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.

log-amp.png
​
  • 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.

Advantages:

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

Disadvantages:

  • Needs temperature correction

Sensor Examples:

​

  Return to Top

© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.