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September 2009
Difference Amplifier Forms Heart of Precision Current Source
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.
August 2009
How to Successfully Apply
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.
July 2009
Measuring Noise of Low-Fixed-Gain Differential Amplifiers
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.
June 2009
Automated Calibration Technique Reduces DAC Offset to Less than 1mV
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.
May 2009
Accelerometers—Fantasy & Reality
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.
April 2009
Skin Impedance Analysis Aids Active and Passive Transdermal Delivery
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.
Notch Filter Reduces Amplifier Peaking and Increases Gain Flatness
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.
March 2009
Reconstruct a DAC Transfer Function from its Harmonic Spectral Content
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.
February 2009
This Should Work: Thermistor Senses Liquid Levels
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.
Power Boost Circuit with Current Sense and Kelvin Connection
In automatic test equipment, low-current adjustable and high-current fixed voltage sources are available. An additional supply must be created when a high-current adjustable voltage source is required. This article shows how a high-current rail-to-rail op amp boosts the current of an adjustable voltage source.
January 2009
Low-Cost
Video Multiplexing Using High-Speed Amplifiers
The large number of video sources connected to a single display makes video switching a requirement in home and automotive entertainment systems. In the home, the set-top box, DVR, VCR, DVD player, video game, and PC all feed one display. In cars, the rearview camera, DVD player, navigation system, and auxiliary devices all feed the display.
Equalization and Pre-Emphasis Enable Use of 30-m Cat-5 UTP Cable
The use of the category-5 unshielded twisted-pair cable has grown due to its respectable performance and low cost. Currently being used for keyboard-video-mouse networking, this type of cable provides an inexpensive solution for connecting HDTV components when long-distance connectivity is required.
December 2008
8-channel data-acquisition system
The principal factors that affect data acquisition systems are: speed, accuracy, power dissipation, package size, and component cost, with varying factors becoming critical depending upon the application. A single op amp can be used to drive the ADC in an 8-channel data-acquisition system, reducing the cost and size of the overall system.
As low-power, handheld devices become more prevalent, printed circuit boards with a mixture of 5-V, 3.3-V, 2.5-V, and 1.8-V devices have become common, making the design of a JTAG chain challenging. The designer must determine both the operating voltage and the order to place devices that operate at different voltages. This article provides some tips and techniques for making a robust design.
November 2008
Residual Noise Measurement Extracts DUT Noise from External Sources
Residual phase noise measurement cancels the effect of power supplies, input clocks, or other external noise sources. This article highlights the attributes of the residual phase noise setup and demonstrates how additive phase noise can be used to identify the source of noise-related issues.
Implementing In-Application Programming on the ADuC702x
The ADuC702x Precision Analog Micro-controller provides a serial downloader for loading an assembled program into on-chip memory, but this requires a user to manually tie a pin low during reset or power on. In-application programming allows upgrades without touching the board. This article provides an easy method for upgrading programs.
October 2008
Adding Test Capability to a Window Comparator
It probably wasn't too long after comparators were invented that someone thought to put two of them together to make a window comparator. This article shows how to add an externally controlled test function to a window comparator in order to test whether the circuit is working properly or not.
The best reason to be an applications engineer is the wide variety of customers, applications, circuits, and questions encountered, all of which provide daily opportunities to learn something new. Each year I receive several questions regarding the kind of performance users might expect from our amplifiers when their power supply is off. I like to refer to these amplifiers as “off-amps.”
August 2008
Linear Variable Differential Transformers
The linear variable differential transformer is an accurate and reliable method for measuring linear distance. LVDTs are position-to-electrical sensors whose output is proportional to the position of a movable magnetic core, which moves linearly inside a transformer. LVDTs find uses in machine-tools, robotics, avionics, and computerized manufacturing.
June 2008
Open-Loop Calibration Techniques for Digital-to-Analog Converters
In principle, you give a digital input to a DAC and it provides an accurate output. In reality, the accuracy of the output voltage is subject to gain and offset errors from the DAC and other components in the signal chain. The system designer must compensate for these errors in order to get an accurate output voltage.
May 2008
AC Shield Enhances Remote Capacitive Sensing
The principle of a user touch causing a capacitance change to activate a switch is well understood, but implementing a PCB sensor design with proper shielding and routing poses a challenge. Analog Devices provide a complete capacitive-sensing solution, including controller, evaluation tools, sensor design libraries, and software for the host microcontroller.
Inexpensive High-Speed Amplifiers Make Flexible Clock Buffers
Consumer electronics, which tends to be lower frequency and less demanding than typical clock buffering applications, can use inexpensive high-speed op amps as an alternative to traditional clock buffers. High-speed amplifiers are less expensive than traditional clock buffers, yet can accommodate a wide range of designs.
