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

Abstract

A new CMOS current-mode circuit to produce the exponential function, 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 0.35μm CMOS process technology indicates that it has superior performance compared to previously reported designs. A nearly 96dB output dynamic range is obtained with the linearity error less than ±0.5dB over an input range −5.75≤x≤5.75. The change in the output current due to temperature variation is ±1.27dB 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.