OLED Pixel Circuit Current Control for IR Drop Compensation
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Solution Overview
Problem
AMOLED display panels face issues with IR drop and threshold voltage variations, which affect the brightness level and quality of display due to their dependence on voltage signals and threshold voltages.
Innovation Solution
An OLED pixel circuit with a charging control module, resetting control module, and driving transistor, where the driving transistor generates a driving current based on the potential difference between its source and a preset potential, independent of the voltage signal and threshold voltage, using capacitors and transistors to reset and compensate the control terminal, thereby eliminating the negative effects of IR drop and threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional OLED pixel circuits use voltage signals to control driving current, then the circuit structure is simple, but the display quality deteriorates due to IR drop and threshold voltage variations
Solution Approach 1:
The patent changes the control parameter from voltage to current. The driving transistor is controlled by a current signal instead of a voltage signal, which makes the driving current independent of IR drop and threshold voltage variations. This parameter change resolves the contradiction by maintaining simple circuit structure while improving display quality through current-mode operation.
Solution Approach 2:
The patent introduces a current mirror circuit as an intermediary between the control signal and the driving transistor. The current mirror circuit converts the control voltage into a stable reference current, which then controls the driving transistor. This intermediary structure eliminates the direct dependence on voltage signals, resolving the contradiction between simple structure and high display quality.
2Ease of operation
If the driving current depends on voltage signal and threshold voltage, then the circuit operation is straightforward, but the brightness level and display quality become unstable
Solution Approach 1:
The patent implements a feedback mechanism through the current mirror circuit that continuously maintains a stable reference current. The current mirror circuit senses and replicates the reference current, providing feedback control that ensures the driving current remains stable despite variations in threshold voltage. This feedback approach maintains straightforward operation while ensuring brightness stability.
Solution Approach 2:
The current mirror circuit automatically compensates for threshold voltage variations without requiring external intervention. The circuit self-adjusts by using the reference current as a stable benchmark, allowing the driving transistor to maintain consistent current output. This self-service mechanism ensures reliability while keeping the circuit operation simple.
3Ease of manufacture
If voltage signals are used to control the driving transistor, then the circuit design is conventional and simple, but IR drop affects the driving current and display quality
Solution Approach 1:
The patent substitutes the voltage-based control mechanism with a current-based control mechanism. Instead of using voltage signals that are susceptible to IR drop, the system uses current signals that are inherently immune to voltage drops. This substitution maintains conventional design simplicity while eliminating the harmful effect of IR drop on driving current and display quality.
Data Source
AI summary
An OLED pixel circuit includes a charging control module (1), a resetting control module (2), and a driving transistor (3). The charging control module (1) is connected to a data signal line and the resetting control module (2). The resetting control module (2) is connected to the driving transistor (3) to reset and compensate the driving transistor (3) to set a control terminal of the driving transistor (3) at a first potential value. The driving transistor (3) is configured to generate a driving current being based on a difference between a potential of a source of the driving transistor and the first potential value, irrespective of a voltage signal at the source of the driving transistor and a threshold voltage of the driving transistor (3).