AMOLED Pixel Circuit Relaxation Driving for Luminance Uniformity
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Solution Overview
Problem
Active-matrix organic light emitting diode (AMOLED) displays experience non-uniform luminance due to pixel degradation over time, leading to discrepancies between intended and actual brightness, affecting image quality.
Innovation Solution
A method and pixel circuit design that includes a driving transistor, storage capacitor, and switch transistors to implement a relaxation driving scheme, where the pixel circuit is programmed with a different voltage to reduce stress and recover from aging, using a relaxation switch transistor to mitigate threshold voltage shift and balance aging across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous operation is maintained to ensure display functionality, then productivity is improved, but pixel degradation accelerates causing luminance non-uniformity
Solution Approach 1:
The patent implements periodic relaxation cycles where the display alternates between normal operation mode and relaxation mode. During relaxation mode, pixels are subjected to reduced stress conditions with adjusted voltage levels and modified driving waveforms. This periodic switching allows pixels to recover from degradation accumulated during normal operation, thereby maintaining luminance uniformity over time while preserving continuous display functionality.
2Measurement precision
If programming voltage is increased to improve image quality, then measurement precision is improved, but stress on pixels increases accelerating degradation
Solution Approach 1:
The patent dynamically adjusts voltage parameters based on the operational phase. During normal operation, higher programming voltages are applied to ensure accurate image rendering and luminance precision. During relaxation phases, voltage levels are reduced and driving waveforms are modified to minimize stress on pixels. This parameter modulation allows the system to achieve high image quality when needed while reducing degradation during recovery periods.
3Reliability
If relaxation operation is implemented to reduce pixel stress, then reliability is improved, but display time is reduced
Solution Approach 1:
The patent implements periodic relaxation cycles where the display alternates between normal operation mode and relaxation mode. During relaxation mode, pixels are subjected to reduced stress conditions with adjusted voltage levels and modified driving waveforms. This periodic switching allows pixels to recover from degradation accumulated during normal operation, thereby maintaining luminance uniformity over time while preserving continuous display functionality.
Data Source
AI summary
A display system and method for the same is provided. A display includes a plurality of pixels, each having a light emitting device and a driving transistor for driving the light emitting device, the driving transistor and the light emitting device being coupled in series between a first power supply and a second power supply. The method includes: at a first frame, programming a pixel with a first programming voltage different from a programming voltage for a valid image, and charging at least one of the first power supply and the second power supply so that at least one of the driving transistor and the light emitting device is under a negative bias. The pixel circuit includes: a light emitting device; a driving transistor for driving the light emitting device, the driving transistor having a gate terminal, a first terminal coupled to the light emitting device, and a second terminal; a storage capacitor; a first switch transistor coupled to a data line for providing a programming data and the gate terminal of the driving transistor; and a second switch transistor for reducing a threshold voltage shift of the driving transistor, the storage capacitor and the second switch transistor being coupled in parallel to the gate terminal of the driving transistor and the first terminal of the driving transistor. The method includes: at a first cycle, implementing an image display operation having programming the pixel circuit for a valid image and driving the light emitting device; and at a second cycle, implementing a relaxation operation for reducing a stress on the pixel circuit, including: selecting a relaxation switch transistor coupled to the storage capacitor in parallel.