A circuit to convert logarithmically encoded signal to real signals. Transistor in inverting input converts input voltage into logarithmically varying currents.
The circuit is shown in figure below. The input Vi for the antilog-amp is fed into the temperature compensating voltage divider R2 and RTC and then to the base of Q2. The output of A2 is fed back to R1 at the inverting input of op amp A1. The non-inverting inputs are grounded
The output Vo of the antilog- amp is fed back to the inverting input of A1 through the resistor R1.
Hence an increase of input by one volt causes the output to decrease by a decade.