HP has a patent on this scheme. The paralleling of the diodes is for
noise reduction. Personally, I would have rejected the patent since this
is the kind of thing that is obvious to those skilled in the art.
http://www.google.com/patents/US4621205?pg=PA1&dq=4621205&hl=en&sa=X&ei=J2DRUKDxF-vcigKtoIH4Ag&sqi=2&pjf=1&ved=0CDgQ6AEwAA#v=onepage&q=4621205&f=false
If surface states are the source of the noise, then it would take an
annealing process to reduce the noise. I never made discrete diodes, so
I don't know what kind of foo they use in processing power diodes versus
varactors.
Your typical analog IC has countless reversed biased diodes. I can't say
I know of anyone who investigated them as a noise source, but in CMOS,
low noise is a relative term.
It wouldn't surprise me if the closer you operate to the breakdown
limit, the more noise you get. When you look at breakdown in the lab,
you are viewing a pretty gross change in characteristics. But it could
certainly be the case that as you approach breakdown, shot type noise
increases.
On 12/18/2012 9:47 PM, Gerhard Hoffmann wrote:
Am 18.12.2012 22:42, schrieb John Miles:
Just curious, what was the 5065A acting like with the bad diode? Mine
seems
to run quietly for days at a time, but then occasionally it generates
excess
low-level random noise for a period of hours to days (see image). Every
time I've tried to get serious about tracking the problem down, it stops
misbehaving. Did yours look like this?
A Heisenbug. Observing it affects the outcome.
Gerhard
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