Image Sensor Pixel With Adjustable Capacitance For Conversion Gain
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Solution Overview
Problem
Conventional image-capturing devices have a low conversion gain when converting added charges into potential, affecting the signal quality and noise ratio in image sensors.
Innovation Solution
The image sensor design includes a pixel with two photoelectric conversion units, accumulation units, and adjustable capacitance to enhance signal output, allowing for independent or combined reading of charges from each unit, thereby improving conversion gain and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charges from two light receiving elements are added and read out as a single potential, then the device can perform image capturing and focus detection, but the conversion gain in converting the added charge into potential is low
Solution Approach 1:
The patent divides the signal reading process into two separate output paths: a first output unit for image capturing signals and a second output unit for focus detection signals. Each output unit has its own conversion path from the light receiving elements, allowing independent optimization of conversion gain for each function without compromising the other.
Solution Approach 2:
The patent employs a switching mechanism that dynamically routes charges from the light receiving elements to different accumulation units based on the desired output. The switch can connect the first accumulation unit to the first output unit for image capturing, or connect the second accumulation unit to the second output unit for focus detection, enabling flexible optimization of conversion gain for different operating modes.
2Reliability
If a single accumulation unit is used for both image capturing and focus detection, then the device structure is simplified, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent implements separate accumulation units for different signal types: a first accumulation unit dedicated to image capturing signals and a second accumulation unit dedicated to focus detection signals. This segmentation prevents noise from one signal type from interfering with the other, thereby improving the signal-to-noise ratio for both functions.
Solution Approach 2:
Instead of combining accumulation functions into a single unit, the patent inverts the approach by providing separate accumulation units for each signal type. This inversion allows each accumulation unit to be optimized independently for its specific signal type, improving overall signal quality despite increased structural complexity.
3Adaptability or versatility
If the capacitance of the accumulation unit is fixed, then the circuit design is simpler, but the adaptability to different signal requirements is reduced
Solution Approach 1:
The patent introduces an adjustment unit that can dynamically change the capacitance of the accumulation unit based on the required output signal type. When image capturing is required, the capacitance is set to a first value optimized for image signals; when focus detection is required, the capacitance is set to a second value optimized for focus detection signals. This dynamic adjustment enables the system to adapt to different signal requirements while maintaining optimal performance.
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 design increases the conversion gain and signal-to-noise ratio, resulting in higher quality image data with reduced noise, particularly in image-capturing and focus detection applications.
Implementation Method 1
a first photoelectric conversion unit and a second photoelectric conversion unit that photoelectrically convert light to generate a charge
Data Source
AI summary
An image sensor includes a pixel, the pixel has: a first photoelectric conversion unit and a second photoelectric conversion unit that photoelectrically convert light to generate a charge; an accumulation unit that accumulates at least one of the charge generated by the first photoelectric conversion unit and the charge generated by the second photoelectric conversion unit; a first output unit and a second output unit that output a signal based on the charge accumulated in the accumulation unit; and an adjustment unit that adjusts a capacitance of the accumulation unit if a signal based on the charges generated by the first photoelectric conversion unit and the second photoelectric conversion unit is output from the first output unit.