Multimode Pixel Readout for Dynamic Range
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Solution Overview
Problem
Conventional image sensors face challenges in capturing high-dynamic-range images without significantly reducing the pixel fill factor, as they require additional transistors to operate in multiple conversion gain modes, which increases the pixel area and reduces light sensitivity.
Innovation Solution
The image sensor pixels are designed to operate in multiple conversion gain modes using shared switches that selectively couple the pixels to a power supply and output path, allowing for low and high conversion gain modes without increasing the transistor count, utilizing a 3-T or 4-T readout scheme to expand dynamic range and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additional transistors are added to enable multiple conversion gain modes, then dynamic range is improved, but pixel fill factor deteriorates
Solution Approach 1:
The pixel circuit is designed to perform multiple functions using the same transistors. The pixel can operate in both low conversion gain mode and high conversion gain mode by selectively configuring the existing transistors, eliminating the need for additional transistors. This multi-functionality allows the pixel to capture both bright and dark regions effectively while maintaining a high fill factor.
Solution Approach 2:
The pixel circuit incorporates dynamic switching mechanisms that allow it to adapt its operation mode based on lighting conditions. By dynamically reconfiguring the connections between existing transistors, the pixel can switch between different conversion gain modes during the readout process, enabling high dynamic range capture without adding permanent structural elements that would reduce the fill factor.
2Adaptability or versatility
If pixel area is increased to accommodate multiple transistors, then multiple conversion gain modes are enabled, but light sensitivity deteriorates
Solution Approach 1:
The same pixel circuit elements are made to serve multiple purposes. The existing transistors are configured to provide both low conversion gain and high conversion gain operation, eliminating the need for additional transistors that would occupy valuable pixel area. This ensures maximum light-sensitive region while maintaining multi-mode capability.
Solution Approach 2:
The pixel achieves different conversion gain modes by changing the electrical configuration and operating parameters of the existing transistors rather than by physical addition of components. By adjusting gate voltages and switching connections, the same hardware structure can operate with different effective gains, maintaining light sensitivity while providing 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 approach enables the capture of high-dynamic-range images while maintaining a high pixel fill factor, effectively balancing dynamic range and noise reduction by selectively configuring the pixel operation based on light conditions.
Implementation Method 1
The pixels may include photodiodes that convert the incoming light into image signals
Data Source
AI summary
An image sensor having image sensor pixels operable in multiple gain modes is provided. An image sensor pixel may include a photodiode, a charge transfer transistor, a reset transistor, a source follower (SF) transistor, a row select transistor, and a capacitor that is directly connected across the gate terminal and a selected source-drain terminal of the SF transistor. The SF transistor and the row select transistor may be selectively coupled to a power supply line and a column output line by asserting either a first control signal or a second control signal. The first control signal is asserted to place the pixel in a low conversion gain mode, whereas the second control signal is asserted to place the pixel in a high conversion gain mode. The charge transfer transistor may always be activated during the low conversion gain mode and may be selectively activated during the high conversion gain mode.