Upload
eeweb
View
234
Download
5
Tags:
Embed Size (px)
DESCRIPTION
Interview with Vikas Vinayak - CEO and Co-Founder of Quantance; The Highs and Lows of Resistance Measurements - Pt. 3; Homemade Tools - Pt. 2; RTZ - Return to Zero Comic
Citation preview
1Visit www.eeweb.com
EEWeb PULSE INTERVIEW
Electrical Engineering CommunityElectrical Engineering Community
VIKAS VINAYAKCEO & CO-FOUNDERQUANTANCE
VIKAS VINAYAKCEO & CO-FOUNDERQUANTANCE
Issue 69 October 23, 2012Issue 69 October 23, 2012
ExpertsExchanging IdeasEvery Day.VISIT DIGIKEY.COM/TECHXCHANGE TODAY!
Digi-Key is an authorized distributor for all supplier partners. New products added daily. © 2012 Digi-Key Corporation, 701 Brooks Ave. South, Thief River Falls, MN 56701, USA
EEWeb PULSE TABLE OF CONTENTS
3Visit www.eeweb.com
Vikas Vinayak QUANTANCE
Interview with Vikas Vinayak - CEO & Co-Founder
How measuring resistances of mega-ohms or more comes with its own set of challenges and requires different measurement methods.
RTZ - Return to Zero Comic
Featured Products
BY JONATHAN TUCKER WITH KEITHLEY
4
9
14
22
Highs and Lows of Resistance Measurements:
Homemade Tools - Part 2
26
BY PAUL CLARKE WITH EBM-PAPSTAfter detailing the beginnings of a homemade temperature data logger in Part 1, this second installment describes how to finish the project using an mbed.
Can You Trust Your Test? Part 3
4
EEWeb PULSE INTERVIEW
EEWeb | Electrical Engineering Community
VikasVinayak
Q U A N T AN
CE
2726 Visit www.eeweb.com
EEWeb PULSE INTERVIEW
EEWeb | Electrical Engineering Community
5Visit www.eeweb.com
EEWeb PULSE INTERVIEW
VikasVinayak
Q U A N T AN
CE
2726 Visit www.eeweb.com
EEWeb PULSE INTERVIEW
EEWeb | Electrical Engineering Community
Quantance is a venture-backed semicon-ductor company based out of Silicon Val-ley. Their goal is to ensure that PAs transmit higher power and operate more efficient-ly for mobile devices. We spoke with Vikas Vinayak, the CEO and Co-founder, about his history in tech start-ups, the qBoost Envelope Tracking technology and how
Quantance is well on its way to changing the LTE market.
6
EEWeb PULSE INTERVIEW
EEWeb | Electrical Engineering Community
Can you tell us about your work experience before becoming the CEO and Co-Founder at Quantance?
After graduating from college, and as the first Gulf War was ending, the monopolistic hold of the Indian government on Indian television was loosened with the emergence of CNN. Suddenly during prime time you could view more than planting wheat – you could watch CNN and learn what was happening in the world. Then came MTV, and I thought people would certainly prefer music videos to planting wheat. As a result, I believed there was an enormous opportunity for products targeting the growing cable television (CATV) market in India.
Will you tell us about co-founding TouchBeam Systems? What were your roles and responsibilities at this company?
My friends and I decided to go after this opportunity, and we founded TouchBeam Systems to address the CATV market. I became the co-CEO. TouchBeam produced and delivered the first Vestigial Sideband Modulator for the CATV market in India, and expanded that to 85 hardware products designed to meet the growing needs of CATV operators. We’re talking about the distribution of equipment used by cable operators in homes across India. Our products got the signal from the satellite to the receiver in those homes.
Can you tell us about Quantance and the technology you are developing?Quantance is a fabless semiconductor company that makes the industry’s highest performance power supplies. Our
mission is to enable high PA (power amplifier) efficiency and associated RF Front End cost reduction while significantly increasing data throughput from 3G and 4G mobile terminals. In this pursuit, we have
“Quantance is working on delivering an optimized system
solution – an ecosystem – that uses a patented algorithmic approach to adjust the
voltage available to the power amplifier for voice and data.”
developed a unique, high-speed, high-efficiency power supply technology known as qBoost™. It does not add cost to a wireless device, yet enables the cellular chipset to track the RF
signal envelope, supplying only the minimum power required by the PA in real time. This approach to closely managing the PA is known in the industry as “Envelope Tracking” or simply “ET.” The qBoost ET solution replaces the DC/DC switching power supply currently used to provide APT (average power tracking) power solutions, and upgrades that functionality.
We noticed an underlying theorem governing the partitioning of energy flow in all power supplies, which could be exploited to make
better power supplies if two different power supplies could be combined. However, combining these two different power supplies is challenging, and we founded Quantance to discover a way to accomplish this task.
In our people, Quantance has a deep knowledge about RF transceiver and digital baseband solutions. Our developers use that knowledge to focus on the battery and the antenna – the two most critical aspects of the mobile device – and the path connecting them.
