Gerhard wrote:
It's bad, but not that bad. 10 times the voltage is 20 dB more. So
0dB = 1nV/sqrt Hz
20 dB = 10 nV
40 dB = 100 nV
60 dB = 1uV
80 dB = 10 uV/sqrt Hz
So I got ~40dB and ~30dB right, but screwed up and turned 10uV into
1mV. How'd I do that?
The wideband noise at, say, 46 dB would be 200 nV/sqrt Hz versus
the claimed 75 nV typical
but the corner frequency is really bad. I bought them last year from
Digi-key, still with
National as manufacturer on the bag, not TI.
I'll test a few more next weekend.
Even Digi-Key is not immune from counterfeits. I received some
counterfeit voltage references last year, but before I used any I got
a message recalling them.
Thinking on it a bit more, your results look like what one might
expect if someone put up bandgap reference dice in fake LM329
packages. On the other hand, they could be from a lot of real NS
parts that had serious fab issues or catastrophic storage issues.
In any case, if the others you have are like that one, throw them out
and get some new ones that meet spec (and just in case, buy from
another vendor, and perhaps another manufacturer). You can buy them
direct from Linear Technology <http://www.linear.com/purchase/LM329>,
but only in the plastic TO-92 package (all the 329s I've used have
been in the hermetic package, but those appear to be history now).
Best regards,
Charles
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