Analog Diablog™

Designing a Low-Power Toxic Gas Detector

2012-01-30T16:16:00.000-05:00

Safety first! Many industrial processes involve toxic compounds, including chlorine, phosphine, arsine, and hydrogen cyanide, so it is important to know when dangerous concentrations exist.This article describes a portable carbon monoxide detector using an electrochemical sensor. CO is relatively safe to handle, but it is still lethal, so use extreme care and appropriate ventilation when testing the circuit described here.

Robust Amplifiers Provide Integrated Overvoltage Protection

2012-01-30T16:15:00.000-05:00

Faulty performance or damage can occur when an op amp’s input voltage exceeds the specified input-voltage range. This article discusses some common causes and effects of overvoltage conditions, how cumbersome overvoltage protection can be added to an unprotected amplifier, and how the integrated overvoltage protection of newer amplifiers provides a compact, robust, cost-effective solution.

Efficient FSK/PSK Modulator Uses Multichannel DDS to Switch at Zero Crossings

2012-01-09T15:51:00.001-05:00

This article describes how two synchronized DDS channels can implement a zero-crossing FSK or PSK modulator. In phase-coherent radar systems, zero-crossing switching reduces the amount of post processing needed for target signature recognition; and zero-crossing switching reduces PSK spectral splatter. Here, the AD9958 two-channel complete DDS is used to switch at the zero crossing.

DDS Devices Generate High-Purity Waveforms Simply, Efficiently, and Flexibly

2012-01-09T15:50:00.001-05:00

Direct digital synthesis (DDS) technology is used to generate and modify high-quality waveforms in a broad range of applications in such diverse fields as communications, defense, medicine, industry, and instrumentation. This article provides an overview of the technology, describes its strengths and limitations, looks at some application examples, and showcases some significant new products.

How to Apply DC-to-DC Step-Up/Step-Down Regulators Successfully

2011-12-08T10:13:00.001-05:00

High efficiency dc-to-dc converters come in three basic topologies: step-down (buck), step-up (boost), and step-down/step-up (buck/boost). The buck converter is used to generate a lower dc output voltage, the boost converter is used to generate a higher dc output voltage, and the buck/boost converter is used to generate an output voltage less than, greater than, or equal to the input voltage.

Oversampled ADC and PGA Combine to Provide 127-dB Dynamic Range

2011-12-08T10:12:00.000-05:00

The need to measure wide dynamic range signals is common, but current technology often has difficulty meeting system requirements. This article presents an alternative that uses a high-speed, successive-approximation ADC, combined with an autoranging programmable-gain amplifier front end with gain that changes automatically based on analog input value to provide a dynamic range of more than 126 dB.

Advanced Data Converters

2011-11-02T14:10:00.000-04:00

Advanced Data Converters offers a stimulating cornucopia of circuit techniques, ideas, and examples, profusely illustrated and supported with extensive documentation by some 416 references to the literature—a veritable catalog of design concepts.

Front End Turns PC Sound Card into High-Speed Sampling Oscilloscope

2011-11-01T11:13:00.000-04:00

Various software packages enable PC sound cards to provide oscilloscope-like displays, but the low-sample-rate, high-resolution ADCs and ac-coupled front ends have limited bandwidths. For repetitive waveforms, a sampling front-end stretches the time axis, allowing the PC to be used as a high-speed sampling scope. This article describes a front end and probe that provide an appropriate adaptation.

Monitoring and Sequencing in Multirail Power-Supply Systems

2011-11-01T11:12:00.000-04:00

Today’s electronic systems are likely to have many different power supply rails. For reliable, repeatable operation, the on-off timing, rise/fall rates, order of application, and magnitude of each voltage must be controlled. Typical system designs may include supply sequencing, tracking, and voltage/current monitoring/control. A variety of integrated power management ICs exist to perform these functions.

Ultrahigh-Performance Differential-Output Programmable-Gain Instrumentation Amplifier

2011-10-04T09:29:00.000-04:00

Data-acquisition systems and PLCs require versatile high-performance analog front ends that interface with a variety of sensors to measure signals accurately and reliably. Depending on the magnitude of the voltage or current being measured, the signal may need to be amplified or attenuated to match the full-scale input range of the ADC used for further digital processing and feedback control.

S-Parameters Allow High-Frequency Verification of RF Switch Models

2011-10-04T09:28:00.000-04:00

S- (scattering) parameters characterize electrical networks using matched impedances. Scattering refers to the way traveling currents or voltages are affected when they meet a discontinuity in a transmission line. S-parameters allow a device to be treated as a “black box” with inputs and outputs, enabling a system to be modeled without having to deal with the complex details of its actual structure.

Analog Dialogue, Volume 45, Number 2

2011-09-06T11:06:00.001-04:00

In this issue:
How to Apply DC-to-DC Step-Down (Buck) Regulators Successfully
AD7879 Controller Enables Gesture Recognition on Resistive Touch Screens
Low-Power, Unity-Gain Difference Amplifier Implements Low-Cost Current Source
Switch and Multiplexer Design Considerations for Hostile Environments (Ask the Apps Eng—40)
High-Resolution Temperature Measurement
Simple Op Amp Measurements

How to Apply DC-to-DC Step-Up (Boost) Regulators Successfully

2011-09-06T10:43:00.000-04:00

Battery-powered systems often stack cells in series to achieve higher voltages, but this is not always possible due to a lack of space. Switching converters use an inductor’s magnetic field to alternately store energy and release it to the load at a different voltage. With low losses they are a good choice for high efficiency. Boost, or step-up converters—covered here—provide higher voltage.

