Pixel Circuit Real-Time Sensing for OLED Degradation
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Solution Overview
Problem
Organic light emitting display devices face issues with luminance variations and image blur due to degradation of organic light emitting diodes and variations in threshold voltage/mobility of driving transistors, as they cannot perform real-time pixel current sensing operations.
Innovation Solution
A pixel circuit is designed with a scan switch, storage capacitor, driving transistor, control switches, and a sensing switch, allowing for real-time sensing of driving transistor and organic light emitting diode characteristics by utilizing specific control signals and power voltage adjustments during vertical blank periods, enabling the detection of sensing currents during image display periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If real-time pixel current sensing operations are implemented, then display quality is improved by compensating for degradation and voltage variations, but device complexity increases due to additional control switches and sensing circuits
Solution Approach 1:
The pixel circuit is segmented into distinct functional blocks: a driving transistor for current generation, storage capacitors for voltage holding, control switches for timing management, and sensing switches for current detection. This segmentation allows each component to perform its specific function efficiently while enabling real-time sensing capabilities without requiring complete circuit redesign.
Solution Approach 2:
The pixel circuit employs multi-functional switches that serve different purposes at different times. The control switches and sensing switches are integrated into the same pixel circuit structure, allowing the circuit to perform both driving functions and sensing functions using shared components. This multi-functionality reduces the need for entirely separate sensing circuits, thereby limiting the increase in device complexity.
2Loss of time
If sensing operations are performed during vertical blank periods, then sensing time is reduced and display quality is maintained, but measurement precision may be affected by timing constraints
Solution Approach 1:
The pixel circuit performs sensing operations during the vertical blank period, which occurs before the next frame's data writing begins. This preliminary sensing action allows the system to detect pixel current and calculate degradation before the display updates, ensuring that compensation can be applied without interrupting the display timing. The sensing is prepared in advance during the available blank time.
Solution Approach 2:
The sensing operation is performed periodically during each vertical blank period between frames. This periodic timing ensures that sensing occurs at regular intervals without conflicting with the continuous display operation. The control signals are synchronized to activate sensing switches only during these predetermined periodic windows, balancing sensing needs with display requirements.
3Difficulty of detecting and measuring
If multiple control switches are added for real-time sensing, then pixel current detection capability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The pixel circuit incorporates feedback mechanisms where the sensing current is detected and used to calculate pixel degradation. The control switches are managed through coordinated control signals that provide timing feedback, ensuring that sensing operations occur at the correct moments. This feedback approach allows the system to adapt to timing variations and maintain measurement accuracy despite manufacturing tolerances.
Solution Approach 2:
The circuit utilizes parameter changes in the control signals to manage the multiple switches. By varying the timing parameters of control signals (such as gate voltages and pulse widths), the system can precisely control when each switch operates. This parameter-based control allows flexible adjustment of switch timing to compensate for manufacturing variations and achieve accurate sensing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for real-time detection and compensation of pixel current, reducing sensing time and maintaining display quality by addressing degradation and voltage/mobility variations of the organic light emitting diode and driving transistor.
Implementation Method 1
An organic light emitting display device displays images using organic light emitting diodes
Data Source
AI summary
A pixel circuit according to example embodiments includes a scan switch connected between a data line and a first node, a storage capacitor, an organic light emitting diode, a driving transistor connected to a first power voltage and configured to generate a driving current, a first control switch connected between the driving transistor and a second node and configured to be turned on during a first sensing period based on a first control signal, a second control switch connected between the second node and an anode of the organic light emitting diode and configured to be turned on during a second sensing period based on a second control signal, and a sensing switch connected between the data line and the second node and configured to be turned on based on a sensing control signal.