Noise from a Zener diode

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Noise from a Zener diode

Postby dons » Mon Sep 24, 2012 6:32 am

Hi

Does anyone know how to calculate the noise from a Zener diode?
Ultimately I want to know this because I want to calculate the SNR of a circuit containing a Zener diode.

I have been looking into Thermal noise theory. I was looking at something like T=(Power/Bandwith)/Kb
Kb: Boltzmann constant 1.381 x 10^-23
Power: 300 [mW]
Bandwith: 24 [Khz]

But this results in an unreasonable number.

By the way.. its a typically standard zener BZX84C5V1.

Am I on the right path? Please comment if you have some thoughts.
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Re: Noise from a Zener diode

Postby danadak » Mon Sep 24, 2012 1:36 pm

Jumping off a bridge, because its an avalanche phenomena, that makes it highly
dependent on doping levels, device geometries, etc.. Note, its NOT thermal noise
that is dominant.

That being said there are a number of IEEE papers on this topic, they might shed some
light, rather noise……

Regards, Dana.
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Re: Noise from a Zener diode

Postby dons » Tue Sep 25, 2012 12:37 am

Thx for your comment...

After some studies, I noticed something important in my scenario anyway....

I use the zener diode as a protection to not exceed 5v1 on a input pin...
But as the zener diode has a very small current drawn in the important range of 0-5 [V] it would have a low noise level. I Think.. ;)
At the breakdown voltage where the diode starts drawing current, the noise is greater. But at this voltage the signal is unusable so It will not matter.

Image
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Re: Noise from a Zener diode

Postby danadak » Tue Sep 25, 2012 5:46 am

The predominant noise mechanism is shot noise for a reversed biased diode.

http://www.qis.ex.nii.ac.jp/qis/documents_YY/y3_02chp6_txt.pdf

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