Development of a SiPM readout circuit and a trigger system for microfluidic scintillation detectors Mikhail asiatici 29/08/2014

Overview Introduction LabVIEW interface PCBs Project context System overview LabVIEW interface Features Post processing algorithms Performances PCBs Overview SiPM breakout Amplifiers Power supply

Overview Measurements Conclusions SiPM pulses Scintillation light Thick plastic scintillator (tile) Microchannels with liquid scintillator SiPM characterization Conclusions

Project context - Target system Microfluidic scintillator detector Multiple photodetectors to allow reconstruction of particle tracks with high resolution (60 μm channel pitch) Very low light level (1.65 photoelectrons per MIP, in average) A. Mapelli et al. - Scintillation particle detection based on microfluidics 1/32

Project context – Trigger system Sensor photosensitive area Photodetectors Scintillating fibers 3/32

USB digital oscilloscope System overview XY table Power supply USB +5 V 65 to 70 V SiPM Trigger(s)/signal(s) From a readout point of view, both the microfluidic channels and the trigger fibers share the same architecture, being a scintillating element coupled with a photodetector – in principle SiPM, but PMTs can still be used. Electrical signal from SiPM is expected to be quite low when few photoelectrons are detected, and therefore some electrical amplifiers have been designed. Signals from SiPM+amplifier chains, or directly from PMTs, are sampled by a digital oscilloscope and then transferred to a computer via USB interface, where they are processed and stored by means of a LabVIEW VI. The same VI controls the position of the XY table, again via USB interface, which defines the detector area from which events are stored. All of the elements of this diagram have been purchased (SiPM, PMT, digital oscilloscope, XY table) or designed (LabVIEW VI and amplifiers), and amplifiers are currently under test. A SiPM PC B USB digital oscilloscope C LabVIEW PMT D ext 2/35

project context – sipm vs pmt A. Mapelli et al. - Scintillation particle detection based on microfluidics N. Otte - Silicon Photomultipliers a new device for frontier detectors in HEP, astroparticle physics, nuclear medical and industrial applications 3/32

Project context – xy table Stepper motors controller 2 x motorized linear stages in XY configuration 4/32

System overview XY table SiPM A SiPM B PicoScope 6403C C PC LabVIEW USB PMT D ext Trigger(s)/signal(s) 5/32

portability + QDC + PC via Ethernet connection? (+ router) + PC via USB 5/32

Labview interface: overview 6/32

Labview interface: features (1) Each channel can be independently Set as signal source, trigger, temperature or disabled Connected to any pulse source (PMT, SiPM) Trigger modes Self trigger (on any signal channel) Single external trigger A function generator can emulate a periodic/random trigger Coincidence trigger with programmable coincidence window Online pulse integral calculation and histogram generation Several post-processing options available 7/32

Labview interface: features (2) Waveforms circular buffer Online monitoring of the capture Temperature acquisition Temperature sensor with voltage output XY table interfacement Automatic scan of an array of points Simplified definition of matrices of points Import/export from/to XML file Manual control of the XY table 8/32

Labview interface: features (3) File logging Events in ROOT format Settings and scan points in XML format Automatically created together with the ROOT file Can be read back in LabVIEW to load scan points and/or capture settings Performances Successful capture of up to 37 000 000 events Event rate up to 9 kHz 9/32

Labview interface: post processing algorithms Baseline compensation Pile up rejection Pile up main cause of events between sharp peaks with SiPM Edge-adapted integration 10/32

Labview interface: pmt acquisitions Tests performed so far: PMT with thick liquid scintillator Acquisition system for Davy’s Master project Higher event rates (up to 1 kHz instead of 10 Hz) Higher number of events in single acquisition (up to 37 million) 10/32

Pcb: overview SiPM (SMD package) PicoScope Low voltage stabilized power supply (4.75 V – 6 V) Optionally -5 V MCX SMD connector USB port LV LV + data 50 Ω coaxial cable Amplifiers HV Step-up switching converter LEMO connector 11/35

SMD SiPM adapter board (dimensions in mm) Connector Holes for mechanical support SiPM (Hamamatsu S12571-050P) 12/32

