# Flicker noise voltage distribution.

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Does anyone have an idea what the distribution (e.g. voltage
distribution) equation is for flicker noise?  You know, the
probability of the voltage being at a specific level. I have looked
high and low for it, without success.

An example is Gaussian distribution, which is used for Johnson noise,

http://en.wikipedia.org/wiki/Gaussian_distribution

Thanks,
Paul

Re: Flicker noise voltage distribution.

Flicker noise (or anything else where the variance is bigger than the
mean) is nonstationary, so you can't uniquely define a PDF.

Cheers,

Phil Hobbs

Re: Flicker noise voltage distribution.
On Nov 13, 9:35A0%am, Phil Hobbs

correlated noise. Still, I'm left with an unsatisfactory understanding
of flicker noise. What would say 5 days worth of flicker noise data
logging look like? Pulses widely ranging in amplitude? Is there an
upper crest limit to such pulses?  I find flicker noise fascinating.

Paul

Re: Flicker noise voltage distribution.

Paul if you have access to a low noise pre-amp (or maybe you can build
one with an op-amp or two) you can make your own 1/f noise source.
All you need is a old carbon reisistor and a battery to bias it with.
A 10k resistor works nice.  First observe the Johnson noise with zero
bias.  Then put several volts across it you will see lots more noise
with a specturm that goes as 1/f.  Which means there is equal power in
each decade of frequency.  ie if you look at the noise between 100Hz
and 1kHz it will be the same as between 10 Hz and 100 Hz.  It's really
'strange' if you are use to 'normal' white noise.

Ohh one trick to look at low frequencies is to put four carbon
resistors in a bridge, then when you bias them you don't have to AC
couple to get rid of the DC offset.

George Herold

Re: Flicker noise voltage distribution.

Hi George,

Thanks for the info. I'll take your advice, as it would be
interesting. I'd like to put it on a data logger, shove it in the
corner of the lab for a few months. Perhaps a 2nd logger recording
temperature would be nice. Hey, some guys web page swears that the
moon has a significant effect on flicker noise, lol. Perhaps a moon
logger? ... Nah.  Anyhow, I have an idea what you mean by the four R
bridge.

BTW, why is it called "flicker" noise?  A flick should have spikes,
no. How could it be ultra low frequency if it has spikes?  The main
cause in semiconductors is the trapping and de-trapping of the
carriers.

Regards,
Paul

Re: Flicker noise voltage distribution.

Paul:
There is an old HP app note on flicker noise - AN 963

Good luck,
Dave

Re: Flicker noise voltage distribution.

AN 963 is "Impedance Matching Techniques for Mixers and Detectors"

AN 956-3 is "Flicker Noise in Schottky Diodes"

Maybe that is the one you were thinking of?

There is a list of old app notes at

http://www.hp.woodshot.com/hprfhelp/lit/diodelit.htm

Does it have the one you were looking for?

Regards,

Mike Monett

Re: Flicker noise voltage distribution.

OK, let me try this again!

"Flicker Noise in Schottky Diodes"
HP App note 956

Agilent document number   5952-0487

Better luck this time!
Dave

Re: Flicker noise voltage distribution.

Dave,

I replied to your original, but it hasn't shown up yet.

Thanks for the update. You can find AN 956-3 here

http://www.hp.woodshot.com/hprfhelp/lit/an_alphn.htm

Regards,

Mike Monett

Re: Flicker noise voltage distribution.

Paul,  I'm not sure what your data logger is recording.  If you want
to record a time record of the noise at say a 1 Hz to 1kHz band
width... you're going to record a lot of data in a month.  Try a few
seconds first.  You'll also need a bunch of gain.

The problem with biasing a single resistor is that you're looking for
this tiny noise voltage on top of several volts of bias.  If you put
four resistors in a bridge and bais with equal magnitude but opposite
sign on two of the opposite nodes, ground the third and sense on the
fourth node you should have a signal closer to gound.  You still have
to deal with the difference in the resistor values... there's several
way to go there.....

have fun!
George

ps
I have no idea why it's called flicker noise.  I call it 1/f noise,
which at least describes the specturm.

Upon further reflection, you can't do this with a single resistor and
battery you need at least two resistors.  (Sorry, I did these
measurements a few years ago and had forgotten the path that led me to
the bridge idea.)

Geo

Re: Flicker noise voltage distribution.

What I meant by data recording, is to convert the output to digital,
ADC, and record the digital data. I would probably use a PC to record
the data, just write to a file since it could be a considerable amount
of data.

I know there are people who have done this kind of research. Studies
have shown flicker noise to remain as 1/f spectrum for weeks on end. I
believe the present record is well over a month, and the flicker noise
remained 1/f frequency. One month would be 373 nHz. It's believed
there must be an end to 1/f noise due to it's power spectrum, since
there's not enough power in the universe to go for ever. :-)

PL

Re: Flicker noise voltage distribution.

Oh, are you saying you want to look at the noise from DC to some upper
frequency?  There are going to be all sorts of issues if you try to
look at the noise at DC.  First are simple things like the op-amp
input offsets.  (you are going to need a total gain of about 10^5 to
10^6)  Then there are going to be all sorts of DC drifts.  As John L.
said earlier, how do you tell the difference between 1/f noise and a
simple drift with temperature.

