Programming instructions

Transistors
Multisim Component Reference Guide 4-12 ni.com
The 4-Terminal Enhanced P-MOSFET is a p-channel enhancement MOSFET. Because the
substrate and source leads are not connected, it has four terminals.
4.7.1 Depletion MOSFETs
Like a JFET, a depletion MOSFET consists of a length of p-type (for a p-channel MOSFET)
or n-type (for an n-channel MOSFET) semiconductor material, called the channel, formed on
a substrate of the opposite type. The gate is insulated from the channel by a thin silicon
dioxide (SiO
2
)
layer. Depletion MOSFETs are used in automatic-gain control (AGC) circuits.
4.7.2 Enhancement MOSFETs
An enhancement MOSFET has no physical channel between the drain and the source, unlike
the depletion MOSFET. Instead, the substrate extends all the way to the silicon dioxide (SiO
2
)
layer. An enhancement MOSFET works only with positive gate-source voltages.
Enhancement MOSFETs are extensively used in digital circuits and large-scale integration
(LSI) applications.
Multisim provides four MOSFET device models, which differ in the formulation of the
current-voltage characteristic. The parameter LEVEL in the model dialog specifies the model
to be used. LEVEL 1 is a modified Shichman-Hodges model. LEVEL 2 defines the geometry-
based analytical model. LEVEL 3 defines the semi-empirical short-channel model. LEVEL 4
defines the BS1M1 model. LEVEL 5 defines a new BS1M2 model.
4.7.3 DC Model
Due to the complexity of the MOSFET models used, only very basic formulas are provided in
the following description.
The DC characteristics are modeled by a nonlinear current source, I
D
.
Forward characteristics (V
DS
≥ 0):
VV VTE TO BS=+ −− > >






γϕ ϕ γ ϕ for 00,
ComponentRef.book Page 12 Thursday, December 7, 2006 10:12 AM