Hi Jory, I have simulated this at length and concur with your experience that the capacitor is best placed at the receiver... In effect, the attenuation associated with the capacitor placement at the receiver (parasitics/pads/vias) is lost in the rise-time degradation of the system. The classic "don't break it until you have to" rule is applicable... OK this is my rule... :-) All the best, Steve Stephen P. Zinck Interconnect Engineering Inc. P.O. Box 577 South Berwick, ME 03908 Phone - (207) 384-8280 Email - szinck@xxxxxxxxxxxxxxxxxxxxxxxxxxx Web - www.interconnectengineering.com ----- Original Message ----- From: "Jory McKinley" <jory_mckinley@xxxxxxxxx> To: <leeritchey@xxxxxxxxxxxxx>; <npatel@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> Sent: Monday, September 24, 2007 5:31 PM Subject: [SI-LIST] Re: AC Coupled Signals >I will elaborate a bit on what I have seen. I have measured (time domain) >in the lab some effects that appears to be location specific in the >placement of the AC coupling caps at the rcvr. Now this may be due in part >to the fact that I am using 50-ohm resistor termination in each lead as >well and the combination (cap plus rcvr reflection) is giving some >imbalance depending on distance. The best rcvr eye that I am seeing is >when I can move the AC/term as close to the rcvr as I can. By the way >these are 5Gb/s signals. > If I have time I will try and isolate what I am seeing and even simulate > it, has anyone else seen or simulated this? > -Jory > > ----- Original Message ---- > From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx> > To: "npatel@xxxxxxxxxx" <npatel@xxxxxxxxxx>; si-list@xxxxxxxxxxxxx > Sent: Monday, September 24, 2007 1:06:06 PM > Subject: [SI-LIST] Re: AC Coupled Signals > > Nikil, > > I have made measurements on test PCBs and the location is not all that > important. In identical pairs, one with AC coupling capacitors and the > other without, the loss vs. frequency is virtually identical at leas out > to > 6 GHz. That would be 12 Mb/S. > > Lee Ritchey > > >> [Original Message] >> From: <npatel@xxxxxxxxxx> >> To: <si-list@xxxxxxxxxxxxx> >> Date: 9/24/2007 10:21:37 AM >> Subject: [SI-LIST] AC Coupled Signals >> >> Hi all, >> In case of AC coupled signals does anyone know of an optimum placement >> for the caps? I mean should they be placed near the source, receiver, >> middle of the transmission line? >> How much difference does it make in the opening of the eye? >> The signals are differential CML running at 3.0Gbps >> >> Thanks, >> Nikhil >> >> >> ------------------------------------------------------------------ >> 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 >> or at our remote archives: >> http://groups.yahoo.com/group/si-list/messages >> Old (prior to June 6, 2001) list archives are viewable at: >> http://www.qsl.net/wb6tpu >> > > > ------------------------------------------------------------------ > 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 > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > > > > > > > > ____________________________________________________________________________________ > Moody friends. Drama queens. Your life? Nope! - their life, your story. > Play Sims Stories at Yahoo! Games. > http://sims.yahoo.com/ > ------------------------------------------------------------------ > 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 > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ 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 or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu