[SI-LIST] Re: AW: Number of bits to simulate
- From: "Al Neves" <al@xxxxxxxxxxxxxxxxx>
- To: "'Havermann, Gert'" <Gert.Havermann@xxxxxxxxxxx>, "'Roopesh Badala'" <roopesh.badala@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 8 Dec 2011 07:37:46 -0800
Gert,
Great answer!
More bits and longer test times provides more data which typically provides
greater confidence levels in the BER and TJ estimates. Everyone seems to
forget that both BER and TJ are estimators for a stochastic process, and things
either improve the confidence or they won't. You "NEVER GET THE RIGHT ANSWER",
since there isn’t an answer, there is only an estimate of a complicated
stochastic process. Longer test times will however reduce the variability of
the estimates. In some cases the estimator can be biased such that no matter
how many samples you acquire, or how long the bit train is you will not
converge on a higher confidence estimate. M. Mueller discusses this a few
years back in a paper related to BERT analysis for Agilent BERT.
Extending Gerts comment a bit... we (Vitesses, LeCroy, and WRT) are writing a
paper describing a method that separates pathologies using some relatively
newly developed tools and a comprehensive library of passive/causal
S-parameters. We essentially analyze the raw S-parameter with a defacto
perfect TX/RX and the channel S-parameters and EQ the channel (we use
SI-Studio), where the EQ is same architecture as the TX/RX.
Anyone unable to attend DesignCon, Ill send you the paper after we present it.
Products for the Signal Integrity Practitioner
Wild River Technology LLC
Alfred P. Neves
Founder – Engineer – Business Development
(503) 718 7172 Office
(503) 679 2429 Mobile
735 South East 16th Ave.
Hillsboro, OR 97123
www.wildrivertech.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Havermann, Gert
Sent: Tuesday, December 06, 2011 8:31 AM
To: Roopesh Badala; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AW: Number of bits to simulate
Roopesh,
if the eye looks bad for long patterns, you shouldn't ask how to test to make
it look better, you should take care of the problems in your channel.
The Longer the bit sequence, the better you see how good your channel is.
Testing with less bits will not solve anything.
BR
Gert
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von Roopesh Badala
Gesendet: Dienstag, 6. Dezember 2011 15:02
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Number of bits to simulate
Hello Experts,
We are simulating a LVDS channel of 800Mbps datarate using ibis models &
cadence channel analysis tool utilities.
We are struck at selecting number of bits for simulation.
How do you decide on the PRBS pattern length for simulation.
with 32 bits the eye opening is good. but for higher pattern length the eye
opening is bad.
Is there any relation between the channel length or data rate to number of bits
to simulate.
kindly advise.
Thanks in advance
Roopesh.
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