Improved Accuracy Function Generator Circuit for Analog Signal Processing

A new current-mode function generator circuit will be presented, having a much smaller complexity per function with respect to the previous reported similar works. The circuit allows to compute an important number of mathematical functions using their n-th order limited polynomial series expansion. The approximation error could be strongly decreased by increasing the number of terms considered in the previous expansion. The selection of the active function is digitally made, the main part of the function generator being common for all the computed functions. The circuit core, the current squarer circuit, will be analyzed in six possible implementations, using exclusively MOS transistors working in the saturation region for improving the circuit frequency response. In order to reduce the circuit complexity, classical MOS active devices will be replaced by a FGMOS (floating gate MOS) transistor. A very important advantage of the proposed function generator circuit is the independence of the computed function on the technological parameters. The circuit is implemented in 0.35 mum CMOS technology, the SPICE simulations confirming the theoretical estimated results.