Pixel PWM Circuit for Micro LED Luminance Control
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Solution Overview
Problem
Existing display apparatuses using micro LEDs face challenges in generating pulse width modulation (PWM) signals efficiently due to high IC chip costs, increased transistor and wiring numbers, and conductivity type inconsistencies, leading to chromaticity deviations and high power consumption.
Innovation Solution
A display apparatus with a pixel circuit comprising a small number of transistors, including a first and second transistor connected to a light-emitting device, generates PWM signals using a ramp wave signal, allowing for efficient luminance control with reduced transistor count and consistent conductivity type, utilizing metal oxide transistors for low power consumption and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If an IC chip including a comparator is mounted in a pixel to generate PWM signals, then PWM signal generation capability is improved, but IC chip cost and mounting cost become extremely high
Solution Approach 1:
The invention extracts the PWM signal generation function from a separate IC chip and implements it directly within the pixel circuit using transistors and capacitors that are already part of the display panel fabrication process. This eliminates the need for additional IC chip mounting while maintaining PWM functionality.
Solution Approach 2:
The invention merges the PWM signal generation circuitry with the existing pixel circuit structures. By using the same transistor types (n-channel or p-channel) and integrating capacitors into the pixel layout, the PWM generation function is combined with the display pixel functions, reducing overall device complexity and manufacturing cost.
2Ease of manufacture
If a CMOS comparator is formed in a pixel using polycrystalline silicon to generate PWM signals, then manufacturing cost is reduced, but the number of transistors and wirings increases leading to reduced resolution capability
Solution Approach 1:
The invention changes the operational parameters of existing pixel circuit components to achieve PWM signal generation. By utilizing the on/off states and capacitance values of existing transistors and capacitors in novel configurations, the system generates PWM signals without adding significant transistor or wiring count.
Solution Approach 2:
The invention makes existing pixel circuit components serve multiple functions. The same transistors used for pixel switching also participate in PWM signal generation, and capacitors used for charge storage also function as timing elements for PWM modulation, thereby avoiding additional component proliferation.
3Extent of automation
If transistors with different conductivity types are used in the pixel circuit to generate PWM signals, then circuit functionality is improved, but consistency and reliability are reduced
Solution Approach 1:
The invention applies local quality by using transistors with uniform conductivity characteristics throughout the pixel circuit. By designing the PWM generation circuit to work with a single transistor type (either all n-channel or all p-channel), the invention maintains local consistency in electrical characteristics while achieving the required PWM functionality through clever circuit arrangement.
4Extent of automation
If a larger number of transistors are used in the pixel circuit for PWM generation, then signal control capability is improved, but power consumption increases
Solution Approach 1:
The invention applies partial action by using only the necessary minimum number of transistors and capacitors to generate PWM signals. Rather than implementing a full comparator circuit or excessive control elements, the invention uses a minimal set of components that leverage the existing pixel circuit operations to achieve PWM functionality with reduced power consumption.
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.