Image Sensor Counter Reset for Photon Counting Saturation
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Solution Overview
Problem
Image sensors using the photon counting method struggle to achieve favorable gradation in images, especially in environments with poor light, due to noise sensitivity and saturation issues.
Innovation Solution
An image sensor design that includes pixels generating pulses corresponding to photon incidence, counters to count these pulses, and a detector to reset counters when a threshold is reached, allowing for effective signal processing and addition of count values to prevent saturation and enhance image gradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photon counting method is used to improve noise resistance and image quality in low-light environments, then the image sensor can obtain good quality images with fewer photons, but the counters may become saturated and fail to provide favorable gradation in the resulting image
Solution Approach 1:
The pixel array is divided into multiple blocks, and each block has its own counter that independently counts photons. This segmentation allows different regions to be optimized for different lighting conditions, preventing saturation in bright regions while maintaining sensitivity in dark regions, thus resolving the contradiction between counting precision and gradation quality
Solution Approach 2:
The counter operates dynamically by resetting when a threshold is reached and using overflow bits to indicate saturation. This dynamic operation allows the system to adapt to varying light intensities across different regions, maintaining measurement precision while preventing reliable degradation from saturation
2Measurement precision
If the counter continuously counts photons without reset to maintain accuracy in low-light conditions, then the count precision is improved, but the counter becomes saturated in brighter conditions causing loss of gradation information
Solution Approach 1:
The counter is pre-configured with a threshold value and overflow detection capability. When the threshold is reached, the counter automatically resets and sets an overflow bit, preventing saturation before it occurs. This preliminary preparation ensures continuous accurate counting across varying light conditions without losing gradation information
Solution Approach 2:
The overflow bit acts as an intermediary between the counter and the readout circuitry. It signals when the counter has reached its maximum capacity, allowing the system to handle saturation gracefully by indicating which pixels require special processing, thus preserving gradation information that would otherwise be lost
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 the acquisition of images with favorable gradation by preventing counter saturation during exposure, improving image quality in various lighting conditions.
Implementation Method 1
CCD image sensors and CMOS image sensors convert a light beam that enters pixels during an exposure period to electric charges using photodiodes
Implementation Method 2
If a reverse bias voltage that is greater than a breakdown voltage is applied to the avalanche photodiode, a carrier that is generated due to incidence of a single photon causes avalanche multiplication, and a large current flows through this avalanche photodiode
Data Source
AI summary
An image sensor comprises: a plurality of pixels each including a sensor portion that generates pulses at a frequency corresponding to a frequency at which photons are incident; counters that count a number of pulses generated by each of the sensor portions; and a detector that detects whether or not a count value obtained by any of the counters has reached a first threshold. The counters are reset based on a result of detection performed by the detector.