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dynamic comparator noise measurement. (Read 1258 times)
yvkrishna
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dynamic comparator noise measurement.
Mar 14th, 2017, 11:20am
 
Hi,

I am simulating dynamic comparator noise using pnoise setup.

In the interest of simulation time I am simulating with 10X clk freq than what I designed for,  does it impact my final result in any manner?


Rgds,
yvkrishna
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DanielLam
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Re: dynamic comparator noise measurement.
Reply #1 - Mar 15th, 2017, 11:47am
 
Why don't you just simulate with different Fclks? The sims should take less than 5 mins. Pnoise sims are pretty fast. Transient noise sims are very slow.

In order to teach others, can you please post what you see?

I'll post what I've seen afterwards.

Regards,
Daniel Lam
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yvkrishna
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Re: dynamic comparator noise measurement.
Reply #2 - Mar 15th, 2017, 6:47pm
 
Hi,

My clk freq is quite low today so the pnoise sim takes 6 hrs atleast which is bothering me to try out few simple  experiments also even during design optimisation.

and the recommendation was to increase sidebands , maxacfreq based on bandwidth of the circuit.

Sure I will getback on my observations.


Rgds,
yvkrishna
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DanielLam
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Re: dynamic comparator noise measurement.
Reply #3 - Mar 15th, 2017, 7:20pm
 
For the pnoise sim, I basically run a jitter sim, integrate the jitter, and divide by a peak gain. I was running a 2-4 GHz clock. Each sim (PSS+Pnoise) took about max a minute. 10 sidebands, moderate tolerances.

For my comparator with different fclk (which means sidebands and integration limit changes). Also, the clock was a square pulse with the same rise/falltime of 5 ps:

100M : 210 uVrms (jitter 70m)
1G : 373 uVrms (jitter 124m)
2G: 376 uVrms (jitter 123m)

I had a difference, and I think it was due to the integrated jitter range (along with the comparator characteristics). I didn't look any deeper after that.
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Ken Kundert
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Re: dynamic comparator noise measurement.
Reply #4 - Mar 15th, 2017, 7:35pm
 
Why would a low clock frequency result in a long simulation time?

-Ken
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yvkrishna
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Re: dynamic comparator noise measurement.
Reply #5 - Mar 15th, 2017, 11:00pm
 
Ken,

Since the bandwidth of my circuit is about 1000X than the clock freq, I think atleast few thousand sidebands are needed in pnoise setup to take of folding effects.
(some people even suggest 10X the ratio of bw to clk frq which is 10,000 sidebands  )

This is the cause of slowness in my setup.

Let me know if I am missing something here.


Thanks,
Vamshi
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Andrew Beckett
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Re: dynamic comparator noise measurement.
Reply #6 - Mar 16th, 2017, 3:56pm
 
You should use the fullspectrum option for pnoise rather than specifying a huge number of sidebands. You need to specify the number of sidebands to be high enough to be above the flicker knee, but other than that, using the fullspectrum method will allow it to use an adaptive approach which is much more efficient.
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yvkrishna
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Re: dynamic comparator noise measurement.
Reply #7 - Mar 16th, 2017, 8:22pm
 
Thanks for the suggestion about fullspectrum Andrew.

So this would be in a 2 step, first give only few (~100) sidebands to get a crude estimate for flicker noise corner at the output of the comaparator and then use that to get the correct estimate for sidebands in the next iterations (??)


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yvkrishna
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yvkrishna
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Re: dynamic comparator noise measurement.
Reply #8 - Apr 18th, 2017, 9:16am
 
DanielLam,

My noise result  with  1X ,2X , 4X clk freq are identical, so this method is beneficial to speedup simtimes.

only thing to make sure is to have sufficiently large maxacfreq in pss setup w.r.t the bandwidth of the DUT.

Thanks,
Vamshi


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Andrew Beckett
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Re: dynamic comparator noise measurement.
Reply #9 - Apr 21st, 2017, 1:36pm
 
yvkrishna wrote on Mar 16th, 2017, 8:22pm:
So this would be in a 2 step, first give only few (~100) sidebands to get a crude estimate for flicker noise corner at the output of the comaparator and then use that to get the correct estimate for sidebands in the next iterations (??)


No, it's not in two steps. I didn't say that... it doesn't work the way you are suggesting.

Did you try it?

Andrew.
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yvkrishna
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Re: dynamic comparator noise measurement.
Reply #10 - May 20th, 2017, 9:22pm
 
Andrew,

I have tried using 20 sidebands for flicker noise first, then tried with default.

both of the cases result is pretty close.

Thanks,
yvkrishna

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