Intensity Scaled Dithering PWM for LED Driver Circuits
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Solution Overview
Problem
Conventional PWM dithering solutions in LED driver circuits are ineffective during high or low brightness transitions, as they apply uniform adjustments to all frame content without considering brightness levels.
Innovation Solution
An intensity-scaled dithering PWM system that adjusts pulse width modulation based on brightness values, selectively applying dithering noise during refresh cycles to create a smoother gradient by varying the pulse width according to greyscale vectors, thereby enhancing brightness transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform PWM dithering adjustments are applied to all frame content, then the implementation is simple, but the effectiveness is poor during high or low brightness transitions
Solution Approach 1:
The patent applies different dithering adjustments to different regions of frame content based on their brightness levels. Specifically, it applies stronger dithering adjustments to highlights (bright regions) and shadows (dark regions) while using weaker adjustments for mid-tone regions, thereby optimizing gradient smoothness locally where needed rather than uniformly across all content
Solution Approach 2:
The patent dynamically adjusts the dithering noise amplitude based on the local brightness level of each pixel or region. The system calculates brightness values and selectively applies dithering with varying intensities, making the dithering behavior adaptive and dynamic rather than static and uniform, which improves effectiveness across different brightness conditions
2Stability of the object's composition
If dithering noise is applied to create smoother gradients, then gradient smoothness is improved, but brightness accuracy may deteriorate
Solution Approach 1:
The patent applies dithering selectively only to specific brightness regions (highlights and shadows) where gradient smoothness is most needed, rather than uniformly to all regions. This localized application preserves brightness accuracy in mid-tone regions while improving gradient smoothness only where abrupt transitions occur
Solution Approach 2:
The patent applies partial dithering action by using different noise amplitudes for different regions - stronger dithering for highlights and shadows where it matters most, and weaker or no dithering for mid-tones where it would unnecessarily degrade brightness accuracy. This partial application optimizes the trade-off between gradient smoothness and brightness precision
Data Source
AI summary
A circuit for driving at least one light emitting diode (LED) of a display based on a greyscale vector. The circuit includes brightness scale detection circuitry to determine a brightness value based on the greyscale vector and refresh cycle selection circuitry to output an indication of a subset of refresh cycles, referred to as dithered refresh cycles. The circuit also includes pulse width determination circuitry to define a pulse width based on the greyscale vector. Pulse adjustment control circuitry, for each dithered refresh cycle, determines a dithered pulse width by adjusting the pulse width by a width adjustment amount, and outputs a dithered pulse width modulation signal including a series of pulses including a pulse having the pulse width determined by the pulse width determination circuitry non-dithered refresh cycles and a pulse having the dithered pulse width for the dithered refresh cycles.