OLED Pixel Driving Circuit Brightness Uniformity
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Solution Overview
Problem
Large display panels using organic light emitting devices (OLEDs) face issues with non-uniform brightness due to varying driving voltages across different positions, and a flicker phenomenon caused by short data voltage emission periods, especially in larger panels.
Innovation Solution
A pixel driving method and apparatus that charges data voltage to a storage capacitor while cutting off the upper or lower power supply voltage to the OLED, allowing the driving transistor to emit light with a consistent brightness by maintaining the driving voltage, and distributing lower power supply voltages across multiple regions to prevent voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If data voltage is supplied continuously to OLED in large display panels, then brightness can be maintained, but non-uniform brightness occurs due to voltage drops at different positions
Solution Approach 1:
The display panel is divided into multiple regions, each with its own independent lower power supply voltage terminal. This segmentation allows each region to have its voltage independently controlled and compensated, preventing voltage drops from affecting the entire panel and ensuring uniform brightness across all regions.
Solution Approach 2:
Different regions of the display panel are provided with tailored voltage compensation based on their specific requirements. Each region's lower power supply voltage is adjusted locally to compensate for position-dependent voltage drops, ensuring that each region maintains optimal driving voltage for uniform brightness.
2Illumination intensity
If data voltage emission period is extended to cover entire frame period, then brightness uniformity improves, but flicker phenomenon occurs due to insufficient emission time
Solution Approach 1:
Data voltages are charged to storage capacitors during the programming period before the emission period begins. This preliminary action ensures that when the emission period starts, the storage capacitors already contain the required data voltages, allowing immediate and sustained light emission without flicker while maintaining brightness uniformity throughout the emission period.
3Measurement precision
If programming period is extended to charge data voltages properly, then data voltage accuracy improves, but emission period becomes insufficient causing flicker
Solution Approach 1:
The programming period is utilized as a preliminary action phase where data voltages are charged to storage capacitors before the emission period. This allows sufficient time for accurate voltage charging without encroaching on the emission period duration, ensuring both data voltage accuracy and adequate emission time for flicker-free display.
Data Source
AI summary
A pixel driving method for an organic light emitting device includes charging a data voltage supplied through a data line to a storage capacitor and driving an N-channel switching transistor while cutting off supply of an upper power supply voltage to an organic light emitting diode; and powering the organic light emitting diode emit light by driving the N-channel driving transistor by the data voltage charged onto the storage capacitor while supplying the upper power supply voltage to the light emitting diode.