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Application Notes

• Download
  Application Considerations for an Instrumentation Lowpass Filter &mdash AN20
  PDF, 2.8 Mb, File published: Sep 1, 1986
  Discusses the principles of operation of the LTC1062 and helpful hints for its application. Various application circuits are explained in detail with focus on how to cascade two LTC1062s and how to obtain notches. Noise and distortion performance are fully illustrated.
  Extract from the document

  Application Note 20
  September 1986
  Application Considerations for an
  Instrumentation Lowpass Filter
  Nello Sevastopoulos
  Description of this, the value of the (R C) product is critically related
  to the filter passband flatness and to the filter stability.
  The internal circuitry of the LTC1062 is driven by a clock
  which also determines the п¬Ѓlter cutoff frequency. For a
  maximally flat amplitude response, the clock should be
  100 times the desired cutoff frequency and the (R, C)
  should be chosen such as: The LTCВ®1062 is a versatile, DC accurate, instrumentation
  lowpass п¬Ѓlter with gain and phase that closely approximate
  a 5th order Butterworth п¬Ѓlter. The LTC1062 is quite different from presently available lowpass switched-capacitor
  п¬Ѓlters because it uses an external (R, C) to isolate the
  IC from the input signal DC path, thus providing DC accuracy. Figure 1 illustrates the architecture of the circuit.
  The output voltage is sensed through an internal buffer,
  then applied to an internal switched-capacitor network
  which drives the bottom plate of an external capacitor to
  form an input-to-output 5th order lowpass п¬Ѓlter. The input
  and output appear across an external resistor and the IC
  part of the overall п¬Ѓlter handles only the AC path of the
  signal. A buffered output is also provided (Figure 1) and …

• Download
  Unique Applications for the LTC1062 Lowpass Filter &mdash AN24
  PDF, 587 Kb, File published: Sep 1, 1987
  Highlights the LTC1062 as a lowpass filter in a phase lock loop. Describes how the loop's bandwidth can be increased and the VCO output jitter reduced when the LTC1062 is the loop filter. Compares it with a passive RC loop filter. Also discussed is the use of LTC1062 as simple bandpass and bandstop filter.
• 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 …

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  Instrumentation Applications for a Monolithic Oscillator: A Clock for All Reasons &mdash AN93
  PDF, 1.1 Mb, File published: Feb 1, 2003
  Instrumentation applications for a monolithic programmable oscillator are presented in this publication. Circuits include platinum and thermistor based thermometers, an isolated thermometer and three relative humidity signal conditioners. Bipolar and FET input chopper stabilized amplifiers with noise below 45nV (0.1Hz to 10Hz) are detailed. Two clock tunable sine wave generators with settable amplitude appear, as well as a tunable notch filter, an interval generator and an A to D converter. The oscillator's performance is contrasted against other approaches and its interval operation discussed.
  Extract from the document

  Application Note 93
  February 2003
  Instrumentation Applications for a Monolithic Oscillator
  A Clock for All Reasons
  Jim Williams INTRODUCTION Clock Types Oscillators are fundamental circuit building blocks. A
  substantial percentage of electronic apparatus utilize oscillators, either as timekeeping references, clock sources,
  for excitation or other tasks. The most obvious oscillator
  application is a clock source in digital systems.1 A second
  area is instrumentation. Transducer circuitry, carrier based
  amplifiers, sine wave formation, filters, interval generators and data converters all utilize different forms of
  oscillators. Although various techniques are common, a
  simply applied, broadly tunable oscillator with good accuracy has not been available. Commonly employed oscillators are resonant element
  based or RC types.2 Figure 1 shows two of each. Quartz
  crystals and ceramic resonators offer high initial accuracy
  and low drift (particularly quartz) but are essentially
  untunable over any significant range. Typical RC types
  have lower initial accuracy and increased drift but are
  easily tuned over broad ranges. A problem with conventional RC oscillators is that considerable design effort is
  required to achieve good specifications. A new device, the
  LTC1799, is also an RC type but fills the need for a simply
  applied, broadly tunable, accurate oscillator. Its accuracy
  and drift specifications fit between resonator based types
  and typical RC oscillators. Additionally, its board footprint, …

Design Notes

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  Sampling of Signals for Digital Filtering and Gated Measurements &mdash DN2
  PDF, 377 Kb, File published: Oct 1, 1987
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  Sampling of Signals for Digital Filtering and
  Gated Measurements – Design Note 2
  William Rempfer
  Introduction
  For many signal processing applications a sample and
  hold function is required in a data acquisition system. It
  is often critical for the processing system to know the
  exact value of an analog input at an exact time. In DSP
  applications such as digital filters, the usable bandwidth
  of the system is limited by the Nyquist frequency and the
  sample and hold bandwidth need only be, and is often
  intentionally limited to, one half the sampling rate. However,
  another area of application requires infrequently capturing
  instantaneous values of relatively fast signals, sometimes
  referred to as gated measurements. In the extreme case
  of pulse height measurements, only one sample point is
  required. Here, the sample and hold bandwidth should
  be as high as possible even though the sampling rate is
  very low.
  The LTC В®1090 excels in both environments. This note
  shows how the LTC1090 sample and hold can be synchronized to an external event and gives two simple
  applications: an 8-channel data acquisition system with
  digital filtering, and the gated measurement of a 1MHz …

