CMOS Image Sensor AD Conversion Architecture for Wide Dynamic Range
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Solution Overview
Problem
CMOS image sensors face challenges in achieving a wide dynamic range without deteriorating picture quality, particularly due to increased chip size from field memory usage and the influence of leak current on sample-held data signals, which affects the dynamic range and resolution of captured images.
Innovation Solution
A solid-state image capturing apparatus with a pixel area and row selection section that uses multiple column signal lines and AD conversion circuits to simultaneously convert analog pixel signals of varying accumulation times into digital pixel values, avoiding the need for field memory and minimizing leak current impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If field memory is used to store image data for wide dynamic range, then the dynamic range is improved, but the chip size increases
Solution Approach 1:
The patent extracts the field memory component from the system and replaces it with a dual AD conversion circuit architecture. By removing the memory storage requirement and directly converting analog signals to digital values through multiple conversion circuits, the chip area is reduced while maintaining wide dynamic range capability through simultaneous short and long exposure processing.
Solution Approach 2:
The patent segments the AD conversion function into multiple independent conversion circuits, each handling different exposure times. This segmentation allows parallel processing of short and long exposure signals without requiring centralized memory storage, thereby achieving wide dynamic range without increasing chip size.
2Productivity
If data signals are sample-held for extended periods, then the processing capability is improved, but the influence of leak current increases
Solution Approach 1:
The patent performs preliminary AD conversion of analog pixel signals to digital values before any further processing or storage. By converting signals early in the pipeline, the system eliminates the need for prolonged analog signal holding, thereby preventing leak current from degrading signal quality while maintaining full processing capability.
Solution Approach 2:
The patent replaces the analog sample-and-hold mechanism with digital signal processing. Instead of holding analog signals in capacitors vulnerable to leak current, the system immediately converts signals to digital domain where values can be stored and processed without degradation from electrical leakage.
3Illumination intensity
If exposure time is adjusted for high brightness portions, then the high brightness signal level is improved, but the low brightness signals become saturated
Solution Approach 1:
The patent employs periodic alternation between short exposure and long exposure modes for different pixel rows. By cycling through different exposure times systematically, the system captures both bright and dark regions at appropriate signal levels, preventing saturation in bright areas while maintaining sufficient signal strength in dark areas.
Solution Approach 2:
The patent dynamically adjusts exposure time based on spatial position and brightness requirements. Different pixel rows use different exposure durations, with brighter regions using shorter exposures and darker regions using longer exposures. This dynamic adaptation allows optimal signal capture across the entire image without uniform exposure limitations.
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 allows for a wider dynamic range in captured images without increasing chip size and reduces the influence of leak current, enabling improved picture quality by simultaneously processing long and short time exposure analog pixel signals into digital pixel values.
Implementation Method 1
pixels for generating a signal charge by a photoelectric conversion on an incident light
Data Source
AI summary
A solid-state image capturing apparatus according to the present invention includes a pixel area in which pixels for generating a signal charge by a photoelectric conversion on an incident light are arranged in a two dimensional matrix; a row selection section for selecting each pixel row of the pixel area; a plurality of column signal lines, to which an analog pixel signal from each pixel of a pixel row selected by the row selection section is readout; and a signal processing circuit for generating a digital pixel value from the analog pixel signal of each pixel that is read out to each of the column signal lines, where the signal processing circuit includes at least two or more AD conversion circuits for simultaneously converting the analog pixel signal of each pixel of the selected pixel row into a digital pixel value.