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Application Notes

• Download
  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 …

• Download
  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.
  Extract from the document

  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. …

• Download
  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 …

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. …

• Download
  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 …

• Download
  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 …

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

Articles

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  Consider New Precision Amplifiers for Updated Industrial Equipment Designs &mdash LT Journal
  PDF, 154 Kb, File published: Sep 1, 2009
  Extract from the document

  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 …

Model Line

Manufacturer's Classification

• Signal Conditioning > Amplifiers > Operational Amplifiers (Op Amps) > Precision Amplifiers (Vos | Low Noise Amplifiers ( | High Voltage Amplifiers (>12V) | High Speed Amplifiers (GBW > 50MHz)
• Space & Harsh Environment > Military Hermetic (M)