Active Pixel Array Charge Binning for High Frame Rate Preview
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Solution Overview
Problem
Active pixel CMOS image sensors face challenges in providing a high frame rate preview mode under low light conditions due to sub-sampling methods, which result in low-quality images and limited frame rate, while passive pixel sensors suffer from high read noise and capacitance issues, making them unsuitable for high resolution applications.
Innovation Solution
A pixel array design that incorporates both active and passive pixel modes, allowing charge binning by selectively transferring charges to a passive pixel/charge binning mode column output line, enabling high frame rate preview and light metering functions with controlled binning patterns, and utilizing existing transistors to minimize additional components and maintain low noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sub-sampling method is used to create low resolution preview image, then readout time is reduced and frame rate is increased, but image quality deteriorates due to aliasing effects and loss of fine details
Solution Approach 1:
The patent combines charge from multiple adjacent pixels into a single pixel output location before readout. By merging the charge signals from neighboring pixels during the integration phase, the system achieves effective sub-sampling without the aliasing problems of traditional methods, maintaining image quality while reducing the data volume for preview generation.
Solution Approach 2:
The patent performs charge binning operations during the exposure and integration phase before the readout phase. By preliminarily combining charges from multiple pixels during integration, the system prepares the data in an optimized state that enables faster readout and higher frame rates without compromising the quality of the preview image.
2Measurement precision
If exposure time is increased to improve signal-to-noise ratio under low light conditions, then image quality is improved, but frame rate is reduced because readout time becomes the limiting factor
Solution Approach 1:
The patent merges charges from multiple pixels during the integration phase, which allows for shorter exposure times while maintaining adequate signal levels. By combining signals from neighboring pixels before readout, the system achieves the necessary signal-to-noise ratio without requiring long exposure times, thus preserving high frame rates even in low light conditions.
3Manufacturing precision
If active pixel mode is used with local charge-to-voltage conversion, then read noise is reduced and image quality is improved, but the ability to perform charge binning is lost
Solution Approach 1:
The patent implements a dynamic system where pixels can operate in different modes. The pixel array can dynamically switch between active pixel mode with local charge-to-voltage conversion for high-quality full-resolution imaging and a binning mode where charges from multiple pixels are combined before conversion. This dynamic adaptability allows the system to optimize performance for different operating conditions, maintaining both low read noise capability and charge binning versatility.
4Productivity
If passive pixel mode is used for charge binning, then frame rate is increased and adaptability is improved, but read noise increases and capacitance issues arise
Solution Approach 1:
The patent merges the advantages of both active and passive pixel modes by performing charge binning operations during the integration phase while maintaining active pixel characteristics during readout. Multiple pixel charges are combined into fewer output channels, achieving the frame rate benefits of passive pixels while preserving the low read noise characteristics of active pixels through local charge-to-voltage conversion.
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 solution overcomes the limitations of sub-sampling by providing a high frame rate preview with reduced noise and increased signal-to-noise ratio, allowing for improved image quality and frame rate under low light conditions, while maintaining low noise and avoiding the capacitance issues of passive pixel sensors.
Implementation Method 1
a photo-sensitive element for generating charges responsive to electromagnetic radiation
Data Source
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AI summary
A pixel array comprises pixels (10) arranged in columns. A pixel (10) comprises a photo-sensitive element (11) for generating charges responsive to electromagnetic radiation and a buffer amplifier (M2) for buffering a voltage proportional to the charges generated by the photo-sensitive element. A first switch (M3) selectively connects an output of the buffer amplifier to an active pixel mode column output line (9). A second switch (M1) selectively transfers at least part of the charges generated by the photo-sensitive element (11) to a passive pixel mode column output line (15). The pixel (10) can be selectively operated in a conventional, active pixel mode, and in a passive pixel/charge binning mode. The second switch (M1) can be a reset switch, with the second output line operable, on a time-shared basis, as a supply line for providing the reference voltage. Another embodiment has the first switch and the second switch connected to a single column output line which is operable, on a time-shared basis, as the active pixel mode column output line and as the passive pixel mode column output line.