Power Management Design for PLLs

2011-09-06T10:42:00.002-04:00

Phase-locked loops are typically used to provide local oscillators in radio receivers and transmitters, for clock-signal distribution and noise reduction, and as the clock source for high-speed A/D and D/A converters. As PLL noise decreases, the impact of power supply noise increases, and can even limit noise performance in some cases. This article considers basic PLLs and the power-management requirements for each PLL building block.

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2011-08-02T15:02:00.000-04:00

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eBooks and Printable Versions

2011-08-02T15:00:00.003-04:00

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System Demonstration Platform Facilitates Quick Prototyping and Evaluation

2011-08-02T15:00:00.001-04:00

System design can be complex, but the ability to prototype and quickly demonstrate subsections of the solution can simplify the process and reduce the risks faced by designers. With the System Demonstration Platform (SDP), system designers can reuse central elements, allowing subsections of their designs to be evaluated and demonstrated prior to the final system implementation.

Insight into digiPOT Specifications and Architecture Enhances AC Performance

2011-08-02T14:58:00.000-04:00

Digital potentiometers provide a convenient way to adjust the output of sensors, power supplies, or other devices that require calibration. Digital setting avoids problems associated with mechanical pots, such as physical size, mechanical wear out, wiper contamination, resistance drift, and sensitivity to environmental effects—and eliminates layout inflexibility resulting from the need for access.

Simple Ambient Light Sensor Circuit

2011-07-06T10:25:00.000-04:00

Ambient light is increasingly considered as a source for harvesting energy to power heartbeat monitors, bathroom fixtures, remote weather sensors, and other low-power devices. At the heart of an energy-harvesting system is the ability to measure ambient light accurately. This design idea describes a simple, cost-effective circuit that provides a voltage proportional to the intensity of ambient light.

Differential Interfaces Improve Performance in RF Transceiver Designs

2011-07-06T10:24:00.000-04:00

Traditional IF and RF transceivers use 50-Ω single-ended interfaces, with interconnected circuits all seeing matching input and output impedances. In modern transceiver designs, differential interfaces provide better performance, but implementing them requires designers to confront impedance matching, common-mode voltage matching, and difficult gain calculations. This article offers some assistance.

AD7879 Controller Enables Gesture Recognition on Resistive Touch Screens

2011-05-31T15:00:00.001-04:00

Resistive touch screens conventionally fill a market niche where only a single touch is required, high resolution is paramount, a stylus facilitates specific functionality, or users must wear gloves. This article offers a new dual-touch concept using an AD7879 resistive touch-screen controller to detect the most common two-finger gestures (zoom, pinch, and rotation) using inexpensive resistive touch screens.

How to Apply DC-to-DC Step-Down (Buck) Regulators Successfully

2011-05-31T14:58:00.000-04:00

Typical low-power systems operate with a Li-Ion battery whose output varies from 4.2 V to 3 V, while the ICs require 0.8 V, 1.8 V, 2.5 V, and 2.8 V. A simple way to reduce the voltage is to use an LDO, but power not delivered to the load is lost as heat, making LDOs inefficient when VIN is much greater than VOUT. Switching converters store energy in a magnetic field, enabling high-efficiency regulation.

Low-Power, Unity-Gain Difference Amplifier Implements Low-Cost Current Source

2011-05-03T10:13:00.000-04:00

In Difference Amplifier Forms Heart of Precision Current Source, published in Analog Dialogue in September 2009, the AD8276 unity-gain difference amplifier and AD8603 micropower op amp were used to implement a precision current source. This article shows how the circuit can be simplified for use in low-cost, low-current applications—achieving ±1.5% accuracy from –40°C to +85°C.

Ask the Apps Eng 40—Switch and Multiplexer Design Considerations for Hostile Environments

2011-05-03T10:12:00.000-04:00

This article describes the challenges that engineers face when designing switches and multiplexers into hostile environments, and suggests solutions that the circuit designer can use to protect vulnerable parts. It also introduces some new integrated switches and multiplexers that provide increased overvoltage protection, latch-up immunity, and fault protection to deal with common stress conditions.

Analog Dialogue Volume 45, Number 1

2011-04-14T09:14:00.001-04:00

Analog Dialogue Volume 45, Number 1 is now available from Smashwords.

Analog Dialogue Volume 45, Number 1

2011-04-14T09:10:00.001-04:00

Analog Dialogue Volume 45, Number 1 is now available from the Kindle store.

Data Conversion Knowledge Resource

2011-04-11T10:38:00.000-04:00

Explore technical fundamentals and design considerations for data conversion functions. Select signal chain topics to access relevant educational material.

