[time-nuts] How to measure regulator noise?
Henk ten Pierick
henk at deriesp.demon.nl
Tue Jan 8 12:18:45 EST 2008
On Jan 8, 2008, at 12:50, Don Collie wrote:
> I`d just hang an AC millivoltmeter[or microvoltmeter] across the
> I use my H/P 400H, which will give readings down to about 50uV. If
> regulator produces less noise than this [say a 723, with
> 2uV], then you`ll need a more sensitive meter.
Electronic voltmeters or microvoltmeters have a noise bandwidth which
is larger than the bandwidth on the front panel. The front panel
bandwidth is related to accuracy and is not the -3dB bandwidth. The
noise bandwidth is nearly always range setting dependent and can vary
very much. I have seen a factor of four in noise bandwidth between
adjacent range settings. The only way to have a good indication on
noise is in a known and constant bandwidth. The noise bandwidth of a
filter is not the same as the 3dB bandwidth and dependent of the
filter order and shape. It is always more.
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