Re: Noise in tantalum SMT caps?

On Jan 18, 6:51 pm, Spehro Pefhany <speffS...@xxxxxxxxxxxxxxxxxxxxxxx>
wrote:
On Fri, 18 Jan 2008 18:12:34 -0800, the renowned John Larkin

<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Fri, 18 Jan 2008 16:29:19 -0500, Spehro Pefhany
<speffS...@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

Any idea what noise I'd see in a tantalum 150uF cap with 1.25V across
it?

Best regards,
Spehro Pefhany

I'd guess just the thermal noise of the esr, which is only a couple
tenths of an ohm maybe.

John

No sub-10Hz voltage noise as aluminum electrolytics under bias are
supposed to have?

I'm looking at a design (not my own) where there's an RC on the output
of a voltage reference feeding a Sigma-Delta 24-bit ADC. The R is
causing a full scale gain error of, oh, 17bits. 8-( Over 1%.

Is the reference input current constant with input voltage?
Temperature? I doubt it. 8-(

I've used tantalums at a point in a noise-filtering circuit where I'd
for sure have noticed noise much above 10 nanovolts/rtHz, and not seen
any. If you'd like, I could make a measurement with an AD797
amplifier connected to a couple biased-up caps, driving an HP89410
analyzer, and get a noise spectral density plot. I'm curious enough
about it now I may just do that anyway...

Cheers,
Tom
.

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