[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[glen english LIST]

Most of those are now delta signma converters, the noise is moved from 
the baseband  to 'elsewhere'.

be careful with levels of  out of band (beyond designed freq response 
say 20kHz) because many of the AFEs are 'economically designed ' and 
slew rate overload of 'loud' super nyquist energy seems to be a bit of 
an issue.

Apart from 1/f  measurement, two tone IMD , a useful measurement to 
ascertain the performance of the converter in a high broadband noise 
environment is a Noise Power Ratio Test. Basically , proceeded by a 
broadband noise source, a notch is used, and what is left over in the 
notch (should be nothing) . It's a great test.

This article talks about ADCs at lower HF, but the technique is equally 
at home for audio band ADCs

https://www.ab4oj.com/test/docs/npr_test.pdf

Adam has written a good article.

-Glen.


On 14/07/2022 4:36 am, Bob kb8tq via time-nuts wrote:
> Hi
>
> One of the “interesting” gotchas with some sound cards:
>
> The frequency response goes to (say) 48 KHz. The noise
> performance goes to (maybe) 20 KHz. Past that point there
> is a nasty rise in the noise floor. How common this is … who
> knows.
>
> For a lot of applications, the system floors out well before
> 10 KHz. There really isn’t a lot of need for phase noise past
> that ( other than for spurs ).
>
> It’s debatable just what the “best” approach for wide band