PWL Current-Mode CMOS Exponential Circuit Based on Maximum Operator

A novel technique to implement an exponential pre-distortion circuit based on a piecewise-linear (PWL) construction method is presented. The technique is based on a maximum operator together with rectified affine functions. The proposed circuit is implemented with current mirrors and a Winner-Take-All circuit, thus achieving a technology-independent exponential circuit with no range limit, ideally. The proposed technique avoids the propagation and accumulation of the linear segment errors, which affect the exponential approximation only locally. To demonstrate the technique, a prototype was fabricated in 0.13 μm CMOS technology and measurement results were obtained revealing a linear-in-decibel range around 41 dB with an error of ±1 dB and 535 μW power consumption.