[SI-LIST] Re: Jitter measurement floor on different high bandwidth oscilloscopes
- From: "Mark Randol" <Mark.Randol@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 11 Jun 2010 07:16:54 -0700
I've done a good amount of work with high performance sub-picosecond
clocks and oscillators, but not serial data. So I know this applies to
clocks, but I don't have the experience to know how or if it applies to
data streams.
When looking at discrete tonal noise components using a 'tuned' receiver
like a spectrum analyzer or phase noise system, the RBW (Resolution Band
Width) of the measurement system and the shaping factor of the RBW
filter do not figure into their contribution. That's because of the
different nature of broadband noise-like signals and spectrally discrete
or CW signals. That is, as the RBW shrinks towards 0Hz, the measured
power of the discrete component remains constant, but the noise power in
the bandwidth decreases as a function of the bandwidth.
I believe (no firm analysis) that a phase noise system or spectrum
analyzer with a sufficiently low noise floor are the best instruments
for correctly characterizing RJ. DJ can be estimated, but its actual
contributions aren't directly measurable since the phase relationships
between the different frequency components are unknown.
Both types of systems, frequency and time domain based, are useful
tools. I've found it useful to use them to cross check each other since
there are perturbations in both types of systems that can lead to much
head scratching without the sanity check.
Gigamax (formerly Wavecrest) offers some interesting alternatives. I've
found their analysis software to be more powerful and easier to use than
any of the oscilloscope manufacturer's packages. The oscilloscope tools
may have improved in the several years since I used them, but if you can
get a look at one, it's worth your while to see. No affiliation other
than using the products.
--
Mark Randol, Evaluation Engineer
ON Semiconductor
My opinions, not ON's.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of T.K. Jeon
Sent: Thursday, June 10, 2010 8:30 PM
To: Alfred P. Neves
Cc: si-list@xxxxxxxxxxxxx; 'prasad'
Subject: [SI-LIST] Re: Jitter measurement floor on different high
bandwidth oscilloscopes
I guess that using a spectrum analyzer is one of the good ideas to
benchmark jitter packages, especially, for PJ-RJ separation.
I noticed that some postprocessing algorithms show poor performance to
separate PJ and RJ effectively when the source is clock-like(1010)
signal. In other words, when there is a spectral peak from the signal
spectrum, which should correspond to PJ, a jitter package could fail to
take that for PJ calculation. The phase noise at a spectral peak can be
easily obtained without any special tools. In order to compute phase
noise from signal spectrum, you can read X dB on the peak in the
sideband using the marker, and then you will need to subtract noise
power bandwidth, which is usually 1.2*RBW(Resolution Bandwidth).
Furthermore, a correction factor (roughly 2.5dB for Agilent spectrum
analyzer) should be added for noise distribution.
Regards,
TK
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