High-Resolution Temperature Measurement

2011-04-04T10:55:00.001-04:00

The AD8494 thermocouple amplifier includes a temperature sensor, normally used for cold-junction compensation. Grounding the thermocouple inputs allows it to be used as a standalone Celsius thermometer. In this configuration, the in-amp produces a 5-mV/°C voltage between its output and reference pins. This article suggests two ways that this output voltage can be offset and scaled to facilitate high-resolution temperature measurement.

Simple Op Amp Measurements

2011-04-04T10:51:00.001-04:00

When testing op amps, their high open-loop gain makes it hard to avoid small voltage errors due to pick-up, stray currents, or the Seebeck effect. The measurement process can be simplified by using a servo loop to force a null at the input, thus allowing the amplifier to measure its own errors. This article describes a versatile circuit that employs an auxiliary op amp as an integrator to establish a stable loop with very high dc open-loop gain.

A Foolish Question about Op Amps and Capacitors

2011-04-01T12:44:00.000-04:00

Can you help with the strange interaction between the op amp and capacitors in my circuit? This sounded more like a Frequently Asked Question than a Rarely Asked Question, but turned out to be neither...

Free Cake and Ice Cream

2011-04-01T07:44:00.004-04:00

Free cake and ice cream all day today. For more information, see our Facebook page at http://www.facebook.com/analogdialogue.

Reducing the size and complexity of isolating data and power

2011-03-14T11:42:00.001-04:00

Reducing the size and complexity of isolating data and power, an Ask the Expert forum on isolation, featuring Brian Kennedy as the expert, will run from 3/14/11 to 5/13/11.

European Seminar Series

2011-03-02T09:16:00.002-05:00

The Analog Dialogue – Discovery through Discussion Seminar Series – Free, one-day sessions on "Solutions for Signal Conditioning and Isolation." This interactive seminar will present useful tips to help make it easier for designers to get their jobs done. May 3 to May 12 in six cities in Central Europe. Register or get more information at http://www.analog.com/en/content/sem_european_seminars/fca.html

Volume 44, Number 4 Printable Edition

2011-02-24T16:59:00.001-05:00

In This Issue
Editors’ Notes; New Product Introductions
Two Ways to Measure Temperature Feature Simplicity, Accuracy, and Flexibility
Inertial Sensors Facilitate Autonomous Operation in Mobile Robots
Multichannel DDS Enables Phase-Coherent FSK Modulation
High-Side Current Sensing with Wide Dynamic Range: Three Solutions
Boost Supply and High-Voltage DAC Provide Tuning Signal for Antennas and Filters
High-Performance Difference Amplifier with Precision Supply-Referenced Level Shift

Volume 44, Number 3 Printable Edition

2011-02-24T16:56:00.005-05:00

In This Issue
Editors’ Notes; New Product Introductions
Low-Voltage Current Sink Controls High-Voltage LED String
New High-Resolution Multiplying DACs Excel at Handling AC Signals
Power Cycling 101: Optimizing Energy Use in Advanced Sensor Products
Dual Difference Amplifier with On-Chip Resistors Implements Precision ADC Driver
Quad, 16-Bit Voltage-/Current-Output DACs Save Space, Cost, and Power in Multichannel PLCs
High-Speed, Current-Feedback Amplifier Drives and Equalizes Up to 100-m VGA Cables

Activate Cell Phone Indicator LEDs While Preserving Standby Time

2011-02-24T16:53:00.001-05:00

Cell phone manufacturers are pressed to provide status LEDs that alert users to messages waiting, impending appointments, and other notifications while the phone is in standby. At the same time, users demand longer battery life. This pair of seemingly simple issues presents manufacturers with a dilemma: how can they power notification LEDs while keeping standby consumption low?

Minimizing Noise and Power Consumption in Automotive Audio Systems with SigmaDSP

2011-02-24T16:52:00.001-05:00

Digital signal processors bring the benefits of home theater to cars, supplanting radio/CD players with multimedia systems, where DSPs enable excellent audio performance and flexibility—and a powerful multimedia experience for passengers. A new approach to minimizing system noise and power consumption uses the SigmaDSP® processor and the SigmaStudio™ graphical development tool.

Cyclic Redundancy Checking Ensures Correct Data Communications

2011-01-31T12:55:00.000-05:00

Electronic systems must often endure temperature extremes, noise, or other harsh conditions. To ensure correct operation, many DACs implement cyclic redundancy checking (CRC), with 24-bit data augmented with an 8-bit checksum. If the received checksum does not agree with the data, an output pin indicates an error. The controller clears the error and resends the data.

HDMI Transceivers Simplify the Design of Home Theater Systems

2011-01-31T12:53:00.002-05:00

As large-screen HDTVs have achieved widespread acceptance, consumers are expanding their home theater systems to include sound bars and AVRs, enhancing the user experience with superb audio to complement the video performance. Home theater systems can now offer all the latest features of the high-definition multimedia interface (HDMI®)—seamlessly integrated within the equipment.

Ask the Expert

2011-01-17T10:22:00.002-05:00

Ask the Expert about designing analog front-ends for high speed A/D converters – Now through February 18.

