Sub-Pixel PWM Driving Circuit for Stable Display Color Coordinates
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Solution Overview
Problem
Existing light emitting display devices face issues with color coordinate distortion due to shifts in the wavelength band of emitted light when the driving current changes, affecting the display of various grayscales.
Innovation Solution
A sub-pixel design incorporating specific transistor configurations and capacitors to control the flow of driving current, including a first transistor with a body electrode connected to a source electrode, a second transistor switching data line connections, and capacitors to maintain voltage levels, ensuring consistent light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the driving current is changed to display various grayscales, then the display can show different brightness levels, but the wavelength band of emitted light shifts causing color coordinate distortion
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to control the light emitting element. Instead of varying the current magnitude continuously, the driving current is supplied in periodic pulses with different duty cycles. This allows brightness control through temporal modulation while maintaining constant current amplitude, thereby preventing wavelength shift and color coordinate distortion.
Solution Approach 2:
The patent changes the control parameter from current magnitude to time duration (duty cycle). By modifying the temporal parameter rather than the electrical parameter, the system achieves brightness variation without affecting the optical properties of the light emitting element, thus resolving the contradiction between brightness control and color accuracy.
2Illumination intensity
If the driving current magnitude is increased to improve brightness, then illumination intensity increases, but color coordinate distortion worsens due to wavelength band shift
Solution Approach 1:
The patent uses periodic pulse signals with varying duty cycles to control brightness. The driving current is delivered as periodic pulses rather than continuous DC, allowing the light emitting element to operate at constant current amplitude while achieving different brightness levels through temporal modulation. This maintains color consistency while varying illumination intensity.
Solution Approach 2:
The patent introduces dynamic temporal control instead of static current magnitude control. The duty cycle of the periodic driving signal is dynamically adjusted to change brightness, while the current amplitude remains static to maintain color consistency. This dynamic parameter control resolves the contradiction between brightness and color reliability.
3Manufacturing precision
If pulse width modulation is used to control grayscale by varying duty cycle, then color coordinate distortion is reduced, but the complexity of the driving circuit increases
Solution Approach 1:
The patent implements periodic pulse signaling with variable duty cycles to achieve grayscale control. This approach maintains color accuracy by keeping current amplitude constant while modulating the temporal characteristics of the driving signal. The periodic nature of the control signal simplifies the circuit design compared to analog current modulation schemes.
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 solution maintains consistent wavelength bands and improves display quality by controlling the duration of the driving current, reducing color coordinate distortion and enhancing grayscale image display.
Implementation Method 1
a light emitting element connected between a second node N2 and a third power line PL3 to which a third power voltage VEE is applied
Data Source
AI summary
A sub-pixel includes a first transistor including a gate electrode connected to a first node, a source electrode connected to a first power line, a body electrode connected to the source electrode, and a drain electrode connected to a second node, a second transistor between a third node and a data line and including a gate electrode connected to a first scan line, a third transistor connected to the first node and including a gate electrode connected to the third node, a fourth transistor between the first node and the second node and including a gate electrode connected to a second scan line, a first capacitor connected to the first node and a second power line, a second capacitor connected to the third node and a sweep line, and a light emitting element connected to the second node.