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

[Mike Monett]

Bob, you wrote:

> Mike. One concern I have with active components as mixer is noise.
> For an SA I designed only a passive DB diode mixer had  low enough
> output noise.  Would a PF detector as being  an  active component,
> not create more noise as output? Erik

> Yes, you are correct. The only thing with a low enough noise floor
> for good  phase noise measurements (via the  quadrature technique)
> is some sort of mixer. Normal digital phase detectors have  way to
> high a noise floor.

> Bob

You are talking about old technology. Old tecnology PFD's were built with
discrete circuits and probably suffered from crosstalk, deadband, ground
bounce, VCC noise, and noisy input oscillator signals.

Modern PFD's have very low noise. For example, the Hittite HMC984LP4E
digital phase-frequency detector has -231 dBc/Hz of noise and goes up to
350MHz:
https://www.analog.com/media/en/technical-documentation/data-sheets/hmc984.pdf

Too bad the price jumped enormously when Analog bought Hittite.

The MC100EP140 Phase-Frequency Detector has 200 femtoseconds of jitter and
goes up to 2GHz. That is not going to match the HMC984LP4E but will be
adequate in many applications:
https://www.onsemi.com/pdf/datasheet/mc100ep140-d.pdf

Modern synthesizer IC's have PFD's as the frequency detector and offer very
low noise.

You also forget that double-balanced mixers are also very noisy. For
example, most receivers need a good low noise preamp in front of the mixer
to get an acceptable noise figure. I am told that part of the reason for
the high DBM noise is multiple harmonics are generated by the internal
signals, which combine as part of the output signal.

Mike