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Impedance Matching for Display Port (Read 6500 times)
george
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Impedance Matching for Display Port
Apr 08th, 2011, 3:58pm
 
Hi,

I am trying to build a breakout board / Pass through board for Display Port. The idea being that it will pass through a Display Port (DP) input signal to a passive output port and feed into a monitor while allowing me to probe the signal and see what it going on. The main links on DP operate at 10.8Gb/s. I am curious on to do this without causing a huge impedance mismatch and therefore reflections leading to corrupted data. I have never done design with high speed IO lines and need help. How do I make probe points that have minimal impact on the signal? Do I have to worry about the traces being mismatched enough to cause serious corruption in my data?

Thanks,
-G
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loose-electron
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Re: Impedance Matching for Display Port
Reply #1 - Apr 10th, 2011, 8:46pm
 
At the data rates mentioned you are not going to be able to just connect wires to the signals.

You need a 50 ohm, matched lines, impedance terminated system, and the addition of "a breakout board" is going to affect your signal integrity in a big ugly way.

Ask yourself what you are trying to do and try to find a way to get it done without directly connecting to the signal path.

At that data rate, you need to be able to pass signals to roughly 40GHz or worse, to not affect the signals you are trying to look at.
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mikki33
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Re: Impedance Matching for Display Port
Reply #2 - Jul 22nd, 2011, 6:09am
 
george wrote on Apr 8th, 2011, 3:58pm:
The main links on DP operate at 10.8Gb/s.


The main link has maximum 4 channels and operates at either 1.62 or 2.7 Gb/s.

Anyway I don't think your board is possible. According to the standard the DP link should have 100 Ohm diff. termination. Any probing on the line will distort the signal.
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Re: Impedance Matching for Display Port
Reply #3 - Jul 25th, 2011, 4:10pm
 
There will always be some distortion when you probe/breakout the board. The question is whether it is tolerable. At those data rates, there is usually some sophisticated pre-emphasis/de-emphasis going on that will "minimize" the distortion.

It may be possible with a high impedence probe arrangement like those used by the latest oscilloscopes.

As pointed out by a lot of people here ... it is not trivial at all.
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