Capacitive Touchpad Ghost Point Detection via Two-Step Self and Mutual Capacitance
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Solution Overview
Problem
Conventional capacitive touchpads struggle to distinguish real touch points from ghost points, especially in multi-touch scenarios, leading to improper identification of touch points.
Innovation Solution
A two-step detection method for capacitive touchpads that first detects self capacitances across multiple sensor traces and then identifies real touch points by measuring mutual capacitance at detected touch points using a self negative capacitance compensator, switching circuits, and a sensing circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If self capacitance detection method is used to identify touch points, then the detection process is simple, but multiple ghost points are detected simultaneously making it impossible to properly identify real touch points
Solution Approach 1:
The detection process is divided into two distinct stages: first detecting all potential touch points using self capacitance, then filtering to identify real touch points using mutual capacitance. This segmentation allows the system to maintain simplicity in the initial detection while achieving precision in the final identification.
Solution Approach 2:
Mutual capacitance detection serves as an intermediary verification step between the initial self capacitance detection and the final touch point identification. This intermediary mechanism filters out ghost points by checking whether the detected point corresponds to an actual finger touch through mutual capacitance measurement.
2Measurement precision
If mutual capacitance detection is added to distinguish real touch points, then touch point identification accuracy is improved, but device complexity increases
Solution Approach 1:
The self capacitance detection circuit and mutual capacitance detection circuit are merged into a single integrated detection system. The same sensor traces (TX and TY) are used for both detection modes, and the control unit coordinates both detection processes, reducing the need for separate independent circuits.
Solution Approach 2:
The capacitance sensor traces TX1-TXN and TY1-TYM serve dual functions: they detect self capacitance for initial touch point identification and simultaneously enable mutual capacitance detection for verification. This multi-functionality eliminates the need for dedicated separate circuits for each detection mode.
3Measurement precision
If two-step detection method is implemented, then real touch points are accurately identified, but detection time increases
Solution Approach 1:
Self capacitance detection is performed first as a preliminary step to quickly identify all potential touch points including ghost points. This preliminary detection narrows down the candidates before the more time-consuming mutual capacitance verification is applied only to the detected points.
Solution Approach 2:
Mutual capacitance detection is applied selectively only to the points identified by self capacitance detection, rather than to all possible intersections of sensor traces. This partial application reduces the overall detection time while maintaining accuracy.
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, enabling accurate identification even in multi-touch situations by utilizing mutual capacitance variations at intersection points.
Implementation Method 1
a self negative capacitance compensator for compensating the self capacitor of a detected capacitance sensor trace
Implementation Method 2
a sensing circuit connected to the mode switching device for detecting the self capacitance of the detected capacitance sensor trace or the mutual capacitance at the intersection to generate a sense signal
Data Source
AI summary
A two-step detection for a capacitive touchpad to identify a real touch point first detects the self capacitances from multiple capacitance sensor traces of the capacitive touchpad to identify any touch point on the capacitive touchpad and then, if multiple touch points are detected, further detects the mutual capacitance at one of the detected touch points to identify whether it is a real touch point.