really bad oscillators

Zener diode noise generator + bandpass + comparator.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Hmm I don't know exactly what you want. But led spads come in all varieties, some are really nice 'ideal' counters, (shine light and get the 'right' statistics.) and others have all sorts of after-pulsing and such, that gives long time frame 1/f type noise... (I don't understand the 1/f part.)

I think I have two led spad's now, a red at 25V and green at 80V... I haven't done the statistics on the green one.

You can get the same sort of thing with an avalanche zener, but no light intensity knob.

George H.

I already use a TPS54302 spread-spectrum switcher in the power supply!

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

John Larkin wrote

74HC4046 with the VCO input connected to noise source? Radioactive decay, noise diode... ?

Just for reference, truly random noise generators are hard. Terry Ritter did some analysis a while back and discovered problems in circuits that appeared to work well.

PRELIMINARY Noise Source Experiments

Experimental measures reveal problems where previously none were suspected

An alternative is a Linear Feedback Shift Register as a pseudorandom noise generator. Here are some examples. Sorry for the wrap.

Is that interpolator the ramp based method? May be simpler to add a test port wherein you can mung up the current source ( or whatever you're using) with some noise.

Am 06.10.2018 um 19:33 schrieb John Larkin:

I do not think that this is a really good idea. If your test signal is REALLY noisy, it will dither away the contributions of your interpolator / pulse stretcher. You get nice statistics, but for a wrong reason.

The standard way to measure linearity of an interpolator is to have two OCXOs that drift very slowly against each other, maybe 20 nsec difference per hour. Then you know the value to be expected and you have enough time to do statistics wrt single vs. 1000 times averaged. Dynamic nonlinearity (arbitrary pulse width, cycle-to-cycle) can only be worse than that.

And it is a task for itself to make sure that the 2 VCXOs do not injection lock, even when they happen to be close. We used our house reference (hydrogen maser based) and an offset generator.

I also had good results with a switchable Synergy CML delay line and measured the resulting pulse width in parallel with a Stanford SR-620. The SR620 is quite old by now (Z80..) but still there are no TICs that are SIGNIFICANTLY better.

Back then, when men still were men and HP still was HP, they published a description of the two-stage time stretcher of the HP54570A sampling scope in HP journal. Still worth reading. All of HP journal.

cheers, Gerhard

Am 06.10.2018 um 21:28 schrieb Gerhard Hoffmann:

Ooohps, 54750A

Good, but the Zener capacitance might have some bandpass as well. A neon lamp, transformer-coupled to a sense/trigger, and biased to conduction, is plenty noisy over a broad band; there's plenty of lore on the corrections for gas diode noise correlations.

As I understand it, good Zener noise sources need aged, selected components.

If you just want noise, and aren't too picky about spectra and such, a maybe 10 volt zener biased to around 1 mA will make about 300 nv/rthz wideband noise.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Yes.

I need to do a closed-box test on both a new design and a legacy version, so I don't want to do inside the DUT.

It's just an interesting little problem in an otherwise tedious design.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

The random pulse histogram thing works well and is fairly fast. It can fine-tune the interpolator to a fraction of an LSB. And it's easy. I just got interested in designing a cheap but statistically-good-jitterey oscillator.

This will be a production test, so I don't have to prove that the theory is right, just that every unit is built and calibrated correctly. One or two spot delay measurements will supplement the statistics thing.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Chua's circuit is the textbook chaotic oscillator:

Adding a single capacitor to the usual "blocking oscillator" can make a chaotic oscillator:

"The output signal of such chaotic oscillator is a series of short term pulses characterized by chaotic fluctuations of time intervals between pulses. Such chaotic pulse signals possess a broad-band continuous power spectrum and short correlation length."

(PDF) Generation of broad-band chaos using blocking oscillator. Available from:

Two sheet-beam tube oscillators, each configured as self-oscillating singly-balanced mixers, cross coupled to each other would probably make a pretty crappy oscillator

Right, that sets the maximum bandwidth. You can tone it down from there as you like, for whatever frequency / phase noise range you want. Presumably, the smaller fraction of the distribution you take, the more sigmas you'll have that look "normal" around f_c. Setting the bandwidth to be a few times the interpolator step would seem appropriate.

And if this is still too slow (~100s kHz would be typical), tack on a high frequency clock and mixer, and bandpass some more. Of course if that doesn't offer enough bandwidth, you'll need to figure something else out, but in any case, noise generators are probably not something John has a shortage of. :)

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

It's chaotic but it still has strong periodicties, and would probably alias against my clock.

Right. A blocking oscilllator is like a super-regen receiver in that, if the time constants are right, the period is dominated by noise.

Again, in my application, I want the oscillator periods to be jitterey at all time scales. I want "the spectrum of the jitter" to be broadband so it doesn't correlate with any periodic clock.

I wish I knew more about the TPS54302 spread-spectrum mechanism. I'll have one on my board, so that noise is free.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Why does the blocking osc pulse generator not fit that requirement? I'm not sure what "spectrum of the jitter" should be broadband means do you mean the process that generates the pulses should be ergodic?

This gentlemen made a random-bit generator just from abusing the race conditions that can naturally occur in multi-core, multi-threaded processors where resource access is not properly synchronized between code in different threads of execution, kinda interesting!

We use to call that "stationary."

No, I want pulses whose period is random, without any periodicities. That corresponds to a flat spectrum. Or if you histogram the periods, that looks pretty flat.

Possibly I could use a crystal oscillator that has some specific frequency ratio to the clock in my DUT time stamper, some relatively-prime thing I guess. But I'd have to be careful about oscillator frequency tolerances, which might require too much thinking.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics