Integrated bandsplit filter system for a dual-tone-multifrequency receiver

A single-chip integrated filter system, consisting of six switched-capacitor low- and high-pass filters, is described. It performs the separation of the high-group and low-group components of the incoming signal of a dual-tone multifrequency (DTMF) receiver, and the hard-limiting of the separated tones. It can thus serve as an analog front end to a DTMF receiver. The filter uses state-of-the-art circuitry to achieve a small spread of element-values and a low sensitivity to stray capacitances. It was fabricated using 5μ CMOS technology; the die measures 123 × 186 mils. The chip needs a single voltage supply, and dissipates about 200mW power