I went back and looked at my notes.  I was using 10 k ohm resistors
and biasing them in a bridge with three 9V transistor batteries in
series (27 Volts of bias).  With a Q3D%1 bandpass filter centered at 100
Hz I found the noise voltage went up about 16 times when the resistors
were biased.  That might give you some idea of what size signal levels
to expect.  Of course this might also change with the make of cabon
composite resistor you use.

George Herold

Re: Flicker noise voltage distribution.

looked

noise,

the

I did some tests a while back with metal-film and cermet (standard
surface-mount) resistors, looking for shot and "excess" noise, noise
that increases with dc bias. With a setup that about resolved the
Johnson noise, I saw no evidence of increased noise with bias.

John

Re: Flicker noise voltage distribution.

"John Larkin"

**   Wrong as usual........

I did a test a few days ago using 0.5 watt MF, 2 watt MF & finally some old
0.5 watt carbon film resistors  -  using two similar resistors in series
with a (well filtered) variable DC supply.

The mid point was cap coupled to a high input Z  JFET pre-amp followed by a
1000 times gain stage ( a balanced mic pre ) and finally an audio band
filter with gain of 10.   This set-up showed only a dB or two more residual
noise than predicted from thermal calculations when using a pair of 100k
resistors ( of  whatever type).

I found no trouble identifying lots of "excess noise" as soon as DC bias was
applied with 20 to 40 volts bringing the excess noise up to a level matching
the previous thermal (ie a 3dB increase).

The oft published figure for MF types of  " 0.1uV/V " per decade of
frequency was found to be about right.

The old carbon film types I tried gave about 2.5 times more excess noise
than the MF ones at similar DC bias voltages.

The 2 watt MF power resistors showed about 50% more noise than their lower
powered cousins, plus exhibited a sharp crackling noise as well as pink
noise. I did not try cermet types but from experience would expect them to
be much noisier than the others.

Also, resistor excess noise is largely independent of value  -   so using
lower values than 100kohms will shift the DC bias level *downwards*  for
similar results re the ratio of thermal to excess noise.

Eg:  for 1 kohms, thermal noise is lower by a factor of 10 (compared to
100kohms ) so he DC bias needed will be 1/10 for the same ratio.

Certainly not a trivial issue nor something one can afford to ignore.

..... Phil

Re: Flicker noise voltage distribution.

Phil, You're great!  Have you ever tried putting an old carbon

George Herold

Re: Flicker noise voltage distribution.

"Phil Allison" :
"John Larkin"
George Herold

** What a nice man George is  ....

** As luck would have it  -  I just located a pair of 1 watt, 100kohm
"carbon comp" resistors taken from a Fender tube guitar amp during
refurbishing.

Plus, I also have a pair of unused 0.5 watt, 150 kohm " Metal Glaze"
resistors ( aka "Cermet" )  -  so the test rig will get another go soon as I
cook dinner and watch my favourite TV shows.

It's about 6pm Saturday, here in Sydney.

Weather is mild and overcast (23C),  could be a thunder storm on its
way.....

.... rgds,    Phil

Re: Flicker noise voltage distribution.

"Phil Allison"
George Herold

**  OK    -  I did a couple more resistor noise tests.

Results as follows:

1 watt carbon composition = 0.22 uV/V ( per decade of frequency)

0.5 watt *Metal Glaze (cermet) = 1.7uV/V  ( !!!!!!!! )

------------------------------------------------------------

From earlier testing:

0.5 watt  MF   =   0.09 uV/V

2 watt  MF  =  0.12 uV/V

0.5 watt carbon film  =  0.22 uV/V

See  ABSE  for pic of the stars of the show.

....   Phil

Re: Flicker noise voltage distribution.

Great data. The cermets have a lot of 1/f noise. I'm betting certain
brands of cermets would have higher 1/f noise since there's such a
wide range of cermet materials. You could get even more 1/f noise from
certain diodes instead resistors since they're non-linear, especially
GaAs?  I'm wondering what the 1/f noise record is for passive
components.

Paul

Re: Flicker noise voltage distribution.

Very nice, much thanks again Phil.  I have to think about how to
convert my measurments to your units...
It was striking that as I clicked the center frequency of the
(constant Q) band pass filter to lower and lower values the average
value of the noise stayed the same...You could also observe the Dicke
noise in the noise, which goes as the square root of the measurement
time times the band width.  At the lower frequencies the fluctuations
in the average value got bigger and bigger.

Your cermet measurement is a bit distrubing.  Is this the same thing
that my conductive plastic pots are made out of?  I like the 1/2 Watt
single turn pots from Clarostat.

George Herold

Re: Flicker noise voltage distribution.

I read somewhere that the noise increased with smaller and smaller
carbon resistors. Too bad I can't find that web page, as it was nice
where it outlined various types of noise.

This type of low frequency noise is good for data loggers, and fed to
a FFT function to display the entire spectrum. If for instance, you
have a chopper (zero-adjust) op-amp, you could see the spike at it's
clock frequency. Most low temp drift and low Vos op-amps have chopper
circuitry.

PL