Noise analysis on dynamic comparator

Hi Mauro,

The way that Rapid Adoption Kits are stored on Cadence Online Support has changed to be a bit more like the rest of the regular content, and because of that the URL no longer works. You can easily get to them by going to support.cadence.com and then Resources->Rapid Adoption Kits and then searching within the Rapid Adoption Kits for "ADC Verification". This should take you to this URL:

ADC Verification Workshop

Regards,

Andrew.

Hi Andrew,

I had some questions regarding the setup for pnoise. In PSS it asks to add another tone at 1/2 sampling frequency. Why is this needed? Usually this would cause unnecessary foldback in periodic analysis. For example, in switched cap you use the clock frequency as beat frequency without any input tone.

Looking forward to hear from you. Thanks!

I've no idea why you would need to add another tone at 1/2 sampling frequency. It should be sufficient to just have the clock frequency, and then the sampled noise analysis allows you to sweep the frequency up to half the PSS fundamental (the sampling in the sampled noise analysis samples at the PSS fundamental rate, so it doesn't make sense to sweep beyond half the PSS fundamental). Do you have a source with that frequency in your circuit somewhere?

Andrew.

I've no idea why you would need to add another tone at 1/2 sampling frequency. It should be sufficient to just have the clock frequency, and then the sampled noise analysis allows you to sweep the frequency up to half the PSS fundamental (the sampling in the sampled noise analysis samples at the PSS fundamental rate, so it doesn't make sense to sweep beyond half the PSS fundamental). Do you have a source with that frequency in your circuit somewhere?

Andrew.

Thanks for the prompt reply. No currently I only have one large signal is PSS and that comes from the clock used to drive the latched comparator. If I dont add that tone its hard to get same results with transient and pnoise. I have a 500uV DC input. I am having trouble matching the transient noise and pnoise results.

If you look at the adc verification tutorial it asks to add this second tone manually in pss setup. It seems they do this to get same result as transient noise but I dont feel this is correct.

A wild guess Do u think I have to measure the sampled gain using pac for getting input referred noise?

I get result more close to transient noise if I use the gain measured with PAC (sampled) and use this to calculate input referred noise. I get 2.9mVRms with transient noise while 2.65mVrms with PAC/PNoise analysis. When I follow the setup direction provided in ADC verification workshop tutorial for Pnoise, I get 4.5mVrms.

Another interesting thing to see is that when I change the reltol, vabstol and iabstol the noise changes aswell. As we tighten these the result changes (both pnoise and pac). So using constant gain (vin*threshold) as suggested depending on this observation would be wrong.

I think either tutorial provided in the workshop is missing some explanation . It would be great if you please provide me with correct steps or get the setup verified on your end. 

I had a very quick look at the tutorial in its current form and I'm not really sure why this double period is used (it's not obvious to me), nor why the results you get don't match. It would need me (or somebody) to look at it closely and work through the tutorial again to check, and realistically I don't have time to do that at the moment (I've just been on vacation for a week and have a lot of catch up to do this coming week with the day job). A little reminder - I answer questions here in my spare time, and it's not part of my role at Cadence to respond here...

So please contact customer support - that's the right channel to ask these kind of clarification/accuracy questions (it may be a mistake has been introduced in the tutorial, or maybe there's a good reason that needs clarification in the instructions).

Thanks,

Andrew.

Thanks a lot for your time. I will contact cadance customer support to check with them.

Hi Andrew,

I dont have a key for get online support. I would have to request it through my professor. Is there anyother way to contact customer support?

BR,

Yunus

Hi Yunus,

For Universities, that's how you do it (unless part of Europractice, in which case you can log a support request with Europractice). You need to go through your University contact:

I believe the details are covered here: https://www.cadence.com/en_US/home/company/cadence-academic-network.html (at least they used to be, I didn't check thoroughly).

Andrew.