Image Sensor Signal Correction for Dark Sun Reading Errors
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Solution Overview
Problem
Image sensors using differential reading circuits often experience a 'dark sun effect' when exposed to strong light, leading to reading errors due to discharge in floating diffusion nodes, which is traditionally addressed by adding a clamp circuit increasing manufacturing costs and circuit size.
Innovation Solution
An image sensor comprising a first and second pixel circuit, a readout circuit, and an image processing circuit that outputs digital sensing signals based on the voltages of the floating diffusion nodes. The image processing circuit automatically judges abnormal digital numbers to decide whether to keep the original value, set a pixel value, or reset the signal, effectively addressing the dark sun effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a clamp circuit is added to solve the dark sun effect, then the reading accuracy is improved, but the manufacturing cost increases and circuit size cannot be reduced
Solution Approach 1:
The harmful effect (dark sun effect) is extracted and detected separately through the image processing circuit, which identifies abnormal digital numbers without requiring additional hardware circuits in the pixel array. This separates the correction function from the sensing function, maintaining circuit simplicity while improving reading accuracy.
Solution Approach 2:
The image processing circuit provides feedback by judging whether digital numbers are abnormal and automatically correcting pixel values or resetting signals. This closed-loop feedback mechanism eliminates the need for complex preventive clamp circuits while ensuring accurate readings.
2Measurement precision
If a clamp circuit is added to solve the dark sun effect, then the reading accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The image processing circuit performs self-service by automatically detecting and correcting abnormal digital numbers caused by the dark sun effect. This self-correcting capability eliminates the need for additional clamp circuits, reducing manufacturing complexity and cost while maintaining high reading accuracy.
Solution Approach 2:
The system uses feedback mechanisms where the image processing circuit monitors digital numbers, identifies abnormalities, and automatically corrects pixel values or resets signals. This feedback-based correction replaces expensive hardware additions with software-based solutions, reducing manufacturing costs.
3Object-affected harmful factors
If the transfer transistors are not turned on during strong light, then the dark sun effect occurs, but adding a clamp circuit increases circuit complexity
Solution Approach 1:
The image processing circuit acts as an intermediary between the pixel array and the output, detecting and correcting dark sun effect artifacts without requiring additional circuits in the pixel array itself. This intermediary approach handles the harmful effect at the processing stage rather than adding complexity to the sensing stage.
Solution Approach 2:
The dark sun effect correction function is extracted from the pixel circuit and moved to the image processing circuit. This separation allows the pixel array to remain simple while the processing stage handles the harmful effect through digital number judgment and automatic correction.
Data Source
AI summary
An image sensor and an image sensing method are provided. A readout circuit outputs a first digital sensing signal according to a floating diffusion node voltage of a first pixel circuit reset after a reset stage and a floating diffusion node voltage of a second pixel circuit reset after the reset stage during a reset signal readout period. The readout circuit outputs a second digital sensing signal according to a sensing result of the first pixel circuit and the floating diffusion node voltage of the second pixel circuit reset after the same reset stage during a sensing signal readout period. The image processing circuit judges whether a digital number of at least one of the first digital sensing signal and the second digital sensing signal is abnormal to decide to keep an original digital number, directly set a pixel value, or reset the second digital sensing signal.