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2.9 Frequency-Domain Analysis of Linear Circuits 161
For standard applications, you do not need to take care of these things as on the one hand Analog Insydes
provides a library with built-in device models and on the other hand there is no need to write netlists by hand
as this is automatically done by ReadNetlist. Following, we explain the internal model mechanism which
is implemented in the Analog Insydes model library.
Consider the following circuit description which contains a model definition for the high-frequency
MOSFET model introduced in Section 2.9.1 (see Figure 9.3). The symbolic element values are given
as arguments to the Symbolic options while the design-point values, denoted by the names with
a trailing $ac, are given as arguments to the Value options. Both sets of symbols must appear in
the parameter lists of the model definitions to allow for passing design-point values from a model
reference to a model instance and to ensure that symbolic parameters are correctly instantiated.
In[35]:= hfMOSmodel =
Circuit[
Model[
Name −> MOSFET,
Selector −> HighFrequency,
Scope −> Global,
Ports −> {D, G, S, B},
Parameters −> {gm, gmb, Gds, Cgs, Cgd, Cbs, Cbd,
GM$ac, GMB$ac, GDS$ac, CGS$ac, CGD$ac, CBS$ac,
CBD$ac},
Definition −> Netlist[
{CGS, {G, S}, Value −> CGS$ac, Symbolic −> Cgs},
{CGD, {G, D}, Value −> CGD$ac, Symbolic −> Cgd},
{VCG, {G, S, D, S}, Value −> GM$ac,
Symbolic −> gm},
{GDS, {D, S}, Value −> GDS$ac, Symbolic −> Gds},
{VCB, {B, S, D, S}, Value −> GMB$ac,
Symbolic −> gmb},
{CBD, {B, D}, Value −> CBD$ac, Symbolic −> Cbd},
{CBS, {B, S}, Value −> CBS$ac, Symbolic −> Cbs}
]
]
]
Out[35]= Circuit
In[36]:= ExpandSubcircuits[hfMOSmodel];
GlobalSubcircuits[]
Out[37]=
MOSFET, HighFrequency, MOSFET, LowFrequency
Generating Design Points
Please consider the circuit description of the differential amplifier circuit from Section 2.9.2 (see
Figure 9.4). From the netlist entries for M1 to M4 it becomes apparent how the design-point
information is specified for each transistor model instance. Values are assigned only to parameters
which represent numerical information. No assignments are made to the corresponding symbolic
model parameters to let them be instantiated automatically. Note again, that this is all taken care of
automatically by the command ReadNetlist.