This week I was mostly double checking all the connections and also all the footprints. There were a few footprints that needed to be modified and rerouted. The I/O ports connected to the FPGA were also rerouted, this time using the differential tracks instead of single ones. That opens up a lot of new functionalities. I also tested the length of the high-speed signals for transmission line effect. However, none of the traces are long enough for it to take place.

Differential routing in Kicad

It is fairly simple to route differential signals in the new version of Kicad. The steps are listed below:

  1. Switch to Open GL mode.(Differential routing is only possible in Open GL mode)
  2. Select Differential pair from the Route menu.
  3. Click on any of the differential pins.(Differential pins are either labeled with +/- or N/P)
  4. Place the track as usual.(The other track will be laid down automatically)

Next step is to match the length of the differential pair:

  1. Select Tune differential pair skew/phase from the Route menu.
  2. Click on the track that is shorter and just move the mouse and the length will automatically be adjusted to match the longer track’s length.

PCB design check list

For the FPGA you can refer to a check list made by Xilinx themselves, that discusses everything that has to be checked. Link