Scrambled PWM Generator for LED Display Driver Pulse Width Correction
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Solution Overview
Problem
Modern LED display panels face limitations in achieving higher gray scale values and refresh rates due to narrow PWM pulses, which result in insufficient voltage rise time for LEDs to emit light, limiting the maximum GCLK frequency and gray scale resolution.
Innovation Solution
The implementation of a scrambled PWM generator in the LED display system that extends the PWM pulse width by an offset value, ensuring the pulse width exceeds the rise time of the LEDs, allowing for higher GCLK frequencies and improved gray scale and refresh rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PWM frequency is increased to improve visual refresh rate, then flicker is reduced, but pulse width becomes too narrow for LEDs to reach forward voltage
Solution Approach 1:
The patent divides a single long PWM period into multiple shorter PWM periods (segments) within the same overall time frame. This segmentation allows the system to achieve high visual refresh rates through multiple rapid updates while each individual pulse maintains sufficient width to charge the LED capacitance to forward voltage, resolving the contradiction between high frequency and adequate pulse duration.
2Measurement precision
If PWM frequency is increased to achieve higher gray scale values, then color depth improves, but pulse width becomes insufficient for proper LED activation
Solution Approach 1:
The patent segments the gray scale control into multiple PWM periods, where each segment contributes to the overall gray scale value. This allows the system to achieve fine gray scale resolution through cumulative effect of multiple pulses while each pulse maintains adequate width for reliable LED activation, resolving the contradiction between high precision and sufficient duration.
Solution Approach 2:
The patent employs periodic PWM action with multiple periods within a single gray scale control cycle. By repeating the PWM signal multiple times with appropriate duty cycles that sum to the desired gray scale value, the system achieves high precision control while ensuring each periodic pulse has sufficient width to properly activate the LED.
3Reliability
If offset value is added to extend PWM pulse width, then LED can emit light consistently, but duty cycle accuracy may be affected
Solution Approach 1:
The patent applies a preliminary offset value to each PWM pulse to ensure the voltage rises sufficiently to activate the LED before the main duty cycle takes effect. This preliminary action guarantees reliable LED emission, and the offset is carefully calculated and compensated for in the overall duty cycle calculation to maintain accuracy.
Solution Approach 2:
The system incorporates feedback mechanisms to monitor and adjust the actual PWM pulse width including the offset, ensuring that the extended pulse width achieves reliable LED activation while maintaining the intended duty cycle accuracy through compensatory adjustments.
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
This approach enables LEDs to emit light consistently by ensuring the anode voltage has sufficient time to rise above the forward voltage, thereby enhancing gray scale values and refresh rates in LED displays.
Implementation Method 1
PWM turns an LED on or off according to the width of the signal pulse (i.e., pulse duration or pulse width). The ratio between the on time and the off time in turn determines the brightness of the LED.
Implementation Method 2
Modern LED display panels require higher gray scale to accomplish higher color depth and higher visual refresh rate to reduce flickering.
Data Source
AI summary
The LED display system comprises an array of LEDs and a driver circuit that employs a scrambled PWM generator. The scrambled PWM generator is configured to generate a plurality of PWM pulses. The PWM pulses are distributed into a corresponding number of refresh segments. The driver circuit is configured so that one or more of PWM pulses are extendable by a certain offset value so that the pulse width in the corresponding refresh segments is wide enough for the LED to emit light.