Display Device Parasitic Capacitor Discharge Control
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Solution Overview
Problem
Organic light emitting display devices often experience light spot defects due to defective pixel circuits or foreign substances, leading to unintended light emission during operation, which degrades display quality.
Innovation Solution
A display device and driving method that include a pixel unit with light emitting elements, driving and switching transistors, and a sensing control transistor, along with a scan driver and sensing unit, which perform sensing operations by sequentially providing scan and sensing control signals to horizontal lines at predetermined discharge cycles to prevent light spot defects by discharging accumulated charges in parasitic capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage corresponding to black grayscale is applied during sensing operation, then the light emitting element should not emit light, but unintended light spots may still occur due to accumulated charges in parasitic capacitors
Solution Approach 1:
The patent implements periodic discharge of parasitic capacitors through the sensing control transistor at predetermined discharge cycles during the sensing operation. This periodic action ensures that accumulated charges are regularly removed, preventing unintended light emission while maintaining the black grayscale display quality throughout the sensing operation.
Solution Approach 2:
The sensing unit continuously monitors the voltage at the first node during the sensing operation and provides feedback to the timing controller. Based on this feedback, the timing controller controls the sensing control transistor to discharge parasitic capacitors when necessary, creating a closed-loop system that prevents light spot defects while maintaining display quality.
2Measurement precision
If sensing operation is performed to acquire transistor characteristics, then display quality is maintained, but unintended light spots may be generated during the sensing process
Solution Approach 1:
The patent applies a voltage corresponding to black grayscale to the data line before and during the sensing operation. This preliminary action ensures that the light emitting element is prepared to remain off-state, and the sensing control transistor is activated to discharge any accumulated charges in parasitic capacitors before the actual sensing measurement begins, preventing unintended light emission during the measurement process.
Solution Approach 2:
During the sensing operation, the sensing control transistor is activated at predetermined discharge cycles to periodically discharge parasitic capacitors. This periodic discharge action continues throughout the sensing process, ensuring that no unintended light spots are generated while allowing accurate measurement of transistor characteristics.
3Reliability
If the sensing control transistor is activated continuously to discharge parasitic capacitors, then light spot defects are prevented, but additional control complexity is introduced
Solution Approach 1:
The sensing control transistor serves multiple functions: it controls the discharge of parasitic capacitors during sensing operations, maintains the black grayscale state during normal display operation, and provides a unified control mechanism for both sensing and display modes. This multi-functionality reduces the need for separate control circuits, thereby managing complexity while ensuring reliable prevention of light spot defects.
Solution Approach 2:
The timing controller dynamically adjusts the activation of the sensing control transistor based on the operational mode. During sensing operations, the transistor is activated at predetermined discharge cycles to discharge parasitic capacitors. During normal display operation, the transistor remains inactive or is activated only when necessary to maintain the black grayscale state. This dynamic control strategy prevents light spot defects while minimizing control complexity by adapting the transistor's behavior to the current operational context.
Data Source
AI summary
A display device for performing a sensing operation according to an embodiment of the present inventive concept includes a pixel unit including pixel circuits each including a light emitting element, a driving transistor, a switching transistor, and a sensing control transistor connected between an anode electrode and an initialization power source; a scan driver connected to the pixel circuits through horizontal lines and sequentially outputting scan signals and sensing control signals; and a sensing unit configured to sense voltages or current of first nodes each disposed between an anode electrode and a driving transistor. The scan driver simultaneously outputs the sensing control signals to the horizontal lines at every predetermined discharge cycle.