Bruce wrote:
Such blanket statements aren't a particularly useful guide unless
calibrated by measurements.
* * *
The input voltage noise @1Hz can't be used directly to estimate the
PN noise at 1Hz offset.
My message referred readers to previous list messages for a more
detailed explanation, and recommended a particular search term. If
you had done that, you would have gone straight to a message in which
I explained that one cannot directly correlate noise density
measurements with PN because each amplifier implementation has its
own specific mechanism of AM-PM conversion.
That said, when one limits the discussion to inductorless, monolithic
amplifiers, I have not observed anywhere near the quantitative
differences between amplifiers (with respect to AM-PM conversion)
that it would take to equalize the PN contributions of two amplifiers
whose baseband noise voltage densities differ by more than 40dB (as
is the case when comparing the MAX477/AD8055 with available low-noise
parts). So, yes, when a part has an input voltage noise density
*that* much worse than other available parts, one can conclude
without detailed measurements that it is not a promising candidate
for use as a low-PN amplifier.
Best regards,
Charles
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