M
Marceli Firlej
- Jan 1, 1970
- 0
Which Zener diode could be used for white noise generator?
Any one rated substantially above 6 V. 12 V devices are often used. Theymail.com.au> wrote (in said:Which Zener diode could be used for white noise generator?
Which Zener diode could be used for white noise generator?
Which Zener diode could be used for white noise generator?
John said:I read in sci.electronics.design that Marceli Firlej <marceli.firlej@oze
Any one rated substantially above 6 V. 12 V devices are often used. They
are really 'avalanche' diodes; true Zener operation occurs at breakdown
voltages below 6 V and is not noisy.
You get better Gaussian probability distribution if you use two diodes
from the same batch and couple them to the + and - inputs of an op-amp.
The output is the difference between the two noises and is good quality
band-limited Gaussian white noise.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
And drive them at "low" current (tens of microamps seem to be ideal).
Zeners tend to get quiet as the operating current approaches the rated
test current.
The drop can be rather fast, and every zener (same voltage and batch)
can have a different current VS noise dropoff characteristic.
You get better Gaussian probability distribution if you use two diodes
from the same batch and couple them to the + and - inputs of an op-amp.
The output is the difference between the two noises and is good quality
band-limited Gaussian white noise.
John Woodgate wrote...
Is there a reason to believe the difference should be any better
than the sum?
Winfield Hill said:John Woodgate wrote...
Is there a reason to believe the difference should be any better
than the sum?
John Woodgate wrote...
Is there a reason to believe the difference should be any better
than the sum?
And drive them at "low" current (tens of microamps seem to be ideal).
Zeners tend to get quiet as the operating current approaches the rated
test current.
The drop can be rather fast, and every zener (same voltage and batch)
can have a different current VS noise dropoff characteristic.
A neon lamp makes lots of nice noise. Old GR noise generators used a
gas tube of some sort with an external magnetic field for some reason.
I have schematics somewhere...
You can just use native opamp noise, but the statistics and spectra
can be awful.
John
On Sun, 15 Aug 2004 11:48:01 -0700, John Larkin
[snip]A neon lamp makes lots of nice noise. Old GR noise generators used a
gas tube of some sort with an external magnetic field for some reason.
I have schematics somewhere...
You can just use native opamp noise, but the statistics and spectra
can be awful.
John
I'd like to see schematics. The magnetic field might be to keep the
discharge from "dancing" around, perhaps adding a "popcorn" noise
element ?
...Jim Thompson
Zener noise can be asymmetric in shape. I think that, given the choice
of summing ++ or +-, the +- might be more symmetric. That sort of
creeps up on the Central Limit Theorem a little quicker.
Assuming the diodes are independent (which certainly seems like a good
assumption), the density of the sum is the convolution of the densities.
For the difference, the result is the same.
I've been playing with various distributions here in MathCad this morning,
and while the sum and difference may result in different offsets, once the
offset is removed the distributions appear to be identical.
-- Mike --
Are you saying that, given two basicly identical random signals having
lopsided probability distributions, the sum won't be lopsided? The
difference will certainly have a symmetric distribution.
I was indeed saying that, but that was before I had my coffee and started
thinking. You're absolutely right.
-- Mike --
Are you saying that, given two basicly identical random signals having
lopsided probability distributions, the sum won't be lopsided? The
difference will certainly have a symmetric distribution.
John Larkin wrote...
It's highly unlikely that two "nearly identical" zener diodes will
have basically identical random signals.
John Larkin said:The issue was John W's observation that the difference between the
noise of two zeners has better stats than the noise of just one, or
the noise of the sum. Obviously, either the sum or the difference will
be better than the noise of just one, but I think he's right in that
the diff is better than the sum, since zener noise tends to be a bit
asymmetric, and always in the same direction.