CMOS Image Sensor Clip Unit for Dynamic Voltage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors experience degradation in image quality due to strong light sources, particularly from the sun, leading to luminance differences and blackening issues, which existing solutions fail to adequately address, especially when the set clip voltage and set saturation voltage are close, causing subthreshold current increases and image graininess.
Innovation Solution
A photoelectric conversion apparatus with a clip unit that includes an amplifying circuitry and an MOS transistor to control the electric potential of the gate, dynamically setting the electric voltage of the output line based on the difference between the gate and source electric potentials, thereby preventing subthreshold current and maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the set clip voltage and set saturation voltage are set close to each other to improve dynamic range, then the voltage utilization is improved, but the subthreshold current increases causing image graininess
Solution Approach 1:
The patent applies dynamics by making the clip voltage adjustable rather than fixed. The clip voltage is dynamically changed based on the input signal level: when the input signal is small, the clip voltage is set to a first value; when the input signal is large, the clip voltage is set to a second value. This dynamic adjustment allows the system to maintain optimal performance across different signal conditions, preventing subthreshold current while preserving dynamic range.
Solution Approach 2:
The patent changes the parameter of clip voltage based on signal conditions. By switching between different clip voltage values (first value for small signals, second value for large signals), the system adapts to different operating conditions. This parameter change strategy resolves the contradiction by selecting appropriate voltage levels that prevent subthreshold current generation while maintaining the ability to utilize the full dynamic range when needed.
2Reliability
If the set clip voltage is lowered to prevent saturation in high light conditions, then the saturation prevention is improved, but the image quality degrades due to gray output
Solution Approach 1:
The clip voltage is dynamically adjusted based on input signal magnitude. For small input signals, a first clip voltage value is used that maintains high image quality. For large input signals that would cause saturation, a second clip voltage value is used that prevents saturation. This dynamic switching resolves the contradiction by applying different voltage strategies for different signal conditions.
Solution Approach 2:
The patent applies different clip voltage values for different signal conditions - using a first value for small signals and a second value for large signals. This local quality approach ensures that each signal range receives the appropriate voltage treatment, maintaining image quality for normal signals while preventing saturation for strong light signals.
3Device complexity
If the clip circuitry uses a fixed clip voltage to simplify the control, then the device complexity is reduced, but the image quality suffers under varying light conditions
Solution Approach 1:
The control system dynamically selects between a first clip voltage value and a second clip voltage value based on the input signal level. This dynamic control adapts to varying light conditions without requiring complex continuous adjustment mechanisms. The system switches between predetermined voltage values, maintaining simplicity while improving image quality across different lighting scenarios.
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
The solution effectively prevents image quality degradation by controlling the subthreshold characteristics and maintaining consistent output voltage, even under strong light conditions, reducing graininess and ensuring uniform luminance across the screen.
Implementation Method 1
a photoelectric conversion unit configured to convert light into electrical charges
Data Source
AI summary
Each pixel has a photoelectric conversion unit configured to convert light into electrical charges and to store the electrical charges, an amplifying unit configured to amplify a signal based on the electrical charges stored in the photoelectric conversion unit and to output the signal to an output line, and a reset unit configured to reset a input part of the amplifying unit. A clip unit, which is configured to limit an electric voltage of the output line, includes an amplifying circuitry for amplifying a signal based on the electric voltage of the output line and an MOS transistor for limiting the electric voltage of the output line based on the difference in electric potential between the gate and source. The clip unit controls the electric potential of the gate of the MOS transistor by the amplifying circuitry.