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Rev. A, October 2003

©2003 Fairchild Semiconductor Corporation

sub-threshold region.

2) The implementation of the network (figure 1) using switches S1 and S2 provided a

method to precisely model the non-linear capacitance. The result is an accurate rep-

resentation of the dynamic transition between blocking and conduction.

The need for this higher level modeling accuracy becomes apparent in high frequency

applications where gate charge losses as a proportion of overall losses become sig-

nificant. The same situation exists for the space charge limiting effect at high drain

current.

The MOSFET model reference on which this work is based has been explained in [1,

2, 3]. The reader is encouraged to refer to these references for a full understanding of

the MOSFET model parameters herein referenced as the standard SPICE MOSFET

model.

Recent works [8, 9] have demonstrated methods of circumventing the SPICE global

temperature definition, providing a means of using the device’s own junction tempera-

ture as a self-heating feedback mechanism.

The model developed in [8] has limitations involving proprietary algorithms, rendering

the method of limited interest. Model implementation is convoluted, involving a MOS-

FET analog behavioral model (ABM) implementation whose operating characteristics

are dependent on a SPICE level-3 NMOS MOSFET. As a result, both the switching

circuit and the load must be duplicated for the model to function. The implementation

in [9] does not model the drain-source avalanche property of a MOSFET. Neither [8]

nor [9] attempt to model the temperature characteristics of the intrinsic body diode.

Introduced self-heating modeling concepts are non-proprietary and may be adapted

to other MOSFET models.

2. Standard SPICE MOSFET Model

The macro-model in Figure 1 is that used in numerous Fairchild MOSFET device

models. It is the evolution of many years of work and improvements from numerous

contributors [1-7]. A significant advantage of this model is that extensive knowledge of

device physics or process details are not required for implementing parametric data

within the model. The following data curves are the basis used to generate the macro-

model model over temperature:

- transfer characteristic

- saturation characteristic