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THE FUNDAMENTALS OF DESIGNING WITH SEMICONDUCTORS FOR SIGNAL

PROCESSING APPLICATIONS

Class 3 - BEYOND THE OP AMP

Presented by David Kress

Analog to Electronic signal processing

Sensor(INPUT)

Digital ProcessorAmp Converter

Actuator(OUTPUT)

Amp Converter

Analog to Electronic signal processing

Sensor(INPUT)

Digital ProcessorAmp Converter

Actuator(OUTPUT)

Amp Converter

Amplifiers and Operational AmplifiersAmplifiers

Make a low-level, high-source impedance signal into a high-level, low-source impedance signal

Op amps, power amps, RF amps, instrumentation amps, etc.Most complex amplifiers built up from combinations of op

ampsOperational amplifiers

Three-terminal device (plus power supplies)Amplify a small signal at the input terminals to a very, very

large one at the output terminal

Specialty Amplifiers

Specialty AmplifiersDesigned for a specific signal typeExtract and amplify only the signal of interestPick off a small differential signal from a large common-mode

voltageCapture and demodulate a low-level AC signalCompress a high-dynamic range signalProvide automatic or controlled gain-changingSend and receive precision signalsProvide high-speed low-impedance power outputUse the analog domain to its best advantage to prepare a clean

signal for the data converter

Specialty Amplifier Types

General Inst. Amps. Differential Amps. Current-sense Amps. Programmable gain Demodulating amps (AD630 and AD698) Thermocouple amps Logarithmic amps with time-gain-controlADC drivers Clamp amps Funnel amplifierLine drivers/receivers Isolation amps

Single-ended vs. Differential Signals

Single-ended signalsSignal is measured referred to groundWhen signals are bipolar (+ and-), negative supplies neededAC signals are typically bipolar or need special ‘floating’, or

capacitive couplingGround often carries high noise from other signals or power,

compromising the signalDifferential signals

Both sides of the signal float ‘off ground’Signals are separated from ground and other signalsHigh frequency and accuracy usually need differential handlingCommon mode (average) can be set for single supplySpecialized differential/difference amplifiers are needed

Instrumentation, Difference and Differential Amplifiers Instrumentation amplifiers

Amplify differential inputs to a single-ended outputNormally both amplifier inputs are high impedanceProvide high gain (up to 10,000) and low noiseNormally handle low-level signals from sensors

Difference amplifiersAmplify differential inputs from high common mode voltage levelsOften include input attenuator to allow operation outside suppliesHigh common model rejection even at high frequencies

Differential amplifiersHigh frequency amplifiers with differential input and outputHandle higher-level signals at lower gainsTypically used for line driving/receiving and ADC driving

The Generic Instrumentation Amplifier (In Amp)

~~

COMMONMODE

VOLTAGEVCM

+

_

RG

IN-AMPGAIN = G

VOUTVREF

COMMON MODE ERROR (RTI) =VCM

CMRR

~

RS/2

RS/2

RS

~

~

VSIG2

VSIG2

+

_

+

_

Op Amp Subtractor or Difference Amplifier

VOUT = (V2 – V1)R2R1

R1 R2

_

+

V1

V2

VOUT

R1' R2'

R2R1 =

R2'R1'R2'R1' CRITICAL FOR HIGH CMR

0.1% TOTAL MISMATCH YIELDS 66dB CMR FOR R1 = R2

CMR = 20 log10

1 +R2R1

Kr

Where Kr = Total FractionalMismatch of R1/ R2 TOR1'/R2'

EXTREMELY SENSITIVE TO SOURCE IMPEDANCE IMBALANCE

REF

The Three Op Amp In Amp

VOUTRG

R1'

R1

R2'

R2

R3'

R3

+

_

+

_

+

_

VREF

VOUT = VSIG • 1 +2R1RG

+ VREFR3R2

IF R2 = R3, G = 1 +2R1RG

CMR 20logGAIN × 100

% MISMATCHCMR 20log

GAIN × 100% MISMATCH

CMR 20logGAIN × 100

% MISMATCH

~~

~~

~~

VCM

+

_

+

_

VSIG2

VSIG2

A1

A2

A3

GENERALIZED BRIDGE AMPLIFIER USING AN IN-AMP

VB

+

-

IN AMP

REF VOUT

RG

+VS

-VSR+DR

VB

DR

RVOUT = GAIN

R+DRR–DR

R–DR

AD620B Bridge Amplifier DC Error Budget

+

–

350100mV FSLOAD CELL

AD620B SPECS @ +25°C, ±15V

VOSI + VOSO/G = 55µV maxIOS = 0.5nA maxGain Error = 0.15%Gain Nonlinearity = 40ppm0.1Hz to 10Hz Noise = 280nVp-pCMR = 120dB @ 60Hz

