Electronics > Projects, Designs, and Technical Stuff
Ultra low power, clean 30V power supply + ultra low power high speed comparator?
<< < (4/10) > >>
David Hess:

--- Quote from: Marco on June 29, 2019, 06:19:51 pm ---
--- 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?
--- End quote ---

It does not matter how linear it is if it draws too much power.


--- Quote ---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?
--- End quote ---

It would be lower than the bias required for an FET.  At the same current, bipolar transistors have greater transconductance than FETs meaning higher gain-bandwidth product.
Spirit532:

--- Quote from: David Hess on June 29, 2019, 07:51:39 am ---20 millivolts out of 30 volts is 667ppm so accuracy over temperature is going to be a problem.

--- End quote ---

That'd be 1200ppm, since +-20 is fine. Could probably push it a bit further, maybe +-40-50mV, but with higher drift the gain might become an issue.


--- 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.


--- Quote from: Marco on June 29, 2019, 04:24:13 pm ---Ultra-low-power boost converter like MAX17220 with a cascode MOSFET
The On Semiconductor SiPMs with fast outputs look interesting too, no need for signal processing to detect multiple events close together.

--- End quote ---

A cascode setup would require quite a serious supply voltage and current to swing an external mosfet, which is outlined in that article, so I'd probably need another boost just to supply this boost...
You can see the OnSemi(formerly SensL) SiPM in that video, though using the regular output. The fast output is only really useful for single-photon counting applications, here we're counting thousands to millions of photons(depending on particle energy) as an analog signal(see below).


--- Quote from: Marco on June 29, 2019, 06:14:09 pm ---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).

--- End quote ---

Yes, it does. The SiPM is never saturated, as the only purpose of a SiPM is to not get saturated, by multiplying the number of mini-SAPDs(Which do get saturated, but there's thousands of them and some do, some don't. It's sort of like an R2R DAC in that regard.).
The output is directly(and mostly linearly) proportional to the energy of the incoming particle. Thus, you can do spectroscopy in a tiny package.

However, for this low-power version I explicitly don't need spectroscopy(or could have a second circuit that can be put to sleep when not in alarm mode), and I'd like to use the SiPM in a saturation-like mode, with just a simple digital output after a certain energy threshold.
SiPMs are not clean - they can have several MHz of self-count rate, but the pulse heights are generally a very small number of SAPDs firing, so it's usually much lower than actual photon amplification signals, so a basic height discriminator cuts off garbage below the ~10keV(equivalent-ish with a CsI:Tl crystal) level, which is not very useful regardless.
You can see that self-counting noise in the video linked above. It's just below the useful scintillation signal.
Kleinstein:
The comparator inside the AVRs (e.g. Mega88PA and similar) uses some 50 µA at 3 V.  I don't know for sure how fast the comparator can react, but it is not that slow and to my surprise also reasonable low noise / jitter (e.g. < 5 mV with a 1 V/µs slope). So the comparator may be just good enough to catch the pulses.
cur8xgo:
just to be clear...operational duty cycle must be 100%? cant do 10ms on 990ms off, or some kind of randomized duty cycle which statistically results in the same end result? Could increase battery life an order of magnitude and make the circuit much easier to design

I mean if you are in a high field do you really need to know that (can it be known?) only by being on constantly?

Spirit532:
It takes a while to stabilize the power supply and get a good background average, so yes, 100%.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod