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2.6 Modeling and Analysis of Nonlinear Circuits 103
1
RB
RC
IB
2
IC
3
Q1
VCE
VCC
VBE
Figure 6.6: Bipolar transistor circuit
For didactic reasons we do not use ReadNetlist to automatically import the netlist, but rather
write the circuit by hand. Moreover, instead of using a BJT transistor model from the predefined
Analog Insydes model library, we select a suitable model from the global database which contains
the two NPNBJT models defined in the previous section. By leaving the model selector unspecified,
Selector −> BJTModel, we can postpone the final choice of the underlying model equations until
we set up circuit equations. The option Pattern −> Impedance in the value field of RB introduces
the current I$RB into the MNA equations. The current I$RB is identical to the base current IB, so we
can compute the latter directly from the equations without having to determine it manually from IC
and IE by KCL.
In[13]:= bjtbias =
Circuit[
Netlist[
{VCC, {1, 0}, Type −> VoltageSource,
Symbolic −> VCC, Value −> 12.},
{RB, {1, 2}, Pattern −> Impedance,
Symbolic −> RB, Value −> 500.*10^3},
{RC, {1, 3}, Symbolic −> RC, Value −> 4000.},
{Q1, {3 −> C, 2 −> B, 0 −> E},
Model −> NPNBJT, Selector −> BJTModel,
betaf −> 100., betar −> 0.2,
Js −> 6.*10^−16, Area −> 4., Temperature −> 300.}
]
]
Out[13]= Circuit
In order to keep model complexity as low as possible, we make the initial assumption that Q1
operates in the forward active region and set up a system of symbolic static circuit equations using
the simplified Ebers-Moll model by setting the options AnalysisMode −> DC and
ElementValues −> Symbolic.