A Novel Stability Margin for Transfer Functions

This work presents a novel stability margin function for use with nodal driving point impedance and admittance transfer functions. Unlike a loop gain or NDF, the nodal driving point transfer functions themselves have units of impedance or admittance whose values are very circuit design dependent, making uniform applicability to all nodes within a circuit, for the purpose of assessing stability margin, impossible. Fortunately, the driving point transfer functions are fundamentally composed of the sum of bidirectional looking impedances or admittances which can then be used to construct a unitless, normalized, proxy function that can be successfully used for stability margin assessment. This new stability margin function is applied to a parametric oscillation discovered in a measured amplifier originally simulated to be stable.