Understanding Trace-to-Trace Coupling - Understanding Signal Integrity - page 105

9.8 Main Points

Inductive and capacitive coupling is present between traces. •

The switching activity of neighboring aggressor traces determines the victim
trace impedance and for microstrip (but not stripline) the propagation delay.

•

When only two traces are involved, the switching patters are called even
mode and odd mode.

•

Odd mode occurs when the victim and aggressor switch out of phase. This
gives the lowest impedance and for microstrip the shortest propagation delay.

•

Even mode occurs when the victim and aggressor switch in phase. This gives
the highest impedance and for microstrip the longest propagation delay.

•

The even- and odd-mode delay is the same for stripline. •

The change in impedance caused by switching modes affects the launched
voltage for both microstrip and stripline traces.

•

Problems

Answers to these problems are available on the Artech House Web site at http://
www.artechhouse.com/static/reslib/thierauf/thierauf1.html.

9.1 Under switching conditions a victim trace in a two-trace system has the fol-

lowing impedance values: 36 Ω , 60 Ω , and 97 Ω . Identify the odd, even, and

characteristic impedances.

9.2 Under switching conditions a victim trace in a two-trace system has the fol-

lowing propagation times: 154 pS/inch and 142 ps/inch. Identify the odd
and even propagation delays.

9.3 A field solver produced the following output file for a five-trace system.

Identify L s , L m , C s , and C m for trace 3.

L MATRIX [H/M]
2.875E-07

3.557E-08 9.705E-09 4.228E-09 2.416E-09

3.557E-08 2.862E-07 3.530E-08 9.620E-09 4.228E-09

9.705E-09 3.530E-08 2.861E-07 3.530E-08 9.705E-09

4.228E-09 9.620E-09 3.530E-08 2.862E-07 3.557E-08

2.416E-09 4.228E-09 9.705E-09 3.557E-08 2.875E-07

C MATRIX [F/M]
1.176E-10 − 5.300E-12 − 5.833E-13 − 2.531E-13 − 1.521E-13

− 5.300E-12 1.180E-10 − 5.261E-12 − 5.677E-13 − 2.531E-13

− 5.833E-13 − 5.261E-12 1.180E-10 − 5.261E-12 − 5.833E-13

− 2.531E-13 − 5.677E-13 − 5.261E-12 1.180E-10 − 5.300E-12

− 1.521E-13 − 2.531E-13 − 5.833E-13 − 5.300E-12 1.176E-10

9.4 Use the inductance and capacitance matrix from Problem 9.3 to find the

two worst-case impedance values for trace 3.