How to create measurement points on a PCB for MIPI lane diagnostics?

Question

I am looking for ways to test specifically MIPI DSI lane signal strength (because I am kind of pushing the envelope on the trace length and width), and am happy to add test points to the PCB design. I really appreciated all the tips in the original question, "How to create measurement points on a PCB for diagnostics?", and the additional information on "How to measure/show MIPI-DSI 4 lane signals on DSO/oscilloscope"?

However, I am concerned about adding any components, even a zero resistor, to the MIPI traces as it might slow the high-speed signal. For example, I noticed that this document had the following warning on the last page, which almost justified my caution (except I don't think they were talking about zero resistors).

"Do not place additional components, such as resistors, electrostatic discharge (ESD) diodes, capacitors, or common-mode chokes on the MIPI CSI-2 traces."

Further, in my search I am also noticing that most MIPI signal strength testing is software-based, and conducted through the processor.

So my main question is: What is the best way to add test points to the PCB to make sure that all of the MIPI traces are functioning?

My secondary question is: Does anyone even add test points to MIPI lanes on the PCB, or is all signal strength testing only conducted via software run through the processor these days?

Answer 1

To get to MIPI signals and check channel fuctionality, the best way is to use MIPI analyzer, like teledynelecroy.com/protocolanalyzer/mipi X34 Eclipse

There are several ways to attach signals.

One is with a set of sophisticated solder-on probes. You will need to have a pair of simple test pads on each differential transmission line, so the probes are soldered with tiny AWG36-AWG40 wires. Round pads with diameter of 0.3-0.5mm will suffice.

The other method is to use a special spring-loaded connector. MIPI traces should be routed accordingly. Unfortunately it takes an extra space.

If you need to test signal eyes, there are differential probes for this, like P7313 etc. for Tektronix 70000 series scopes. They also can be soldered to simple spot-like test points along the M-PHY diff lines.

Agilent/Keysight also offers similar tools and probes, with solderable tips like N6381A, usually with a typical with 1169A InfiniiMax amplifier:

which are usually soldered over test spots on MIPI channel. They also have MIPI analyzers as well like U4421A model.

But all this would cost you quite a bit.