Design Feature:September 1, 1995
In Spice-2G6 and other Spice derivatives, a dc-bias-current effect, modeled by a polynomial equation, is a part of the basic inductor model. This equation is built into the source code, so you need only specify the coefficients of the polynomial equation. The Spice-2G6 netlist is as follows:
In version 3 of Spice, such as Spice 3E2 or later, the polynomial inductor model is no longer available. You need a more complex method of modeling the bias effect. You can model the polynomial current effect by using a zero-voltage source to measure the current passing through the inductor and a nonlinear current source (the B element) that offsets the applied current. The derivation of the current-source coefficients that correlate with the Spice-2G6 polynomial inductor model produces a general form for the current coefficients:
This expression produces a zero value for the constant term because with no applied current, you need no compensation. You can now specify the polynomial inductor in Spice 3 as a subcircuit by calculating and manually entering the coefficients. Or, you can pass the inductor coefficients to the subcircuit for evaluation within Spice. The Spice-3E2 polynomial-inductor netlist for the model in Fig 1 is as follows: