[SI-LIST] Re: METASTABILITY
- From: "Derek Walton" <lfresearch@xxxxxxx>
- To: AHorvath@xxxxxxxxxxxx
- Date: Thu, 5 Jan 2006 16:19:51 -0600
Actually,
this topic is highly relivant to me. I have been tracking a noise issue
that I believe is causing metastability. I have a digital device driver
( older technology ) that appears to get in a state where it won't let
the relay it's driving, release.
Noise on the power pin appears to get into the driver and cause it to
become neither on nor off. Now, normally, I think of metastability as
being caused directly by the deliberate switching event: more
specifically by the timing of logic changes within a device once a
switching event comes in.
So, is it correct to call my noise induced intermediate state Metastable?
Just curious,
Derek.
Alex Horvath wrote on 1/5/2006, 1:39 PM:
> 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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--
Cheers,
Derek Walton
L F Research
Poplar Grove, IL 61065, USA
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