Capacitive Touch Panel Noise Filtering via Frequency Switching
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Solution Overview
Problem
Capacitive touch panels face precision issues in determining touch positions due to noise from users and environmental factors like electromagnetic radiation, leading to inaccurate readings.
Innovation Solution
A device and method that rapidly switch alternating current (AC) scan signal frequencies across the touch panel's corners, filter out noise frequencies based on current variations, and calculate final current values to improve precision in determining touch coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC scan signals with single frequency are used for touch detection, then the detection process is simple, but noise from electromagnetic radiation and user interference causes measurement errors
Solution Approach 1:
The patent applies parameter changes by varying the frequency parameter of the AC scan signals. Multiple AC scan signals with different frequencies are sequentially applied to the four corners of the touch panel, allowing the system to detect current values at multiple frequency points and identify noise frequencies through comparison, thereby improving measurement precision despite noise interference.
Solution Approach 2:
The patent implements periodic action by sequentially and repeatedly applying AC scan signals at different frequencies to each corner of the touch panel. This periodic variation in frequency allows the system to distinguish between genuine touch-induced current changes and periodic noise patterns, enhancing the ability to filter noise while maintaining detection accuracy.
2Measurement precision
If multiple frequencies are used for noise filtering, then noise reduction effectiveness improves, but the complexity of the detection system increases
Solution Approach 1:
The patent applies segmentation by dividing the frequency spectrum into multiple discrete frequency points. Instead of using a continuous range of frequencies or complex filtering algorithms, the system segments the detection process into multiple sequential measurements at specific frequency points, simplifying the overall system while achieving effective noise filtering through comparative analysis.
Solution Approach 2:
The system performs self-service by using its own multiple frequency measurements to automatically identify and filter noise frequencies. The controller compares current values obtained at different frequencies and autonomously determines which frequency points are affected by noise, eliminating the need for external noise filtering hardware or complex preprocessing systems.
3Measurement precision
If rapid frequency switching is implemented, then noise filtering capability is enhanced, but the detection time for each touch point increases
Solution Approach 1:
The patent applies partial action by measuring current values at more frequency points than strictly necessary for basic detection. While this increases the total measurement time, it provides redundant data that enables robust noise identification and filtering. The system uses this excess measurement capacity to ensure accurate touch position detection even in noisy environments, where the additional time invested in frequency switching pays off through improved measurement reliability.
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
Significantly reduces noise effects, enhancing the precision of touch position determination on capacitive touch panels by filtering out noise frequencies and averaging current values, thus providing more accurate coordinates.
Implementation Method 1
In the capacitive touch panel, a capacitive mechanism is used for position determination where several currents are supplied onto the touch panel when a touch is impinged on the touch panel and are measured and then a relationship among the measured currents is deduced to obtain the touch position
Implementation Method 2
the currents I1, I2, I3 and I4 vary since the touch point, e.g. a fingertip of a user, P is electrically conductive and thus changes the resistance of the touch point P on the sensing area 11
Implementation Method 3
a frequency switching unit rapidly switching the frequency of the AC scan signal associated with each of the four corners among a group of specific frequencies
Implementation Method 4
a valid frequency selecting unit receiving the current value of the AC scan signal of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively, and selecting a group of selected frequencies according to a noise filtering procedure from the group of specific frequencies
Data Source
AI summary
Described is a device and a method for determining a touch position on a sensing area of a capacitive touch panel. In the device and method, an alternating current (AC) scan signal having a frequency and a current value is supplied to each of four corners of the capacitive touch panel. Next, the frequencies of the AC scan signals are each rapidly switched among a group of specific frequencies. The current values of the AC scan signals detected. In response, a group of selected frequencies is selected according to a noise filtering procedure from the group of specific frequencies based on the current values. Final current values are obtained by calculating the current values of the AC scan signals of the group of selected frequencies. Finally, the touch position on the capacitive touch panel is determined based on the final current values.