Overlapping Shutter Operations in CMOS Image Sensors
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Solution Overview
Problem
Current image sensors, particularly rolling-shutter CMOS image sensors, face challenges in reducing shutter noise and optimizing shutter operation efficiency, which affects image acquisition performance.
Innovation Solution
The implementation of a row driver that performs a preliminary shutter operation and a main shutter operation sequentially on different rows of a pixel array, overlapping these operations to minimize shutter noise and enhance performance by securing specific intervals for signal reset and read-out.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single shutter operation is performed on each row, then the shutter operation is simple, but shutter noise cannot be effectively reduced
Solution Approach 1:
The shutter operation is divided into two distinct segments: a preliminary shutter operation that resets accumulated charges before integration, and a main shutter operation that performs the actual shuttering during integration. This segmentation allows each operation to serve a specific function, effectively reducing shutter noise while maintaining operational clarity.
Solution Approach 2:
The preliminary shutter operation is performed before the main integration process to reset any accumulated charges in the photo detectors. By performing this preliminary action, the system ensures that the subsequent main shutter operation starts with a clean state, preventing noise from carryover charges.
2Object-affected harmful factors
If the shutter operation time is increased to reduce noise, then noise reduction is improved, but the scanning time for rows increases
Solution Approach 1:
The shutter operations are performed in periodic intervals: the preliminary shutter operation occurs at the beginning of each row scan to reset charges, followed by the main shutter operation during integration. This periodic structure ensures noise reduction without continuously extending the scanning time, as each operation is timed to occur only when necessary.
Solution Approach 2:
By performing the preliminary shutter operation at the start of each row scan before integration begins, the system resets charges in advance. This preliminary action prevents the need for extended shutter operation times during the main integration process, thereby reducing noise without increasing overall scanning time.
3Object-affected harmful factors
If the preliminary shutter operation and main shutter operation are performed on the same row, then the operation sequence is simple, but noise reduction effectiveness is reduced
Solution Approach 1:
The pixel array is divided into multiple rows, and the preliminary shutter operation on one row is overlapped with the main shutter operation on a different row. This spatial segmentation allows both operations to proceed simultaneously without interfering with each other, effectively reducing noise while managing operational complexity through row-based parallelism.
Solution Approach 2:
The operations are arranged in the row dimension rather than being sequential within a single row. By overlapping the preliminary shutter operation on row N with the main shutter operation on row N+1, the system utilizes the row dimension to achieve temporal overlap, effectively reducing noise without complicating the operation sequence within individual rows.
4Object-affected harmful factors
If overlapping operations on different rows are implemented, then noise reduction is enhanced, but the control complexity increases
Solution Approach 1:
The row driver controls are segmented into distinct signal lines for different operations: a first transfer control signal for the preliminary shutter operation and a second transfer control signal for the main shutter operation. This segmentation allows independent control of each operation, simplifying the management of overlapping operations across different rows despite the enhanced noise reduction capability.
Solution Approach 2:
The control complexity is managed by utilizing the row dimension for parallel operations. The row driver applies different control signals to different rows, allowing the preliminary shutter operation on one row to overlap with the main shutter operation on another row. This dimensional approach distributes control complexity across multiple rows rather than concentrating it in a single sequential control sequence.
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 reduces shutter noise and improves image sensor performance by efficiently eliminating accumulated charges and optimizing the time required for scanning rows, thereby enhancing image acquisition capabilities.
Implementation Method 1
Respective ones of the unit pixels may include a photo detector, a transfer transistor, a reset transistor, a sensing transistor and a selection transistor. The photo detector may convert the incident light to the electric signal
Data Source
AI summary
An image sensor can include a pixel array including a plurality of unit pixels and a row driver arranged in a matrix form that includes a plurality of rows and a plurality of columns. Respective ones of the unit pixels may convent an incident light to an electric signal and may store the electric signal. The row driver may sequentially scan the plurality of rows and may sequentially perform an electronic shutter operation and read-out operation. The electronic shutter operation may reset the stored electric signal in each unit pixel and the read-out operation may read-out the stored electric signal in each unit pixel. The electric shutter operation can include a preliminary shutter operation and a main shutter operation which are sequentially performed on one row. The row driver may overlap the main shutter operation on a first row and the preliminary shutter operation on a second row.