Backlight Drive Circuit for Display Flicker Compensation

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Solution Overview

Problem

Conventional liquid crystal display devices experience flicker due to current leakage, data writing, and parasitic capacitance effects, which are not adequately reduced by existing solutions, particularly in mobile devices requiring high-quality displays with low power consumption.

Innovation Solution

An active-matrix display device with a backlight control system that adjusts luminance based on predicted values to compensate for potential fluctuations, incorporating a scanning signal line driver circuit, video signal line driver circuit, and a backlight drive circuit to manage scanning and hold-off periods, and detects display patterns to optimize backlight operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by stationary object

If scan stop periods are extended to reduce power consumption, then power consumption decreases, but current leakage in capacitive elements increases causing voltage reduction and conspicuous luminance changes (flicker)

Engineering Contradiction:

Improvepower consumptionVSAvoiddisplay quality

Core Design Contradiction:

Use of energy by stationary objectVSReliability

Solution Approach 1:

The backlight is controlled to perform preliminary dimming before the scan stop period begins and preliminary brightening before the scanning period begins. This anticipatory adjustment compensates for the voltage changes caused by capacitor discharge during the scan stop period, preventing the conspicuous luminance changes that would otherwise occur when the backlight turns on after voltage reduction.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The system performs preliminary actions by adjusting backlight luminance in advance of the actual voltage changes. Specifically, the backlight is dimmed before the scan stop period (when voltage will drop due to leakage) and brightened before the scanning period (when voltage will be restored), thereby pre-compensating for the inevitable voltage fluctuations and maintaining stable perceived luminance.

Inventive Principle:

Principle #10Preliminary action

2Stress or pressure

If polarity inversion frequency is increased to reduce voltage stress on driver IC, then voltage stress decreases, but power consumption increases

Engineering Contradiction:

Improvevoltage stress on driver ICVSAvoidpower consumption

Core Design Contradiction:

Stress or pressureVSUse of energy by stationary object

Solution Approach 1:

The system employs periodic backlight dimming and brightening actions that are synchronized with the scan stop periods. By periodically adjusting the backlight luminance to compensate for voltage fluctuations during scan stop periods, the system can use longer scan stop periods (which reduce driver IC voltage stress) without sacrificing display quality, thereby indirectly reducing power consumption compared to maintaining high polarity inversion frequencies.

Inventive Principle:

Principle #19Periodic action

3Use of energy by stationary object

If scan stop periods are used to reduce overall inversion frequency, then power consumption decreases, but luminance changes during the period are visually recognized as flicker

Engineering Contradiction:

Improvepower consumptionVSAvoidflicker

Core Design Contradiction:

Use of energy by stationary objectVSObject-affected harmful factors

Solution Approach 1:

The backlight performs preliminary dimming before the scan stop period begins and preliminary brightening before the scanning period begins. This preliminary adjustment counteracts the voltage changes that occur during the scan stop period, preventing the luminance changes from being visually perceived as flicker while maintaining the power-saving benefits of extended scan stop periods.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The system converts the potentially harmful effect of voltage drop during scan stop periods (which causes flicker) into a controlled and compensated phenomenon. By using the scan stop period to enable longer dimming intervals and by pre-adjusting backlight luminance, the system transforms what would be a display defect into an opportunity for more aggressive power management while maintaining display quality.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS9520097B2Display device with compensating backlight drive circuit and method for driving same

Publication Date: 2016.12.13 SHARP KK

AI summary

In a display control circuit (200) of a display device, an image pattern detection portion (230) detects whether an image is an anti-flicker pattern or not, and when it is an anti-flicker pattern, a backlight source is driven (typically, such that its luminance changes in the opposite phase relative to luminance changes that would occur), on the basis of predicted values, which are predetermined so as to compensate for the luminance changes that would occur. Moreover, the backlight is not turned on during the scanning period. As a result, flicker due to current leakage, etc., can be reduced or eliminated in a display device for which a scanning period and a scan stop period are set.