TOM3 capacitance model: linking large- and small-signal MESFET models in SPICE

Improved accuracy in the modeled gate capacitance of GaAs metal-semiconductor field-effect transistors (MESFET's) is obtained in SPICE using conservation of charge in an implanted layer. The gate junction creates a natural partition between mobile and fixed channel charges. Relating the gate charge to the channel current creates gate capacitances dependent upon the channel current derivatives linking the small-signal model to the large-signal equations. Results are illustrated using a depletion-mode MESFET.