We created a new architecture, which had an interesting and unanticipated consequence of making an AC Boost power supply out of a high performance buck convertor. This solved all the front-end problems of heat, mismatch, broadbanding, throughput, unwanted antenna radiation and signal clarity in a unified way. There are many ways to solve one or more of these problems with other engineering techniques, but we believe our approach is the only holistic and systemic one.
Now we have commercialized this power supply over three generations of continually improving and evolving product designs.
A lot of companies are building chips to solve a growing pain for the electronics industry – how to deal with the greater power needed for data in handsets/technology originally designed for voice. If you think about it, the radio signals, or RF, used to transmit voice on a handset are not optimized for data, which requires more power to transfer. Current models are operating inefficiently, creating excessive heat and causing batteries to drain faster.
Quantance is working on delivering an optimized system solution – an
7Visit www.eeweb.com
EEWeb PULSE INTERVIEW ecosystem – that uses a patented algorithmic approach to adjust the voltage available to the power amplifier for voice and data. By doing so, the solution would result in greater efficiency, reduced heat, improved battery life, and better performance in terms of fewer dropped calls. We are building this on the fastest power supply to deliver the exact amount of power required for a specific application at the exact time it’s needed.
The Quantance qBoost ET solution is an entire ecosystem of innovation – soft wrapping around a hard product that delivers unique differentiation to our customers. Handsets are just the first market we’re targeting. The consumer electronics market is wide open and now with the growing use of wireless networks, most devices can benefit from our unique approach.
Can you tell us more about Quantance’s products?
Our main product is our third generation single-chip ET product known as the Q845. Featuring the latest qBoost ET innovations, the Q845 is a very high-speed power supply that generates the supply voltage to deliver the exact amount of power to the most power-hungry circuit inside a cell phone when needed. The most power-hungry circuit is the power amplifier that generates the radio frequency waves that carry the data bits back and forth from your handset to the base station many miles away. The power requirements of the circuit change very rapidly. As cell phones evolve from 2G to 3G to 4G, the rate at which these power requirements change becomes even more rapid and therefore, if you have a very high-speed and high-performance power supply, you can deliver the
exact amount of power, no more, no less. When you deliver only the exact amount of power, there is no excess power that gets burned up as heat and circuits get cooler and when circuits run cooler, they work faster. The net result is, with our technology, an increase in the upload speed of your phone by up to three times.
a car analogy: if you expect your car to go faster, you expect your engine to produce more power, not less. When you go from voice to data, you actually reduce the maximum power that you transmit. The reason is that when you go from voice to data, you add more variation to the signal that you’re transmitting, because you have to incorporate more bits. Because the maximum power of an amplifier is fixed, if you increase the maximum-to-average ratio, that average must go down, because the maximum absolute power is constant.
Can you tell us about Quantance’s qBoost™ Envelope Tracking technology?
With qBoost, we are able to deliver the highest performing, end-to-end ET ecosystem. It includes the Quantance power supply silicon, proprietary noise reduction algorithms that run on the cellular baseband, power amplifiers optimized for envelope tracking, backward compatibility with APT, field measurements audited by carriers, and unique removal of MPR (maximum power reduction) to increase data transmission speeds.
Does this technology compensate for other variables?
The maximum power that a power amplifier can put out is normally constant. An interesting fact is that in every phone—big-name brands included—puts out half the power in data mode as compared to voice mode. Data obviously takes more bits per second than voice. To use
8
EEWeb PULSE INTERVIEW
EEWeb | Electrical Engineering Community
Our ET solution combines analog and digital power supplies using a patented and deeply mathematical approach involving algorithms from statistical communication theory to create very fast power supplies that work well with sensitive RF front-end circuits while meeting all system noise requirements. The result is fast, efficient power supply that boosts PA voltage above the battery level to meet RF peak demand for higher power and data throughput. It then lowers PA voltage to match reduced RF output power demand for higher efficiency and reduced current. Our power supply has the equivalent switching rate of 400 MHz for best-in-class ET technology.
Do most power amplifiers in current phones work with your power supply technology?
The power amplifiers that are being shipped to 800 million cell phones
a year are designed to work with very slow power s u p p l i e s . They include capacitors to absorb the t r a n s i e n t s that occur in t r a d i t i o n a l designs. In ET systems these c a p a c i t o r s become both unnecessary and an impediment. For amplifiers, we need to remove this capacitor, which is normally a discrete capacitor in the PA module.
In the last 12 months, the momentum behind this technology has been accompanied by a push and a pull. Every single carrier that we are aware of understands the benefits that envelope tracking brings to
the user experience and to network capacity, and they are creating the pull for it. Every single handset manufacturer is coming in to push this technology for additional smart phone performance benefits. Once the ecosystem has signed up to an explicit recognition of the need of this technology, every power amplifier manufacturer will embrace envelope tracking-compliant amplifiers. Today, we are engaged
“ When you deliver only the exact amount of power,
there is no excess power that gets burned up as heat and circuits get
cooler and when circuits run cooler, they work
faster. The net result is, with our technology, an increase in the upload speed of your phone by
up to three times. “
9Visit www.eeweb.com
EEWeb PULSE INTERVIEW
with several PA manufacturers that have sampled us ET optimized PAs.
What direction do you see Quantance heading in the next few years and what challenges do you foresee along the way?
As the LTE market continues on its exponential growth path, we believe there will be a greater a need for a holistic way to solve the RF problem from the antenna back to the battery, and Quantance participates by contributing more to the system.
Quantance will continue to deploy our unique power supply in all forms of wireless technologies. Many modern consumer devices – even beyond smartphones – transmit radio signals. Almost all of those devices can benefit from our technology.
The proliferation caused by
geographies and newer data standards, such as LTE, has forced an explosion in the RF transmit chains that must be supported in handsets. This is leading to increased strains on cost and size – which is critically important to device makers because of the cost and innovation required to meet consumer demands. Devices must be able to work in multiple modes and geographies, while supporting multiple frequency plans. All of this requires multiple power amplifiers. We hope that with judicious use of other technologies, Quantance can help to eliminate many of those problems.
Optocouplers are the only isolation devices that meet or exceed the IEC 60747-5-5 International Safety Standard for insulation and isolation. Stringent evaluation tests show Avago’s optocouplers deliver outstanding performance on essential safety and deliver exceptional High Voltage protection for your equipment. Alternative isolation technologies such as ADI’s magnetic or TI’s capacitive isolators do not deliver anywhere near the high voltage insulation protection or noise isolation capabilities that optocouplers deliver.
For more details on this subject, read our white paper at: www.avagoresponsecenter.com/672
Take the Risk out of High Voltage Failure with Certifi ed Avago Optocouplers
Technology You Can Trust
IEC 60747-5-5 Certifi ed
FEATURED PRODUCTS
11Visit www.eeweb.com
High Definition Oscilloscope w/12-Bit ADCTeledyne LeCroy introduced two series of High Definition Oscilloscopes with HD4096 high definition technology, the HDO4000 and HDO6000. Oscilloscopes with HD4096 acquire waveforms with high resolution, high sample rate, and low noise. Waveform displays are cleaner and crisper with 16 times more vertical resolution than traditional 8-bit instruments. The HDO4000 and HDO6000 are available in bandwidths from 200 MHz to 1 GHz. All HDO models sport a large 12.1” touch-screen display and intuitive interface to enhance operation and also provide powerful debug tools, plus a full complement of automatic measurements and waveform math capabilities. For more information, please click here.
Standalone 4-10 Cell Precision ProtectorThe bq77910A is a battery protection and cell balancing device intended for Li-ion and Li-Polymer battery packs.The bq77910A monitors 4- to 10-series individual cell voltages and provides fast-acting outputs which may be used to drive N-channel MOSFETs to interrupt the power path. Activation delays and recovery methods for safety conditions are fully programmable in non-volatile memory. Automatic cell balancing is provided using internal 50-mA cell circuits. A robust balancing algorithm ensures optimum performance by maintaining all cell voltages in balance. For more information, please click here.
First CAN-Based Sensor for Auto Battery MonitoringFreescale Semiconductor introduced the MM9Z1J638 Xtrinsic battery sensor, the industry’s first CAN-based battery sensor that accurately measures the voltage, current and temperature of lead-acid and lithium-ion batteries, as well as calculating the battery state – all while operating in harsh automotive conditions. Accurate knowledge of these battery parameters has become critical due to the increase in hybrid vehicles and overall electronic content, as well as the introduction of start-stop systems in automobiles. For more information, please click here.
Low Power 16-bit 20Msps ADCsLinear Technology Corporation introduces three low power 16-bit, 20Msps analog-to-digital converters (ADCs), the LTC2269, LTC2270 and LTC2271, offering the lowest input-referred noise and tight integral nonlinearity error (INL) for very high precision DC measurements. With only 46µVRMS input noise and maximum guaranteed INL error of ±2.3LSB, these ADCs are suitable for very low noise, high linearity sampling applications such as digital x-ray, infrared and medical imaging, pachymeters, spectrometry and cytometry. These devices achieve signal-to-noise ratio (SNR) performance of 84dB and SFDR of 99dB at baseband. For more information, please click here.
Optocouplers are the only isolation devices that meet or exceed the IEC 60747-5-5 International Safety Standard for insulation and isolation. Stringent evaluation tests show Avago’s optocouplers deliver outstanding performance on essential safety and deliver exceptional High Voltage protection for your equipment. Alternative isolation technologies such as ADI’s magnetic or TI’s capacitive isolators do not deliver anywhere near the high voltage insulation protection or noise isolation capabilities that optocouplers deliver.
For more details on this subject, read our white paper at: www.avagoresponsecenter.com/672
Take the Risk out of High Voltage Failure with Certifi ed Avago Optocouplers
Technology You Can Trust
IEC 60747-5-5 Certifi ed
En
a b l i ng t h e S m a r t S o c i e t y
Join us this Fall! Hands-on Labs, Seminars, Meet the Experts, Demos, Partner Solutions and much more!
Machine to MachineComputing ArchitecturesCloud ComputingAnalog & PowerDevelopment ToolsConnectivityOperating Systems
SESSION TRACKS
Human Machine InterfaceDisplay Technologies
System DesignMotor Control
AutomotiveSecurity
Guest SpeakerDean Kamen
R E G I S T E R N O W !
RenesasDevCon.com
O C T O B E R 2 2 - 2 5 , 2 0 1 2
For all things DevCon – including up-to-date course information, lodging and registration details – go to:
O C T O B E R 2 2 - 2 5 , 2 0 1 2
Computing Architectures
Hosted by the Number One
MCU Supplier Worldwide*
Dean Kamen landed in the limelight with the Segway, but he has been innovating since high school, with more than 150 patents under his belt. Recent projects include portable energy and water purification for the developing world.
Hyatt Regency Orange County, CAHyatt Regency Orange County, CAHyatt Regency Orange County, CAHHHHHHHyatt Regencyyatt Regencyyatt Regencyyatt Regencyyatt Regencyyatt Regencyyatt RegencyOrange County, CAOrange County, CAOrange County, CAOrange County, CAOrange County, CAOrange County, CAOrange County, CAHyatt Regency Orange County, CA
K e y S p o n s o r s
© 2012 Renesas Electronics America Inc. *Source: Gartner 2011 Worldwide Semiconductor Market Share Database, March 2012 results
Meet the Experts
Design Issues for Systems That Use LCD Panels
M2M Development
Development Ecosystem and Services
Customer Feedback
Expert Panel: The Auto Industry Speaks
Expert Panel: The Future of Auto Software/System Development
Model-based Development
Simulation: Expert Insights into Modelling Microcontrollers
Automotive
Cost Effective HIL for Rapid Prototyping
Virtual HIL test/ISO 2626 using Processor Models
Introduction to Velocity Lab
Infotainment & Instrumentation Solutions
QuantiPhi for RL78: The Fastest Path from Idea to Implementation
Simulation: Moving Development into the Virtual World
Active Safety SolutionsGraphic System Design Considerations
Insights into MCU & Mixed Signal Design
Automotive Quality/Failure Analysis
Working with AUTOSAR
Trends in Automotive Communication
Improve a Product’s User Experience with Model-based UI Design
Intelligent Power Devices
Mastering Functional Safety and ISO 26262
Advanced SOC for Telematics and Infotainment
MICON Racing – Qualify using QuantiPhi for RL78
Using Processor Models for Software Development and Validation
HEV/EV Traction Motor Control Lab
Computing Architecture
Renesas Next-generation Microcontroller and Microprocessor Technology Roadmap
Microcontroller Solutions Enabling a Greener Society
The Core Difference: When the Core Matters
RH850 & RL78: Introducing the Next Generation of Microcontollers for Automotive Applications
Benchmarking using EEMBC
Optimizing Performance of RX-based Applications
Connectivity
Industrial Ethernet
Instant Connectivity for the “Internet of Things”
PLM-1 Modem
Renesas Connecting through 802.15.4 Radio
CMX TCP-IP
LibUSB: Create a Solution Without the Class Struggle
CAN In a Day: Using the RX CAN API
IR and Bluetooth Connectivity Using the RL78
Development Tools
Getting Started with Renesas Development Tools
Introduction to e2studio, The New Eclipse-based IDE from Renesas
Getting the most out of the Renesas Demonstration Kits (RDKs)
Trends in Embedded Software Development
High-performance Compiler Solutions for Renesas MCUs
Getting the Most Out of the GNU Toolchain
Getting Started with e2studio, The New Eclipse-based IDE from Renesas
Introduction to the RX Arduino
Using Embedded Tools for I2C, SPI, and USB Debugging and Develop-ment on the Renesas RX63N RDK
Seeing Inside your Target at Run-time with µC/Probe
Advanced Debugging with the RX600
Migration from HEW to Eclipse
Migration from Cube Suite to Eclipse
Using Software Building Blocks for Faster Time-to-market
VectorCAST Tools: A Complete Test Environment for Safety-critical Applications
Using a Renesas Code-generation Tool for RL78 Devices
e2studio Advanced Topics
Advanced Debugging on RX with IAR Embedded Workbench
Security
NFC Ecosystem and Solutions
Hardware Roots of Trust – A Foundation for Security
Security Solutions for the Automotive Industry
Security Solutions Part 1: Javacard Applet Development Training
Security Solutions Lab 2: Secure Host Firmware Upgrade using BoardID Secure Solution
Human Machine Interface
Audio Solutions on the RX MCU Family
Capacitive Touch Based User Interfaces and Hardware-based Solutions
Enhance Embedded Designs with Low-cost TFT LCD Solutions
Embedded Vision: Creating “Machines that See”
Driving E Ink Displays
Direct-drive LCD
Using Altia to Design a GUI and Deploy it on Renesas SH7269
Extreme Makeover with the RX600: Adding Touch/Graphics to Your Product
Direct-drive LCD Software Integration for the RX62N/RX63N
Incorporating a Capacitive Touch Interface into Your Design
Industrial Controls GUI Application Using emWin
Display
Flat Panel Displays: LCD Technologies and Trends
Flat Panel Displays: Touch Panel Technologies and Integration
Flat Panel Displays: Beyond the Basics
Flat Panel Displays: How to Over-come High Ambient Light Conditions
Flat Panel Displays: Exploring a 2D/3D Solution
Flat Panel Displays: Advanced Technology TrendsM2M and Cloud Solutions
Energy-efficient Communications with Wi-Fi
Adding Wi-Fi to Embedded Applications
Wireless Connectivity for Embedded Systems
M2M: How to Create Revenue- generating Services and Applications
Wireless SensorsWireless TransceiversM2M: Cloud Connectivity with RX and Exosite
Power
IGBT vs. Mosfet: Which Device to Select?
