[SI-LIST] Re: METASTABILITY

Tom, the CoolRunners do have very metastable resistant FF's.  But until you 
find an infinite gain amplifier, it is impossible to achieve zero 
metastability.  There will always be some window that causes the resolution 
time to stretch.  I contend that the combinatorial section that Philips 
uses, reduces the resolution time in most cases by effectively increasing 
the gain.  For practical purposes it may have a nearly undetectable 
metastability, but never zero.  The finite gain of the gates in the XOR and 
AND gate have the same limitation as the cross-coupled NAND gates.

Other opinions may vary.

Regards,


Steve.
At 10:52 AM 1/9/2006 -0800, Tom Biggs wrote:


>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Mike Greim
>"However fast we make the device, =3D there is always the possibility =
>that
>the input events will be so close =3D together that it cannot detect =
>which
>one happened first. It is therefore =3D logically impossible to build a
>perfectly metastable-proof flip-flop."
>----------------
>
>Actually, that's not true. Philips used to sell PLDs with
>metastable-proof flip-flop.
>I think they sold their PLD line to Xilinx, but I haven't heard of these
>parts since.
>
>I found an apnote describing them:
>http://noel.feld.cvut.cz/hw/philips/acrobat/8175.pdf
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