Re:OpenRex – Open Source Hardware Project
by akiselev on Thursday January 10, 2019 @08:10PM
(#18880167)
Not just parallel buses. You can see several differential pairs as well, which look a lot like the parallel buses except the pairs are routed much closer together.
Differential pairs carry polar opposite signals so that any noise can be canceled out by comparing the two. While parallel bus traces need to be routed to 1/20-1/40th of a wavelength, the differential pairs need to be routed to within 20mils of each other with impedance controlled traces (which depends on distance to each other and other traces as well as material variability, hence the tight routing).
Differential pairs carry polar opposite signals so that any noise can be canceled out by comparing the two. While parallel bus traces need to be routed to 1/20-1/40th of a wavelength, the differential pairs need to be routed to within 20mils of each other with impedance controlled traces (which depends on distance to each other and other traces as well as material variability, hence the tight routing).