Spad games III

So I built (copied) an active quench circuit with capacitive coupling. It follows Mario's first circuit. here

formatting link
Here's a blow up of fig 2 with some values.. either gleaned from the report or figured out.
formatting link

A few changes in the circuit. I couldn't find any use for the I_3 reset part. And I put a one shot in front of I_2.

The Schottky diode is normally biased on, when the spad fires the current stops flowing, voltage drops and that's what the comparator senses. The diode (I think) is mostly to isolate the spad from the comparator input capacitance. (Hmm I'll have to try it without the schottky.)

So this is all working fine up to about 5V of over voltage. 'scope shot with 1 sec persistence.

formatting link
The top is the comparator output. and the bottom is the voltage on the spad anode. (x10 probe and 2 pF coupling cap.)

Above 5V I run out of quenching voltage. And I start to see events like this,

formatting link

Where it takes a few micro seconds to reset itself. I'm not really sure what's going on here.

Anyway, long story short I'm ready for a fast mosfet driver.

John L. you mentioned these before, got a recommendation?

George H. ps piglet, I wound a little pulse transformer,

formatting link
about 80 uH of inductance each side, but also 7 pf of capacitance. I think I might need something on a toroid.

If I drive that through 100 ohms I get L/R ~1 us, but knowing nothing of transformers... well I've got to think about it. (or solder something up.) Geo

Reply to
George Herold
Loading thread data ...

The '4427' series is generic.

formatting link

I like the IXYS parts too, like IXDN602. They are good for a lot more than driving mosfet gates.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

Thanks... I liked this 30V part from your first link.

formatting link

shorter

formatting link
$file/IX4426-27-28.pdf

but the IXD602 is 35V and 2A. (I need ~10 maybe 100 mA into at least

5 pF, but probably more.) Does this into ~1k ohm loads?

Oh dear, I was looking at the spec sheet again. It's says a propagation delay of 70 ns. I can't wait that long.

OK here's a 'pooh bear' idea. How about I drive a 1:5 transformer (voltage boost) into the quench cap ?

George H.

Reply to
George Herold

At your speeds, it had better be a transmission line transformer, and stacking transmission lines to get voltage gain is non-trivial.

formatting link

A 1:5 voltage boost might mean that a 50R drive impedance would get transformed to a 1250R output impedance, which might be a bit high to deliver the kind of current you might need.

--
Bill Sloman, Sydney
Reply to
bill.sloman

The IXDN602 has a typ prop delay of 35 ns into a 1000 pF load; lightly loaded, it might be a little faster. It would be happy driving light loads. There are probably faster gate drivers around.

For serious speed, use an opamp. Don't use it to clamp the SPAD voltage; use it to make the SPAD voltage.

Something like this might work:

formatting link

A transformer would be messy. They usually are.

--
John Larkin         Highland Technology, Inc 

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

Yup. Those IDX parts do look pretty nice--40V, ~8 ns rise and fall times.

For somewhat beefier parts, I've had good luck with the LM5112, but they're restricted to lower supply voltages.

Cheers

Phil Hobbs

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

True, up to point, but the point here is that John Larkin was frightened by a transformer at a very early age, and finds all kinds of excuses for not using them, and even more for not designing them.

They are scary, but they are also powerful.

--
Bill Sloman, Sydney
Reply to
bill.sloman

OK, I was reading the wrong table. I'll do a little more searching on DK.

Hmm that's a little like this, that I did last week.

formatting link

OK maybe a transistor for a higher voltage pulse.

George H. (thanks as always)

Reply to
George Herold

Bill, I appreciate any sincere comments/ help. When you start out by bashing John L, I just stop reading. I would ask you to please be civil, or just not comment at all.

George H.

Reply to
George Herold

Better yet, contract him to design the transformer (and its driver circuit) for you. Only pay him if it works.

Actually, you could do the spad reset with a stock transformer, but it's not worth the effort.

I'm still concerned about an edge-driven or AC-coupled SPAD reset hanging up, if it misses just once. Depends on whether enough current is available to latch the SPAD on.

--
John Larkin         Highland Technology, Inc 

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

That's a cool part. It can swing below ground, which is sometimes useful.

--
John Larkin         Highland Technology, Inc 

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

I had this silly idea... one-shots in parallel

formatting link

I couldn't figure out how to make the outputs work together.

