3.5. SIMULATING CROSSTALK USING EQUIVALENT CIRCUIT
Equivalent circuit models are the most general method of simulating crosstalk.
depicts an N-segment equivalent circuit model of two coupled lines as modeled in SPICE,
where N is the number of sections required such that the model will behave as a continuous
transmission line and not as a series of lumped inductors, capacitors, and resistors. As
, the number of segments, N, in a transmission line model depends
on the fastest edge rate used in the simulation. A good rule of thumb is that the propagation
delay of a single segment should be less than or equal to one-tenth of the rise time (see
for a full explanation).
Figure 3.6: Equivalent circuit model of two coupled lines.
The mutual inductance is typically modeled in SPICE-type simulators with a coupling factor
is the mutual inductance between lines 1 and 2, and L
are the self-
inductances of lines 1 and 2, respectively.
Example 3.4: Creating a Coupled Transmission Line Model.
Assume that a pair of coupled transmission lines is 5 in. long and a digital signal with a rise
time of 100 ps is to be simulated. Given the following inductance and capacitance matrices,
calculate the characteristic impedance, the total propagation delay, the inductive coupling
factor, the number of required segments, the maximum delay per segment, and the
maximum L, R, C, G, C
, and K values for one segment.
SOLUTION: Characteristic impedance: