Steve, Thanks for your very thorough reply. It gives me a lot of things to look at. One thing that I noticed in getting to this point is that adding any pre/post-emphasis increases the BER. To me that indicates that channel loss would seem less likely to be an issue. Would you agree? Chris On 7/15/2011 1:19 AM, steve weir wrote: > Chris, the maximum run lengths of a given PRBSn pattern are: n 1's, and > n-1 0's. Failure of PRBS15/23/31 indicates that you have frequency > dependent distortions. Those could be coming from your channel, or from > your PDN. An brief list of things I would check first: > > 1. Tx eye quality. This will tell you if the problem is excessive > distortion and/or attenuation in the channel. > If the Tx eye looks good then you will need to look at the channel > > 1.S parameters on the channel from VNA or TDT measurements > 2. Preemphasis settings for the transmitter > 3. Equalization settings for the receiver > 4. AC coupling capacitor values and termination arrangement > > If the Tx eye is poor then you will need to look at the PDN and the > reference clock. > > PDN > 1. Tx driver PDN Z vs F > 2. PLL PDN Z vs F > > Reference clock > 1. Reference oscillator stability > > Steve > On 7/14/2011 9:53 PM, Chris Johnson wrote: >> I am debugging a board with a Virtex-6 HX380 chip and having some issues >> with getting low error rates using the Xilinx IBERT tool. I can tweak >> the MGTH parameters to have zero or near-zero errors for a PRBS7 >> pattern, but not for longer patterns, such as PRBS15/23/31. Is there a >> particular design flaw that is more likely to cause pattern sensitive >> failure for longer PRBS patterns, or could it be just about anything? >> The links are running at 10.3125 Gbps. >> >> Thanks, >> Chris >> >> ------------------------------------------------------------------ >> To unsubscribe from si-list: >> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field >> >> or to administer your membership from a web page, go to: >> //www.freelists.org/webpage/si-list >> >> For help: >> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >> >> >> List technical documents are available at: >> http://www.si-list.net >> >> List archives are viewable at: >> //www.freelists.org/archives/si-list >> >> Old (prior to June 6, 2001) list archives are viewable at: >> http://www.qsl.net/wb6tpu >> >> >> > -- Principal Engineer ZRL 500 Wood St. Bldg 34-2 Bristol, RI 02809 Telecommute Phone: 860-658-7899 (most days) Corporate Phone: 401-254-0270 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu