Capacitive Touch Panel Drive Pulse Width Variation
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Solution Overview
Problem
The detection accuracy of electrostatic capacitance type touch panels is compromised by noise caused by AC chargers, particularly when the frequency of the drive pulse coincides with the charging frequency, leading to reduced detection signal quality and accuracy.
Innovation Solution
The implementation of a drive circuit that outputs drive pulses with multiple pulse widths for each signal period, allowing for the selection of optimal detection data and minimizing noise buildup by varying the pulse width to avoid synchronization with the AC charger frequency, thereby reducing noise interference without changing the drive pulse frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the drive pulse frequency is changed to avoid noise synchronization, then detection accuracy is improved, but device complexity increases due to frequency switching requirements
Solution Approach 1:
The patent changes the pulse width parameter of the drive signal instead of changing the frequency. By varying the pulse width among multiple values (first, second, and third pulse widths), the system avoids noise synchronization without requiring frequency switching mechanisms, thereby improving detection accuracy while maintaining device simplicity
Solution Approach 2:
The patent employs periodic variation of pulse widths in a repeating pattern (first pulse width, second pulse width, third pulse width, then repeating). This periodic action allows the system to avoid continuous noise synchronization while using a simple, predictable sequence that does not require complex control logic
2Measurement precision
If multiple drive pulse frequencies are used to reduce noise, then detection accuracy is improved, but the pulse signal period increases affecting productivity
Solution Approach 1:
The patent varies the pulse width parameter within the existing signal period rather than extending the period by switching frequencies. This allows multiple pulse width values to be tested within a single detection cycle, maintaining fast detection speed while achieving noise reduction through parameter variation
Solution Approach 2:
The patent applies multiple pulse widths (excessive action) to ensure noise avoidance, but does so within the constraints of a single detection cycle. By using more pulse width variations than strictly necessary (first, second, and third pulse widths), the system guarantees noise avoidance without significantly extending the detection period
3Device complexity
If the drive pulse width is fixed, then device complexity is reduced, but noise buildup occurs when synchronized with AC charger frequency
Solution Approach 1:
The patent makes the pulse width dynamic by selecting from multiple possible values (first, second, and third pulse widths) based on the detection cycle requirements. This dynamic adjustment prevents fixed synchronization with AC charger frequency while keeping the control logic simple through predetermined patterns
Solution Approach 2:
The patent pre-establishes multiple pulse width values and their selection patterns before operation. By having the pulse width variations predetermined and ready, the system avoids noise buildup without requiring real-time complex calculations or adjustments during operation
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 suppresses noise-induced reductions in detection signals and maintains detection accuracy by ensuring the drive pulse width does not coincide with the AC charger frequency, even when the charger's voltage fluctuates, thus preventing the cumulative buildup of undesired voltage components.
Implementation Method 1
a mutual capacitance-type touch panel which enables a multi-touch detection includes: a plurality of drive electrodes; a plurality of detection electrodes; and a plurality of crossing parts formed by the drive electrodes and the detection electrodes, wherein a fluctuation in capacitive coupling state at each crossing part can be obtained
Data Source
AI summary
It becomes possible to use drive pulses having different pulse widths for one kind of drive pulse signal period. Therefore, even if a voltage acting on a crossing part of drive and detection electrodes is periodically changed through a stray capacitance attributed to an external object such as a finger in an undesired manner, the pulse width of the drive pulse is never fixed with respect to the period, and the periodic buildup of a certain voltage on a detection signal, which would make appreciable noise, is suppressed. Thus, the reduction of detection signals can be suppressed in quantity without switching the pulse signal frequency of the drive pulse of a touch panel.