3.25 Tr Pixel Circuit with Shared Output Switches
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Solution Overview
Problem
Existing active-matrix organic electroluminescent (EL) display devices face challenges in achieving high-definition display with efficient power management and uniformity due to variations in mobility and threshold voltage of driving transistors, leading to issues like poor display quality and increased frame size.
Innovation Solution
The implementation of a 3.25 Tr circuitry with shared output switches and a specific timing control for scanning line driving circuits, including source initialization, gate initialization, offset cancel, image signal write, and luminescence operations, to manage driving current and luminescence effectively, using a combination of thin-film transistors and auxiliary capacitance for improved space utilization and display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel circuit with separate switches for each function is used, then the display quality can be maintained, but the frame size increases and manufacturing precision deteriorates
Solution Approach 1:
The patent merges the output switch and pixel switch into a single integrated switch structure. The output switch is configured to function both as an output switch connecting the luminescent element to the power source and as a pixel switch controlling the pixel state. This integration reduces the number of discrete components in the pixel circuit, thereby reducing frame size while maintaining display quality through unified switch control.
Solution Approach 2:
The output switch is designed with multi-functionality, serving dual purposes: it acts as an output switch for the luminescent element and simultaneously functions as a pixel switch for controlling the pixel on/off state. This universal design reduces component count and simplifies the pixel circuit structure without compromising display performance.
2Device complexity
If the number of transistors per pixel is reduced, then the frame size decreases, but the ability to compensate for mobility and threshold voltage variations deteriorates
Solution Approach 1:
The patent combines the output switch and pixel switch functions into a single transistor, reducing the transistor count per pixel from 4 to 3.5 (3.25 Tr circuitry). This merging reduces frame size while the retained transistors are optimized to provide necessary compensation functions for mobility and threshold voltage variations through precise timing control.
Solution Approach 2:
The patent implements preliminary initialization actions through dedicated initialization periods before image display. The output switch is controlled to initialize pixel circuits in advance, ensuring that compensation for mobility and threshold voltage variations is established before actual image rendering. This preliminary action maintains display quality despite reduced transistor count.
3Manufacturing precision
If separate initialization signals are provided for source and gate, then the display quality improves, but the number of signal lines increases
Solution Approach 1:
The patent merges source initialization and gate initialization into a unified initialization process controlled by the multi-functional output switch. A single initialization signal line controls the output switch to perform both source and gate initialization functions at different timing phases, reducing the number of signal lines while maintaining display quality through sequential initialization operations.
Solution Approach 2:
The patent uses periodic timing control to separate initialization functions in time. During specific time periods within the driving cycle, the output switch is controlled to perform source initialization; during other periods, it performs gate initialization. This temporal separation allows dual initialization functions with a single signal line, maintaining display quality without increasing signal line count.
Data Source
AI summary
According to one embodiment, a display device includes a plurality of pixels each including a plurality of subpixels, each subpixel including a luminescent element, a plurality of scanning lines, a plurality of image signal lines, a plurality of reset power source lines, a first power source line, a scanning line driving circuit and a signal line driving circuit, wherein at least one subpixel comprises an output switch, a driving transistor, a retaining capacitance, a pixel switch and a reset switch, and the output switch is shared with a plurality of subpixels included in at least one pixel.