OLED Pixel Circuit Compensation for Luminance Uniformity
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Solution Overview
Problem
Existing organic light emitting display devices face issues with non-uniform luminance due to variations in threshold voltage and mobility of driving transistors, requiring changes in power supply electric potential and additional circuit components, which can lead to heat generation.
Innovation Solution
An organic light emitting display device with a pixel circuit that includes multiple transistors and a storage capacitor, allowing compensation for threshold voltage and mobility without altering the power supply electric potential, using a scan driver, data driver, and specific timing signals to control transistor operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the electric potential of the power supply is changed to compensate for threshold voltage and mobility variations, then uniform luminance can be achieved, but extra circuit components (e.g., filter) are required and heat generation increases
Solution Approach 1:
The patent changes the timing parameters of power supply voltage levels rather than altering circuit topology. By applying different voltage levels (ELVDD1, ELVDD2) at different time periods during the pixel operation cycle, the invention compensates for transistor variations without adding extra components. This temporal parameter change resolves the contradiction by achieving luminance uniformity through timing-based control instead of hardware additions.
Solution Approach 2:
The patent employs periodic voltage switching where the power supply alternates between different voltage levels in different periods of the pixel operation cycle. During the first period, a first voltage level is applied, and during the second period, a second voltage level is applied. This periodic action enables continuous compensation for threshold voltage and mobility variations throughout operation, achieving uniform luminance without requiring additional circuit components beyond the existing pixel structure.
2Manufacturing precision
If the electric potential of the power supply is changed to compensate for threshold voltage and mobility variations, then uniform luminance can be achieved, but heat generation increases requiring heat sink
Solution Approach 1:
The patent uses parameter changes in voltage timing and levels to achieve compensation. By carefully selecting voltage levels (ELVDD1, ELVDD2) and their application timing, the invention achieves luminance uniformity while managing power consumption. The periodic switching between voltage levels allows the system to average out power dissipation, reducing peak heat generation compared to continuously operating at high compensation voltages.
Solution Approach 2:
The periodic switching between different voltage levels allows thermal management by distributing power dissipation over time. Instead of maintaining high compensation voltage continuously (which would generate excessive heat), the patent alternates voltage levels in different periods, allowing thermal dissipation during lower-voltage periods while maintaining compensation effectiveness over the full operation cycle.
3Manufacturing precision
If multiple transistors and storage capacitor are added to the pixel circuit for compensation, then threshold voltage and mobility can be compensated, but pixel circuit complexity increases
Solution Approach 1:
The patent makes the existing pixel circuit components serve dual purposes. The existing transistors and capacitors in the pixel are utilized to perform both their original functions and the compensation function. By controlling the timing and voltage levels supplied to these existing components, the invention enables them to self-compensate for threshold voltage and mobility variations without requiring additional dedicated compensation components, thus avoiding increased circuit complexity.
Data Source
AI summary
An pixel of an organic light emitting display device includes: an organic light emitting diode (OLED); a second transistor for supplying a current to the OLED; a first transistor coupled between a data line and a gate electrode of the second transistor, the first transistor being turned on when a scan signal is supplied to its gate electrode; a third transistor for supplying an initialization voltage to a drain electrode of the second transistor, the third transistor being turned on when a control signal is supplied to its gate electrode; a fourth transistor coupled between the drain electrode of the second transistor and a first power supply, the fourth transistor being turned-off when a light emitting control signal is supplied to its gate electrode and turned-on when the light emitting control signal is not supplied; and a storage capacitor coupled between the source and gate electrodes of the second transistor.