[ibis-macro] concern on Rx_Noise
- From: <fangyi_rao@xxxxxxxxxxx>
- To: <ibis-macro@xxxxxxxxxxxxx>
- Date: Mon, 20 May 2013 18:02:36 -0600
Experts;
While thinking about how to handle Rx_Noise in redriver, I came to realized
that Rx_Noise's behavior in the downstream channel can't be defined. As
described in BIRD 123, Rx_Noise is the RMS of a Gaussian voltage noise, and its
unit is Volt. That information is inadequate to determine how the noise is
transferred when passing through a filter because to compute the filtered noise
one needs to know the input noise Power Spectral Density (PSD) in
Volt/sqrt(Hz), but not RMS.
Take a simple example and consider a low pass filter that performs a time
average on the signal within a window of 1UI. Assume N time points are used per
UI. It's well known that the RMS of the average over N random noise samples is
(1/N) * Rx_Noise / sqrt(N)
where 1/N is the weight of each sample interval. Now the filter output noise
depends ambiguously on the number of time points per UI, which is a simulation
setting.
Am I missing something?
Fangyi
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