1. A Temperature Compensated Power Supply for Silicon-Photomultiplier
Pankaj Rakshe
WAPP – 2014
20th December 2014

2. Acknowledgment Prof. S. R. Dugad (TIFR) Prof. P. D. Khandekar (VIIT)
Mr. Sergey Los (FNAL)
Mr. Raghunandan Shukla (TIFR)
Ms. Sarrah Lokhandwala (TIFR)
Prof. C. S. Garde (VIIT)
Prof. S. K. Gupta (TIFR)

3. Introduction
Sensitive Photo-detectors like PMT’s are of great interest to scientific community due to their use for examining processes that emit very low photon signal.
For example, In GRAPES-3 experiment PMT’s are used to detect scintillation light from wavelength shifting fibres.

4. Photo-Multiplier Tube (PMT)
Gain ~ 106
Response time ~ 2 ns
Size : Dia 2”, Length 6”
Operating Voltage ~ 2000 V
Quantum Efficiency < 20 %
Affected by Magnetic fields
Expensive !

5. Silicon Photo-Multiplier (SiPM)
Compact Device
Operating voltage (30-120V)
Resolution - Single photon detection
Response time – ~100 ps
High gain
High Quantum Efficiency – 90%
High Photon Detection Efficiency – 60%
Immunity to Magnetic Field
1-3 mm
1-3 mm

6. SiPM
SiPM is a 2-D array of Avalanche Photo Diode’s (APD’s) , all resistively coupled together.
SiPM is generally biased above its breakdown voltage , called as Geiger mode.
Each pixel (APD) acts as a binary device, indicating presence or absence of photon. Device as whole gives analog signal indicating number of pixels fired.
Typical size of each APD (pixel) is 50 µm × 50 µm and a typical gain of ~ 106

7. Limitations of SiPM Dark Counts After Pulsing Cross-Talk
Thermally Generated Carriers will give signal that appears as genuine photon signal
After Pulsing
Carrier Trapping and Delayed Release
Cross-Talk
Pixel Firing Due to Photon Detection in Adjacent Pixel
Temperature Dependence of Breakdown Voltage
SiPM Gain is Affected by Changes in Applied Over-Voltage
(Applied Voltage – Breakdown Voltage)

8. SiPM Temperature Dependence
Geiger mode: above breakdown
VS = VBR + Over-Voltage
Gain dependant on amount of Over-voltage applied
But, Breakdown Voltage is dependent on temperature
Effectively, gain changes by 3-5%/˚C
Over-Voltage should be constant for constant gain
𝑽 𝑺 𝑻 = 𝑽 𝑩𝑹 𝑻 +𝑶𝒗𝒆𝒓 𝑽𝒐𝒍𝒕𝒂𝒈𝒆
* Bajarang Sutar
* S. R. Dugad and K. C. Ravindran

9. Solutions to Temperature Dependency
Constant Temperature
Indoor Applications - applicable
Temperature control of detectors in outdoor environment is not possible e.g. GRAPES-3 experiment containing detectors in large area outdoor field of about m2 with temperature variations ˚C
Temperature Dependant Biasing Conditions
The Bias Voltage of SiPM can be controlled for changing the operating point
Temperature dependent Power Supply that will keep over-voltage constant (i.e. Gain constant)
Two solutions to Gain stability
Constant temperature : possible for indoor application
But for outdoor applications: biasing change is option

