MicroLED Driving Circuit PWM Control for Contrast Stability
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Solution Overview
Problem
Light-emitting devices, such as OLEDs and microLEDs, exhibit characteristics that cause display defects like color shift and low contrast due to changes in current density, leading to inefficiencies and poor performance.
Innovation Solution
A driving circuit and method that control the grayscale of microLEDs by adjusting both the current magnitude and duration using a current source circuit and a time control circuit, maintaining current density within a stable range to prevent these defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If current density is increased to improve brightness, then illumination intensity is improved, but color shift occurs and display contrast deteriorates
Solution Approach 1:
The patent employs pulse width modulation (PWM) to drive the microLEDs, switching them on and off periodically at high frequency. By controlling the duty cycle of these periodic pulses, the perceived brightness is adjusted without changing the peak current density, thereby maintaining color stability and display contrast while achieving variable illumination intensity.
Solution Approach 2:
The driving circuit dynamically adjusts the pulse width (duration) in real-time based on the desired grayscale level. This dynamic control of the on-time within each periodic cycle allows precise brightness control while keeping the current density during the on-state within the optimal range to prevent color shift and maintain contrast.
2Adaptability or versatility
If current density varies to control grayscale, then brightness control is achieved, but color shift occurs and efficiency decreases
Solution Approach 1:
Instead of changing current density to control grayscale, the patent changes the temporal parameter (pulse width) while maintaining current density within a fixed optimal range. This parameter substitution allows grayscale control from 0 to 255 levels by varying the duty cycle, ensuring color stability and efficiency are maintained across all brightness levels.
3Device complexity
If simple current control is used to drive microLEDs, then device complexity is reduced, but display performance deteriorates due to color shift and low contrast
Solution Approach 1:
The driving circuit uses periodic PWM signals with simple on/off switching control. Each pixel receives rectangular pulse waves where the pulse width varies according to grayscale requirements. This approach maintains relatively simple circuit architecture while achieving high-performance display through temporal control rather than complex analog current regulation.
Data Source
AI summary
A driving circuit for driving a target element with a driving current, including: a current source circuit connect to the target element and a first data line, wherein the current source circuit is configured to receive a first data signal through the first data line, and to control the magnitude of the driving current provided to the target element based on the first data signal; a time control circuit connected to the current source circuit, a second data line, and a pulse signal terminal, wherein the time control circuit is configured to receive a second data signal through the second data line, and to receive a periodic pulse signal via the pulse signal terminal, and to control the duration of the driving current provided to the target element in every driving period based on the second data signal and the periodic pulse signal.