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Application Notes

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  Risk Assessment Advice for High Reliability Amplifiers &mdash AN141
  PDF, 299 Kb, File published: Oct 7, 2013
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  Application Note 141
  October 2013
  Risk Assessment Advice for High Reliability Amplifiers
  Tim Regan and James Mahoney Introduction
  In long life, high reliability systems, supplied power is
  provided only to essential circuitry. As a result many of
  the unpowered circuits may have voltages applied to inputs and outputs without proper supply biasing. As part
  of any diligent system safety risk assessment, a question
  often arises; will the unpowered components be damaged,
  degraded, or impair circuit performance under these
  abnormal operating conditions?
  The purpose of this article is to provide advice for what
  lies within the pins of several common amplifiers used in
  these applications. Most of the amplifiers of interest are the
  radiation hard amplifiers so indicated with a device prefix
  of RH. Another amplifier, the LT6016, is particularly robust
  with over, under and reversed polarity voltage conditions
  and is included for reference.
  With no power applied to the amplifier, forcing a voltage
  between two pins will cause a current to flow. The magnitude of this current differs from pin to pin and device to
  device. A curve tracer is used to show the current vs voltage
  characteristic when overdriving specific pin combinations.
  Referencing these curve trace plots will provide an indication of the magnitude of current flow for a particular …

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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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  Bridge Circuits &mdash AN43
  PDF, 3.8 Mb, File published: Jun 1, 1990
  Subtitled "Marrying Gain and Balance," this note covers signal conditioning circuits for various types of bridges. Included are transducer bridges, AC bridges, Wien bridge oscillators, Schottky bridges, and others. Special attention is given to amplifier selection criteria. Appended sections cover strain gauge transducers, understanding distortion measurements, and historical perspectives on bridge readout mechanisms and Wein bridge oscillators.
  Extract from the document

  Application Note 43
  June 1990
  Bridge Circuits
  Marrying Gain and Balance
  Jim Williams
  Bridge circuits are among the most elemental and powerful
  electrical tools. They are found in measurement, switching, oscillator and transducer circuits. Additionally, bridge
  techniques are broadband, serving from DC to bandwidths
  well into the GHz range. The electrical analog of the mechanical beam balance, they are also the progenitor of all
  electrical differential techniques. and stability of the basic configuration. In particular, transducer manufacturers are quite adept at adapting the bridge
  to their needs (see Appendix A, “Strain Gauge Bridges”).
  Careful matching of the transducer’s mechanical characteristics to the bridge’s electrical response can provide a
  trimmed, calibrated output. Similarly, circuit designers
  have altered performance by adding active elements (e.g.,
  amplifiers) to the bridge, excitation source or both. Resistance Bridges
  Figure 1 shows a basic resistor bridge. The circuit is
  usually credited to Charles Wheatstone, although S. H.
  Christie, who demonstrated it in 1833, almost certainly
  preceded him.1 If all resistor values are equal (or the two
  sides ratios are equal) the differential voltage is zero. The
  excitation voltage does not alter this, as it affects both
  sides equally. When the bridge is operating off null, the
  excitation’s magnitude sets output sensitivity. The bridge …

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  Measurement and Control Circuit Collection &mdash AN45
  PDF, 1.2 Mb, File published: Jun 5, 1991
  A variety of measurement and control circuits are included in this application note. Eighteen circuits, including ultra low noise amplifiers, current sources, transducer signal conditioners, oscillators, data converters and power supplies are presented. The circuits emphasize precision specifications with relatively simple configurations.
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  Application Note 45
  June 1991
  Measurement and Control Circuit Collection
  Diapers and Designs on the Night Shift
  Jim Williams
  Introduction
  During my wife’s pregnancy I wondered what it would
  really be like when the baby was finally born. Before that
  time, there just wasn’t much mothering and fathering to
  do. As a consolation, we busied ourselves watching the
  baby’s heartbeat (Figure 1) on a thrown-together fetal heart
  monitor (see References). feedings. As such, the circuits are annotated with the
  number of feedings required for their completion; e.g., a
  “3-bottle circuit” took three feedings. The circuit’s degree
  of difficulty, and Michael’s degree of cooperation, combined
  to determine the bottle rating, which is duly recorded in
  each figure.
  Low Noise and Drift Chopped Bipolar Amplifier
  Figure 2’s circuit combines the low noise of an LT®1028
  with a chopper based carrier modulation scheme to achieve
  an extraordinarily low noise, low drift DC amplifier. DC
  drift and noise performance exceed any currently available
  monolithic amplifier. Offset is inside 1ОјV, with drift less …

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  Using the LTC Op Amp Macromodels &mdash AN48
  PDF, 297 Kb, File published: Nov 8, 1991
  LTC's op amp macromodels are described in detail, along with the theory behind each model and complete schematics of each topology. Extended modeling topics are discussed, such as phase/frequency response modifications and asymmetric slew rate for JFET op amp models. LTC's macromodels are optimized for accuracy and fast simulation times. Simulation times can be further reduced by using streamlining techniques found throughout AN48.
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  Application Note 48
  November 1991
  Using the LTC Op Amp Macromodels
  Getting the Most from SPICE and the LTC Library
  Walt Jung INTRODUCTION This application note is an overview discussion of the
  Linear Technology SPICE macromodel library. It assumes
  little if any prior knowledge of this software library or its
  history. However, it does assume familiarity with both the
  analog simulation program SPICE (or one of its many
  derivatives), and modern day op amps, including bipolar,
  JFET, and MOSFET amplifier technologies.
  Some Preliminary SPICE Facts of Life
  In the past few years, SPICE simulations have really begun
  to capture a high level of attention on the part of analog
  circuit designers. Perhaps this is due to more affordable
  high performance computers, or perhaps the time for
  simulation is now upon us. In any event, the bottom line is
  that IC vendors are now making macromodels for op amps
  available to their customers.
  For the analog circuit designer, there can be no better fate
  for simulations, viewing this situation in terms of which
  model to use. Designers no longer need worry about
  whether the third party supplier’s model can really cut it. …

