Image Sensor Dynamic Full Well Capacity Control
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Solution Overview
Problem
Time-of-flight (ToF) sensors face challenges in accurately measuring distances in environments with varying light conditions, as they can become saturated in high-light conditions, leading to degraded performance and noise issues in low-light environments.
Innovation Solution
The proposed solution involves an image sensor with a unit pixel and control circuit that dynamically adjust the full well capacity based on ambient brightness by using three taps with specific drive signals, allowing for flexible operation in both high and low-light conditions, thereby enhancing distance measurement performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the full well capacity is increased to prevent saturation in high-light conditions, then the dynamic range is improved, but the noise performance deteriorates in low-light conditions
Solution Approach 1:
The patent applies dynamics by making the full well capacity adjustable rather than fixed. The control circuit dynamically changes the capacitance value of the floating diffusion region based on ambient light conditions, allowing the sensor to adapt its capacity in real-time to match lighting environments and optimize both saturation resistance and noise performance.
Solution Approach 2:
The patent changes the electrical parameter (capacitance) of the floating diffusion region. By controlling the capacitance value through different voltage levels applied to the control electrode, the system can adjust the full well capacity to match different lighting conditions, thereby resolving the contradiction between handling bright and dark environments.
2Reliability
If the full well capacity is decreased to improve noise performance in low-light conditions, then the noise is reduced, but the sensor becomes saturated more easily in high-light conditions
Solution Approach 1:
The system dynamically adjusts the full well capacity based on detected ambient light levels. In low-light conditions, the capacitance is reduced to minimize noise, while in bright conditions, the capacitance is increased to prevent saturation, thus resolving the contradiction through time-varying adaptation.
Solution Approach 2:
The patent modifies the capacitance parameter of the floating diffusion region in response to changing light conditions. By controlling the voltage on the control electrode, the system changes the effective capacitance value to optimize the trade-off between noise performance and saturation resistance for current lighting conditions.
3Device complexity
If a fixed full well capacity is used, then the device complexity is reduced, but the adaptability to different light conditions deteriorates
Solution Approach 1:
The control circuit provides multi-functionality by enabling the same pixel structure to operate in multiple modes (different full well capacities) depending on lighting conditions. This allows a single sensor design to handle both bright and dark environments effectively, achieving adaptability without requiring physically separate sensor arrays.
Solution Approach 2:
The system introduces dynamic control capability to a previously static parameter. By adding the control electrode and associated control circuitry, the floating diffusion capacitance becomes可调 (adjustable), enabling the sensor to adapt to varying light conditions while maintaining a relatively simple overall structure.
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 improves the image sensor's ability to measure distances accurately across different light environments, preventing saturation in bright conditions and reducing noise in dark conditions, thus enhancing overall performance and usability.
Implementation Method 1
a photoelectric conversion region configured to generate photocharges in a substrate from reflected light
Data Source
AI summary
An image sensor includes: a unit pixel configured to output pixel data in response to a drive signal being input to the unit pixel; and a control circuit configured to provide the unit pixel with a first drive signal and a second drive signal each having a first phase, and a third drive signal having a second phase with a phase difference of 180 degrees with respect to the first phase in a first mode, the control circuit providing the unit pixel with the first drive signal having the first phase, the second drive signal having the second phase, and the third drive signal having a deactivation voltage in a second mode.