Pixel Circuit Scanning Compensation for OLED Luminance Uniformity
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Solution Overview
Problem
In pixel circuits, the shift in threshold voltage of the driving transistor leads to unstable driving currents for OLED and QLED displays, affecting uniformity and display quality by causing non-uniform luminance.
Innovation Solution
A pixel circuit design incorporating a scanning compensation sub-circuit with a storage capacitor, a reset and precharge sub-circuit, a driving sub-circuit, and a light-emission control sub-circuit, which compensates for the threshold voltage influence by charging the storage capacitor according to a scanning signal, thereby maintaining a consistent voltage difference between nodes to isolate the driving current from the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel circuit without scanning compensation is used, then the circuit structure is simpler, but the driving current becomes unstable due to threshold voltage shift
Solution Approach 1:
The pixel circuit is divided into distinct functional sub-circuits: a reset and precharge sub-circuit, a scanning compensation sub-circuit with storage capacitor, a driving sub-circuit, and a light-emission control sub-circuit. This segmentation allows each sub-circuit to perform its specific function independently, with the scanning compensation sub-circuit specifically addressing threshold voltage shift to stabilize driving current.
Solution Approach 2:
The storage capacitor in the scanning compensation sub-circuit performs preliminary compensation for threshold voltage shift before the driving transistor operates. By pre-charging the storage capacitor according to the scanning signal and using it to compensate for threshold voltage variations, the circuit proactively counteracts potential instability rather than reacting to it.
2Reliability
If threshold voltage compensation is implemented, then driving current stability improves, but the circuit complexity increases
Solution Approach 1:
The scanning compensation sub-circuit with storage capacitor serves multiple functions: it compensates for threshold voltage shift of the driving transistor, maintains consistent voltage difference between nodes, and works across different operating conditions. This multi-functionality achieves reliable driving current stability without requiring separate dedicated circuits for each compensation need.
Solution Approach 2:
The storage capacitor automatically compensates for threshold voltage shift through its charging and discharging cycles controlled by the scanning signal. The circuit uses its own internal resources (the storage capacitor and scanning signal) to perform compensation, eliminating the need for external complex compensation mechanisms.
3Illumination intensity
If the storage capacitor is charged according to scanning signal, then luminance uniformity improves, but the control circuit complexity increases
Solution Approach 1:
The scanning compensation sub-circuit maintains equipotential conditions by ensuring consistent voltage difference between the first node (coupled to light-emission control sub-circuit) and second node (coupled to driving sub-circuit) through the storage capacitor. This equipotential approach ensures uniform luminance across the display by compensating for voltage variations that would otherwise cause luminance non-uniformity.
Data Source
AI summary
A pixel circuit, a method for driving a pixel circuit and a display device are provided. The pixel circuit includes a reset and precharge sub-circuit, a scanning compensation sub-circuit, a driving sub-circuit and a light-emission control sub-circuit, the scanning compensation sub-circuit comprises a storage capacitor, the light-emission control sub-circuit is configured to control a light-emitting device to emit light, the reset and precharge sub-circuit is coupled to the scanning compensation sub-circuit and the light-emission control sub-circuit, and is configured to reset the light-emission control sub-circuit according to a reset signal, and reset a second electrode of the storage capacitor of the scanning compensation sub-circuit according to a scanning signal; the scanning compensation sub-circuit is further coupled to the driving sub-circuit and the light-emission control sub-circuit, and is configured to charge the storage capacitor of the scanning compensation sub-circuit according to the scanning signal.