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Temperature compensated logarithmic circuit

  • US 4,604,532 A
  • Filed: 01/24/1985
  • Issued: 08/05/1986
  • Est. Priority Date: 01/03/1983
  • Status: Expired due to Term
First Claim
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1. A log circuit for producing an output signal proportional to the logarithm of an input signal and free from temperature induced variations, comprising:

  • input means responsive to said input signal and including means to develop a first signal proportional to the product of (1) the logarithm of said input signal and (2) absolute temperature;

    circuit means including a PTAT (proportional-to-absolute-temperature) source producing a second signal and coupled to said input means;

    said circuit means further including means for modulating the magnitude of said second signal in accordance with said logarithm while effecting cancellation of the temperature-related factors of said two signals; and

    output means for developing an output signal corresponding to said modulation of said second signal.

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