Capacitance Touch Sensor Integrated in LCD Panel
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Solution Overview
Problem
Conventional touch panels integrated with liquid crystal displays (LCDs) often compromise the optical characteristics and increase the thickness of the LCD, necessitating a solution to incorporate a touch sensor within the LCD panel without these drawbacks.
Innovation Solution
A touch sensor is integrated within the liquid crystal display panel, comprising x-axis and y-axis read-out lines with sensor units that include a reset unit, capacitance detector, and output units, converting capacitance variations into leakage current differences to enhance sensitivity and detect touch events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a touch panel is provided separately on top of the liquid crystal display panel, then touch detection function is achieved, but the thickness of the LCD increases and optical characteristics are lowered
Solution Approach 1:
The touch sensor is merged with the liquid crystal display panel by integrating the touch sensor electrodes and read-out circuits directly into the LCD structure. The sensor units are formed in the same pixel structure as the display pixels, sharing common electrodes and signal lines, thereby eliminating the need for a separate touch panel layer and maintaining the original thickness of the LCD.
Solution Approach 2:
The liquid crystal display panel serves dual functions: display and touch detection. The same pixel electrodes and liquid crystal cells are used for both displaying images and detecting touch events. The read-out circuits are designed to handle both display signal output and touch capacitance measurement, allowing one structure to perform multiple functions without requiring additional components.
2Reliability
If a touch panel is provided separately on top of the liquid crystal display panel, then touch detection function is achieved, but optical characteristics (brightness, viewing angle) are lowered
Solution Approach 1:
The touch sensor is merged with the liquid crystal display panel by integrating the touch sensor electrodes and read-out circuits directly into the LCD structure. The sensor units are formed in the same pixel structure as the display pixels, sharing common electrodes and signal lines, thereby eliminating the need for a separate touch panel layer and maintaining the original thickness of the LCD.
3Measurement precision
If capacitance variation is directly measured, then touch event detection is achieved, but sensitivity is insufficient due to small voltage output differences
Solution Approach 1:
The reset unit pre-charges the capacitor to a known initial state before the measurement phase. By establishing a predetermined charge state beforehand, the system can more accurately detect changes in capacitance caused by touch events, as the baseline is clearly defined and any deviation from this baseline can be reliably attributed to touch input rather than initial condition variations.
Solution Approach 2:
The read-out circuit operates in periodic cycles, alternating between a reset phase where the capacitor is recharged to a known state and a measurement phase where capacitance changes are detected. This periodic resetting and measuring allows the system to maintain high sensitivity by continuously establishing a fresh baseline before each measurement, enabling reliable detection of small capacitance variations caused by touch events.
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 configuration improves sensitivity by magnifying the difference between touch and non-touch events, allowing for more significant voltage output variations and maintaining the optical characteristics and thickness of the LCD.
Implementation Method 1
The capacitance detector changes the first reset signal based on a variation of a cell gap of the liquid crystal display panel caused by a touch event
Implementation Method 2
a liquid crystal display panel, a touch sensor, a coordinate detection circuit, and a driver. The liquid crystal display panel includes a plurality of pixels to display an image
Data Source
AI summary
A touch sensor configured to be disposed in a liquid crystal display panel includes a plurality of x-axis read-out lines crossing and insulated from a plurality of y-axis read-out lines and a plurality of sensor units. Each sensor unit includes a reset unit, a capacitance detector, a first output unit, and a second output unit. The reset unit outputs a first reset signal based on a first control signal. The capacitance detector changes the first reset signal based on a variation of a cell gap of the liquid crystal display panel caused by a touch event. The first output unit changes an electric potential of a corresponding x-axis read-out line in response to the first reset signal changed in the capacitance detector. The second output unit changes an electric potential of a corresponding y-axis read-out line in response to the first reset signal changed in the capacitance detector.