CMOS Image Sensor Dual Holding Units for Global Shutter
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Solution Overview
Problem
Current CMOS image sensors face challenges in achieving a global electronic shutter operation without increasing pixel size or degrading image quality, as they require either large storage capacity in photoelectric conversion units or short accumulation periods that lead to image degradation and jerkiness.
Innovation Solution
The implementation of an image pickup apparatus with two holding units per pixel, where signal charge is alternately held and transferred between the units for each frame period, allowing simultaneous holding and reading of signal charge without increasing the storage capacity of the photoelectric conversion unit, and the use of an overflow transistor to adjust accumulation periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If signal charge corresponding to one frame is accumulated in the photoelectric conversion unit, then the storage capacity is sufficient, but the pixel size increases
Solution Approach 1:
The photoelectric conversion unit is divided into a first photoelectric conversion unit and a second photoelectric conversion unit. These units alternately accumulate signal charge for one frame period, allowing each unit to have reduced storage capacity while collectively maintaining sufficient capacity for one frame. This segmentation resolves the contradiction by distributing the storage burden across multiple smaller units.
2Speed
If the readout speed is not high, then the accumulation period is short, but image quality degrades and jerkiness occurs
Solution Approach 1:
Signal charge is accumulated in advance in the photoelectric conversion units during the accumulation period before readout begins. This preliminary accumulation ensures that sufficient signal charge is available for high-quality image capture even when readout speed is limited, preventing degradation and jerkiness by having the data ready before output.
3Quantity of substance
If signal charge is transferred sequentially from the photoelectric conversion unit to the holding unit, then the storage capacity of the photoelectric conversion unit is reduced, but the accumulation period becomes short causing information loss
Solution Approach 1:
The system uses multiple photoelectric conversion units (first and second units) that alternately accumulate signal charge while others are being read out. This segmentation allows continuous accumulation without interruption, eliminating information loss periods while keeping individual unit storage capacity reduced.
Solution Approach 2:
While one photoelectric conversion unit is having its signal charge read out to the holding unit, another unit simultaneously accumulates new signal charge. This continuous operation ensures that accumulation never stops, eliminating information loss periods and maintaining continuous useful action throughout the frame period.
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 configuration enables efficient accumulation and holding of signal charge, eliminating information loss periods and maintaining image quality without increasing pixel size, while allowing for dynamic adjustment of accumulation periods to handle varying light conditions.
Implementation Method 1
a photoelectric conversion unit that accumulates signal charge generated by photoelectric conversion of irradiated light
Data Source
AI summary
An image pickup apparatus according to the present invention includes a plurality of pixels arranged in rows and columns, and each of the pixels includes a photoelectric conversion unit that accumulates signal charge generated by photoelectric conversion of irradiated light, a first holding unit and a second holding unit that hold the signal charge transferred from the photoelectric conversion unit, and an output unit that outputs, to a column signal line, a signal based on an amount of the signal charge held by the first holding unit or the second holding unit. The first holding unit and the second holding unit alternately hold the signal charge generated in the photoelectric conversion unit for each frame period, and in a period in which the signal charge is not transferred from the photoelectric conversion unit, the first holding unit and the second holding unit output the signal charge to the output unit.