DS90UB933-Q1: 933 934 layout review to solve EMI problem

Hi Amelie,

We typically use Microstrip but Stripline should perform fine because the trace is actually buried. I noticed a few things and some other comments that I've mentioned below which might help.

1) To help narrow down the issue or the location of the issue. We use a flexible EMC Absorber sheet. This can be placed in different regions of the board and you can observed if it changes the frequency that you're failing at. That region will likely be the cause for the issue.

2) Is the connector backend exposed? and What direction is the field coming from? for example, in the picture you showed, if the field is coming from right to left and hits an exposed connector backend, the noise from that backend could cause issues with your reading. We recommend using a shielded connector to help avoid this.

3) On the GND layer underneath the high speed, we recommend Anti-Pads or GND cutouts for the PoC network. This will help maintain a 50Ohm impedance when the signal passes by the PoC network.

4) Are you using a through hole connector? If so, what is the orientation/mounting of the through hole connector? We recommend bringing the signal on the oppoite side of the connector mounting. For example, if the connector is mounted on the top, then the signal should come out from the bottom then got through a via and into the signal pin of the part. This helps avoid creating a large stub where the connector signal pin is placed. A large stub will cause reflections which can lead to noise being radiated during testing.

5) Please ensure that whether you use stripline or microstrip, 50Ohm impedance is maintained throughout the length of the trace.

6) We typically use 6-8 layer board, so there's a GND reference for any layers adjacent to the high speed.

7) To avoid power coupling, I suggest adding a GND reference in between any two power islands that you have on layer 3. I also noticed some yellow traces on the bottom of layer 3, if those are high speed, I recommend having a good ground between that and power. We typically provide a full GND layer just so there's no coupling issues as I mentioned earlier.

Regards,

Mandeep Singh

Hi Mandeep,

Thanks for your detail information.

Wire 1 is  DATA0-7 CLK HS VS.

Wire 2 is Dout of 934 connected to the connector.

May I ask:

wire2 is much more important for EMI comparing to wire1, is it right? Because customer only can keep wire 1 or wire 2 shorter. I recommend they to consider wire2 first and keep wire 2 much shorter first.

Thanks!