Image Sensor ADC Slope Ratio Correction
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Solution Overview
Problem
Existing image capturing apparatuses face challenges in maintaining tone accuracy and reducing signal level gaps due to fluctuations in gain error and offset error correction values, particularly with increased pixel density and framerate, leading to unnatural video artifacts.
Innovation Solution
An image capturing apparatus with an analog-digital conversion unit using reference signals with different slopes, a voltage supply unit for varying output levels, and a calculation unit that calculates correction coefficients on a frame-by-frame basis, incorporating a filtering process for offset correction values to stabilize signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If correction values are calculated on a frame-by-frame basis to adapt to temperature changes and driving method switches, then adaptability improves, but signal level gaps and unnatural video artifacts occur due to fluctuations in correction values
Solution Approach 1:
The patent applies preliminary action by calculating correction values in advance for multiple driving methods and storing them in a lookup table. When a driving method switch occurs, the pre-calculated correction values are immediately applied without fluctuation, preventing signal level gaps while maintaining adaptability to different operating conditions
Solution Approach 2:
The patent implements beforehand cushioning by pre-computing and storing correction values for various temperature conditions and driving methods. This cushioning of pre-calculated values prevents sudden fluctuations when conditions change, ensuring smooth transitions without visible artifacts
2Manufacturing precision
If multiple AD converter circuits are used to expand dynamic range and improve S/N ratio, then image quality improves, but device complexity increases
Solution Approach 1:
The patent applies universality by designing a single AD converter circuit that can operate in multiple conversion modes (first conversion mode and second conversion mode). This multi-functional approach allows the circuit to expand dynamic range and improve S/N ratio without requiring separate dedicated circuits for each function, thereby controlling device complexity
Solution Approach 2:
The patent implements dynamics by making the AD converter circuit reconfigurable between different conversion modes based on signal conditions. The circuit dynamically switches between first and second conversion modes to optimize performance for different signal levels, achieving enhanced tone accuracy and dynamic range with a single adaptable circuit rather than multiple fixed circuits
Data Source
AI summary
Analog signals having different output levels are converted into a plurality of digital signals using a plurality of reference signals having mutually different slopes, and a ratio of the plurality of different slopes and an offset amount are calculated on the basis of the digital signals. Then, on a frame-by-frame basis, a correction coefficient for correcting digital signals obtained by carrying out analog-digital conversion on analog signals output from a pixel section of an image sensor is calculated on the basis of the ratio of slopes and the offset amount. The correction coefficient includes the ratio of slopes and an offset correction value, and the offset correction value is obtained by carrying out a filtering process that performs weighted adding of the offset amount and the offset correction value calculated in a previous frame using a cyclic coefficient.