Photoelectric Conversion Element Transistor Channel Width Optimization
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Solution Overview
Problem
Conventional techniques fail to effectively reduce Random Telegraph Noise (RTN) in CMOS linear image sensors, leading to image quality degradation due to vertical streaks caused by crystal defects in transistors, particularly in source follower transistors.
Innovation Solution
The effective channel width of transistors, especially source follower transistors, is increased relative to other transistors to minimize the impact of RTN by avoiding crystal defects, thereby reducing noise and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the size of the amplification transistor is reduced to prevent capacitance hanging in FD area, then charge voltage conversion gain is improved, but RTN impact increases due to smaller channel area
Solution Approach 1:
The patent applies local quality by making the effective channel width of specific transistors (source follower transistors and amplification transistors) larger than other transistors in the pixel circuit. This localized enlargement of channel width in critical positions reduces RTN impact where it most affects image quality, while keeping other transistor sizes optimized for overall circuit performance and miniaturization.
2Object-affected harmful factors
If detailed setting of transistors is implemented to reduce RTN, then RTN impact on image is reduced, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by specifically adjusting the effective channel width parameter of certain transistors to be larger than others. This single parameter modification (effective channel width) provides a straightforward method to reduce RTN impact without requiring complex circuit architectures or multiple additional components, thus minimizing the increase in device complexity.
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 reduces RTN impact, resulting in improved image quality by increasing the probability of current flow through defect-free areas, making vertical streaks less noticeable and enhancing overall image clarity.
Implementation Method 1
a photoelectric conversion unit (PD)
Data Source
Figure 1
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AI summary
A photoelectric conversion element (1) includes a plurality of pixels (10) to receive light; and a signal processor (11) to process a signal of the pixels. The signal processor (11) includes: a first element (SF1; SF2), being a transistor, having a first effective channel width (We1) through which a current can effectively pass through in the first element; and a second element (RS, T, SL, SW; Is2; SF1), being a transistor, having a second effective channel width through which a current can effectively pass through in the second element (We2). The first effective channel width of the first element (We1) is larger than the second effective channel width (We2) of the second element.