OLED Pixel Circuit Current Control via Segmented Transistors
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Solution Overview
Problem
Conventional organic light emitting displays face limitations in finely controlling the current and expanding the voltage range of data signals due to errors in digital-to-analog converters and difficulties in controlling the voltage between the gate and source electrodes of the driving transistor.
Innovation Solution
A pixel design that includes a pixel circuit with a first transistor, an amplifier, a load, and a storage capacitor, which supplies a desired current to an organic light emitting diode regardless of the anode voltage, and uses a bias circuit to set a narrower output voltage range for the gate electrode of the driving transistor, allowing for wider voltage range settings of the data signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the data signal voltage range is widened to improve control flexibility, then the adaptability of the display system is improved, but the manufacturing precision of the DAC and pixel circuits must be significantly improved to maintain current control accuracy
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a first transistor for current control, a second transistor for voltage level shifting, and a third transistor for additional control. This segmentation allows each transistor to handle specific voltage ranges and control functions, enabling the overall circuit to achieve wide voltage range adaptability while maintaining precise current control through coordinated operation of individual components with standardized characteristics.
Solution Approach 2:
The second transistor functions as an intermediary between the data signal input and the organic light emitting diode. It receives the data signal with wide voltage range and transforms it into a controlled current through its transistor characteristics, mediating between the voltage domain and current domain. This intermediary approach allows the system to accept wide voltage ranges while maintaining precise current control for the OLED.
2Device complexity
If the voltage between gate and source electrodes of the driving transistor is used for current control, then the device complexity is reduced, but the measurement precision of current control deteriorates
Solution Approach 1:
Different transistors in the pixel circuit are assigned different local functions with optimized characteristics. The first transistor is optimized for precise current control with specific W/L ratios, while the second transistor is optimized for voltage level shifting. This local quality differentiation allows each component to excel at its specific function, achieving high current control precision without requiring the entire circuit to be overly complex.
Solution Approach 2:
The pixel circuit employs dynamic control where the first transistor's current control capability is enhanced through its specific W/L ratio configuration, allowing it to respond dynamically to voltage changes with high precision. The coordinated dynamic operation of multiple transistors with different characteristics enables fine current control while maintaining reasonable device complexity.
Data Source
AI summary
Disclosed is a pixel capable of finely controlling the amount of current and increasing the voltage range of a data signal. A pixel includes an organic light emitting diode, a first transistor, a storage capacitor, a load and an amplifier. The first transistor is coupled between a scan line and a data line, and supplies a data signal supplied to the data line to a first node when a scan signal is supplied to the scan line. The storage capacitor is coupled between the first node and a first power source, and charges a voltage corresponding to the data signal. The load is coupled between the organic light emitting diode and the first power source. The amplifier controls a voltage applied to the load corresponding to the voltage charged in the storage capacitor.