The circuit is a modification of an op-amp inverting amplifier, replacing the input resistor with a diode to create an inverting antilogarithmic/exponential amplifier.
This variant is for processing positive input voltage and the output is a negative voltage.
Rf has a very low value of 20 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 antilogarithmic/exponential relation between the output and input voltages. The magnitude of Vin was limited so that the current through the diode will not exceed its maximum rating when the magnitude of the input voltage goes to its maximum. Then the value of Rf was determined so that the expected maximum value of the magnitude of the output voltage is about at the same scale as the maximum value of the magnitude of the input voltage.