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  Complex Data Acquisition System Uses Few Components &mdash DN24
  PDF, 84 Kb, File published: Jul 1, 1989
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  Complex Data Acquisition System Uses Few Components
  Design Note 24
  Richard Markell
  Introduction
  Sophisticated п¬Ѓlter system designs frequently demand
  expensive printed circuit boards chock-full of operational amplifiers and precision capacitors. Digital filters
  require fewer but more expensive devices and a lot of
  software. However, advances in switched capacitor
  п¬Ѓlters have made the design of elegant п¬Ѓlter systems
  cheaper, easier and much smaller. The system shown
  in block diagram form in Figure 1 is a good example. It
  is a typical system for п¬Ѓltering transducer signals. Its
  input is a DC-to-20kHz signal; its output allows signals
  to be analyzed in three frequency bands.
  INPUT
  DC-20kHz 400Hz HPF 10kHz LPF OUTPUT 1
  400Hz–10kHz
  BPF 1kHz LPF OUTPUT 2
  10Hz–1000Hz
  BPF 100Hz LPF OUTPUT 3
  10Hz–100Hz
  BPF 10Hz HPF 400Hz 10kHz 10Hz 1000Hz 10Hz 100Hz
  DN024 F01 Figure 1. Filter System Block Diagram Implementation …

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  DC Accurate Filter Eases PLL Design &mdash DN7
  PDF, 203 Kb, File published: Feb 1, 1988
  Extract from the document

  DC Accurate Filter Eases PLL Design – Design Note 7
  Nello Sevastopoulos and Phillip Karantzalis
  The LTC В®1062 is a versatile, DC accurate, instrumentation lowpass filter with gain and phase that closely approximate a 5th order Butterworth filter. The LTC1062
  is quite different from presently available lowpass
  switched capacitor filters because it uses an external
  (R, C) to isolate the IC from the input signal DC path, thus
  providing DC accuracy. The DC accurate output, pin 7
  of Figure 1, is buffered by an internal op amp from the
  switched capacitor network. The output of the switched
  capacitor network drives the bottom of C1. The input and
  output appear across an external resistor and, the IC part
  of the overall filter handles only the AC path of the signal.
  A buffered output is also provided (Figure 1) and its
  maximum guaranteed offset voltage over temperature is
  20mV. Typically the buffered output offset is 0-5mV and
  drift is 1ВµV/В°C. The use of an input (R, C) also provides
  other advantages, such as lower noise and antialiasing.
  With commercially available PLLs, the loop filter is designed by the user to optimize the loop performance. For
  a variety of applications, a 1st or 2nd order lowpass passive or active R, C filter will do the job. When minimum
  output jitter and good transient response are required simultaneously, the design of the loop filter becomes more
  sophisticated. For instance, a fast transient response
  implies wide filter bandwidth and a reduced VCO output
  jitter implies minimum ripple at the VCO input. This is …

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  Chopper Amplifiers Complement a DC Accurate Low-Pass Filter &mdash DN9
  PDF, 369 Kb, File published: Mar 1, 1988
  Extract from the document

  Chopper Amplifiers Complement a DC
  Accurate Low-Pass Filter – Design Note 9
  Nello Sevastopoulos
  Monolithic switched-capacitor low-pass filters, although
  they offer precise frequency responses, cannot usually be used for DC accurate applications because of
  their prohibitive DC offsets and poor gain linearity. The
  LTC В®1062, however, is quite different from currently
  available low-pass switched capacitor filters because it
  uses an external (R, C) to isolate the IC from the inputsignal DC path and to provide antialiasing for incoming
  signals larger than half its clock frequency. The LTC1062
  is ideal when used in conjunction with high performance
  chopper-stabilized op amps.
  The LTC1050 is an ultra low offset, low noise chopper with
  the sampling capacitors internal. It can remove residual
  clock noise without adding further DC error. Also, the
  internal capacitor minimizes board area.
  Figure 1 shows a low cost, 7th order DC accurate, 10Hz
  low-pass filter where amplitude and phase response
  closely approximate a Bessel filter. The required clock
  frequency is 2kHz, thus yielding clock to cutoff frequency
  ratio of 200:1. VIN R'
  196k R
  16k …

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Manufacturer's Classification

• Signal Conditioning > Filters > Lowpass Filters