Crosstalk, Part 1Understanding Forward vs. Backward
Crosstalk can be a difficult phenomenon for PCB designers to grasp, particularly since there are two types of crosstalk, forward and backward, which behave quite differently. Although the magnitude of forward crosstalk increases as the length of the coupled region increases, its pulse width remains nearly constant and independent of the length of the coupled region. Backward crosstalk, on the other hand, has a nearly constant magnitude that is independent of the length of the coupled region (as long as the coupled region is “long enough”). But its pulse width is twice as long as the coupled region. This article is Part 1 of a three-part series on crosstalk.
Crosstalk seems to be one of those concepts that confuses many PCB designers. It does have some subtle aspects to it, and it can be a serious problem in some designs. But even more serious, it has some very subtle effects that are hard to recognize. This article, and others to follow in this series, discuss these effects and is intended to help PCB designers understand this signal integrity problem.
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