[ibis-macro] Re: Question about Receiver Sensitivity

  • From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
  • To: <ibis-macro@xxxxxxxxxxxxx>
  • Date: Wed, 26 May 2010 14:22:27 -0700

Thanks Mike and Walter for the explanation.  This
reminds me to another question I asked a while ago
about eye templates.  It seems that this sensitivity
parameter could be interpreted as two horizontal
lines across the eye diagram serving as if they were
an eye template.  The only difference is that it
doesn't contain the timing component of the eye
template, only the voltage or amplitude portion.
Is my understanding correct?


From: Mike Steinberger [mailto:msteinb@xxxxxxxxxx] 
Sent: Wednesday, May 26, 2010 2:45 PM
To: Muranyi, Arpad
Cc: ibis-macro@xxxxxxxxxxxxx
Subject: Re: [ibis-macro] Question about Receiver Sensitivity


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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