How to Make Your House Smarter
Digital Power: Design and Architectural Trade-offs
Increasing the Performance of PFC and LED Driver IC Applications
Optical Isolation, SSR Switching, and Ambient Light Sensing in MCU-based Applications
IGBTs for HEV/EV
Motor Control
Power Factor Correction: Why and How?
Sensorless Vector Control and Implementation: Why and How
Know your Precise Position with RX600 MCUs
Field-oriented Control Using a 16-bit Low-power MCU
Operating Systems
Using ThreadX and IAR Embedded Workbench on the RX Processor
Introduction to RoweBots’ Ultra Tiny Linux™ RTOS
Embedding USB: Implementation Challenges and Limitations
FreeRTOS Lecture
Rapid Development on the Renesas RX63N RDK using µEZ® and FreeRTOS
Introduction to Python
Software Development with an Open Source Real-time Operating System
HTML5 HMI Development with QNX
Developing Next-gen Automotive User Interface using EB GUIDE 5.3 w/Windows Embedded Automotive 7 and Renesas R-Car H1
Getting Started with Micriµm’s µC/OS-III Kernel
Embedding TCP/IP: Working Through uC/TCP-IP Usage
Introduction to the .NET Micro Framework
System Design Technologies
Are all Batteries Created Equal?
A/D Converter Fundamentals
Designing Modern Medical Systems
Digital Filtering on a MCU
Infinite Runtime: Energy Harvesting with Renesas MCUs
Moving from 8-bit to 32-bit MCUs
Battery Management
ADC Resolution: Myth and Reality
Exploring the Safety Features of the RX210
Low-power Design
Increase the Dynamic Range and Precision of Digital Filters Using a FPU
RL78 Project Configuration Tips
RX Project Configuration Tips
Sensor Fundamentals
Extreme Low-power Design: Tools, Design Techniques and Implementation
Creating Virtual EEPROM on Renesas MCUs
Implementing Bootloaders on Renesas MCUs
Designing Energy Harvesting Applications with the RL78
Portable Instrumentation Applications with the RL78
Embedded Systems Bootcamp
For course descriptions, visit RenesasDevCon.com
RenesasDevCon.comRegister Today! Limited Space Available.
EEWeb PULSE TECH ARTICLE
14 EEWeb | Electrical Engineering Community
The Highs and Lows ofResistance Measurements:Can You TrustYour Test?
Part 3
Jonathan TuckerSenior Marketer And Product ManagerTektronix/Keithley Instruments
EEWeb PULSE TECH ARTICLE
15Visit www.eeweb.com
The Highs and Lows ofResistance Measurements:Can You TrustYour Test?
Part 3
Jonathan TuckerSenior Marketer And Product ManagerTektronix/Keithley Instruments
Measuring resistances of mega-ohms or more comes with its own set of challenges and requires different measure-ment methods. The sources of error for high resistance measurements are also quite different than those that af-fect low ohms measurements. High impedance insulators are an integral part of today’s high performance electron-ic products. The purity of the materials used to construct these insulators can make the difference between a prod-uct that works properly and one that doesn’t work at all. For example, crystalline materials are fundamental to modern electronics and optoelectronics.
EEWeb PULSE TECH ARTICLE
16 EEWeb | Electrical Engineering Community
Therefore, the electrical properties of these materials, such as their (anisotropic) conductivity and photoconductivity, as well as the temperature dependencies associated with these properties, are of great interest to researchers. The crystals grown using a number of crystallization techniques may be small in size and often exhibit very high resistances (Figure 1).
When resistances greater than one mega-ohm must be measured, an electrometer, SMU, or picoammeter/voltage source combination is usually required. An electrometer may measure high resistance by either the constant-voltage or the constant-current method. Some electrometers allow the user to choose either method. The constant-voltage method uses an ammeter and a voltage source, while the constant-current method uses an electrometer voltmeter and a current source, similar to most DMMs.
The most accepted method of measuring high resistance is to apply a large voltage to a sample and measure the small currents stimulated through that sample. However, for high resistance samples, the levels of current that must be measured are extremely low, so testing these materials accurately and repeatably can be a challenge. Other current sources, such as piezoelectric effects or discharging capacitive elements, can obscure the stimulated current that must be observable in order to calculate resistance.
The basic configuration of the constant-voltage method using an electrometer or picoammeter is shown in Figure 2a. As shown in Figure 2b, an SMU can also be used for making high resistance measurements using the constant-voltage method.
