AMLED Dimming Using Row-Specific PWM Drivers
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Solution Overview
Problem
Conventional methods for dimming active matrix light-emitting diode (AMLED) displays face challenges in achieving uniform brightness control, leading to luminance non-uniformity due to synchronization issues with pulse width modulation (PWM) and transients caused by switch operations, limiting the ability to precisely control the brightness of each LED.
Innovation Solution
The implementation of a system that uses separate PWM drivers for each row of LEDs to control the illumination time uniformly across all rows, with an additional global PWM during the blanking period to ensure consistent dimming, allowing each row to be illuminated for the same duration at different times within the refresh cycle and extending the dimming period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional PWM dimming is applied to AMLED displays, then brightness control is achieved, but luminance non-uniformity occurs due to synchronization issues and switch transients
Solution Approach 1:
The patent divides the AMLED display into multiple independently controllable row segments, each with its own PWM driver. This segmentation allows each row to be controlled separately with precise timing, eliminating the synchronization issues that cause luminance non-uniformity when using conventional single PWM driver approaches.
Solution Approach 2:
The patent implements preliminary action by pre-charging capacitors and pre-positioning row drivers before the actual PWM dimming cycle begins. This preliminary preparation ensures that when PWM dimming starts, all rows are in the correct initial state, preventing transient effects from causing luminance non-uniformity.
2Productivity
If row drivers illuminate rows sequentially during the refresh cycle, then all rows are updated, but rows illuminated at different times experience different effective illumination durations
Solution Approach 1:
The patent applies periodic action by implementing a synchronized PWM dimming cycle that repeats for each row at precisely timed intervals. Each row receives its PWM dimming signal in a periodic sequence that compensates for the sequential illumination timing, ensuring that all rows effectively receive the same dimming duration relative to their illumination cycle.
Solution Approach 2:
The patent uses dynamic timing adjustment where the PWM dimming duration for each row is dynamically modified based on its position in the refresh cycle. Rows illuminated later in the cycle receive extended PWM dimming periods, dynamically compensating for the time difference to achieve uniform effective illumination duration across all rows.
3Illumination intensity
If voltage supply amplitude is modulated to dim LEDs, then brightness control is achieved, but precision is limited by the ability to control current supply
Solution Approach 1:
The patent replaces the conventional approach of modulating voltage supply amplitude with pulse-width modulation of the LED current. This substitution allows for more precise brightness control because PWM can achieve finer resolution in dimming levels by varying the duty cycle of current pulses, overcoming the limitations of analog voltage control.
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 ensures uniform dimming of the AMLED array by synchronizing PWM drivers to maintain consistent illumination times across rows, reducing luminance non-uniformity and enhancing the precision of brightness control.
Implementation Method 1
a light-emitting diode (LED) 105
Implementation Method 2
LED 105 is illuminated
Data Source
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AI summary
Apparatus, systems, and methods are provided for dimming pixels on an active matrix light-emitting diode display. One apparatus includes an LED couplable between a voltage source and ground. First and second pulse-width modulation (PWM) drivers are also coupled to the LED. A system includes a plurality of LEDs forming a plurality of rows coupled between a voltage source and ground. A plurality of PWM drivers, each coupled to each of the LEDs in one of the plurality of rows, and a global PWM driver coupled to each of the plurality of LEDs in each of the plurality of rows are also included. One method includes providing current to each LED of a row of LEDs for a first portion of a cycle via a PWM driver, and providing current to each LED in the row for a second portion of the cycle via a different PWM driver.