MIPI differential Impedance

Normaly MIPI differential Impedance is 100 ohm.

This guide is 90 ohm.

Do Colibri-iMX8X carrier boards have to be designed at 90 ohm?

Best regards.

@peter.tx @diego.tx Can you let us know about this? Thanks!

Layout design-guide is 90 ohm +/- 15%.

Probably the recommended value for tegra system. 90ohm +/- 15%
https://forums.developer.nvidia.com/t/mipi-csi-signal-routing-requirements/36869

i.MX8X is 100ohm +/- 10%
https://www.nxp.com/webapp/Download?colCode=IMX8HWDG

Best regards.

Hi @developer0916

Thank you for your patience. Your assumptions are correct, the 90ohm recommendation for DSI is originating from Nvidia, which was the first Colibri module with a DSI interface. The traces on the module itself are routed with 90R differential impedance. We kept this impedance for being consistent with the other Colibri modules. Therefore, I also recommend you to use 90R on your carrier board. Impedance changes in the transmission line should be avoided for reducing reflections.

However, if the DSI signals are connected to a long cable that has 100R, not 90R, it might be better to route also the carrier board with 100R. The traces on the module are rather short and therefore, I expect better results since the 100R of the cables are dominating the transmission line.

Just as a side note. For the new Verdin module, we will change the impedances of the DSI/CSI to 100R for having more common values.

Thank you for your reply.

Our customers use the CSI line, but is it the same as DSI?

Best regards.

Dear Kirikawa-san, should be, since both CSI and DSI uses D-PHY at the hardware level.

Correct, DSI and CSI-2 are identical from an HW point of view.