[time-nuts] Low noise power supplies?

[John Ackermann N8UR]

And this (very interesting) thread brings up the question of measurement 
methods.  Some time ago I searched around and didn't find much on a 
standard way to measure noise on low voltage DC supplies.

John
----

On 1/31/2013 11:36 AM, Bob Camp wrote:
> Hi
>
> I think the comparison of PSD on a power supply to phase noise and phase
> noise plots is a pretty good one in this case.
>
> For most applications nV/sqrt(Hz) is a pretty good way to check things out
> on a supply or regulator. It's not quite the same thing as dbc / sqrt(Hz)
> but it conveys the same sort of information. Unless you have a *very*
> sensitive part, anything below 10 nV/ sqrt(Hz) is likely to be "a very quiet
> supply". The main limit you hit is in the sub 100 Hz region where you likely
> see things like popcorn noise.
>
> AC ripple is no different than spurs in phase noise testing. You sometimes
> see people who ignore them when plotting phase noise. I'd suggest that they
> are an important part of characterizing a power supply.
>
> As with phase noise, frequency ranges are going to be application dependant.
> I may not care about 0.1 to 10 Hz phase noise for project A. It may be the
> only thing I care about for project B. Same thing with power supplies.
>
> With a good enough voltmeter you could carry the analogy one step further
> and compute an ADEV like number on the output voltage. I suspect that's
> carrying things a bit far.
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Tom Van Baak
> Sent: Thursday, January 31, 2013 9:43 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Low noise power supplies?
>
> Hi Rick,
>
> I'll answer the question with anther question -- how does one properly
> measure power supply noise? Does it boil down to a single number, a couple
> of key numbers, or is it a plot, or several plots?
>
> I ask because without some sort of standard test and reporting method it
> just becomes a word game. Like, "use batteries because they are better";
> "use my design because it is quiet"; "this has lower noise than that". RMS
> AC ripple or nV/rtHz sounds like a good start, but I'm wondering if there's
> something more complete.
>
> I was never quite satisfied with the outcome of comparing a half dozen power
> supplies this way:
> http://www.leapsecond.com/pages/tbolt/noise.htm
>
> We have rigorous ways to compare and report oscillator performance; both as
> numbers and as plots. Is there something equivalent for power supplies?
>
> Thanks,
> /tvb
>
>> I know this topic has been discussed in the past on the list, but
>> a colleague is asking if there are any off the shelf low
>> noise power supplies for testing oscillators.  Something
>> a cut above an HP "brick" lab power supply etc.  They are hoping
>> to avoid having to homebrew a power conditioning circuit.
>> Did we ever arrive at a concensus as to the state of the art
>> in homebrew power conditioning circuits?
>>
>> Any help would be appreciated.
>>
>> Rick Karlquist N6RK
>
>
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