Network Theory, Filters, and Equalizers

Resistance attenuators of the T, L, ladder, and bridged-T types are considered, and design formulas are given. Decimal attenuators are described. The relation existing between attenuation and phase shift in a four-terminal network is stated in several forms, including the phase-area theorem, and a formula which gives phase shift directly as a function of the rate of change of attenuation. The latter shows that the phase shift that exists at a particular frequency is determined primarily by the way in which the slope of the attentuation characteristic varies in the vicinity of this frequency. Consideration is also given to the case where the desired attenuation is constant over a portion of the frequency spectrum, while the phase shift is to be kept constant over the remainder of the spectrum. It is shown that a complete phase and attenuation characteristic is specified when such attenuation and phase fragments are given. This case corresponds to the transmission characteristics desired in the feedback loop of an ideal feedback amplifier. The application of these principles to the design of practical feedback amplifier circuits is considered in detail. It is shown that nonoscillating feedback amplifiers can be designed by considering only the transmission characteristics of the feedback loop, since the transmission characteristics control the phase shift.