Apalis Parallel CSI Impedance Matching

Hi everyone,

we will be using both Camera Interfaces of the Apalis QuadCore SOM. What i currently cannot figure out was how the Impedance matching is done on APALIS Side. When i took a look into the Evaluation Board Schematic i see Series Resistors placed in the Single Ended Signal Lines everywhere, as also in the Paralell Camera Interface. They are placed near the SOM Connector, but i wonder why this is done, if the Impedance of the trace is matched to 50Ohm?

Furthermore the Layout Design Guide says that all single ended Signals should be routed with 50Ohm Impedance, but where are the termination resistors placed? In the imx6 Datasheet i found no Information about some integrated switchable Termination Resistors, so i expect the matching Resistors on the Apalis Module itself.

So if i want to use IPU1_CSI0_DATA10 and IPU1_CSI0_DATA11 because i have to, i am afraid that there wont be any matching resistors on the module, because this pins share UART1.
Please give me some advice about CSI termination, i am very new to designing with SOMs.
Thanks in advance,
BR Christian

There are no termination resistors on the module, neither on the dedicated serial camera input pins nor on the other ones that feature the camera interface as alternate function. On the module, all GPIO capable signals are routed with 50R impedance. That is the reason why we also suggest to route the signals on the carrier board with 50R.

On the evaluation board we place in general 22R for additional protection of the signals. The parallel camera input as well as the parallel LCD interface are often the most critical signals for passing EMC tests. In order to reduce radiation of the parallel camera interface, it is recommended adding series resistors for reducing the slew rate of the signals. We recommend placing these resistors close to the camera, not close to the module connector as on the evaluation board. The value of the resistors is a trade off between signal quality and the electromagnetic radiation. Normally a good choice is to start with 22R and then adjust the values in the prototype.

Thanks for your really fast response, since i had too much things to do i am really sorry that i could not reply earlier.
I expected that purpose of the series resistors. When you are saying “protection” you mean protection regarding signal integrity, since for HV Pulses like ESD it seems that 22R do not have big impact.
Thanks a lot,
BR Christian