2N2222 Zener noise

tage?

You are snookered by the physics. Reverse-biased diodes break down by two different mechanisms depending on the voltage applied acorss the junction, the Zenner (quantum tunneling) mechanism at alow voltages - less than 5V - and the avalanche (impact ionisation) mechanism at higher voltages.

Avalanche breakdown gives a noisier leakage current than quantum tunnelling - with avalanche breakdown there is always the chance that an electron will make it all the way across the gap without generating a second electron-hole pair, killing the leakage current until a cosmic ray or a radioative atom in the vicinity generates a new charge carrier pair to restart the avalanche process. Quantum mechanical tunnelling is also a random process, but it is a single random process, without the second stage of avalanche multipication to generate lots of outliers.

With a 3V supply rail you are stuck with Zener breakdown. You may have to settle for a pseudo-random binary sequence generator, or amplifying the Johnson noise from a resistor - 1nV per root hertz for a 50R resistor at room temerature, rising as the square root of the resistance, bearing in mind that "low noise" integrated circuit op amps typically also generate 1nV per root hertz white noise at room temperature.

-- Bill Sloman, Nijmegen

Thanks for your reply and for the enlightenment regarding the difference between breakdown mechanisms. Instead of trying to amplify Johnson noise, perhaps I can use a spare opamp section of the project as a hysteretic oscillator and make a charge pump to kick the voltage up above the 5 volt threshold? I wonder if a low voltage op amp like the LM324 acting as a charge pump would be able to get the voltage high enough to initiate the avalanche breakdown mode - I'm not sure what the '324's output can swing at such low voltages, but I bet getting 5 volts with a 3 volt supply with such a circuit might be pushing it.

Oh really, I've also been led to believe and educated, years ago, that zener mode and impact mode is a balance at 5 volts and anything under that goes into "impact" mode and above is zener. Looking at the behavior of the commonly known 5.1 Vref diode where a diode is in series with the zener stabilizes the effects between the two.

I think you may want to do a better job of memorizing that document you red before posting your proclaimed expertise drivel.

If it were me, I would've suggested to look at a "NOISE DIODE" and not throw a crap load of physics that you most likely barely understand.

Things like SHot and Johnson Noise could also be a good help as references to loop up..

Now, I've seen some tricks done using a tunnel diodes in my day..

Jamie.

Dudes, dudes ... what is so difficult about making a higher voltage from 3V?

You win't find a transistor that zeners at 3 volts. Well, maybe an exotic microwave one.

Do you need high-quality, flat, Gaussian noise?

How about doing it digitally, with a pseudo-random shift register?

John

oltage?

Then you had better go and get yourself a better education.

e is in series with > the zener stabilizes the effects between the two.

You would be thinking of the 1N821 through 1N829 6.2V voltage reference diodes, which did include a a forward diode to compensate for the temperature coefficient of a 5.6V "zener" diode.

http://206.209.106.106/datasheets/Zeners/AppNotes.pdf

The breakdown voltage you get with a pure zener (quantum tunnelling) mechanism decreases with increasing temperature, while an avalanche breakdown voltage increases with increasing temperature. At 5.6V the balance between the two mechanisms favours the avalanche route enough that the voltage across the reverse biassed diode increases by the same 2mV/K that the voltage across the forward diode decreases.

Since you managed to confuse the the 5.1V "zener" diode, which has a roughly zero temperature coefficient, with the 6.2V reference diodes which do include a forward diode, your own advice can be seen as less than reliable.

not

Google doesn't throw up much on noise diodes. The nearest thing to something useful came from here

I did refer to Johnson noise. Google on that and you get to

which does include a reference to shot noise.

Neither is going to be of much help to the OP, who wants a solution to a problem - not the education that you obviously failed to absorb.

The real trick with tunnel diodes today is finding where you can buy one. The difficulty with tunnel diodes is that they are broadband devices. If you don't mount them in a properly designed transmission line environment, they will oscillate at a frequency your oscilliscope can't follow, and the voltage levels that you will see - at frequencies that your oscilliscope can follow - won't look anything like what you wanted and expected.

-- Bill Sloman, Nijmegen

Are MOVs noisy? Luxeon Rebel LEDs flicker in the 2V/microamp range, which I'm hoping is their MOV rather than defects in the chip slowly burning away.

What on earth is flat Gaussian noise?

A flat, ie. even distribution is not a Gaussian, so perhaps I'm misunderstanding this statement. Please enlighten...

