Steve, >Now, if we couple the lines tightly, then we would want to add a fourth >resistor in place of the original 100 ohms to match the line to line=20 >coupling. This would be something like 500 to 1000 ohms. What is this fourth resistor? I mean, what are the other three resistors? Best regards, Venu Babu. -----Original Message----- From: steve weir [mailto:weirsp@xxxxxxxxxx]=20 Sent: Monday, August 30, 2004 5:03 PM To: shekhar sharma; Ummalaneni, Venu Babu (Venu); si-list@xxxxxxxxxxxxx Subject: Re: [SI-LIST] Re: LVDS center tap capacitor termination No, that isn't right. Take the view Lee likes to emphasize, and that is at=20 the driver, we have two single ended signals that are coded as complements=20 with low skew. If we do not couple these lines significantly, and blast them down a Tx line, then we need to terminate each line into the=20 single-ended impedance of 50 ohms. But 50 ohms needs to be to a Vtt that=20 is at the center of the swing. The capacitor does that. Now, if we couple the lines tightly, then we would want to add a fourth=20 resistor in place of the original 100 ohms to match the line to line=20 coupling. This would be something like 500 to 1000 ohms. Steve. At 12:04 PM 8/30/2004 +0100, shekhar sharma wrote: >Steve, > >Thanks for correction. Some mixing.... >Anyway, I think, this termination terminates the even >mode (AC termination) upto some extent, coz the the >resistance values are 50 ohm each with their common >point connected to a capacitor. Diff pair with 100 ohm >diff impedance will have common mode impedance more >than 50 ohm. > > > --- steve weir <weirsp@xxxxxxxxxx> wrote: > > You are right that it terminates both modes. You > > just have the modes > > confused. Even is the common mode, odd is the diff. > > mode. The AC > > termination is to the even mode. > > > > Steve. > > At 11:37 AM 8/30/2004 +0100, shekhar sharma wrote: > > >Two resistor with centre tap capacitor termination provides AC=20 > > >termination to odd-mode impedance which terminates common mode=20 > > >signal. May I right ??? > > > > > >Shekh > > > > > > > > > --- steve weir <weirsp@xxxxxxxxxx> wrote: > > > > The two resistor termination is a double > > > > single-ended termination. The > > > > single resistor termination presumes a virtual > > > > ground at the center of the > > > > resistor. > > > > > > > > What noise sources do you think LVDS is trying > > to > > > > reject? > > > > What noise sources do you think LVDS can reject? > > > > What noise sources do you think LVDS cannot > > reject? > > > > > > > > Steve. > > > > At 03:34 PM 8/30/2004 +0530, Ummalaneni, Venu > > Babu > > > > (Venu) wrote: > > > > >Hi=3D20 > > > > > > > > > >This query is regarding termination schemes at > > the > > > > LVDS receiver inputs. > > > > > > > > > >Can some one explain me the difference between > > a > > > > 'single resistor > > > > >termination' and 'the two resistors with center > > tap > > > > capacitor' ? > > > > > > > > > >I read some where that the 'center tap > > capacitor > > > > scheme' filter's the > > > > >common mode noise. My doubt is that even in > > 'single > > > > resistor scheme' > > > > >also if we run the differential traces verly > > > > closely the common mode > > > > >noise pick-up by the two traces is equal and > > the > > > > Receiver can reject > > > > >this common mode part, right? So why we need to > > go > > > > for center tap > > > > >capacitor scheme? It unnecessarily increase the > > > > component count on the > > > > >board, right? > > > > > > > > > >Any inputs are appreciated. > > > > > > > > > >Best regards > > > > >Venu Babu. > > > > > > > > > > > > > > > >------------------------------------------------------------------ > > > > >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 FAQ wiki page is located at: > > > > > > > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > > > > > >List technical documents are available at: > > > > > http://www.si-list.org > > > > > > > > > >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=20 > > > > '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 FAQ wiki page is located at: > > > > > > > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > > > > > > List technical documents are available at: > > > > http://www.si-list.org > > > > > > > > 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 > > > > > > > > > > > > > > > > > > >_____________________________________________________________________ > >___ > > >Yahoo! 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