $5 dsp."

One company that alreadyincorporates a wide range ofperipherals on its dsps is Zilog.

"Typically a dsp has hardly anyi/o," said Adam Provis, anapplication engineer with Zilog."We add the sort of peripheralsfound in microcontrollers. Forinstance: a phase -locked loop toallow the chip to run from alow-cost 32kHz crystal, counter -timers, SPI serial port, 8 -bit a -to -dconverter and i/o ports."

He sees this as an advantage insimple consumer products."Typically, a microcontrollercannot handle voice compressionfor storage into flash memory orfor transmission, whereas a dspcan. In walkie-talkies, baby alarmsand similar products, you canchoose to use a dsp forcompression and a microcontrollerto handle the housekeeping


DIGITAL DESIGN

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functions like battery managementand operating the human interface,or you can use a single dsp part thatdoes everything."

This 'everything' includes storingits own program code, as Zilog'srange includes one-timeprogrammable and mask-romon -chip memory options, but notyet flash. "We will have flashmemory in the second quarter ofnext year," said Provis.

He sees two other ways to makedsps more attractive.

One is to offer them in smallpackages. Zilog has one in a44 -pin PLCC; the other is to keepdevelopment tool costs low.Provis said, "Our lowest cost in -circuit emulator is $99. This is afull function emulator, the onlything that it hasn't got is ahardware trace."

Motorola's 56800 family,currently at 35Mips and mappedto 100Mips in 2000, is anotherwith multiple microcontroller-likeperipherals laying claim to asimilar range to Zilog's.

Power consumption is alsoimportant, not only in portableequipment, but as a way ofreduced fixed and recurring costsin mains -powered installations.

DSP chip makers are not blindto this and are taking steps to droppower consumption even asperformance increases.

"Because of the processes used,"said Analog Devices' AndrewLanfear, "in some cases 32 -bitdsps can cost less than 16 -bitalternatives."

This can make the 32 -bit devicelook attractive, even when theapplication only demands 16 -bitcapability. "But the 16 -bit dsp islikely to consume less power inthe application," said Lanfear.

As an example of low powerconsumption, he puts forward theADSP2189. "It is a 75Mipsdevice that can run two V.90[56kbit/s] modemssimultaneously. But it consumesonly 0.4mA/Mip at a core voltageof 2.5V."

The core behind the ADSP21xxfamily has been around for awhile now, constantly increasingin performance. Now at 75Mips,"we expect it to top -out at100Mips," said Lanfear, "Infuture we are looking at a newinstruction set architecture and anew core. This will be furtherdown in power consumption andwith much higher performance.

But we are not releasing datesyet."

Analog Devices and TI are the`big two' in dsp. Is TI looking atarchitectural changes for its low -end processors?

"I suspect not," said TI'sDarchy. His argument is largelyfinancial: "Going to smaller, fasterprocesses is quickly movinglow -end dsps towards top -endmicroprocessors. A $40 to $50 dspthree years ago is only $10 now."

There is also a reason whymoves to new architectures areactively undesirable. "Keeping thesame architecture is a more robust,efficient and economic way to getthe best out of a company'sexisting software base and tools,"said Darchy.

Up-to-date semiconductorprocesses, combined withmicrocontroller peripherals arepushing 16 -bit fixed-point dspsinto applications formally reservedfor microcontrollers. Power isgoing down and speed is going up.

The likely result is 'high-tech'consumer goods that feature voiceand video compression; speakerphones, security products andbaby alarms are the kind ofproducts that should benefit.

Peripherals areappearing ondsps, movingthem on in thesame way thatthey turnedmicroprocessorsintomicrocontrollers.


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ELECTRONICSAPPOINTMENTSElectronics World February 1999 Te1:0181 652 3620

HardwarePOWER

SUPPLY/ANALOGUEVV.London DC -DC, Magentics toL30K

Kent SMPS Designer L20 -30K

Sussex Power/Analogue, MedicalL3OK

VV.Sussex Power Elec, Servo, ampsLopen

Essex Switch Mode P.S.U'sto £28K

Midlands Switch Mode P.S.U's L34K

Herts PVVM, 18-30K

Hants Power Elec, Motors L32K

Staffs Power Elec, GBT, GTOto L3OK

Herts/Cambs Power Elec, P.S.U, DrivesL I 8-35K

Ref: AL590EWd

ANAL./DIG/FPGAfASIC

SOUTH WALES E I 8-30KNew positions for 5 Engineers withexperience of Analogue/Digital or FPGA/VHDL/ASIC design experience to work anew major project developing SecureNetworking systems.The first position will involve the design ofelectronic hardware including: digital/microprocessor, analogue, test equipmentand EMC, and the second position will haveresponsibility for the design of devicesASIC's and FPGA's using VHDL designtechniques.If your experience covers (I) Analogue,Digital, Microprocessor, or (2) FPGA,VHDL, ASIC and you'd be interested inworking in S.Wales please get in touch.

