SPAD Pixel Active Quenching and Reset for Low EPP
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Solution Overview
Problem
Existing single photon avalanche diode (SPAD) circuits suffer from low quench efficiency, leading to dual voltage peaks, increased recharge time, and limitations such as afterpulsing, count losses, and variations in pulse amplitude, particularly in applications like time-of-flight ranging and LIDAR.
Innovation Solution
Incorporation of active quenching and active reset techniques in SPAD pixel circuits, utilizing cascode transistors, passive quenching circuits, and negative voltage to rapidly quench and reset SPADs, minimizing charge flow and afterpulsing, and optimizing quenching time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive quenching circuits with large quenching resistance are used, then quenching efficiency is improved, but recharge time increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor during the stable period before avalanche occurs. When avalanche happens, the capacitor is already charged and can immediately discharge through the SPAD to quench the avalanche, eliminating the need for slow passive charging through large resistance. This resolves the contradiction by preparing the quenching energy in advance.
Solution Approach 2:
The patent implements periodic action through the oscillating circuit that periodically charges and discharges the capacitor in sync with the avalanche events. The circuit operates in periodic cycles: charging during stable periods, discharging during avalanche events. This periodic operation ensures the capacitor is always ready to provide rapid quenching current when needed, achieving both high quenching efficiency and fast recharge time.
2Adaptability or versatility
If fully depleted SPADs are used, then suitability for near infrared applications is improved, but quench efficiency decreases
Solution Approach 1:
The patent introduces an intermediary element - the capacitor - between the power supply and the SPAD cathode. This capacitor acts as a buffer that can rapidly discharge to quench the avalanche, providing the necessary quenching current without requiring large series resistance. This intermediary enables fully depleted SPADs to maintain both their near-infrared suitability and high quenching efficiency.
3Reliability
If large quenching resistance is used, then charge carrier flushing is improved, but pulse amplitude variations worsen
Solution Approach 1:
The patent changes the parameter of quenching current delivery from resistance-limited (passive) to capacitor-driven (active). By using a capacitor with appropriate capacitance value, the quenching current pulse can be precisely controlled in duration and magnitude. This parameter change allows complete charge carrier flushing while maintaining consistent pulse amplitude, as the capacitor discharge is less sensitive to variations in SPAD characteristics compared to resistance-based quenching.
4Reliability
If passive quenching circuits are used, then quenching capability is improved, but control over reset time is lost
Solution Approach 1:
The patent implements feedback by monitoring the avalanche event and using this information to control the discharge of the capacitor. The control circuit detects the avalanche occurrence and triggers the capacitor discharge at the precise moment needed, providing active control over the quenching process. This feedback mechanism enables precise control of reset time while maintaining effective quenching capability.
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
Enhances SPAD performance by reducing energy per pulse, increasing maximum count rates, and improving reliability through faster quenching and reset times, thereby enhancing detection efficiency.
Implementation Method 1
When a photon-generated carrier (via the internal photoelectric effect) is injected into the depletion region of the PN junction, a self-sustaining avalanche is caused
Implementation Method 2
a self-sustaining avalanche is caused, and detection of this avalanche can be used to indicate detection of the photon that generated the carrier
Data Source
AI summary
Disclosed herein is a single photon avalanche diode (SPAD) pixel circuit, including a SPAD having an anode coupled to a negative voltage and a cathode and a cascode transistor having a drain coupled to the cathode of the SPAD, a gate controlled by a cascode control signal, and a source. A readout circuit is coupled to the source of the cascode transistor and configured to detect a voltage change at the source of the cascode transistor and generate a pulse indicating an occurrence of an avalanche event. An active quenching circuit is coupled to the cathode of the SPAD and configured to detect an onset of the avalanche event and pull the cathode of the SPAD to a negative voltage to quench the avalanche event.