Low Dropout Regulators—Why the Choice of Bypass Capacitor Matters

2011-01-05T09:36:00.001-05:00

Widely seen as a panacea for solving noise issues, capacitors deserve more respect. Designers think that adding capacitors will cure noise problems, but give little thought to parameters other than value and voltage rating. But capacitors are not perfect; they possess parasitic resistance and inductance, their value varies with temperature and voltage, and they are sensitive to mechanical effects.

Electromagnetic Interference Filtering Reduces Errors in Precision Analog Applications

2011-01-05T09:34:00.001-05:00

An often-overlooked problem in equipment using strain gages, transducer interfaces, and current monitors in medical, automotive, and industrial applications is high-frequency interference from external signals. This electromagnetic interference (EMI) can cause large dc offsets in precision analog circuitry through asymmetrical rectification of the RF signal in the input stages of an amplifier.

Boost Supply and High-Voltage DAC Provide Tuning Signal for Antennas and Filters

2010-12-13T15:13:00.001-05:00

Antenna arrays and filters are often tuned by varying the voltage on a barium strontium titanate capacitor. Voltages applied to this ferroelectric material cause small variations in the crystal structure, changing the dielectric constant and, thus, the capacitance. The capacitor is tuned by applying a voltage of up to 30 V. This article shows an easy way to generate a high-voltage tuning signal in a low-voltage system.

High-Side Current Sensing with Wide Dynamic Range: Three Solutions

2010-12-13T15:08:00.001-05:00

Precision current sensing allows designers to measure motor torque, dc-to-dc converter efficiency, bias current in a power transistor, and other critical parameters in the presence of high common-mode voltages. This article describes three solutions—discrete, integrated, and application-optimized—that provide high-accuracy, high-resolution current sensing for a variety of applications.

Multichannel DDS Enables Phase-Coherent FSK Modulation

2010-11-02T11:26:00.000-04:00

Common single-channel direct-digital synthesizers produce phase-continuous frequency transitions. In Doppler radar, NMR/MRI spectrometry, and other applications, however, phase-coherent transitions are preferred. This article demonstrates how to configure the AD9958/AD9959 multichannel DDS as a robust phase-coherent frequency-shift keyed (FSK) modulator by summing the DDS outputs.

Inertial Sensors Facilitate Autonomous Operation in Mobile Robots

2010-11-02T11:19:00.003-04:00

Ground-based robot systems must often handle dull, dirty, and dangerous tasks in missions where direct human involvement is expensive, dangerous, or ineffective. Some robotic platforms can operate autonomously, using navigation systems to monitor and control their motion. Accuracy is key for useful autonomous operation. MEMS gyroscopes provide a mechanism for optimizing navigation performance.

Ask the Expert

2010-10-21T16:28:00.006-04:00

Designing for >16-bit performance in your precision DAC application? Ask the Expert a question, now through December 22, 2010.

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2010-10-05T14:12:00.001-04:00

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Volume 44, Number 2 Printable Edition

2010-10-05T13:17:00.001-04:00

In This Issue:
Editors’ Notes and Product Introductions
The 20-Bit DAC Is the Easiest Part of a 1-ppm-Accurate Precision Voltage Source
Difference Amplifier Enables Low-Power, High-Performance Absolute Value Circuit
Synchronous Inverse SEPIC Topology Provides High Efficiency Buck/Boost Voltage Converters
Ultralow Distortion Audio Panpot Amplifier
Differential-Output Difference Amplifier System with G = ½
Full-Featured Pedometer Design Realized with 3-Axis Digital Accelerometer

Two Ways to Measure Temperature Feature Simplicity, Accuracy, and Flexibility

2010-10-05T12:20:00.000-04:00

Thermocouples are widely used for measuring temperature. This article suggests two signal conditioning solutions. The first combines reference-junction compensation and signal conditioning in a single analog IC for convenience and ease of use; the second separates the reference-junction compensation from the signal conditioning to provide greater flexibility and accuracy.

High-Performance Difference Amplifier with Precision Supply-Referenced Level Shift

2010-10-05T12:18:00.000-04:00

Designed on small-geometry processes, high-performance ADCs typically run on single 1.8-V to 5-V supplies. When processing ±10-V or larger signals, an amplifier circuit ahead of the ADC can attenuate the signal to keep it from saturating the ADC inputs. A difference amplifier (diff amp) is commonly used when the signal includes a large common-mode voltage.

A Dozen Ways to Make a Circuit Fail

2010-09-01T11:34:00.001-04:00

Some practical reasons why your analog circuit didn't do what you expected.

Low-Voltage Current Sink Controls High-Voltage LED String

2010-08-26T10:09:00.001-04:00

Portable displays using white LED backlights also need auxiliary LED lighting, an inductive boost to maximize backlight efficiency, a charge pump to allow independent control of each auxiliary LED, and programmable current sinks to control color and brightness. This tip shows how a programmable LED driver and low-cost boost converter can achieve a flexible, high-efficiency, easy-to-program solution.

New High-Resolution Multiplying DACs Excel at Handling AC Signals

2010-08-26T10:08:00.001-04:00

All digital-to-analog converters (DACs) provide an output proportional to the product of the digitally set gain and an applied reference voltage. A multiplying DAC differs from a fixed-reference DAC in that it can apply a high-resolution digitally set gain to a varying wideband analog signal. ADI’s new resistance-ladder multiplying DACs are inherently suitable for ac signal-processing applications.

