OLED Pixel Circuit Sharing Signal Lines for Brightness Uniformity
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Solution Overview
Problem
In OLED displays, the non-uniformity of threshold voltages in driving TFTs leads to inconsistent current flow and brightness across pixels, and the traditional pixel circuit design is complex, resulting in higher production costs and lower pixel density due to the need for multiple signal lines.
Innovation Solution
A pixel circuit comprising two sub-pixel circuits that share signal lines, each with a specific configuration of switch units, a driving unit, an energy storage unit, and an electroluminescent unit, where the operating current is not affected by the threshold voltage of the driving transistor, allowing for shared signal lines and reduced IC costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If each pixel circuit corresponds to one pixel with separate signal lines, then the display brightness uniformity can be maintained, but the production process becomes more complicated and pixel pitch cannot be reduced
Solution Approach 1:
The patent merges the control of two adjacent pixels into a single shared pixel circuit. The pixel circuit includes a driving transistor and capacitor that control the driving current for two OLEDs simultaneously. The scanning signal lines and data voltage lines are shared between the two pixels, reducing the total number of signal lines required while maintaining independent control capability for each pixel through sequential scanning.
Solution Approach 2:
The pixel circuit is designed with multi-functionality to serve two pixels. The same driving transistor, capacitor, and signal lines perform dual functions by sequentially controlling different pixels during different time periods. The circuit can switch between controlling the first pixel and the second pixel, making the components universal rather than dedicated to a single pixel.
2Device complexity
If threshold voltage variations in driving TFTs are not compensated, then the circuit design remains simple, but the current flow and brightness become non-uniform across pixels
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the driving transistor's gate voltage is adjusted based on the actual current flow through the OLED. The capacitor stores the compensated voltage value that accounts for threshold voltage variations. By measuring the actual operating conditions and adjusting the gate voltage accordingly, the circuit compensates for manufacturing variations in the driving TFT threshold voltages, ensuring uniform brightness across all pixels.
3Difficulty of detecting and measuring
If more signal lines are used for each pixel circuit, then the control precision can be improved, but the pixel pitch increases and pixel density decreases
Solution Approach 1:
The patent combines the signal lines for two pixels into a shared infrastructure. The scanning signal lines and data voltage lines are commonly used by both pixels, reducing the total number of signal lines required. This merging approach reduces the space needed for signal routing, thereby decreasing the pixel pitch while maintaining the necessary control precision through sequential access and timing control.
4Reliability
If separate pixel circuits are used for each pixel, then the driving current control can be optimized, but the IC costs increase
Solution Approach 1:
The patent merges two pixel circuits into a single integrated circuit unit that controls two pixels. By sharing common components such as the driving transistor, capacitor, and signal line interfaces, the total component count is reduced. This consolidation lowers the IC manufacturing complexity and cost while maintaining the ability to independently control the driving current for each pixel through sequential operation and timing 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 configuration ensures uniform brightness across pixels, reduces the number of signal lines, decreases pixel pitch, and increases pixel density by isolating the operating current from threshold voltage variations, thus enhancing display performance and reducing production complexity.
Implementation Method 1
an electroluminescent unit; a first terminal of the second switch unit is connected to an output of the driving unit, a second terminal of the second switch unit is connected to the electroluminescent element, and the second switch unit is configured to introduce a driving current provided by the driving unit into the electroluminescent element
Data Source
Figure 1~2
Figure 3(a)~3(b)
Figure 3(c)~3(d)
AI summary
Provided is a pixel circuit comprising two sub-pixel circuits(P1, P2) of the same structure. Each sub-pixel circuit(P1, P2) comprises five switch units(T1, T2, T3, T4, T5), a driving unit(DT), an energy storage unit(C) and an electroluminescent unit(L). The two sub-pixel circuits (P 1, P2) are connected to the same operating voltage line(Vdd), the same data voltage line(Vdata), the same first scanning signal line(Scan[1]), and the same third scanning signal line(Scan[3]), and are connected to different second scanning signal lines(Scan[2]), so that in the pixel circuit, the operating current flowing through the electroluminescent unit(L) is not affected by the threshold voltage of the corresponding driving transistor, completely solving the problem of non-uniformity in the display brightness due to drifting of the threshold voltage of the driving transistor. Meanwhile, a compensation circuit is used to drive two pixels(P1, P2), and two adjacent pixels(P1, P2) share a plurality of signal lines, thus reducing the number of signal lines for the pixel circuits in a display apparatus, decreasing the pixel pitch, and increasing the pixel density. Also provided is a display apparatus using the pixel circuit.