[time-nuts] Low noise power supplies?

[Bob Camp]

Hi

If you are driving a spectrum analyzer, the 10,000X mentioned in the app note simply is not needed. A gain of 10X or less will get you to below 2 nv / sqrt(Hz)  at 100 Hz and beyond. A 10 Hz blocking cap does not need to be a "24 hours to stabilize" device.  An AD 797, a couple of metal film resistors, and a fairly large (say 47 uf) plastic cap work pretty well.

Bob

On Jan 31, 2013, at 7:20 PM, Charles P. Steinmetz <charles_steinmetz at lavabit.com> wrote:

> tvb wrote:
> 
>> 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?
> 
> There are a number of "standard" ways, some of which have been mentioned by others, none of which is all that helpful IMO.
> 
> What I find most useful is a plot of noise density vs. frequency from, say, 0.1 Hz to as high as you require.  The data should be taken and processed with sufficient frequency resolution to show any spurs in the band of interest.  It is often helpful to have several plots, each covering part of the band of interest, to improve the displayed resolution of spurs.
> 
> NOTE:  Designing a preamp for collecting the data is far from trivial.  Articles have been written about it (see, for example, Linear Technology Application Note 124 by Jim Williams <www.linear.com/docs/28585>).
> 
> Best regards,
> 
> Charles
> 
> 
> 
> 
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