Dual Difference Amplifier with On-Chip Resistors Implements Precision ADC Driver

2010-07-29T16:06:00.001-04:00

Discrete difference amplifiers exhibit mediocre accuracy, significant drift over temperature, poor CMR, and a small input voltage range. Monolithic diff amps have better CMR, but still suffer from gain drift due to the mismatch between on-chip devices and the external gain resistor.The AD8270 dual diff amp overcomes these limitations, providing a complete, inexpensive, high-performance solution.

Power Cycling 101: Optimizing Energy Use in Advanced Sensor Products

2010-07-29T16:05:00.001-04:00

Highly integrated sensor systems allow system developers to readily use sensors that embrace technologies with which they may have little experience—with minimal investment and risk. Although accuracy is specified at a given power level, power cycling provides an opportunity to reduce average power consumption in applications where energy use must be tightly managed.

How does one measure temperature outside the silicon range?

2010-07-06T13:23:00.002-04:00

If only King Alfred had had better oven temperature measurement he need not have allowed the peasant woman’s cakes to burn. And even in 880 A.D. it would have been possible to make a thermocouple had he known how.

Thermocouples are very simple devices which can measure temperature over a very wide range.

If we have two conductors of different material joined at two points which are at different temperatures, there will be an emf (electromotive force) in the loop so formed–this emf is a function¹ of the temperature difference and can be used to measure temperatures as high as 2300°C and as low as a few Kelvin. One junction is at the temperature to be measured and the other (often known as the "cold" junction, even if it is at a higher temperature than the one being measured) is at a reference temperature (in the past a mixture of ice and water was often used to provide a 0°C reference).

Two pieces of wire of different materials are simple and, usually, inexpensive², so thermocouples are widely used. Where the reference will normally be within ±10°C of room temperature and accurate measurement is unnecessary, it is quite usual to use an uncompensated thermocouple for measurements. An example is the flame sensor in a boiler.

If reasonable accuracy is required, the cold junction must be held at a known reference temperature–which is inconvenient, as ice may be unavailable. But the cold junction need not be at a constant temperature as long as it is always known. The cold junction temperature, which is unlikely to be outside –55°C to +155°C, may be measured with a silicon sensor; we then use the emf and the cold junction temperature to calculate the "hot" junction temperature.

This "cold junction compensation" may be done by a digital controller, but it is quite possible to integrate the cold junction sensor, the thermocouple amplifier, and the compensation in a simple analog chip. The AD594/AD595 and AD8494/AD8495/AD8496/AD8497 are examples of such circuits; if King Alfred had had one the cakes would have been perfect.

¹ The function is (approximately) a polynomial of 5th - 13th order, but for some thermocouples simple proportionality is adequate over some ranges.
² Platinum (B, R & S) and chromel/gold-iron thermocouples are among the expensive exceptions to this.

High-Speed, Current-Feedback Amplifier Drives and Equalizes up to 100-m VGA Cables

2010-07-06T13:22:00.000-04:00

In classrooms, lecture halls, and conference rooms, PCs transmit RGB video signals to projectors through VGA cables. The cable length depends on the room size and ceiling height, but most cables are shorter than 100 m. This article shows how the ADA4858-3 triple high-speed current-feedback op amp with integrated charge pump can drive and equalize up to 100 m of VGA cable.

Quad 16-Bit Voltage-/Current-Output DACs Save Space, Cost, and Power in Multichannel PLCs

2010-07-06T13:02:00.001-04:00

Programmable logic controllers use deterministic functions to control machines and processes. As the number of sensor and control nodes continues to increase, some distributed control systems can handle thousands of nodes. A major challenge is to provide greater efficiency and reduced power consumption. The AD5755 4-channel, 16-bit DAC offers an integrated solution to resolve these issues.

Digital Media Processing: DSP Algorithms Using C

2010-06-21T17:15:00.005-04:00

Digital Media Processing: DSP Algorithms Using C, by Hazarathaiah Malepati, Newnes, 2010, ISBN 978-1-85617-678-1.

This book discusses various algorithms—related to the processing of data, signals, images, speech, audio, and video—that are used in present-day cutting-edge technologies—and the C simulation and implementation techniques to run them in real time on embedded processors.

Differential-Output Difference Amplifier System with G = ½

2010-05-26T16:33:00.002-04:00

High-performance ADCs typically run on low-voltage supplies. To process ±10 V or larger signals, an amplifier precedes the ADC, attenuating the signal to keep it from saturating or damaging the inputs. Differential outputs are desirable to capture the full benefits of the differential-input ADC, including increased dynamic range, improved common-mode rejection, and reduced noise sensitivity.

Full-Featured Pedometer Design Realized with 3-Axis Digital Accelerometer

2010-05-26T16:30:00.003-04:00

Pedometers that use MEMS inertial sensors and sophisticated software to accurately detect steps can encourage individuals to get fit and lose weight. Small, low-cost, low-power MEMS sensors allow pedometers to be integrated into music players and mobile phones. This design uses an accelerometer in a full-featured pedometer that can count steps, measure distance, speed, and calories burned.

