79-op-amp-logarithmic-amplifier

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

Simulate logarithmic amplifier.

op-amp-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

log_amp_eq01

Current IIN flows through diode D. I-V characteristic of the diode is

log_amp_eq02

In here, IS is the saturation current, VT is the thermal voltage and VD is diode voltage.
It means that

log_amp_eq03

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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