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Science Forum Index » Electronics - Components Forum » op-amp nV input offset voltage...
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| Phil Hobbs... |
 Posted: Wed Jul 02, 2008 7:21 am |
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Pieter wrote:
Quote: To prevent thermoelecric voltages, keep all pins at the same
temparature. But also all surrounding resistors etc. A cooling airflow
gives temperature differences. And resistors and opamps that get warm
may give some effects.
Pieter
This is especially true of temperature gradients across devices that
aren't metallic throughout, e.g. metal oxide resistors and
semiconductors. The thermocouple constants between silicon and any
metal are up in the 700-1500 mV/K range, depending on doping---which
dwarfs the slope of any metal/metal thermocouple.
Cheers,
Phil Hobbs |
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| Phil Hobbs... |
| Posted: Wed Jul 02, 2008 4:20 pm |
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Tom Bruhns wrote:
Quote: Seems like there should be some good references on applying low
offset, low bias amplifiers. I know that Bob Pease has had some good
articles on the trials and tribulations of testing amplifiers down in
the fA region--not trivial! His articles can be found with a search
on the web...
One good set is Jim Williams' 2001 trio of articles on his 1 ppm
accuracy DAC. They're on the EDN web site someplace--search on "1 ppm"
and "20 bit DAC", and they'll come right up. He even goes into details
like the thermocouple constant of two different vendors' copper wire:
+-0.2 uV/K, believe it or not--as big as Cu:Au or Cu:Ag.
Cheers,
Phil Hobbs |
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