Capacitive Touch Driving Frequency Selection
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Solution Overview
Problem
Capacitive multi-touch systems face issues with high power consumption, increased data processing time, and noise interference due to the need for multiple driving frequencies, which affects the touch report rate and sensing resolution.
Innovation Solution
A driving frequency selection method that alternates between self and mutual capacitance sensing using multiple frequencies in idle and active modes to determine the most noise-resistant frequency for active use, reducing data processing and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple driving frequencies are used to sense the capacitive touch panel, then noise resistance is improved, but power consumption increases
Solution Approach 1:
The system performs preliminary sensing using self-capacitance mode to identify the most noise-resistant frequency before switching to mutual-capacitance mode for actual touch detection. This preliminary action allows the system to pre-determine the optimal frequency, avoiding the need to continuously use multiple frequencies and thereby reducing power consumption while maintaining noise resistance.
Solution Approach 2:
The system periodically switches between self-capacitance sensing (for frequency identification) and mutual-capacitance sensing (for touch detection) in a cyclic manner. This periodic action allows the system to use multiple frequencies only when necessary for frequency identification, rather than continuously, thus reducing overall power consumption while maintaining reliable noise-resistant operation.
2Reliability
If multiple driving frequencies are used to sense the capacitive touch panel, then noise resistance is improved, but touch report rate decreases
Solution Approach 1:
The system performs preliminary frequency identification using self-capacitance mode, which requires minimal processing time, before switching to mutual-capacitance mode for actual touch detection. This preliminary action is performed only once or periodically, allowing the system to maintain high touch report rates during normal operation while still benefiting from noise-resistant frequency selection.
Solution Approach 2:
The system implements a periodic sensing scheme where self-capacitance sensing for frequency identification is performed intermittently, and mutual-capacitance sensing for touch detection is performed continuously at the identified frequency. This periodic alternation ensures that the time-consuming multi-frequency sensing is minimized, thereby maintaining high touch report rates while preserving noise resistance.
3Reliability
If multiple driving frequencies are used to sense the capacitive touch panel, then noise resistance is improved, but data processing time increases
Solution Approach 1:
The system performs preliminary frequency identification using self-capacitance mode, which generates minimal data requiring little processing time, before switching to mutual-capacitance mode for actual touch detection. This preliminary action reduces the overall data processing burden by determining the optimal frequency in advance, allowing the system to process only the necessary touch detection data at the identified frequency.
Solution Approach 2:
The system periodically performs self-capacitance sensing for frequency identification and then uses the identified frequency for continuous mutual-capacitance sensing. This periodic approach ensures that multi-frequency data processing is performed only when necessary, significantly reducing overall data processing time while maintaining noise resistance through periodic frequency verification.
4Use of energy by moving object
If self capacitance sensing is used, then power consumption is reduced, but ghost point effect occurs in multi-touch applications
Solution Approach 1:
The system performs preliminary frequency identification using self-capacitance mode (which consumes low power) before switching to mutual-capacitance mode for actual touch detection. This preliminary action allows the system to benefit from low-power self-capacitance sensing without suffering from its ghost point effect, as the subsequent mutual-capacitance sensing at the identified frequency provides accurate multi-touch detection.
Solution Approach 2:
The system periodically alternates between self-capacitance sensing for frequency identification and mutual-capacitance sensing for accurate touch detection. This periodic action allows the system to use low-power self-capacitance mode for frequency identification while relying on accurate mutual-capacitance mode for actual multi-touch detection, thereby combining the advantages of both modes.
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 method reduces power consumption and improves touch report rate by identifying the most noise-resistant frequency for active use, enhancing the accuracy and efficiency of capacitive multi-touch systems.
Implementation Method 1
a capacitive touch panel uses a capacitance change generated in an electrostatic combination of the arranged transparent electrodes with the touching part of a human body to generate a current or voltage for detecting the coordinate of the touching part
Implementation Method 2
a capacitance change generated in an electrostatic combination of the arranged transparent electrodes with the touching part of a human body
Implementation Method 3
The self capacitance or the grounded capacitance is not a physical capacitor, but parasitic and stray capacitance on every conductor line
Implementation Method 4
The mutual capacitance sensing indicates that a capacitance coupling is generated between two adjacent conductor lines when a touch occurs
Data Source
AI summary
A driving frequency selection method is used in a capacitive multi-touch system. When the system operates in an idle mode, an active driving frequency is selected randomly from N candidates, and a self-capacitance driving and sensing is used to detect touch points. When there are touch points, the capacitive multi-touch system is switched to an active mode to acquire an image raw data for finding the positions of touch points. In the active mode, noise is calculated from the image raw data. When the noise exceeds a predetermined value, the system is switched back to the idle mode, and the self-capacitance driving and sensing is applied to N−1 active driving frequencies other than the previously selected active driving frequency to acquire N−1 self-capacitance image raw data. The method determines one with a minimum noise and selects the corresponding frequency as a currently active driving frequency.