Pixel PWM Circuit for High-Resolution Micro LED Displays
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Solution Overview
Problem
Existing display apparatuses using micro LEDs face challenges in generating PWM signals with a small number of transistors, high IC chip costs, increased transistor and wiring numbers leading to high resolution issues, and high power consumption, while maintaining reliable display characteristics.
Innovation Solution
A display apparatus with a pixel circuit comprising a specific configuration of transistors and a capacitor generates PWM signals using a small number of transistors, including a metal oxide transistor with In, Zn, and M in the channel formation region, and a light-emitting device like an LED or organic EL element, controlled by a ramp wave signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a comparator is used to generate PWM signals in microdisplay, then display precision is improved, but device complexity increases due to Si wafer substrate requirement
Solution Approach 1:
The patent extracts the PWM signal generation function from the complex comparator-based circuit and implements it using a simple transistor switching circuit. By removing the comparator component and using only transistors and capacitors, the invention achieves PWM generation with significantly reduced device complexity while maintaining the essential function of luminance control through pulse width modulation.
Solution Approach 2:
The patent creates a simplified version of the comparator function by using a transistor switching circuit that replicates the essential PWM generation capability. Instead of using a full comparator circuit requiring Si wafer substrate, the invention copies the core functionality using simpler transistor-based switching that achieves the same pulse width modulation effect with fewer components.
2Measurement precision
If IC chip with comparator is mounted in pixel for large display, then PWM signal generation is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive IC chips with simple transistor circuits that can be manufactured using standard thin-film transistor processes. By using readily available transistor components and eliminating the need for specialized IC chip mounting, the invention significantly reduces manufacturing costs while maintaining PWM signal generation capability essential for LED luminance control.
Solution Approach 2:
The patent extracts the PWM generation function from expensive IC chips and implements it using basic transistor switching circuits. This extraction eliminates the need for costly IC chip mounting processes and allows direct integration using standard display manufacturing techniques, thereby reducing overall manufacturing cost.
3Measurement precision
If CMOS comparator is formed over insulating substrate, then PWM signal generation is achieved, but transistor and wiring numbers increase leading to resolution issues
Solution Approach 1:
The patent removes the complex CMOS comparator circuit with its multiple transistors and wirings and replaces it with a minimal transistor switching circuit. By extracting only the essential PWM generation function and eliminating unnecessary circuit components, the invention achieves significant reduction in transistor and wiring counts, enabling high-resolution displays.
Solution Approach 2:
Instead of using a complex comparator circuit to generate PWM signals, the patent inverts the approach by using a simple transistor switching circuit controlled by a ramp wave signal. This inverted methodology achieves the same PWM generation function with far fewer components, solving the resolution issue caused by excessive transistor and wiring counts.
4Measurement precision
If conventional pixel circuit is used for LED control, then current control is achieved, but chromaticity deviation occurs
Solution Approach 1:
The patent implements PWM control using periodic ramp wave signals to switch the LED on and off at high frequency. This periodic switching action maintains constant current amplitude while varying the duty cycle, ensuring that the LED operates at consistent current levels that prevent chromaticity deviation while achieving the desired luminance variation through temporal averaging.
Solution Approach 2:
The patent uses the ramp wave signal as a reference for PWM generation, creating a controlled feedback mechanism that ensures accurate duty cycle modulation. By comparing the data signal with the ramp wave and generating PWM output accordingly, the circuit maintains precise control over LED current, preventing chromaticity shifts that would occur with simple analog current control.
Data Source
AI summary
A display apparatus including a pixel circuit that generates a PWM signal is provided. In the display apparatus, a pixel has a function of generating a PWM signal. The PWM signal can be generated by an operation of comparing gate-source voltage or on-state resistance of each of two transistors provided in the pixel. Light emission of a light-emitting device such as a micro LED or an organic EL element is controlled with a duty ratio using the generated PWM signal. The PWM signal is generated in a circuit formed of a small number of transistors, which is effective in increasing the definition and the area of the display apparatus.