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Application Notes

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  Methods for Measuring Op Amp Settling Time &mdash AN10
  PDF, 277 Kb, File published: Jul 1, 1985
  The AN10 begins with a survey of methods for measuring op amp settling time. This commentary develops into circuits for measuring settling time to 0.0005%. Construction details and results are presented. Appended sections cover oscilloscope overload limitations and amplifier frequency compensation.
  Extract from the document

  Application Note 10
  July 1985
  Methods of Measuring Op Amp Settling Time
  Jim Williams
  Servo, DAC and data acquisition amplifiers all require
  good dynamic response. In particular, the time required
  for an amplifier to settle to final value after an input step
  is especially important. This specification allows setting
  a circuit’s timing margins with confidence that the data
  produced is accurate. The settling time is the total length
  of time from input step application until the amplifier remains within a specified error band around the final value. 10mV or less for a 10V step is of interest. No generalpurpose pulse generator is meant to hold output amplitude
  and noise within these limits. Generator output-caused
  aberration appearing at the oscilloscope probe will be
  indistinguishable from amplifier output movement, producing unreliable results. The oscilloscope connection
  presents additional problems. As probe capacitance rises,
  AC loading of the resistor junction will influence observed
  settling waveforms. The 20pF probe shown alleviates this
  problem but its 10X attenuation sacrifices oscilloscope
  gain. 1X probes are not suitable because of their excessive
  input capacitance. An active 1X FET probe will work, but
  another issue remains. Figure 1 shows one way to measure amplifier settling
  time (see References 1, 2, and 3). The circuit uses the
  “false sum node” technique. The resistors and amplifier …

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  Circuit Techniques for Clock Sources &mdash AN12
  PDF, 150 Kb, File published: Oct 1, 1985
  Circuits for clock sources are presented. Special attention is given to crystal-based designs including TXCOs and VXCOs.
  Extract from the document

  Application Note 12
  October 1985
  Circuit Techniques for Clock Sources
  Jim Williams
  Almost all digital or communication systems require some
  form of clock source. Generating accurate and stable clock
  signals is often a difficult design problem.
  Quartz crystals are the basis for most clock sources. The
  combination of high Q, stability vs time and temperature,
  and wide available frequency range make crystals a
  price-performance bargain. Unfortunately, relatively little
  information has appeared on circuitry for crystals and
  engineers often view crystal circuitry as a black art, best
  left to a few skilled practitioners (see box, “About Quartz
  Crystals”).
  In fact, the highest performance crystal clock circuitry does
  demand a variety of complex considerations and subtle
  implementation techniques. Most applications, however,
  don’t require this level of attention and are relatively easy
  to serve. Figure 1 shows five (5) forms of simple crystal
  clocks. Types 1a through 1d are commonly referred to
  as gate oscillators. Although these types are popular,
  they are often associated with temperamental operation, …

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  Composite Amplifiers &mdash AN21
  PDF, 330 Kb, File published: Jul 1, 1986
  Applications often require an amplifier that has extremely high performance in several areas. For example, high speed and DC precision are often needed. If a single device cannot simultaneously achieve the desired characteristics, a composite amplifier made up of two (or more) devices can be configured to do the job. AN21 shows examples of composite approaches in designs combining speed, precision, low noise and high power.
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  Application Note 21
  July 1986
  Composite Amplifiers
  Jim Williams
  Amplifier design, regardless of the technology utilized, is
  a study in compromise. Device limitations make it difficult
  for a particular amplifier to achieve optimal speed, drift,
  bias current, noise and power output specifications. As
  such, various amplifier families emphasizing one or more
  of these areas have evolved. Some amplifiers are very good
  attempts at doing everything well, but the best achievable
  performance п¬Ѓgures are limited to dedicated designs. designed with little attention to DC biasing considerations
  if a separate stabilizing stage is employed.
  Figure 1 shows a composite made up of an LTВ®1012 low drift
  device and an LT1022 high speed amplifier. The overall circuit is a unity-gain inverter, with the summing node located
  at the junction of three 10k resistors. The LT1012 monitors
  this summing node, compares it to ground and drives the
  LT1022’s positive input, completing a DC stabilizing loop
  around the LT1022. The 10k-300pF time constant at the
  LT1012 limits its response to low frequency signals. The
  LT1022 handles high frequency inputs while the LT1012
  stabilizes the DC operating point. The 4.7k-220О© divider
  at the LT1022 prevents excessive input overdrive during …

