Display Pixel Pulse-Width Circuit for μLED Color-Shift Control
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Solution Overview
Problem
The color shift phenomenon occurs in display devices using pulse amplitude modulation (PAM) due to wavelength shifts in micro light emitting diodes (μLEDs) caused by varying driving currents, leading to image distortion.
Innovation Solution
A pixel design incorporating a pulse generating circuit with series-connected inverters and a feedback capacitor, which generates a pulse signal based on a constant current, preventing color shifts by adjusting pulse width rather than current amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse amplitude modulation (PAM) method is used to drive the light emitting element, then the gray level can be represented by adjusting the amount of driving current, but a color shift phenomenon occurs due to wavelength shifts in μLEDs
Solution Approach 1:
The patent changes the control parameter from current amplitude (PAM) to pulse width (PWM). By varying the duration of the driving current pulse while maintaining constant current amplitude, the invention achieves gray level control without causing wavelength shifts in μLEDs, thus preventing color shift phenomenon
Solution Approach 2:
The invention employs periodic pulse signals with variable pulse widths to control the light emitting element. The emission transistor switches the constant current in periodic pulses, where the duty cycle of the pulse determines the perceived brightness, eliminating continuous current variation that causes color shifts
2Duration of action of moving object
If the emission time of the light emitting element is extended to improve image quality, then the pulse width of the pulse signal must be increased, but this may affect the response time and switching performance
Solution Approach 1:
The patent uses dynamic control of the pulse width through the pulse generating circuit, which adjusts the emission time adaptively. The circuit responds to input signals and generates appropriately timed pulses that balance emission duration with response time requirements, optimizing both image quality and switching performance
Solution Approach 2:
The feedback capacitor in the pulse generating circuit provides timing feedback to control the pulse width. This feedback mechanism ensures that the emission time is precisely controlled to achieve the desired balance between duration and response time, maintaining optimal performance
Data Source
AI summary
A pixel of a display device includes a light emitting element, a constant current generating circuit which generates a constant current, a pulse generating circuit which generates a pulse signal, and an emission transistor which provides the constant current to the light emitting element in response to the pulse signal. The pulse generating circuit includes a plurality of inverters connected to each other in series, where the plurality of inverters outputs the pulse signal at a pulse output node based on a voltage of a first node, and a feedback capacitor including a first electrode connected to the first node, and a second electrode connected to the pulse output node.