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3.2 Subcircuit and Device Model Definition 207
The Circuit object shown below describes a common-source amplifier with a MOSFET device. In
the model definition for MOSFET, the bulk terminal B is defined as an optional port. Since this node
is not connected in the top-level netlist, the bulk terminal is connected implicitly to the source node.
This netlist describes a
common-source amplifier.
Expand the MOSFET
model.
In[4]:= csamp = Circuit[
Netlist[
{V1, {1, 0}, Value −> {DC −> 1.5, AC −> 1}},
{M1, {"out" −> "D", 1 −> "G", 3 −> "S"},
Model −> "MOSFET", Selector −> "DCSmallSignal",
GM −> 2.*^−4, GMB −> 3.*^−5, GDS −> 1.*^−6},
{RD, {"VDD", "out"}, Symbolic −> Rd, Value −> 1.*^6},
{RS, {3, 0}, Symbolic −> Rs, Value −> 5000.},
{VDD, {"VDD", 0}, Value −> {DC −> 3.3, _ −> 0}}
],
Model[
Name −> "MOSFET", Selector −> "DCSmallSignal",
Ports −> {"D", "G", "S", Optional["B", "S"]},
Parameters −> {gm, gmb, Gds, GM, GMB, GDS},
Definition −> Netlist[
{VCG, {"G", "S", "D", "S"}, Symbolic −> gm,
Value −> GM},
{VCB, {"B", "S", "D", "S"}, Symbolic −> gmb,
Value −> GMB},
{GDS, {"D", "S"}, Symbolic −> Gds,
Value −> GDS}
]
]
]
Out[4]= Circuit
In[5]:= ExpandSubcircuits[csamp] // DisplayForm
Out[5]//DisplayForm=
Netlist Flat, 7 Entries:
V1, 1, 0, Value DC 1.5, AC 1
VCG$M1, 1, 3, out, 3, Symbolic gm$M1, Value 0.0002, Hierarchy VCG,
VCB$M1, 3, 3, out, 3, Symbolic gmb$M1, Value 0.00003, Hierarchy VCB
GDS$M1, out, 3, Symbolic Gds$M1, Value 1. 10 6 , Hierarchy GDS, M1
RD, VDD, out, Symbolic Rd, Value 1. 10 6
RS, 3, 0, Symbolic Rs, Value 5000.
VDD, VDD, 0, Value DC 3.3, _ 0
This example shows the effect of the argument Symbolic in a Model statement. The model equations
describe the DC behavior of a linear resistor including first-order temperature dependence. Note that
although there are four model parameters, only the resistance appears explicitly in symbolic circuit
equations. Note also that the alias name R is used instead of RES to denote the resistance.