Hi,
On 2022-04-25 01:57, Joseph Gwinn wrote:
I'm digging into the basic math of how cross-correlation phase noise
test sets (like the 53100A) work, so I'm looking for good articles on
the complex-exponentials math.
One item of interest is the effects of imperfections in the power
dividers that make a pair of perfect copies of the reference signal
in a residual-PN setup. I gather from Walls 1992 that the limit on
cancellation of signal-source PN is the imperfect isolation of the
power divider.
I'm more interested in clarity of exposition and the physics than in
solid walls of pure math.
I recommend you to look at the NIST T&F archive on the topic. Also their
AM and PM calibration document.
The field have developed over the years, covering a range of aspects,
including 2014 article describing the noise cancelling errors and 2016 a
proposal for how to address that.
The 2014 paper (David Howe, Craig Nelson and Archita Hati) is a good
paper as it sums thing up. The 2016 paper provide new hints in addition.
Quick explanation: you cross-correlate with two independent channels, so
only the DUT noise correlate. Averaging on the complex outputs of the
FFT based cross-correlation output removes the channel noises. Your
result will be on the real axis and your imaginary axis should be a
small vector of noise. When the real axis goes negative, as it does when
reaching thermal noise level, do not believe the measurement.
Cheers,
Magnus
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