[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Bob kb8tq]

HI

> On Jul 8, 2022, at 7:44 PM, Mike Monett via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> To Erik:
> 
> …….
> Another item that might be of interest is the PFD. The Hittite
> HMC984LP4E has -231 dBc/root(Hz) of noise, which is quite low. The
> datasheet is at
> https://www.analog.com/media/en/technical-documentation/data-sheets/hmc984.pdf
> 
> …...
> 
> If you would like to eliminate the problem of quadrature lock, the
> Hittite HMC984LP4E PFD might be of interest. The -231 dBc/Hz of
> noise is very low and might be hard to reach with a DBM.
> 
> If you are interested in following up on phase-frequency detectors
> to eliminate the narrow lock range of double-balanced mixers, I can
> supply you with a wealth of information on the design, implementation, 
> and testing. Just let me know if this would help.
> 
> Mike
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Ok, since this keeps coming up ….

The chip guys rate their phase detectors in a somewhat unique way. It works
for their product so that’s fine. However you can’t just toss out their number
and quickly compare it to another number from an entirely different approach.
You need to do the math.

The -231 dbc / Hz number quoted above is a “normalized to one hertz carrier”
number. They call it a FOM or “Figure of Merit” due to the normalization. Other
data sheets phrase things slightly differently when referring to the same number.

The first hint you get that there’s something going on with the > 200 db noise
number is in figures 11,12, and 13 where they show actual performance at
a couple of frequencies. The noise at “phase noise test set” sort of offsets isn’t 
making it past 120 dbc / Hz on those plots.

The quick and dirty explanation is that you translate the “FOM” number by 
10 Log F to get the noise at the operating frequency. So, if you are at 100 MHz,
you add 80 db to the magic 231 db. That gets you to -151. That still sounds ok ….
but … this is the broadband FOM and not the close in number. It gets worse as
you go closer to carrier …. 

So no, that’s not going to beat a typical RPD-1 based setup.

Bob