OLED Display Array Brightness Uniformity via Transistor Compensation
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Solution Overview
Problem
In organic light emitting display panels, uneven brightness across different regions due to non-identical driving transistors results in unequal light-emitting intensity, leading to uneven images.
Innovation Solution
Incorporating a current source realized by a PMOS transistor to adjust the source-gate voltage of driving transistors, ensuring identical electrical characteristics within regions, thereby maintaining consistent light-emitting intensity across OLEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If driving transistors are used in different regions of the display array, then the display can cover larger area, but the threshold voltages of driving transistors become unequal resulting in uneven brightness
Solution Approach 1:
The patent applies local quality by dividing the display array into multiple regions and assigning different compensation values to each region based on the threshold voltage characteristics of driving transistors in that region. This allows each region to be optimized independently, maintaining brightness uniformity across the entire large-area display despite variations in transistor parameters.
Solution Approach 2:
The patent changes the voltage parameter by applying different compensation voltages to driving transistors in different regions. The compensation value is calculated based on the threshold voltage of each driving transistor and added to the video signal voltage, thereby adjusting the driving current to achieve uniform brightness across the display array.
2Device complexity
If standard driving transistor circuit is used, then the circuit design is simple, but the driving current varies due to threshold voltage differences causing uneven light-emitting intensity
Solution Approach 1:
The patent applies preliminary action by pre-calculating the compensation value for each driving transistor based on its threshold voltage characteristics before the display operation. This compensation value is stored and applied to adjust the driving current in advance, eliminating the need for complex real-time adjustment circuits while ensuring uniform light-emitting intensity.
3Ease of operation
If no compensation is applied, then the device operation is simple, but unequal threshold voltages result in unequal driving current and uneven images
Solution Approach 1:
The patent implements feedback by measuring or characterizing the threshold voltage of each driving transistor and using this information to calculate a compensation value. This compensation value is then applied to adjust the driving current, creating a closed-loop system that compensates for manufacturing variations and ensures high image quality without requiring complex real-time control.
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 ensures that OLEDs in different regions provide similar light-emitting intensity, resulting in evenly displayed images by managing the decrement of driving current over time.
Implementation Method 1
a current source realized by a PMOS transistor to adjust the source-gate voltage of driving transistors
Implementation Method 2
the driving transistor T11 provides a driving current Id1 to drive the OLED D1 to emit light
Data Source
AI summary
A display array. The display array applied in the panel of an organic light emitting display device comprises a plurality of data lines, a plurality of scan lines and a plurality of display units. Each display unit corresponds to one set of the data and scan lines and comprises a control unit, a driving transistor and a light emitting diode. In each display unit, the control unit adjusts light-emitting intensity of the light emitting diode in a frame cycle time according to the driving capability of the driving transistor.