Figure 3.8: Large signal model of an n-channel MOSFET
Figure 3.8 shows the large-signal model for a n-channel MOSFET, to account for the charge-storage effects in a MOSFET. SPICE used the gate capacitance model similar to the one proposed by Meyer [21]. The charge-storage effects in the large-signal model are represented by three non-linear capacitances: 
, 
and 
. These capacitance are implemented in SPICE LEVEL1 and LEVEL2 models as written in the following equations.
Accumulation region
Depletion region
Saturation region
Linear region
where 
and 
if 
is provided
else 
and 
; 
In addition to the gate capacitance, the capacitance of the diffused regions of the source and drain is simulated with the pn-junction capacitances(
and 
) as shown in Figure 3.8. The total capacitance of the diffused region is calculated from the sum of an area and perimeter capacitance, which are implemented in SPICE as written in Equations 3.25 and 3.26.
where 
and 
are SPICE3 constants whose values are given in equation 3.5 and the other parameters required to represent a large-signal model of a MOSFET are listed in the Table 3.8.
Table 3.8: MOSFET large-signal model parameters
