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2.9 Frequency-Domain Analysis of Linear Circuits 147
In[2]:= lfMOSmodel =
Circuit[
Model[
Name −> MOSFET,
Selector −> LowFrequency,
Scope −> Global,
Ports −> {D, G, S, B},
Parameters −> {gm, gmb, Gds},
Definition −>
Netlist[
{VCG, {G, S, D, S}, gm},
{VCB, {B, S, D, S}, gmb},
{GDS, {D, S}, Gds}
]
]
]
Out[2]= Circuit
To store the model definition in the global subcircuit database we expand the Circuit object using
the function ExpandSubcircuits (Section 3.4.1). The contents of the database can be inspected with
the command GlobalSubcircuits (Section 3.3.4).
In[3]:= ExpandSubcircuits[lfMOSmodel];
GlobalSubcircuits[]
Out[4]= MOSFET, LowFrequency
2.9.2 Transfer Functions
A CMOS Differential Amplifier
The most basic application of linear symbolic circuit analysis is to compute transfer functions as
analytic expressions of the circuit parameters and the Laplace frequency s. For instance, consider the
single-ended CMOS differential amplifier stage shown in Figure 9.4 where we might be interested in
computing the AC transfer function from the input voltage at node 1 to the output voltage across
the load capacitor CL.