OLED Pixel Sensing via Reverse Bias Current Integration
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Solution Overview
Problem
Existing organic light emitting display devices face challenges in accurately sensing the driving characteristics of OLEDs due to small differences in parasitic capacitances caused by process variations or deterioration, leading to image sticking phenomena and luminance deviations.
Innovation Solution
A pixel sensing device and method that involves a driving transistor connected in series with the OLED, with specific voltage and timing control phases to accurately sense the pixel current, using a storage capacitor and current integrator to generate corrected image data based on sensed voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional parasitic capacitance sensing method is used, then compensation can be applied, but the small differences in parasitic capacitances due to process variation or deterioration make accurate sensing difficult
Solution Approach 1:
The patent introduces an intermediary sensing current that flows through the OLED during a dedicated sensing period. This current is generated by turning on the driving transistor while the OLED is reverse-biased, creating a measurable signal that indirectly reflects the OLED's driving characteristics without requiring direct measurement of the small parasitic capacitance differences. The sensing current serves as a mediator that amplifies the detection capability.
Solution Approach 2:
The patent changes the operating parameters of the OLED by applying reverse bias voltage during the sensing period, which alters the OLED's electrical characteristics. This parameter change enables the generation of a sensing current that is proportional to the OLED's driving characteristics, making it possible to accurately detect process variations and deterioration that would be invisible under normal forward-bias operating conditions.
2Reliability
If OLED driving characteristics are not compensated, then device complexity is reduced, but image sticking phenomenon occurs due to luminance deviations
Solution Approach 1:
The patent performs preliminary sensing of the OLED's driving characteristics during a dedicated sensing period before the actual display period. By measuring the sensing current and determining the operating point voltage in advance, the system can pre-calculate compensation values that will be applied during subsequent display periods, preventing image sticking before it occurs rather than correcting it after.
Solution Approach 2:
The patent implements a feedback mechanism where the sensed operating point voltage and sensing current are used to generate compensation values that adjust the drive signals for the OLED. This closed-loop feedback ensures that any drift in OLED characteristics due to process variation or deterioration is continuously compensated, maintaining image quality stability without requiring overly complex open-loop compensation circuits.
3Measurement precision
If multiple voltage levels and timing phases are implemented for sensing, then accurate operating point voltage determination is achieved, but operation complexity increases
Solution Approach 1:
The patent employs periodic action by dividing the operation into distinct time periods: a sensing period where the OLED is reverse-biased and the driving transistor is turned on to generate sensing current, and a display period where normal operation resumes. This periodic switching between sensing and display modes, controlled by timing signals, enables accurate measurement while maintaining manageable operational complexity through systematic phase management.
Data Source
AI summary
The present disclosure relates to a display device and sensing method. A display device includes a plurality of pixels. At least one of the pixels includes an organic light emtting diode (OLED) and a driving transistor. The driving transistor is connected in series with the OLED with a node between the OLED and the driving transistor. During a programming period the driving transistor is turned off and the OLED is turned on. During a discharging period the driving transistor is turned off and a voltage charged on the node during the programming period is discharged through the OLED. During a sensing period the OLED is turned off and the driving transistor is turned on to generate a pixel current to be sensed.