TABLE OF CONTENTS One of the major applications of switched capacitor circuits is linear filters. In Section 9.1, we showed that the accuracy of the circuit time constants was proportional to the relative accuracy of capacitors. This accuracy was sufficient to implement practical filters in CMOS technology. During the late 1970s and early 1980s, the use of switched capacitor circuits to implement monolithic filters was developed to maturity [ [17], [18]]. Because of the maturity of this field, it is important to provide a brief overview of the application of switched capacitor filters. More details concerning switched capacitor filter design can be found elsewhere [ [15], [19], [20]].
The objective of linear filters is frequency-dependent processing on continuous time signals. In other words, signals with various frequencies will be processed differently than signals made up from different frequencies. The processing is constrained to the amplitude and phase of a sinusoid. In an ideal low-pass filter, the frequencies of a signal below a certain frequency are amplified by 1 and the frequencies above are rejected. Although the phase is important, most filter applications focus on the magnitude. It must be realized, however, that if the phase is not linear with frequency, then the group delay of various signals will be different and a phase distortion will be seen in the signal processing of the filter.
An ideal filter would have a range of gain that is finite ( passband) and...
