Routing the CSI-2 signal traces between the CSI-2
pins and the CSI-2 connector is also important for a successful DS90UB954-Q1 PCB layout. GUID-73083034-C234-4773-A11D-D0E91A7E533A.html#SNLS5066928 shows essential details for routing the
CSI-2 traces. Additional recommendations are given in the following list:
- Route CSI_D0N, CSI_D0P, CSI_D1N, and CSI_D1P pairs as differential coupled striplines with controlled 100-Ω differential impedance (±10%)
- Keep the trace length difference between CSI-2 traces to 5 mils of each other.
- Length matching should be near the location of mismatch.
- Each pair should be separated at least by 5 times the signal trace width.
- Keep away from other high-speed signals.
- Keep the use of bends in differential traces to a minimum. When bends are used, the number of left and right bends must be as equal as possible, and the angle of the bend should be ≥ 135 degrees. This arrangement minimizes any length mismatch caused by the bends and therefore minimizes the impact that bends have on EMI.
- Route all differential pairs on one or two inner layers.
- Keep the number of signal vias to a minimum — TI recommends keeping the via count to the maximum of two per CSI-2 trace.
- Keep traces on layers adjacent to ground plane.
- Do NOT route differential pairs over any plane split.
- Adding Test points causes impedance discontinuity and therefore negatively impacts signal performance. If test points are used, place them in series and symmetrically. Test points must not be placed in a manner that causes a stub on the differential pair.