Improved Assessment of Stability Margins in Repeater Amplifiers

A new method of stability assessment possessing important advantages over existing methods is described. It is based upon the theory due to H. W. Bode applied to the results of network analyzer measurements made at a few nodes in linear, multiloop feedback amplifiers such as those used in high capacity FDM or high speed PCM systems. Meaningful stability margins were obtained, and hence reliable predictions of instability even when computed values of loop gain and of the Kretz criterion failed to predict instability. More insight and information, greater assurance in circuit design, and a potential tool for more realistic feedback shaping have been achieved.