Logarithmic Amplifier

The circuit below shows a logarithmic amplifier (D1A and the MCP6XXX op amp) that coverts the sensor current (ISEN) to a voltage proportional to the logarithm of the current. R1 maintains negative feedback when ISEN is small and negative. D1B (VCOR) is used to correct D1A for temperature changes.

  • D1A and D1B are matched pair in the same package.
  • If the source (ISEN) is bi-directional, add a diode in parallel with R1 and D1A, and with the opposite polarity to D1A.


  • Wide dynamic range of current
  • Good impedance buffering of source
  • Simplicity


  • Needs temperature correction

Sensor Examples:

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