Amplitude-dependence of 1/f noise

(I'm not an RF or spice guy.. can I still comment? :^)

I assume you are talking about section 3. Does this also applies to amps as well as oscillators? (I assume it does.) For amps the 1/f noise is a device specific parameter... I mean each opamp has it's own amount of 1/f noise. (I've got lotsa data, at least for the opa134.)

Given the above, it seems rather obvious to me that the corner freq depends on the size of the 1/f noise... given that the "white" noise in opamps is pretty much the same from device to device.

George H.

This may be a duplicate.. google puked as I posted.

(I'm not an RF or spice guy.. can I still comment? :^)

I assume you are talking about section 3. Does this also applies to amps as well as oscillators? (I assume it does.) For amps the 1/f noise is a device specific parameter... I mean each opamp has it's own amount of 1/f noise. (I've got lotsa data, at least for the opa134.)

Given the above, it seems rather obvious to me that the corner freq depends on the size of the 1/f noise... given that the "white" noise in opamps is pretty much the same from device to device.

George H.

Disclaimer: I'm no expert on noise. But I suspect the author is assigning _excess_ noise to 1/f ??

"Fluctuation" is separate from 1/f.

But I stand ready to model it in Spice if someone can make a case for it ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

Makes sense. Analogous to an IMD measurement but with internal sources.

If "noise" was introduced as an actual voltage and current waveform at each source component in a time domain simulation SPICE would get it right. An FFT of the TD data would show the spectral distribution of nonlinear mixing products. I'm thinking that the "noise" should be discrete frequencies (stepped, perhaps) as this would make it fairly simple to determine the order of nonlinearity and relative sensitivity to amplitude of each noise contributor.

--
Grizzly H.

Drawning a 1/f signal in lots of white noise would reduce the

1/f corner, and that makes the 1/f corner somehow ill-defined. I think Rubiola has a proposal against that with his noise coefficients; I wished I had the time to read his book and not only to sample a few pages from time to time.

Suppose, we have a circuit with +49R and -51R in series. Do the -51R have thermal noise? I guess: yes. Will the average simulator get that right? I guess: probably not. The size of the conductivity matrix is extremely costly in terms of execution time, so the simulator will probably try its best to eliminate redundant nodes and simply add the resistors and skip the junction.

Yes, I'm pessimistic and I create more questions than I answer.

Last weekend, I have measured the noise of some LEDs and Zeners. The preamplifier averaged 20 ADA4898 op amps, 220pV/sqrt Hz, I think I have described that here already. FFT analyzer is an Agilent 89441A vector signal analyzer, one FFT per decade, controlled from a Linux PC, combined and plotted with gnuplot. One measurement takes 6 minutes of wall clock time, most for the lowest decade.

Setup: preamp with shorted input to see the noise floor, input terminated with 47R wire resistor, 47R + 2K to 14V from 10 NiMH cells. No additional noise visible from the battery:

< >

LEDs: fed from 14V with 1K or 2 K, red & blue Osram SMD LEDS, Toshiba 0603 LED red.

< >

BZX84: sot-23 fed from 14V via 1K

< >

Regarding the LEDs, a well-known chip designer oracled about Lorentzian noise and lots of G/R noise but I have no idea if that invalidates the measurement or is an interesting discovery.

Nevertheless, the BZX84-xVy 1/f corner is low, as is their noise level.

The preamp has 3 poles at 0.1Hz and is currently overcompensated, so flatness > 300 KHz is not given. The limitations are visible.

regards, Gerhard

I'm no noise expert either. (But it's fun to measure.) It seems to me a model that defines the corner freq. (where white noise = 1/f noise, or something like that.) Is just fine... as long as that is a parameter I can change in the model.

George H.

I like it! Do the batteries couple to local sound vibrations?

I'm not sure I understand the other plots. (I mostly need someone to draw pictures for me.)

When I went to look for shot noise in forward biased pn junctions, I had to put a cap across the bias resistor, (feed by a voltage source.) else the diode (as noise source) had too low a source resistance, to "let the noise out".

George H.

[snip]

See InputReferredNoise.zip on the Device Models & Subcircuits Page of my website. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Very "enlightening" -- especially that the Zeners are so competitive with t he LEDs, and that the Toshiba LED performs so much worse than the Osram par t. Looks like it's a bad idea to mindlessly replace Zeners with LEDs in lo w-noise bias applications, or to consider all red LEDs interchangeable.

Questions:

- Why is there such a non-monotonic relationship between noise and Zener vo ltage? Have you tried an avalanche-mode Zener for comparison (i.e., one t hat's rated at more than ~7V)?

- What happens if you expose the LEDs to other sources of ambient light -- particularly a fluorescent lamp or other modulated source -- while measurin g them? I wonder if they remain sensitive to other wavelengths while they' re emitting their own light.

- Where do you get those nice metal castings you're using for your boards i n those photos?

-- john, KE5FX

Am 02.10.2015 um 02:25 schrieb George Herold:

There is nothing that could vibrate. The 10 AA cells are in a plastic holder that forms a solid stone from them, stored in a cast aluminium box, isolated from the preamp with some books, and all that in another alu transport box the size of a small coffin, with double female BNC feedthroughs as the only connection to the outer world. Inside the connections are SMA / semi rigid. Poor man's shielded room.

The books are AOE3 for the preamp, Conelly-Motchenbacher for the DUT box. A solid foundation. :-) Any additional connection between DUT and preamp results in a loop that will fill the plots with spurs. Those PicoVolts are hard to please...

That's just the way you use a Z-diode normally. 14V source,

1K current limiting resistor, diode to gnd, measure the voltage over the diode, ac-coupled.

We do not want to measure the supply noise (which probably would not even be the limit with NiCds btw).

The low impedance of the diode is necessary since

60 Ohms are 1nV/sqrt Hz thermal noise already.

Gerhard

Thanks for the response Gerhard, I didn't know of Connelly-Motchenbacher, a bit spendy.. they need to come out with a second edition. :^)

OK, I've not looked at zener noise.. excpet for HV zeners (V>10V) I thought low voltage zeners were a bit like forward biased diodes, with a resistance given by 25mV/I bais. And voltage noise that is 1/2 the johnson noise of that resistance.... (Essentially the shot noise of the current times the resistance.) But your plots say that isn't so.... Have you looked at just simple pn junctions as a function of forward voltage?

The LED's look to be all 1/f noise. I don't understand that. G/R noise should be white.

(And a cap multiplier on the supply does wonders.)

Yup, Thanks again.

George H.