Pixel Circuit Mobility Compensation for OLED Brightness Uniformity
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Solution Overview
Problem
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 existing 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, where a compensation voltage is written to the coupling capacitor to correct for mobility variations, ensuring uniform brightness across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Vth correction circuit is used to correct threshold voltage variations, then threshold voltage compensation is improved, but mobility variations cannot be corrected and brightness uniformity deteriorates
Solution Approach 1:
The patent applies parameter changes by introducing a mobility compensation voltage (Vmob) in addition to the threshold voltage compensation voltage (Vth). The gate-source voltage of the driving transistor is composed of both Vth and Vmob components, allowing independent correction of threshold voltage and mobility variations. This dual-parameter compensation approach resolves the contradiction by expanding the compensation capability beyond just Vth correction.
2Ease of manufacture
If transistor characteristics vary between pixels, then manufacturing simplicity is improved, but emission brightness uniformity deteriorates
Solution Approach 1:
The patent implements feedback compensation by measuring the actual transistor characteristics (Vth and mobility) through dedicated circuitry and using these measurements to adjust the gate-source voltage of the driving transistor. The compensation voltages are derived from the transistor's own characteristics, creating a closed-loop system that automatically corrects for manufacturing variations without requiring complex fabrication processes.
3Manufacturing precision
If mobility compensation is added to correct carrier mobility variations, then brightness uniformity is improved, but circuit complexity increases
Solution Approach 1:
The patent achieves multi-functionality by designing the pixel circuit to perform both threshold voltage compensation and mobility compensation using a unified compensation mechanism. The same circuit structure and control methodology are used for both Vth and Vmob compensation, allowing the circuit to handle multiple compensation tasks without proportionally increasing complexity. The compensation voltages are generated and applied through integrated circuit elements that serve dual purposes.
Data Source
AI summary
In order to efficiently execute threshold value compensation for a driving transistor, a coupling capacitor has one end connected to a data line. Another end of the coupling capacitor is connected to a selection transistor and one end of a reset transistor. A control terminal of a driving transistor is connected to the other end of the selection transistor, and an organic EL element is connected to this driving transistor via a light emission control transistor. A data voltage, corresponding to a gradation signal supplied to the data line, is written to a storage capacitor via the coupling capacitor, and with the selection transistor and the light emission control transistor in an off state and the reset transistor turned on, a compensation voltage corresponding to a degree of mobility of the driving transistor is written to the coupling capacitor.