OLED Pixel Compensation Circuit for Extended Threshold Sampling
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Solution Overview
Problem
Conventional compensation methods for organic light emitting display devices fail to adequately compensate for differences in drive characteristics between pixels, particularly in high-resolution and high-speed applications, leading to luminance deviations and visible spots on the screen due to insufficient threshold voltage sampling periods.
Innovation Solution
The display device incorporates an internal compensation circuit with a compensation transistor and a wider gate ON pulse to extend the threshold voltage sampling period, and includes a compensation capacitor to maintain data voltage during an additional sampling period, utilizing oxide semiconductor transistors for improved pixel control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional compensation method is used, then device complexity is reduced, but measurement precision of threshold voltage sampling deteriorates due to insufficient sampling period
Solution Approach 1:
The patent segments the gate ON pulse into multiple phases: a first gate ON pulse for initial threshold voltage sampling during the horizontal period, and a second gate ON pulse for additional sampling after the horizontal period. This segmentation allows threshold voltage sampling to extend beyond the conventional time limit, improving measurement precision without requiring a longer overall horizontal period.
Solution Approach 2:
The compensation capacitor stores the data voltage applied to the gate electrode before the second gate ON pulse occurs. This preliminary action preserves the voltage state, enabling accurate threshold voltage sampling during the extended period after the horizontal period without losing the original data voltage information.
2Manufacturing precision
If oxide semiconductor transistor is used, then manufacturing precision is improved, but device complexity increases due to additional compensation circuit components
Solution Approach 1:
The compensation transistor serves multiple functions: it acts as a switching element during normal operation and simultaneously functions as the core component for threshold voltage compensation during the extended sampling period. The compensation capacitor also serves dual purposes by maintaining data voltage and enabling the extended sampling process. This multi-functionality reduces the need for separate dedicated compensation components.
Solution Approach 2:
The patent employs dynamic control of the compensation transistor through time-varying gate signals with different pulse widths. The transistor's operational state changes dynamically between the first and second gate ON pulses, allowing the same hardware structure to adapt to different sampling phases without requiring additional static compensation components.
Data Source
AI summary
A display device includes a display panel on which gate lines, data lines and subpixels are disposed; a gate driving circuit which drives the gate lines; and a data driving circuit which drives the data lines. Each of the subpixels includes: a light emitting device; a second transistor which has a first node, a second node that is a gate node, and a third node electrically connected to the light emitting device, and drives the light emitting device; a first transistor electrically connected between the third node and the data line; a third transistor electrically connected between the first node and the second node; and a fourth transistor electrically connected between the third node and the light emitting device. The third transistor performs a turn-off operation later than the first transistor, so that a voltage applied to the third node is transmitted to the second node via the first node.