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  Thermocouple Measurement &mdash AN28
  PDF, 988 Kb, File published: Feb 1, 1988
  Considerations for thermocouple-based temperature measurement are discussed. A tutorial on temperature sensors summarizes performance of various types, establishing a perspective on thermocouples. Thermocouples are then focused on. Included are sections covering cold-junction compensation, amplifier selection, differential/isolation techniques, protection, and linearization. Complete schematics are given for all circuits. Processor- based linearization is also presented with the necessary software detailed.
  Extract from the document

  Application Note 28
  February 1988
  Thermocouple Measurement
  Jim Williams
  Introduction Thermocouples in Perspective In 1822, Thomas Seebeck, an Estonian physician, accidentally joined semicircular pieces of bismuth and copper
  (Figure 1) while studying thermal effects on galvanic arrangements. A nearby compass indicated a magnetic disturbance. Seebeck experimented repeatedly with different
  metal combinations at various temperatures, noting relative
  magnetic п¬Ѓeld strengths. Curiously, he did not believe that
  electric current was flowing, and preferred to describe the
  effect as “thermo-magnetism.” He published his results in
  a paper, “Magnetische Polarisation der Metalle und Erze
  durch Temperatur-Differenz” (see references). Temperature is easily the most commonly measured
  physical parameter. A number of transducers serve temperature measuring needs and each has advantages and
  considerations. Before discussing thermocouple-based
  measurement it is worthwhile putting these sensors in
  perspective. Figure 2’s chart shows some common contact
  temperature sensors and lists characteristics. Study reveals
  thermocouple strengths and weaknesses compared to
  other sensors. In general, thermocouples are inexpensive,
  wide range sensors. Their small size makes them fast and
  their low output impedance is a benefit. The inherent voltage output eliminates the need for excitation. Subsequent investigation has shown the “Seebeck Effect”
  to be fundamentally electrical in nature, repeatable, and
  quite useful. Thermocouples, by far the most common …

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  Applications for a Switched-Capacitor Instrumentation Building Block &mdash AN3
  PDF, 1.5 Mb, File published: Jul 1, 1985
  This application note describes a wide range of useful applications for the LTC1043 dual precision instrumentation switched capacitor building block. Some of the applications described are ultra high performance instrumentation amplifier, lock-in amplifier, wide range digitally controlled variable gain amplifier, relative humidity sensor signal conditioner, LVDT signal conditioner, charge pump F/V and V/F converters, 12-bit A/D converter and more.
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  Application Note 3
  July 1985
  Applications for a Switched-Capacitor Instrumentation
  Building Block
  Jim Williams
  CMOS analog IC design is largely based on manipulation
  of charge. Switches and capacitors are the elements used
  to control and distribute the charge. Monolithic п¬Ѓlters, data
  converters and voltage converters rely on the excellent
  characteristics of IC CMOS switches. Because of the importance of switches in their circuits, CMOS designers have
  developed techniques to minimize switch induced errors,
  particularly those associated with stray capacitance and
  switch timing. Until now, these techniques have been used
  only in the internal construction of monolithic devices. A
  new device, the LTCВ®1043, makes these switches available
  for board-level use. Multi-pole switching and a self-driven,
  non-overlapping clock allow the device to be used in circuits
  which are impractical with other switches. Conceptually, the LTC1043 is simple. Figure 1 details its
  features. The oscillator, free-running at 200kHz, drives a
  non-overlapping clock. Placing a capacitor from Pin 16 to
  ground shifts the oscillator frequency downward to any
  desired point. The pin may also be driven from an external
  source, synchronizing the switches to external circuitry. …

