TABLE OF CONTENTS By introducing additional op amps to the active- RC circuit, one can derive several benefits, often simultaneously. Such benefits include:
Lower sensitivities to both active and passive components.
Reduced dependence of critical resistance ratios and/or closed-loop op-amp gain(s) on the filter Q.
Ease in tuning, perhaps, allowing ? 0 and Q to be independently adjusted.
Fewer passive components.
A more universal filter structure, which permits general biquad realization with the minimum number of topological changes.
The most significant price paid for these features is the increased power dissipated by the filter and noise. For some applications the added power dissipation may outweigh the advantages gained from a multiple-amplifier topology. It is then good practice to carefully evaluate the filter performance and power requirements before departing from a practical SAB design. However, since low-cost monolithic integrated-circuit op amps are available with either one, two, three, or four op amps on a single chip, single-op amp biquads offer little size and cost advantage. This is particularly true when the area required to realize the passive components is reduced in the multiple-op amp implementation.
For very high Q, design benefits 1 through 3 are particularly important. Q's of 50 and higher, which are impractical for SAB realization, can be realized with one of several multiple-op amp topologies. As we show in the remaining sections of this chapter, the use of multiple op amps can lead to biquad active-filter sections which are capable...
