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| Ultra low power, clean 30V power supply + ultra low power high speed comparator? |
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| Kleinstein:
I don't think the ripple would be such a big problem - it just needs a relatively large capacitor for filtering. At 30 V it could be tricky to find a suitable low power and low noise linear regulator though - though there could be a few. I would be more worried about low frequency noise than higher frequency ripple. The idea with a charge amplifier sounds very good, as it reduces the need for high speed parts. The charge amplifier could end up being more like a pulse stretcher. However the amplitude after the charge amplifier will be likely rather small, so that it would need amplification first. It is essentially impossible to build a fast discrete low power comparator, as parasitic capacitance is critical and very small transistors would be needed. The comparators build in low power µCs are relatively good, as they use a relatively fine structure CMOS process, normally not found with analog parts. The nice point about the charge amplifier solution would be that it could still read the pulse hight |
| Marco:
--- 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 --- Ultra-low-power boost converter like MAX17220 with a cascode MOSFET followed by ultra low power linear regulator like STLQ020PUR with some more external transistors so it can form a higher voltage linear regulator? (Can't immediately find any description of such a circuit, but should be possible.) --- Quote ---2: How do you detect a 20-80mV, 50-200ns pulse and turn it into a longer digital output for counting(interrupts)? --- End quote --- The unbuffered inverter trick trick seems interesting, one of the inverters is biased linearly with a 10k-100k feedback resistor to become a transimpedance amplifier. Then more unbuffered inverters as amplifiers (if they are on the same die they should be biased linearly by the DC coupled output of the transimpedance one). Maybe some of the very low voltage logic families will be fast enough at low enough supply voltage to work and low enough power. The On Semiconductor SiPMs with fast outputs look interesting too, no need for signal processing to detect multiple events close together. |
| David Hess:
--- Quote from: Marco on June 29, 2019, 04:24:13 pm ---The unbuffered inverter trick trick seems interesting, one of the inverters is biased linearly with a 10k-100k feedback resistor to become a transimpedance amplifier. Then more unbuffered inverters as amplifiers (if they are on the same die they should be biased linearly by the DC coupled output of the transimpedance one). Maybe some of the very low voltage logic families will be fast enough at low enough supply voltage to work and low enough power. --- End quote --- Operating a CMOS inverter in its linear region gives good sensitivity and frequency response but at the cost of high power. --- Quote from: Kleinstein on June 29, 2019, 08:22:42 am ---I don't think the ripple would be such a big problem - it just needs a relatively large capacitor for filtering. At 30 V it could be tricky to find a suitable low power and low noise linear regulator though - though there could be a few. I would be more worried about low frequency noise than higher frequency ripple. --- End quote --- I have built these kinds of circuit before and the problem was always high frequency noise from the switching converter coupling through the detector (or supply connections) into the discriminator. It is not insurmountable but care must be taken filtering the output from the switching regulator. There are lower noise options but the micropower requirements in this case dictate a hard switched micropower switching controller. |
| Marco:
--- Quote from: Kleinstein on June 29, 2019, 08:22:42 am ---The nice point about the charge amplifier solution would be that it could still read the pulse hight --- End quote --- Does pulse height actually mean anything useful though? The number of optical photons per high energy photon depend on the energy, which is an unknown. AFAICS pulse height is either irrelevant or constant (if the SiPM is saturated). |
| Marco:
--- Quote from: David Hess on June 29, 2019, 05:53:15 pm ---Operating a CMOS inverter in its linear region gives good sensitivity and frequency response but at the cost of high power. --- End quote --- Anything which has amplification at >100 MHz is relatively high power ... but does it give good bang for buck when you don't really care much about linearity? What would a RF BJT need to be biased at to allow a decent trans-impedance amplifier to be made at those speeds? 100 uA? |
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