Re: Cross Talk
Yair, let me put my 2 cents into this one. As we go through detailed
analyses we will see a number of specific noise contributors that may be
unique for our application. We certainly need to understand that these
individual contributors to noise are properly bounded within our overall
noise margin. Based on this requirement, the issues you have raised are
important ones to evaluate.
We must then look at these noise sources and compare them to the uncounted
contributors that are external to our application, such as noisy flourescent
ballasts, and cheap electric pencil sharpeners. Our challenge is that we
are building on a standard (100BASE-T) that does not have an explicit budget
for external noise. We must develop an approach which may be based on
analysis, measurement, or a combination of the two, that gives us confidence
that our application will work at the required bit error rate. This issue
is central to the concerns that the Mid-Span powering Ad-Hoc is addressing.
Robert D. Love
President, LAN Connect Consultants
7105 Leveret Circle
Raleigh, NC 27615
Phone: 919 848-6773
Fax: 720 222-0900
----- Original Message -----
From: Yair Darshan <YairD@xxxxxxxxxxxxxx>
To: 'R karam' <rkaram@xxxxxxxxx>
Sent: Sunday, August 13, 2000 6:09 AM
Subject: RE: Cross Talk
> Hi Roger,
> Regarding cross talk issue, to my opinion the situation is more
> since there is more than one port caring power
> to the media and it is not clear to me what will be the impact of
> and other noise issues in the following cases:
> 1. If a single power supply output is connected to the center tap of the
> data transformer (Phantom connection)
> and obviously we have more than one Data+Power output (12 or 24
> than we can say that all center taps of all
> data transformers are "shorted" together at high frequency signals.
> (Each Receive-Transmitt center tap of the transformer is shorted by
> power supply output capacitor. All the Receive
> transformer center taps are shorted together and the same applies for
> all the transmit center taps.)
> 2. Same as 1, but all outputs has separate power supply output. In this
> case there is some parasitic capacitance between each
> DC output although they are isolated from each other.
> 3. Add to the above description the fact that from EMI reasons there is
> about 1 to 10nF between power supply output to
> power supply chassis ( = system gnd) thus the construction of the
> connections may not be balanced.
> Questions raised from the above cases are:
> 1. What will be the impact on the requirements for cross talks between one
> port to other ports,
> is there a problem here?
> 2. Is there any restrictions in the 802.3 standards (or any other
> for zero voltage isolation between each data path
> to an other port data path?
> (If there is, We will need isolated power supply for each port)
> What is your opinion regarding the above issue?
> Darshan Yair
> Chief Engineer
> PowerDsine Ltd. - The Intelligent Telecom Power
> POB 7220, Neve Ne'eman Industrial Zone, Hod Hasharon 42451, Israel
> Tel: +972-9-775-5100, Ext. 210, Fax: +972-9-775-5111
> Mobile : +972-54-893019
> E - mail :yaird@xxxxxxxxxxxxxx
> > -----Original Message-----
> > From: R karam [SMTP:rkaram@xxxxxxxxx]
> > Sent: &he; &alef;&vav;ℷ&vav;&samekh;&tet; 10 2000 2:30
> > To: stds-802-3-pwrviamdi@xxxxxxxx
> > Subject: Cross Talk
> > Hi Avinom
> > your question about cross talk is a valid concern, my 2 cents on this
> > are that any noise generated out of the power supply sitting across
> > the center taps assuming no capacitors to chassis ground are present
> > at each center tap, would cause us EMI headaches way a head of any
> > interference.
> > please keep the filter needed to pass EMI radiated and Conducted testing
> > out of the system in mind.also please keep in mind that the center tap
> > at lower frequencies has good common mode tolerance per the graphof my
> > last presentation (at frequencies below 1MHZ or so the receiver does not
> > suffer). of course I may be missing your point....
> > roger