[SI-LIST] Re: (no subject)
- From: "Robert Sefton" <rsefton@xxxxxxxxxxxxx>
- To: <ahilton@xxxxxxxxxxxxx>
- Date: Mon, 11 Mar 2002 21:30:17 -0800
> Goutham.S@xxxxxxxxxx wrote:
> > 1.0 2.5V signals should refer only to 2.5V or GROUND PCB plane and not
3V/5V
> > plane.
> >
> > >-----If 2.5V signals on signal layer are having 5V reference
plane
> > adjacent to the signal layer then what is the problem?
>
> The problem with running the 2.5 V signals beside a 5V palne is this -
>
> Controlled impedance implies a relationship between the conductor that
carries
> the signal and the conductor that is used for the return path. In order
for a
> plane to be a return path for a signal, the plane *must be connected* to
the
> circuitry for the signal. The 2.5V drivers and receivers are not
*connected* to
> the 5V plane, except through what is likely to be a very high-inductance
path.
>
> If you really must do this, you could put a decoupling capacitor from 2.5V
to 5V
> at both ends of the signal to provide a lower-inductance path to the
plane. For
> very high speed signals with tight timing parameters, this inductance may
still
> be too high.
If the 2.5V and 5V supplies have the same impedance to ground, what
difference does the DC voltage on the plane make?
Robert Sefton
------------------------------------------------------------------
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 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
Other related posts:
