Large-signal frequency responses of 2nd-order filters containing multiple amplifiers

The describing-function technique is extended to predict the large-signal performance of active filters containing any number of operational amplifiers. This is achieved by generalising the theory of active filters whose amplifiers are each represented by a dominant pole and a saturation nonlinearity. As examples, the jump-resonance amplitude and phase characteristics of several popular 3-amplifier 2nd-order bandpass filter circuits are then evaluated and compared. The conditional-stability problem appears to be more severe than for single- and double-amplifier filters.