Limitations of criteria for testing transistor circuits for multiple DC operating points

Addresses the problem of determining whether a transistor circuit possesses multiple dc operating points. We investigate how the sign change of the determinant corresponding to the Jacobian matrix associated with circuit equations can be used to indicate the number of dc operating points in a transistor circuit. We give circuit examples that illustrate that these criteria may not be reliable, and show that resistor values that determine the number of a circuit´s dc operating points, may or may not affect the value of the calculated determinant. Even if the mere existence of a feedback structure depends on whether a particular resistor is open- or short-circuited, the resistor value may not affect the value of the determinant. Hence, the determinant criteria is not always indicative of the number of a circuit´s dc operating points.