TABLE OF CONTENTS In this chapter we considered the design and performance of single-amplifier and multiple-amplifier active- RC and active- R( C) biquad circuits. Negative-feedback single-amplifier circuits were shown to have low- Q sensitivities to passive components but large ? 0 and Q sensitivities to the op amp GB. The latter property restricted negative feedback circuits to low Q. On the other hand, positive-feedback circuits were shown to offer the ability of trade-off between active and passive sensitivities and can be designed for higher Q than the negative-feedback circuits. It was further shown that by employing both negative and positive feedback, an optimum compromise between these conflicting requirements can be achieved.
By isolating the passive- RC networks with additional amplifiers, the design equations were seen to be decoupled, thus rendering a noniterative tuning sequence. Furthermore, multiple types of transfer functions could be made available simultaneously. A comprehensive comparison of various three op amp biquads available in literature has been presented. The comparisons include sensitivity as well as enhancement considerations. The TG and PMG circuits were shown to be particularly suited, because of their low sensitivities, to the passive components and op amp GBs (for unmatched op amps) and to high- Q applications. However, because of the lower power consumption, the DF single-amplifier biquad has proven to be a most suitable workhorse circuit for Q ? 30. For larger Q's, low sensitivities and the ability to tune ? 0,