So far I think it's OK... I was starring at this trace last night.

formatting link

The chan 1 scale should be ~5V/ div*. The first down step is about 5V, that's the spad over voltage. The next bump down is the cap quenching. But there's not enough voltage... (I played around with this on the bench this morning and if I make the quench pulse longer (in time) it helps a little.)

Anyway after the failed quench there's a bump up I don't quite understand, and then the spad voltage returns to where it was before the failed quench. It's still conducting... you can see there's a slight up-slope though and in ~1-3 us it resets.

This is obviously not good, a failed quench/ count.. but it wasn't permanent. I'll see if this continues as I raise the over voltage.

George H.

Reply to
George Herold

I think I need to drive a resistor string, with some sort of power supply balancing string, but mostly won't the string of one shots (74hc14) 'self balance' if the load is equal?

Dang, weekend is full.. no lab time till Monday.

George H.

Reply to
George Herold

Jon Larkin's comments about transformers are unnecessarily and misleadingly negative, and decidedly unhelpful.

My comment was designed to educate you, and any lurkers, about transmission line transformers which might work for you. It even had a link to more information.

John Larkin's comment was purely negative and correspondingly unhelpful, and deserved to bashed.

--
Bill Sloman, Sydney
Reply to
bill.sloman

There are stock transmission line transformers. The give-away is that there is about 100pF of interwinding capacitance.

If John had been kind enough to list the part he had in mind, we could have made our own assessment of the effort required - John finds it painful to even think about transformers so his assessment of the effort required isn't entirely reliable.

That state is detectable. If the SPAD stays conducting for long enough, you could always reset it again.

--
Bill Sloman, Sydney
Reply to
bill.sloman

In the voice of Ronald Regan (who I didn't vote for) "There you go again." Here's the deal, we're all smart enough to figure out who's ideas are helpful and whose aren't. Your commentary only insults our intelligence.

Ughh, look I don't see why anyone needs to be bashed, that just seems out of control crazy. We're here to talk electronics, if you think someone's making a mistake, point it out. If they don't pay attention, it's their problem.

Signing off, George H.

Reply to
George Herold

It might insult your intelligence, but this is a text only group, and gets archived.

I want it on the record when John has insulted our intelligence, and I didn't like it.

Disapproving looks - which do work in face to face conversations - don't get recorded here.

Sci.electronics.design is a remarkably popular and long-lived user-group. A certain amount of feedback about the quality of the material posted does seem to play a part in that.

John Larkin pays very little attention, and posts a lot. That makes him a problem for the rest of us.

When he does pay attention he can make useful contributions - the drivers he came up with are interesting, if too slow to be useful - but a lot of the time he's just posing as an expert without delivering any expertise.

--
Bill Sloman, Sydney
Reply to
bill.sloman

:

e:

Fine by me. It would be an interesting project. I'd need to know a lot more about what George is actually trying to do, and why - presumably he wants something that can be sold to university physics classes as a teaching tool , and built cheaply. This is the sort of thing that can be picked up rapidl y with face to face contact, and can be quite difficult if you have to rely on document swapping.

Reply to
bill.sloman

A bit of an aside here, but my curiosity prompts me: how do they know it's only a single photon? Or is "single photon" a loose phrase that really means "a very few photons"?

Reply to
Bob Engelhardt

No. Single photon detection means just that.

It goes back to Einstein's 1905 paper

formatting link

You turn the light level down low enough that your detector sees single iso lated events.

If you turn it down lower you see a steady background - which tends to come from cosmic rays with blue sensitive phototubes but from thermal noise in SPAD and red-sensitive phototubes.

Ideally, you'd look at your single photon events,and they would all be the same size, but the multiplication process that gets you up from a single el ementary particle to something that you can detect has statistical noise, s o your "single photon pulses" come in a Gaussian distribution of sizes.

The RCA 8850 phototube with the GaP first dynode, which offered a first sta ge gain of something between 35 and 50, was an exception.

If you ran the pulse heights from that into a pulse height discriminator, y ou could set up a situation where there were distinguishable peaks correspo nding to single, double, triple, and quadruple photon events, though they d id start to smear out when you got above about six or seven photons.

--
Bill Sloman, Sydney
Reply to
bill.sloman

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.