On 4/9/22 10:03 AM, use...@teply.info wrote:
On 09.04.22 15:31, Richard (Rick) Karlquist wrote:
I am seeing a lot of unsupported "theories" about what should be done
to make devices with low 1/f noise. It might be instructive for
everyone
to read Marv Keshner's PhD dissertation (Stanford) discussing 1/f noise.
He looks at all kinds of theories and shows that there is no valid
cookbook for how to make low 1/f noise devices. It's the classic
non reproducible process. I remember an FCS
talk many years ago that NIST guru Fred Walls gave with some theory
on how to get low 1/f noise. Unlike his other papers which were
well received (and rightly so), this one was rapidly debunked.
I felt bad for Fred, getting out too far over his skills.
Thanks for the hint towards the thesis, I'll ask our library to fetch
a copy.
Recently I was discussing some measurement results with my colleagues
as we're trying to come up with a low noise JFET which can
successfully be integrated into a SiGe BiCMOS process, and quite often
we're also struggling to identify why exactly variant A has
significantly lower noise than variant B, or why a new approach does
not improve noise the way it was expected.
So from a manufacturing process design point of view, achieving low
1/f noise indeed is closer to sheer dumb luck than the proverbial
"more art than science" suggest.
This is very, very true. Some manufacturers get very low noise or very
low leakage (or both), essentially by being "lucky". From what I've
been told, there's no good models, nor predictions - so people share
"lore" of "if you get these 2Nxxxx FETs from the mfr in England, they're
really good" until they aren't. There isn't enough market for these,
so I suspect research money to "solve the problem" isn't available.
Like all those microwave MMICs with low noise, they worry about 100 MHz
and up (if not 1GHz), they certainly don't worry (or control) for noise
at 5 MHz, or where the 1/f knee is. So just because you got good results
with a batch of them, the next batch might not. It's not even clear you
could come up with a standardized test method, because the noise depends
on a lot of other factors (drain current, for instance).
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