User Guide

Chapter 6 Analog behavioral modeling
176
Refer to the online OrCAD PSpice A/D Reference Manual for
detailed information.
Modeling mathematical or instantaneous
relationships
The instantaneous models (using VALUE and TABLE
extensions to PSpice “E” and “G” devices in the part
templates) enforce a direct response to the input at each
moment in time. For example, the output might be equal
to the square root of the input at every point in time. Such
a device has no memory, or, a flat frequency response.
These techniques can be used to model both linear and
nonlinear responses.
Note
For AC analysis, a nonlinear device is first linearized around the
bias point, and then the linear equivalent is used.
EVALUE and GVALUE parts
The EVALUE and GVALUE parts allow an instantaneous
transfer function to be written as a mathematical
expression in standard notation. These parts take the
input signal, perform the function specified by the EXPR
property on the signal, and output the result on the output
pins.
<ABM
keyword>
specifies the form of the transfer
function to be used, as one of:
VALUE arithmetic expression
TABLE lookup table
LAPLACE Laplace transform
FREQ frequency response
table
CHEBYSHEV Chebyshev filter
characteristics
<ABM
function>
specifies the transfer function as a
formula or lookup table as required
by the specified <ABM keyword>
Pspug.book Page 176 Wednesday, November 11, 1998 1:14 PM