# [SI-LIST] Re: Diff.Pairs

*From*: "Todd Westerhoff" <twesterh@xxxxxxxxx>*To*: <si-list@xxxxxxxxxxxxx>*Date*: Mon, 6 Oct 2003 10:56:21 -0400

RTL = Rock Transistor Logic. Saw it in an old Flintstones episode. Sorry, couldn't help myself ... Todd ;-) Todd Westerhoff High Speed Design Specialist Cisco Systems 1414 Massachusetts Ave - Boxboro, MA - 01719 email:twesterh@xxxxxxxxx ph: 978-936-2149 ============================================ "When did the choices get so hard, with so much more at stake? Life gets mighty precious when there's less of it to waste" - Bonnie Raitt, "Nick of Time" -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Cheng Sent: Friday, October 03, 2003 5:23 PM To: 'si-list@xxxxxxxxxxxxx' Subject: [SI-LIST] Re: Diff.Pairs Two words, "IBM TCM". -----Original Message----- From: Michael_Greim@xxxxxxxx [mailto:Michael_Greim@xxxxxxxx] Sent: Friday, October 03, 2003 2:20 PM To: chris.cheng@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: RE: [SI-LIST] Re: Diff.Pairs Hi Chris, There were many a supercomputer that was made with that mix of technology. You needed the ECL speed for the processing but the memory was CMOS. A great chance for noise when converting between the two. Unfortunately I remember when greater than 8 mils was state of the art. Anyone remember DIP packaging.....8-) Best regards and have a great weekend. Michael -----Original Message----- From: Chris Cheng [mailto:chris.cheng@xxxxxxxxxxxx] Sent: Friday, October 03, 2003 2:15 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Diff.Pairs I thought you are old enough to remember the days when board traces are wide (6-8 mils were state of the art) and technology don't mix (either you have ECL or CMOS as critical highspeed design on the system but not both). It is easy to justify tight coupling of different pairs then. It still makes sense for many designs where differential I/O is the only thing you care (e.g. FCAL or 3GIO subsystems or clusters). -----Original Message----- From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx] Sent: Friday, October 03, 2003 11:41 AM To: Duane Takahashi; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Diff.Pairs More than that, it does not have any benefit. Tight coupling of differential pairs forces the traces to be narrower increasing the skin effect losses. Also, this tight coupling is going to result in good old cross talk that actually degrades the edges. How the notion of tight coupling of differential pairs as beneficial got started is a mystery to me. There are several references that show that tight coupling is not beneficial, one of them is Howard Johnson's latest book, at least one column he has written and my recently released book. Lee Ritchey ------------------------------------------------------------------ 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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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

**References**:**[SI-LIST] Re: Diff.Pairs***From:*Chris Cheng

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