Amplifiers simulations For SiPM: equivalent model by F. Corsi et al.1 Parameters from one of the devices presented in the paper (SiPM IRST), with Q = e*M ≈ 200 fC (M ≈ 1.25 x 106 for the devices received) Amplifier 1: transconductance amplifier + voltage amplifier (single stage from C. Piemonte et al.)2 with wide-band voltage-feedback op amp (ADA4817) ≈ 10 mV/pe single stage ≈ 20 mV/pe double stage (slightly slower) Tsettle5% ≈ 50 – 150 ns (trade gain for speed) Very low noise (EIN = 4.4 nV/sqrt(Hz)) 1 F. Corsi et al. – Modelling a silicon photomultiplier (SiPM) as a signal source for optimum front-end design 2 C. Piemonte et al. – Development of an automatic procedure for the characterization of silicon photomultipliers 13/32

Pcb: overview Low voltage power supply (4.75 V – 6 V) Optionally -5 V SiPM (SMD package) PicoScope MCX SMD connector LV LV Amplifiers Step-up switching converter Coax cable HV LEMO connector 11/32

Amplifiers Dual supply (+/- 5 V): short J13, J11. Single supply (+ 5 V): short J12, J10 (like in picture). External 5 V: short J9 (like in picture) Obtain 5 V from linear regulator MCP1700: short J8, and connect at least 6 V on the + 5 V input. External 5 V: short J9 Second amplification chain removed (impossible to stabilize, probably some positive feedback effect between the two amplification chains) J9 Vbias J8 + 5 V J10 - 5 V (optional) J11 J12 GND J13 14/32

Single stage amplifier on evaluation board PD Vbias Connected to GND (useful to short –IN to GND with a jumper) GND + 5 V 15/32

Power supply board Step-up switching voltage regulator, to avoid the need of an high-voltage supply just for SiPM biasing Output voltage tuning Integrated DAC with serial interface Digital pins available for a possible future integration with e.g. a microcontroller Potentiometer (here not shown) Input voltage range: 4.75 V – 6 V Output voltage range: 65 V – 70 V, 2 mA max Vop of the available SiPM: 66.6 V ± 1.3 V Recommended Vop range: 2.1 V Same architecture used for SiPM biasing in the Schwarzschild-Couder CTA Telescope K. Meagher (Georgia Tech) – SiPM Electronics for the Schwarzschild-Couder Telescope (presentation) 16/32

Vbias power supply Short J4: voltage is regulated with R4. Short J3: voltage is regulated by MAX1932 DAC. Default at power up: lowest Vbias (around 65.35 V). Use this if you want to use the USB to SPI bridge (next slide). J2 is the SPI interface. From top to bottom, pins are nCS, SCLK, MOSI, GND. 4.75 V to 6 V GND Vbias 17/32

USB to SPI bridge With these connections, the power supply board is powered via USB. Command-line interface Set Vbias between 65.3 V and 70.3 V with ≈ 20 mV resolution (8 bit) Turn off voltage conversion (Vbias ≈ 4.5 V) + 5 V from USB GND from USB 18/32

Sipm pulses 5 p.e. 4 p.e. Dual stage board ≈ 20 mVpk/p.e. ≈ 800 mV*ns/p.e. (R ≈ 4 kΩ) tr = 12 ns (amplifier limited) tf = 45 ns (mostly SiPM limited) 1 p.e. 2 p.e. 3 p.e. 3 p.e. 4 p.e. 5 p.e. 2 p.e. 1 p.e. + afterpulses INFN board ≈ 7 mVpk/p.e. ≈ 100 mV*ns/p.e. (R ≈ 500 Ω) tr ≈ 1 ns (oscilloscope limited) tf = 38 ns (SiPM limited) 1 p.e. (tr and tf are 10-90% and 90-10% rise and fall time, considering absolute value of V) SiPM biased at 66.7 V 10 mV/div, 20 ns/div 19/32

Measures – sipm characterization Self trigger histogram, in darkness 1 p.e. -> primary dark count 2+ p.e. -> primary dark count + crosstalk Fit with Borel distribution -> Gain Crosstalk probability gain 20/32

Measures – sipm characterization Self trigger histogram, in darkness P(crosstalk) proportional to ∆V2 Gain proportional to ∆V V = 67.5 V -> ∆V = 3.0 V V = 68.0 V -> ∆V = 3.5 V V = 67.0 V -> ∆V = 2.5 V V = 65.5 V -> ∆V = 1.0 V V = 66.0 V -> ∆V = 1.5 V V = 66.5 V -> ∆V = 2.0 V 21/32

Measures – sipm characterization Slope: Cd+Cq (for SiPM SPICE model) VBD 22/32

Measures – sipm characterization 23/32

Measures – sipm temporal characterization Characterization VI inspired by C.Piemonte et al.- Development of an automatic procedure for the characterization of silicon photomultipliers 24/32

