Flicker noise voltage distribution.

ge

the

ve looked

nson noise,

than the

noise is

standing

data

e an

inating.

build

e.

with.

th zero

noise

power in

s really

AC

ur R

es,

ain

want

ew

ut

ave

to

Hmmm, The metal films I looked at showed a bit of bias noise. This could have been the batteries. I'll have to try this again with a bettre filter on the battery. I think I saw about a factor of two increase in noise at 100 Hz and 27 Volt bias. At what frequency/ bias did you make your measurements?

George Herold

ld

ies

by a

dual

was

ing

sing

Phil, You're great! Have you ever tried putting an old carbon composite resistor in your setup?

George Herold

"Phil Allison" : "John Larkin" George Herold

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

"Phil Allison" George Herold

Results as follows:

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

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

From earlier testing:

2 watt MF = 0.12 uV/V

( * leaded resistors made by IRH about 20 years back. )

See ABSE for pic of the stars of the show.

.... Phil

Paul, I'll try and get this right. Hopefully if I make a mistake Phil H. the noise expert will correct me. When you talk about white and Gaussian you are talking about two different things. White refers to how the power is distributed in frequency space. V^2/ Hz. White just means there's equal power in each Hz of the spectrum. I think you could make a white noise source out of a purely digital signal. Then Gaussian refers to how the power is distributed in voltage space. Hmm, As I write this I realize that I don't know how to measure the distribution... but anyway the digital noise source would have an amplitude distribution that non-Gaussian, but still white. The same will apply to 1/f noise. 1/f refers to the frequency distribution. The amplitude distribution of 1/f noise will be source dependent. Someone else wrote the same thing much earlier in this thread.

George Herold

Phil,

Did you try different values and better resistors to rule out temperature fluctuations? 1 part in 10**7 is only 5 millikelvins for a

I've made those sorts of measurements too, and found no 1/f noise down to a part in 10**8, using ~10k ohm RN55C resistors and battery power.

Cheers,

Phil Hobbs

y a

al

wer

to

on as I

"so the test rig will get another go soon as I cook dinner and watch my favourite TV shows." Wow, That's what I call quick service. Thanks Phil. The carbon composition resistors I used were not the carbon film type, but the solid dark brown body. These use to be made by Allen-Bradley (sp) in the US. I didn't record the wattage but it was either 1/4 or

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

Rainy and 50 F. (10 C) here in Buffalo NY. It's also the start of deer hunting season (shotguns) so there's a lot of "blamming" going on...

George

hm

soon as

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

hm

soon as

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

kohm

o soon as

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

"Phil Hobbs"

That's 1 part in 10*7 when using only 1 volt bias.

..... Phil

Very nice, much thanks again Phil. I have to think about how to convert my measurments to your units...

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.

Never good practice to have a carbon or cermet pot passing small signals have a DC bias at the same time, unless you like noise.

But it is very unlikely that a signal voltage alone will generate enough excess noise to be significant - after all 2ppm equates to -114 dB.

..... Phil

"Earth to Allison....come in Allison... Sorry, Captain, the circuit is dead. I've tried all hailing frequencies." "Keep trying, Lieutenant Uhura."

Sorry? You don't think you can get 5 mK fluctuations due to air currents in a 1-10 Hz bandwidth? Guess again. Or better yet, try the same measurement with a thermistor and see what you get.

And the makers set an *upper limit* of 1 part in 10**7, not a spec plus or minus so many percent. Sort of like the input current spec of a CD4000-series gate, which is probably 6 orders of magnitude above the actual median value. (You wouldn't sit still for that sort of sophistry from someone else, you know.)

Cheers,

Phil Hobbs

Try ACTUALLY reading my post - pal.

See the bit about "... audio band filter " ??

Cretin.

- normally 0.07 uV/V for MF types.

Ie 30% less.

Yawnnnnnnnnnnnnn....

Kindly f*ck off.

..... Phil

C'mon, Phil, quit trying to butter me up. I appreciate the praise and all, but let's keep it to electronics.

Cheers,

Phil Hobbs

"Phil Hobbs"

** The mind numbingly idiotic sophistry YOU spend your time pouring all over Usenet would choke an elephant.

Kindly f*ck off.

You ridiculous, autistic wanker.

.... Phil

On Sun, 16 Nov 2008 11:08:03 +1100, "Phil Allison" wrote:

I tried a similiar test, except I used a 10Hz fixed bandwidth on a HP3581A wave analyzer. I wanted to verify the Johnson noise (no DC current), and then apply a DC current, and see if the noise spectrum changed as I varied the center frequency. In other words, when and where is the noise pink or white. I tried using wirewound, metal film, and the traditional carbon film cheapy resistors (Philips 1/4W) under those conditions. The value was 100Kohms. With no DC, they all produced the Johnson noise predicted by v=sqtr(4KTBR), within about 20%. The spectrum was white, ie, as I moved the center freq. from about 20Hz - 2KHz, there was little change in amplitude. The measured bandwidth was kept at 10Hz. With DC current (25V across 100K), the wirewounds showed no change, the metal films increased noise very slightly. With DC current the carbon film resistors put out about 10 times the Johnson noise (at 100Hz center). I checked the noise vs. center frequency, and by about 1-2KHz the noise dropped back to the thermal noise. At 30Hz noise was about 25-30 times greater than thermal. When I plotted the noise vs 1/f I got more or less a straight line (up to about 1KHz), which confirmed the pink noise nature of the current noise. These carbon resistors give a noise distribution of white noise above a "break frequency" of 1-2 KHz, and 1/f noise (pink) below that. Many electronic devices (ie.,MOSFETs, BJTs) have similiar distributions, with white and pink areas. The metal film resistors gave me 10-20% more total noise at 30Hz than the Johnson noise. At frequencies above that, the total noise was the same as the Johnson noise. I wouldn't be surprised if they to would give 1/f noise, but the corner frequency would be 10-20 Hz, too far down for my meter. It could be the equipment, but the amplitude distribution did not seem to be the same for the Johnson noise as the current noise. It's hard to clearly define it, but the current noise seemed to have much more pronounced dips and peaks than the thermal noise. The Johnson noise swung the meter by about 10-20% (very roughly), and for the same position on the scale, the current noise would vary 20-40%. Both had the same "smoothing" on the analyzer, both at 10Hz bandwidth. This is not an authoritative claim that the current noise is non-gaussian! There may have been an additional noise effect (shot noise, moisture tracks?) that was showing up.

Paul G.

"Paul G." "Phil Allison"

Lower R values will have higher break frequencies for the same DC voltage.

Noisier types similarly have higher break frequencies for the same DC voltage.

As my tests show, there is a circa 1 to 20 ratio between MF and cermet for

For example, a 1 kohm cermet resistor with 25 volts DC bias ( ie 42uV per decade of frequency ) would have its break frequency at about 100MHz.

..... Phil