Jayasuryan, the coupling between individual traces of a differential pair is a function of distance. The wider you put the traces apart, the lower the coupling. In your case with 45Ohm individual and 90 Ohm differential impedance, you will go for zero coupling, thus the traces need to be far away. For stripline, as a rule of thumb, 1.5 times the Signal Plane to GND Plane distance (prepreg thicknes) would be a good starting point for zero coupling. Just couriosity, why do you need 45 Ohm single ended impedance? In many differential applications a tighter coupling is beneficial. BR Gert -------------------------------------------------------------------------- Absender ist HARTING Electronics GmbH & Co. KG; Sitz der Gesellschaft: Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596; persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH; Sitz der Komplementär-GmbH: Espelkamp; Registergericht der Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH: HRB 8808; Geschäftsführer: Edgar-Peter Duening, Torsten Ratzmann, Dr. Alexander Rost -----Ursprüngliche Nachricht----- Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im Auftrag von Jayasuryan KG Gesendet: Freitag, 1. Juli 2011 10:05 An: Rohit MISHRA Cc: si-list@xxxxxxxxxxxxx Betreff: [SI-LIST] Re: Differential Pair - Impedance Question Dear Rohit, Thanks for the detailed reply. Is there any tool to make sure that the impedance of the individual trace is 45 Ohm and it is 90 Ohm (no mutual coupling) when it will be differential? How can we make sure it is meeting the our requirement in manufacturing too. Impedance coupons are the only way or do we have any other solution(s)? Best Regards, Jayasuryan -----Original Message----- From: Rohit MISHRA Sent: Thursday, June 30, 2011 7:06 PM To: si-list@xxxxxxxxxxxxx Cc: suryan_tvm@xxxxxxxxxxx Subject: RE: [SI-LIST] Re: Differential Pair - Impedance Question Jayasuryan, When you talk about "45 Ohm impedance for individual", you are talking about characteristic impedance(Z0) of individual or single ended line which is intrinsic to that line only and can't be changed by changing differential impedance actually it is other way around, once you have set the characteristic impedance of your single ended line then differential impedance between two lines depends on characteristic impedance(Z0) of lines and mutual coupling between them. So if characteristic impedance of single ended line (D+ & D-) is Z0 and coupling coefficient between them is k then Zdiff = 2 * Z0 ( 1- k) or = 2 (Z11 - Z12) -> k = 0, Zdiff = 2 * Z0 Hope it should be clear now. Rgds, Rohit -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir Sent: Thursday, June 30, 2011 1:21 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Differential Pair - Impedance Question The single-ended impedance can be half the differential impedance when the lines have no mutual coupling. Steve On 6/30/2011 12:02 AM, Jayasuryan KG wrote: > Dear Experts, > > > I have a question regarding differential pair. > > In my UBS differential pair, the impedance is 90 Ohm. > > > > Is it possible to achieve 45 Ohm impedance for individual (D+ and D+) > traces(45 Ohm+45 Ohm Ohm) in the differential traces? > > > > Kindly share your feedbacks. > > > > Thanks in advance. > > > > Best Regards, > > - Jayasuryan > > ------------------------------------------------------------------ > 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. 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