OVERVIEW

Until the early 1970s, analog signal-processing circuits used continuous time circuits consisting of resistors, capacitors, and op amps. Unfortunately, the absolute tolerances of resistors and capacitors available in standard CMOS technologies are not good enough to perform most analog signal-processing functions. In the early 1970s, analog sampled-data techniques were used to replace the resistor, resulting in circuits consisting of only MOSFET switches, capacitors, and op amps [ ^[1], ^[2]]. These circuits are called switched capacitor circuits and have become a popular method of implementing analog signal-processing circuits in standard CMOS technologies. One of the important reasons for the success of switched capacitor circuits is that the accuracy of the signal-processing function is proportional to the accuracy of capacitor ratios. We have seen in previous chapters that the relative accuracy of capacitors implemented on standard CMOS technology can be quite good. The primary advantages of switched capacitor circuits include (1) compatibility with CMOS technology, (2) good accuracy of time constants, (3) good voltage linearity, and (4) good temperature characteristics. The primary disadvantages are (1) clock feedthrough, (2) the requirement of a nonoverlapping clock, and (3) the necessity of the bandwidth of the signal being less than the clock frequency.

The important component of signal-processing circuits are the signals. Signals can be characterized by their time and amplitude properties. From a time viewpoint, signals are categorized as continuous and discrete. A continuous time signal is defined for all time whereas a discrete time signal is defined...