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3.2 Subcircuit and Device Model Definition 209
A differential pair with
emitter degeneration
resistors.
This netlist describes a
differential amplifier on
the basis of the subcircuit
implemented above.
Set up circuit equations.
In[8]:= dpwedr = Subcircuit[
Name −> "DifferentialPair", Selector −> "DeviceLevel",
Ports −> {"H1", "H2", "IN1", "IN2", "L"},
Parameters −> {Area, RED},
Definition −> Circuit[
Netlist[
{"Q1", {"H1" −> "C", "IN1" −> "B", "ED1" −> "E"},
Model −> "BJT", Selector −> Selector["BJT", "Q1"],
Parameters −> "LocalNPN"},
{"RED1", {"ED1", "L"}, RED},
{"Q2", {"H2" −> "C", "IN2" −> "B", "ED2" −> "E"},
Model −> "BJT", Selector −> Selector["BJT", "Q2"],
Parameters −> "LocalNPN"},
{"RED2", {"ED2", "L"}, RED}
],
ModelParameters[Name −> "LocalNPN", Type −> "NPN",
IS −> 2.*^−15, BF −> 200., RC −> 50./Area,
RE −> 2./Area]
]
]
Out[8]=
SubcircuitDifferentialPair, DeviceLevel, 5
In[9]:= diffamp = Circuit[
Netlist[
{V0, {"VCC", 0}, Value −> {DC −> 9., _ −> 0}},
{V1, {2, 0}, Value −> {DC −> 4.5, AC −> 1}},
{V2, {3, 0}, Value −> {DC −> 4.5, AC −> 0}},
{R1, {"VCC", 4}, 5000.},
{R2, {"VCC", 5}, 5000.},
{DP1, {4 −> "H1", 5 −> "H2", 2 −> "IN1",
3 −> "IN2", 6 −> "L"},
Model −> "DifferentialPair",
Selector −> "DeviceLevel",
RED −> 100., Area −> 2.},
{IBIAS, {6, 0}, Value −> {DC −> 0.001, _ −> 0}}
],
dpwedr
]
Out[9]= Circuit
In[10]:= diffampeqs = CircuitEquations[diffamp,
AnalysisMode −> DC, ElementValues −> Symbolic]
Out[10]= DAEDC, 25 25
The nominal collector and
emitter resistances have
been divided by the area
factor.
In[11]:= {RC$Q1$DP1, RE$Q1$DP1} /. GetDesignPoint[diffampeqs]
Out[11]= 25., 1.
The following code is a slightly more complex example for a behavioral model definition. The
Model statement implements a nonlinear DC model for a bipolar junction diode, taking into account
junction voltage reduction due to series resistance (Rs) and DC convergence issues (GMIN).