Thank you Lee! Best Regards Charles Grasso Compliance Engineer Echostar Communications (w) 303-706-5467 (c) 303-204-2974 (t) 3032042974@xxxxxxxxx (e) charles.grasso@xxxxxxxxxxxx (e2) chasgrasso@xxxxxxxxx -----Original Message----- From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx] Sent: Monday, September 26, 2011 4:50 PM To: Grasso, Charles; steve weir; si-list@xxxxxxxxxxxxx Subject: Re: [SI-LIST] Re: Routing differential lines as single ended traces ? Charles, I knew someone would ask that question! I usually design stackups with 4 mils of laminate between the stripline layer and its plane. When I do that, a 10 mil edge to edge separation results in one trace diminishing the impedance of its neighbor by about 1%. That's not a big drop and 10 mil separation has not turned out to be a problem for routing the board. As you can see, there is a judgment call to be made here. 5% would be half the entire impedance error budget we allow and 10% would be all of it. Hope this helps. lee -------------------------------------------------- From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx> Sent: Monday, September 26, 2011 1:04 PM To: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>; "steve weir" <weirsi@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> Subject: [SI-LIST] Re: Routing differential lines as single ended traces ? > Hello Lee - How much interaction is too much? 1% 5% - 10%?? > > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications > (w) 303-706-5467 > (c) 303-204-2974 > (t) 3032042974@xxxxxxxxx > (e) charles.grasso@xxxxxxxxxxxx > (e2) chasgrasso@xxxxxxxxx > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Lee Ritchey > Sent: Monday, September 26, 2011 10:11 AM > To: steve weir; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Routing differential lines as single ended traces ? > > I always route differential pairs to a "not closer than" rule. This > guarantees that there will be no unwanted interaction such as one line > driving the impedance of the other down. I have seen no cases where this > has resulted in a lack of board space for routing. Perhaps there are some > somewhere. > > > I arrive at the "not closer than" rule by using a field solver to > determine > how close the two lines can be without adversely affecting the impedance > of > either one. > > When you use the "not closer than" rule all traces are single ended and > usually 50 ohm. That means you don't need to add complexity to bare board > test by insisting on a 100 ohm diff pair measurement. Makes life much > easier. The drivers always wanted to see 50 ohm lines any way. > > Lee > > -------------------------------------------------- > From: "steve weir" <weirsi@xxxxxxxxxx> > Sent: Sunday, September 25, 2011 7:22 PM > To: <si-list@xxxxxxxxxxxxx> > Subject: [SI-LIST] Re: Routing differential lines as single ended traces ? > >> On 9/25/2011 6:57 PM, Low Jerry wrote: >>> Hi, >>> I recently came across a validation platform where the LVDS differential >>> lines are routed as single ended traces traces instead of tightly >>> coupled >>> differential pairs. The motivation I found was so that they could use >>> each >>> of the pairs as single ended traces when needed as well. When I probed >>> deeper it seems like the person who proposed this scheme has left. So I >>> would like to seek help here on some clarification >>> >>> - Will a scheme like this impact the performance of the differential >>> pair >> The scheme itself will not. >>> ? Since I understand that differential routing is more immune to >>> noise. >> That is largely a myth. There are only a few very special circumstances >> where tightly coupled pairs exhibit better noise rejection to PCB trace >> noise aggressors than reasonably routed, loosely coupled pairs. >>> - What are the considerations/feasiblity studies that need to be >>> done >>> before implementing a scheme like this ? >> They are the same as with any signal integrity requirements. The scheme >> doesn't impose anything extra. It does remove some headaches. >>> - Since this is a validation platform what measures can be taken >>> ensure >>> that the performance seen are similar to a production platform if >>> the >>> production platform is routed in differential. >> Homework gets done or it doesn't. >> >> Steve >>> >>> Thanks in advance for the feedbacks. Have a great day. >>> >>> >>> ------------------------------------------------------------------ >>> 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 >>> >>> >>> >> >> >> -- >> Steve Weir >> IPBLOX, LLC >> 150 N. Center St. #211 >> Reno, NV 89501 >> www.ipblox.com >> >> (775) 299-4236 Business >> (866) 675-4630 Toll-free >> (707) 780-1951 Fax >> >> >> ------------------------------------------------------------------ >> 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 >> >> > ------------------------------------------------------------------ > 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 > > > > > ------------------------------------------------------------------ > 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 > > ------------------------------------------------------------------ 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