[ibis-macro] Re: Question about Receiver Sensitivity

  • From: Mike Steinberger <msteinb@xxxxxxxxxx>
  • To: Arpad_Muranyi@xxxxxxxxxx
  • Date: Wed, 26 May 2010 14:45:00 -0500


The Rx_Receiver_Sensitivity is needed for the EDA tool to do an accurate job of estimating the bit error rate.

Let me describe one of my favorite experiments. It's one my former group at Cray performed many times. 1. Take a signal directly out of a data generator and put it into a receiver. Measure the BER.
   - The BER should be indistinguishable from zero.

2. Using microwave attenuators, decrease the amplitude going into the receiver. Measure the BER. - Up to some attenatuation, the BER will remain zero. Then, with 1dB increase in attenuation, the BER will go from zero to 10e-3 or so.

Anyone can perform this experiment with an eval board and a bag full of attenuators. It doesn't take a lot of time, skill, or money, and the same behavior will be observed for every SerDes on this planet, albeit with different minimum receive amplitudes.

So, what happened in this experiment? The shape of the eye diagram remained the same (because microwave attenuators are nearly constant with frequency), but the amplitude decreased. At some minimum amplitude, the receiver stopped working even though the eye diagram (for example, as displayed on a sampling oscilloscope) is still absolutely beautiful.

An EDA tool must be able to reproduce this experiment, and in order to do so accurately, it needs to know the Rx_Receiver_Sensitivity.

The definition we currently have for Rx_Receiver_Sensitivity is exactly what we need and is successfully fulfilling the role it was originally intended for.

Mike S.

On 05/26/2010 01:42 PM, Muranyi, Arpad wrote:
Hello AMI experts,

I know this was discussed before but it is still not
clear to me how the Rx_Receiver_Sensitivity parameter
is supposed to be used.

This parameter is Type Info, meaning that it is not
passed to the DLL, it is only information for the EDA
tool.  The question is, what is the tool supposed to
do with this?

I assume that if the DLL is written correctly, it would
account for this sensitivity parameter in its algorithms
(for example in CDR), so the EDA tool wouldn't need to
adjust the returned times for the threshold (in)sensitivity.
Is the EDA too expected to do anything with the returned
waveforms when displaying eye diagrams and/or BER plots,
etc...?  If yes, what should be done?  If no, what is
the purpose of this parameter?



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