A CMOS narrow-band signaling filter with Q reduction

A circuit for extracting signaling information from its associated voice channel in frequency-division multiplexing has been integrated in metal gate CMOS technology. It uses a frequency translation technique that effectively enhances the Q of the filter to >100. It contains a programmable prefilter, a programmable modulator, and a highly selective bandpass filter. The frequency translation was accomplished through the use of a balanced modulator, which is well suited to a switched-capacitor realization. Design considerations that must be addressed in choosing an optimum architecture and a method of analyzing the ill effects of aliasing in a sampled data modulator were also presented. The technique described here is applicable to the design of a filter with an effective Q of much greater than 100.