Capacitive Touch Panel Noise Removal via Periodic Demodulation
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Solution Overview
Problem
Surface capacitive touch panels are susceptible to external noise, struggle with noise removal when noise frequencies are close to the excitation frequency, have limited frequency resolution, and experience decreased signal-to-noise ratio due to short signal acquisition times and intervening materials like polarizers or protective glass.
Innovation Solution
An electronic device with a sensor system that generates intermittent sinusoidal waves and uses demodulation units to process signals from both periods with and without sinusoidal wave excitation, allowing for noise removal by subtracting noise vectors from true signal vectors, even when they have the same frequency, and utilizing mean vectors of preceding and succeeding noise to enhance noise removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surface capacitive touch panel uses conventional noise removal methods, then noise removal capability is improved, but frequency resolution is limited and cannot remove noise close to the excitation frequency
Solution Approach 1:
The patent applies periodic action by alternating between excitation periods (when sinusoidal wave is output) and non-excitation periods (when sinusoidal wave is stopped). During non-excitation periods, the sensor system captures noise signals without the excitation signal interfering. This periodic switching enables the system to separate noise from signal by comparing measurements taken during different periods, thereby achieving high frequency resolution and effective noise removal even for noise close to the excitation frequency.
2Productivity
If the signal acquisition time is shortened, then productivity is improved, but signal-to-noise ratio decreases
Solution Approach 1:
The patent uses periodic action with alternating excitation and non-excitation periods to overcome the time constraint. During non-excitation periods, the system quickly captures noise characteristics without requiring long continuous acquisition times. By combining measurements from multiple short periods, the system achieves sufficient signal-to-noise ratio while maintaining high productivity through rapid periodic sampling rather than prolonged continuous measurement.
Solution Approach 2:
The patent implements feedback by using noise signals captured during non-excitation periods to correct and refine the signal measurements taken during excitation periods. The noise characteristics obtained from non-excitation periods are fed back to compensate for noise in the excitation period measurements, thereby improving signal-to-noise ratio without requiring extended acquisition time.
3Manufacturing precision
If materials like polarizers or protective glass are placed between the resistive sheet and finger, then manufacturing precision is improved, but signal-to-noise ratio decreases due to signal attenuation
Solution Approach 1:
The patent uses the non-excitation period as an intermediary mechanism to capture noise characteristics that are present regardless of the intervening materials (polarizers or protective glass). By measuring noise during these periods, the system can compensate for signal attenuation caused by these materials, allowing the touch panel to maintain adequate signal-to-noise ratio even with such layers present.
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 effectively removes noise regardless of touch presence, accurately separates true signals from noise, and improves signal-to-noise ratio by removing noise close to the true signal frequency, making the touch panel more robust to external noise.
Implementation Method 1
a capacitor is formed by capacitive coupling between the position sensing conductive film and the finger or the like
Implementation Method 2
capacitance of a capacitor formed by capacitive coupling between the resistive sheet and a pointing object is detected
Data Source
AI summary
When the excitation frequency of a touch panel and the frequency of external noise match or are close, noise cannot be removed by a bandpass filter. In addition, when a touch detection operating period is limited to a short period such as the no addressing period, the signal-to-noise ratio (S/N) decreases because frequency separation decreases and the noise removal effect by averaging is degraded. An electronic device of the present invention includes a sensor system (101), an excitation generator (102) that generates an intermittent sinusoidal signal and applies this signal to the sensor system, and a demodulator (105) that demodulates the amplitude modulated signal that is the output of the sensor system. The demodulator uses both the response x1(t) of the sensor system in the period in which the excitation generator outputs the sinusoidal signal, and the response z1(t) of the sensor system in the period in which the excitation generator does not output the sinusoidal signal at least either immediately before or immediately after the signal output to generate the demodulated signal D(t).