orcad pspice Benutzerhandbuch

Chapter 6    Analog behavioral modeling

lossy transmission line. R, L, and C are the resistance, 
inductance, and capacitance of the line per unit length. 

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 42.

The parameters R, L, and C can be defined in a .PARAM 
statement contained in a model file. (Refer to the online 
OrCA D 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 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.

Pspug.book  Page 166  Wednesday, November 11, 1998  1:14 PM