Pixel Circuit Retention Capacitor for Luminance Uniformity
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Solution Overview
Problem
Existing active-matrix flat self-emission display apparatus with organic EL devices face challenges in achieving higher-definition displays due to variations in threshold voltages and mobilities of drive transistors and organic EL devices, which affect light emission luminance, and current pixel circuits are complex and not suitable for high-definition displays.
Innovation Solution
The display apparatus incorporates a threshold voltage correcting function, mobility correcting function, and bootstrapping function in each pixel, using power supply voltage as switching pulses to reduce the number of components and interconnects, allowing for reduced pixel area and improved light emission luminance stability despite variations in organic EL device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing pixel circuits with correcting function are used, then light emission luminance can be uniformly controlled, but pixel circuit structure becomes complex with many components
Solution Approach 1:
The patent combines multiple correction functions (threshold voltage correction, mobility correction, and bootstrapping) into a single integrated pixel circuit design. The retention capacitor serves multiple purposes: correcting threshold voltage variations, correcting mobility variations through bootstrapping operation, and maintaining gate voltage during light emission. This merging of functions reduces the number of separate components needed while achieving uniform light emission luminance control.
Solution Approach 2:
The retention capacitor is designed to perform multiple functions simultaneously: it acts as a threshold voltage correction element, a mobility correction element through bootstrapping, and a voltage holding element during light emission. This multi-functionality allows a single component to address multiple sources of luminance variation without requiring separate dedicated components for each correction function.
2Manufacturing precision
If more components are added to pixel circuits for correction functions, then light emission luminance uniformity improves, but pixel area increases
Solution Approach 1:
The patent merges threshold voltage correction, mobility correction, and voltage holding functions into a single retention capacitor structure. This integration eliminates the need for multiple separate components that would each occupy additional pixel area, while still achieving comprehensive correction of luminance variations across the display.
Solution Approach 2:
The retention capacitor is designed as a multi-functional element that simultaneously corrects threshold voltage variations, corrects mobility variations through bootstrapping operation, and maintains gate voltage during light emission. This universal design allows one component to replace what would traditionally require multiple separate components, thereby reducing overall pixel area while maintaining correction effectiveness.
3Device complexity
If power supply voltage is used as switching pulses, then number of components and interconnects is reduced, but control precision must be maintained
Solution Approach 1:
The power supply voltage is designed to serve multiple control functions: it acts as switching pulses for the sampling transistor, as bootstrapping pulses for mobility correction, and as a reference for timing control. This multi-functional use of a single voltage source reduces the need for separate control signals and components while maintaining precise control over the pixel circuit operations through carefully designed timing and voltage levels.
Data Source
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AI summary
Disclosed herein is a display apparatus including a pixel array and a driver configured to drive the pixel array, the pixel array having scanning lines as rows, signal lines as columns, a matrix of pixels disposed at respective intersections of the scanning lines and the signal lines, and power supply lines disposed along respective rows of the pixels, the driver having a main scanner for successively supplying control signals to the scanning lines to perform line-sequential scanning on the rows of the pixels, a power supply scanner for supplying a power supply voltage, which selectively switches between a first potential and a second potential, to the power supply lines in synchronism with the line-sequential scanning, and a signal selector for supplying a signal potential, which serves as a video signal, and a reference potential to the signal lines as the columns in synchronism with the line-sequential scanning.