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From: Bosken on 21 Mar 2010 11:13
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.



---------------------------------------
Posted through http://www.Electronics-Related.com
From: MooseFET on 21 Mar 2010 11:33
On Mar 21, 8:13 am, "Bosken" <jens.bossaert(a)n_o_s_p_a_m.kahosl.be>
wrote:
> 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?

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?


>
> Thanks in advance.
>
> ---------------------------------------        
> Posted throughhttp://www.Electronics-Related.com

From: George Herold on 21 Mar 2010 11:48
On Mar 21, 11:13 am, "Bosken" <jens.bossaert(a)n_o_s_p_a_m.kahosl.be>
wrote:
> 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.
>
> ---------------------------------------        
> Posted throughhttp://www.Electronics-Related.com

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.
From: Robert Baer on 22 Mar 2010 16:00
Bosken wrote:
> 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.
>
>
>
> ---------------------------------------
> Posted through http://www.Electronics-Related.com
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!
From: Bill Sloman on 22 Mar 2010 11:15
On Mar 22, 9:00 pm, Robert Baer <robertb...(a)localnet.com> wrote:
> Bosken wrote:
> > 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.
>
> > ---------------------------------------            
> > Posted throughhttp://www.Electronics-Related.com
>
>    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!

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
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