Pixel Circuit Voltage Segmentation for Display Uniformity
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Solution Overview
Problem
High-resolution electroluminescent displays face challenges in achieving uniform image quality due to variations in driving characteristics between pixels, exacerbated by voltage drops in supply lines, which lead to non-uniform luminance and increased power consumption.
Innovation Solution
The implementation of a pixel circuit with a driving transistor, switching transistors, and capacitors that manage supply voltages and reference voltages to compensate for driving characteristic differences, ensuring uniform image quality without the need for low-resistance VDD lines, and preventing short-circuiting of high potential driving voltage and reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the width of VDD line is increased to reduce voltage drop, then the voltage uniformity is improved, but the area occupied by VDD line increases and resolution is degraded
Solution Approach 1:
The VDD line is divided into multiple segments with different voltage levels (first VDD line at higher voltage, second VDD line at lower voltage). This segmentation allows each segment to be optimized independently, reducing the need for a single wide low-resistance line while maintaining voltage uniformity across the display panel.
Solution Approach 2:
Different regions of the display panel are provided with different voltage levels through the segmented VDD lines. The first VDD line supplies higher voltage to regions experiencing greater voltage drops, while the second VDD line supplies lower voltage to regions with adequate voltage levels, creating local quality optimization.
2Reliability
If the width of VDD line is increased to reduce voltage drop, then the voltage uniformity is improved, but the device complexity increases
Solution Approach 1:
The power supply system is segmented into multiple VDD lines with different voltage levels, managed by switching transistors. This segmentation distributes the complexity across multiple simple components rather than requiring a single complex low-resistance line, making the overall system more manageable and manufacturable.
Solution Approach 2:
The voltage supply to different regions is made dynamic through switching transistors that can selectively connect pixels to different VDD lines based on their specific needs. This dynamic adjustment capability allows the system to adapt to varying voltage requirements without permanent complex routing.
3Reliability
If internal compensation circuit is used to compensate for driving characteristic differences, then the image quality is improved, but the luminance uniformity is degraded due to VDD variation
Solution Approach 1:
The power supply is segmented into multiple VDD lines with different voltage levels to compensate for position-dependent voltage drops. This segmentation ensures that pixels at different locations receive appropriate voltage levels, maintaining luminance uniformity across the display while allowing internal compensation circuits to function effectively for image quality.
Solution Approach 2:
The voltage parameter of VDD is changed across different regions (higher voltage for distant regions, lower voltage for near regions) to compensate for IR drops. This parameter change approach allows the system to maintain both luminance uniformity and enable effective internal compensation for pixel characteristic variations.
Data Source
AI summary
An electroluminescent display is disclosed. An electroluminescent display comprises a display panel including a plurality of pixels, each of the plurality of pixels including subpixels. A pixel circuit of each subpixels includes a driving transistor configured to drive the electroluminescent diode, a first switching transistor configured to supply a first voltage to a gate of the driving transistor in response to a first scan signal, a second switching transistor configured to supply a second voltage to the gate of the driving transistor in response to a second scan signal, a third switching transistor configured to supply the second voltage to a first electrode of the driving transistor in response to the second scan signal, a fourth switching transistor configured to supply a first supply voltage to a second electrode of the driving transistor in response to an emission control signal, a first capacitor between a first node connected to the gate electrode of the driving transistor and a second node connected to the second electrode of the driving transistor, and a second capacitor between the second node and a power supply line supplied with the second voltage or the first supply voltage.