FIR and IIR SC interpolation filters using parallel cyclic‐type circuit for high frequency

Abstract

AbstractHigh‐frequency responses of switched‐capacitor filters deteriorated mostly as a result of the finite gain bandwidth product of an operational amplifier. the authors previously proposed a type of FIR and IIR switched‐capacitor filter using a parallel cyclic‐type circuit in order to improve high‐frequency performance. In the parallel cyclic‐type circuit, an operational amplifier is not used as a delay element. Instead, both delay and weighting operations are implemented with switches and a coefficient capacitor simultaneously. Only one operational amplifier is used for a summing operation. Consequently, the maximum operational frequency of the filter is extended up to the unity gain frequency of the operational amplifier.This paper proposes a new type of FIR and IIR switched‐capacitor interpolation filter that can be operated in a high‐frequency region by using the parallel cyclic‐type circuit. Effects of both the finite gain bandwidth of the operational amplifier and parasitic capacitances on filter performance are analyzed by applying the analysis method of periodically time‐varying digital filter. These effects are found to be very few in number below the unity gain frequency of the operational amplifier. Third‐order FIR and biquadratic IIR interpolation filters are constructed with discrete components and verified to have good frequency performance that coincides with the analyzed one.