In this method, a constant voltage source (V) is placed in series with the unknown resistor (R) and an ammeter (IM). Given that the voltage drop across the ammeter is negligible, essentially all the test voltage appears across R. The resulting current is measured by the ammeter and the resistance is calculated using Ohm’s Law (R= V/I).
High resistance is often a function of the applied voltage, which makes the constant-voltage method preferable to the constant-current method. By testing at selected voltages, a resistance vs. voltage curve can be developed and a voltage coefficient of resistance can be determined. Some of the applications that use this method include testing two-terminal high resistance devices, measuring insulation resistance, and determining the volume and surface resistivity of insulating materials.
The constant-voltage method requires measuring low current. The two most common error sources when measuring high resistance are electrostatic interference and leakage current. Electrostatic interference can be minimized by shielding the high impedance circuitry. Interferences due to leakage current can be controlled by guarding.
Figure 1: High resistance measurement on crystalline material. (2003 photo courtesy of Dr. Felix Budde, formerly of the MacDiarmid Institute of Advanced Materials and Nanotechnology in Wellington, New Zealand)
Figure 2: Constant-voltage method for measuring high resistance
EEWeb PULSE TECH ARTICLE
17Visit www.eeweb.com
Guarding high resistance test connections can significantly reduce the effects of leakage resistance and improve measurement accuracy. Consider the unguarded resistance measurement setup shown in Figure 3. Here, an electrometer ohmmeter is forcing a current (IR) through the unknown resistance (RS) and then measuring the voltage (VM) across the DUT.
Assuming that the meter has infinite input resistance, the measured resistance is RM = VM / IR. However, because the cable leakage resistance (RL) is in parallel with RS, the actual measured resistance (RM) is reduced.
The loading effects of cable resistance (and other leakage resistances) can be virtually eliminated by driving the cable shield with a unity-gain amplifier, as shown in Figure 4.
Given that the voltage across RL is essentially zero, all the test current (IR) now flows through RS, and the source resistance value can be accurately determined. The leakage current (IG) through the cable-to-ground leakage path (RG) may be considerable, but that current is supplied by the low impedance output of the ×1 amplifier rather than by the current source (IR).
Guarding
Figure 3: Effects of cable resistance on high resistance measurements
Figure 4: Guarding cable shield to eliminate leakage resistance
EEWeb PULSE TECH ARTICLE
18 EEWeb | Electrical Engineering Community
The settling time of the circuit is particularly important when making high resistance measurements. The settling time of the measurement is affected by the shunt capacitance, which is due to the connecting cable, test fixturing, and the DUT. As shown in Figure 5, the shunt capacitance (CSHUNT) must be charged to the test voltage by the current (IS). The time period required for charging the capacitor is determined by the RC time constant (one time constant, = RSCSHUNT).
Therefore, it becomes necessary to wait four or five time constants to achieve an accurate reading. When measuring very high resistance values, the settling time can range up to minutes, depending on the amount of shunt capacitance in the test system. For example, if CSHUNT is only 10 pico-farads, a test resistance of one tera-ohm will result in a time constant of 10 seconds. Therefore, a settling time of 50 seconds would be required for the reading to settle to within 1% of final value. In order to minimize settling times when measuring high resistance values, keep shunt capacitance in the system to an absolute minimum by keeping connecting cables as short as possible. Also, guarding may be used to decrease settling times substantially. Finally, the source voltage, measure current method of resistance measurement is generally faster because of reduced settling times.
REFERENCES
1. Joseph F. Keithley, The Story of Electrical and Magnetic Measurements: From 500 BC to the 1940s, IEEE Press, 1999, p. 93.
2. Keithley Instruments, Inc., Low Level Measurements Handbook, 6th Edition, 2004.
3. “Making High Resistance Measurements on Small Crystals in Inert Gas or High Vacuum with the Model 6517A Electrometer/High Resistance System,” Application Note #2464, Keithley Instruments, 2003.
4. Keithley Instruments, Inc., “Improving the repeatability of ultra-high resistance and resistivity measurements,” White Paper, 1997.
About the AuthorJonathan Tucker is a Senior Marketer and Product Manager for Keithley Instruments in Cleveland, Ohio, which is part of the Tektronix test and measurement portfolio. He is responsible for business development of Keithley’s research and education business with emphasis in the areas of nanotechnology, semiconductor, energy, printable/organic electronics, and electrochem. He is also product manager for Keithley’s sensitive measurement instruments. He joined Keithley Instruments in 1987 and has held numerous positions, including test engineer, applications engineer, applications manager, and product marketer.
Figure 5: Settling time is the result of RSCSHUNT time constant
EEWeb PULSE TECH ARTICLE
Low Voltage ORing FET ControllerISL6146The ISL6146 represents a family of ORing MOSFET controllers capable of ORing voltages from 1V to 18V. Together with suitably sized N-channel power MOSFETs, the ISL6146 increases power distribution efficiency when replacing a power ORing diode in high current applications. It provides gate drive voltage for the MOSFET(s) with a fully integrated charge pump.
