On the design of parallel-T resistance capacitance networks for maximum selectivity

Abstract

A simple analysis is presented for obtaining an expression for the transfer function and hence the selectivity, Q_T,of a general parallel-T resistance capacitance network. The maximum value of Q_T obtainable by a suitable choice of clements is shown to be ½. A design procedure for approaching this maximum value is given. An expression has been given for estimating the departure from linearity of the amplitude response characteristic at a particular frequency. This is used to find an optimum value of Q_T for best performance of the network as an F.M. discriminator at low frequencies. It is shown that the required value of Q_T is very near its maximum value.An expression for the selectivity Q_A, of an amplifier using a general parallel-T resistance capacitance network in the negative feedback line has been deduced and the advantages of having an increased Q_T explained.