[SI-LIST] Re: METASTABILITY
- From: Alex Horvath <AHorvath@xxxxxxxxxxxx>
- To: arpad.muranyi@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Thu, 5 Jan 2006 11:39:57 -0800
I used to do some metastability analysis when I worked on avionics.
Obviously I can't present the whole theory of metastability in this forum
but suffice it to say that the actual metastable window, that is the window
in which metastability will occur, was on the order of 100 ps in the LSTTL
days. With modern high speed logic I believe it is on the order of 10 ps and
in fact I have seen some old app notes describing a test fixture where they
could apply a variable delay to the D flop input to try to find the
metastable window and it's very difficult to get the flop to go metastable
due to the small size of the window.
Note that the metastable window has nothing to do with the flop setup time.
The best app note I saw on metastable probability calculations including the
settling time of the flop output when it goes metastable(which is a
probability function) was from Altera corp. Try a search.
In my experience if you chain 2 modern flops together and assuming your
asynchronous input signal is much slower than the flop clock and you have no
logic between the flops (to allow max settling time during metastable event
on first flop) the prob of a metastable event on the output of the second
flop is infinitesimal.
-----Original Message-----
From: Muranyi, Arpad [mailto:arpad.muranyi@xxxxxxxxx]
Sent: Thursday, January 05, 2006 10:21 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: METASTABILITY
Thanks for the numerous replies, public and private.
I agree that there is a strong relationship between
signals and metastability in general. I guess the
reason I said that I didn't see the relationship in my
first reply to this thread was because I was thinking
of signal integrity as the art of making sure that the
signal is clean, has the correct amplitude and slew
rate, that it is timed correctly, along with dealing
with transmission line effects, terminations, cross
talk, etc... to avoid any possibilities for metastability.
In that sense an SI engineer is working on signal
quality problems, not so much on the metastability
problem itself. The tricks an SI engineer uses to
solve these problems and the tricks a circuit designer
uses to reduce the metastability problem are quite a
different world to me.
This is why asking an explanation for what the "concept
of *METASTABILITY*" is in an SI forum seemed inappropriate
to me. Most SI experts are not circuit designers,
therefore may not be knowledgeable enough to answer this
question in depth.
Arpad
-----------------------------------------------------------
-----Original Message-----
From: Peterson, James F (FL51) [mailto:james.f.peterson@xxxxxxxxxxxxx]=20
Sent: Thursday, January 05, 2006 9:16 AM
To: Muranyi, Arpad; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: METASTABILITY
a good question, but I believe they are indeed related : a lot of signal
integrity problems are timing problems (if we had enough time, they =
wouldn't
be signal integrity problems), some of those timing problems are =
problems
because they cause a signal to slide inside the setup/hold timing =
boundaries
of a flop, and this is where Metastability happens...=20
best regards,
Jim Peterson
Honeywell
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On
Behalf Of Muranyi, Arpad
Sent: Thursday, January 05, 2006 11:37 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: METASTABILITY
Maybe I am missing the point, but I don't see that metastability and SI =
are
related subjects...
Arpad
-----------------------------------------=3D20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
=3D
On Behalf Of Somesh Dhavala
Sent: Thursday, January 05, 2006 6:54 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] METASTABILITY
Hi All,
I am very new to the SI.
I am unable to understand the concept of *METASTABILITY*, I am very =3D =
thank
ful to you if you explain me in detail.
Please suggest me some documents.
Thanks & Regards
Somesh Dhavala
CG-CoreEl
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