OLED Pixel Circuit Threshold Compensation for Uniform Emission
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Solution Overview
Problem
OLED display devices suffer from issues such as short-term residual images and non-uniform display due to threshold voltage drift and leakage currents in drive transistors, which are exacerbated by manufacturing variations and temperature changes.
Innovation Solution
A pixel circuit with a drive circuit, data writing circuit, compensating circuit, reset circuit, and light emitting control circuits is employed, which maintains a constant off-bias or on-bias state for the drive transistor and compensates for threshold voltage variations, thereby alleviating residual image issues and improving display uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit is used, then the device structure is simple, but short-term residual images and non-uniform display occur due to threshold voltage drift and leakage currents
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: drive circuit, data writing circuit, compensating circuit, reset circuit, and light emitting control circuit. Each module performs a specific function to address different aspects of the display uniformity problem, allowing the complex compensation tasks to be distributed across specialized sub-circuits rather than requiring a single complex circuit design.
Solution Approach 2:
The compensating circuit performs preliminary compensation for threshold voltage variations before the light emitting phase. By pre-compensating the drive transistor threshold voltage using the scan signal and written data signal, the circuit ensures that the drive transistor operates at the correct bias level, preventing residual image formation before it occurs.
2Stability of the object's composition
If the drive transistor is kept in a constant bias state, then residual image issues are reduced, but additional circuit components are required to maintain the bias state
Solution Approach 1:
The compensating circuit establishes a feedback mechanism that uses the scan signal and written data signal to continuously monitor and adjust the drive transistor gate voltage. This feedback loop ensures the drive transistor maintains a constant off-bias or on-bias state by compensating for threshold voltage drift, thereby stabilizing the bias state without requiring excessive additional components.
Solution Approach 2:
The scan signal serves multiple functions: it acts as a control signal for row selection, a reference signal for threshold voltage compensation, and a trigger for the compensation operation. By making the scan signal multi-functional, the patent reduces the need for separate dedicated compensation signals or circuits, thereby limiting the increase in device complexity.
3Reliability
If compensation for threshold voltage variations is implemented, then display uniformity is improved, but the circuit requires more components and control signals
Solution Approach 1:
The compensating circuit merges the threshold voltage compensation function with the existing scan signal distribution network. By utilizing the scan signal that already traverses the pixel circuit for row selection, the patent integrates compensation functionality into the existing signal path, avoiding the need for completely separate compensation circuitry and minimizing additional component requirements.
Solution Approach 2:
The compensating circuit acts as an intermediary between the scan signal and the drive transistor gate. It processes the scan signal and written data signal to generate the appropriate compensation voltage, which then adjusts the drive transistor threshold voltage. This intermediary approach allows for precise compensation while maintaining a relatively simple circuit architecture by leveraging existing signals.
Data Source
Figure 1A~1C
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AI summary
A pixel circuit and a method of driving the same, and a display panel. The pixel circuit (10) includes a drive circuit (100), a data writing circuit (200), a compensating circuit (300), a reset circuit (400) and a first light emitting control circuit (500). The drive circuit (100) includes a control terminal (130), a first terminal (110) and a second terminal (120), and the drive circuit (100) is configured to control a drive current for driving a light emitting element (600) to emit light; the data writing circuit (200) is configured to write a data signal to the first terminal (110) of the drive circuit (100) in response to a scan signal; the compensating circuit (300) is configured to compensate the drive circuit (100) in response to the scan signal and the written data signal; the reset circuit (400) is configured to apply a reset voltage to the control terminal (300) of the drive circuit (100) and the first terminal (610) of the light emitting element (600) in response to a reset signal; the first light emitting control circuit (500) is configured to apply a first voltage of the first voltage terminal to the first terminal (110) of the drive circuit (100) in response to a first light emitting control signal. The pixel circuit may alleviate the problem of a short-term residual image and compensate the threshold voltage of the drive circuit.