Signal Integrity and Radiated Emission of High-Speed Digital Systems

6

Crosstalk

Owing to the high density of traces in high-speed printed circuit boards and the fast rise and fall time of the switching devices, the electromagnetic coupling between adjacent lines, defined as crosstalk, is a very important topic. To cope with this problem, it is essential to have suitable circuit models to simulate complicated structures. Simplified but accurate models are of great help in understanding the crosstalk mechanism. This chapter starts with the description and discussion of a lumped model of two coupled lines that can be easily implemented in SPICE-like circuit simulators. By virtue of its simplicity, this is the first approach for inexperienced users when dealing with crosstalk and using a commercial circuit simulator that usually does not offer efficient coupled line models in its library.

In high-speed digital circuits, the analysis of symmetrical coupled lines in differential signal transmission is very often required to predict crosstalk or signal integrity (SI). The concept of even or common mode (CM) and of odd or differential mode (DM) will be introduced. This distinction will also be very useful in understanding the radiated emission mechanism from PCBs with attached cables, and EMI performance of differential signaling. An efficient distributed model based on common mode and differential mode will be presented for crosstalk computation. The main advantage of this model is that it is exact and provides results without the frequency limitation ...