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  Thermal Techniques in Measurement and Control Circuitry &mdash AN5
  PDF, 175 Kb, File published: Dec 1, 1984
  6 applications utilizing thermally based circuits are detailed. Included are a 50MHz RMS to DC converter, and anemometer, a liquid flow meter and others. A general discussion of thermodynamic considerations involved in circuitry is also presented.
  Extract from the document

  Application Note 5
  December 1984
  Thermal Techniques in Measurement and Control Circuitry
  Jim Williams
  Designers spend much time combating thermal effects in
  circuitry. The close relationship between temperature and
  electronic devices is the source of more design headaches
  than any other consideration. regulator’s output low, biasing Q1. As the heater warms,
  the thermistor ’s value decreases. When its inputs finally
  balance, A1 comes out of saturation and the LT3525A pulse
  width modulates the heater via Q1, completing a feedback
  path. A1 provides gain and the LT3523A furnishes high
  efficiency. The 2kHz pulse width modulated heater power
  is much faster than the thermal loop’s response and the
  oven sees an even, continuous heat flow. In fact, instead of eliminating or compensating for thermal
  parasitics in circuits, it is possible to utilize them. In particular, applying thermal techniques to measurement and
  control circuits allows novel solutions to difficult problems.
  The most obvious example is temperature control. Familiarity with thermal considerations in temperature control
  loops permits less obvious, but very useful, thermallybased circuits to be built. The key to high performance control is matching the gain
  bandwidth of A1 to the thermal feedback path. Theoretically, it is a simple matter to do this using conventional
  servo-feedback techniques. Practically, the long time
  constants and uncertain delays inherent in thermal systems
  present a challenge. The unfortunate relationship between …

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  Applications of New Precision Op Amps &mdash AN6
  PDF, 784 Kb, File published: Jan 1, 1985
  Application considerations and circuits for the LT1001 and LT1002 single and dual precision amplifiers are illustrated in a number of circuits, including strain gauge signal conditioners, linearized platinum RTD circuits, an ultra precision dead zone circuit for motor servos and other examples.
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  Component and Measurement Advances Ensure 16-Bit DAC Settling Time &mdash AN74
  PDF, 980 Kb, File published: Jul 1, 1998
  DAC DC specifications are relatively easy to verify. AC specifications require more sophisticated approaches to produce reliable information. In particular, the settling time of the DAC and its output amplifier is extraordinarily difficult to determine to 16-bit resolution. This application note presents methods for 16-bit DAC settling time measurement and compares results. Appendices discuss oscilloscope overdrive, frequency compensation, circuit and optimization techniques, layout, power stages and a historical perspective of precision DACs.
  Extract from the document

  Application Note 74
  July 1998
  Component and Measurement Advances Ensure
  16-Bit DAC Settling Time
  The art of timely accuracy
  Jim Williams
  Introduction
  Instrumentation, waveform generation, data acquisition,
  feedback control systems and other application areas are
  beginning to utilize 16-bit data converters. More specifically, 16-bit digital-to-analog converters (DACs) have
  seen increasing use. New components (see Components
  for 16-Bit Digital-to-Analog Conversion, page 2) have
  made 16-bit DACs a practical design alternative1. These
  ICs provide 16-bit performance at reasonable cost compared to previous modular and hybrid technologies. The
  DC and AC specifications of the monolithic DAC’s
  approach or equal previous converters at significantly
  lower cost.
  DAC Settling Time
  DAC DC specifications are relatively easy to verify. Measurement techniques are well understood, albeit often
  tedious. AC specifications require more sophisticated
  approaches to produce reliable information. In particular,
  the settling time of the DAC and its output amplifier is
  extraordinarily difficult to determine to 16-bit resolution. …

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  A Standards Lab Grade 20-Bit DAC with 0.1ppm/В° Drift: The Dedicated Art of Digitizing One Part Per Million &mdash AN86
  PDF, 540 Kb, File published: Jan 1, 2001
  This publication details a true 1ppm D-to-A converter. Total DC error of this processor corrected DAC remains within 1ppm from 18-32°C, including reference drift. DAC error exclusive of reference drift is substantially better. Construction details and performance verification techniques are included, along with a complete software listing.
  Extract from the document