VOS

IOS

Gain Error

Gain Nonlinearity

CMR Error

0.1Hz to 10Hz 1/f Noise

TotalUnadjusted

Error

ResolutionError

55µV ÷ 100mV

350 × 0.5nA ÷ 100mV

0.15%

40ppm

120dB 1ppm × 5V ÷ 100mV

280nV ÷ 100mV

9 Bits Accurate

14 Bits Accurate

550ppm

1.8ppm

1500ppm

40ppm

50ppm

2.8ppm

2145ppm

42.8ppm

MAXIMUM ERROR CONTRIBUTION, +25°CFULLSCALE: VIN = 100mV, VOUT = 10V

+10V

AD620B

REF

499

RG

G = 100

VCM = 5V

SINGLE-SUPPLY DATA ACQUISITION SYSTEM

+2V

+2V 1V

VCM = +2.5V

G = 100

High Common-Mode Current Sensing Using the AD629 Difference Amplifier

VCM = 270V for VS = 15V

AD8253

AD8251/53 Digitally Programmable Gain Instrumentation Amplifier (PGIA)

A1 A0DGND WR

AD8253

+VS –VS REF

OUT

+IN

LOGIC–IN 1

10

8 3

7

4562

9

-IN

+IN

A1A2

REF

OUT

+

-

Gain Logic

A1

A2

A3

+VS

-VS

AD8251

AD8251 Fine Gain Setting of 1,2,4,8 AD8253 Coarse Gain Setting of 1,10,100,1000

Low noise and low offset with 10MHz bandwidth

Demodulating Amplifiers

AC demodulationLow-level low-frequency AC signal processing can be used for

capturing low-level signalsA modulated signal bypasses issues of offset and noise in

amplifiersUseful for transformer-coupled position detectorsLock-in amplifier can find narrow band signal 100db below the

interfering noise

IMPROVED LVDT OUTPUT SIGNAL PROCESSING

~AC

SOURCE

+ ABSOLUTEVALUE

ABSOLUTEVALUE

FILTER

FILTER

+

_

VOUT

_

POSITION +_

VOUT+

_

LVDT

Lock-in Amplifier

A

B

10k

100R

C OUTPUT

LOW-PASSFILTER

A

B

C

R

100RAD630

10k

5k

2.5k

2.5k

20

1917

1

16

AD54213

AD542

14

10

9

CLIPPEDBAND-LIMITEDWHITENOISE

100dBATTENUATION

0.1HzMODULATED

400HzCARRIER

CARRIERPHASEREFERENCE

1

AD630 demodulates 400Hz signal 100dB below noise

Thermocouple Amplifiers

Cold junction compensationThermocouples use two different metals that develop a voltage

varying with temperatureThe temperature effect also occurs at the point where the

thermocouple wires connect to the instrumentThis ‘cold junction’ effect must be compensated for to get

accurate measurementsVarious techniques have been used including ice bathsModern thermocouple amplifiers include accurate compensation

circuitry

Using a Temperature Sensor for Cold-Junction Compensations

TEMPERATURECOMPENSATION

CIRCUIT

TEMPSENSOR

T2V(T2)T1 V(T1)

V(OUT)

V(COMP)

SAMETEMP

METAL A

METAL B

METAL A

COPPERCOPPER

ISOTHERMAL BLOCKV(COMP) = f(T2)

V(OUT) = V(T1) – V(T2) + V(COMP)

IF V(COMP) = V(T2) – V(0°C), THEN

V(OUT) = V(T1) – V(0°C)

TEMPERATURECOMPENSATION

CIRCUIT

TEMPSENSOR

T2V(T2)T1 V(T1)

V(OUT)

V(COMP)

SAMETEMP

METAL A

METAL B

METAL A

COPPERCOPPER

ISOTHERMAL BLOCKV(COMP) = f(T2)

V(OUT) = V(T1) – V(T2) + V(COMP)

IF V(COMP) = V(T2) – V(0°C), THEN

V(OUT) = V(T1) – V(0°C)

