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Introduction Background Results CDM Results FDM Conclusion
SiPM Array Multiplexing (SAM)
Nathaniel Kaneshige1 and Nikki Rousslang1
1University of Hawaii at Manoa
7 December 2018
N. Kaneshige, N. Rousslang PHYS 475 - Fall ’18 7 December 2018 1 / 16
Introduction Background Results CDM Results FDM Conclusion
Project Objective
Increasing need for high channelcounts in radiation detectors (PositronEmission Tomography (PET),Compton Cameras, Neutron Imaging,etc.)
Multiplexing is used to combinemultiple signal channels for simplifieddigitization
Different multiplexing schemes areapplicable to pulse-mode radiationdetectors
Hybrid multiplexing methods couldprovide unique advantages
Key Objective:
Develop and test Charge-DivisionMultiplexing (CDM) and Frequency-DivisionMultiplexing (FDM) for application in ahybrid concept.
Figure: Schematic of scattered back-projection. (Kim et.al. 2013)
Figure: 3D model of neutron imaging prototype usingplastic scintillating fibers and SiPM arrays.
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Introduction Background Results CDM Results FDM Conclusion
Silicon Photomulitplier (SiPM)
SiPM = Light sensitive device suitedfor detection of scintillation pulses
Photo-detection signals are fastcurrent pulses
The ArrayJ-60035-64P contains 646mm J-series sensors in an 8x8 array.
Position-sensitive SiPM readouts haveapplications in PET sensors.
Figure: Schematic of SiPM array at the pixel level. (ArrayJManual)
Figure: Image of a SiPM Array. (European SpaceAgency)
Figure: Typical signal for single SiPM.
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Introduction Background Results CDM Results FDM Conclusion
Charge-Division Multiplexing (CDM)
Each pixel in the array is sent to anode in a row of discrete resistors.
Signal from the SiPM is sharedbetween two outputs (X+,X−)
The signal position is related toattenuation of current from resistivechain.
This method of multiplexing is simpleand uses only passive electricalcomponents.
Figure: CDM for a single row.
X =X+ − X−
X+ + X− (1)
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Introduction Background Results CDM Results FDM Conclusion
Frequency-Division Multiplexing (FDM)
Resonator op-amp circuit described byMishra et. al. (2018) for conventionalPhoto-Multiplier Tubes
Used to identify fired detector
Impulse response is a decayingsinusoid
Possibly has coincidence resolvingpower through power spectrum (powervs. frequency) analysis.
fLC =1
2π√
LC, Q = R1
√CL
(2)
ωT = ωLC
√1−
14Q2
(3)
Vout (t) = e−ωLC t/2Q cos(ωT t + φ) (4)
Figure: Schematic of Resonant op-amp circuit. The dif-ferentiator was used to generate SPICE simula-tions. During data collection, the CDM outputpulse was fed directly into the op amp’s non-inverting input.
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Introduction Background Results CDM Results FDM Conclusion
Hybrid Project Concept
Charge-division is first used tomultiplex SiPMs within a row.
Frequency-division is then used tomultiplex the charge-division outputsacross multiple rows.
Event position and energy can befound by analyzing the powerspectrum of the outputs.
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Introduction Background Results CDM Results FDM Conclusion
Project Block Diagram
Det. 1
Det. 8
Det. 9
Det. 16
ChargeDivisionNetwork
[1]
ChargeDivisionNetwork
[2]
Resonator [L1]
Resonator[R1]
Resonator[L2]
Resonator[R2]
Fan-in Left
Fan-in Right
Row
1
Row
2
Digitizer
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Introduction Background Results CDM Results FDM Conclusion
Project Block Diagram
Det. 1
Det. 8
Det. 9
Det. 16
ChargeDivisionNetwork
[1]
ChargeDivisionNetwork
[2]
Resonator [L1]
Resonator[R1]
Resonator[L2]
Resonator[R2]
Fan-in Left
Fan-in Right
Row
1
Row
2
Digitizer
How Far We Got
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Introduction Background Results CDM Results FDM Conclusion
PCB Prototyping
Two versions of the CDM board andtwo frequencies of the FDM boardswere fabricated
Printed Circuit Board (PCB)production was done in-house usingtoner transfer and acid etching
Figure: Prototyped boards.
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Introduction Background Results CDM Results FDM Conclusion
CDM: Simplified Schematic Description
Version One:No gainResistor values chosen to be 150Ohm w/o anode termination fromMassari et. al. (2015)Agrees well with SPICE model
Version Two:SPICE optimization on pulse widthand height showed improvementsusing 1 Ohm with 50 Ohm terminationWith non-inverting gain (OPA-847G=12V/V)
Figure: Pulses from CDM version one.
Figure: CDM for a single row.
Figure: Depiction of CDM board test setup usingthe Array using LYSO Crystal and Cs-137.
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CDM: Typical Waveforms Version Two
With the OPA-847 as a non-invertingamplifier (G= 12V/V)
Improved width and amplitude
Ringing where we did not want it...
Overall pulse shape does not agreewith simulation
Figure: Pulses from CDM version two.
Figure: Charge Division as average normalized waveforms.
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Charge Histograms
Figure: Cs137 integrated charge distribution. Each Photopeak represents the total amount of chargecollected at either CDM output. The purple spectrum represents the left-hand output and thegreen the right-hand. The anode pulse was injected at the leftmost node.
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Charge vs. Position of Photopeak
Figure: The charge collected at each CDM output varies linearly with the position of the node whichwas fired. The leftmost node corresponds to position 1.
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Asymmetric Noise on Outputs
Asymmetric noise characterized as450 MHz self resonance in theOp-Amp
Cause indicated as improper PCBlayout.
Failure to meet phase marginrequirements
Figure: Non-inverting output PCB-layout.Figure: Charge Division Output.
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FDM Simulation
Figure: SPICE FDM circuit. Anode pulses were modeled by a differentiated 1 kHz square wave.
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FDM Experimental
Like Mishra et. al. (2018), we used theLM6171, 100 MHz, Unity-gain stableop-amp and chose similar frequencyvalues
Resonant circuit did not resonate atall, observed a flat gain of 1 whendriven with a 100 mVpp Sine wave
Pulse shape agrees with simulation inthat the circuit does not resonate
Figure: Image of the fabricated resonator circuit.
Figure: FDM PCB tested using an artificial photo-multiplier pulse (RC high-pass of squarewave).
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Conclusion
Results:
Charge Division Multiplexer (CDM)CDM PCB designed, fabricated, and tested through two versionsCharge-division feature verifiedPCB layout indicated as likely cause for noise from amplifierOdd shape on the amplifier output
Frequency Division Multiplexer (FDM)FDM PCB designed and fabricated as described in Mishra et. al. (2018)SPICE simulation of the circuit showed conflicting results to that of MishraExperimental results agree with the SPICE simulation in that there is no resonance
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Project Implementation
PC
DRS4Digitizer
Ribbon Cable Biasing & Signal
ProjectBoard
SiPM Array and
Breakout Board 16 SiPMChannels
TwoChannels
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Introduction Background Results CDM Results FDM Conclusion
CDM: Schematic
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CDM: Board
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Introduction Background Results CDM Results FDM Conclusion
FDM: Schematic
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Introduction Background Results CDM Results FDM Conclusion
FDM: Board
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Op-Amp: OPA847
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Op-Amp: LM6171
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