I would like to get suggestions from all the high speed PCB layout experts on my PCB design.

I have a board with HDMI transmitter IC whose output is going to HDMI switch IC. The switch IC also has an HDMI input coming from a HDMI connector. The output from switch IC also goes to HDMI connector as well. So its a 2:1 switch.

The switch IC seems to works fine and it switches when enabled. On the HDMI transmitter IC side, my HDMI output only works on TV or displays which are <=32 inches. Any bigger display like 50" or 55" inch TV of any brand would not work with when it switches to HDMI transmitter side, but it works fine when its switched to other input coming from the HDMI connector.

In my Rev A layout, I had my differential pairs going through 4 layers, and they were longer than 2 inches. I believe its a signal integrity issue on PCB layout, where on higher resolutions it didn't work on the HDMI tx side of output.

So I made some changes in my PCB layout in Rev B and made differential pairs shorter and only kept them in top and bottom layer.

"Side Note: HDMI tx works fine with bigger displays on evaluation board."

Below is the picture of my Rev B PCB layout. In the picture, yellow arrow shows the HDMI tx IC, and white arrow is pointed to HDMI switch IC.

enter image description here

Now is the second picture, white arrow again shows HDMI switch IC, but with both HDMI connectors on the other side. HDMI connector on top left is input and HDMI connector on the top right is output. This side of the layout is also new and needs verification as well.

enter image description here

On my PCB layout I also made sure to match impedance, differential pair lengths, and followed all the high speed rules.

I would really appreciate your suggestions on the layout so I can make sure it would work in Rev B.

Thank you

  • \$\begingroup\$ All that layer swapping is not good for high speed signals. There are ways to do it with low loss, but controlled impedance layers will have different impedances layer to layer to say nothing of via capacitance. You should try to route all but breakout on a single layer. \$\endgroup\$ – Peter Smith Mar 15 at 15:11
  • \$\begingroup\$ What are the HDMI switch and transmitter chips? Any chance Silicon Image or Analog Devices? What kind of max TMDS speeds are we talking about here (165, 225, 300, or 600 MHz)? Note that TV size does not really affect the signal being received or not - Except when large TVs support high resolutions and they need higher bandwith mux chips, or EDID management to remove unsupported formats. Or HDCP2.2 or SCDC issues. \$\endgroup\$ – Justme Mar 15 at 15:47
  • \$\begingroup\$ I don't see any SMD CM chokes and 1nH vias are not allowed. The trace width to me suggests higher impedance than required. Bigger resolution displays demand higher bit rate and PSSR noise between Tx and Rx can be an issue. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 15 at 15:49
  • \$\begingroup\$ @Justme HDMI switch is TS3DV642, and tx chip is TDA19988. Max TMDS speed can be 1.5GHz. I have tested the mux chip with large TV on the evaluation board and it worked fine with both inputs, but on the custom board it just works with external input. \$\endgroup\$ – Sam Mar 15 at 17:21
  • 1
    \$\begingroup\$ For example pins 1,3 of the HDMI connector (TMDS DATA2+, TMDS DATA2-) are going to TS3DV642 pins D0+, D0- which will get switched to pins D0+A, D0-A. Those pins are connected to TDA19988 pins TX0+, TX0-. So you have data channel 0 of the transmitter connected to data channel 2 of the HDMI connector. \$\endgroup\$ – EE_socal Mar 15 at 22:38

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