Design and use of RC parallel-T networks

The RC parallel-T network with a transmission null at f0is described and the symmetrical lattice approach to its analysis is outlined, following a notation of Guillemin. The selection of design parameters for various principal applications, with relevant references to published work, is given. The common applications requiring a response curve symmetrical about f0, such as the single-frequency notch filter, the ac derivative network and the frequency discriminator are treated. In this class falls the feedback amplifier with a very narrow notch. The use of the parallel-T as a low pass or a high pass is covered briefly, and it is shown how a net of more complexity can be derived to give an improvement in response. Using the symmetrical lattice equations, typical examples are worked out. The resulting networks are usually three T nets in parallel, or a triple-T. A simple feedback amplifier for obtaining a response equal to an m-derived LC filter is described as a further solution to the problem. Typical feedback amplifier circuits giving either one-pole or two-pole response are presented. The detailed analysis of a two-pole RC feedback net is given, followed by practical design equations and experimental response data. The engineering problem of component selection for network stability is discussed, since this is a major consideration in designing satisfactory circuits. Frequently, stability is the only problem not readily solved by the potential user. Temperature compensation techniques are given, together with typical experimental data on temperature errors.