AD594/AD595 Monolithic Thermocouple Amplifier with Cold-Junction Compensation

ICEPOINTCOMP

+

OVERLOADDETECT

VOUT10mV/°C

+5V

BROKENTHERMOCOUPLE

ALARM

4.7k

G

+

–TC––

+TC+

+ATHERMOCOUPLE

G

AD594/AD595

TYPE J: AD594TYPE K: AD595

0.1µF

ICEPOINTCOMP

+

OVERLOADDETECT

VOUT10mV/°C

+5V

BROKENTHERMOCOUPLE

ALARM

4.7k

G

+

–TC––

+TC+

+ATHERMOCOUPLE

G

AD594/AD595

TYPE J: AD594TYPE K: AD595

0.1µF

Log Amplifiers

Signal compressionMany applications must capture signals over a very wide dynamic

rangeRadio antennas capturing broadcast signalsPhotomultipliers and photodiodes capture light signals over a very

wide rangeTo process and use these signals, they need to be compressed to

a much smaller rangeLogarithmic amplifiers

Log amplifiers compress signals over ranges of as much as 120db – a million to one -- to a normal range of 1 to 10 volts

Accuracy is typically 0.1 to 0.5 dB -- 1 to 5%

Log Amp Transfer Function

IDEAL

ACTUAL

SLOPE = VY

2VY

VY

IDEAL

ACTUAL

VYLOG (VIN/VX)

+

-VIN=VX

VIN=10VX VIN=100VXINPUT ONLOG SCALE

VOUT = VY log10

0

VIN

VX

IDEAL

ACTUAL

SLOPE = VY

2VY

VY

IDEAL

ACTUAL

VYLOG (VIN/VX)

+

-VIN=VX

VIN=10VX VIN=100VXINPUT ONLOG SCALE

VOUT = VY log10

0

VIN

VX

Log Amplifier Accuracy

5

4

3

2

1

–4

–5

500MHz

100MHz

10MHz

–3

–2

–1

0

–80 –70 –60 –50 –40 –30 –20 –10 0 10 20

ER

RO

R(d

B)

INPUT LEVEL (dBm)

AD8307 covers 80dB with 0.5dB accuracy

AD8307 six-decade RF power measurement

TOANTENNA

VP

604Ω

100kΩ1/2W

NC

2kΩ

VR12kΩ

INT ±3dB

51pF

51pF

0.1µF

NC

OUTPUT

LEAD-THROUGH

CAPACITORS,1nF

1nF

NC = NO CONNECT

+5V

VOUT

AD8307INP VPS ENB INT

INM COM OFS OUT

8 7 6 5

2 3 41

50Ω INPUTFROM P.A.

1µW TO1kW

22Ω

Time-gain-control with AD8335

BEAMFORMERCENTRAL CONTROL

Rx BEAMFORMER(B AND F MODES)

COLORDOPPLER (PW)PROCESSING

(F MODE)

IMAGE ANDMOTION

PROCESSING(B MODE)

SPECTRALDOPPLER

PROCESSINGMODE

DISPLAYAUDIOOUTPUT

TX BEAMFORMER

CW (ANALOG)BEAMFORMER

LNAs

TRANSDUCERARRAY

128, 256 ETC.ELEMENTS

BIDIRECTIONALCABLE

HVMUX/

DEMUX

T/RSWITCHES

TX HV AMPs

MULTICHANNELTGC USES MANY VGAs

TGCTIME GAIN COMPENSATION

VGAsAD8335

Ultrasound processor changes AD8335 gain to account for changes in signal strength with tissue depth

ADC driver amplifiers

High performance ADCsRecent high performance ADCs have 16-bits and more at 200MSPS

and higherSuch performance requires a differential input signal

Differential amplifiersDifferential or single-ended input converted to differential outputLow impedance output stage rejects ADC switching spikesCommon mode level set and gain setting allow optimum match to

ADC range

ADC driver

2.4MHzBPF

FROM50ΩSIGNALSOURCE

ADA4932-1

VCM VDD1 VDD2 VIO

VOCM

AD8031

AD7626

0.1µF

0.1µF

+5V

+5V +2.5V +2.5V

R3499Ω

R5499Ω

R253.6Ω

R153.6Ω

C12.2nFR439Ω

0.1µF

0.1µF

0.1µF

R7499Ω

R6499Ω

+2.048V

1

5 6 7 8

–FB

2

9

+IN

3 –IN

4 +FB

16 15 14 13

+7.25V

–2.5V

+VS

–VS

–OUT

+OUT

PAD

R833Ω

R933Ω

11

10

C556pF

C656pF

IN–

IN+

0V TO+4.096V

+4.096VTO 0V

GND

0.1µF 0.1µF 0.1µ

ADA4932 differential output drives differential input of 16-bit 10MSPS AD7626 ADC

ADC Input Clamp Amplifiers

Imaging systemsUltrasound and imaging systems often exhibit high-level

transients in practiceInput signals can easily exceed supply and ADC input rangeLong recovery times can impair image stability

Clamp amplifiersClamp amplifiers capture and suppress input transientsAmplifier output does not exceed ADC rangeTransient recovery takes a few nanoseconds

AD8036/AD8037 Clamp Amplifier Equivalent Circuit

+

-A1

RF

140

VOUT

-VIN

+VIN

VH

+1

+1

+1

+

-

+

-

CH

CL

VL

A

B

C

S1

A2+1

S1 A B C

VIN > VH 0 1 0

VL VIN VH 1 0 0

VIN < VL 0 0 1

Comparison of Input and Output Clamping

AD8475: Differential Funnel Amp & ADC DriverKEY FEATURES Active precision attenuation

(0.4x or 0.8x) Level-translating

VOCM pin sets output common mode Single-ended to differential conversion Differential rail-to-rail output Input range beyond the rail

KEY SPECIFICATIONS 150 MHz bandwidth 10 nV/√Hz output noise 50 V/μS slew rate -112dB THD+N 1 ppm/°C max gain drift 500 μV max output offset 3 mA supply current

BENEFITS Connect industrial sensors to high

precision differential ADC’s Simplify design Enable quick development Reduce PCB size Reduce cost

APPLICATIONS Process control modules Data acquisition systems Medical monitoring devices ADC driver

Low Voltage ADC Inputs

Large InputSignal

AD8475 AD7982

REF

+5V

10kΩ

10kΩ

+IN 0.4x

-IN 0.4xVOCM

+5V

+IN

-IN

20Ω

20Ω270pF

270pF

1.35nF

0.5V – 4.5VVOUT(DIFF) ±4V

0.1µF

4V 2.5V

0.5V – 4.5VVOUT(DIFF) ±4V

4V 2.5V

SNR=97dBTHD=-113dB

ADR435

0V±10V

Interface ±10V or ±5V signal on a single-supply amplifier Integrate 4 Steps in 1

Attenuate Single-Ended-to-Differential Conversion Level-Shift Drive ADC

Drive differential 18-bit SAR ADC up to 4MSPS with few external components

AD8475 : Funnel Amplifier + ADC Driver

Balanced Audio Transmission System

Video Difference Amplifier with Variable Common

GM

VP

VOUT

INPUTCOMMON

VN

0.1µF

AD8301

2

3

4

8

7

6

5

A = 1

C

0.1µF

INPUTSIGNAL

V1

V2

OUTPUTCOMMON

V3VOUT = V1 – V2 + V3

AD830 allows different input and output common mode voltage for matching ADC input range

APPLICATIONS FOR ISOLATION AMPLIFIERS

Sensor is at a High Potential Relative to Other Circuitry(or may become so under Fault Conditions)

Sensor May Not Carry Dangerous Voltages, Irrespective of Faults in Other Circuitry(e.g. Patient Monitoring and Intrinsically Safe Equipment for use with Explosive Gases)

To Break Ground Loops

AD210 3-PORT ISOLATION AMPLIFIER

MODDEMODFILTER+

_ _

+

INPUTPOWERSUPPLY

OUTPUTPOWERSUPPLY

POWEROSCILLATOR

T1

T2 T3

INPUT OUTPUT

POWER

FB

–IN

+IN

ICOM

+VISS

–VISS

PWR PWR COM

VO

OCOM

+VOSS

–VOSS

AD210 ISOLATION AMPLIFIER KEY FEATURES

Transformer Coupled

High Common Mode Voltage Isolation:

2500V RMS Continuous

±3500V Peak Continuous

Wide Bandwidth: 20kHz (Full Power)

0.012% Maximum Linearity Error

Input Amplifier: Gain 1 to 100

Isolated Input and Output Power Supplies,

±15V, ±5mA

MOTOR CONTROL CURRENT SENSING

MODDEMODFILTER+

_ _

+

INPUTPOWERSUPPLY

OUTPUTPOWERSUPPLY

POWEROSCILLATOR

T1

T2 T3

INPUT OUTPUT

POWER

FB

–IN

+IN

ICOM

+VISS

–VISS

PWR PWR COM

VO

OCOM

+VOSS

–VOSS

REF

+15V

–15V

HIGH VOLAGEAC INPUT < 2500V RMS

M

RG0.01W AD620

AD210

+15V

+

_

RG = 499W

FOR G = 100

OUTPUT

Fundamentals Webcasts 2011

January Introduction and Fundamentals of Sensors February The Op Amp March Beyond the Op Amp April Converters, Part 1, Understanding Sampled Data Systems May Converters, Part 2, Digital-to-Analog Converters June Converters, Part 3, Analog-to-Digital Converters July Powering your circuit August RF: Making your circuit mobile September Fundamentals of DSP/Embedded System design October Challenges in Industrial Design November Tips and Tricks for laying out your PC board December Final Exam, Ask Analog Devices

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