Adaptive switched-capacitor filters based on the LMS algorithm

The implementation of adaptive FIR filters based on the LMS algorithm using SC circuits is described. Basically, the filters consist of a delay element, a summing circuit, an integrator, and a multiplier. The influence of nonideal effects of SC networks on the behavior of a given filter is investigated. It is shown that the nonidealities in the FIR filter part of the circuit can be eliminated by an additional constant tap element, whereas the main error source in the adaptation part is the multiplier- and integrator offset-errors. The errors can be compensated for using special offset-free circuits. Using the proposed offset-compensation schemes, the accuracy of a switched-capacitor adaptive filter is mainly determined by the nonlinearity errors of the multipliers.>