[time-nuts] Phase noise and jitter

[SAIDJACK at aol.com]

Hello Javier,
 
Wavecrest makes a point of saying they do not operate like a sampling  scope, 
rather like a Time Intervall Analyzer with very high resolution, and up  to 
40.000 measurements/s. See for example page 12 in the manual at this  location:
 
   
_http://www.mhzelectronics.com/ebay/manuals/wavecrest_dts-2079-77-75_digital_time_system_manual.pdf_ 
(http://www.mhzelectronics.com/ebay/manuals/wavecrest_dts-2079-77-75_digital_time_system_manual.pdf) 
 
A sampling scope has all sorts of aliasing issues, and typically much lower  
resolution and noise floor, and is not very good at single-shot events.
 
Their Visi software does have an Oscilloscope view as well btw.
 
The Wavecrest website is gone, maybe they are bankrupt?
 
I have most of their manuals and appnotes in PDF form if you need  them.
 
They do a time intervall measurement using counters running at 100MHz and  
analog interpolators, similar to an HP5334A etc. They took this to another  
dimension though with 800ps resolution at 40000 samples per second and gated  
arming capability etc, up to several GHz bandwidths.
 
The Visi Windows software has special routines for PLL measurement etc.,  and 
this also includes TIA-to-Phase Noise graphing, although I do not find that  
feature very useful.
 
What is extremely useful in your application is the Jitter histogram (you  
can see and quantify immediately if jitter is deterministic, and/or random, and  
what the side lobes values are etc). See the attached example plot, you can 
see  the jitter being split into left, right, random, total, deterministic 
jitter etc  etc. (That happens to be a very low noise OCXO)
 
Since they are concerned about edge-to-edge jitter, it is best to have nice  
fast rising/falling edges on your signal. While Sine Wave signals do work, the 
 unit will give you a lower phase noise floor if you buffer these from Sine 
Waves  to say LVDS signals, or CMOS signals.
 
They are somewhat rare to find, and some distributors try to get $30K or  
more for them, but I have been able to buy several for around $500 on Ebay  in 
the past.
 
bye,
Said
 
 
 
In a message dated 10/13/2008 14:06:09 Pacific Daylight Time,  
javier.serrano.pareja at gmail.com writes:

Said,  what is the operating principle of the Wavecrest Jitter Analyzer?
Is it a  sampling scope like the ones Agilent and Tektronix offer? How
does it  compare to them? I've googled it but I only found a Chinese site
with  little information in English. Another advantage I see for
time-based  measurements is that you can go arbitrarily low in offset
from the carrier.  In the 5052B you have a PLL with non-zero bandwidth,
so below some offset  you probably get an optimistic estimate because the
PLL is actually  following the noise. Another item to bear in mind, if my
understanding is  right, is that integrating the phase noise plot gives
you the rms jitter  between your noisy waveform and the perfect sinewave,
or rather an  approximation of it, which is what comes out of the PLL in
say the 5052B. A  sampling scope typically measures the time jitter
between two (noisy)  rising edges of a clock waveform. In the simplistic
case of white phase  noise this should give you a factor sqrt(2) more
jitter than the loose PLL  measurement, right? 
Thanks  again,
Javier





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