Optical Sensor Circuit for LCD Backlight Power Reduction
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Solution Overview
Problem
Liquid crystal display (LCD) devices consume excessive power due to constant backlight brightness, even in ambient environments with sufficient light, leading to increased power consumption.
Innovation Solution
An optical sensor is integrated into the LCD to detect peripheral light intensity and adjust backlight luminance accordingly, using a circuit with transistors and capacitors to control current flow and generate a sensing signal that reduces backlight power when ambient light is sufficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the backlight supplies light of constant brightness to the pixel region, then the image quality is maintained, but the power consumption increases
Solution Approach 1:
The patent implements dynamic backlight control by replacing the constant brightness backlight with a variable brightness system that adjusts according to ambient light conditions detected by the optical sensor. The backlight driver circuit receives the sensing signal and dynamically adjusts the backlight luminance to match environmental lighting levels, thereby reducing power consumption while maintaining appropriate image quality.
Solution Approach 2:
The patent employs a feedback mechanism where the optical sensor continuously monitors ambient light intensity and generates a sensing signal that is fed back to the backlight driver circuit. This feedback loop enables the system to automatically adjust backlight brightness based on real-time environmental conditions, optimizing power consumption while maintaining visual comfort.
2Reliability
If the optical sensor uses a larger second transistor to increase current control range, then the sensing reliability improves, but the area occupied increases
Solution Approach 1:
The patent resolves the area constraint by transitioning from a planar layout to a three-dimensional stacked configuration. The optical sensor is integrated into the black matrix region at a depth dimension, utilizing the vertical space within the display structure. This allows the sensor circuitry to occupy minimal surface area while maintaining sufficient transistor size for reliable current control.
Solution Approach 2:
The patent applies local quality by positioning the optical sensor specifically within the black matrix region, which is a peripheral area that does not contribute to the active display area. This localized placement allows the sensor to utilize otherwise wasted space, enabling reliable sensing functionality without encroaching on the pixel region or reducing the effective display area.
3Duration of action of stationary object
If the first transistor remains always on to ensure continuous sensing, then the sensing continuity is maintained, but the power consumption increases
Solution Approach 1:
The patent implements periodic action by controlling the first transistor to operate in alternating on/off states synchronized with the display refresh cycle. During specific time intervals when sensing is required, the first transistor is turned on to enable current flow through the second transistor. During other intervals, it is turned off to minimize power consumption, while the sensing results are maintained through the capacitance of the first capacitor.
Solution Approach 2:
The patent applies preliminary action by pre-charging the first capacitor during the off-period of the first transistor, so that when the transistor turns on during the sensing interval, the capacitor is already charged and ready to immediately establish the sensing current. This preliminary preparation ensures continuous sensing capability without requiring the transistor to remain constantly on.
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 reduces power consumption by adjusting backlight brightness based on ambient light conditions, enhancing reliability in peripheral light sensing and minimizing power usage without compromising image quality.
Implementation Method 1
an optical sensor for sensing peripheral light... which generates a sensing signal corresponding to an intensity of the peripheral light
Data Source
AI summary
An optical sensor providing enhanced reliability in sensing peripheral light and reduced power consumption, and a liquid crystal display device incorporating this optical sensor. In the optical sensor, a first transistor is electrically coupled between a first power supply and a second transistor, which is electrically coupled between the first transistor and a second power supply having a voltage less than that of the first power supply. The first transistor is either turned-on or turned-off according to a control signal. The second transistor controls an amount of an electric current flowing from the first transistor to the second power supply corresponding to an intensity of peripheral light. A sensing section is constructed with a first capacitor electrically coupled to the second transistor in parallel. A gate electrode of the second transistor is electrically coupled to the second power supply.