Avalanche Photodiode Pixel with Threshold-Based Signal Selection
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Solution Overview
Problem
Existing photon counting systems using avalanche photodiodes require complex signal processing due to the need for characteristic curves based on multiple signal outputs, which complicates the detection of weak light at a single photon level.
Innovation Solution
A photoelectric conversion apparatus with a pixel configuration that includes both high-sensitivity and low-sensitivity avalanche photodiodes, where a counter circuit counts signals from each diode and processes them differently based on threshold values, simplifying the signal processing by selecting the appropriate count value for image formation based on sensitivity ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple avalanche photodiodes with different sensitivity are used to expand dynamic range, then measurement precision is improved, but device complexity increases due to complicated signal processing requirements
Solution Approach 1:
The pixel is divided into multiple avalanche photodiodes with different sensitivity characteristics (first APD with higher sensitivity, second APD with lower sensitivity). Each APD independently counts photons in its optimal range, and the counter circuit selects appropriate count values based on saturation detection, avoiding complex characteristic curve calculations while expanding the measurable dynamic range.
Solution Approach 2:
A counter circuit acts as an intermediary between the multiple APDs and the output, automatically selecting count values from different APDs based on saturation detection. This intermediary handles the complexity of multi-signal processing internally, presenting a simplified output to external systems while maintaining high measurement precision across different light intensities.
2Measurement precision
If multiple signal outputs are used to obtain characteristic curves, then measurement precision is improved, but ease of operation deteriorates due to complex signal processing procedures
Solution Approach 1:
The counter circuit automatically performs saturation detection and selects appropriate count values from different APDs without requiring external intervention for characteristic curve calculations. The system self-regulates by detecting when each APD saturates and switching to the appropriate APD's count data, simplifying operation while maintaining high luminance detection precision across varying light conditions.
3Measurement precision
If high sensitivity avalanche photodiodes are used to detect weak light, then measurement precision is improved, but reliability deteriorates due to counter circuit saturation in brighter conditions
Solution Approach 1:
The system changes the operational parameter (which APD's count value is used) based on light intensity conditions. The counter circuit detects saturation in the first APD (higher sensitivity) and switches to using count values from the second APD (lower sensitivity), thereby maintaining reliable detection across the full dynamic range from weak to bright light conditions.
Solution Approach 2:
The counter circuit dynamically selects between count values from different APDs based on real-time saturation detection. This dynamic switching ensures that the system always uses the most appropriate sensor output for current lighting conditions, maintaining high reliability whether detecting weak light with the first APD or brighter light with the second APD.
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
This approach simplifies signal processing, reduces power consumption, and expands the dynamic range by preventing counter circuit saturation, enabling accurate photon counting in varying light conditions while maintaining linearity.
Implementation Method 1
Using the avalanche multiplication phenomenon generated by an intense electric field induced in a pn junction of a semiconductor, the APD amplifies about several times to a million times the amount of signal charges excited by photons.
Implementation Method 2
the amount of signal charges excited by photons
Data Source
AI summary
A photoelectric conversion apparatus includes a pixel and a counter circuit. The pixel includes a first avalanche photodiode and a second avalanche photodiode having different sensitivity to light. The counter circuit is configured to count a first signal based on charges generated in the first avalanche photodiode, and a second signal based on charges generated in the second avalanche photodiode. Processing on the count value is different between a case where a count value output from the counter circuit is larger than a threshold value and a case where the count value output from the counter circuit is smaller than the threshold value.