Capacitive Touch Panel Noise Filtering via Segmented Sensing
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Solution Overview
Problem
Capacitive touch panel systems in electronic devices face challenges in accurately distinguishing touch inputs from noise sources, particularly time-varying noise generated by nearby electronic components like display panels, which degrades signal-to-noise ratios and affects touch input resolution.
Innovation Solution
The system employs a processing unit to detect and adjust for time-varying noise by isolating noise signals from input-protected sensing points, normalizing sensed values, and filtering out common mode noise, allowing for accurate determination of touch inputs even in the presence of significant time-varying noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive touch panel systems use grid sensors to detect self-capacitance or mutual capacitance changes, then touch input detection capability is provided, but time-varying noise from nearby electronic components degrades signal-to-noise ratio and reduces touch input resolution
Solution Approach 1:
The system divides the sensing points into two distinct groups: input-protected sensing points that are shielded from touch inputs but exposed to noise, and input-sensitive sensing points that detect both touch inputs and noise. This segmentation allows independent measurement of noise and touch signals, resolving the contradiction between detection accuracy and noise interference.
Solution Approach 2:
The input-protected sensing points act as intermediaries or reference elements that measure only the noise component. By using these protected points as a reference, the system can subtract noise from the measurements taken at input-sensitive points, thereby eliminating the harmful noise effect while preserving touch detection capability.
2Measurement precision
If the system scans sensing points sequentially to detect capacitance variations, then touch input detection is enabled, but processing time increases and response speed decreases
Solution Approach 1:
The system performs preliminary measurements at input-protected sensing points to characterize noise before touch input detection. By pre-measuring noise characteristics and storing them in lookup tables, the system eliminates the need for sequential scanning during actual touch detection, thereby reducing processing time while maintaining detection accuracy.
3Measurement precision
If excitation signals are applied to sensing points to detect capacitance changes, then touch input sensing is achieved, but electronic noise is generated and added to the signal
Solution Approach 1:
The system converts the harmful electronic noise generated by excitation signals into a useful reference measurement. By measuring noise at input-protected sensing points that experience the same excitation but no touch input, the system transforms noise into a characterizable parameter that can be subtracted from actual measurements, thereby eliminating its harmful effect.
Solution Approach 2:
The input-protected sensing points create a copy or replica of the noise signal that does not contain touch input information. This noise copy can then be used to compensate for and eliminate noise in the actual touch detection measurements, effectively separating noise from the useful signal.
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 approach enhances the accuracy of touch input detection and resolution by effectively filtering time-varying noise, improving signal-to-noise ratios and enabling more precise location determination of touch inputs in capacitive touch panel systems.
Implementation Method 1
sense changes in self capacitance (e.g., between a sensor and ground) or mutual capacitance (e.g., between two sensors) as a result of a touch input
Implementation Method 2
changes in the capacitance of a sensing point 102 can be detected by measuring the change in the discharge time of the sensing point 102. The discharge time is measured by measuring the output voltage decay as a function of time after application of an input signal burst
Implementation Method 3
The system employs a processing unit to detect and adjust for time-varying noise by isolating noise signals from input-protected sensing points, normalizing sensed values, and filtering out common mode noise
Data Source
AI summary
An electronic device is operable to determine a touch input applied to a capacitive touch panel system thereof so as to account for time-varying noise affecting the touch panel system. The electronic device includes the touch panel system, an analog-to-digital conversion (ADC) unit, and a processing unit. The processing unit is operable to: receive digital signal values from the ADC unit representing capacitances detected by sensing points of the touch panel system; adjust at least one of the digital signal values based at least on a time-varying noise to produce at least one noise-adjusted value; and determine the touch input based on the at least one noise-adjusted value. In one embodiment, the electronic device determines the time-varying noise prior to adjusting the digital signal values. In another embodiment, the time-varying noise is produced by a display panel of a touchscreen display that also includes the touch panel system.