All CMOS current-mode exponential function generator

This paper proposed an ultra low-voltage low-power all CMOS current-mode exponential function circuit. The design of the circuit is based on Taylor series expansion for realizing the exponential characteristic and composed of MOS transistors operating in the saturation region. The advantages of the circuit are that its input range can he tuned by adjusting the biased current and its output current presents a very low temperature coefficient. The simulations, based on a 0.25 μm CMOS process, show a 20 dB linear output current range and a 15 dB-linear range with the linearity error less than ± 0.5 dB at 1.2SV supply voltage. The proposed circuit could he used for the design of an extremely low-voltage low-power automatic gain control (AGC) and variable gain amplifier (VGA).