The ISL6146 allows users to adjust with external resistor(s) the VOUT - VIN trip point, which adjusts the control sensitivity to system power supply noise. An open drain FAULT pin will indicate if a conditional or FET fault has occurred.
The ISL6146A and ISL6146B are optimized for very low voltage operation, down to 1V with an additional independent bias of 3V or greater.
The ISL6146C provides a voltage compliant mode of operation down to 3V with programmable Undervoltage Lock Out and Overvoltage Protection threshold levels
The ISL6146D and ISL6146E are like the ISL6146A and ISL6146B respectively but do not have conduction state reporting via the fault output.
Features• ORing Down to 1V and Up to 20V with ISL6146A, ISL6146B,
ISL6146D and ISL6146E
• Programmable Voltage Compliant Operation with ISL6146C
• VIN Hot Swap Transient Protection Rating to +24V
• High Speed Comparator Provides Fast <0.3µs Turn-off in Response to Shorts on Sourcing Supply
• Fastest Reverse Current Fault Isolation with 6A Turn-off Current
• Very Smooth Switching Transition
• Internal Charge Pump to Drive N-channel MOSFET
• User Programmable VIN - VOUT Vth for Noise Immunity
• Open Drain FAULT Output with Delay- Short between any two of the ORing FET Terminals- GATE Voltage and Excessive FET VDS- Power-Good Indicator (ISL6146C)
• MSOP and DFN Package Options
Applications• N+1 Industrial and Telecom Power Distribution Systems
• Uninterruptable Power Supplies
• Low Voltage Processor and Memory
• Storage and Datacom Systems
TABLE 1. KEY DIFFERENCES BETWEEN PARTS IN FAMILY
PART NUMBER KEY DIFFERENCES
ISL6146A Separate BIAS and VIN with Active High Enable
ISL6146B Separate BIAS and VIN with Active Low Enable
ISL6146C VIN with OVP/UVLO Inputs
ISL6146D ISL6146A wo Conduction Monitor & Reporting
ISL6146E ISL6146B wo Conduction Monitor & Reporting
FIGURE 1. TYPICAL APPLICATION FIGURE 2. ISL6146 GATE HIGH CURRENT PULL-DOWN
VIN GATE VOUT
GND
ADJ
+
-
+
VOUT
+
-
+ COMMONPOWERBUS
Q1
ISL6146BFLT
BIAS
VOLTAGE
DC/DCVOLTAGE
DC/DC
EN
(3V - 20V)
(3V - 20V)
Q2
COMMONPOWERBUS
VIN GATE VOUT
GND
ADJISL6146B
FLT
BIAS
EN
GATE FAST OFF, ~200ns FALL TIME~70ns FROM 20V TO 12.6V ACROSS 57nFGATE OUTPUT SINKING ~ 6A
October 5, 2012FN7667.3
Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011, 2012All Rights Reserved. All other trademarks mentioned are the property of their respective owners.
Get the Datasheet and Order Samples
http://www.intersil.com
Transform Your iPhone, iPad or iPod into an Oscilloscope
with the iMSO-104
Experience the iMSO-104 as Joe Wolin, co-founder of EEWeb,
gives you an in-depth look into the future of oscilloscopes.
2012
UBM ELECTRONICSUBM ELECTRONICS
WINNER
Begin Your Experience NowBegin Your Experience Now
BeStar®
ACOUSTICS & SENSORS
Teamwork • Technology • Invention • Listen • Hear
PRODUCTSSpeakers
Buzzers
Piezo Elements
Back-up Alarms
Horns
Sirens/Bells
Beacons
Microphones
Sensors
INDUSTRIESAutomotive
Durables
Medical
Industrial
Mobile
Fire / Safety
Security
Consumer
Leisure
QS9000 • TS/ ISO16949 • ISO14001 • ISO13485 • ISO9001
bestartech.com | [email protected] | 520.439.9204
Preferred acoustic componentsupplier to OEMs worldwide
BeStar®
ACOUSTICS & SENSORS
Teamwork • Technology • Invention • Listen • Hear
PRODUCTSSpeakers
Buzzers
Piezo Elements
Back-up Alarms
Horns
Sirens/Bells
Beacons
Microphones
Sensors
INDUSTRIESAutomotive
Durables
Medical
Industrial
Mobile
Fire / Safety
Security
Consumer
Leisure
QS9000 • TS/ ISO16949 • ISO14001 • ISO13485 • ISO9001
bestartech.com | [email protected] | 520.439.9204
Preferred acoustic componentsupplier to OEMs worldwide
From design to service, Microtips offers a variety of competitively priced Liquid Crystal Display modules which includes standard character and graphic monochrome, passive and active color displays with white LED as well as custom LCD modules and complete OEM services.
For your own design needs please contact Microtips Technology: [email protected]
7” High Bright
240 x 160 COG w/LED Backlight
QVGA Green w/LED Backlight
LCD for Any Application
Microtips Technology
Automotive, Medical, Telecom, POSLCD for Any Application
Microtips Technology
Automotive, Medical, Telecom, POS
EEWeb PULSE TECH ARTICLE
22 EEWeb | Electrical Engineering Community18
Back in July I introduced the idea of building your own homemade tools -- stuff that can give you features that tools in the shops can’t, or perhaps just less expensive than those available in stores.
