Passive Quenching SPAD Pixel With Second-Order Pulse Shaping
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Solution Overview
Problem
Existing single photon avalanche diode (SPAD) photodetectors face limitations in achieving high count rates in high light environments due to dead time constraints and the complexity of active reset circuits, which can lead to instability and reduced quantum efficiency.
Innovation Solution
A stacked die arrangement integrating a quench circuit, AC coupling element, filter component, and inverter within a pixel design, utilizing a second-order high pass filter to sharpen voltage pulses and enable high count rates in high light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a passive quenching circuit is used to simplify the circuit design, then the device complexity is reduced, but the maximum count rate is limited due to dead time constraints
Solution Approach 1:
The patent applies dynamics by making the quenching resistance variable rather than fixed. The quenching resistance is dynamically adjusted based on the detection rate and light conditions, allowing the system to optimize between dead time reduction and circuit simplicity. This dynamic adjustment enables high count rate operation without requiring complex active reset circuits.
Solution Approach 2:
The patent changes the resistance parameter of the quenching circuit adaptively. By varying the quenching resistance value based on operational conditions (detection rate, light intensity), the system achieves high count rate performance while maintaining circuit simplicity. This parameter change strategy allows the passive quenching circuit to overcome dead time limitations without adding complexity.
2Productivity
If an active reset circuit is used to reduce dead time and increase maximum count rate, then the productivity is improved, but the device complexity increases and quantum efficiency may be reduced
Solution Approach 1:
The patent extracts the essential function of active reset (dead time reduction) while removing the complex circuitry associated with it. By using a simplified passive quenching approach with variable resistance, the system achieves the same dead time reduction benefit without the complexity and quantum efficiency penalties of traditional active reset circuits.
Solution Approach 2:
The patent employs a simple, easily implementable passive quenching circuit that can be quickly adjusted, replacing complex active reset circuits. The variable resistance quenching mechanism provides sufficient performance improvement without the need for sophisticated active control circuitry, effectively using a simpler substitute to achieve the same functional goal.
3Productivity
If the quenching resistance is reduced to decrease dead time, then the maximum count rate is improved, but the voltage pulse amplitude may be reduced affecting detection accuracy
Solution Approach 1:
The patent dynamically adjusts the quenching resistance to maintain optimal voltage pulse amplitude while minimizing dead time. The resistance value is varied based on real-time detection conditions, ensuring that sufficient voltage pulses are generated for accurate detection even at high count rates. This dynamic optimization balances speed and accuracy requirements.
Solution Approach 2:
The patent prepares the quenching circuit by pre-configuring variable resistance elements that can be adjusted before high-speed operation begins. This preliminary setup allows the system to optimize the balance between quenching speed and pulse amplitude maintenance, ensuring detection accuracy is preserved while achieving high count rate 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
The pixel design allows for high count rate detection in high light environments by enhancing the detection of individual photo events, improving the detection capability in high light conditions.
Implementation Method 1
When a photon-generated carrier (via the internal photoelectric effect) is injected into the depletion region of the PN junction
Implementation Method 2
When a photon-generated carrier (via the internal photoelectric effect) is injected into the depletion region of the PN junction, a self-sustaining avalanche ensues
Implementation Method 3
The avalanche is stopped by lowering the reverse bias across the SPAD for a short time interval
Data Source
AI summary
An array of single photon avalanche diodes (SPADs) includes a plurality of pixels. Each pixel includes a SPAD having a cathode connected to a first intermediate node and an anode coupled to first negative voltage, a quench circuit connected between the first intermediate node and the low voltage supply node, an AC coupling element connected between the first intermediate node and a second intermediate node, a filter component connected between the high voltage node and the second intermediate node, and an inverter having its input connected to the second intermediate node and its output providing an output signal. A resistance associated with the quench circuit, a capacitance associated with the SPAD, a capacitance associated with the AC coupling element, and a resistance associated with the filter component form a variable second order filter.