[SI-LIST] Re: Power sum crosstalk calculation method--is there an error in OIF-CEI or 10GBase-KR?
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: zhenshui.qin@xxxxxxx
- Date: Mon, 29 Jul 2013 08:38:45 -0400
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> 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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--
Scott McMorrow
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