A prototype switched-capacitor voltage-wave filter realized in NMOS technology

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Abstract
Presents a novel approach to the realization of monolithic filters. The method is based on using sampled analog signals and is related to the wave digital filter in its design techniques. The eventual monolithic realization in NMOS technology is in the form of a switched-capacitor structure. The design is exact and there is no requirement for a high relative clock frequency. Only unity-gain buffers are required, as opposed to high-gain differential-input operational amplifiers, and so the technique is well suited to CMOS technology. Performance is determined by capacitance ratios and the design is optimally insensitive to parameter variations. Capacitance ratios are moderate relative to those encountered in existing switched-capacitor filters. Results are presented for a prototype integrated circuit design containing fifth- and seventh-order low-pass Chebyshev filters with a designed cutoff at one-eighth clock frequency. The responses achieved for the prototype design show excellent agreement with the theory.

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