Digital PWM Backlight Control for LCD Ripple Reduction

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Solution Overview

Problem

Conventional transmissive LCD monitors experience reduced display quality due to ripples caused by the interaction between image processing circuits and PWM modules, which are implemented with additional analog circuits.

Innovation Solution

A flat panel display device and controller that incorporates a digital pulse width modulation module synchronized with horizontal and vertical synchronization signals to control the backlight, allowing for precise adjustment of luminance and preventing overlapping control signals that could damage the power transformation module.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If additional analog PWM circuits are used to control backlight luminance, then dimming range is widened, but display quality decreases due to ripples and interference

Engineering Contradiction:

Improvedimming rangeVSAvoiddisplay quality

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the traditional analog PWM control circuit with a digital PWM module that operates at frequencies synchronized to the display refresh rate. This substitution eliminates the harmful ripples and interference caused by analog circuits while maintaining the ability to control backlight luminance across a wide dimming range through digital signal processing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating frequency parameter of the PWM control signal to match the display refresh rate (e.g., 60Hz, 75Hz). This parameter synchronization ensures that the backlight modulation does not create visible ripples or interference patterns, thereby improving display quality while maintaining adaptability for different luminance levels.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If image processing circuit and PWM module operate independently, then control flexibility is improved, but harmful interference and ripples are generated on display panel

Engineering Contradiction:

Improvecontrol flexibilityVSAvoidinterference and ripples

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent merges the control functions of the image processing circuit and PWM module by integrating the PWM control signals into the existing display timing framework. The digital PWM module operates in conjunction with the horizontal and vertical synchronization signals, creating a unified control system that eliminates independent operation and its associated interference.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent implements feedback mechanisms where the PWM control signals are synchronized with the display refresh rate and timing signals. This feedback ensures that the backlight modulation is coordinated with the display panel's scanning process, preventing harmful interference and ripples while maintaining control flexibility for various display modes.

Inventive Principle:

Principle #23Feedback

3Device complexity

If PWM control signals are not synchronized with display frequency, then control simplicity is maintained, but visible interference and reduced image quality occur

Engineering Contradiction:

Improvecontrol simplicityVSAvoidvisible interference

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent employs periodic action by synchronizing the PWM control signals with the periodic display refresh rate. The digital PWM module generates control signals at regular intervals that match the display's horizontal and vertical synchronization signals, creating a coordinated periodic operation that eliminates visible interference while maintaining relatively simple control through standard timing protocols.

Inventive Principle:

Principle #19Periodic action

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 solution improves display quality by synchronizing the luminance frequency of the backlight with the display frequency, reducing visible interference and enhancing the overall image quality while preventing damage to the power transformation module.

Implementation Method 1

a phosphorescence material, spread on the inner surface of the CCFL, transforms ultraviolet into visible light

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

the CCFL excites mercury vapor therein to a high energy level by discharging the electricity. The excited mercury vapor returns to its initial energy state while the extra energy becomes ultraviolet

Methodology Applied

Scientific EffectElectrical discharge excitation: Electric Arc

Data Source

PatentUS8542181B2Flat panel display device, controller, and method for displaying images

Publication Date: 2013.09.24 MEDIATEK INC

AI summary

A flat panel display device, LCD controller and associated method is provided. The flat panel display device includes a display panel, a lamp for providing a backlight source for the display panel, a power transformation module for providing a power source for the lamp, a non-volatile storage unit for storing program code, and a display controller. The display controller includes an image processing module for processing image data and outputting processed results to the display panel, and a digital pulse width modulation module for adjusting on and off time of the power transformation module according to a synchronization signal.