AMOLED Pixel Circuit Compensation for Line Propagation Delay
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Solution Overview
Problem
Active Matrix Organic Light Emitting (AMOLED) displays face challenges due to non-uniformity, aging, and hysteresis of OLED and backplane devices, which introduce time-invariant and time-variant factors affecting image quality, particularly in large area applications with high refresh rates, and are exacerbated by propagation delays in data and monitor lines.
Innovation Solution
The implementation of pixel circuits that allow for monitoring of degradation via a monitoring switch transistor, enabling independent programming of pixels regardless of switching transistor resistance, and isolating storage capacitors from driving transistors to prevent charge interference during programming, along with techniques to characterize and eliminate propagation delays in data and monitor lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monitoring systems are added to measure time dependent parameters for compensation, then image uniformity and aging compensation are improved, but device complexity increases due to additional transistors and lines
Solution Approach 1:
The pixel circuit is designed to perform both display function and monitoring function using the same transistors and circuit elements. The first transistor serves as both a switching element for display and as a monitoring element for degradation detection, eliminating the need for separate monitoring circuitry.
Solution Approach 2:
The pixel circuit monitors its own degradation by measuring the threshold voltage shift of its internal transistors. The circuit uses its own operating characteristics to detect aging effects, eliminating the need for external monitoring systems and additional dedicated monitoring transistors.
2Measurement precision
If additional transistors and lines are incorporated for monitoring, then degradation measurement capability is improved, but pixel-pitch decreases
Solution Approach 1:
Existing pixel circuit transistors are utilized for dual purposes: display operation and degradation monitoring. The first transistor's threshold voltage is measured to detect aging, eliminating the need for additional dedicated monitoring transistors and preserving pixel-pitch.
Solution Approach 2:
The monitoring function is extracted from a separate dedicated circuit and integrated into the existing pixel circuit operations. By measuring parameters during normal display operation, the patent eliminates the need for separate monitoring hardware that would consume pixel area.
3Productivity
If programming time is reduced for high refresh rates, then productivity is improved, but propagation delay effects and settling issues worsen
Solution Approach 1:
The pixel circuit is pre-configured with compensation capabilities built into its structure. The monitoring and measurement functions are prepared in advance within the circuit design, allowing rapid characterization of propagation delays and settling effects without requiring extended programming time during operation.
Solution Approach 2:
The patent utilizes changes in transistor threshold voltage as a function of aging and operating conditions to compensate for propagation delay effects. By measuring and adjusting based on these parameter changes, the system achieves accurate compensation with minimal programming time.
Data Source
AI summary
A method for characterizing and eliminating the effect of propagation delay on data and monitor lines of AMOLED panels is introduced. A similar technique may be utilized to cancel the effect of incomplete settling of select lines that control the write and read switches of pixels on a row.