Avalanche Photodiode Pixel Gating to Prevent False Counting
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Solution Overview
Problem
Avalanche photodiode pixel matrices face challenges in securely disabling individual pixels to prevent cross-talk and compromised counting in shared counter subsets, particularly due to process defectivities that can leave pixels permanently enabled, impacting the entire sub-area.
Innovation Solution
Incorporating a transistor controlled by an enable signal to couple the avalanche photodiode to a substrate voltage and an output circuit that provides a pixel output signal when enabled and blocks it when disabled, with an output AND gate ensuring correct signal integration by the counter, even in cases of damaged enable/disable functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If pixels are divided into subsets coupled to common counters, then the device complexity is reduced, but the reliability of pixel disabling is compromised due to process defectivities
Solution Approach 1:
The pixel is segmented into functionally independent parts: a transistor for coupling/disconnecting the photodiode, and an output circuit with AND gate for signal control. This segmentation allows independent control of each function, ensuring that even if one part fails, the other can maintain proper operation and prevent false counting.
Solution Approach 2:
The output circuit includes an AND gate that receives both the pixel signal and enable signal as inputs. This redundant control mechanism is built in beforehand to cushion against process defectivities that might leave pixels permanently enabled, ensuring that the counter only receives valid signals when both conditions are met.
2Reliability
If a transistor is added to control pixel enabling, then the reliability of pixel disabling is improved, but the device complexity increases
Solution Approach 1:
The transistor serves multiple functions: it acts as a switch to connect or disconnect the photodiode from the substrate voltage, and simultaneously controls the enabling/disabling of the pixel output. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while maintaining improved reliability.
Solution Approach 2:
The enable signal control is merged into the existing pixel circuitry by integrating the transistor control mechanism with the output circuit's AND gate. This merging allows the enable signal to simultaneously control both the photodiode coupling and the output signal generation, achieving reliable pixel disabling without proportionally increasing device complexity.
3Measurement precision
If the output circuit is controlled by the enable signal, then the accuracy of discharge counting is improved, but the energy consumption increases
Solution Approach 1:
The output circuit is controlled to operate periodically based on the enable signal, which is activated only during specific time windows when photon detection is required. This periodic operation ensures accurate discharge counting only when needed, while allowing the circuit to remain in a low-power state during intervals when counting is not required, thereby balancing measurement precision with energy consumption.
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 effectively disables pixels and prevents false counting, enhancing robustness against process defectivity without adding complex circuits, ensuring accurate operation and efficient energy use.
Implementation Method 1
A SPAD, like an APD, exploits the photon-triggered avalanche current of a reverse biased p-n junction to detect an incident radiation
Implementation Method 2
In a SPAD, a single photogenerated carrier can trigger an avalanche in the depleted zone by impact ionization effect
Implementation Method 3
a transistor adapted to be controlled by an enable signal having a first state for controlling the enabling of the pixel and a second state for controlling the disabling of the pixel, the transistor being configured to couple an avalanche photodiode of the pixel to a node of application of a substrate voltage when the enable signal is in the first state
Implementation Method 4
an output circuit adapted to be controlled by the enable signal and configured to provide a pixel output signal when the enable signal is in the first state and to block the pixel output signal when the enable signal is in the second state
Data Source
AI summary
The present disclosure relates to an avalanche photodiode pixel including: a transistor adapted to be controlled by an enable signal having a first state for controlling the enabling of the pixel and a second state for controlling the disabling of the pixel, the transistor being configured to couple an avalanche photodiode of the pixel to a node of application of a substrate voltage when the enable signal is in the first state; and an output circuit adapted to be controlled by the enable signal and configured to provide a pixel output signal when the enable signal is in the first state and to block the pixel output signal when the enable signal is in the second state.