Noise diode?
Greg Thoman
|>I'm looking for ways to generate random (thermal or shot) noise.
|>For my application, digital techniques (MM5387 noise generator, etc.)
|>will not do.
|>
|>Right now I'm using a reverse-biased Zener diode, but it requires a
|>15-volt supply to perform well. I'd rather go to a 5-volt supply.
|>I'm thinking of trying various kinds of forward-biased diodes, or maybe
|>even a low-voltage Zener, but would be appreciate of any suggestions.
|>What kinds of components are *noisy* at 5 volts?
I have an idea you might consider. Get a low input current
op-amp and build a large-gain amplifier using unusually large
resistors (say, a 10 or 22 M-ohm feedback resistor). The "input"
signal here is a large resistor connected to ground for a
non-inverting version, or just connection of an inverting-amp's
input resistor directly to ground. The non-inverting amp has one
more noise souce, while the inverting amp has one fewer parts.
With this, you can adjust the gain to get the average noise
amplitude you want and the amplifier itself doubles as the noise
source. Of course, lots of audio folks whose lives revolve around
--
-----
Greg Thoman: The opinions expressed herein are mine alone, and I am
solely irresponsible for them.
Michael Covington
For my application, digital techniques (MM5387 noise generator, etc.)
will not do.
Right now I'm using a reverse-biased Zener diode, but it requires a
15-volt supply to perform well. I'd rather go to a 5-volt supply.
I'm thinking of trying various kinds of forward-biased diodes, or maybe
even a low-voltage Zener, but would be appreciate of any suggestions.
What kinds of components are *noisy* at 5 volts?
--
< Michael A. Covington, Assc Rsch Scientist, Artificial Intelligence Programs >
< The University of Georgia, Athens, GA 30602-7415 USA mcov...@ai.uga.edu >
< Unless specifically indicated, I am not speaking for the University. > <><
For information about any U.Ga. graduate program, email gra...@uga.cc.uga.edu.
John Whitmore
Michael Covington <mcov...@aisun3.ai.uga.edu> wrote:
>I'm looking for ways to generate random (thermal or shot) noise.
>For my application, digital techniques (MM5387 noise generator, etc.)
>will not do.
>Right now I'm using a reverse-biased Zener diode, but it requires a
>15-volt supply to perform well. I'd rather go to a 5-volt supply.
>I'm thinking of trying various kinds of forward-biased diodes, or maybe
>even a low-voltage Zener, but would be appreciate of any suggestions.
>What kinds of components are *noisy* at 5 volts?
The problem with noise generation at low voltages is
that amplification introduces nonrandom noise. Avalanche effect
(either in conducting gases or in an avalanche diode) gives
whiter noise than the amplify-a-resistor approaches.
Consider using an oscillator and voltage tripler to
make the bias current (it is a rather SMALL current requirement)
for your Zener. Below about 5V, 'Zener' diodes actually
break down by the mechanism Zener proposed (tunneling), which
is not noisy. It's only at higher voltages that avalanche charge
multiplication (and the attendant gain in current) effectively
amplifies thermal noise to measurable levels.
The only other approach that might work is high-gain
amplification (with VERY good power supply rejection required),
and careful impedance matching, with a resistor-noise source
(which could be an incandescent lamp, if you want... get that
temperature high to make a good input). Mechanical
stability and shielding from magnetic fields will be key.
John Whitmore
p.s. I've seen a variety of gas-discharge noise sources; that
seems to work quite well, if you can supply 70V or more.
Michael Covington
>In article <2qc12a$s...@hobbes.cc.uga.edu>,
>Michael Covington <mcov...@aisun3.ai.uga.edu> wrote:
>>Right now I'm using a reverse-biased Zener diode, but it requires a
>>15-volt supply to perform well. I'd rather go to a 5-volt supply.
>>I'm thinking of trying various kinds of forward-biased diodes, or maybe
>>even a low-voltage Zener, but would be appreciate of any suggestions.
>>What kinds of components are *noisy* at 5 volts?
>
> The problem with noise generation at low voltages is
>that amplification introduces nonrandom noise. Avalanche effect
>(either in conducting gases or in an avalanche diode) gives
>whiter noise than the amplify-a-resistor approaches.
So I had begun to suspect. The avalanche effect amplifies each noise
event (each bunch of electrons suddenly deciding to come through), right?
> Consider using an oscillator and voltage tripler to
>make the bias current (it is a rather SMALL current requirement)
>for your Zener. Below about 5V, 'Zener' diodes actually
>break down by the mechanism Zener proposed (tunneling), which
>is not noisy. It's only at higher voltages that avalanche charge
>multiplication (and the attendant gain in current) effectively
>amplifies thermal noise to measurable levels.
Will do. In fact I have a couple of CMOS inverters available to make
the oscillator. Four diodes and four capacitors, and there it is.
> The only other approach that might work is high-gain
>amplification (with VERY good power supply rejection required),
>and careful impedance matching, with a resistor-noise source
>(which could be an incandescent lamp, if you want... get that
>temperature high to make a good input). Mechanical
>stability and shielding from magnetic fields will be key.
Because this is probably going to be a construction project for
a magazine, I think I want to stay away from potentially unstable
circuits. If it oscillates, it *might* look like it's working just
fine, in the complete setup, except that the statistics of the output
aren't *quite* right.
>p.s. I've seen a variety of gas-discharge noise sources; that
>seems to work quite well, if you can supply 70V or more.
Do tell me more. And thanks for the information.