Volume 44, Number 1 Print Edition

2010-05-05T09:45:00.001-04:00

In This Issue:
Editors’ Notes and Product Introductions
Termination of High-Speed Converter Clock Distribution Devices
ADIsimPower Provides Robust, Customizable DC-to-DC Converter Designs
New Touch-Screen Controllers Offer Robust Sensing for Portable Displays
Driving PIN Diodes: The Op-Amp Alternative
Ask the Application Engineer—39 Zero-Drift Amplifiers
Free and Open-Source Software—An Analog Devices Perspective

Ultralow Distortion Audio Panpot Amplifier

2010-05-05T09:44:00.000-04:00

An audio "panpot" circuit continuously varies the position of a monophonic audio signal between left and right channels in response to a potentiometer setting. This circuit can be built discretely, but integrating the amplifiers and resistors on a single chip offers improved specifications, less PCB area, and lower production cost. The AD8273 dual low-distortion difference amplifier uses on-chip gain-setting resistors to ensure excellent matching.

Synchronous Inverse SEPIC Topology Provides High Efficiency Buck/Boost Voltage Converters

2010-05-05T09:43:00.000-04:00

Demand is increasing for efficient noninverting dc-to-dc converters that can operate in either buck or boost mode—with minimal cost and component count. The inverse SEPIC (single-ended primary inductor converter) is ideal for this function. An analysis of its operation and implementation with the ADP1877 dual-channel synchronous switching controller will reveal its many useful properties.

Difference Amplifier Enables Low-Power, High-Performance Absolute Value Circuit

2010-04-05T14:58:00.001-04:00

Traditional precision half- and full-wave rectifiers use carefully selected high-speed op amps, fast diodes, and precision resistors, but this expensive solution suffers from crossover distortion and temperature drift. A dual-channel difference amplifier—with no external components—can provide an absolute value output that achieves better precision, lower cost, and lower power consumption.

The 20-Bit DAC Is the Easiest Part of a 1-ppm-Accurate Precision Voltage Source

2010-04-05T14:57:00.001-04:00

High precision applications require 18- and 20-bit, 1-ppm-accurate digital-to-analog converters, a performance level previously achieved only with cumbersome, expensive, and slow Kelvin-Varley dividers. Now, the 20-bit AD5971 DAC provides a cost-effective way to achieve 1-ppm linearity. Easy to use, it offers guaranteed specifications without requiring calibration or constant monitoring.

Ask the Applications Engineer 39—Zero-Drift Operational Amplifiers

2010-03-02T09:45:00.002-05:00

Zero-drift amplifiers dynamically correct their offset and reshape their noise density. Two commonly used types—auto-zero and choppers—achieve nanovolt-level offsets and extremely low drift. 1/f noise is seen as a dc error, so it is removed as well. In addition, zero-drift amplifiers have higher open-loop gain, power-supply rejection, and common-mode rejection than standard amplifiers.

Free and Open-Source Software—An Analog Devices Perspective

2010-03-02T09:44:00.001-05:00

The rapid increase in use of Free and Open-Source Software (FOSS) represents a significant long-term trend. FOSS licenses make source code available and grant developers the right to study, change, and improve the design. FOSS, already playing a role in every major software category from 64-bit servers to 8-bit microcontrollers, will fundamentally change the nature of software for all users and developers.

New Touch-Screen Controllers Offer Robust Sensing for Portable Displays

2010-02-01T14:33:00.001-05:00

Touch-screen displays are replacing mechanical buttons in smart phones, MP3 players, navigation systems, laptop computers, and other devices. First generation devices suffered from low accuracy, false detection, and high power consumption. New devices--which offer improved accuracy, lower power consumption, and result filtering--can also sense temperature, supply voltage, and touch pressure.

Driving PIN Diodes: The Op-Amp Alternative

2010-02-01T14:32:00.000-05:00

PIN diodes, which sandwich a lightly doped intrinsic region between heavily doped P and N regions, are used extensively in RF and microwave applications. PIN diode drivers--which provide a controlled forward bias current and reverse bias voltage--use discrete designs or specialized ICs. As an alternative, widely available op amps can be used. Op amps in this class feature wide bandwidth, high slew rate, and enough steady-state current to drive PIN diodes.

ADIsimPower Provides Robust, Customizable DC-to-DC Converter Designs

2010-01-05T17:35:00.000-05:00

Designers of dc-to-dc converters are faced with an overwhelming number of options for power management ICs. Finding the best combination of features, performance, integration level, and price can be difficult enough, and the actual design work can be daunting. ADIsimPower™ simplifies the IC selection process and provides the information required to build an optimized dc-to-dc converter.

Termination of High-Speed Converter Clock Distribution Devices

2010-01-05T17:17:00.000-05:00

When using clock distribution devices or clock fanout buffers to clock ADCs and DACs, two main sources of signal degradation need to be dealt with: PCB traces behave like low-pass filters, attenuating clock signals and distorting clock edges as they travel along the trace; and reflections can cause undershoot and overshoot, severely degrading the signal and the overall clock performance.

