Demultiplexer Switching Circuit for Organic Light Emitting Display
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Solution Overview
Problem
Existing active matrix organic light emitting displays face issues with current deviation due to parasitic capacitance kickback voltage, leading to longitudinal dimming and reduced image quality, especially when pixels displaying the same color are connected to different demultiplexer switches, which increases the visibility of unwanted current deviations.
Innovation Solution
The design includes a demultiplexer switching circuit that ensures pixels of the same color have the same number of times of influence from kickback voltage by synchronizing demux control signals to rise and fall sequentially, and using auxiliary switches to time-divide the supply of reference and data voltages, ensuring all pixels are affected equally by kickback voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If demultiplexer switching circuit is used to reduce the number of output channels of data driving circuit, then the cost and complexity of data driving circuit is reduced, but current deviation between pixels occurs due to kickback voltage from parasitic capacitance
Solution Approach 1:
The patent applies local quality by making pixels of the same color connected to different demux switches have different connection timings. Specifically, pixels connected to first demux switches are connected during a first time period, while pixels connected to second demux switches are connected during a second time period. This local differentiation in connection timing compensates for the kickback voltage effects that occur uniformly across all pixels, thereby maintaining current uniformity while using a simplified demultiplexer circuit structure.
2Productivity
If pixels of the same color are connected to different demux switches, then the demultiplexer can operate with fewer output channels, but the visibility of longitudinal dim increases due to current deviation
Solution Approach 1:
The patent changes the timing parameter of pixel connection to demux switches based on the pixel's color. Red pixels, green pixels, and blue pixels are connected at different times relative to the demux switching cycles. This parameter change in connection timing ensures that pixels of the same color experience the same number of kickback voltage events, preventing current deviation and reducing longitudinal dim visibility while maintaining efficient demultiplexer operation.
3Manufacturing precision
If demux switches are turned on at different timings to reduce kickback voltage influence, then current deviation is reduced, but the complexity of control signals increases
Solution Approach 1:
The patent segments the pixel connection process into distinct time periods for different pixel groups. Pixels are divided into groups based on their color and connection timing, with each group connected during its specific time period. This segmentation approach simplifies control signal design because each demux switch has a clear, non-overlapping activation window, making the control logic more manageable while still achieving current uniformity across pixels.
Data Source
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AI summary
An organic light emitting display includes a display panel including first pixels displaying a first color, second pixels displaying a second color, and third pixels displaying a third color, a data driving circuit generating a data voltage, a demultiplexer (demux) switching circuit, which includes first to Nth demux switches connected to each output channel of the data driving circuit, where N is a positive integer equal to or greater than 2, and time-division supplies the data voltage to N data lines of the display panel, and a control signal generator generating first to Nth demux control signals for controlling operations of the first to Nth demux switches. The first to Nth demux control signals sequentially rise to an on-level and then sequentially fall to an off-level in a programming period, in which a scan signal is held at the on-level.