[SI-LIST] Re: SDA bandwidth

Hi:

I hate to over-promote a paper (I sent a link to this paper a few weeks
ago), but you'll want to look
at this paper for guidelines for bandwidth requirements:

http://www.lecroy.com/tm/Library/WhitePapers/PDF/Eye_Patterns_in_Scopes-designcon_2005.pdf

My rule of thumb is that the bandwidth should be at the very least 1.8
times the bit-rate (really 2).
You can use the 2x rule when the risetime is less than 30% of the unit
interval (UI) which is your case.

So you'll need an 18-20 GHz scope.  Tek has such a scope in real-time, but
you'll want to to look at other
signal fidelity aspects.

I have gotten good measurements from scopes as low as 12 GHz for the case
that you're talking about but you're really looking for something higher in
bandwidth.

In real-time scopes, you want something whose sample rate is at least twice
the bandwidth (3 times is good for a high-end scope).

Don't worry about points on an edge and that sort of thing - rely on the
fact that if Nyquist's criteria is met, you will get accurate measurements
(i.e. sample rate should be >= 2x bandwidth of interest).

There are some very good sampling scopes out there for these types of
measurements that do not impose the bandwidth limitations, but then you
have to deal with the non real-time nature of these scopes.  You will want
to look at the LeCroy WaveExpert and others.

There are other tools as well, but I'll let these members provide their
advertising.

Pete



                                                                           
             gypse                                                         
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Hi all,

Have you got an idea of the required features (bandwidth + sampling rate)
for a
SDA to analyse 10Gbits/s serial links ?

Bandwidth:
Thumbs rules for the bandwidth would lead me to choose 5 times the
fundamental
frequency to see the 5th harmonics ie 25 GHz. But high speed devices have a
rise
time of only 40ps, so the estimated bandwidth of such signals would rather
be
0.5/30ps = 12 Ghz ... So, what to choose ?

Sampling rate:
Am I wrong if I say that with a sampling rate of 60 Gsamples/s, I
will capture an eye with only 6 points and therefore I will be able to
measure
jitter with an accuracy of only 16 %. Should I need a higher sampling
rate ?

Thanks.
Jean.

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