Capacitive Touch Sensing Circuit for Ghost Point Detection
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Solution Overview
Problem
Capacitive touch panels face difficulties in accurately identifying real touch points from ghost points, especially in multi-touch applications, due to capacitance variations that result in incorrect identification of touch points.
Innovation Solution
A sensing method and circuit that applies different voltages to traces of a capacitive touch panel across a sensing capacitor in alternating clock phases to distinguish real points from ghost points by sensing capacitance variations at the intersection of traces, utilizing a switching circuit and operational amplifier to determine the presence of a finger based on voltage changes across a sensing capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance variations of traces are scanned to locate touch points, then single-touch positioning is achieved, but multi-touch applications produce ghost points that prevent accurate identification of real touch points
Solution Approach 1:
The invention segments the touch detection process into two distinct phases: a first clock phase that charges the sensing capacitor through one trace, and a second clock phase that charges through the other trace. By separating the charging operations into distinct time segments, the system can compare the charging characteristics to distinguish real touch points from ghost points, thereby resolving the ambiguity in multi-touch scenarios.
Solution Approach 2:
The invention employs periodic alternating clock phases to sequentially charge the sensing capacitor through different traces. This periodic action allows the system to observe capacitance variations at different time intervals, enabling the differentiation between real touch points (which show consistent capacitance changes across phases) and ghost points (which show inconsistent or opposite changes).
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
Effectively differentiates real touch points from ghost points by analyzing capacitance changes, ensuring accurate identification of touch points even in multi-touch scenarios, thereby enhancing the reliability of capacitive touch panels.
Implementation Method 1
the capacitance values of the traces TX8 and TY3 are changed, so it can be determined that the finger is at the intersection 12 of the traces TX8 and TY3
Data Source
AI summary
A sensing method and circuit for a capacitive touch panel sense the capacitance variation of a lateral capacitor formed at the intersection of two traces of the capacitive touch panel, to distinguish a real point from a ghost point. A sensing cycle includes two non-overlapping clock phases. In the first clock phase, the voltages across the lateral capacitor and across a sensing capacitor are set. In the second clock phase, the voltage at a first terminal of the lateral capacitor is changed, and a second terminal of the lateral capacitor is connected to a first terminal of the sensing capacitor, causing a voltage variation at a second terminal of the sensing capacitor. This voltage variation is used to determine whether the intersection is touched. The sensing method and circuit reflect the status of the lateral capacitor in real-time and prevent the location of the touch point from being misjudged.