Photon Counting Image Sensor Pulse Correction Circuit
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Solution Overview
Problem
Photon counting-type image sensors face accuracy issues due to multiple pulse signals combining into a single signal when photons are incident at high frequencies, leading to undercounting in bright environments.
Innovation Solution
The implementation of a correction circuit that calculates a correction coefficient based on pulse signal widths and generation frequencies to accurately count incident photons, and an exposure control circuit that adjusts exposure settings to mitigate undercounting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If photon counting is performed in bright environments with high photon incident frequency, then the image sensor can capture more light information, but multiple pulse signals combine into a single signal resulting in undercounting and reduced measurement precision
Solution Approach 1:
The patent applies preliminary action by extending the pulse width of avalanche multiplication signals before they are input to counter circuits. This is achieved by adjusting the potential applied to the light-receiving element during the avalanche multiplication process, thereby lengthening the pulse duration. The extended pulse width ensures that subsequent photons incident during the original short pulse period are detected as separate events, preventing signal combination and maintaining accurate photon counting in high-light conditions.
2Measurement precision
If the pulse width of avalanche multiplication signals is extended to prevent signal combination, then measurement precision improves, but the duration of each signal processing operation increases reducing productivity
Solution Approach 1:
The patent applies dynamics by making the pulse width extension adjustable rather than fixed. The control circuit can dynamically adjust the potential applied to the light-receiving element based on incident light conditions, thereby adapting the pulse width to match the photon incident frequency. This dynamic adjustment allows the system to maintain high measurement precision when needed while optimizing productivity under different lighting conditions.
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 the accuracy of photon counting by correcting for pulse signal overlap and adjusting exposure settings, resulting in improved image quality and reliability in high-light conditions.
Implementation Method 1
By operating the APD with a reverse-bias voltage greater than the breakdown voltage (that is, in Geiger mode), avalanche multiplication can be produced in response to a photon being incident.
Implementation Method 2
an optical image can be converted into digital data without performing A/D conversion by using light-receiving elements capable of detecting individual photons
Data Source
AI summary
An image capturing apparatus comprises a plurality of light-receiving circuits, each outputting a pulse signal in response to a photon being incident; a plurality of counter circuits that count the respective pulse signals output by the plurality of light-receiving circuits; and a correction circuit that corrects counts from the plurality of counter circuits and outputs the corrected counts as image data. The correction circuit calculates a correction coefficient on the basis of counts obtained by the plurality of counter circuits in a state where pulse widths of the pulse signals differ or under conditions where generation frequencies of the pulse signals differ, and performs the correction using the correction coefficient.