Pixel Circuit for OLED Luminance Uniformity Correction
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Solution Overview
Problem
Active-matrix organic electroluminescence (EL) display units face irregular luminance issues due to variations in threshold voltage and mobility of driving transistors, affecting uniformity and image quality.
Innovation Solution
A pixel circuit configuration including a driving transistor, a write transistor, and multiple switching transistors, along with storage capacitors, is used to control gate-source voltage and apply signal voltages, allowing for threshold and mobility corrections to stabilize the luminance of organic EL devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If line sequential scanning and basic correction operation are implemented, then irregular luminance is reduced to some extent, but further reduction of irregular luminance is still needed to achieve uniform image quality
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks: driving transistor for current control, write transistor for signal voltage application, first switching transistor for gate voltage control during correction, and second switching transistor for conductive path control. Two storage capacitors are also segmented to store different voltages. This segmentation allows each component to perform its specific function efficiently, enabling further reduction of irregular luminance through coordinated operation.
Solution Approach 2:
The correction operation is performed before the display operation by controlling the gate voltage of the driving transistor to come close to the threshold voltage. The first storage capacitor stores a voltage corresponding to the threshold voltage in advance. This preliminary correction action compensates for threshold voltage and mobility variations before the actual image display, thereby reducing irregular luminance.
2Manufacturing precision
If correction operation controls gate voltage to approach threshold voltage, then irregular luminance is reduced, but additional switching transistors and storage capacitors increase device complexity
Solution Approach 1:
The first storage capacitor serves multiple functions: it stores the threshold voltage for correction operation and maintains the gate voltage during display operation. The second storage capacitor stores the signal voltage and maintains it during both correction and display phases. The second switching transistor provides a conductive path that is utilized during both correction and normal operation. This multi-functionality reduces the need for additional dedicated components.
Solution Approach 2:
The correction operation and display operation are merged into a unified pixel circuit design. The same driving transistor, storage capacitors, and switching transistors are used for both correction and display functions. The conductive path controlled by the second switching transistor is shared between correction operation (connecting gate to source) and display operation (normal current flow path), thereby reducing overall circuit complexity.
Data Source
AI summary
A pixel circuit includes a driving transistor, a write transistor, a first switching transistor, a second switching transistor, a first storage capacitor, and a second storage capacitor. The driving transistor controls a current flowing in a light-emitting device. The write transistor controls application of a signal voltage to a gate of the driving transistor. The first switching transistor controls a gate voltage of the driving transistor upon correction operation that allows a gate-source voltage of the driving transistor to come close to a threshold voltage of the driving transistor. The second switching transistor is provided at a path between first and second terminals. The first storage capacitor is provided at a path between the gate of the driving transistor and the first terminal. The second storage capacitor is provided at a path between the gate of the driving transistor and the second terminal.