1FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

SINGLE-PHOTON AVALANCHE DIODE

DEMYSTIFIED

Fabrizio Guerrieri

2FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

LET’S CONSIDER THE TYPICAL PN JUNCTION I-V CHARACTERISTICS…

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SPAD DEMYSTIFIED

AVALANCHE CURRENT(JUNCTION BREAKDOWN)

DIRECT CURRENT

INVERSE CURRENT DUE TO THERMAL GENERATION IN THE DEPLETED ZONE

PN JUNCTION

4FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

AVALANCHE CURRENT(JUNCTION BREAKDOWN)

DIRECT CURRENT

INVERSE CURRENT DUE TO THERMAL GENERATION IN THE DEPLETED ZONE

PN JUNCTION

THE SPAD WORKS HERE

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SPAD DEMYSTIFIED

HOW DOES A SPAD WORK?

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SPAD DEMYSTIFIED

WITH A REVERSE VOLTAGE BELOWBREAKDOWN NO CURRENT FLOWS

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

AT THE BEGINNING,

NO CURRENT FLOWS EVEN WITH A REVERSE VOLTAGE ABOVE BREAKDOWN

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

AN AVALANCHE CURRENT IS TRIGGERED BY THEFIRST PHOTON GENERATING AN ELECTRON/HOLE

PAIR IN THE DEPLETED REGION

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

THE BRANCHED CHARACTERISTIC OF A SPAD

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SPAD DEMYSTIFIED

OBVIOUSLY A FRONT-END CIRCUIT (WE CALL ITQUENCHING CIRCUIT) IS NEEDED IN ORDER TO:

1. ENABLE THE SPAD RISING THE REVERSE VOLTAGE ABOVE BREAKDOWN

2. DETECT THE AVALANCHE CURRENT

3. QUENCH THE AVALANCHE CURRENT LOWERING THE REVERSE VOLTAGE BELOW BREAKDOWN

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SPAD DEMYSTIFIED

TWO MAIN ADVANTAGES

1. SINGLE-PHOTON LEVEL SENSITIVITY

2. ELECTRONIC PULSE’S RISING EDGE WITH VERY LOW TIME JITTER(30 ps OR BETTER)

HOW CAN I USE A SPAD?

15FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

1. TIME CORRELATED SINGLE-PHOTON COUNTING (TCSPC)(WE INFORMALLY CALL IT “PHOTON TIMING”)

2. TIME OF FLIGHT (TOF)

3. PHOTON-COUNTING

HOW CAN I USE A SPAD?

16FABRIZIO GUERRIERI

SPAD DEMYSTIFIED

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

After somelaser pulses…

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

After somelaser pulses…

After morelaser pulses…

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

After somelaser pulses…

After morelaser pulses…

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

After somelaser pulses…

After morelaser pulses…

After MANYlaser pulses…

1 - PHOTON TIMING

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SPAD DEMYSTIFIED

2 – TIME-OF-FLIGHT

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SPAD DEMYSTIFIED

2 – TIME-OF-FLIGHT

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SPAD DEMYSTIFIED

2 – TIME-OF-FLIGHT

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SPAD DEMYSTIFIED

Laser pulse’s shapeEstimated TOF

2 – TIME-OF-FLIGHT

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SPAD DEMYSTIFIED

3 - PHOTON COUNTING

THE QUENCHING CIRCUIT DELIVERS AN OUTPUT PULSE EVERYTIME THE SPAD DETECTS A PHOTON

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SPAD DEMYSTIFIED

3 - PHOTON COUNTING

IN OUR ARRAYS EVERY PIXEL CONTAINS EVERYTHING TO DO PHOTON-COUNTING

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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SPAD DEMYSTIFIED

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