Adjustable-Gain Difference Amplifier Circuit Measures Hundreds of Volts, Rejects Large Common-Mode Signals

2009-12-01T10:51:00.000-05:00

A diff-amp in a feedback loop with an inverting op amp is useful for measuring differential signals up to 500 V. This circuit also rejects large common-mode voltages, and allows the differential gain to be set by a ratio of resistors, enabling the user to select the level of attenuation.

Designing High-Performance Phase-Locked Loops with High-Voltage VCOs

2009-12-01T10:50:00.000-05:00

Phase-locked loops are used to provide the local-oscillator function in radio receivers and transmitters; for clock distribution and noise reduction, and as the clock source for high-sampling-rate analog-to-digital converters. This article considers the basics of PLLs, examines the current state-of-the-art in PLL design, discusses pros and cons of typical architectures, and introduces some alternatives to high-voltage VCOs.

Using Isolated RS-485 in DMX512 Lighting Applications

2009-11-03T13:41:00.001-05:00

Theatrical lighting applications have evolved from lanterns in open-air theatres into the more complex systems available today. Modern lighting equipment includes dimmers, flashing lights, moving lights, colored lights, and gobos. These lighting systems are often controlled over long distances—up to 4000 feet—using the DMX512 communications protocol.

Synchronizing Device Clocks Using IEEE 1588 & Blackfin Embedded Processors

2009-11-03T13:40:00.000-05:00

IEEE 1588 defines a protocol to synchronize distributed clocks on a network. The preferred clock synchronization method for many applications, it is cost-effective, supports heterogeneous systems, and provides nanosecond-level synchronization. The ADSP-BF518 Blackfin® processor includes dedicated hardware support for IEEE 1588. This article shows clock synchronization performance obtained using this solution.

Automobile Tail Lamp and Brake Lamp Controller

2009-10-06T14:53:00.000-04:00

Light emitting diodes (LEDs) are recently finding uses in automobiles, where they provide signaling, daytime running lights, and interior lighting. As this technology hits the road, manufacturers continue to investigate new ways to apply it, taking advantage of the styling possibilities afforded by LED headlights and taillights.

Isolation in High-Voltage Battery Monitoring for Transportation Applications

2009-10-06T14:47:00.001-04:00

Battery stacks for transportation can provide hundreds of volts. These high voltages can prove lethal to human beings—and even lower voltages can damage electronic equipment—so safety is a key concern. Although these stacks are inherently dangerous, they must still communicate with the cell monitoring electronics. Galvanic isolation is thus required to make the communications method safe and reliable.

Phase Response in Active Filters, Part 2: Low-Pass and High-Pass Responses

2009-09-01T15:04:00.002-04:00

The transfer function of an active filter can be viewed as the cascaded response of the filter transfer function and an amplifier transfer function. This article examines the phase shift of the filter transfer function itself. While filters are designed primarily for their amplitude response, the phase response can be important in applications such as time delay simulation, cascaded filter stages, and especially process-control loops.

Difference Amplifier Forms Heart of Precision Current Source

2009-09-01T15:04:00.001-04:00

Precision current sources are used to provide excitation for RTDs in process-control systems; to measure unknown elements in digital multimeters; and to drive 4 mA to 20 mA current loops, which are widely used to transmit information over long distances. This article shows how a difference amplifier can be used to implement a precision current source.

Understanding Data Converter Errors and Specifications

2009-08-04T09:15:00.000-04:00

Perplexed by data converter specifications and how they impact end-system performance? View this webinar and learn how to derive the vital facts from the data sheet.

The Basics of Video Decoders in Supervision and Inspection

2009-08-04T09:13:00.000-04:00

Video cameras—which range from inexpensive, low-definition black-and-white closed-circuit television systems to state-of-the-art high-definition digital-video systems—are found in diverse applications including product inspection, traffic monitoring, and real-time face recognition. Dropping unneeded data and passing only the essential parts of the picture can simplify the video system—saving memory and computational cycles.

How to Successfully Apply Low-Dropout Regulators

2009-08-04T09:12:00.000-04:00

A low-dropout regulator (LDO) is capable of maintaining a specified output voltage over a wide range of load current and input voltage, down to a very small difference between input and output voltages. This difference, known as the dropout voltage or headroom requirement, can be as low as 80 mV at 2 A.

Measuring Noise of Low-Fixed-Gain Differential Amplifiers

2009-06-24T15:40:00.002-04:00

Measuring noise of low-gain differential amplifiers presents a challenge, as their integrated feedback and gain resistors preclude high-gain configurations, and a differential-to-single-ended conversion is needed to match the spectrum analyzer. A second amplifier stage can provide gain and the differential-to-SE conversion, neatly solving both of these problems.

Detecting Human Falls with a 3-Axis Digital Accelerometer

2009-06-24T15:39:00.002-04:00

Elderly individuals can suffer accidental falls due to weakness or dizziness. The initial injury can be further aggravated if treatment is not obtained within a short time. MEMS-based fall detectors can sense changes in body position by tracking acceleration, determine when an individual is falling, and issue an alert for assistance. This article describes the use of an ADXL345 three-axis digital accelerometer as a fall detector.

What shall we do with an unused op-amp?

