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

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

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

4. 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
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5. Project context – Trigger system
Sensor photosensitive area
Photodetectors
Scintillating fibers
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6. 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
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7. 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
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8. Project context – xy table
Stepper motors controller
2 x motorized linear stages in XY configuration
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9. System overview XY table SiPM A SiPM B PicoScope 6403C C PC LabVIEW
USB
PMT D
ext
Trigger(s)/signal(s)
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10. portability + QDC + PC via Ethernet connection? (+ router)
+ PC via USB
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11. Labview interface: overview
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12. 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
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13. 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
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14. 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 events
Event rate up to 9 kHz
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15. Labview interface: post processing algorithms
Baseline compensation
Pile up rejection
Pile up main cause of events between sharp peaks with SiPM
Edge-adapted integration
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16. 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)
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17. 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
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18. SMD SiPM adapter board (dimensions in mm) Connector
Holes for mechanical support
SiPM (Hamamatsu S P)
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19. 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
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20. 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
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21. 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
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22. Single stage amplifier on evaluation boardPD
Vbias
Connected to GND (useful to short –IN to GND with a jumper)
GND
+ 5 V
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23. 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)
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24. 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 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
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25. 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 V with ≈ 20 mV resolution (8 bit)
Turn off voltage conversion (Vbias ≈ 4.5 V)
+ 5 V from USB
GND from USB
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26. 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
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27. 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
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28. 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
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29. Measures – sipm characterization
Slope: Cd+Cq (for SiPM SPICE model)
VBD
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30. Measures – sipm characterization
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31. Measures – sipm temporal characterization
Characterization VI inspired by C.Piemonte et al.- Development of an automatic procedure for the characterization of silicon photomultipliers
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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)
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33. 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
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34. Measures – sipm temporal characterization
DCR proportional to ∆V
Afterpulse probability proportional to ∆V2
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35. Measures - setup coincidence trigger
2 x PMT for trigger fibers (not shown)
Microchannels (or plastic tile)
Amplifiers connected via coax cable (not shown)
SiPM
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36. Measures – plastic tile
6 p.e.
Measures – plastic tile
0 p.e.
21 p.e.
16 p.e.
counts
(mV s)
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37. 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)
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38. 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
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39. 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, …)
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40. Thank you

41. backup

42. 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)
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43. 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
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44. 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
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45. SMD SiPM adapter board (dimensions in mm) Connector
Holes for mechanical support
SiPM (Hamamatsu S P)
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46. 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)
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