Design-oriented analysis of DC operating-point instability

A previously published test for detecting unstable DC operating points is shown to be expressible in a simpler form. The new form is much easier to compute, especially in manual symbolic analysis, which is necessary for use in circuit design. The key parameter /spl Gamma/ is shown to be a generalization of the desensitivity factor, adapted for circuits with multiple feedback loops. The test of /spl Gamma/ is shown to fail to detect instability in a significant class of circuits. A new test based on negative differential resistance is devised that detects most such circuits.