Pixel Circuit Reset Scheme for OLED Ghosting Compensation
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Solution Overview
Problem
The threshold voltage of drive transistors in electroluminescent display devices shifts due to process variations and aging, leading to hysteresis effects that cause ghosting during gray scale transitions, and existing pixel circuits fail to adequately compensate for these changes.
Innovation Solution
A pixel circuit with a voltage control circuit that resets the control and electrodes of the drive transistor before data input, and includes a threshold compensation circuit to adjust the threshold voltage, along with a data writing circuit to input the data voltage, ensuring consistent electrode voltages across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit without voltage control circuit is used, then the device complexity is low, but threshold voltage shifts cause ghosting effects and display uniformity deteriorates
Solution Approach 1:
The voltage control circuit performs preliminary reset action on the control electrode, first electrode, and second electrode of the drive transistor before data voltage input. This preliminary resetting action eliminates hysteresis effects and threshold voltage shifts that would otherwise cause ghosting, ensuring consistent voltage levels across all electrodes at the start of each frame without requiring complex continuous adjustment mechanisms
Solution Approach 2:
The voltage control circuit acts as an intermediary component between the data writing circuit and the drive transistor. It introduces a reset switch and storage capacitor that mediate the voltage application process, ensuring proper initialization of transistor electrodes before data voltage is applied, thereby eliminating direct coupling issues and hysteresis effects
2Reliability
If reset operation is added to voltage control circuit, then ghosting effect is mitigated, but the duration of action increases
Solution Approach 1:
The voltage control circuit implements periodic reset operations at the beginning of each frame, rather than continuous operation. The reset switch is activated only during the reset period before data voltage input, and remains inactive during the light emission period. This periodic action pattern eliminates ghosting effects while minimizing the duration of active reset operation to only when needed
Solution Approach 2:
The reset function is extracted as a separate, dedicated operation within the voltage control circuit, isolated from the data writing and light emission functions. By separating the reset operation temporally and functionally, the circuit can perform rapid initialization without interfering with the subsequent data voltage input and light emission processes, thereby reducing overall operation duration
Data Source
AI summary
Provided are a pixel circuit and a drive method therefor, a display panel and a display device. The pixel circuit includes: a light emitting device; a drive transistor configured to generate, according to a data voltage, a drive current for driving the light emitting device to emit light; a data writing circuit coupled to the drive transistor, where the data writing circuit is configured to input the data voltage in response to a signal applied to the data writing circuit; and a voltage control circuit coupled to the drive transistor, where the voltage control circuit is configured to reset a control electrode, a first electrode and a second electrode of the drive transistor in response to a signal applied to the voltage control circuit before the data voltage is input.