OLED Pixel Circuit Power Line Reduction via Time-Multiplexed Switching
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Solution Overview
Problem
The challenge in designing high-resolution display devices is the increased space required due to the number of power lines needed to supply voltages to pixels in organic light emitting diode (OLED) displays, which limits the density of pixels in a limited area.
Innovation Solution
A display device configuration that reduces the number of power lines by using a pixel circuit with specific transistor connections and voltage control signals, allowing for reduced power lines and converters, thereby minimizing space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple power lines are supplied to each pixel to provide different voltages, then the pixel circuit can be properly controlled, but the space required for each pixel increases
Solution Approach 1:
The patent merges the functions of multiple power lines by using a single power line that sequentially provides different voltages (ELVDD, ELVSS, initialization voltage) through time-multiplexed control. The fourth transistor acts as a switch to connect the single power line to different circuit nodes at different times, eliminating the need for separate dedicated power lines for each voltage type.
Solution Approach 2:
The patent employs dynamic voltage control where a single power line dynamically switches between providing different voltages based on timing signals. The fourth transistor is controlled by gate signals to dynamically connect or disconnect the power line from different circuit nodes, enabling one line to perform the function of multiple static power lines.
2Area of stationary object
If the number of power lines is reduced, then the pixel space is minimized, but the circuit complexity increases due to additional transistors and control signals
Solution Approach 1:
The fourth transistor serves multiple functions: it acts as a switch for initialization, a connection element for voltage switching, and part of the overall pixel circuit operation. By making this transistor multi-functional, the patent reduces the total number of dedicated components needed, offsetting the complexity added by its versatile role.
Solution Approach 2:
The patent changes the operational parameters of the fourth transistor based on timing - it operates in different states (on/off, connected to different nodes) during different phases of the pixel operation cycle. This parameter-based control allows a single transistor to replace what would traditionally require multiple dedicated transistors for each function.
3Productivity
If more pixels are formed in limited space, then high resolution is achieved, but the number of power lines required increases
Solution Approach 1:
By merging multiple power line functions into a single time-multiplexed power line, the patent significantly reduces the physical space required for power line routing. This allows more pixels to be packed into the same area without proportionally increasing the power line infrastructure, thereby achieving higher pixel density.
Data Source
AI summary
A display device includes a plurality of pixels. A pixel includes an organic light emitting diode and a pixel circuit including a first transistor that includes a gate electrode connected with a first node, a first electrode connected with a second node, and a second electrode connected with a third node; a second transistor that includes a gate electrode connected with a first gate line, a first electrode connected with a data line, and a second electrode connected with the second node; a third transistor that includes a gate electrode connected with a third gate line, a first electrode connected with the third node, and a second electrode connected with the first node; and a fourth transistor that includes a gate electrode connected with a second gate line, a first electrode connected with the third gate line, and a second electrode connected with the first node.