Logarithmic Amplifier (Diode Feedback, Negative Input - Positive Output)

The circuit is a modification of an op-amp inverting amplifier, replacing the feedback resistor with a diode to create an inverting logarithmic amplifier. This variant is for processing negative input voltage and the output is a positive voltage. Note: Rin has a very low value of 10 Ω, this was done because of an effort to find suitable scaling of the input and output voltages so that their simultaneous graphs can be conveniently viewed. Moreover, the graph should convey insight about the logarithmic relation between the output and input voltages. The magnitude of Vin was first determined so that it is about at the same scale as the expected maximum value of the magnitude of the output voltage. Then the value of Rin was determined so that the current through the diode will not exceed its maximum rating when the magnitude of the input voltage goes to its maximum.