CMOS Image Sensor AD Conversion and Timing Correction
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Solution Overview
Problem
Conventional CMOS linear image sensors face challenges in reducing size while maintaining image quality due to the need for high capacitance analog memory for signal holding and sequential exposure methods, which can lead to color shifts and degraded image quality.
Innovation Solution
A photoelectric conversion element with light receiving elements arranged in both main-scanning and sub-scanning directions, accumulating electric charge at different timings, and AD conversion units converting analog signals into digital signals for each group of pixels, with a correction unit to reduce timing differences, allowing for a one-shot exposure method that omits the need for analog memory and prevents color shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CMOS linear image sensors use sequential exposure method with analog memory for signal holding, then image quality can be maintained, but the size of the sensor increases due to required capacitances
Solution Approach 1:
The patent extracts and eliminates the analog memory component from the conventional sensor architecture. By using a correction unit that processes signals after AD conversion rather than holding analog signals in memory, the patent removes the need for large capacitances and reduces sensor size while maintaining image quality through post-conversion correction.
Solution Approach 2:
The patent performs AD conversion before the correction process rather than holding analog signals for sequential processing. This preliminary action of converting to digital format early in the process eliminates the need for analog memory holding, reducing sensor size while preserving image quality through subsequent digital correction.
2Productivity
If conventional CMOS linear image sensors use sequential exposure method, then processing can be done per-column, but color shift occurs and image quality degrades
Solution Approach 1:
The patent performs AD conversion in advance for each pixel before the correction process begins. This preliminary conversion to digital format allows subsequent correction operations to be performed without time delays that would cause color shifts, maintaining both processing efficiency and image quality.
Solution Approach 2:
The correction unit operates as a feedback mechanism that adjusts and corrects the converted signals to eliminate color shifts and quality degradations. By feeding back the corrected signals after AD conversion, the patent maintains image quality while preserving the processing speed benefits of sequential column processing.
3Duration of action of stationary object
If high-capacity analog memory is used for signal holding in conventional sensors, then signal holding time is extended, but manufacturing cost increases
Solution Approach 1:
The patent replaces the mechanical/analog memory holding system with a digital correction system. Instead of using large-capacity analog memory to hold signals for extended periods, the patent converts signals to digital format early and uses a correction unit to maintain signal integrity, reducing manufacturing complexity and cost.
Solution Approach 2:
The patent extracts and removes the high-capacity analog memory component from the system. By eliminating the need for extended analog signal holding through the use of early AD conversion and post-conversion correction, the patent reduces manufacturing cost and complexity while maintaining functional performance.
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 enables a reduction in sensor size, prevents color shifts, and maintains image quality equivalent to one-shot exposure methods, while avoiding the increased costs and size issues associated with high-capacity analog memory.
Implementation Method 1
a plurality of light receiving elements that are arranged in a main-scanning direction, are arranged in a sub-scanning direction according to colors of light to be received, and accumulates electric charge due to light exposure
Data Source
AI summary
A photoelectric conversion element includes: a plurality of light receiving elements that are arranged in a main-scanning direction, are arranged in a sub-scanning direction according to colors of light to be received, and accumulates electric charge due to light exposure; and a plurality of AD conversion units that convert analog signals that indicate quantities of electric charge accumulated in the light receiving elements into digital signals are provide for each of groups each consisting of a predetermined number of pixels corresponding to the light receiving elements arranged in the sub-scanning direction. The AD conversion units convert the analog signals into the digital signals in an order in which the light receiving elements in the group are exposed to light. The light receiving elements constitute a correction unit that performs correction so as to reduce a difference relating to the timings in the sub-scanning direction.