The problem with sampling 'scopes is that you cannot get a continuos samples stream. I think that the TimePod correlates continuously in time.
On Thu, Jun 13, 2013 at 11:56 AM, Stefan Heinzmann <stefan_heinzm...@gmx.de> wrote: > Marek Peca wrote: >>>> >>>> My point was, that DSO is basically an ADC. Therefore, there is some >>>> amount of noise, nonlinearity and drift, limiting the jitter measurement. >>>> Do >>>> you think any method can dig more information from given data than sinc() >>>> interpolation and zero-crossing computation? >> >> >>> The cross-spectrum averaging does indeed do just that, relying on two >>> ADCs to produce uncorrelated noise, which can be averaged out. >>> >>> Or am I misunderstanding your point? >> >> >> Nothing against that. It depends on what noise level after averaging you >> require. I only posted my experience with a very low-quality DSO, which has >> 100psRMS single-shot. Using sinc() interpolation, but my point was, that I >> suppose there is no way to obtain better single-shot performance than this. >> To average out 100psRMS to, say, 1psRMS, it would require 10^4 edges (under >> the assumption, that the 100psRMS is well behaved noise). >> >> What performance it could yield with a better scope? I hope I'll try >> LC584AL some day, I guess it might give sth like 10psRMS single-shot... > > > John Miles' Timepod uses 16-bit ADCs which by definition can't have better > than roughly 100dB noise floor, yet it is able to measure down to around > -170 dBc phase noise, isn't it? > > A scope like the RTO which I mentioned has 8-bit ADCs with 10 GS/s, which > could for example be downsampled by a ratio of 128 to yield an effective > sampling rate similar to what is used in the Timepod, with a corresponding > increase in resolution. It would still not be equivalent to a 16-bit ADC, > but as long as there are no prominent spurs, it should not be radically > worse. And since it is not a low-quality scope, I would expect reasonable > jitter performance from the oscillator in the scope. The oscillator used in > the Timepod isn't going over the top, either, since the measurement method > does not rely on that clock being pristine. > > Still, I may very well have overlooked something important, so tell me if my > reasoning is faulty. > > Cheers > Stefan > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
