Show description

The nonlinear element can be described by an equivalent circuit that includes a linear conductance G1 and controlled current sources representing the higher-degree terms in the series. Of course, the linear component G1V could also be represented by a current source if it were more convenient to do so. 2 The substitution theorem: (a) source-conductance equivalence; (b) nonlinear element equivalence. 5) is rarely used. Indeed, we shall see in Chapter 3, when we Solid-State Device Modeling for Quasistatic Analysis 35 discuss harmonic-balance analysis, that using only voltage-controlled nonlinearities simplifies the description of the linear subcircuit considerably, and a gyrator can be used in the rare cases when a current-controlled element cannot be avoided.

However, before deleting terms wildly, one should be careful not to throw out the baby with the bathwater. 31) generate different frequency components under sinusoidal steady-state conditions, so deleting certain terms, even if they are very small, may delete the intermodulation component of interest. 31) is circumvented; in Chapter 3 we shall show that the process of taking the derivative in the time domain can be performed in the frequency domain merely by multiplying a matrix by a diagonal matrix.

C(V) is the capacitance that would be measured if the nonlinear element were biased at dc voltage V, and a small ac voltage were applied to it. 17) implies that fQ can be measured indirectly, by first measuring C(V) and then integrating it to obtain charge. Another method is to differentiate fQ to obtain C(V), and to fit the parameters of C(V) to the measured capacitance. One of these approaches is almost always necessary, as it is usually impossible to measure charge directly. 5 Small-Signal Nonlinear Capacitance Initially, we assume that the voltage V = V0 is the sole dc control voltage and that it is applied to the capacitor’s terminals.