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Eye diagram overshoot..

Eye diagram overshoot..

Eye diagram overshoot..

(OP)
I have a digital data stream displayed as an eye diagram.  The data is comming out of my circuit.  When displayed on the scope, the overshoot (ringing) is high and a little out of spec.  The spec is 10% or less and I am getting about 13%.  

I have tried a number of things and cannot control this ringing except by cutting bandwidth down.

The ringing frequency looks like about 2GHz which is on the high end of my band.  

When I put the signal into a long length of cable (which acts as an LPF),  the ringing is filtered out.

THis is an HDTV application.

As an engineer, I am not too concerned about the ringing because I am thinking of the signal as being pre-emphasized.  With the high frequency content being boosted.

The ringing doesn't reduce the size of the eye at all and maybe helps keep it open.

Am I being blissfully ignorant?  Is there something I am missing?  Will the overshoot hurt some other aspect of the system that I am not aware of?

THanks,
Groundhog1

RE: Eye diagram overshoot..

Are you using a scope probe with grounding pins close to the tip or does it use a ground lead that goes to the back of the probe?  Getting the scope ground very close (1/4") to the test point will reduce ringing and overshoot that is an artifact of the inductance in the testing probe created by having a large enclosed area.  Your scope probes probably also have an adjustment, usually where it connects to the scope, to balance out line capacitance.  To measure a 3% error on a digital signal you should check that it is compensated properly.

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