Temperature insensitive current-mode CMOS exponential function generator and its application in variable gain amplifier

A new CMOS current-mode circuit to produce the exponential function, y=exp(x)y=exp(x), is proposed. The proposed design has large input and output dynamic ranges while keeping very small linearity error. The functionality of the proposed design, confirmed using Tanner tool with 0.35 μm CMOS process technology indicates that it has superior performance compared to previously reported designs. A nearly 96 dB output dynamic range is obtained with the linearity error less than ±0.5 dB over an input range −5.75≤x≤5.75. The change in the output current due to temperature variation is ±1.27 dB over 100 °C range. Application of the proposed exponential function generator in the design of an exponentially controlled variable gain amplifier is presented and its functionality is confirmed using simulation. 71 Linear-in-dB variable gain was achieved. The dB gain is controlled linearly by the control current, resulting in simple and low power structure.