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Design >> Mixed-Signal Design >> no metastability problem in comparator at lower frequencies
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Message started by seenu on Nov 1^st, 2011, 9:49am

Title: no metastability problem in comparator at lower frequencies
Post by seenu on Nov 1^st, 2011, 9:49am

Hi,
when iam using this dynamic comparator with equal inputs iam not getting metastability state for the given circuit for different values of (W/L) ,,,,but metastability occuring only when the enable frequency is higher i.e is in Ghz range.
Why i didnt get the metastability problem for low frequencies
Can anybody suggest me the solution ?

Thanks in Advance
srinu

Title: Re: no metastability problem in comparator at lower frequencies
Post by boe on Nov 1^st, 2011, 12:35pm

Hi,
Did you use same rise/fall times for the signals? Did you consider the delay of the comparator? Simulator (accuracy) settings may depend on things like sim end time...
- B O E

Title: Re: no metastability problem in comparator at lower frequencies
Post by wave on Nov 1^st, 2011, 6:25pm

How are you simulating metastability?
Are you just looking at gross failures? Noise analysis?

Title: Re: no metastability problem in comparator at lower frequencies
Post by loose-electron on Nov 5^th, 2011, 1:04pm

metastability is usually an issue with small inputs where the circuit does not have enough gain to make the device take one state or the other.

more info needed...

Title: Re: no metastability problem in comparator at lower frequencies
Post by Vladislav D on Dec 10^th, 2011, 3:47am

First, you should understand for yourself what metastability is. I'd define it as an event when a comparator cannot resolve the input within particular amount of time .
Secondly, metastability is a probability-thing, i.e it occurs always! At high frequency, comparator has less time to resolve input and so you see a lot of metastable events. However, it is very difficult to see metastability issue at low frequency because probability is much-much lower.

Title: Re: no metastability problem in comparator at lower frequencies
Post by loose-electron on Dec 10^th, 2011, 10:11am

Vladislav D wrote on Dec 10^th, 2011, 3:47am:

Agreed - and add to that - higher frequency = less gain.

one perspective is time domain and the other is frequency. Both are valid.