2009-06-24T15:30:00.003-04:00

Rarely Asked Questions -- Strange but true stories from the call logs of Analog Devices. View current and archived Rarely Asked Questions at http://www.analog.com/raq

Designing with Switching Regulators in High-Speed A/D Converter

2009-06-24T15:26:00.000-04:00

Webinar Series -- View this webinar, recently archived webinars, or webinars by category at www.analog.com/webinars

Automated Calibration Technique Reduces DAC Offset to Less than 1 mV

2009-06-11T14:34:00.000-04:00

The AD5360 16-bit, 16-channel DAC is factory trimmed, but an offset of several millivolts can still exist. This idea shows how a simple software algorithm can reduce an unknown offset to less than 1 mV. This technique can be used for factory calibration, or for offset correction at any point in the DAC’s life cycle.

Digital Isolator Simplifies USB Isolation in Medical and Industrial Applications

2009-06-11T14:33:00.000-04:00

Despite its low speed and point-to-point nature, RS-232 was tolerated in medical and industrial applications because it was universally available, well supported, and allowed easy implementation of the required isolation. The ADuM4160 digital isolator allows simple, inexpensive isolation of full- and low-speed USB peripherals—including the D+ and D– lines—increasing the usefulness of USB in medical and industrial applications.

Understanding and Optimizing Sampled Data Systems (Part II)

2009-05-13T10:32:00.003-04:00

Webinar Series

Next topic: Understanding and Optimizing Sampled Data Systems (Part II)
Wednesday, May 20, 2009, 12:00 PM ET

View this webinar, recently archived webinars, or webinars by category at www.analog.com/webinars

Accelerometers—Fantasy & Reality

2009-05-01T14:17:00.001-04:00

High sensitivity, small size, low cost, rugged packaging, and the ability to measure both static and dynamic acceleration have made numerous new applications of surface micromachined accelerometers possible. Many of these were not anticipated because they were not thought of as classic accelerometer applications. New applications are limited only by the imagination of designers.

“Rules of the Road” for High-Speed Differential ADC Drivers

2009-05-01T14:16:00.001-04:00

Most modern high-performance ADCs use differential inputs to reject common-mode noise and interference, increase dynamic range by a factor of two, and improve overall performance. ADC drivers—circuits often specifically designed to provide differential signals—perform many important functions including amplitude scaling, single-ended-to-differential conversion, buffering, common-mode offset adjustment, and filtering.

Volume 42, Number 4, 2008 Print Edition

2009-03-31T14:35:00.002-04:00

In This Issue:

2 -- Editors’ Notes
3 -- Analog Front End for 3G Femto Base Stations Brings Wireless Connectivity Home
8 -- Considering Multipliers (Part 1) [The Wit and Wisdom of Dr. Leif—7]
15 -- Design, Simulate, and Document Proprietary Wireless Systems
18 -- Tales From the Back Burner
19 -- Product Introductions

Subscribe at http://www.analog.com/library/analogDialogue/subscribe.html

Notch Filter Reduces Amplifier Peaking and Increases Gain Flatness

2009-03-31T14:32:00.000-04:00

Although the ADA4817 is unity-gain stable, a high-frequency pole increases its GWP from 410 MHz at high gains to 1 GHz at unity gain, while decreasing its phase margin. Adding a discrete RLC notch filter maintains the high bandwidth and input impedance, while dramatically reducing peaking, increasing gain flatness, and reducing overshoot.

Skin Impedance Analysis Aids Active and Passive Transdermal Delivery

2009-03-31T14:31:00.000-04:00

Pharmaceutical firms are developing alternatives to injections. Transdermal methods, which feature noninvasive delivery of medication through a patient’s skin, overcome the protective barrier in one of two ways: passive absorption and active penetration. Skin impedance analysis facilitates proper dosing.

PLC Evaluation Board Simplifies Design of Industrial Process-Control Systems

2009-03-31T14:30:00.000-04:00

The applications for industrial process-control systems range from simple traffic control to complex electrical power grids, from environmental control systems to oil-refinery process control. The intelligence of these systems lies in their measurement and control units. The two most common computer-based systems to control machines and processes are programmable logic controllers and distributed control systems.

Reconstruct a DAC Transfer Function from its Harmonic Spectral Content

2009-03-03T17:18:00.001-05:00

DAC output spectrums contain harmonic content due to their non-ideal transient and static behavior. This article defines a method for deriving the DAC transfer function from the observed harmonic content, assuming that the static errors, rather than the transient characteristics, are the dominant source of the distortion.

Analog Microcontroller Forms Heart of Low-Cost, High-Efficiency PA Monitor

2009-03-03T17:16:00.001-05:00

Saving energy is crucial for efficient wireless network operation. Power amplifiers (PA), the core of base stations and repeaters, can account for more than half of their total power consumption. Monitoring and controlling the PA can: improve efficiency and reduce operating costs; maximize output power and achieve the highest possible linearity; and allow the system operator to discover problems and improve reliability.

This Should Work: Thermistor Senses Liquid Levels

2009-02-03T09:08:00.001-05:00

In precision temperature measurement applications using thermistors, RTDs, or other resistive temperature sensors, care must be taken to avoid self-heating errors caused by the excitation current. In some applications, however, the self-heating effect can be put to good use. The design concept presented here should work, but it has not been fully tested.