Synthesis of active R allpass networks

Abstract Many reports have been made on the synthesis of active R filters which operate in the high‐frequency band using general‐purpose operational amplifiers. Most of these reports were on low‐pass and band‐pass filters. A solution to the problem of obtaining a transfer function whose nominator and denominator polynomials are of the same order as the degree of s similar to other filter functions, that is, high‐pass and allpass filters, still has not been reported. Hence, this paper considers allpass functions which are especially useful in proposing active R networks which are very simple and can be synthesized in an easily designed construction. Three kinds of circuit synthesis methods are presented. Since in networks of this kind, as is well known, the internal signal level generally is higher than the output level, e.g., similar to bandpass filters, it was important to suppress it. Using a concrete example, we show that one of the three kinds of proposed networks is improved considerably with respect to this point compared with other networks. Moreover, we make a detailed concrete examination of networks for (1) the center frequency realizable, (2) the design in the event that GB products of operational amplifiers are all different, (3) influence by the secondary pole on the amplitude and phase characteristics, and (4) the temperature characteristic.

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