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Termination of High-Speed Converter Clock Distribution Devices - January 2010 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 Diff-Amp Circuit Measures Hundreds of Volts, Rejects Large Common-Mode Signals - December 2009 To monitor power line voltages or other large signals, a differential amplifier 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. Using Isolated RS-485 in DMX512 Lighting Applications - November 2009 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. Automobile Tail Lamp and Brake Lamp Controller - October 2009 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. Difference Amplifier Forms Heart of Precision Current Source - September 2009 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.
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. Measuring Noise of Low-Fixed-Gain Differential Amplifiers - July 2009 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. Automated Calibration Technique Reduces DAC Offset to Less than 1mV - June 2009 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. Accelerometers—Fantasy & Reality - May 2009 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. Skin Impedance Analysis Aids Active and Passive Transdermal Delivery - April 2009 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 - April 2009 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. Reconstruct a DAC Transfer Function from its Harmonic Spectral Content - March 2009 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. This Should Work: Thermistor Senses Liquid Levels - February 2009 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 - February 2009 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. Low-Cost Video Multiplexing Using High-Speed Amplifiers - January 2009 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 - January 2009 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. 8-channel data-acquisition system - December 2008 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. Multi-Voltage JTAG Chain - December 2008 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. Residual Noise Measurement Extracts DUT Noise from External Sources - November 2008 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 - November 2008 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. Adding Test Capability to a Window Comparator - October 2008 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. Protecting Off-Amps - October 2008 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.” Linear Variable Differential Transformers - August 2008 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. Open-Loop Calibration Techniques for Digital-to-Analog Converters - June 2008 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. AC Shield Enhances Remote Capacitive Sensing - May 2008 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 - May 2008 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. The Contaminator of Signals: HF Common-Mode-Generated Errors - March 2008 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. BIST for Analog Weenies - 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. IC provides temperature, bias, and gain in single-supply applications - December 2007 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.” Providing an Edge in Capacitive Sensor Applications - December 2007 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. ESD Diode Doubles as Temperature Sensor - November 2007 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 - November 2007 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. Solving Dynamic Range Problems in Analog Systems - October 2007 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 - October 2007 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. Highly Integrated, Programmable Single-Component Sensors for Industrial System Design - September 2007 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 - September 2007 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. Boost Precision and Accuracy with Single Chip Capacitance- and Impedance-to-Digital Converters - August 2007 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 - August 2007 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. High-Speed DAC Controls Power Amplifier Ramp Profile - June 2007 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. Amplifier Input Protection... Friend or Foe? - May 2007 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. Motionless Bandwidth Test for MEMS Sensors - April 2007 For industrial systems that use MEMS accelerometers and gyroscopes, optimizing the bandwidth can be a critical consideration. This article explains how to characterize the bandwidth of accelerometers and gyroscopes without using a shaker table. Single Accelerometer Enhances Pedometer Performance - March 2007 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. ADuC702x Analog Microcontroller Generates Programmable Waveforms - February 2007 Three methods for generating a clock using an ADuC702x Analog Microcontroller. Leif's Teaser Number 1 - January 2007 Infinite Bandwidth Op Amp with Limited Bandwidth Feedback Measuring Ambient Temperature - January 2007 Many designers want to measure the ambient temperature, not that of the... Measuring PCB Temperature - January 2007 More than sixty percent of the heat generated on a PC board is transferred... Pulse Oximeter Uses ADuC7024 - January 2007 Heart rate, blood pressure, respiratory rate, temperature, and pulse oximetry...
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