Inorganic LED Pixel Driver Circuit for Luminance Uniformity
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Solution Overview
Problem
Inorganic light-emitting diodes (LEDs) exhibit luminance deviations and image quality deterioration when driven similarly to organic LEDs, as their light emission wavelength varies with the driving current.
Innovation Solution
A display device with specialized pixel drivers and transistors that control the driving current and pulse width modulation to minimize luminance deviations, using transistors connected in series and capacitors to stabilize gate electrode voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If inorganic LEDs are driven in the same manner as OLEDs by controlling driving current magnitude, then the control method is simple and unified, but the light emission wavelength varies causing luminance deviations and image quality deterioration
Solution Approach 1:
The patent applies dynamics by making the driving current waveform adjustable rather than fixed. The pixel driver dynamically changes the current waveform shape (square wave, triangular wave, sinusoidal wave) and duty cycle based on grayscale levels to compensate for transistor threshold voltage variations, thereby maintaining consistent luminance output across different pixels and grayscale levels while using a unified control architecture.
Solution Approach 2:
The patent changes multiple parameters of the driving current including waveform shape (square, triangular, sinusoidal), duty cycle, and magnitude. By adjusting these parameters based on grayscale level and transistor characteristics, the system compensates for threshold voltage distribution effects and maintains uniform luminance output from inorganic LEDs across the display.
2Illumination intensity
If the driving current is increased to improve luminance output, then the brightness increases, but the wavelength variation increases causing greater luminance deviations
Solution Approach 1:
The patent changes the waveform shape and duty cycle of the driving current in addition to magnitude control. By using different waveform shapes (square, triangular, sinusoidal) and adjusting duty cycles, the system achieves luminance output control without relying solely on high current magnitude, thereby reducing wavelength variation and maintaining luminance uniformity across pixels.
Solution Approach 2:
The patent implements feedback through the pixel driver that monitors and adjusts the driving current parameters based on the actual transistor threshold voltage and desired grayscale level. This feedback mechanism ensures that luminance output remains consistent even when current magnitude increases, by compensating through waveform and duty cycle adjustments.
3Stability of the object's composition
If multiple transistors are used in series to stabilize gate electrode voltage, then the voltage stability improves, but the device complexity increases
Solution Approach 1:
The patent segments the gate driver function into multiple series-connected transistors (e.g., first, second, third transistors) that work together to stabilize the gate electrode voltage. This segmentation allows each transistor to contribute to voltage stability while distributing the complexity across multiple simple components rather than requiring a single complex transistor.
Solution Approach 2:
The patent merges multiple transistor functions into a unified gate driver structure where series-connected transistors collectively perform voltage stabilization. By combining the functions of multiple transistors in series, the system achieves stable gate voltage control while maintaining a relatively simple overall device architecture that can be integrated into the pixel structure.
Data Source
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AI summary
A display device includes a first pixel driver connected to a sweep line, the first pixel driver generating a control current based on a first data voltage, a second pixel driver connected to a scan control line, the second pixel driver generating a driving current based on a second data voltage and controlling a period for which the driving current flows, based on the control current, and a light-emitting element connected to the second pixel driver to receive the driving current. The first pixel driver includes a first transistor generating the control current based on the first data voltage, a second transistor providing the first data voltage to a first electrode of the first transistor based on a scan write signal, and a first capacitor including a first capacitor electrode connected to a gate electrode of the first transistor, and a second capacitor electrode connected to the sweep line.