CMOS Image Sensor Merge Gate Transistor Dynamic Capacitance
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Solution Overview
Problem
Conventional CMOS image sensors have limited dynamic range, leading to issues with image quality under varying illumination conditions and reduced sensitivity due to low voltage operation in portable devices, which restricts the expansion of dynamic range without increasing pixel size.
Innovation Solution
Incorporating a merge gate transistor between the reset transistor and the floating diffusion in the CMOS image sensor, which increases the potential well capacitance, allowing for expanded dynamic range by controlling the capacitance of the floating diffusion, enabling the generation of both low-sensitivity and high-sensitivity image signals through specific transistor operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If pixel size is reduced for miniaturization, then device size is reduced, but dynamic range cannot be ensured
Solution Approach 1:
The patent applies dynamics by making the floating diffusion capacitance adjustable through the merge gate transistor. The capacitance is dynamically changed between two states (with and without merge gate transistor conducting) to adapt to different signal levels, enabling wide dynamic range in a miniaturized pixel structure.
Solution Approach 2:
The patent changes the capacitance parameter of the floating diffusion by controlling the merge gate transistor. This parameter change allows the same pixel to handle both bright and dark scenes effectively, resolving the contradiction between small pixel size and adequate dynamic range.
2Use of energy by moving object
If low voltage driving is used for portable devices, then power consumption is reduced, but sensitivity is reduced
Solution Approach 1:
The merge gate transistor dynamically adjusts the floating diffusion capacitance to match the signal strength. For weak signals (dark scenes), the capacitance is reduced to amplify sensitivity. For strong signals (bright scenes), the capacitance is increased to prevent saturation, all while operating at low voltage.
Solution Approach 2:
The patent changes the capacitance parameter dynamically to compensate for low voltage operation. By reducing capacitance when needed, the system maintains sensitivity despite low voltage driving, resolving the contradiction between power consumption and sensitivity.
3Volume of moving object
If dynamic range is expanded without increasing pixel size, then device miniaturization is maintained, but device complexity increases
Solution Approach 1:
The patent merges the reset transistor and merge gate transistor into a single pixel circuit structure. The merge gate transistor is integrated between the reset transistor and floating diffusion, combining multiple functions (resetting and capacitance control) in a compact arrangement that expands dynamic range without proportionally increasing complexity.
Solution Approach 2:
The merge gate transistor serves multiple functions: it controls the capacitance of the floating diffusion, enables dynamic range expansion, and works cooperatively with the reset transistor. This multi-functionality reduces the need for separate dedicated components, managing complexity while achieving the goal.
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 allows for an expanded dynamic range without increasing pixel size, maintaining sensitivity and improving image quality by generating wide dynamic range and high-sensitivity signals through controlled capacitance manipulation.
Implementation Method 1
a photodiode receiving light and generating photocharges
Implementation Method 2
a merge gate transistor controlling capacitance of the floating diffusion
Implementation Method 3
In order to expand a dynamic range of an image sensor, a merge gate transistor for controlling a potential well of a floating diffusion is inserted between a reset transistor and the floating diffusion
Data Source
AI summary
A CMOS image sensor is provided. The CMOS image sensor includes a photodiode receiving light and generating photocharges, a transfer transistor connected to the photodiode and transferring the photocharges, a floating diffusion accumulating the photocharges transferred from the transfer transistor, a reset transistor discharging the photocharges accumulated in the floating diffusion, and a merge gate transistor controlling capacitance of the floating diffusion. The CMOS image sensor may obtain a wide dynamic range signal without an increase in size of a pixel.