Logarithmic Amplifier

Last modified by Microchip on 2023/11/09 09:03

The following figure of the circuit shows a logarithmic amplifier (D1A and the MCP6XXX op-amp) that converts 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.

logarithmic amplifier schematic

  • D1A and D1B are a 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:

  • Photodiode, e.g., Pulse Width Modulation (PWM) encoded digital signal

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