Generalized Feedback Analysis of Cascaded Null Networks

A necessary and sufficient criterion for the stability of a feedback system with isolated cascaded null networks in the feedback path of an amplifier is developed, making use of a generalized transfer function for the feedback path which can be adapted to , lumped and/ or distributed, passive or active null networks. The analysis is based on some principles of root locus. It has been proved that a comb-filter type of response could be realized using this configuration and low-gain wideband amplifiers could be used advantageously for filters covering a wide range of frequencies. Experimental results confirm the conclusions drawn from the analysis. The generality of the method makes the system suitable for a wide range of applications and is readily adaptable to integrated-circuit design.