I've been experimenting with zener diode based noise sources. I have such a source for which I want to determine the peak to peak noise voltage. I've measured the noise with my trusty multimeter and it's approximately 15 mV which I believe is RMS. The noise from these things is white.
So how can I obtain the peak to peak voltage, as I don't have an oscilloscope? I think that it should be possible to calculate it from the RMS voltage and some statistics knowledge. My multimeter is a digital Maplin Precision Gold (M-5010EC) from 1989. The specification booklet says that it has a frequency range for AC measurements of 45 Hz – 500 Hz. This is calibrated for a sine wave of course and not a white waveform. Is that enough to obtain Vp-p?
Best Answer
Thermal noise (approximately white) has a gaussian distribution and we can use statistics to state what the probability is that a certain p-p level is exceeded: -
For instance in the diagram above a range of 6 sigma tells you that the probability of 1 V of noise remaining within the bounds of 6 Vp-p is 99.7% or put another way, 1 V RMS will remain below 6 Vp-p for 99.7% of the time.
It will also remain below 8 Vp-p 99.99% of the time.
Most engineers use 6.6 sigma - this produces a confidence level of 99.9% i.e. 1 V RMS remains within 6.6 Vp-p for 99.9 % of the time.
MT-048 page 5 from ADI is a useful reference for this: -
As for zener noise this article states that zener noise is "shot" noise and this article states it can be modeled as a Poisson process. This type of distribution can be very similar to a normal distribution: -
Picture taken from here. See also this article about the limiting cases for Poisson and normal distributions being the same.