10. Approaches To Temperature Compensation
Method Used
Author
Year
Remarks
Limitations
Dark Current Control
Miyomoto et al.
2009
Dark Current and Temperature relation approximated to exponential function and use of Thermistor (similar relation) for compensation
Uses Expensive Commercial Power Supply
Limited to one/two channels
External control required for temperature compensation
Li et al.
2012
Dark current and Bias Voltage relation used for designing the voltage controlled current sink that changes bias condition
Bias Voltage Control
Bencardino et al.
Use of Temp. to voltage converter and a Op-amp based circuit for changing the bias return potential w.r.t. temperature variations
Licciulli et al.
2013
Blind SiPM used as a temperature sensor and amplitude of Dark pulses of Blind SiPM is maintained constant using Op-amp based feedback circuit for constant gain of other SiPM in parallel
Gil et al.
2011
External Input of the power supply is controlled by a micro-controller based system to change the output voltage w.r.t. temp.
Dorosz et al.
LabVIEW based feedback system for controlling the power supply output
Explain the approaches used till now
Commercial power supply is used. --- costly, single channel, no temperature compensation provision, high current (not necessary)
SiPM is in still research stage. New structures are coming everyday.
Hence only one or two channels are sufficient for purpose of research.
But if one needs to replace the PMT with SiPM, then for large scale experiment (~1000 detectors), mutiple commercial power supplies are not an option.
Very costly and not feasible (3.5 Lacs cost) Hence need of multichannel power supply with temperature compensation at low cost

11. Specifications Sr. No. Parameter Value 1. Output Voltage 0 to 100V 2.
Temperature Reading Resolution
0.1 ˚C 3.
Temperature Compensation Factor
10 to 100 mV/˚C 4.
Number of Channels 8 5.
Output Voltage Resolution
10 mV 6.
Maximum Current Limit per Channel
100 µA 7.
Full Scale Leakage Current per Channel
40 µA

12. Block Diagram High Voltage Generation (Voltage Multiplier Chain) PC
USB
Control Unit (Micro-controller)
Voltage Regulation Scheme
Temperature Sensors
DAC
Divided into following parts:
High Voltage generation
High Voltage Regulation
Control Unit: microcontroller and PC
Current Sense
Current Sense
SiPM

13. Prototype Power Supply (SiPM-PPS-v1)

14. Features of SiPM Power Supply
Programmable Output Voltage ( V) with resolution of ~12 mV
Programmable Temperature Compensation Factor (~12 – 100 mV/˚C)
In-built Data Acquisition System for recording Temperature and Leakage Current via USB

15. Ripple = 5 mVP-P 0.04113% for 10% change in line voltage
No load to Full load (100uA) regulation %
Ripple = 5 mVP-P
Stable within 10 mV for 0 – 100 V

16. Compensation Algorithm Verification
Comp. factor = 240 mV/˚C
Comp. Factor = (0.029x2-1.4x) /˚C

17. SiPM Experimental Setup

18. SiPM Test: Without Compensation
Gain Variation of about 4 %/˚C

19. SiPM Test: With Compensation
Gain Variation of 0.8 %

20. In Conclusion Without compensation gain variation nearly 4 %/˚C
With compensation gain variation %/˚C
Output Ripple of 5 mV with the Resolution of 12.5 mV in 100 V with temperature correction at each 0.2 ˚C change

21. Compared to Keithley 6487 Unit
SiPM Programmable Power Supply
Temperature Compensation Feature
Small Size and Light Weight (portable)
Multi-channel (8/16 channels)
Cost – Inexpensive !!!
(₹ 750/channel) which is 400 times less
Voltage Source and Pico-ammeter

22. SiPM-PPS-v2 Number of channels = 16 Better output resolution = 6.25 mV
DAC resolution = 14 bits
Better current sensing resol. = 1 nA
ADC resolution = 16 bits
Provision for expandability
I2C for multiple boards

23. Specifications Comparison
Sr. No.
Parameter
Required Value
Prototype Board
SiPM_PPS v2 1.
Output Voltage
0 to 100V
0 to 100 V 2.
Number of Channels 8 16 3.
Output Voltage Resolution
10 mV
12.5 mV
6.25 mV 4.
Maximum Current Limit per Channel
100 µA 5.
Full Scale Leakage Current per Channel
40 µA
35 µA 6.
Temperature Reading Resolution
0.1 ˚C 7.
Temperature Compensation Factor
12.5 to 100 mV/˚C
6.25 to 100 mV/˚C

24. Summary
SiPM has some outstanding features that in some respect could replace PMT in near future.
Newer versions of SiPM are being developed to overcome its limitations.
The temperature dependence is one of the major limitation preventing the use of SiPM in outdoor applications. The programmable temperature compensated power supply is useful for operating the SiPM in different environmental conditions.