Zener-noise (current)

Hi all,

I have made a noise generator based on a zener diode. But I want to know how the noise reacts when I increase the current through de zener diode.

With PSpice a simulated the circuit and it seems when the current increased, sigma (RMS voltage) decreases..

But when I do the practical test, it seems when the current increased, sigma (RMS voltage) also increased..

Does anyone have any explanation for this?

Thanks in advance.

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Reply to
Bosken
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In absolute terms, the current noise in the zener rises as you increase the current. The rate of rise is less than linear so the portion of the current that is noise decreases.

The voltage noise on a zener ideally decreases with current. If there is a resistance in series, the combined effect can be an increase in noise voltage with increasing current.

Does this help?

Reply to
MooseFET

What was the Zener voltage. I looked at the current noise from an

8.2V zener. I was hoping to see big current spikes. Instead I observed that the noise increased till you reached the knee in the I-V curve. As the voltage approached the knee I started to see little current pulses of fixed height. The width of the pulses changed till at the 'center' of the knee I was seeing what looked like random telegraph noise. (random steps between two voltages.) The size and width depended on how diode was biased. (a series resistor and parallal capacitor) As the voltage was increased above the knee the noise first went down... But then increased at higher currents. You should remember that the zener impedance changes rappidly near the knee.

George H.

Reply to
George Herold

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There's also the distinction between Zener didoes that work by the Zener mechanism - breakdown voltages below about 6.2V - and the hgiher voltage Zener diodes that work by an avalanche mechaism, which is noisier.

8.2V zener's are avalanche devices. At low currents, there is a finite chance that the avalanche will fail because none of the electrons trvalling theough the - tiny - avalanche region produce a secondary electron and the current stops dead for a few microseconds until thermal noise injects anither electron into the junction to get the alavanche going again.

It's all fun stuff, and Spice doesn't model any of it.

The 1997 thread on "ZENER DIODE OSCILLATION" has lots of good information on the subject.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

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Thanks for the 'hint' Bill. I've found some of the old papers from the 50's and will read them over. Sounds like you all had some fun back in the summer of '97.

George H.

Reply to
George Herold

One cannot use any version of Spice to even guesstimate noise of any zener diode at any given current - from nanoamps to tens of milliamps. Firstly, a given 1N zener will have different noise characteristics at a specified current from vendor to vendor. Secondly, noise and usually concurrent negative resistance will vary all over the map for a given diode as current is varied from near zero to (say) 20mA. Usually, noise and negative resistance starts very close to zero current and usually dies out in the 5-20mA region (and does not return even up to burnout). And there are a number of exceptions to put the lie to the word "usually" above. Some seem to have no visible negative resistance over some (nondescript) current range, either abruptly starting as current is increased, or abruptly stopping as current increased (the other "end" being "graceful"), and others are "graceful" startup / stopping. Variables: manufacturer, zener voltage rating, current drive. change any one and you are not only in a different ballpark but could be in a different city or even planet!

Reply to
Robert Baer

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This is Great! Just finished K.G. McKay "Avalanche Breakdown in Silicon", Phys. Rev ('54) 94, 877. The discussion of Breakdown Instabilty at the end of the paper is exactly what I observe. (Nice to know I can see what was done before I was born at Bell labs.) John L. I know you've measured zener voltage noise, but have you looked at the current noise?

McKay also talks about a temperature dependence which sounds like more potential fun!

I'd really like avalanche zeners to behave like PMT's and give shot noise that is much larger than that for single electron events, but still finite. I guess I have to run them below the 'knee' but at a point where there is still some multiplication, just not infinite. (Hmm, thermal stability might be an issue???)

George H.

Reply to
George Herold

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Hi all,

Thanks for the reaction!! I did some extra test on temperature and I see similarities with what you all are saying.

But now I only measure the RMS Voltage so I get an idea about the Thermal Noise.

How can I get some information about the Shot Noise, is there also a simple way to measure this??

Thanks in advance.

Bosken

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Reply to
Bosken

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Hi Bosken, You still haven't told us the voltage of the Zener, nor what current you are running it at. Just because you are measuring voltage I wouldn't call it thermal noise. A few months ago I would have been tempted to call it shot noise, but I would have been wrong. Let's just call it zener noise. You can measure the zener voltage noise as you have been doing. To measure the current noise from a zener you can put a resistor in series with the zener and measure the voltage across it. You need to keep the value of the resistor below the impedance of the zener at the operating point... determined from the I-V slope at that point. You can also run the zener into an opamp configured as a current to voltage converter... 'course then your bandwidth will be limited by the opamp. Depending on how you are biasing the zener you may also need to 'short out' the bias resistor with a capacitor. (You need to supply a low impedance path for the AC noise current.)

Have fun,

George H.

Reply to
George Herold

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Hi George.

The zener that I use is a 6.2 voltage zenerdiode, the current will be around

1mA..

Do you say that the contribution of Shotnoise also can be measured by measuring the Noise Voltage? It seems strange to me because Shotnoise comes from the current thought the potential barrier. Or is my approach to literally? I just want to get an idea of what I am measuring...

I will test the current measurement with a resistor, thanks for the tips!

Bosken

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Reply to
Bosken

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