  Application Note 86
  January 2001
  A Standards Lab Grade 20-Bit DAC with 0.1ppm/В°C Drift
  The Dedicated Art of Digitizing One Part Per Million
  Jim Williams
  J. Brubaker
  P. Copley
  J. Guerrero
  F. Oprescu INTRODUCTION
  Significant progress in high precision, instrumentation
  grade D-to-A conversion has recently occurred. Ten years
  ago 12-bit D-to-A converters (DACs) were considered
  premium devices. Today, 16-bit DACs are available and
  increasingly common in system design. These are true
  precision devices with less than 1LSB linearity error and
  1ppm/В°C drift.1 Nonetheless, there are DAC applications
  that require even higher performance. Automatic test
  equipment, instruments, calibration apparatus, laser trimmers, medical electronics and other applications often
  require DAC accuracy beyond 16 bits. 18-bit DACs have
  been produced in circuit assembly form, although they are
  expensive and require frequent calibration. 20 and even
  23+ (0.1ppm!) bit DACs are represented by manually
  switched Kelvin-Varley dividers. These devices, although …

Design Notes

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  Updated Operational Amplifier Selection Guide for Optimum Noise Performance &mdash DN140
  PDF, 74 Kb, File published: Oct 1, 1996
  Extract from the document

  Operational Amplifier Selection Guide for
  Optimum Noise Performance – Design Note 140
  Frank Cox
  Eight years ago, George Erdi wrote a very useful Design
  Note (DN6) that presented information to aid in the
  selection of op amps for optimum noise performance,
  in both graphical and tabular form. Design Note 140 is
  an update of DN6. It covers new low noise op amps as
  well as some high speed op amps. Although a great deal
  has changed in eight years, especially in electronics,
  noise is still a critical issue in op amp circuit design
  and the LTВ®1028 is still the lowest noise op amp for
  low source impedance applications.
  The amount of noise an op amp circuit will produce
  is determined by the device used, the total resistance
  in the circuit, the bandwidth of the measurement, the
  temperature of the circuit and the gain of the circuit. A
  convenient п¬Ѓgure of merit for the noise performance
  of an op amp is the spectral density or spot noise. This
  is obtained by normalizing the measurement to a unit
  of bandwidth. Here the unit is 1Hz and the noise is reported as “nV/√Hz.” The noise in a particular application
  bandwidth can be calculated by multiplying the spot
  noise by the square root of the application bandwidth. …

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  Noise Calculations in Op Amp Circuits &mdash DN15
  PDF, 224 Kb, File published: Sep 1, 1988
  Extract from the document

  Noise Calculations1 in Op Amp Circuits – Design Note 15
  Alan Rich
  Noise calculations in op amp circuits are one of the most
  confused calculations that an analog engineer must
  perform.
  One cannot just look at noise specifications; the total op
  amp circuit including resistors and operating frequency
  range must be included in calculations for circuit noise. A
  “low” noise amplifier in one circuit will become a “high”
  noise amplifier in another circuit.
  As part of this Design Note, an IBM-PC2 or compatible
  computer program, NOISE, has been written to perform
  the noise calculations. This program allows the user to
  calculate circuit noise using LTC op amps, determine the
  best LTC op amp for a low noise application, display the
  noise data for LTC op amps, calculate resistor noise, and
  calculate circuit noise using noise specs for any op amp.
  At the end of this Design Note there are detailed operating
  instructions for the computer program NOISE.
  To calculate noise for an op amp circuit, one must consider the op amp voltage and current noise density and
  1/f corner frequency, the frequency range of interest, and
  the resistor noise.
  The most comprehensive specification for voltage or current noise is the noise density frequency response curve …

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  Operational Amplifier Selection Guide for Optimum Noise Performance &mdash DN3
  PDF, 224 Kb, File published: Oct 1, 1987
  Extract from the document

  Operational Amplifier Selection Guide for Optimum Noise
  Performance – Design Note 3
  George Erdi
  The LTВ®1028 is the lowest noise op amp available today.
  Its voltage noise is less than that of a 50О© resistor. In
  other words, if the LT1028 is operated with source resistors in excess of 50О© , resistor noise will dominate. If the
  application requires large source resistors, the LT1028’s
  relatively high current noise will limit performance, and
  other op amps will provide lower overall noise. The table below lists which op amp gives minimum total
  noise for a specified equivalent source resistance. A two
  step procedure should be followed to optimize noise: In general, the total noise of any op amp (referred to the
  input) is given by: The table actually has two sets of devices: one for low
  frequency (instrumentation), one for wideband applications. The slight differences between the two columns
  occur because voltage and current noise increase at low
  frequencies (below the so-called 1/f corner) while resistor
  noise is flat with frequency. total noise = (voltage noise) + (resistor noise) + (current noise R )
  2 2 2 eq where, (2) Enter the table to find the optimum op amp. Best Op Amp for Lowest Noise vs Source Resistance resistor noise = 0.13 Re q in nV Hz
  and Req = equivalent source resistance
  = R2 + R1//R3
  R3
  R1 – R2 + DN003 F01 Several conclusions can be reached by inspection of the
  equation:
  (a) To minimize noise, resistor values should be minimized to make the contribution of the second and …

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  Chopper vs Bipolar Op Amps—An Unbiased Comparison &mdash DN42
  PDF, 70 Kb, File published: Dec 1, 1990
  Extract from the document

  Chopper vs Bipolar Op Amps—An Unbiased Comparison
  Design Note 42
  George Erdi Table 1 lists the parameters of importance. In all input
  parameters (except noise) the advantage unquestionably goes to the choppers. 5ОјV maximum offset voltage, 0.5ОјV/В°C maximum drift are commonly found
  Table 1. Chopper Stabilized vs Precision Bipolar Op Amps
  ADVANTAGE
  PARAMETER
  Offset Voltage
  Offset Drift
  All Other DC Specs CHOPPER BIPOLAR COMMENTS
  вњ“
  вњ“
  вњ“ No Contest Wideband, 20Hz to
  1MHz вњ“ See Details in Text Noise вњ“ See Details in Text вњ“ Rail to Rail Swing
  2mA Limit on
  Choppers Output: Light Load
  Heavy Load
  Single Supply
  Application вњ“ вњ“ Inherent to
  Choppers Needs
  Special Design
  Bipolars В±15V Supply Voltage вњ“ Except LTC1150 Prejudice/Tradition вњ“ Still a Chopper
  Problem Cost 08/90/86_conv вњ“ Unless DC …

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  Operational Amplifier Selection Guide for Optimum Noise Performance &mdash DN6
  PDF, 137 Kb, File published: Jan 1, 1988

Articles

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  Component and Measurement Advances Ensure 16-Bit DAC Settling Time (Part One) &mdash LT Journal
  PDF, 262 Kb, File published: Aug 1, 1998
  Extract from the document

  DESIGN INFORMATION Component and Measurement
  Advances Ensure 16-Bit DAC
  by Jim Williams
  Settling Time (Part One)
  Introduction
  Instrumentation, waveform generation, data acquisition, feedback
  control systems and other application
  areas are beginning to utilize 16-bit
  data converters. More specifically, 16bit digital-to-analog converters (DACs)
  have seen increasing use. New components (see the sidebar “Components
  for 16-Bit Digital-to-Analog Conversion” on page 31) have made 16-bit
  DACs a practical design alternative.
  These ICs provide 16-bit performance
  at reasonable cost compared to previous modular and hybrid technologies.
  The DC and AC specifications of the
  monolithic DACs approach or equal
  previous converters at significantly
  lower cost. DAC Settling Time
  DAC DC specifications are relatively
  easy to verify. Measurement techniques are well understood, albeit often
  tedious. AC specifications require
  more sophisticated approaches to
  produce reliable information. In particular, the settling time of the DAC …

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Manufacturer's Classification

• Signal Conditioning > Amplifiers > Operational Amplifiers (Op Amps) > Precision Amplifiers (Vos | Low Noise Amplifiers ( | High Voltage Amplifiers (>12V)