Two first issues with the PCB are grounding and grounding. Impedance matching is of course important as well as matched lengths. BTW, have you checked that PCBs you ordered matches calculations? PCB manufacturers have several impedance profiles for customers to choose from.
But anyway, the main issue is grounding. Electrically you have connected all the grounds (based on the quick look at least). However, without a proper ground plane, long ground traces wont work in this kind of applications. Also, it looks like there are two thick ground traces coming outside of the picture and presumable they are connected somewhere else. That is very bad, because current has two alternative paths. Oh... are there third GND trace in the middle.
In short, you "need" to have a solid ground plane, connect all GND pins to the plane using short traces (and only one trace). Then the rest is matter of standard PCB designing.
What you now see on screen is more or less the outcome of signal reflections and cross-talking.
Here is one example. Orange is ground plane, red is top layer (CM4 connector) and blue is bottom signal layer. On the right hand side there is impedance matched traces (USB).
But anyway, the main issue is grounding. Electrically you have connected all the grounds (based on the quick look at least). However, without a proper ground plane, long ground traces wont work in this kind of applications. Also, it looks like there are two thick ground traces coming outside of the picture and presumable they are connected somewhere else. That is very bad, because current has two alternative paths. Oh... are there third GND trace in the middle.
In short, you "need" to have a solid ground plane, connect all GND pins to the plane using short traces (and only one trace). Then the rest is matter of standard PCB designing.
What you now see on screen is more or less the outcome of signal reflections and cross-talking.
Here is one example. Orange is ground plane, red is top layer (CM4 connector) and blue is bottom signal layer. On the right hand side there is impedance matched traces (USB).
Statistics: Posted by gotaf80307 — Sun Mar 17, 2024 9:38 pm