Introduction Background Results CDM Results FDM Conclusion

SiPM Array Multiplexing (SAM)

Nathaniel Kaneshige1 and Nikki Rousslang1

1University of Hawaii at Manoa

7 December 2018

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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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

FDM Simulation

Figure: SPICE FDM circuit. Anode pulses were modeled by a differentiated 1 kHz square wave.

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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

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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Introduction Background Results CDM Results FDM Conclusion

Op-Amp: OPA847

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Introduction Background Results CDM Results FDM Conclusion

Op-Amp: LM6171

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