Ref: ALS92EWd

ASIC/FPGA/VHDL

Surrey Gate Array,VHDL,ASICL28 -38K

S.Hants VHDL.Verilog,ASIC L25 -35K

Bucks ASIC, FPGA, Comms, BroadL23 -33K

Swindon VLSI, DSP,VHDL L20 -30K

Sheffield ASIC/FPGA/VHDL to &40K!Birmingham Digital, ASIC,VHDL E28K+S.Wales ASIC/FPGA/VHDL LopenHerts ASIC ,Verilog, Synopsys

L28 -38KM25/M3 Digital/ASIC Team Ldr

L24 -30KRef: AL577EWd

WSUSSEX TO cL3OKSenior design role with a Britishcompany who are at the forefront ofmedical electronics in the field ofhigh dose rate brachy therapyused for internal radiation

DATACO

N.W. SURREY L23 -28KThis is a new position with a company whodesign/manufacture a successful range ofDatacommunications products - ATM,LAN/ WAN and who are looking to recruita Senior Hardware Engineer to joint theirexpanding R&D team.You will be responsible for productdevelopment from initial design through tocustomer support using VHDL high speeddigital hardware, FPGA's and PC basedsystems.Experience of: ATM, LAN, i906, XILINX,FPGA's,VHDL or PCI bus would be usefulbut not essential. Ref: ALS84EWd

therapy treatment.Expansion within theirR&D team has creat-ed a position for aHardware Engineerto design circuit boardsusing digital/microprocessor/programmable logic andanalogue electronics togetherwith some software in C.A good base in digital/analogueelectronics is essential, plus experience ofsoftware in C/VVindows would be useful,Interested? Ref: ALS87EWd

CL3OK + PENSION & BENSNew position for a Hardware Engineer

to join one of the world leaders inthe design and manufacture of

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SWPRFC-At:1.1'1'1,1EN ITel: 01442 212555Fax: 01442 231555

multidiscipline R&Dteam and be

responsible for thedevelopment and

support of Firmware -BIOS for mother/

daughter and control boardsfor current and future

generation systems.Your experience should include 2

years plus of Intel/Motorolaprocessors, PCBIOS. C, and a good

background in hardware electronics.Ref: ALS8 I EWd

Contact - Andrew Langridge on 01442 403513

HARDWARE &MUSIC

LAMBS TO L34KDo you have an interest in Music, andwould you like to progress your careerdesigning digital electronic systems for themusic business?We currently have three companies whohave positions for qualified HardwareEngineers to work on new products for theprofessional recording and soundmixing/distribution market.Ideally you will have a BSc/HND/HNCqualification with experience of digitalelectronics/microprocessors, programma-ble logic devices (PLD & FPGA, EPLD etc)and have a keen interest in Music, eitherfrom work or social activities. Interested?

Ref: ALS86EWd

LPESIGNERSISLE OF WIGHT cL25KNew positions for Digital HardwareEngineer to join one of Britain's expandingcompanies who are a major force in thedefence/ avionics industry.Their Radar design site on the Isle of Wightis looking for a couple of HardwareEngineers to work on control/signalprocessing systems which form the basis ofthe central processing unit for their nextgeneration system.We are looking for Engineers with a goodbase digital hardware (primarily discretedevices) and high speed synchronousdesign, experience of control, DSP. VHDLor FPGA's would be very useful.Interested? Ref: ALS89EWd

R F/C OMMSSENIOR/PRINCIPAL

RF ENGINEERSHERTS UPTO L45KThis company offer varied and interestingdesign positions of a senior nature in theTest and Measurement industry.You will be responsible for RF andanalogue circuit design up to 6 GHz:wideband RF amplifiers, control compo-nents, up/down converters, modulators,demodulators and synthesis (PLL).Degree qualified with a minimum of 3 yearsexperience in any of the followingenvironments - basestations, satellitecommunications, microwave or TV/broadcast. Able to use simulation tools eg.HPEesoff, Libra etc.

