Capacitive Sensing Isolation for Thin Touchscreen Accuracy
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Solution Overview
Problem
Capacitive touchscreens with thin cover layers in mobile devices experience inaccuracies in touch operation detection due to differences in induced current between floating and non-floating states, leading to misjudgment and reduced signal quality.
Innovation Solution
A capacitive sensing system with an isolation module that generates a floating supply voltage and ground voltage, using an isolation circuit to maintain the touchscreen and sense circuit in a floating state, isolating them from the ground voltage, thereby stabilizing the touch sensing signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a thin touchscreen is used to reduce device thickness, then the device becomes thinner and more compact, but the induced capacitance between the electrode and human body increases, causing larger induced current leakage to ground in non-floating states and reducing touch detection accuracy
Solution Approach 1:
The system separates the power supply into two independent parts: a ground voltage power supply connected to ground and a floating supply voltage power supply isolated from ground. This segmentation allows the sensing circuit to operate in a floating state, preventing induced current from leaking to ground and maintaining accurate touch detection despite the thin touchscreen structure.
Solution Approach 2:
An isolation module is introduced as an intermediary component between the ground voltage power supply and the sensing circuit. This isolation module generates a floating supply voltage that is electrically isolated from ground, acting as a mediator to prevent the harmful effect of ground connection on touch sensing accuracy while still providing necessary power to the sensing circuit.
2Reliability
If the mobile device is in a non-floating state with ground connection, then the device has stable grounding, but a larger portion of induced current flows to ground via the human body instead of the detection electrode, increasing noise voltage proportion and reducing signal quality
Solution Approach 1:
The power supply system is divided into two independent segments: one providing ground voltage for stable grounding reference and another providing floating supply voltage for the sensing circuit. This segmentation allows the sensing circuit to operate without ground connection, preventing induced current from taking the low-impedance ground path and ensuring current flows through the detection electrode for accurate measurement.
Solution Approach 2:
The system transitions from a single-grounded voltage system to a two-dimensional voltage system with both ground voltage and floating supply voltage. This dimensional change creates an additional voltage reference level that is electrically isolated from ground, allowing the sensing circuit to operate in a floating state and eliminating the current leakage path to ground while maintaining grounding stability for other device functions.
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 improves the accuracy and stability of touch operation detection by maintaining consistent voltage differences between floating and non-floating states, enhancing the signal-to-noise ratio and user experience.
Implementation Method 1
an isolation circuit to generate a floating supply voltage and a floating ground voltage according to a supply voltage and a ground voltage, respectively, and to provide the floating supply voltage and the floating ground voltage to the touchscreen and the sense circuit
Implementation Method 2
mutual-capacitance touch sensing uses a sensing panel disposed at a backside of a touchscreen panel for touch sensing. A distribution of an electromagnetic field of the touchscreen varies according to a position at which a user touches, thus causing a change in the mutual-capacitance between electrodes of the sensing panel
Implementation Method 3
the sensing panel may determine the user's touch operation by detecting a variation of a current flowing through the electrodes
Data Source
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AI summary
The present disclosure provides a mobile device. The mobile device includes a casing, configured to accommodate or support the mobile device; a thin touchscreen, including at least one driving electrode and at least one receiving electrode, wherein the driving electrode is configured to receive a driving signal, and the receiving electrode is configured to generate a sensing signal to sense a touch operation; a capacitive sensing system, including a sense circuit, coupled to the at least one receiving electrode and configured to generate the driving signal and receive the sensing signal to determine the touch operation; and a power supply unit, configured to output a supply voltage and a ground voltage; and an isolation module, configured to isolate the supply voltage from the ground voltage.