Imaging Device kTC Noise Cancellation via Ramp Voltage
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Solution Overview
Problem
Existing imaging devices face challenges in reducing kTC noise, which affects image quality due to capacitive coupling and line-to-line coupling, leading to shading issues in images.
Innovation Solution
The imaging device employs a configuration with a first and second voltage terminal, a voltage generator for a ramp voltage, and switching circuits to selectively connect these voltages, reducing noise mixing and enabling effective noise cancellation through a feedback loop and ramp voltage usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a stacked imaging device structure is used to increase light receiving area, then higher definition is achieved, but kTC noise cannot be removed by simple correlated double sampling
Solution Approach 1:
The patent applies dynamics by making the gate voltage of the transfer transistor time-dependent and continuously variable. Instead of using a fixed voltage level, the gate voltage varies dynamically to control the transfer of signal charge to the floating diffusion, enabling effective kTC noise cancellation while maintaining the stacked structure's large light receiving area
Solution Approach 2:
The patent changes the voltage parameter from a static value to a time-varying ramp voltage. The gate voltage of the transfer transistor is changed as a function of time, allowing the transfer characteristics to be optimized dynamically and enabling complete signal charge transfer that removes kTC noise, thus resolving the contradiction between maintaining stacked structure benefits and achieving noise removal
2Ease of manufacture
If metal lines or metal layers are provided in the interlayer insulator to connect photoelectric conversion layer to circuitry, then stacked structure is formed, but complete signal charge transfer to floating diffusion becomes difficult
Solution Approach 1:
The patent uses parameter changes by varying the gate voltage of the transfer transistor as a time-dependent ramp voltage. This dynamic voltage adjustment compensates for the presence of metal lines and interlayer insulators in the stacked structure, enabling complete signal charge transfer through the complex multi-layer architecture while maintaining ease of manufacture
3Reliability
If feedback loop with time-increasing voltage is applied to reset transistor gate, then kTC noise is cancelled, but device complexity increases
Solution Approach 1:
The patent applies universality by making the transfer transistor serve multiple functions: it acts as both the reset transistor for kTC noise cancellation and the signal transfer transistor. The same transistor and its time-varying gate voltage perform dual roles, simplifying the overall device structure while achieving effective kTC noise cancellation, thus reducing the complexity associated with separate feedback loop components
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 configuration effectively reduces noise, minimizes shading, and enhances image quality by reducing capacitive and line-to-line coupling, allowing for more efficient noise cancellation.
Implementation Method 1
a voltage generator generating a ramp voltage which is a voltage varying with time
Implementation Method 2
pixels each including a photoelectric converter generating a signal
Data Source
AI summary
An imaging device includes. a first terminal to which a first voltage is applied; a second terminal to which a second voltage different from the first voltage is applied; a voltage generator generating a ramp voltage which is a voltage varying with time; a first switching circuit connected to the second terminal and the voltage generator; a second switching circuit connected to the first terminal and the first switching circuit, and pixels each including a photoelectric converter generating a signal, and a signal detection circuit detecting the signal, at least one of the pixels connected to the second switching circuit. The first switching circuit selectively connects one of the second terminal and the voltage generator with the second switching circuit. The second switching circuit selectively connects one of the first voltage terminal and the first switching circuit with the at least one of the pixels.