Capacitor-Coupled Mobility Correction for OLED Brightness Uniformity
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Solution Overview
Problem
Existing organic EL displays face challenges in maintaining uniformity of emission brightness due to variations in transistor characteristics such as threshold voltage (Vth) and mobility, which are difficult to correct using traditional Vth correction circuits.
Innovation Solution
A display device with a pixel circuit structure that includes a coupling capacitor, selection transistor, driving transistor, emission control transistor, current-driven light-emitting element, storage capacitor, and reset transistor, allowing for compensation of both Vth and mobility by writing compensation voltages and controlling transistor states to ensure uniform drive current across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Vth correction circuit is used to compensate for threshold voltage variations, then Vth uniformity is improved, but mobility variations cannot be corrected and brightness uniformity deteriorates
Solution Approach 1:
The invention changes the correction approach from only Vth compensation to dual compensation of Vth and mobility parameters. By introducing a mobility correction circuit that writes compensation voltages to the storage capacitor based on mobility characteristics, the system corrects both threshold voltage and mobility variations, thereby achieving high brightness uniformity across all pixels.
2Ease of manufacture
If transistor characteristics vary between pixels, then manufacturing simplicity is maintained, but emission brightness uniformity deteriorates
Solution Approach 1:
The invention implements feedback compensation by measuring or characterizing the mobility variations of transistors and using this information to generate compensation voltages. The mobility correction circuit writes these compensation voltages to the storage capacitor, creating a feedback loop that compensates for transistor characteristic variations and ensures uniform brightness across pixels manufactured with standard processes.
3Device complexity
If mobility variations between pixels are present, then device complexity is reduced, but brightness uniformity over wide gradation range deteriorates
Solution Approach 1:
The invention performs preliminary correction by pre-calculating and storing mobility compensation voltages in the storage capacitor before the actual display operation. The mobility correction circuit writes the compensation voltage corresponding to mobility characteristics to the storage capacitor in advance, so that when gradation signals are applied, the compensation is already in place, ensuring uniform brightness across the entire gradation range without adding complex real-time correction circuits.
Data Source
AI summary
In order to efficiently execute threshold value compensation for a driving transistor, a coupling capacitor (6) has one end connected to a data line (8). Another end of the coupling capacitor (6) is connected to a selection transistor (3) and one end of a reset transistor (4). A control terminal of a driving transistor (2) is connected to the other end of the selection transistor (3), and an organic EL element (1) is connected to this driving transistor via a light emission control transistor (5). A data voltage, corresponding to a gradation signal supplied to the data line (8), is written to a storage capacitor (7) via the coupling capacitor (6), and with the selection transistor (3) and the light emission control transistor (5) in an off state and the reset transistor (4) turned on, a compensation voltage corresponding to a degree of mobility of the driving transistor (2) is written to the coupling capacitor (6).