[time-nuts] Low noise power supplies?

[Ulrich Bangert]

Linear Technology application note 83

"Performance Verification of Low Noise, Low Dropout Regulators"

holds some interesting information. I am however unsure whether what was low
noise in 2000 is still low noise in 2013

Best regards
Ulrich Bangert

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Bob Camp
> Gesendet: Freitag, 1. Februar 2013 13:38
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Low noise power supplies?
> 
> 
> Hi
> 
> The circuit I described, is (as stated) quiet down to 100 Hz. 
> It's 3 db bandwidth is well below 10 Hz with the 47 uF cap. 
> If you need it quiet down to 10 Hz or 0.000000001 Hz, you 
> will need to buy a few more caps. It's still not rocket science.
> 
> For most OCXO or atomic standard testing applications out 
> there, 10 Hz is low enough. 
> 
> Bob
> 
> On Jan 31, 2013, at 9:41 PM, Charles P. Steinmetz 
> <charles_steinmetz at lavabit.com> wrote:
> 
> > Bob wrote:
> > 
> >> An AD 797, a couple of metal film resistors, and a fairly 
> large (say 
> >> 47 uf) plastic cap work pretty well.
> > 
> > The band from 10 Hz down to 0.1 or 0.01 Hz is generally 
> important when 
> > testing oscillators.  To keep the 797 input noise density 
> below a few 
> > nV per root Hz, the terminations must have very low 
> resistance.  With 
> > such low resistance, a 47 uF cap won't even get you to 10 Hz, much 
> > less 0.1 or 0.01 Hz.
> > 
> > One more thought: Many oscillators have internal regulators 
> that are 
> > not nearly as good as what you can build.  No sense using 
> an external 
> > supply with 5 nV per root Hz noise density if it will be 
> re-regulated 
> > inside the oscillator by a circuit that has a noise density 
> of 250 nV 
> > per root Hz.
> > 
> > Best regards,
> > 
> > Charles
> > 
> > 
> > 
> > 
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