[SI-LIST] Re: Power sum crosstalk calculation method--is there an error in OIF-CEI or 10GBase-KR?
- From: "Qin, Zhenshui (NSN - CN/Shanghai)" <zhenshui.qin@xxxxxxx>
- To: ext Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Tue, 30 Jul 2013 06:21:44 +0000
Hi Scott,
Thanks for your explanation, that's the same as my intuitive guess.
Bruce
From: ext Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Monday, July 29, 2013 8:39 PM
To: Qin, Zhenshui (NSN - CN/Shanghai)
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Power sum crosstalk calculation method--is there an
error in OIF-CEI or 10GBase-KR?
Bruce
your understanding is absolutely correct. The assumption made by the committee
is that when all the sources of crosstalk are considered, a voltage sum is too
stringent a criteria, since the probability of all crosstalk sources being in
phase with respect to a victim is extremely unlikely. As a result they chose
to use power sum, which is roughly equivalent to an RMS summation of the
aggressor impacts on the victim.
regards,
Scott
On Mon, Jul 29, 2013 at 4:57 AM, Qin, Zhenshui (NSN - CN/Shanghai)
<zhenshui.qin@xxxxxxx<mailto:zhenshui.qin@xxxxxxx>> wrote:
Hi,
I am working on an simulation for 25G operation, the results is targeted to
meet CEI 25G LR mask.
An interesting thing I found in OIF-CEI 25G mask is the method used to power
sum the crosstalk sources, actually the same method use also for IEEE
10GBase-KR standard.
For example, If I have two crosstalk source, the equation should be like below:
PSXT=-10*log10(10^(-Xtk1/10)+10^(Xtk2/10))
But my question is, in SI area, our S-parameter is calculated using Voltage
rather than Power, it means we calculate the value use
S12 *log10(Vout/Vin).
So the problem happened when we use the equation above, two -40dB crosstalk add
up to
PSXT=-10*log10(10^(-40/10)+10^(-40/10))=-37dB
While the reasonable value should be -40dB corresponding to 0.01, and two of
them makes 0.02, so
PSXT *log10(0.02)=-34dB
Does anyone know the trick behind the equation? Or what's wrong with my
understanding?
Thanks.
Bruce
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