13
Off diagonal elements are the mutual capacitances for conductors i and j.
Terms of the inductance matrix L are described by
Lij gives the flux between the ith conductor and the ground plan when conductor j carries 1.0 Amp, and all
other conductors are floating. Off diagonal terms are mutual inductances.
In PSpice, the mutual parameters of a coupled transmission line structure are:
LM - Mutual inductance between adjacent tlines per unit length
CM - Mutual capacitance between adjacent tlines per unit length
The methods of [1] and [2] are used to decouple the transmission line parameters, subject to the following
assumptions:
1. All of the line parameters, C, L, R, G, CM, and LM, must be the same for all of the lines in the set.
2. Coupling is modeled across adjacent lines only.
3. Edge effects are neglected as a result of the first limitation.
The following models are available for coupled transmission lines:
Model Description Parameters
T2COUPLED 2 Symmetric Coupled Lines R, L, C, G, LM, CM, LENGTH
T3COUPLED 3 Symmetric Coupled Lines R, L, C, G, LM, CM, LENGTH
T4COUPLED 4 Symmetric Coupled Lines R, L, C, G, LM, CM, LENGTH
T5COUPLED 5 Symmetric Coupled Lines R, L, C, G, LM, CM, LENGTH
KCOUPLE2 2 Line Coupling LM, CM
KCOUPLE3 3 Line Coupling LM, CM
KCOUPLE4 4 Line Coupling LM, CM
KCOUPLE5 5 Line Coupling LM, CM
Table 5. Transmission line coupling parts.
In some cases it is desirable to use a lumped circuit to model coupling. Here we present a symmetric,
coupled, 3 conductor, lumped model:
* symmetric coupled 3 conductor lumped
.subckt C3L in1 in2 in3 out1 out2 out3
+params: len=1 r=0 l=1 c=1 lm=1 cm=1
* first conductor
r1 in1 1 {len*r+1u}
l1 1 2 {len*l/2}
c1 2 0 {len*c}
l2 2 out1 {len*l/2}
* second conductor
r3 in2 3 {len*r+1u}
j
ij ii ig
C C C
j
i
ij
I
F
L
