Image Sensor Overflow Control for Blooming and Saturation Balance
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Solution Overview
Problem
In CMOS image sensors using InGaAs sensors, it is challenging to form an effective overflow path for holes, leading to blooming issues due to the recombination of holes and electrons, which affects the reverse bias voltage and current flow, resulting in image quality degradation.
Innovation Solution
Incorporating a PMOS transistor as a discharge transistor to manage the overflow path and adjust the gate voltage of the discharge transistor to balance blooming suppression and saturation signal amount, allowing for dynamic control of the overflow path formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If holes are used as carriers for photoelectric conversion in InGaAs sensors, then long-wavelength light such as infrared light can be captured with high sensitivity, but it becomes difficult to form an overflow path for saturated holes, causing blooming to occur
Solution Approach 1:
The patent applies dynamics by making the off voltage of the discharge transistor adjustable rather than fixed. The voltage control unit dynamically changes the off voltage based on imaging conditions to optimize both charge accumulation capacity and overflow path formation. This resolves the contradiction by allowing the system to adapt between high sensitivity mode (higher off voltage) and blooming suppression mode (lower off voltage) as needed
Solution Approach 2:
The patent changes the electrical parameter (off voltage) of the discharge transistor to control the balance between charge accumulation and overflow. By adjusting the off voltage parameter, the system can optimize photoelectric charge accumulation for high sensitivity while simultaneously enabling overflow path formation to prevent blooming, thus resolving the technical contradiction
2Quantity of substance
If the off voltage of the discharge transistor is increased to maintain high saturation charge amount, then charge accumulation capacity improves, but overflow path formation becomes difficult, leading to blooming
Solution Approach 1:
The system dynamically adjusts the off voltage based on imaging conditions. During normal operation, a higher off voltage maintains large saturation charge amount for high dynamic range. When blooming risk is detected or in high-light conditions, the voltage control unit lowers the off voltage to enable overflow path formation, thus preventing blooming while maintaining charge accumulation capability when needed
Solution Approach 2:
The off voltage parameter is made variable to resolve the contradiction. By changing this electrical parameter, the system can switch between two operational states: one optimized for maximum charge accumulation (high off voltage) and another optimized for overflow path formation (low off voltage), thereby addressing both requirements
3Reliability
If the off voltage of the discharge transistor is decreased to form an overflow path and suppress blooming, then blooming suppression improves, but saturation charge amount reduces
Solution Approach 1:
The system uses dynamic voltage control to provide different off voltage levels for different operational requirements. The voltage control unit monitors imaging conditions and adjusts the off voltage accordingly, providing low off voltage for blooming suppression in high-light areas while maintaining high off voltage for charge accumulation in normal conditions, thus resolving the trade-off
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 effectively suppresses blooming while maintaining a high saturation charge amount, improving image quality by adjusting the overflow path ease and charge accumulation according to each pixel's needs.
Implementation Method 1
a photoelectric conversion unit that generates a photoelectric charge
Data Source
AI summary
An image sensor (102) includes a photoelectric conversion unit (10) that generates a photoelectric charge, a sense node (SN) (21) that is connected to the photoelectric conversion unit (10) and holds the photoelectric charge generated by the photoelectric conversion unit (10), a discharge transistor (15) for discharging the photoelectric charge held by the sense node (SN) (21) to the outside, and a voltage control unit (114) that controls a voltage value of an off voltage to be applied to a gate of the discharge transistor (15) when the discharge transistor (15) is turned off.