TABLE OF CONTENTS Second-order circuits have the advantage of potentially realizing complex poles and zeros, which can be more efficient in designing frequency domain filters. One approach to designing higher-order filters is to take the design in polynomial form and break it into products of second-order products. The implementation of each product can then be accomplished by a cascade of second-order circuits that each individually realize a pair of complex conjugate poles and two zeros (which may be at infinity or zero or in between). If the filter order is odd, then one of the products will be first order, requiring a realization from the last section. Figure 9.6-1 illustrates the concept of cascade filter design.
In this section, we will focus on the second-order circuits implemented as switched capacitors. We will introduce several second-order biquad circuits that provide general flexibility in cascade design. The biquad circuit has the ability to realize both complex poles and complex zeros. The poles are generated by the primary feedback path, which generally consists of a noninverting integrator and an inverting integrator. One of the integrators is damped to avoid oscillation. The zeros are generated by how the input signal is applied to the circuit. If there is more than one parallel signal path from the input to the output, zeros will result. The zero locations will determine the global frequency behavior of the...
