[time-nuts] Distribution amplifier phase noise

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Mar 14 14:02:44 EDT 2013

Ulrich Bangert wrote:
> Gentlemen,
> although it has been discussed here by Bruce et al how the noise floor of
> integrated distribution amplifiers designs may compare to discrete designs I
> have never seen a *real* phase noise measurement of a *real* amplifier here.
> My own measurements on a DIY AD8007 based distribution amplifier indicate a
> noise floor of abt. -160 dBc @ 100 kHz which may not meet the specs of the
> absolutely top line of oscillators by some 15 dB but is well in reach of
> Bruce's predictions for integrated designs.
> Did any of you Timepod owners make measurements of your own on amplifier
> noise? Please note that I am not only out for the noise floor specs. Instead
> I am specially interested in specs for power supply induced spurs.
> I just received an article covering ultra low noise oscillators to be found
> here:
> http://www.crystek.com/documents/appnotes/ImpactUltralow.pdf
This paper is very sloppily written. e.g.:
-174dBm/Hz is the available thermal noise power of any resistor at 290K 
not just 1 ohm.
There is no explicit consideration of the contribution of thermal noise 
power to phase noise.

> Clearly the phase noise diagram shows a power induced spur @ -100 dBc. Is
> this the measure for the amplifier to take care for? I.e. if the amplifiers
> has spurs down -120 dBc, is that good enough?
> Or to put it another way: What is the best phase noise that we can expect
> from an amplifier concerned power supply induced spurs? Can it be that the
> spurs to be seen are not a problem of the amplifier itself but are inherent
> to the measurement setup? If so, is there a recommended setup to minimize
> such problems?
I routinely achieve mains related PN spurs below -150dBc and often below 
Such spurs can be enhanced by low frequency ground loops and magnetic 
Using RF isolation transformers with capacitive grounding of the 
isolated winding helps considerably in suppressing mains related ground 
> Thanks in advance for your suggestions. I appreciate the expertise in this
> group a lot!
> Ulrich Bangert
> www.ulrich-bangert.de
> Ortholzer Weg 1
> 27243 Gross Ippener
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