Deriving stability criteria for nonlinear circuits with application to worst-case noise margin of I2L

A simplified method of deriving stability criteria for nonlinear circuits is introduced. Unlike the conventional approach which requires construction of a small-signal equivalent circuit and identification of loops, only the basic nonlinear circuit equations are needed. The method is applied to the calculation of the worst-case static noise margin of I2L, which is shown to be much smaller than a recently published result.