Passive Matrix LED Driving with Subframe PWM and Channel Compensation
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Solution Overview
Problem
Passive matrix LED displays face challenges in achieving high dynamic range and high response speed simultaneously, leading to display illumination uniformity issues due to varying capacitances across different electroluminescent elements, resulting in intensity differences between pixels.
Innovation Solution
A subframe pulse width modulation (PWM) driving method with channel-to-channel compensation is introduced, dividing each frame into subframes with primary, middle, and auxiliary waveforms, and mapping N-bit digital driving data into these subframes to ensure uniform illumination by extracting and distributing driving data bits effectively across subframes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the voltage across the electroluminescent element is increased to turn on the pixel and control brightness, then the dynamic range is improved, but the response speed deteriorates due to the uncontrollable duration caused by combined capacitance
Solution Approach 1:
The patent segments the driving waveform into three distinct parts: pre-charge waveform, primary driving waveform, and auxiliary driving waveform. This segmentation allows independent optimization of each phase - the pre-charge phase prepares the capacitance without causing uncontrollable duration, the primary driving phase provides the main brightness control, and the auxiliary phase compensates for channel variations, thereby resolving the contradiction between dynamic range and response speed
Solution Approach 2:
The pre-charge waveform is applied before the main driving signal to pre-charge the combined capacitance of electroluminescent elements and source electrode. This preliminary action prepares the electrical state in advance, eliminating the uncontrollable duration that would otherwise occur when the main signal is applied, thus improving response speed while maintaining the ability to control brightness through the subsequent primary and auxiliary waveforms
2Adaptability or versatility
If the combined capacitance of electroluminescent elements varies across different source lines, then the manufacturing adaptability is improved, but the display illumination uniformity deteriorates due to different uncontrollable durations
Solution Approach 1:
The patent applies local quality by introducing channel-specific auxiliary driving waveforms that are tailored to each source line's characteristics. The auxiliary waveform parameters (amplitude, duration) are adjusted locally for each channel to compensate for its specific combined capacitance, ensuring that all pixels across different channels achieve uniform illumination despite manufacturing variations
Solution Approach 2:
The patent implements a feedback mechanism where the auxiliary driving waveform is designed based on measured or characterized channel-to-channel variations in combined capacitance. By measuring the actual performance of each channel and applying compensatory adjustments through the auxiliary waveform, the system achieves uniform display illumination across all channels while maintaining manufacturing adaptability
Data Source
AI summary
A passive matrix LED display driving scheme based on subframe pulse width modulation (PWM) to increase frame scan rate and further with channel-to-channel compensation is provided. The scheme may comprise: dividing each frame of the display video into T number of subframes; converting a driving signal for a pixel into a N-bit driving data, compensating the driving data with a compensation value; mapping the compensated driving data into the T number of subframes respectively.