Ref: AJ 143EWd98

WILTS L20 -40KA company who manufacture and developwireless products, software and supportfor the service providers within the mobilecommunications industry requireSenior/Principal RF Design Engineers.You will be responsible for control loop,poweramplifiers, receiver and transmitterdesign and will therefore requireknowledge of GSM systems architectures.With a flexible approach to problemsolving you should be able to work incross -functional teams.MSc/BSc in Electronics or Communicationswith high frequency design knowledge(GSM/CDMA frequencies/technology) andRF simulation experience (HP/EESOF,SPICE etc). Ref: AJ82EWd98

RF/ANALOGUEDESIGN

E.ANGLIA L20 -27KA world leader in the supply of advancedelectronic systems, is seeking an RF/

Analogue Design Engineer to carry out thedesign and development of radio basedMilitary Electronics equipment.You will be involved from initial designstudies and concepts through tomanufacture and product support.Working as part of a team, you will requirea minimum of an HND or equivalent and 3years practical design/ developmentexperience in transmitters, receivers etc.You should have a proven ability with RFand Analogue circuitry up to at least400MHz. Ref: Al I 3SEWd98

MICROWAVE/ANTENNADESIGN

ESSEX LNEGA company who designand manufacturemarinecommunicationsrequire a DesignEngineer with bothmicrowave andantenna skills inthe 3 to 10GHz range.Responsible for the development ofantennas, waveguide systems, coaxialcomponents, radar systems andmeasurements.You will need to be Degree qualified in arelevant discipline with 5 years experiencein a microwave field. Ret: AJ I 23EWd98

SYSTEMS ENGINEERS- SATELLITE

M4 CORRIDOR UPTO L3SKA major player in the Defence Sector,supplying advanced electronic warfaresystems, military radars and commandinformation systems for land, sea and airapplications require Systems Engineers.Working in the Satellite CommunicationsDepartment, currently on a project todevelop and manufacture a man -portablesystem.Degree qualified in a relative discipline within-depth knowledge of datacomms andsystems engineering as well as digital

hardware design preferably from a

commercial manufacturing environment.Ref: AJ97EWd98

2nd Floor,89 Marlowes,

Hemel Hempstead,Herts HP1 1XY

email:[email protected]

Web:http://www.swpjobs.com

F TESTENGINEER

E.ANGLIA L 14-20KA company with over 20

years experience in thedesign and manufacture

of isolators andcirculators,

amplifiers and sub-systems have an

immediate vacancy for anRF Test Engineer.

You will be responsible for fault-finding on amplifiers, power

splitters and other products for use incellular base stations. Two years

experience in an RF or MW test role is

required coupled with the ability to fault -find to component level and carry outcircuit tuning/testing. Ref: AJ I 34EWd98

Contact - Alison Jones on 01442 403522

RF DESIGN x4NORTH cL20-30KA company involved in the research,development and manufacturing ofmicrowave filters and subsystems for bothdefence and civil applications is

experiencing continuous growth and there-fore requires four RF Design Engineers towork on their high technology products.You will need to be degree qualified with aminimum of 2 years experience in either acivil or defence environment in the designof components (filters and filter modulesupto 45GHz) or sub -systems (activemicrowave for Electronic Warfare andRadar applications).Relocation is offered with this company,who also believe in encouraging theirEngineers to continue part-time highereducation. Previous applicants with theabove experience need to re -apply.

Ref: AJ I 37EWd98

WITSBERKSHIRE 420-35KA company involved in the research anddevelopment of the '3rd generationnetwork' - UMTS are seeking a StandardsEngineer. You will be responsible fordeveloping network architectures forUMTS, representing the company atstandards meetings and preparingdocumentation for internal and externaluse.

Degree qualified with 2 yearsstandards experience, good communicationskills and ability to meet deadlines underpressure with a good knowledge oftele/data comms. Ref: AJ I 4IEWd98

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Radio CommunicationsRELIABILITY ENGINEER - Bristol to £26k+

We're looking for an individual to shake, rattle and rollthis company's wireless products ready for thedemanding environments they'll be working in. Thesuccessful applicant will be the 'first in' in this type ofrole and our client seeks someone to bring in thenecessary expertise. A background in radio technologywould be a distinct advantage. Quote WW9811-53.

