Equivalent Circuits for the Analysis and Synthesis of Switched Capacitor Networks

Over the past several years, many researchers 1-15 have searched for the means to realize monolithic analog recursive filters, particularly for voice frequency applications. Initial attempts to realize a monolithic filters technology led to the development of active-R or resistor-only active filters. 1 " 6 By removing the large external capacitors (C ~ 5000 pF), such filters are, in principle, highly suited to integration with standard bipolar processing. The frequency dependence for these filters is derived1"5 from the single-pole rolloff due to a compensation capacitor (C ~ 30 pF) to achieve a unity gain frequency of 1 MHz. This method of operation posed two significant barriers to the practical application of active-R filters; namely, large resistor ratios1"5 are required to reach audio frequencies and the unity gain frequencies are not sufficiently stable1"1 for precise filter realization. Although these barriers have to some degree been overcome, 5 ' (> it has become clear that the future of integrated circuits is in MOS large-scale integration and very large-scale integration processing, LSI has substantially reduced the cost of digital logic and memory, and VLSI will bring even further cost reductions. 729