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  Measure Resistances Easily, without Reference Resistor or Current Source &mdash LT Journal
  PDF, 154 Kb, File published: May 1, 2000
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  DESIGN IDEAS Measure Resistances Easily, without
  Reference Resistor or Current Source
  by Glen Brisebois
  Measuring the resistance of a
  device, for example a thermistor, usually requires biasing it with a precision
  current source or combining it with
  several other precision resistors in a
  bridge. The circuit of Figure 1 shows
  how to use the new LT1168 instrumentation amplifier to achieve a
  precision resistance-to-voltage conversion as simply as possible.
  Normally, the resistor across pins 1
  and 8 is the gain-set resistor and the
  voltage across pins 3 and 2 is the
  variable to be measured. In this case, however, the 1.25V reference establishes a fixed input voltage so that the
  variable to be measured is now the
  resistance. The equation for VOUT vs
  RT is VOUT = 1.25V 49.4kΩ/RT. Given
  the limitation on output swing (with
  the supply voltages shown), the smallest measurable resistance is about
  4.5k. The highest resolvable resistance is limited to about 200M by the
  300ВµV output offset voltage of the
  LT1168. The 0.05% accuracy of the
  LT1634 is not an issue here, because …

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  New Instrumentation Amplifier: Single-Resistor Gain Set and Precision Front End Make Accuracy Easy &mdash LT Journal
  PDF, 159 Kb, File published: May 1, 2000
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  DESIGN FEATURES New Instrumentation Amplifier: SingleResistor Gain Set and Precision Front
  End Make Accuracy Easy
  by Glen Brisebois
  The LT1168 is a low power,
  single-resistor gain-programmable
  instrumentation amplifier that is easy
  to apply. It is a pin-compatible upgrade
  for the AD620 (and the INA118 with a
  resistor-value change) and is available in C and I grades. With negligible
  60µV (Max) offset voltage and ultrahigh 1TΩ input impedance, it can
  sense bridges with source impedances
  from 10Ω to 100k without degrading
  the signal. Its 120dB CMRR at 60Hz
  (AV = 100V) is achieved even with a 1k
  source impedance imbalance. Matching the LT1168’s CMRR using discrete
  op amps would require the use of
  0.001% resistors. The LT1168’s
  robust inputs meet IEC1000-4-2
  Level 4 ESD tests with the addition of
  two external 5k series resistors. These
  5k resistors will contribute only a
  negligible 6ВµV of DC error. Table 1. Examples of series resistors for precision gain Desired Gain RG
  (Theoretical) RG1 …

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Manufacturer's Classification

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

Other Names:

LT1168CN8PBF, LT1168CN8 PBF