Solid-State Image Sensor Global Shutter Pixel Circuit
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Solution Overview
Problem
CMOS-type solid-state image-sensing devices face challenges in achieving global shutter mode without increasing pixel size, while maintaining a wide dynamic range and high signal-to-noise ratio, due to limitations in existing configurations that often result in noise and distortion, especially under varying light conditions.
Innovation Solution
The integration of an integration operation controller that allows for simultaneous control of integration operations across all pixels, utilizing an integrating transistor and capacitive element, which can be turned on and off to enable global shutter mode without increasing pixel size, and includes additional components like photoelectric conversion transistors and switching elements to manage integration and signal output effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If global shutter mode is implemented in CMOS-type solid-state image-sensing devices, then simultaneous image capture across all pixels is achieved, but pixel size must be increased
Solution Approach 1:
The patent merges the photoelectric conversion function and integration function into a single pixel structure. The photodiode directly integrates photoelectric charges during the exposure period, eliminating the need for separate transfer paths and intermediate storage structures. This integration allows global shutter mode to be achieved without increasing pixel size, as the same photodiode performs both photoelectric conversion and charge accumulation.
2Extent of automation
If existing configurations are used to achieve global shutter mode, then simultaneous image capture is possible, but noise and distortion increase
Solution Approach 1:
The patent extracts and eliminates the transfer path from the conventional global shutter structure. By removing the need to transfer photoelectric charges through complex electrode structures, the source of distortion and noise associated with charge transfer is eliminated. The photodiode directly outputs integrated charges to the readout circuit, avoiding the harmful effects of intermediate transfer operations.
3Adaptability or versatility
If dynamic range is widened through conventional methods, then brightness information is preserved, but device complexity increases
Solution Approach 1:
The patent changes the operational parameters of the photodiode to achieve logarithmic conversion characteristics. By adjusting the bias voltage and operating point of the photodiode, the device naturally performs logarithmic compression of the brightness range, enabling wide dynamic range (5-6 digit figures) without adding complex conversion circuits. This parameter-based approach maintains simplicity while achieving enhanced adaptability.
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 allows for image sensing in global shutter mode with a high signal-to-noise ratio, maintaining a wide dynamic range without the need for increased pixel size, and effectively reduces noise and distortion across varying light conditions.
Implementation Method 1
a photodiode PD that serves as a photosensitive element performing photoelectric conversion
Implementation Method 2
an N-channel MOS transistor T1 that has its gate and drain connected to the anode of the photodiode PD and that operates in a sub-threshold region
Data Source
AI summary
A solid-state image-sensing device has a MOS transistor (T1) connected to a photodiode PD (PD) and performing photoelectric conversion, and has, as an integrating circuit for amplifying and integrating the photoelectric current obtained by the photoelectric conversion, a MOS transistor T2 and a capacitor C. In the solid-state image-sensing device, integration operation is controlled by a MOS transistor T6 connected to the gate of the MOS transistor T2.