ADV7611 Datasheet have no discription about the max length of digital output trace. Can anybody help me? The trace length (both data and clock) on my system will be 30cm. I don't know if the board can work when LLC runs at 160MHz.
TMDS signal performance is dependent on layout meeting the impedance constraints. As long as you maintain Eye diagram Mask at the sink you should be fine. (See the HDMI 1.4 specifications) The keys are to keep the correct single ended and differential impedances, matching trace lengths within pairs and low pair to pair skew. I would run signal integrity on any layout to verify the constraints.
No maximum length on boards are defined nor are maximum cable lengths defined. The specification only details the impedance. I've run 16cm on my FR4 board without issues and I believe I can run farther.
From another thread:
With regards to TMDS length matching through the backplane, because of the share number of routes, we tried to match the transmission line lengths of the TMDS signals to within 1000 mils (25mm), which for standard FR4 dielectric computes to approximately 166ps of inter-pair skew.
Thanks for your comment. There are three kinds of boards in my system. Both ADv7611 decoder board and encoder board pluged on backplane board through different connectors. So the signal impedance should be changed three times. Since the backplane is two-layer board. It's difficult to maintain the same impedance as decoder/encoder board. I'm realy worried about it if working properly.
Impedance for high speed signals is important. Normally I would use a 4 layer board with controlled impedance signals being on a outer layer referenced to a solid ground plane right below it.
If you're going through multiple connectors you will have problems too, they effect signal integrity a lot. Transitions across connectors will cause impedance mismatch. You must pay attention to the entire path, it can be done if your are very diligent with impedances.
You are right to worry, what you have is not a good plan.
I have a similar design to this, I paid close attention to impedance and used 9GHz daughter card to back plane connectors. Let me know if you have anymore questions
TMDS signals should be fine in my system. I worry about if encoder can correctly receive the data from adv7611 since them run a long distance.
If there are impedance problems or skew between the receiver and the encoder, there will be problems. Since you are running at 160MHz you need to make sure the digital path is clean. And running data and clocks like this over long runs can cause EMI and cross-talk issues. High speed single ended digital buses have been around for a long time so you should be able to do it.
In my design I actually ran TMDS signals to the back plane along with digital signals.
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