Pixel Circuit Mobility Correction for OLED Uniformity
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Solution Overview
Problem
In organic electroluminescence (EL) displays, variations in threshold voltage and carrier mobility among thin film transistors lead to non-uniform luminance across the screen, affecting display uniformity.
Innovation Solution
A pixel circuit with a correction unit that adjusts the input voltage to cancel the dependence of output current on carrier mobility by negatively feeding back the output current to the capacitive part, thereby correcting the gate voltage before the emission period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If thin film transistors are used to control current in pixel circuits, then active-matrix display functionality is achieved, but variations in threshold voltage and carrier mobility cause non-uniform luminance across the screen
Solution Approach 1:
The patent applies feedback by negatively feeding back the output current of the drive transistor to the capacitive part. The correction unit detects the output current and adjusts the input voltage accordingly, creating a closed-loop control system that compensates for transistor parameter variations and maintains uniform luminance across the display.
Solution Approach 2:
The patent changes the input voltage parameter dynamically to compensate for variations in transistor threshold voltage and carrier mobility. By adjusting the input voltage based on the detected output current, the system maintains consistent luminance despite manufacturing variations in transistor characteristics.
2Device complexity
If the output current is directly controlled by the drive transistor without correction, then the circuit structure is simple, but the luminance depends on carrier mobility variations causing display non-uniformity
Solution Approach 1:
The correction unit introduces feedback control by detecting the output current and negatively feeding it back to the capacitive part. This allows the system to compensate for carrier mobility variations and achieve uniform luminance while maintaining a relatively simple circuit structure with minimal additional components.
3Ease of operation
If the input voltage is not corrected for mobility dependence, then the circuit operation is straightforward, but pixels with different mobility values produce different luminance levels
Solution Approach 1:
The system automatically corrects the input voltage through feedback control, eliminating the need for manual calibration or complex operation. The correction unit continuously monitors the output current and adjusts the input voltage to compensate for mobility differences, maintaining uniform luminance with straightforward operation.
Solution Approach 2:
The pixel circuit performs self-correction by using its own output current as the feedback signal. The correction unit automatically adjusts the input voltage based on the actual output, enabling the circuit to compensate for its own mobility variations without external intervention.
Data Source
AI summary
The invention provides a pixel circuit that can cancel the influence of the mobility of a drive transistor. A drive transistor supplies a light-emitting element with an output current dependent upon an input voltage. The light-emitting element emits light with a luminance dependent upon a video signal in response to the output current supplied from the drive transistor. The pixel circuit includes a correction unit that corrects the input voltage held by a capacitive part in order to cancel the dependence of the output current on the carrier mobility.