Spad games III

The schottky serves to protect the comparator input from exceeding its Vcm+ limit by becoming reverse biased during detection events and quench pulse.

But you may be able to find a fast comparator able to withstand the

25V-30V quench pulse.

piglet

Reply to
Piglet
Loading thread data ...

Thanks! But I think 80uH is way too much inductance. I was thinking more of 1 or 2uH at most. A multi-filar "transmission line" type of five or six wires wound together and then connected to make a 5:1 or 6:1 step up auto-transformer would take a fast 5V swing from a logic line driver up to 25 or 30V. The smallest Versa-Pac 6 coil inductor might be the easiest option? The high inter-winding capacitance can work to advantage if the coil start to coil end capacitance is kept down. If you see what I mean.

piglet

Reply to
Piglet

It means "at least one photon". MPPCs are arrays of SPADs wired in parallel, so the pulse height tells you approximately how many detection events occurred.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

A cooled PMT can easily detect visible-wavelength single photons with low background count rates. Solid-state detectors can detect singles, but with fairly high background count rates.

More energetic photons, hard UV or gammas, are grossly obvious.

If you split an energetic photon into two lower-energy photons, and direct them into a pair of noisy SPAD type detectors, you can correlate the paired signals and ignore the random background counts and demonstrate single-photon detection.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

Here's some more goofy ideas, without transformers:

That needs an auxialliary 5V power rail floating up at (say) 40V and keeps Mario's schottky decoupled detector.

or

Which keeps one side if the Spad at ground. The lower sketch replaces the 22pF coupling capacitor with the C-B capacitance of the quench NPN but will attenuate the detection event with B-E capacitance shunt. It solves the comparator input protection - looks attractively simple but not sure if enough signal remains for reliable detection?

For other ideas on making fast rise short pulses of high voltage I think I need to read up old-time books on radar pulse modulators!

piglet

Reply to
Piglet

About 1E6 times higher on an areal basis. APDs are competitive only for highly spatial-coherence sources, where you can focus them down onto a tiny area. They're hopeless for diffused-light measurements.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

If all you want is fast level shifting without DC coupling, a capacitor will do that. But DC is probably better here.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

Pity PMTs are so expensive. They'd be great for LIDAR.

Hey, did Hamamatsu ever decide to sell their cute little MEMS PMT? They shouldn't cost much to make, less than a VF display. It will be interesting when the patents expire.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

The old RadLab books are great. Vol 5, Pulse Generators, is still worth reading.

Nowadays we use mosfets, SiC fets, drift step-recovery diodes, transmission-line transformers, things like that.

Here's a few:

formatting link

formatting link

formatting link

I don't like HV design much, because things blow up too often.

I think George only needs about 10 volts to un-latch the SPAD.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

Yeah, AC coupling is workable but the capacitive loading must stay low, perhaps more blocking diodes?

piglet

Reply to
Piglet

Hmm, Well stepping back you have to look at how the photon is detected. So maybe a better thing to say is that it's a single electron, and how do we know it's a single electron? Well we know the electron charge and we do the statistics on the current we measure. (by doing statistics, I mean measuring the noise.) Doing the statistics works for things with no gain. (like photodiodes at low bais voltage, vacuum photodiodes (see Schottky and shot noise.) In detectors with gain, pmt's avalanche photodiodes, you have to measure the gain to do the statistics. With photon counting things (spads, pmts) you are in a different realm. And you can look at the count rate as a function of light intensity. You can also look at the time distribution of the pulses.

One dream I have with this spad, (which at low bias is just a photodiode) is to measure intensity from the linear region up through gain to counting. I sorta 1/2 did that, and it's harder than I thought. I need a count rate of ~1 MHz. to link counting to the gain region. but a dead time of 100ns at 1 MHz (1 us average spacing) means a 10% error.

George H.

Reply to
George Herold

solated events.

me from cosmic rays with blue sensitive phototubes but from thermal noise i n SPAD and red-sensitive phototubes.

e same size, but the multiplication process that gets you up from a single elementary particle to something that you can detect has statistical noise, so your "single photon pulses" come in a Gaussian distribution of sizes.

tage gain of something between 35 and 50, was an exception.

you could set up a situation where there were distinguishable peaks corres ponding to single, double, triple, and quadruple photon events, though they did start to smear out when you got above about six or seven photons.

Spad pulses are all the same size.. unless the photon comes while the spad C is still recharging... then you get a smaller pulses.

GH

Reply to
George Herold

Yeah that too. The circuit I'm using now resets through the 1k (and

3 k ?) resistor. I don't know what the comparator input C is.

George H.

Reply to
George Herold

This will have to wait, my weekend is full! GH.

Reply to
George Herold

Thanks. Interesting.

I got it into my head George needed 25-30V ... 10V is a bit easier.

piglet

Reply to
Piglet

Hi piglet, If the transformer is on the 'swinging' spad node, then with the circuit I've got now, I think I really care about the node capacitance.. It's an active quench and passive reset. I'm resetting it through ~4k ohm (which could be reduced.)

I tried the circuit without the coupling diode and it just broke into oscillations everywhere at crossover. (my layout is pretty messy at the moment.) (I didn't spend much time with it.) I could try adding some more R on Monday. Or add 30 pF (?) to the current circuit.

But now I just want a transformer to drive a capacitor-resistor-3pf spad C (plus strays.) From ~5V logic... paralleling a few for more current would be fine.

George H.

Reply to
George Herold

My spad at room temp and biased to a decent QM efficiency over-voltage, 10V say, has a dark count higher than 10k Hz.. less than 30k, but I'd have to check. If you can pay more you can buy better ones.

George H.

Reply to
George Herold

Right, that is one experiment to do. If you cool 'em off the dark count goes down a lot. -10C is the sweet spot, according to some papers. (There's more after pulsing as you cool more.)

Then you can buy a magic x-tal, two pieces cut and glued together such that with the right laser polarization you get two down converted photons that are entangled polarization-wise. And you can do Bell's inequality on a table top.

George H.

Reply to
George Herold

Some fierce TinyLogic buffers can run at 6.5 volts, and you could double that with a transmission-line transformer. But that's a hassle. You can drive a 2N7002 from a Tiny gate to make 50 volt pulses with 1 ns rise and fall times. You can buy hundreds of 2N7002s for what it will cost to make one transmission-line transformer.

Here are some. They are not popular in production.

formatting link

This is better:

formatting link

Unless you need isolation or high voltage, a transformer doesn't make sense.

I've played with the idea of stacking TinyLogic buffers, sort of Marx generator style.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

They're also a bit fragile and vulnerable to magnetic fields, and have short lifetimes (5 years or so) due to caesium migrating around inside. A PMT wouldn't last long in a sunny Arizona parking lot.

Yes, you can buy them now. Dunno if there'll be any competition--their last competitor (Photonis) went out of the PMT business some years ago.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.