Field Sequential Color LCD with Burst Mode PWM Dimming

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Solution Overview

Problem

Conventional field sequential color (FSC) mode liquid crystal displays (LCDs) face challenges with luminance efficiency, color distortion, and reduced resolution due to their white LED driving schemes, which complicate the structure and degrade color reproduction compared to color LED-based displays.

Innovation Solution

An FSC mode LCD is developed with a burst mode PWM dimming applied to a field sequential driving scheme, utilizing a controller, DC/DC converter, color LED backlight with red, green, and blue LED arrays, and an FSC generator to produce sequential color PWM signals, allowing for independent luminance control of each color LED array.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a white LED driving scheme is used in conventional FSC mode LCDs, then the structure becomes more complex and color reproduction degrades, but the display can still function with color filters

Engineering Contradiction:

Improvestructure complexityVSAvoidcolor reproduction quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent removes the color filters from the LCD structure and extracts only the necessary color separation function by using color LED backlights (red, green, blue) that sequentially illuminate the liquid crystal panel. This eliminates the need for color filters and their associated complex control structures, directly resolving the contradiction between structural complexity and color reproduction quality.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/optical filtering system (color filters) with an electrical/optical control system (color LED arrays with sequential driving). Instead of using white LED + color filters to separate colors, the system uses three color LED arrays that are sequentially activated, substituting a simpler electronic control mechanism for the complex optical filtering approach.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Illumination intensity

If color filters are used in conventional LCDs, then color can be adjusted, but luminance efficiency decreases and power consumption increases

Engineering Contradiction:

Improveluminance efficiencyVSAvoidpower consumption

Core Design Contradiction:

Illumination intensityVSUse of energy by moving object

Solution Approach 1:

The patent implements periodic action by sequentially driving the red, green, and blue LED arrays in alternating fields. Each color LED array is activated only during its designated field period, allowing the liquid crystal to modulate the light for that specific color. This periodic activation eliminates the need for continuous illumination through color filters, significantly improving luminance efficiency and reducing power consumption while maintaining color adjustment capability.

Inventive Principle:

Principle #19Periodic action

3Reliability

If white LED backlight unit is used, then the display can be driven, but color reproduction is degraded compared to color LED

Engineering Contradiction:

Improvecolor reproduction qualityVSAvoidbacklight structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the single white LED backlight unit into three separate color LED arrays (red, green, blue). Each array is independently controlled and sequentially activated, allowing precise color reproduction without the need for color filters. This segmentation improves color reproduction quality while the shared control structure keeps the overall system complexity manageable.

Inventive Principle:

Principle #1Segmentation

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 enhances luminance efficiency, reduces color distortion, and improves color reproduction and resolution while reducing power consumption by enabling field sequential driving with color LED backlights, eliminating the need for color filters and simplifying the structure.

Implementation Method 1

a first, second and third color LED arrays LA1, LA2 and LA3 connected in parallel and operating by the driving voltage outputted from the DC/DC converter

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

A liquid crystal display (LCD) includes an LCD back panel and a backlight unit

Methodology Applied

Scientific EffectElectro-optic effect: Electro-Optic Effects

Data Source

PatentUS8643587B2Field sequential color mode liquid crystal display

Publication Date: 2014.02.04 SAMSUNG ELECTRONICS CO LTD

AI summary

In an FSC mode LCD, a controller operates in response to an external adjustment, and a DC/DC converter converts a battery voltage into a driving voltage under control of the controller. A color LED backlight includes first, second and third color LED arrays connected in parallel, which are operated by the driving voltage. An FSC generator generates first, second and third color PWM signals according to an internal sawtooth voltage and a dimming voltage. A 3-channel current source generates first, second and third driving currents under control of the controller, and on/off switches paths of the first, second and third driving currents flowing through the first, second and third color LED arrays according to the first, second and third color PWM signals generated from the FSC generator, thereby adjusting luminance of the first, second and third color LED arrays of the color LED backlight.