CMOS Image Sensor Overflow Control for InGaAs Blooming
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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
A solid-state imaging device is designed with a PMOS transistor to accumulate and discharge holes, incorporating a voltage control unit to adjust the gate voltage of the discharge transistor, allowing for the formation of an overflow path and control of the saturation charge amount, thereby suppressing blooming and maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If holes are used as carriers for photoelectric conversion, then sensitivity to long-wavelength light such as infrared light is improved, but it becomes difficult to form an overflow path for releasing saturated holes
Solution Approach 1:
The gate voltage of the discharge transistor is made dynamically adjustable through the voltage control unit. By changing the gate voltage, the overflow path formation can be controlled - at higher voltages the path is suppressed to maintain saturation charge, while at lower voltages the path opens to release excess holes and prevent blooming. This dynamic control resolves the contradiction between maintaining sensitivity and enabling overflow path formation.
Solution Approach 2:
The invention changes the electrical parameter (gate voltage) of the discharge transistor to control the overflow path behavior. By adjusting this parameter, the system can switch between different operational states - suppressing or enabling the overflow path - thereby resolving the difficulty of forming an appropriate overflow path while maintaining the photoelectric conversion characteristics.
2Quantity of substance
If no overflow path is formed, then saturation charge amount is maintained, but charges flow into adjacent pixels causing blooming
Solution Approach 1:
The voltage control unit provides feedback control by monitoring the need for overflow path formation and adjusting the gate voltage accordingly. When blooming is detected or predicted, the control unit adjusts the voltage to open the overflow path, allowing excess charges to be released. This feedback mechanism maintains the saturation charge amount while preventing blooming by dynamically responding to charge accumulation conditions.
Solution Approach 2:
The system transitions from a static overflow path configuration to a dynamic one controlled by gate voltage. This allows the overflow path to be activated only when necessary - when charge saturation occurs and blooming risk arises - while remaining closed during normal operation to maintain saturation charge. This dynamic control resolves the contradiction between maintaining charge and preventing harmful overflow.
3Object-affected harmful factors
If gate voltage of discharge transistor is increased to suppress blooming, then blooming is reduced, but saturation charge amount decreases
Solution Approach 1:
The gate voltage is adjusted periodically or as needed rather than maintained at a constantly high level. During normal operation, the voltage remains at a level that maintains saturation charge. When blooming becomes an issue, the voltage is temporarily increased to open the overflow path, then returned to the normal level to restore saturation charge. This periodic adjustment resolves the contradiction by applying high voltage only when necessary for blooming suppression.
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 suppresses blooming and secures saturation charge amounts in each pixel, improving image quality by dynamically adjusting the overflow path formation and charge management in the CMOS image sensor.
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.