SPAD Quenching Circuit for Reduced Dead Time
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Solution Overview
Problem
Existing single photon avalanche diode (SPAD) systems face challenges in compactness and reduced dead time between successive photon detections, limiting their performance in applications such as image sensors.
Innovation Solution
A device comprising a SPAD with an integrated extinguishing circuit that includes a resistor, a MOS transistor switch, and control circuits to manage the avalanche quenching process, allowing for reduced dead time and compact design by controlling the switch's opening and closing based on pulse duration and slope adjustment potentials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a conventional quench circuit with high resistance value is used to extend the quenching time, then the extinction time is improved, but the dead time between detections increases and the system size increases
Solution Approach 1:
The patent applies dynamics by making the quenching process controllable and adaptive. The control circuit dynamically adjusts the quenching time based on the detected avalanche duration, optimizing the balance between complete extinction and minimal dead time. This allows the system to adapt the quenching duration to actual detection needs rather than using a fixed high resistance value.
Solution Approach 2:
The patent changes the resistance parameter dynamically during operation. Instead of using a fixed high resistance value, the control circuit adjusts the resistance value based on the avalanche characteristics, allowing optimal quenching performance with minimized dead time. This parameter adaptation resolves the contradiction between extinction completeness and detection speed.
2Duration of action of stationary object
If a conventional quench circuit with high resistance value is used to extend the quenching time, then the extinction time is improved, but the system size and power consumption increase
Solution Approach 1:
The patent replaces static high-resistance components with dynamic control circuitry that adjusts resistance values as needed. This allows the system to achieve extended quenching times only when necessary, reducing the need for permanently large resistance values and associated circuit complexity.
Solution Approach 2:
The patent changes the resistance parameter from a fixed high value to a dynamically adjustable value. The control circuit modifies the resistance based on detection requirements, allowing the system to maintain compact dimensions while achieving adequate extinction times through intelligent parameter management rather than hardware scaling.
3Loss of time
If the switch closes quickly after avalanche detection, then the dead time is reduced, but the quenching may be incomplete leading to afterpulsing
Solution Approach 1:
The patent implements feedback control where the control circuit monitors the avalanche detection signal and uses this information to determine when to close the switch. The quenching process is controlled based on feedback from the actual avalanche characteristics, ensuring complete extinction while minimizing dead time. This feedback mechanism prevents both incomplete quenching and excessive dead time.
Solution Approach 2:
The patent makes the switch closing timing dynamic rather than fixed. The control circuit adjusts the switch closing time based on the detected avalanche duration and intensity, optimizing the balance between complete quenching and minimal dead time for each detection event. This dynamic adaptation resolves the contradiction between quenching completeness and detection speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a compact and efficient SPAD system with reduced dead time between detections, enhancing the dynamic performance of image sensors by maintaining the same extinction time while minimizing the resistance value, thus reducing the overall system size and power consumption.
Implementation Method 1
a switch, preferably a MOS transistor, to a second node configured to receive a reference potential; a control circuit configured to control an opening of the switch in response to the start of said pulse and to control a closing of the switch in response to the end of said pulse
Implementation Method 2
a photodiode of which a first terminal is connected by a resistor to a first node configured to receive a high supply potential
Implementation Method 3
a SPAD diode or photodiode is reverse biased to a voltage higher (in absolute value) than its avalanche voltage... when a single photon reaches the diode, the free carriers photogenerated from this single photon are sufficiently accelerated by the electric field present at the diode junction to create additional free carriers. The diode then enters avalanche mode and a current flows through the diode
Implementation Method 4
a reading circuit configured to provide a pulse when the diode enters avalanche mode
Data Source
Figure 1
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AI summary
This description relates to a device (1) comprising: a photodiode (100) having a first terminal connected by a resistor (R) to a first node (104) configured to receive a high supply potential (VH) and having a second terminal connected by a switch (102) to a second node (106) configured to receive a reference potential (GND); a readout circuit (110) configured to provide a pulse (OUT) when the diode (100) enters avalanche; and a control circuit (126) configured to control an opening of the switch (102) in response to the beginning of said pulse (OUT) and to control a closing of the switch in response to the end of said pulse (OUT).