Contact Mark Wheeler for more information.

PRODUCTION ENGINEER - Bristol to £30k

A sound knowledge of small to medium volumeproduction and manufacturing techniques is requiredhere. Experience of liaising with small multi -disciplinedR+D teams and being able to pro -actively work withoutside contractors is essential. A general electronicsbackground is required, ideally with radiocommunications experience. Quote WW9811-54.


RF IC DESIGN ENGINEER - Bristol to £45k

Make a mark for yourself and be the first IC designer inthis established and fast growing Radio Systems DesignHouse. You'll be working alongside a very finemultidisciplinary team of Engineers involved in someof the most stimulating projects around. Competenthands on skills are required including experience up to3GHz together with some good ideas. Quote WW9712-17.


RF PA DESIGN EXPERTS - Bristol to £40k

Involved in projects that seem to go on forever? Stuckin a corner working on the bit your boss says you haveto do? Yes? Then your salvation is at hand with this fastgrowing Wireless Communications company whereyour talents can be truly realised. Accomplished designskills up to 3.5GHz in high power PA's ideal, receiverand synthesisers development experience very useful.Quote WW9707-56.


BENCH TECHNICIANS - Notts £10k - £22k

Component level expertise? Board level diagnosis?Shiny new technical qualification? This leading cellularmaintenance organisation wants you!! You don't haveto have communications product experience (althoughit would help), but you'll be keen to keep abreast of thelatest technology. All this in a positive, friendlyenvironment too! Quote WW9703-37.


DSP SOFTWARE ENGINEER - Bristol to £34k

For this one, you'll need to bring to the table at least ayear's expertise in DSP Algorithm development, realtime embedded software and an understanding ofhardware design. You would be working on radiomodems, linear amplifiers and many other interestingand challenging projects. A radio background is

desirable but not essential. Call us today if it soundslike you. Quote WW9804-30.


TEST ENGINEER - Surrey to £25k

Working within a group responsible for the design ofswitching software for UMTS mobile commsinfrastructure, you will be involved in setting up andundertaking complex test and systems integrationprocesses. Ideally HNC qualified, it would be useful ifyou had experience in mobile, cellular, GSM, etc and anappreciation of switch signalling. Quote WW 9808-86.

Contact Malcolm Masters for more information.

RF STANDARDS ENGINEER - Surrey to £30k

Working within a new group, you will be ultimatelyresponsible for setting in place procedures, policies andstrategies to comply with international regulations formobile comms equipment. You should be qualified toHND standard and have several years experience in asimilar environment, ideally in 3rd generation mobiletechnology. Quote WW9808-82.


DIGITAL DESIGN ENGINEER - N. Wilts to £35k

This role has been created to work within a small teamon the latest digital communications systems. Youwill be involved in developing VHDL code for FPGAand ASICs for radio base stations. Significantexperience in digital design, VHDL and FPGA is

required along with strong academic achievements.Quote WW9811-34.


CELLULAR REPAIR SUPERVISOR -.- N.W Lon. to £19k

Our client is a significant player in the sales andservice of cellular products. They are activelylooking for a supervisor from the cellular/comms/PMR industry to repair and test a wide varietyof cellular phones and run a start-up servicedept. CEtG/HNC or relevant industrial experiencerequired. Quote WW9811-46.

Contact Rich Wootten for more information.

Cri=====131This is a great opportunity for a keen RF technician towork in a lively atmosphere for a major manufacturerof PMR equipment. You'll need to be able to serviceand repair to component level and have relevantmobile comms involvement. Some Band 3 andinstallation experience would be desirable but is notessential. Quote WW9811-52.


PRODUCT SUPPORT ENGINEER - Berks to £25k

Our client is at the forefront of mobile telecoms,having released several of the most popular productson the market. Now it's your turn to get a slice of theaction. You'll need to be able to support theintroduction of complex mechanical parts intomanufacture and maintain build standards in a

demanding industry. HNC and electro-mechbackground required. Quote WW9811-09.


