Pixel Compensation Circuit for AMOLED Luminance Uniformity
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Solution Overview
Problem
The luminance uniformity of AMOLED display devices is compromised due to non-uniformity in the manufacturing process of thin film transistors and drifting threshold voltages, leading to uneven display effects.
Innovation Solution
A pixel compensation circuit is introduced, comprising a data signal writing sub-circuit, high voltage signal writing sub-circuit, reference voltage writing sub-circuits, a voltage maintaining sub-circuit, and a driving transistor, which writes reference voltages to the driving transistor to isolate the driving current from threshold voltage variations and maintains a constant voltage difference across the capacitor, ensuring consistent luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the 2T1C driving circuit is used to drive AMOLED pixels, then the device complexity is reduced and manufacturing is simplified, but luminance uniformity deteriorates due to threshold voltage variations in the second transistor
Solution Approach 1:
The pixel circuit is segmented into multiple functional sub-circuits: a first transistor for data signal input, a second transistor for high voltage signal input, a third transistor for compensation, and multiple capacitors for voltage storage. This segmentation allows independent control and compensation of threshold voltage variations, improving luminance uniformity while maintaining manageable complexity
Solution Approach 2:
Capacitors are introduced as intermediary elements to store reference voltages and compensate for threshold voltage variations. The first capacitor stores a reference voltage at the gate of the second transistor, while the second capacitor stores a reference voltage at the source of the second transistor, acting as mediators to stabilize the driving current against transistor parameter variations
2Manufacturing precision
If threshold voltage compensation is implemented to improve luminance uniformity, then manufacturing precision improves, but device complexity increases due to additional transistors and capacitors
Solution Approach 1:
The compensation mechanism performs preliminary action by writing reference voltages to the gate and source of the second transistor before the light emission phase. This preliminary voltage writing compensates for threshold voltage variations in advance, ensuring stable driving current during light emission without requiring continuous complex control during operation
3Ease of operation
If the gate voltage of the second transistor is maintained using a capacitor, then the ease of operation is improved, but luminance uniformity deteriorates due to threshold voltage drifting during light emission
Solution Approach 1:
A second capacitor is introduced as an intermediary to store a reference voltage at the source of the second transistor. This intermediary capacitor, combined with the third transistor, enables dynamic compensation of threshold voltage drifting during light emission by adjusting the source voltage to maintain constant Vgs, thereby improving luminance uniformity while preserving the ease of voltage maintenance
Data Source
AI summary
The present disclosure relates to a pixel compensation circuit and an AMOLED display device. The pixel compensation circuit includes a data signal writing sub-circuit, a high voltage signal writing sub-circuit, a first reference voltage writing sub-circuit, a second reference voltage writing sub-circuit, a voltage maintaining sub-circuit, a driving transistor, a capacitor, and a light emitting device. The data signal writing sub-circuit is connected to a first terminal of the capacitor, the first reference voltage writing sub-circuit is connected to a control electrode of the driving transistor, and the second reference voltage writing sub-circuit is connected to a drain of the driving transistor. The high voltage signal writing sub-circuit is connected to a second terminal of the capacitor, and the voltage maintaining sub-circuit is connected to the first terminal of the capacitor and the control electrode of the driving transistor.