A General Approach to Twin-T Design and Its Application to Hybrid Integrated Linear Active Networks

In 1934, H. W. Augustadt invented the twin-T network while carrying out investigations for an economical rectifier filter for phonograph amplifiers. 1 The two main fields of application of the twin-T network were introduced in 1938 by H. H. Scott who discussed its uses as a feedback network to obtain highly selective amplifiers and stable oscillators. 2 In the following years the circuit was thoroughly analyzed in the unloaded state 3 - 6 and, later, in the loaded state when driven from a nonideal voltage source. 7-9 Consideration was also given to the network's selectivity properties and to the effects of loading and network asymmetry. 1 0 - 1 2 In the early 1960s, a somewhat new application was introduced for the twin-T when synthesis methods based on root locus techniques were developed to employ the twin-T as a compensation network in dc servo systems. 13-15 These investigations were limited to the symmetrical twin-T with fixed source and load resistances. They were later expanded to include wide ranges of source and load impedances10 and to provide prescribed pole-zero locations 17 using parameter plane techniques. Recently, with the advent of linear integrated circuits, interest in the twin-T network has been revived yet again, this time by network theoreticians attempting to generate, by RC network synthesis tech1105