[time-nuts] Effect of EFC noise on phase noise

Gerhard Hoffmann dk4xp at arcor.de
Wed Aug 3 15:48:09 EDT 2016

Am 03.08.2016 um 18:30 schrieb Richard (Rick) Karlquist:
> 1.  Back in those days at least, there were
> vendors who supposedly specialized in providing
> low noise zener diodes.  The particular breakdown
> voltage of zener diodes was important.  IIRC,
> at low voltages, it is a true "zener" diode and
> at higher voltage it is merely an avalanche diode.
> The physics are somehow different.  There is also

It is still important.

In these noise density plots that I made in January
you can see the NXP BZX84 family. 0 dB is 1 nV/sqrt hz
so the 2V7 and 3V3 versions are near 2 nV/sqrt Hz. Methinks
that is really good, given that the best low noise op amps
feature a input-referred noise density of 0.9 nV/sqrt Hz.

With rising voltage, 4V7, 6V8.. the diodes get worse and worse
and the LM399 is the complete catastrophe.
Well, in comparison.

The light blue line is an ancient 3.3V glass diode.
BZX84 are cent devices in SOT-23. Note their low 1/f corner.
The lowest dark blue line is the measurement limit.
Bias was 10 NiMH cells via a 1 or 2 KOhm wire resistor.
The bias added no visible noise.

BTW Prof. Zener sued against the manufacturers that they
should not use his name in vain for avalanche diodes
because it was not "his" effect. They settled on the name
Z-Diode for the form of the characteristic curve but in the
long term it was a Pyrrhus victory.


Gerhard, dk4xp

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