Inorganic LED Pixel Circuit Using PWM for Grayscale Control
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Solution Overview
Problem
Inorganic light emitting diodes experience image quality deterioration due to varying wavelengths of emitted light when driven similarly to organic light emitting diodes, leading to issues in luminance and grayscale adjustment.
Innovation Solution
A display device design that includes a pixel structure with transistors and capacitors to control driving current and pulse width, maintaining constant current driving regions and optimizing luminous efficiency by adjusting the period of driving current application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If inorganic light emitting diodes are driven with variable driving current to adjust luminance, then luminance adjustment is achieved, but wavelength varies causing image quality deterioration
Solution Approach 1:
The patent applies pulse width modulation (PWM) to drive the inorganic light emitting diode, switching it on and off periodically at a high frequency. The duty cycle of these periodic pulses controls the perceived luminance, while the diode operates at constant current during each pulse, maintaining stable wavelength and preventing color shift that would occur with analog current dimming.
2Ease of operation
If driving current magnitude is adjusted to control grayscale, then grayscale adjustment is achieved, but constant current driving region decreases
Solution Approach 1:
The patent employs dynamic switching control through multiple transistors that adjust the pulse width and duty cycle in real-time. This dynamic PWM approach allows grayscale control across the full range while maintaining constant current conditions during active periods, preserving the constant current driving region and ensuring stable wavelength operation at all brightness levels.
3Device complexity
If inorganic light emitting diode is driven similarly to organic light emitting diode, then driving simplicity is maintained, but image quality deteriorates due to wavelength variation
Solution Approach 1:
The patent replaces the simple analog current control method (mechanical/direct control) with a digital-style PWM switching control system. Although this increases circuit complexity with additional transistors and control logic, it successfully maintains constant current operation and stable wavelength, dramatically improving image quality and color consistency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design maintains consistent color coordinates and luminous efficiency across different grayscale levels, preventing image quality deterioration and enhancing low gray level expression.
Implementation Method 1
an inorganic light emitting display device including an inorganic light emitting element
Implementation Method 2
the wavelength of light emitted from the inorganic light emitting diode varies depending on the driving current
Data Source
Figure 1
Figure 2
Figure 3(a)~3(c)
AI summary
A display device including: a first transistor configured to control a control current based on a voltage of a first node; a second transistor configured to electrically connect a second node that is a first electrode of the first transistor to a first data line in response to a scan write signal; a third transistor configured to control a driving current based on a voltage of a third node; a fourth transistor configured to electrically connect a fourth node that is a first electrode of the third transistor to a second data line in response to the scan write signal; a fifth transistor configured to control the driving current based on a voltage of a fifth node having received the control current; and a light emitting element configured to receive the driving current, wherein the fifth transistor is of a different type from that of the first to fourth transistors.