Pixel Cell Readout Circuit for Rolling and Global Shutter Imaging
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Solution Overview
Problem
Existing pixel cells require dedicated camera modules for rolling and global shutter modes, leading to space constraints and increased costs in modern electronic devices, and existing solutions with dedicated color and infrared pixels suffer from interpolation and resolution issues.
Innovation Solution
A pixel cell design that allows individual pixels to be read out either sequentially in rolling shutter mode or simultaneously in global shutter mode, using a readout circuit with a floating diffusion and sample-and-hold stage to manage electrical information, enabling operation in both modes without interpolation and maintaining high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dedicated camera modules are used for rolling and global shutter modes, then each mode can be optimized for its specific operation, but space constraints and costs increase due to requiring multiple separate modules
Solution Approach 1:
The pixel cell is designed to perform both rolling shutter and global shutter operations using the same hardware components. The readout circuit can be configured to operate in either mode through control signals, eliminating the need for separate dedicated modules for each shutter type while maintaining optimized performance for both modes.
Solution Approach 2:
The patent combines the functionality of separate rolling shutter and global shutter modules into a single integrated pixel cell. The photodiode array, transfer gates, and readout circuit are merged into one structure that can execute both operating modes, thereby reducing device space and component count.
2Reliability
If dedicated color pixels and infrared pixels are used, then each pixel type can be optimized for its specific wavelength range, but interpolation is required for missing information and resolution is reduced
Solution Approach 1:
The pixel cell utilizes the spectral response characteristics of silicon photodiodes, which naturally exhibit sensitivity across both visible and infrared wavelength ranges. By adjusting operational parameters and readout timing, the same pixel can capture information in both wavelength domains without requiring dedicated pixels for each range, thereby maintaining full resolution.
3Area of stationary object
If a single image sensor is used for both visible and infrared imaging, then space and cost are reduced, but the sensor must handle different wavelength ranges and shutter modes with a unified design
Solution Approach 1:
The pixel cell employs universal components that can operate across multiple functions: silicon photodiodes detect both visible and infrared light, transfer gates enable both sequential and simultaneous readout, and the readout circuit adapts to provide either rolling or global shutter output. This multi-functionality reduces device space while managing complexity through standardized components.
Solution Approach 2:
The readout circuit is designed with dynamic reconfigurability, allowing it to switch between rolling shutter and global shutter modes through control signals. The transfer gates can be activated in different sequences or simultaneously, enabling the same hardware to adapt its behavior based on the required operating mode without increasing physical complexity.
4Productivity
If rolling shutter mode is used for visible band imaging, then sequential readout is efficient, but the exposure period is shifted in time for each row reducing temporal consistency
Solution Approach 1:
The pixel cell incorporates a dynamic readout circuit that can adjust its operation mode. When temporal consistency is required, the circuit switches to global shutter mode where all pixels are exposed and read out simultaneously. When readout efficiency is the priority and temporal consistency is less critical, it operates in rolling shutter mode. This dynamic adaptability allows the system to optimize based on real-time requirements.
5Stability of the object's composition
If global shutter mode is used for infrared imaging with active illumination, then all pixels capture during the same time period, but power consumption increases and critical light levels must be managed
Solution Approach 1:
The pixel cell employs periodic activation of the transfer gates to control charge transfer timing. In global shutter mode, all transfer gates are activated simultaneously at the end of the exposure period, enabling simultaneous readout of all pixels. The periodic gating mechanism allows precise control over when charge is transferred and read out, enabling simultaneous exposure while managing power consumption through controlled activation periods.
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
Enables flexible imaging capabilities in both visible and infrared domains with a single image sensor, reducing the need for separate modules and improving efficiency by eliminating the need for interpolation, while maintaining high resolution and sensitivity.
Implementation Method 1
the working principle of the pixels is the conversion of optical intensity into a photocurrent using a photodiode
Data Source
AI summary
A pixel cell includes a pixel set with a plurality of pixels, with each pixel of the pixel set being configured to capture optical information incident upon the respective pixel and generate electrical information representative of the optical information. The pixel cell further includes a readout circuit which is configured to manage collection and output of the electrical information from each pixel of the pixel set and to operate the pixel set in a global shutter mode and in a rolling shutter mode of operation. In the global shutter mode, the electrical information from each pixel is combined for generating a global shutter output signal, while in the rolling shutter mode, the electrical information from each pixel is used to generate individual rolling shutter output signals.