For more vacancies visit our website http://www.mdm.co.uk[1k

ELECTRONICSAPPOINTMENTSElectronics World February 1999 Tel:0181 652 3620

UK Wide VacanciesGraduate Electronics Engineer - Hampshire. Qualified to degree level, to work with the design team developing andproving new hardware and software for engine management and power conditioning systems. Training in various disciplinesincluding embedded micro -controller design and power electronics systems to 250kW. Salary negotiable.

Test & Repair Engineer - Hampshire. Minimum of HNC with at least 2 years experience of fault diagnosis of analogue anddigital circuits to component level. Computer literate, familiarity with Windows packages and able to work under pressure.Salary negotiable.

Project Manager -West Yorks. RF/Microwave. To ensure a development project is delivered in line with customerprototype commitments and that the product is developed to enable cost effective manufacture in volume. To £35k.

Test Design Engineer - Hampshire. Minimum of HND and knowledge of Visual Basic and/or C in a Windows environmentto design, maintain and document test procedures, systems and software using Pcs and telecommunications testequipment. Familiarity with telecommunications protocols and report writing ability would be helpful.

Electronics Engineer - Cheshire. Embedded Controllers. To develop electromechanical devices for the test of PCBsusing embedded controllers, analogue instrumentation and PC based software (VB, C++, Win NT/95). Must be able to faultfind complex electronic systems with at least 2 years experience in a related field.

Software Development Engineer - Hampshire. For low power embedded systems using C and assembly languages.Knowledge of NEC 75X, 75XL 4 bit and 78K/0 8 bit microprocessors and digital or analogue hardware design ability wouldbe useful. To £28k.

Senior RF Development Engineer - Hampshire. Development of low power RF circuitry up to 1Ghz and experience ofLNA, oscillator, mixer and IF design. Experience of synthesiser design and low power transmitter work would also be useful.Supervision of junior engineers and project management is also envisaged as part of the role. Salary to £32k.

Electronics Design Engineer - Cheshire. Development of high frequency analogue circuits (to 500Mhz) Degree qualifiedwith a minimum of 2 years experience of analogue circuit design. Exposure to DFM issues and PCB design using Cadstar.£Neg.

For details of these and other electronics vacancies telephone Roy Parrick on01703 237200 or fax on 01703 634207.Alternatively E-mail to [email protected]

KELLYTECHNICAL

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ADVERTISE FREE OF CHARGESubscribers* to Electronics World can advertise their

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* This free offer applies to private subscribers only. Your ad will be placed in the first available issue.This offer applies to private sales of electrical and electronic equipment only.

Trade advertisers - call Joannah Cox on 0181-652 3620All adverts will be placed as soon as possible. However, we are unable to guarantee insertion dates. We regret thatwe are unable to enter into correspondence with readers using this service, we also reserve the right to reject adverts

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ELECTRON ICSAPPOINTMENTSElectronics World February 1999 Tel:0181 652 3620

iv Calling all Radio/Engineers14, ,47

We have excellentopportunities within Research,Design and Test for Radio Engineersto work at all levels in the fields of:

GSM

Fixed Radio Access / WLLMilitary CISPMR DECT TETRASatellite CommunicationsMobile Switching

RV

John ProdgerRecruitment

Connecting people with opportunities

We would be glad to focus our effortson securing your next move.Please call John Darby, ref 2984H.Tel: 01727 818704 Fax: 01727 838272Email: [email protected]

JPR, The Courtyard, Alban Park, Hatfield Rd, St Albans, Herts AL4 OLA.173

MasterCard I 0; t VISA

9 TA%,V"SUPPLIER OF QUALITY USED

TEST INSTRUMENTS

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, .

Cooke InternationalUnit Four, Fordingbridge Site, Barnham,

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Web: http://www.cooke-int.comE-mail: [email protected]

catalogue available


VISA

OPERATING & SERVICE MANUALS

Cooke InternationalUnit Four, Fordingbridge Site, Barnham,

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FLANN precision rotary waveguide attenuator 22110 0-70db 26.40GHz£750

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8590A 1.8GHz spectrum analyser86222A 10MHz-2.46Hz sweep generator plug-in unit862908 2-18GHz sweep generator plug-in unit86846 signal generator 5.4GHz-12.5GHz £1000

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176

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Figure 7

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WEB DIRECTORY - see page ELECTRONICS WORLD · 2020. 5. 3. · Recruitment ads start on page 1 70 9 I I 77095 83304. 1 ... 8920A R/F Comms Test (various options) 8922 BGH G.S.M. Test