fast(ish) one-shot

Zero bias would be the obvious measurement point, but they had no voltage:capacitance points to offer. Any point would allow me to hack an approximate Spice model for my driver. I finally got some lasers and measured them on my AADE in a jiffy. 274 pF in my case.

I think they resell a lot of stuff.

Threshold and maximum power would be the relevant points in my book. If you want the highest speed, you have to bias the laser somewhere near threshold, and even if you don't, it's the behaviour once lasing sets in that really matters. The capacitance goes through the roof.

Cheers

Phil Hobbs

German technical people can read English - they have to be able to to do their jobs - and most of them can write entirely comprehensible English.

E-mail is probably your friend. A phone call can well work better - the US sales people should be able to give you contact names and numbers.

ice sharp

nd diode to positive rail. I think R_min is 500 ohm. Well, that's more de lay than

ve (NFB), no matter what, and this feedback is derived from either the SPAD current or voltage. Since the voltage is so much larger and a more certain magnitude than current, it is advisable to use voltage. Your comparator sh ould trip on SPAD voltage dipping below a fixed threshold, and this trip sh ould cause an immediate PFB to be applied to the comparator which 1) endure s for the entire quench process and 2) establishes a new upper threshold fo r the SPAD voltage at which the comparator turns off. Since this takes time , it advisable to introduce a gate delay between application of the PFB and the NFB. The comparator also sets in motion the active quench, which by de finition induces a NFB on the comparator. Since the PFB has set a new thres hold, the NFB due to the quench in process will not affect the comparator o utput until the SPAD is actually quenched. The comparator can now flip and the SPAD stays quenched.

et to

o think about other ways... A fast quench would stop the current flow soone r..

ults in the highest possible count rates, like 14 Mcps. It's your project, do whatever.

Right, I think you're describing the circuit in Mario1 here,

The second active circuit. I tried that and didn't have the whole loop under control, oscillation or rails. So the more 'localized' oneshot is easier. I should give it another try...

George H.

I assume that happens with all diodes, is there some guesstimate?

There's a graph here, (scroll down), from which I read the C doubles (3-6) at about 0.5V... it does go up faster after that. :^)

George H. That graph has one data point.. maybe not so good, (But always makes for a nice fit :^)

Geo

Hul

George Herold wrote:

Huh, I don't have any. The lvds came in from digikey today... faster (delivery) than usual.

George H.

te:

nice sharp

and diode to positive rail. I think R_min is 500 ohm. Well, that's more delay than

tive (NFB), no matter what, and this feedback is derived from either the SP AD current or voltage. Since the voltage is so much larger and a more certa in magnitude than current, it is advisable to use voltage. Your comparator should trip on SPAD voltage dipping below a fixed threshold, and this trip should cause an immediate PFB to be applied to the comparator which 1) endu res for the entire quench process and 2) establishes a new upper threshold for the SPAD voltage at which the comparator turns off. Since this takes ti me, it advisable to introduce a gate delay between application of the PFB a nd the NFB. The comparator also sets in motion the active quench, which by definition induces a NFB on the comparator. Since the PFB has set a new thr eshold, the NFB due to the quench in process will not affect the comparator output until the SPAD is actually quenched. The comparator can now flip an d the SPAD stays quenched.

eset to

do think about other ways... A fast quench would stop the current flow soo ner..

esults in the highest possible count rates, like 14 Mcps. It's your project , do whatever.

Thanks for the link, I never could find the pdf for that article. Triggerin g on the voltage across the SPAD is a good idea IMHO. Looks like he's quenc hing via current stealing which is another good idea. Do have an idea of th e range of avalanche currents you're dealing with? The data sheet is inform ation-poor.

e:

rote:

a nice sharp

R and diode to positive rail. I think R_min is 500 ohm. Well, that's mor e delay than

gative (NFB), no matter what, and this feedback is derived from either the SPAD current or voltage. Since the voltage is so much larger and a more cer tain magnitude than current, it is advisable to use voltage. Your comparato r should trip on SPAD voltage dipping below a fixed threshold, and this tri p should cause an immediate PFB to be applied to the comparator which 1) en dures for the entire quench process and 2) establishes a new upper threshol d for the SPAD voltage at which the comparator turns off. Since this takes time, it advisable to introduce a gate delay between application of the PFB and the NFB. The comparator also sets in motion the active quench, which b y definition induces a NFB on the comparator. Since the PFB has set a new t hreshold, the NFB due to the quench in process will not affect the comparat or output until the SPAD is actually quenched. The comparator can now flip and the SPAD stays quenched.

reset to

I do think about other ways... A fast quench would stop the current flow s ooner..

.)

results in the highest possible count rates, like 14 Mcps. It's your proje ct, do whatever.

ing on the voltage across the SPAD is a good idea IMHO. Looks like he's que nching via current stealing which is another good idea. Do have an idea of the range of avalanche currents you're dealing with? The data sheet is info rmation-poor.

Sure, here's Mario2.

Re Currents: The spec sheet lists a maximum CW current as 200 uA. I haven't tried to push that number 'cause I still only have one $250 spad. And to be on safe side I have a 100uA current limit on the HV line.

I think mostly about charge per event... so sorta average current. I see this as two pieces, there's the charge on the Spad (+ stray) capacitance. V_over * C_s. And then there's the avalanche current that flows before I have a chance to quench it. And that is something like V_over * t_on/R_reset. R_reset is ~3k and t_on is something like 20 nS... If I turn t_on / R into a capacitance it's ~7 pF, which is about the same as my 'best guess' for the spad plus stray C... So I can gain some by faster, and some by keeping C_s small.

(V-over is 10V typ.)

George H.

e:

rote:

a nice sharp

R and diode to positive rail. I think R_min is 500 ohm. Well, that's mor e delay than

gative (NFB), no matter what, and this feedback is derived from either the SPAD current or voltage. Since the voltage is so much larger and a more cer tain magnitude than current, it is advisable to use voltage. Your comparato r should trip on SPAD voltage dipping below a fixed threshold, and this tri p should cause an immediate PFB to be applied to the comparator which 1) en dures for the entire quench process and 2) establishes a new upper threshol d for the SPAD voltage at which the comparator turns off. Since this takes time, it advisable to introduce a gate delay between application of the PFB and the NFB. The comparator also sets in motion the active quench, which b y definition induces a NFB on the comparator. Since the PFB has set a new t hreshold, the NFB due to the quench in process will not affect the comparat or output until the SPAD is actually quenched. The comparator can now flip and the SPAD stays quenched.

reset to

I do think about other ways... A fast quench would stop the current flow s ooner..

.)

results in the highest possible count rates, like 14 Mcps. It's your proje ct, do whatever.

ing on the voltage across the SPAD is a good idea IMHO. Looks like he's que nching via current stealing which is another good idea. Do have an idea of the range of avalanche currents you're dealing with? The data sheet is info rmation-poor.

Oh my trick for finding papers is to search for the paper title plus arxiv. GH