Voltage Compensator for OLED Pixel Circuit Brightness Uniformity
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Solution Overview
Problem
Conventional organic EL display pixel circuits experience degraded image quality due to non-uniform power supply voltage, leading to inconsistent current flow to OLEDs, especially as display size and brightness increase, causing voltage drops that affect current delivery.
Innovation Solution
The implementation of a voltage compensator in each pixel circuit that adjusts the data voltage based on both power supply voltages, ensuring consistent current flow to the OLED by isolating the power supply voltage influence and compensating for threshold voltage deviations, thereby maintaining uniformity across all pixel circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the area of the organic EL display is increased and brightness is improved, then the display performance is enhanced, but the voltage drop on the power supply line increases causing non-uniform power supply voltage
Solution Approach 1:
The patent divides the pixel circuit into multiple functional blocks: a driving transistor for current control, a voltage compensator with first and second transistors for voltage compensation, and a capacitor for voltage storage. This segmentation allows each block to perform its specific function independently, with the voltage compensator specifically addressing the power supply voltage non-uniformity issue while the driving transistor controls the OLED current, thus resolving the contradiction between improved brightness and maintained voltage uniformity across large display areas.
2Power
If the power supply voltage is increased to maintain current flow despite voltage drop, then current delivery is improved, but the voltage drop effect is amplified causing further non-uniformity
Solution Approach 1:
The voltage compensator implements a feedback mechanism by sensing the actual power supply voltage at each pixel location and adjusting the gate voltage of the driving transistor accordingly. The first transistor receives the data signal while the second transistor compensates for the voltage drop by comparing the actual power supply voltage with the expected voltage level. This feedback loop ensures that even when power supply voltage increases to compensate for line resistance, the uniformity is maintained through real-time adjustment, resolving the contradiction between maintaining current flow and preventing voltage non-uniformity amplification.
3Device complexity
If conventional voltage programming method is used to drive OLEDs, then the circuit structure is simple, but the current flowing to OLED is influenced by power supply voltage variations degrading image quality
Solution Approach 1:
The voltage compensator acts as an intermediary component between the data signal input and the driving transistor gate. It includes a first transistor that receives the data signal from the data line and a second transistor that provides voltage compensation based on the power supply voltage level. This intermediary structure processes the data signal and adds the necessary voltage compensation before applying it to the driving transistor, thereby isolating the OLED current from direct influence by power supply voltage variations while maintaining a relatively simple circuit structure.
Data Source
AI summary
A light emitting display including data lines for transmitting data voltages, scan lines for selecting select signals, and pixel circuits. The pixel circuit is coupled to a data line and a scan line. The pixel circuit includes a transistor including first, second, and third electrodes, wherein the third electrode outputs a current corresponding to a voltage between the first and second electrodes. A light emitting element coupled to the third electrode emits light corresponding to the current outputted by the third electrode. A first switch transmits a data voltage in response to a select signal from the scan line. A voltage compensator receives the data voltage transmitted by the first switch and a second power supply voltage and applies a compensated data voltage based on the data voltage, a first power supply voltage and the second power supply voltage to the first electrode of the transistor.