Pixel Layout Shielding for Stable Photosensor Output
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Solution Overview
Problem
Parasitic capacitance between a node storing charge and signal lines in CMOS sensors leads to changes in potential, affecting imaging quality in both imaging and display devices.
Innovation Solution
Incorporating shielding wires between the node and signal lines to reduce or eliminate parasitic capacitance, using capacity lines as shielding to stabilize the potential of the node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If signal lines are placed close to the node storing charge to reduce wiring complexity, then device complexity is reduced, but parasitic capacitance increases causing potential fluctuations and imaging quality degradation
Solution Approach 1:
A shielding wire is introduced as an intermediary element between the signal line and the node storing charge (FD). This shielding wire acts as a mediator that blocks the parasitic capacitance coupling between the signal line and FD, preventing potential fluctuations in the FD while allowing the signal line to maintain its routing. The shielding wire is connected to a fixed potential (VDD or GND) to provide a stable reference that eliminates the harmful capacitive coupling.
2Reliability
If shielding wire is added between node and signal line to reduce parasitic capacitance, then imaging quality is improved, but device complexity increases
Solution Approach 1:
The shielding wire is merged with existing capacitor lines in the pixel circuit. Specifically, one of the capacitor lines that connects to the node storing charge is utilized as the shielding wire, eliminating the need for a separate dedicated shielding structure. This merging approach provides the necessary shielding function while reducing the overall number of discrete components and simplifying the circuit layout.
Solution Approach 2:
The capacitor lines in the pixel circuit are given multiple functions: they serve both as electrical connections for the capacitor and as shielding wires against parasitic capacitance from signal lines. This multi-functionality approach allows the same structural element to perform both capacitive coupling and electromagnetic shielding, thereby improving imaging quality without adding extra dedicated shielding structures.
3Length of stationary object
If node is positioned centrally to balance connections, then wiring length is reduced, but susceptibility to signal line interference increases due to unavoidable proximity
Solution Approach 1:
The shielding wire is positioned between the signal line and the node storing charge to act as a protective intermediary. This shielding structure blocks the harmful capacitive coupling from the signal line to the node, allowing the node to maintain its optimal central position for minimized wiring length while being protected from signal line interference through the shielding wire.
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 changes in the potential of the node, thereby enhancing imaging quality by reducing parasitic capacitance and maintaining stable output from photosensors.
Implementation Method 1
In case of presence of parasitic capacitance during these three operations which occurs between an FD that stores charge resulting from photocurrent generated by a photodiode and either wire that supplies a control signal or another signal line, changes in the signal causes changes in the potential of the FD.
Data Source
AI summary
An object is to provide a pixel structure of a display device including a photosensor which prevents changes in an output of the photosensor and a decrease in imaging quality. The display device has a pixel layout structure in which a shielding wire is disposed between an FD and an imaging signal line (a PR line, a TX line, or an SE line) or between the FD and an image-display signal line in order to reduce or eliminate parasitic capacitance between the FD and a signal line for the purpose of suppressing changes in the potential of the FD. An imaging power supply line, image-display power supply line, a GND line, a common line, or the like whose potential is fixed, such as a common potential line, is used as a shielding wire.