*From*: steve weir <weirsi@xxxxxxxxxx>*To*: Vinu Arumugham <vinu@xxxxxxxxx>*Date*: Tue, 09 Nov 2010 13:27:43 -0800

Vinu, perhaps I am just tired this afternoon, but Zdiff = 4*Zcm pretty much stipulates zero line to line coupling. Otherwise the ratio would be less than 4. Steve. Vinu Arumugham wrote: > True, but the spec. does not require zero line to line coupling at the > transmitters or receivers either. > > Thanks, > Vinu > > steve weir wrote: > >> If the Z matrix has essentially zero line to line coupling at the >> transmitters and receivers, then I am at a loss as to how a channel >> that does not match that will not suffer some amount of mode >> conversion. The reality is that a perfect match is unattainable. But >> the further one deviates, the more degradation will result. >> Steve. >> Vinu Arumugham wrote: >> >>> I don't think the cited section of the spec. below can be interpreted >>> as requiring loosely coupled 50 ohm single ended lines. "XFI >>> differential reference impedance for driver, *transmission line*, and >>> receivers are defined as 100 Ohms. XFI common mode reference >>> impedance for >>> driver, *transmission lines*, and receivers are specified as 25 Ohms." >>> >>> The reference impedance is the port reference impedance used to check >>> compliance of the driver, receiver or transmission line parameters. >>> >>> I don't think the spec. places a direct limit on the actual common >>> mode impedance of the interconnect. Only differential insertion and >>> return loss requirements are specified. So, a 90 ohm differential >>> pair with 30 ohm common mode impedance could be compliant. >>> >>> Thanks, >>> Vinu >>> >>> steve weir wrote: >>> >>> >>>> It's basically telling you to use loosely coupled pairs where each >>>> line has a single ended impedance of 50 Ohms. For zero line to line >>>> coupling: Zcm = Zse /2, and Zdiff = Zse*2. >>>> >>>> Steve. >>>> >>>> >>>> Alvaro alkschbirs wrote: >>>> >>>> >>>>> Hi gurus, >>>>> I have a question about differential pairs routing. >>>>> >>>>> The XFP MSA Specifications says: >>>>> >>>>> "XFI differential reference impedance for driver, *transmission >>>>> line*, and >>>>> receivers are defined as 100 Ohms. XFI common mode reference >>>>> impedance for >>>>> driver, *transmission lines*, and receivers are specified as 25 Ohms." >>>>> >>>>> I think that it says that my signal need to have both 25ohms commom >>>>> mode >>>>> impedance and 100ohms differential impedace. In pratical terms, I >>>>> need to >>>>> make this traces thinner and more spaced. Thinner traces are more >>>>> critical >>>>> and add too. >>>>> >>>>> Is this requirement true for any type of 100ohms differential >>>>> impedance >>>>> pair? >>>>> >>>>> If yes, this requeriment will add some problems to make BGA fanouts >>>>> without >>>>> route the pairs separately by other pins fanout vias. >>>>> >>>>> Why I need control common mode impedance? >>>>> How critical is this requirement? >>>>> Is 30 ohms commom mode impedance acceptable? >>>>> >>>>> I will appreciate your help! >>>>> Rgds, >>>>> Álvaro >>>>> >>>>> ------------------------------------------------------------------ >>>>> 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 technical documents are available at: >>>>> http://www.si-list.net >>>>> >>>>> List archives are viewable at: >>>>> http://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: >>> http://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: >>> http://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: > http://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: > http://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: http://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: http://www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu

**Follow-Ups**:**[SI-LIST] Re: Differential pairs commom mode impedance***From:*Vinu Arumugham

**References**:**[SI-LIST] Differential pairs commom mode impedance***From:*Alvaro alkschbirs

**[SI-LIST] Re: Differential pairs commom mode impedance***From:*steve weir

**[SI-LIST] Re: Differential pairs commom mode impedance***From:*Vinu Arumugham

**[SI-LIST] Re: Differential pairs commom mode impedance***From:*steve weir

**[SI-LIST] Re: Differential pairs commom mode impedance***From:*Vinu Arumugham

- » [SI-LIST] Differential pairs commom mode impedance - Alvaro alkschbirs
- » [SI-LIST] Re: Differential pairs commom mode impedance - Scott McMorrow
- » [SI-LIST] Re: Differential pairs commom mode impedance - steve weir
- » [SI-LIST] Re: Differential pairs commom mode impedance - Alvaro alkschbirs
- » [SI-LIST] Re: Differential pairs commom mode impedance - steve weir
- » [SI-LIST] Re: Differential pairs commom mode impedance - Jory McKinley
- » [SI-LIST] Re: Differential pairs commom mode impedance - Scott McMorrow
- » [SI-LIST] Re: Differential pairs commom mode impedance - Vinu Arumugham
- » [SI-LIST] Re: Differential pairs commom mode impedance - steve weir
- » [SI-LIST] Re: Differential pairs commom mode impedance - Vinu Arumugham
- » [SI-LIST] Re: Differential pairs commom mode impedance - steve weir
- » [SI-LIST] Re: Differential pairs commom mode impedance - Vinu Arumugham