In Part Two I will document the building of my own home tempera-ture data logger using an mbed.
Part 2HomemadeTools Part 1
Paul ClarkeElectronics Design
Engineer
Part 2Back in July I introduced the idea of building your own homemade tools — stuff that can give you features that tools in the shops can’t, or perhaps just less expensive than those available in stores.
In Part Two I will document the building of my own home temperature data logger using an mbed.
EEWeb PULSE TECH ARTICLE
23Visit www.eeweb.com 19
HomemadeTools Part 1
Paul ClarkeElectronics Design
Engineer
EEWeb PULSE TECH ARTICLE
24 EEWeb | Electrical Engineering Community
Using the mbed gets you right off the ground very fast with its microcontroller, compiler online, and wealth of tools, sample code, and available help. I started by looking at the temperature inputs I wanted, and I decided I wanted three temperature inputs. Two of these would use NTC temperature sensors, and the other a thermocouple.
The NTCs are resistors that change value as the temperature around them alters. Having a negative temperature coefficient (NTC) means that as the temperature rises the resistance drops. These sensors come in different shapes and sizes. The ones I have have a resistance of 10k at 25’c. You will find all NTCs have their resistance listed in this way.
My circuit for the NTC could not be more sim-ple. I’m only looking for a basic input, so I will use the NTC as part of a resistor network across the mbeds supply. The center tapping will then be used as an input (analog) to the mbed. The input is very basic and has no filtering, gain, or range control. You could achieve this with a opamp, but I have found that for normal room temperature readings using a matched resistor in the fixed side of the network works well.
To the right, you will see our NTC and 10k re-sistor. This gives a voltage of half rail voltage at 25’c. When the temperature goes up the volt-age at the input goes down.
NTC Circuit
The mbed itself is just as easy to set up by us-ing the AnalogIn class and telling the compiler what pin you have connected your signal too. Each time you want to read the value after that you just use the variable declared. However, for my code I have decided to use the raw values that come from the internal ADC, so I am ac-
cessing the variable using the read_u16 func-tion as shown below:
- Analog In Ain1(p19);
- some Value = Ain1.read_u16();
Thermocouple Input
The thermocouple input is a little more diffi-cult as you can’t just connect it to your mbed. The theromocouple input needs a chip that can amplify the weak signal it generates and then pass it to the mbed. Old chips used to give you a analog voltage, but these days you can connect to these devices over communication buses like SPI. To make our life simpler I have selected the max31855 IC that does just this. And to make things even easier,I got this on a prototype board from TAUTIC. This means no fiddly surface mount soldering – you just have to connect the data and power pins.
NTC Circuit
EEWeb PULSE TECH ARTICLE
25Visit www.eeweb.com
The SPI interfaces to the max chip using a 32 bit block of data. However the pre-written func-tion within the mbed that allows direct access to the SPI bus only goes up to a 16 bit format. This would have made interfacing to the device as easy as the NTC and analog pins. However SPI is really easy to deal with anyway, so below I have written my own code to interface to the device.
SPI_CodeThe last thing I’ll need to add this time round is a serial connection to use for debugging and then later for our Xbee.
Once again this is really easy to add to your mbed. Add the Serial class with the pre-defined RX and TX pins and then install the mbed USB to serial driver on your PC, and you are done!
I use a small free program called putty.exe that can be used as a serial terminal. Set the baud rate to 9600 and coms port (you can find this in device manager under “Serial Ports” in Windows) and then you can get data from your mbed.
Last thing to do this time round is to send the col-lected data, one second at a time, and send it over the se-rial port (code below). The data from the NTCs is still raw ADC counts and not in T’c as yet but the data from the max chip is.
Output Code
Next time I will turn the raw ADC counts into T’c and also
look at storing the data on the mbed’s flash. If you would like to see the full code you can download it form here: http://mbed.org/users/monpjc/code/temperature_logger_Pt2/
You will see that I only need the block of bits from bit 1 (where 0 is the first) to 11. The rest are thrown away. A little shift register in c code and you can quickly get your data from the max chip. I really should look at the timings on a scope but it’s work-ing right now -- I will check the details later on but I suspect I’m well within limits.
Output Code
NXP’s proven interface products enable medical and health system designers
to add features with minimal modifications. Within our portfolio you’ll find LCD
displays and capacitive touch interfaces, system connectivity bridges & UARTs, LED
controllers, real-time clocks, and I2C-bus peripherals & enablers.
To learn more, visit http://www.nxp.com/campaigns/medical-interfaces/2248
Breathe new life into medical product interfaces
NXP’s proven interface products enable medical and health system designers
to add features with minimal modifications. Within our portfolio you’ll find LCD
displays and capacitive touch interfaces, system connectivity bridges & UARTs, LED
controllers, real-time clocks, and I2C-bus peripherals & enablers.
To learn more, visit http://www.nxp.com/campaigns/medical-interfaces/2248
Breathe new life into medical product interfaces