A CMOS digitally programmable filter technique for VLSI applications

A novel technique for designing analog CMOS integrated filters is proposed. The technique uses digitally controlled current amplifiers (DCCAs) to provide precise frequency and/or gain characteristics that can be digitally tuned over a wide range. This paper provides an overview of the possibilities of using the DCCA as the core element in programmable filters. In mixed analog/digital systems, the digital tuning feature of the proposed approach allows direct interfacing with the digital signal processing (DSP) part. Basic building blocks such as digitally programmable amplifiers, integrators, and simulated active inductors are given. Systematic designs of second-order filters are presented. Fully differential architectures of the proposed circuits are developed. Experimental results obtained from 0.5 μm standard CMOS chips are provided.