March 2008
The Contaminator of Signals: HF Common-Mode-Generated Errors
High-frequency common mode exists everywhere. When people are working, high-frequency trash is being generated. Its presence may be recognized by the mysterious errors it generates, but these errors are frequently blamed on thermal effects that almost never exist. Even transducers and their excitation supplies are subject to this error source.
February 2008
Built-in self-test (BIST), once reserved for complex digital chips, can now be found in devices with relatively small amounts of digital content. The move to fine-line process geometries has enabled data converters to include BIST functionality. This allows hierarchical test strategies to be implemented, providing a powerful feature for enhancing system reliability.
December 2007
IC provides temperature, bias, and gain in single-supply applications
Single-supply op-amp applications have inherent problems that are not usually encountered in dual-supply circuits. A reference voltage, usually at midpoint of the amplifier’s output range, must be established to allow a symmetrical output swing with respect to “common.”
Designers continuously search for ways to give their products an edge in a crowded marketplace,
and simple low-to-medium sensitivity devices are no longer sufficient to
meet the demands of embedded
sensor applications. Thick molding compounds, noisy environments,
reliability, and long interconnects are just some of the new challenges facing capacitance sensor
applications.
November 2007
ESD Diode Doubles as Temperature Sensor
ESD diodes can be used to accurately measure the junction temperature of a high-speed amplifier. This article shows how, and compares this measurement with estimates obtained from the thermal specifications found on the data sheet.
Broadband I/Q Modulator Eases Radio Design
Modern digital radio transmitter design poses increasing challenges for equipment designers. The trend towards greater data throughput is increasing the modulation density and carrier bandwidth of transmitted signals. To maintain good adjacent channel power ratio (ACPR) without increasing the rms power level, components with lower intermodulation distortion and lower noise must be used.
October 2007
Solving Dynamic Range Problems in Analog Systems
Cell phones, ultrasound imagers, fault analysis equipment, and many other applications require very wide dynamic range, with signals that vary from a few microvolts to several volts. Designers must provide both high sensitivity and operation under severe overload conditions. An X-amp or VGA can help.
ADC Helps Solve Design Challenges in 3G and 4G Wireless Infrastructure
Manufacturers of wireless infrastructure must constantly reduce the size and cost of newly installed equipment, while maintaining high levels of performance, functionality, and quality of service. Selecting the right converter can improve the overall system design, breaking through barriers such as size and cost.
September 2007
Highly Integrated, Programmable Single-Component Sensors for Industrial System Design
Inertial sensors can improve performance in industrial systems, but a gap has long existed between sensor technology and its implementation. The iSensor™ family is closing this gap in industrial sensor applications. The ADIS16201 is the first implementation of the new technology.
Data and Power Isolation in One Package Provides Total Isolation Solution
Systems that require galvanic isolation need a small, low-cost way to isolate both power and data. Optocouplers can isolate data but cannot generate power; transformers can provide power but are not effective at isolating data. isoPower™ technology offers a new approach.
August 2007
Boost Precision and Accuracy with Single Chip Capacitance- and Impedance-to-Digital Converters
Precision capacitance- and impedance sensing traditionally required discrete components to be skillfully combined. Design, qualification, and component selection were time consuming. Now, two devices deliver higher accuracy, faster TTM, and reduced size, cost, and power.
Single-Chip Clock Generator with 14-Channel Distribution Solves Timing Challenges in Networks
Clock and timing requirements range from system-level synchronization to local signal distribution. Signal integrity experts interpret specifications, oversee testing, and recommend components guaranteed to maintain clean, low jitter clocks throughout the network.
June 2007
High-Speed DAC Controls Power Amplifier Ramp Profile
A high-speed current-output DAC and a single op amp can generate a power amplifier (PA) ramp profile that fits the RF gain requirements for TDMA. The ramp is applied to the voltage control pin of a variable-gain amplifier (VGA) to control the gain of the RF signal entering the PA.
May 2007
Amplifier Input Protection... Friend or Foe?
Many high-speed op amps have on-chip input
protection. Typically transparent to the user, it can sometimes be a circuit’s
Achilles’ heel. This article discusses the advantages and
disadvantages of input protection, and presents circuit solutions
using amplifiers with
input protection.
April 2007
Motionless Bandwidth Test for MEMS
Sensors
March 2007
Single Accelerometer Enhances Pedometer Performance
A single 2- or 3-axis accelerometer can be used to make a simple but relatively accurate pedometer for cost-sensitive applications such as cellular handsets. This note presents an improved algorithm that provides accurate results while running or walking.
February 2007
ADuC702x Analog Microcontroller Generates Programmable Waveforms
Three methods for generating a clock using an ADuC702x Analog Microcontroller.
January 2007
Infinite Bandwidth Op Amp with Limited Bandwidth Feedback
Many designers want to measure the ambient temperature, not that of the...
More than sixty percent of the heat generated on a PC board is transferred...
Heart rate, blood pressure, respiratory rate, temperature, and pulse oximetry...
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