[time-nuts] Phase noise measurement with a scope

Stefan Heinzmann stefan_heinzmann at gmx.de
Wed Jun 12 17:26:29 EDT 2013


Marek Peca wrote:
>>> (..) I have tried it with a very cheap one, Rigol 2-channel, 
>>> originally 50MHz, reflashed to 100MHz. 2 signals, ref&measured, into 
>>> Ch1, Ch2. Waveforms (2x500Msps) acquired, sinc() interpolated. 
>>> Results: short-term single-shot jitter around 100ps RMS. Long-term 
>>> was of no interest for my purpose now, so no observations here.
>>>
>>> Therefore, it is almost of no use at all for higher precision needs.
>>
>> I was thinking about using a 4-channel scope with cross-spectrum 
>> averaging. Look at the Timepod by John Miles for an example of the 
>> method. I'm trying to guesstimate if the R&S RTO scope, perhaps with 
>> the aid of the I/Q option, is capable of doing such measurements, and 
>> with what kind of performance.
>
> 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?

Cheers
Stefan

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