Measures – sipm temporal characterization Amplitude vs distance from preceeding pulse 5 p.e. 4 p.e. 3 p.e. 2 p.e. 1 p.e. Delayed crosstalk? Primary dark count Afterpulses Afterpulses + crosstalk Measures with INFN board (leading edge must be as rapid as possible) 25/32

Measures – sipm temporal characterization Primary dark count -> exponential distribution (distorted due to log binning not normalized) Maximum = 1/DCR, without effect from afterpulses Projection along time axis, log-log scale, log binning Oscilloscope bandwidth limit Afterpulses: Exponential distribution with tau much shorter ≈ 10 ns (trap lifetime) Fit to find afterpulse probability. Peak is constant, amplitude increases 26/32

Measures – sipm temporal characterization DCR proportional to ∆V Afterpulse probability proportional to ∆V2 27/32

Measures - setup coincidence trigger 2 x PMT for trigger fibers (not shown) Microchannels (or plastic tile) Amplifiers connected via coax cable (not shown) SiPM 28/32

Measures – plastic tile 6 p.e. Measures – plastic tile 0 p.e. 21 p.e. 16 p.e. counts (mV s) 29/32

Measures – microchannels 0 p.e. Mean number of p.e. (sub-mm channels, trigger and SiPM aligned by eye…) 1 p.e. Fit with branching Poisson distribution, to model SiPM crosstalk 2 p.e. Pedestal (no channels) … Gain (mV s per p.e.) counts 9 p.e. (mV s) 30/32

Conclusions Developed an automatic characterization and acquisition system for microfluidic scintillation detectors Events processing and logging to ROOT file XY table interfacement Both light yield (PMT and/or SiPM as photodetectors) and spatial characterization Compact and portable Tools for SiPM characterization Confirmed literature results, SiPM excellent photodetectors for low light yield 31/32

perspectives 32/32 Electronics SiPM Software Investigate gain vs bandwidth tradeoff on existing amplifiers, test amplifiers based on current feedback amplifiers Integration of all the electronics (amplifiers, bias and USB interface) on a single board – beware of switching noise! Towards multi channel acquisition On-board digitalization (pulse shapers, fast ADCs) and processing (FPGA) EASIROC SiPM Consider other manufacturers Investigate temperature effects (expect DCR reduction, VBD reduction, afterpulse time constants increase) Software Automatic SiPM characterization (gain, DCR and P(AP) vs V, pulse time constants, Corsi model parameters) Full waveform digitalization enables endless processing possibilities Noise reduction Discrete p.e. histogram (pulse fitting, combine pulse peak and integral, …) 32/32

Thank you

backup

Amplifiers simulations Amplifier 2: transconductance amplifier + non-inverting amplifier with wide band current-feedback op amp (AD8000) from F. Giordano et al. ≈ 10 mV/pe single stage ≈ 80 mV/pe double stage Tsettle5% ≈ 40 – 60 ns (fast) Higher noise (EIN = 520 nV/sqrt(Hz)) F. Giordano et al. – Tests on FBK SiPM sensor for a CTA-INFN Progetto PREMIALE demonstrator (presentation) 12/32

Amplifiers performances summary Gain in the order of 10s mV/pe, time constants in the order of 10s-100s ns Amplifier 1 less noisy Amplifier 2 faster 13/32

Amplifiers pcb requirements The PCB is meant as a test board from which possibly derive a definitive configuration, so it is important to ensure the maximum possible flexibility For both the configurations, the signal can be extracted after single or double stage For all of the 4 signal sources, the output can be exctracted before/after a decoupling capacitor Capacitor performs on-board AC coupling, but might results in signal reflections Optional dual supply +/- 5 V as an additional way to produce a signal with no DC component (but maybe decoupling capacitor is enough) All the feedback resistors are potentiometers, to allow gain tuning There is always a certain degree of gain-bandwidth tradeoff Avoid saturation for events with a higher number of photoelectrons Bypassable on-board linear voltage regulator Compare noise with on-board/external voltage regulation 14/32

SMD SiPM adapter board (dimensions in mm) Connector Holes for mechanical support SiPM (Hamamatsu S12571-050P) 15/32

Amplifiers board Jumpers for on-board/external voltage regulation choice SiPM connectors: LEMO Output connectors: LEMO Jumpers for single/dual voltage supply choice Power supply (HV, LV, optional -5 V, GND) 16/32