Capacitive crosscoupling biquad polyphase filter

Abstract

In this paper, the design of biquad polyphase filters with capacitive crosscouplings is presented. Based on the elementary equation s → s − j ωc, which describes the frequency shifting, system theoretic modeling is used for design. Some important observations simplifying the design process are denoted. The developed structures have been simulated in Cadence using operational amplifier models with adjustable gain and bandwidth. Results are compared to those of a Tow-Thomas polyphase filter with comparable sum capacitance but with an operational amplifier amount twice as high. By limiting the gain bandwidth product of the models to reasonable values it is shown that operational amplifier performance does not need to be improved and hence a reduced power consumption can be expected.