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Ultra low power, clean 30V power supply + ultra low power high speed comparator?

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Spirit532:
I'm working on a radiation detector based on a scintillation crystal and a silicon photomultiplier, and I'm stuck with a few decisions regarding low power operation.
SiPMs are basically a massively parallel array of single-photon avalanche photodiodes operating in reverse bias in the Geiger region, at roughly 30V. When a photon hits the SiPM, some SAPDs fire, so you get a current proportional to the number of photons.

While I do have a working prototype of this detector already, it's consuming an abysmal ~1000-1100uA at 3V, which is completely unacceptable for a device meant to operate continuously in standby mode for weeks or months on small batteries.

So here's two interesting problems:
1: What's the easiest way to build a very low power(<30uA average) power supply capable of delivering ~30V at no load(the average SiPM current with a scintillator is in the nA range) with less than 10mVp-p of noise? The noise is critical, as the signal from a SiPM is very very tiny.
2: How do you detect a 20-80mV, 50-200ns pulse and turn it into a longer digital output for counting(interrupts)? Most nanopower/micropower comparators have a minuscule bandwidth and a very low slew rate. I'm guessing I'd have to build something discrete.
It's also possible to operate the SiPM in current mode with a transimpedance amp, but high slew rate, high bandwidth, ultra low power opamps simply don't exist as far as I'm aware.

David Hess:

--- Quote from: Spirit532 on June 28, 2019, 08:40:18 pm ---1: What's the easiest way to build a very low power(<30uA average) power supply capable of delivering ~30V at no load(the average SiPM current with a scintillator is in the nA range) with less than 10mVp-p of noise? The noise is critical, as the signal from a SiPM is very very tiny.
--- End quote ---

Does the 10mVpp only apply to high frequency noise or does that include regulation?

If regulation is not a problem, then I think any burst mode or hysteretic boost controller can meet your requirements with passive filtering.  These have the advantage of the lowest quiescent power and are commonly used for micropower regulators.


--- Quote ---2: How do you detect a 20-80mV, 50-200ns pulse and turn it into a longer digital output for counting(interrupts)? Most nanopower/micropower comparators have a minuscule bandwidth and a very low slew rate. I'm guessing I'd have to build something discrete.
--- End quote ---

I might have it set the state of a CMOS flip-flop which is then reset by the counter but that still leaves how to amplify the signal enough without drawing too much power.


--- Quote ---It's also possible to operate the SiPM in current mode with a transimpedance amp, but high slew rate, high bandwidth, ultra low power opamps simply don't exist as far as I'm aware.
--- End quote ---

What about integrating the current output and periodically reading the output voltage and resetting it as needed?  Each pulse should create a step in the integrated output.

Or integrate the output with a low integration capacitance making a charge amplifier.  What is the minimum amount of charge which must be detected?

2N3055:
Take a look at this for some ideas

https://indico.cern.ch/event/615174/contributions/2481471/attachments/1557307/2449642/Photomultiplier.pdf

https://www.mdpi.com/2072-666X/9/10/507/htm

https://wikihost.uib.no/ift/images/0/05/MagneLauritzenMasters.pdf

Tons of stuff on Google...

Spirit532:

--- Quote from: David Hess on June 28, 2019, 09:03:57 pm ---Does the 10mVpp only apply to high frequency noise or does that include regulation?
If regulation is not a problem, then I think any burst mode or hysteretic boost controller can meet your requirements with passive filtering.  These have the advantage of the lowest quiescent power and are commonly used for micropower regulators.

--- End quote ---

Regulation can be within +-20mV or so, going beyond that will make a rather nonlinear response. The gain rises very very rapidly, with some of my SiPMs shooting through an order of magnitude with just 100mV.
It's 10mV p-p for any noise above ~1kHz, I'm afraid, or it'd need amplification(again, not low power for this high of a speed).


--- Quote from: David Hess on June 28, 2019, 09:03:57 pm ---I might have it set the state of a CMOS flip-flop which is then reset by the counter but that still leaves how to amplify the signal enough without drawing too much power.

--- End quote ---

A discrete flip flop? I don't think 100ish mV is enough to flip something digital, and that's a very high energy photon(cosmic ray-ish).


--- Quote from: David Hess on June 28, 2019, 09:03:57 pm ---What about integrating the current output and periodically reading the output voltage and resetting it as needed?  Each pulse should create a step in the integrated output.
Or integrate the output with a low integration capacitance making a charge amplifier.  What is the minimum amount of charge which must be detected?

--- End quote ---

The idea is for the host device to sleep until there's an interrupt on one of the inputs, rather than continuously sampling and determining whether there was another particle or not.
The charges are pretty tiny, though I don't have any figures.



--- Quote from: 2N3055 on June 28, 2019, 09:05:58 pm ---Tons of stuff on Google...

--- End quote ---
High power, large stuff is easy. Slap in a few 100V/us slew opamps with a massive GBWP, a filtered high voltage supply, and you'll get a clean signal.
Miniaturizing this stuff and making it ultra low power is the hard part.


Here's an earlier test with an opamp and a bit of pulse stretching:

cur8xgo:
Well if I wanted to have a fun afternoon I would get the sim going and see if I could detect these pulses by:

arranging a circuit which nulls itself with a time constant much slower than the pulse width but much faster than the typical time between pulses

and design it so it consumes basically no power once its nulled

then this pulse upsets the balance and causes some kind of cascade or avalanche which either greatly increases the pulse voltage or the pulse length or both

there are physical analogies to this so I think it might be workable..and has probable been done a million times

also might want to consider using the fast rise time of the pulse to ring a resonant circuit of some kind of in that way extend the pulse "length"

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