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

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Spirit532:

--- Quote from: Marco on June 30, 2019, 06:48:26 am ---It also seems useful for very high counts, if high energy photons strike the scintillator every say 10 ns you can still detect that.

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If high energy photons strike the scintillator every 10 nanoseconds, the issue you should be worried about is your body evaporating. What are you doing inside a live fissioning reactor anyway?


--- Quote from: Someone on June 30, 2019, 06:50:40 am ---And that is before considering the thermal characteristics of the SiPM its self, though the discrimination technique planned by the OP makes it less sensitive than it could have been. For reference Hamamatsu include temperature compensation on their MPPC (SiPM) supplies.

--- End quote ---

With a clean power supply, temperature compensation isn't really required for counting. It'll be clean and linear enough to provide a rough(+-10% is standard) dose rate estimate, and certainly more than enough to alert you if things go sour.

David Hess:

--- Quote from: Spirit532 on June 29, 2019, 08:42:15 pm ---
--- Quote from: David Hess on June 29, 2019, 07:51:39 am ---A charge amplifier removes the requirement for high bandwidth as long as fast response is not required so supply current can be very low.
--- End quote ---

I'm estimating that the maximum count rate will be around 2-5kHz for really high radiation fields on such a small crystal(several mSv/hr), so it may be an option worth exploring.
--- End quote ---

I looked at something like this for a proportion counter a couple years ago.  The charge amplifier catches everything through continuous integration but the ability to distinguish adjacent pulses depends on bandwidth just like a transimpedance amplifier.  The difference is every pulse is captured even at low bandwidth; pulses which are too close together are combined.

The problems are how to handle drift since a charge amplifier will happily integrate any leakage current at its input and how to reset it.  The leakage current can be cancelled with a temperature compensated bias current cancellation circuit or through an automatic calibration routine.  Limiting DC gain with a resistive feedback network like I described (AC shunted t-network) also helps and may be sufficient.

Resetting the output between counts can be done with the various integrator reset methods but I suspect a better way would be to subtract a fixed amount of charge similar to how a charge balancing ADC works.  This allows the charge amplifier to continuously integrate the input without missing anything.

Spirit532:
The issue here is the power supply. Signal processing doesn't incur that much cost.

Marco:

--- Quote from: Spirit532 on June 30, 2019, 04:31:10 pm ---With a clean power supply

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On second thought I don't think any ready made boost converters will do you much good, they are tuned for far too high a frequency and far too low a turn on time AFAICS. How about simply having a MSP430 in low power mode 3, pulsing a BSS123 for 1 tick of a 32768 Hz crystal clock at ~1 kHz to boost the voltage using a 100 mH inductor? Then just a question of how to tune the pulse frequency, I'd guess error amplifier and using the ADC in the microcontroller (or maybe use a microcontroller which can do ultra low power PWM but has a better ADC like the MSP432). Due to the low currents and the relatively large smoothing capacitor it doesn't need to be very fast. No linear regulator or ripple killer is really necessary, with a 100k/100nF smoothing filter ripple would be dominated by the SiPM current pulses (might have to increase the output capacitor a little more to give the microcontroller time to respond to varying pulse counts).

The TLV7011 seems the best ultra low power comparator around, with ~5nF SiPM and ~200 Ohm anode resistor it should be fast enough ... connect the output to a MSP430 external clock input for a timer to count.

David Hess:

--- Quote from: Spirit532 on July 01, 2019, 07:07:03 pm ---The issue here is the power supply. Signal processing doesn't incur that much cost.
--- End quote ---

The digital side does not but the analog side will if it requires high bandwidth.

I do not consider the power supply to be the most difficult part.

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