FEDEVEL
Platform forum

HasanTheSyrian_ , 11-11-2025, 01:18 PM

https://www.altium.com/viewer/?token=%2BWfb27nTjk609L4fgLyKE7%2Fq

https://imgur.com/a/CPrJwV1

**Notes:**

HDMIs use different banks as Vivado internal noise calculations (SSN) report high noise margins when the entire bank is used at once, especially at higher drive strengths, which might be needed because of the somewhat long trace length. AC termination used (resistors unplaced/DNP) since series termination can't be placed on the SOM. HDMI 2 (left) data, clk, and syncs length matched to +-10mm.

Ethernet length matched 2mm between pairs, 1mm within pairs. PHY on SOM; using FPGA hardcore.

MIPI length matched 1mm between pairs, 2mm within pairs. Implemented XAPP894 MIPI D-PHY (passively via the resistors you see).

JTAG/UART can be used via USB (at the same time) or via headers. Right USB connector can be toggled to be used as normal USB or for prog/debug.

USB PHY on SOM, USB Hub on dev board

There are no power planes, power is routed. All planes are ground. SIG/GND/SIG/GND/GND/SIG

Used return vias whenever possible to minimize reflections within the dielectric.

**Possible concerns:**

Power inductor choice: XGL4020-222MEC

HDMI_1V8 and FTDI_1V8 switching on at the same time

Length matching within MIPI pairs seem too much for the amount that they are misaligned.

Floating copper (star and constellation) acting as antennae

Sniper2 , 11-11-2025, 05:00 PM

did u also post on reddit?

Sniper2 , 11-11-2025, 05:00 PM

seems super familiar

HasanTheSyrian_ , 11-11-2025, 05:08 PM

yh

QDrives , 11-11-2025, 09:16 PM

Make sure you have the reset circuit correct with FTDI.
I have some bad experience with FTDI (as a user, not designer).

QDrives , 11-11-2025, 09:22 PM

Is Vbus1 (perhaps also others) a power input or power output?

QDrives , 11-11-2025, 09:24 PM

Both HDMI_1V8 and FTDI_1V8 are from linear regulators. Both get their power from VDD_3V3.
So what is your question about 'switching'?

QDrives , 11-11-2025, 09:28 PM

You could place a big copper area for the star and constellation. 'Ground' it with multiple vias. And just use solder mask to open parts to get the same effect.
Change some 'stars' to vias (not tented!)

Sniper2 , 11-12-2025, 05:46 AM

Did you check hdmi chip power up sequence?

Sniper2 , 11-12-2025, 05:47 AM

Also how does vivado signal integrity thinking work?