An exponential-law element with temperature compensation

A temperature compensated exponential-law like element is presented. The circuit is intended for gain-control of amplifiers in sonar applications. Simulations has been carried out using transistor parameters from a 1.2 /spl mu/m BiCMOS process. The output of the circuit is two currents. The ratio between these two output-currents changes exponentially from -63.5 dB to 63.5 dB as a control-voltage changes linearly from V/sub ss/ (0V) to V/sub DD/ (5V). Without temperature compensation the deviation from the exponential like transfer function is typically 18.2 dB in the -40/spl deg/C to 100/spl deg/C temperature range. With temperature compensation the deviation is 0.7 dB.