Capacitive Touch Sensor with Harmonic Signal Filtering
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Solution Overview
Problem
Capacitive touch sensors for liquid crystal displays face challenges in detecting objects stably across various environments due to external noise interference, which complicates the circuit configuration and limits their flexibility and integration with display circuits.
Innovation Solution
A capacitive touch sensor design that uses a common drive voltage for both display and touch detection, incorporating filters to pass fundamental and harmonic detection signals, allowing for stable object detection without changing the detection drive frequency, thereby reducing noise influence and simplifying the configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a capacitive touch sensor is formed between a conductive film and the outer surface of a polarizing plate, then the thickness of the liquid crystal display element is reduced, but external noise interference increases making stable object detection difficult
Solution Approach 1:
The patent combines the display common electrode and touch sensor drive electrode into a single electrode structure. This merging allows the touch sensor to utilize the existing display electrode, reducing the need for additional components and minimizing the increase in display element thickness while maintaining stable detection performance through integrated design
Solution Approach 2:
The patent introduces a noise removal circuit as an intermediary component that processes the detection signal from the touch sensor. This circuit actively removes external noise interference from the detection signal, enabling stable object detection even when the touch sensor is positioned close to the outer surface where noise susceptibility is higher
2Reliability
If the conductive film for the touch sensor is arranged deep in the liquid crystal display element, then external noise interference is reduced, but the degree of flexibility in design is reduced
Solution Approach 1:
The patent employs dynamic noise removal through a noise removal circuit that actively processes detection signals in real-time. This dynamic approach allows the system to maintain high noise resistance while keeping the conductive film positioned optimally for design flexibility, as the noise compensation is handled electronically rather than through fixed physical positioning
Solution Approach 2:
The patent shifts the solution from the spatial dimension (positioning the conductive film deep inside) to the signal processing dimension (using noise removal circuits). By addressing noise resistance through signal processing rather than physical positioning, the system maintains design flexibility in electrode placement while achieving reliable noise resistance
3Ease of operation
If a separate circuit section for touch sensor drive is arranged, then touch detection function is achieved, but integration of circuits for whole apparatus becomes difficult
Solution Approach 1:
The patent merges the touch sensor drive electrode with the display common electrode, and combines the noise removal circuit with the existing display drive circuitry. This integration eliminates the need for separate touch sensor drive circuits, reducing overall circuit complexity while maintaining full touch detection functionality
Solution Approach 2:
The patent makes the display common electrode serve dual functions: driving the liquid crystal display and driving the capacitive touch sensor. This multi-functionality eliminates the need for dedicated touch sensor drive circuits, simplifying the overall circuit architecture while achieving complete touch detection capability
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
Enables stable object detection with reduced noise interference across different environments, simplifying the circuit configuration and enhancing integration with display circuits, making it suitable for mobile devices with unsteady potentials.
Implementation Method 1
a touch detection electrode forming a capacitance between the touch detection electrode and the common electrode
Implementation Method 2
a first filter allowing a fundamental detection signal, contained in the detection signal and having a frequency same as a fundamental frequency of the touch sensor drive signal, to pass therethrough, a plurality of second filters separately allowing two or more harmonic detection signals, contained in the detection signal and having frequencies same as respective harmonic frequencies of the touch sensor drive signal, to pass therethrough
Data Source
AI summary
A display includes: display pixel electrodes; common electrodes; a display layer; a display control circuit; touch detection electrodes; and a touch detection circuit detecting an external proximity object based on a detection signal obtained from the touch detection electrodes with use of a common drive voltage for display applied to the common electrode as a touch sensor drive signal. The touch detection circuit includes: a first filter allowing a fundamental detection signal, contained in the detection signal and having a frequency same as a fundamental frequency of the touch sensor drive signal, to pass therethrough, a plurality of second filters separately allowing two or more harmonic detection signals, contained in the detection signal and having frequencies same as respective harmonic frequencies of the touch sensor drive signal, to pass therethrough, and a detection section performing a detection operation based on the fundamental detection signal and the harmonic detection signals.