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  Video Circuit Collection &mdash AN57
  PDF, 559 Kb, File published: Jan 2, 1994
  AN57, the Video Circuit Collection, features a variety of video circuits designed at LTC. The LT1204 70MHz multiplexer is featured in a number of circuits which require excellent video isolation from channel to channel. High speed voltage and current feedback amplifiers are highlighted throughout the section on video processing circuits. There is a section on applying Current Feedback Amplifiers (CFAs) and a number of articles taken from the Linear Technology magazine.
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  Application Note 57
  January 1994
  Video Circuit Collection
  Jon Munson and Frank Cox
  INTRODUCTION
  Even in a time of rapidly advancing digital image processing, analog video signal processing still remains eminently
  viable. The video A/D converters need a supply of properly
  amplified, limited, DC restored, clamped, clipped, contoured, multiplexed, faded and filtered analog video before
  they can accomplish anything. After the digital magic is
  performed, there is usually more amplifying and п¬Ѓltering
  to do as an adjunct to the D/A conversion process, not to mention all those pesky cables to drive. The analog way
  is often the most expedient and efficient, and you don’t
  have to write all that code.
  The foregoing is only partly in jest. The experienced engineer
  will use whatever method will properly get the job done;
  analog, digital or magic (more realistically, a combination
  of all three). Presented here is a collection of analog video
  circuits that have proven themselves useful. CIRCUIT INDEX
  I. Video Amplifier Selection Guide . 2 II. Video Cable Drivers . 3
  AC-Coupled Video Drivers . 3
  DC-Coupled Video Drivers . 4
  Clamped AC-Input Video Cable Driver . 5
  Twisted-Pair Video Driver and Receiver . 5 III. Video Processing Circuits . 6 …

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
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  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
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  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
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  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
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  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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  Performance Verification of Low Noise, Low Dropout Regulators &mdash LT Journal
  PDF, 1.2 Mb, File published: Sep 1, 2000
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  DESIGN IDEAS Performance Verification of
  Low Noise, Low Dropout Regulators
  by Jim Williams and Todd Owen
  Introduction
  In an increasing trend, telecommunications, networking, audio and
  instrumentation require low noise
  power supplies. In particular, there is
  interest in low noise, low dropout
  linear regulators (LDOs). These
  5Hz SINGLE ORDER
  HIGHPASS components power noise-sensitive circuitry, circuitry that contains
  noise-sensitive elements or both.
  Additionally, to conserve power, particularly in battery-driven apparatus 10Hz 2nd ORDER
  BUTTERWORTH HP GAIN = 60dB IN such as cellular telephones, the
  regulators must operate with low
  input-to-output voltage differentials.
  Devices presently becoming available
  meet these requirements. 100kHz 4th ORDER
  BUTTERWORTH LP 5Hz SINGLE ORDER
  HIGHPASS
  10Hz TO 100kHz Figure 1. Filter structure for noise testing LDOs; Butterworth sections provide the appropriate response in the desired frequency range. EXTERNAL INPUT +
  +
  INPUT 100Ω + 330ВµF 100Ω A1 …

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  JFET Op Amps Equal Low Noise Bipolars and Have Picoamp Current Noise &mdash LT Journal
  PDF, 160 Kb, File published: Sep 1, 1999
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  DESIGN FEATURES JFET Op Amps Equal Low Noise
  Bipolars and Have Picoamp
  by Alexander Strong
  Current Noise
  The LT1792 and LT1793 are single
  JFET op amps that offer both very low
  voltage noise (4nV/в€љHz for the LT1792
  and 6nV/в€љHz for the LT1793) and low
  current noise (10fA/в€љHz for the
  LT1792 and 0.8fA/в€љHz for the
  LT1793), providing the lowest total
  noise over a wide range of transducer
  impedance. Traditionally, op amp
  users have been faced with a choice:
  which op amp will have the lowest
  noise for the transducer at hand. For
  high transducer impedance, the
  LT1792/LT1793 JFET op amps will
  win over the lowest voltage noise
  bipolar op amps due to lower current
  noise. The current noise (2qIB) of an
  amplifier is a function of the input
  bias current (IB). For lower transducer impedance, bipolar op amps …

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  Consider New Precision Amplifiers for Updated Industrial Equipment Designs &mdash LT Journal
  PDF, 154 Kb, File published: Sep 1, 2009
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  L DESIGN FEATURES Consider New Precision Amplifiers for
  Updated Industrial Equipment Designs
  by Brian Black Introduction
  Industrial equipment is designed for
  long life cycles, so the electronic components used in industrial applications
  are often chosen with significant emphasis on proven performance, quality
  and reliability. Precision amplifiers are
  no exception. Even if new and innovative amplifiers become available over a
  product’s lifetime, a redesigned board
  is often built using the same proven
  op amps in the old board. Even for
  entirely new applications, designers
  will choose amplifiers that have proven
  their mettle in other circuits, making a
  choice based more on familiarity than
  performance.
  Although an amplifier may have
  been tried and proven in a design, it
  is not necessarily the best solution for
  every new design. Many can benefit
  from using more recently released
  amplifiers, which can improve overall
  system performance, reduce power …

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Manufacturer's Classification

• Signal Conditioning > Amplifiers > Operational Amplifiers (Op Amps) > Precision Amplifiers (Vos | High Voltage Amplifiers (>12V) | High Speed Amplifiers (GBW > 50MHz) | Low Noise Amplifiers (