BTW, the new Agilent 3352x arb. generators have a nice feature that lets you adjust the bandwidth of the noise, which is Gaussian.

They also have a LFSR noise generator, but it's not analog but rather on/off. I guess if it were to be analog, it would have to let you select some number of bits to gather for each output. This would give a flat analog noise. It would have been nice if you could select the distribution of the noise. Perhaps I'll send these ideas on to Agilent. They have been very nice to me over the years, taking many of my ideas directly to the scope and generator prod. devel. managers.

It can also use the noise to modulate a PWM signal, so coupled with a little flyback pulse generator, can be used to simulate a lot of jittery physical phenomena, like laser pulses.

It'd probably be easier to get a single transistor blocking oscillator to work, the charge pump gives just under Vccx2, if you need more you have to cascade doubler stages.

For a one-off you could liberate the erase oscillator from a scrap cassette deck - the inductor is usually styled like an IFT, so nice neat finished job.

LM324? Yuck, you'll be lucky to get anything at all...

You'd be better off with a blocking oscillator, which only takes another transistor and can be made with a common transformer, nothing custom needed. Depending on supply regulation, you may need to consider a control loop, which will add a few transistors to the total.

Tim

The bandwidth is gaussian? :-)

Now... is it gaussian over linear or logarithmic frequency? That could be handy... And a kurtosis adjustment to tweak the band skirts...

Tim

Reading the appendix in one of my ARRL handbooks, I remember seeing a strange device. IIRC, diode with 2.5V 2A filament, 100V or so plate, waveguide connection. It was a thermionic saturation noise diode. So it worked from shot noise of emitted electrons, and current was controlled by filament temperature. The characteristic of such a device is constant-current above a certain voltage. I guess it was good enough for a few dB of noise in the microwave band (>1000MHz?). I'll have to see if I can find what number it is.

Tim

...

What ever happened to Watson A Name's micropower switchers for LEDs? I don't remember what he called them, but it's one transistor, a ferrite core and a few resistors and caps.

I wonder how "good" a noise source just a piece of wire dangling in the air might be, picking up random radio, TV, and telephone signals? You'd need a sharp filter at your local line frequency, of course.

I also wonder if it would work to use the ion source from an ionizing smoke detector?

Good Luck! Rich

Pardon my ambiguous wording.

The noise is temporally gaussian. The high-pass cutoff bandwidth may be set.

Noise with configurable parametric band shape would be quite impressive, but unfortunately not yet available in generators of this caliber.

The main improvement of this gen. over the competing Tek AFG30xx series, aside from the usual generational improvements in memory and sampling rate, is that the new Agilent has a finely adjustable sampling rate for arbs., making it a true arbitrary waveform architecture, vs. just an arbitrary function generator, which has a fixed sampling rate, ie., the Tek.

There is a special discount for the 2 channel model until mid January. After buying two for work, I'm tempted to buy one for home. Trouble is, I spent too much this year on numeric display tubes and now fixing my car :-(

Do you mean Joule-Thief?

John Larkin has something suitable right there, he probably just needs a paperclip stuck into a BNC jeck to get tons of random signal from Sutro Tower.

Wouldn't necessarily have that on my lab table :-)

Flat in the frequency doamin, Gaussian in probability distribution, like really good noise should be.

We have a couple of 8-channel ARBs that do that, too. Here's one:

We use a DDS channel to clock a digital random number generator and also clock a downstream digital lowpass filter. So the RMS voltage is independent of the noise bandwidth. Everything just rubberbands in time.

We can do that too! Also AM, FM, PM, summing, and complex combinations of all the above. That was fun to design.

John

Buy our 8 channel version!

John

Yeah sure, I take my education religiously, and use it. You on the other hand, are just blowing smoke. You better check your references again.

in series with > the zener stabilizes the effects between the two.

What a blow hard... Save your breath, it only shortens your life..

rest of this non-sense is deleted..

Jamie.

Well, like ALwaysWrong, you are always wrong.

Zener breakdown occurs at less than ~6V. Avalanche breakdown above (the two balance at about 6V). *Avalanche* mode is the "impact" mode where the electric field accelerates electrons such that when they hit atoms they knock free more electrons, which are accelerated hitting more atoms... That's why it's an "avalanche". Zener breakdown is tunneling.

in series with > the zener stabilizes the effects between the two.

YOu should have snipped a few dozen lines higher.