Variable gain amplifiers based on a new approximation method to realize the exponential function

A new current mode variable-gain amplifier (VGA) is developed. The new circuit is based on a novel approximation function that is very close to the ideal exponential relation over a very wide range. Pspice simulations are provided based on Mietec 0.5-μm CMOS technology. The simulations show that the dynamic range achieved is over 50 dB in a single stage. The proposed circuit consumes average power less than 1.2 mW using ±1.5 V supply voltages.