Question

The input voltage, 6v and reference voltage, 4 v are applied to a log-amp with saturation current and temperature compensation.  Find the output voltage of the log-amp?

(a) 6.314(kT/q)v

(b) 0.597(kT/q)v

(c) 0.405(kT/q)v

(d) 1.214(kT/q)v

The question was asked by my college director while I was bunking the class.

This intriguing question originated from Log and Antilog Amplifier topic in portion Operational Amplifier Applications of Linear Integrated Circuits

Answer 1

The correct option is (c) 0.405(kT/q)v

Simply put: The output voltage of saturation current and temperature compensation log-amp, VO = (kT/q)×ln(Vi / Vref) =(kT/q)×ln(6v/4v) =(kT/q)×ln(1.5)

VO = 0.405(kT/q)v.