For a project I'm starting, I am trying to create an array of silicon photomultipliers (start small, 4 or 6) which can be connected to one channel, and when they fire, you can detect which photomultiplier fired. I apologize, but I never designed anything like this before, so perhaps my description might be too abstract.

In a sense, this is a step-up from my previous work done with SiPMs: one/multiple SiPMs going through a pre-amp in a channel. You can see the associated schematic below:


simulate this circuit – Schematic created using CircuitLab

Sorry for the small schematic. This was just to give you an idea of my previous work with SiPMs. This schematic is based off of the SensL Read out circuit: http://sensl.com/products/j-series/. I'm using their J-series photomultiplier, though with one photomultiplier rather than two. You can see their schematic in the user manual. Reading from the cathode instead of the anode provides a negative current signal, and the feedback circuit filters out noise while inverting it, and turning the current signal into a voltage signal.

I'm still debating whether to have my 'array/network' of SiPMs go through multiple channels or if they will go through preamp circuits such as with the previous schematic. I'm really just trying to get some ideas on how to approach this. Logically speaking, if all the SiPMs go through one channel with a PreAmp, the voltage level from the output won't really tell which SiPM fired, just probably how many fired depending on the summing configuration. Therefore, how might I go about this?

  • \$\begingroup\$ 470 Ohms seems like very little gain. Its only -470 V/Amp of photocurrent. Therefore if you have a 1nA signal, which can be considered very large in many systems depending on the application, will only yield a signal voltage of 0.47uV. But then again I am not very familiar with silicon photomultipliers. I do know that if you were to multiplex the sensors to a single preamp, charge-injection from the signal routing circuitry and surface leakage will most likely make your system almost useless for anything but the largest of signals. best to have multiple preamps and mux their signals to the A/D \$\endgroup\$ – Luke Gary May 23 '17 at 21:46
  • \$\begingroup\$ If you want to know which one fired, you need a design which permits that detection. Normally, people would set up a separate first stage amplifier, at the very least, and perhaps multiplex them into a shared, following amplifier chain. If there is some reason forcing you to share the entire amplifier chain, then you might consider some method to modulate/chop the SiPM devices so that you can later separate them. This can be done optically (shutters, rotating or otherwise, etc.) Or it can be done using other means. But only you are in a position to know which approach to take. \$\endgroup\$ – jonk May 23 '17 at 22:34
  • \$\begingroup\$ @LukeGary Thanks for your reply. The circuit is based off of the recommended readout circuit provided by SensL, the manufacturers of the photomultiplier (sensl.com/products/j-series). I'm using their J-Series product, and you can see their circuit in the user manual. I was just following what it says, though with one photomultiplier rather than two. Gain aside, the photomultiplier is being read from the cathode, and the output signal there was negative in simulation. The OpAmp circuit filters out excess noise, and converts the current signal into a voltage signal. \$\endgroup\$ – user101402 May 26 '17 at 12:30
  • \$\begingroup\$ @jonk Thanks for your reply. I'm having trouble visualizing the part with multiplexing them into a shared amplifier chain. Assuming that my circuit above for one SiPM works as the first stage amplifier, all of the arrays would just go into one multiplexer, and the output of said multiplexer would go into another amplifier, correct? If true, how would detection occur, and how would you choose which input is read out by the multiplexer? Don't you need some kind of selector? In a sense, if you see the output as digital 'bits', it's like combining them into one long bus. \$\endgroup\$ – user101402 May 26 '17 at 12:51
  • \$\begingroup\$ @user101402 I'm starting with your desire to detect which diode is involved in an 'event.' One approach is to have an MCU continually scan (by changing the analog mux, or by alternately switching reed relays, for example) through each 1st stage, one at a time. This means there will be times when other diodes are not under observation, though. You can speed up the muxing, but the same limitations still apply. Another is to modulate the arriving light and to use the modulation itself to separate the signals. But that's a whole different deal. \$\endgroup\$ – jonk May 26 '17 at 18:52

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