Crosstalk is everywhere.\u00a0 Really, in a more general sense, noise coupling is everywhere.\u00a0 Usually the method of noise coupling is traditional “crosstalk” – the unwanted transfer of noise from one place to another through coupled electric fields.\u00a0 This most often occurs on PCB designs with dense routing, and on wide parallel busses.\u00a0 Even on newer SERDES busses, however, it is still an issue, as many such busses have multiple lanes, such as PCI Express.\u00a0 And crosstalk is also an issue on SERDES busses when they are routed close to slower, much higher voltage signals such as 3.3V and\u00a05V signals.\u00a0 Crosstalk can also occur in a similar fashion between higher-voltage switching power supplies and sensitive lines like resets.<\/p>\n
But it is not only crosstalk that causes noise coupling.\u00a0 Shared return paths\u00a0are another common method of noise coupling.\u00a0 This occurs most often in connectors without sufficient ground pins.\u00a0 Since ground pins act as the return paths in connectors, an insufficient number of ground pins will cause shared return paths and hence coupling between signals travelling through the connectors.\u00a0 A similar type of situation can occur in boards without enough stitching vias near signal layer transitions.<\/p>\n
And coupling can also occur through the PDN.\u00a0 An inadequately designed PDN can directly result in simultaneous switching noise, or SSN.<\/p>\n