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100 2. Tutorial
the base current, i.e. Β f and Β r , than in terms of the model parameters Α f and Α r in the original
Ebers-Moll equations. The relationship between Α f and Β f , as well as between Α r and Β r is given by
or, equivalently,
Β ⩵
Α ⩵
Α
Α
Β
Β
By making use of parameter translation rules in the model definition (see Section 2.3.7), we can let
Analog Insydes compute the values for Α f and Α r automatically from given values for Β f and Β r .
Implementation of Nonlinear DC Transistor Models
With the above background information on transistor models we are now ready to define a largesignal
BJT model for DC circuit analysis. We start by implementing a global DC model for an NPN
transistor using the unsimplified device equations after Ebers and Moll from the previous subsection.
Name −> NPNBJT,
Selector −> EbersMoll,
Scope −> Global,
Ports −> {C, B, E},
Let’s decide that we do not want to characterize a transistor by the Ebers-Moll model parameters Is,
alphaf, alphar, and Vt but want to use the parameters Js, Area, betaf, betar, and Temperature
instead. We do not need to rewrite the model equations if we specify translation rules which
translate our model parameters to those of the Ebers-Moll model. Remember that the function
ThermalVoltage has already been defined in Section 2.6.2.
Parameters −> {betaf, betar, Js, Area, Global[Temperature]},
Translation −>
{alphaf −> betaf/(1+betaf), alphar −> betar/(1+betar),
Is −> Js*Area, Vt :> ThermalVoltage[Temperature]},
The Ebers-Moll equations describe the functional relations between the voltages and currents at
two electrical branches, the base-collector branch and the base-emitter branch, which we use as the
port branches of our model. Associated with the port branches are the variables Voltage[B, E],
Current[B, E], Voltage[B, C], and Current[B, C], which must be specified as