There is no shortage of design rules available when people talk about differential traces on circuit boards. At various times you can hear people argue that there is a need for, or there is no need for, a variety of special rules regarding continuity of ground planes underneath the traces, equal length traces, equal separation between traces, differential impedance control, etc. So let’s set the record straight. NONE of these rules are inherently required by the fact that we are using differential signals! But some of them might be required if we are worried about signal integrity issues in our designs. This article looks at these individual types of rules from the standpoint of various signal integrity issues to see when, if ever, they need be applied.

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