User`s guide

6
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20 Analo
g
Behavioral Modelin
g
If R is small, the characteristic impedance of such a line is
Z=((R+j·ω·L)/(j·ω·C))
1/2
, the delay per unit length is (L C)
1/
2
, and the loss in dB per unit length is 23·R/Z. This could be
represented by the device in Figure 6-8.
The parameters R, L, and C can be defined in a .PARAM
statement contained in a model file. (Refer to the online
MicroSim PSpice A/D Reference Manual for more information
about using .PARAM statements.) More useful, however, is for
R, L, and C to be arguments passed into a subcircuit. This part
has the following characteristics:
NUM = EXP(-SQRT(C*s*(R+L*s)))
DENOM = 1
This produces a PSpice A/D netlist declaration like this:
GLOSSY 5 0 LAPLACE {V(10)} = {exp(-sqrt(C*s*(R + L*s)))}
The Laplace transform parts are, however, an inefficient way, in
both computer time and memory, to implement a delay. For
ideal delays we recommend using the transmission line part
instead.