Basic Antilog Amplifier Using Diode:

The circuit diagram of basic antilog amplifier using diode is shown in the Fig. 2.70.

The positions of diode and resistance are exchanged as compared to log amplifier circuit. The node A is grounded and hence node B is at virtual ground. Hence V_B = 0.

Now the current flowing through the diode is I_f and the voltage across diode is V_in itself, as B is at virtual ground. Hence from the diode current equations we can write,

As op-amp input current is zero, the current I must be same as I_f.

The product I_o R_f can be assumed to be V_ref, so we get,

Thus the output voltage is proportional to the exponential function of V_in. The exponential function is nothing but the antilog and thus circuit works as an antilog amplifiers.