How to calculate Maximum length mismatching allowed

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akael

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Hello,
I have a converter board DVI to RGB, I conected this board to a TFT LCD MODULE using several cables, i didnt paid much attention to the signal length, and it works perfectly.


I've got another TFT LCD (different company) and i've decided to do a simple PCB board, but it doesn't work well, it has a lot of noise and if i set the full screen to be blue, it seems ligth blue, if i set red, it seems pink and so on.



The clock signal is 25MHz, and the max difference of lengths between the clock signal and the RGB signal is 3cm , is this the the problem?

How could i determine the max length mismatch between the clock and the RGB signal allowed knowing the clock frequency?

Thanks in advanced,
Akael
 
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Solution
It's not the clock frequency that matters, it's the setup and hold time of the signals relative to the clock edge. CAT5 cable, for example, has a propagation delay of about 5nS/meter. So, 3 cm difference would give a skew of about 15 pS. A 25MHz clock is 40 nS, so it doesn't seem to me like 15pS should make a big difference.
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It's not the clock frequency that matters, it's the setup and hold time of the signals relative to the clock edge. CAT5 cable, for example, has a propagation delay of about 5nS/meter. So, 3 cm difference would give a skew of about 15 pS. A 25MHz clock is 40 nS, so it doesn't seem to me like 15pS should make a big difference.
 

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