A Depletion-Mode MOSFET Model for Circuit Simulation

A four-terminal model is formulated for the depletion-mode MOSFET using simple charge-voltage relationships. Different regions of operation are taken into account according to the surface conditions such as accumulation, depletion, and inversion. This simple formulation is then modified to account for the second-order effects such as mobility reduction, drift-velocity saturation, and channel length modulation. Simple expressions are used to express the model parameters in terms of device dimensions. A charge-based capacitance model is used to compute transient currents. The depletion-mode model is implemented in the circuit simulation program HP-SPICE and the simulation results are discussed.