[ibis-macro] Re: Question about Receiver Sensitivity

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: <Arpad_Muranyi@xxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
  • Date: Wed, 26 May 2010 18:05:23 -0400

Arpad,

First, you have to think of the eye as a series of eye contours of
probability that the eye will be inside that contour. Where the two
horizontal lines you suggest cross each eye probability contour is
essentially the bathtub curve.

Walter

Walter Katz
303.449-2308
Mobile 720.333-1107
wkatz@xxxxxxxxxx
www.sisoft.com

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]On Behalf Of Muranyi, Arpad
Sent: Wednesday, May 26, 2010 5:22 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Question about Receiver Sensitivity

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?

Arpad
======================================================

  _____

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
Arpad-

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.

Thanks.
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?

Thanks,

Arpad
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