Wave digital biquads derived from RC-active configurations

Abstract

A general method for deriving digital-filter structures from corresponding RC -active configurations is presented. The method is then used to derive digital-filter structures from various low-sensitivity RC -active configurations such as the three-amplifier state-variable biquad, and the corresponding summing four-amplifier biquad. The new digital structures are found to have the salient features of the reference configurations. For example, the structures based on the summing four-amplifier biquad embody the simultaneous realization of a variety of filter transfer functions, namely, a low-pass, a bandpass, and a general biquadratic transfer function. In addition, it is shown that in these structures, limit cycles can be eliminated by using a known technique based on magnitude truncation.