Download - Wolfram Research

70 2. Tutorial
An advanced application of such a parameter translation scheme would be the calculation of transistor smallsignal
parameters from given operating-point voltages and currents via a set of predefined device equations.
Alternative Ways to Assign Values to Parameters
In combination with the Parameters setting there is one further useful application of the argument
Translation. Specifying a translation rule for a symbol which is also designated as a parameter of
the same subcircuit definition allows us to choose whether we let the instance value of the symbol be
calculated from other parameters or whether we assign a value to this symbol directly. For example,
let’s add the transconductance gm to the list of model parameters while leaving the translation rule
for gm unchanged:
Parameters −> {RB, beta, gm},
Translation −> {gm :> Transconductance[beta, RB]},
The value field of a reference to the transistor model can now be written in two alternative ways.
Just as in the previous subsection we can assign values to RB and beta only and let Analog Insydes
calculate gm from the two quantities automatically. Alternatively, we can bypass the translation rule
by directly assigning a value to gm, such as gm −> 0.5. Any value given for beta is then effectively
ignored because it is not needed anywhere else than in the argument list of the translation rule. In
the netlist below, we let gm$Q1 be computed from RB and beta by means of the translation rule. In
the case of Q2, however, we do not specify a value for beta but make a direct assignment to gm:
gm −> gm2. Therefore, the parameter translation function Transconductance is not called for gm$Q2: