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Design >> High-Speed I/O Design >> relation between group delay variation and horizontal eye closure
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Message started by vivkr on Dec 15^th, 2009, 7:18am

Title: relation between group delay variation and horizontal eye closure
Post by vivkr on Dec 15^th, 2009, 7:18am

I have a front-end which has rather significant group delay variation when I perform an AC sim. The group delay varies from lower to higher frequencies within the band of interest by about 25% of the bit period.

I would logically expect that a PRBS simulation would show the eye closing in the X-direction by a similar amount. However, such a PRBS-sim shows negligible closure in the X-direction.

I have checked that I really do have a PRBS input, and that I have taken a large enough number of samples (5000 or so). Is my understanding of the relationship between group delay variation and eye closure incorrect ? Note: The model being used is linear.

Regards,

Vivek

Title: Re: relation between group delay variation and horizontal eye closure
Post by love_analog on Apr 7^th, 2010, 2:05pm

eye closure would occur because of ISI (ie Bandwidth limitation). It might be you are getting group delay variation due to some other factors (other than BW limitation).