[SI-LIST] Re: LVDS center tap capacitor termination
- From: shekhar sharma <sinnovate88@xxxxxxxxxxx>
- To: weirsp@xxxxxxxxxx, venubabu@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Mon, 30 Aug 2004 12:04:53 +0100 (BST)
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 termination to odd-mode impedance which
> >terminates common mode 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=20
> > > >
> > > >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.
> > > >
> > >
> >
>
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