Shared Pixel Circuit for OLED Brightness Uniformity
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Solution Overview
Problem
In OLED displays, the non-uniform threshold voltages of driving transistors lead to uneven current flow through pixels, resulting in inconsistent display brightness, and the complex pixel driving circuit design increases production costs and reduces pixel density due to the need for multiple signal lines per pixel.
Innovation Solution
A pixel circuit design where two pixels share a common compensation circuit and signal lines, with switch units and driving units configured to isolate the operating current from threshold voltage fluctuations, using a single compensation circuit to drive two pixels and reducing the number of signal lines required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If each pixel has its own independent driving circuit, then the display brightness uniformity can be maintained, but the device complexity and production cost increase
Solution Approach 1:
The patent merges the driving circuits of two adjacent pixels into a single shared circuit structure. The driving transistor and compensation transistor are commonly shared between two pixels, while each pixel maintains its own electroluminescent unit and storage capacitor. This merging approach reduces the overall number of transistors per pixel from 2-3 to 1-2, simplifying the circuit complexity while preserving brightness uniformity through the shared compensation mechanism.
Solution Approach 2:
The driving transistor and compensation transistor serve dual functions by being shared between two adjacent pixels. A single transistor performs the driving function for two different electroluminescent units, and the compensation mechanism simultaneously compensates for threshold voltage variations in both pixels. This multi-functionality reduces device complexity without sacrificing display quality.
2Ease of operation
If multiple signal lines are used per pixel, then the pixel driving function is complete, but the pixel pitch increases and pixel density decreases
Solution Approach 1:
The patent merges the signal line requirements of two adjacent pixels, allowing them to share common data voltage lines and scanning signal lines. By combining the circuit structures, the number of independent signal lines per pixel is reduced, enabling closer pixel spacing and higher pixel density while maintaining complete driving functionality through the shared signal distribution network.
3Reliability
If threshold voltage variations are compensated in traditional circuits, then brightness uniformity improves, but the circuit complexity and production cost increase
Solution Approach 1:
The patent merges the compensation functionality for two pixels into a single compensation transistor and shared compensation circuit. Instead of requiring separate compensation circuits for each pixel, the design uses a shared compensation mechanism that reduces the number of transistors and capacitors needed, thereby lowering production costs while maintaining brightness uniformity across the display.
Solution Approach 2:
The compensation transistor performs universal compensation function for two adjacent pixels simultaneously. By designing the compensation circuit to serve multiple pixels, the patent reduces the overall component count and production complexity while achieving the same brightness uniformity result that would require separate compensation circuits for each pixel.
Data Source
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Figure 3(a)
AI summary
A pixel circuit, comprises two sub-pixel circuits(P1, P2) and a sixth switch unit(T6); a first terminal of the sixth switch unit(T6) is connected to an operating voltage line(Vdd), and a control terminal of the sixth switch unit is connected to a first scan signal line(Em); each of the sub-pixel circuits(P1, P2) comprises five switch units(T1, T2, T3, T4, T5), a driving unit(DT), a energy storage unit(C) and an electroluminescent unit(L), a first switch unit(T1) and a fourth switch unit(T4) in a first sub-pixel circuit(P1) share a scan signal line(Scan[3]) with a first switch unit(T1') and a fourth switch unit(T4') in a second sub-pixel circuit(P2), and a third switch unit(T3) in the first sub-pixel circuit(P1) share a scan signal line(Scan[2]) with a third switch unit(T3') in the second sub-pixel circuit(P2). The pixel circuit completely solves the problem of non-uniformity in the display brightness due to drifting of the threshold voltage of the driving transistor. Meanwhile, one compensation circuit is used to drive two pixels, and two adjacent pixels share multiple signal lines, which can reduce the number of signal lines for the pixel circuit in a display apparatus, lower the cost of the integration circuit, decrease the pixel pitch, and increase the pixel density.