Logarithmic amplifier is realized with op-amp is given in figure bellow.

Simulate logarithmic amplifier.

Logarithmic amplifier provides a logarithmic output for a linear voltage input. In the given schematic, output voltage can be calculated via equaling currents. Input current is

Current **I _{IN}** flows through diode D. I-V characteristic of the diode is

In here, **I _{S}** is the saturation current,

**V**is the thermal voltage and

_{T}**V**is diode voltage.

_{D}It means that

Input voltage is positive, and output voltage is negative natural logarithm scaled.

Go to logarithmic amplifier simulation.

**External links:**

Op-amp Logarithmic amplifier on CircuitsToday

Op-amp Logarithmic amplifier on Wikipedia

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