Variable gain current input amplifier and method

Abstract

Variable gain circuitry includes a first input transistor (M) having a source coupled to a first conductor (), a gate coupled to a first input voltage (Vin+), and a drain coupled to a second conductor (). An input of a first current mirror (M,M) is coupled to the second conductor to receive a current corresponding to the difference between the first input voltage and a second input voltage (Vin−). An output of the first current mirror is coupled to a source of current (M). A first transistor (M) has a gate coupled to a third conductor (), a source coupled to a reference voltage (V), and a drain coupled to conduct output current (Iout). A second transistor (M) and a resistive element (M) are coupled in series between the third conductor and the first reference voltage (V), a gate of the second transistor being coupled to the third conductor to produce a nonlinear relationship between currents of the first transistor and the second transistor.