Crosstalk

Abstract

When this chapter is finished, you should be able to understand crosstalk. Crosstalk is, arguably, the best-known signal-integrity problem, the arch villain of signal integrity. For that reason, it is commonly blamed for signal-integrity issues. Sometimes the blame is warranted and sometimes not. It is important to understand what crosstalk is, so that you can identify when it is (and is not) causing your signal-integrity problems.

Homework

Construct a coupled triple transmission line with LEN = 5, L = 100 nH, C = 10 pF, LM = 10 nH, and CM = 5 pF. Connect a source to input 1 and 2 and a load to input 3 (and the opposites to outputs 1–3). See the diagram below, and note which sides have the source and which have the load. The “source” in line 1 and 3 is just the source impedance – no voltage source – and input 2 has a voltage source in series with its source resistance and a 500 ps risetime.

• 1. Compute the Z ₀ and T _p of the transmission lines. (Note that the SPICE L is L _L and the SPICE C is C _L.)

• 2. Simulate with no termination (R _L = 1 megohm and R _S = 10 Ω). Note where R _S and R _L are located!

• 3. Repeat the simulation, but with load termination (R _L = Z ₀ and R _S = 10 Ω).

For both simulations, plot the voltage at the source and load of the second line and the loads of the first and third lines.