Ghost Cancellation in Multi-Touch Sensing Arrays
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Solution Overview
Problem
The projective sensing method in multi-touch devices often results in 'ghost points' due to false touch detection, while the matrix sensing method is too time-consuming and costly for practical use.
Innovation Solution
A ghost cancellation method that uses the projective sensing method to identify touch point candidates and then verifies them using the matrix sensing method to eliminate ghost points, by applying driving signals to the sensing array lines and detecting changes in capacitance to distinguish actual touches from false ones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the projective sensing method is used, then the detection speed is improved, but ghost points are generated causing false touch detection
Solution Approach 1:
The sensing array is divided into multiple independent sensing channels (rows and columns). Each channel is detected separately through selective signal application, allowing the system to process touch detection in segments rather than requiring full matrix scanning, thus maintaining speed while improving accuracy
Solution Approach 2:
A verification mechanism is introduced as an intermediary step between initial touch detection and final touch confirmation. The system applies test signals to verify detected touch points, using this intermediate verification process to distinguish real touches from ghost points without requiring complete matrix scanning
2Measurement precision
If the matrix sensing method is used, then ghost points are eliminated, but the detection time increases significantly
Solution Approach 1:
Instead of performing complete matrix scanning on all sensing elements, the system applies partial action by selectively testing only the specific rows and columns where touches are initially detected. This partial verification approach provides sufficient accuracy to eliminate ghost points without the time cost of exhaustive matrix scanning
Solution Approach 2:
The system performs preliminary touch detection using the fast projective sensing method to identify potential touch locations before conducting verification. This preliminary action narrows down the verification scope to only relevant sensing elements, saving time compared to complete matrix scanning while maintaining accuracy
3Speed
If the projective sensing method is used, then the detection speed is improved, but the cost of implementing ghost cancellation is increased
Solution Approach 1:
The same sensing channels and signal paths used for fast projective sensing are reused for verification purposes. The control system performs multiple functions (initial detection and verification) using the same hardware infrastructure, avoiding the need for additional dedicated verification hardware and reducing overall system complexity
Solution Approach 2:
The sensing array itself is used to verify touch points by applying test signals through the existing row and column lines. The system serves its own verification needs using its existing sensing infrastructure, eliminating the need for separate verification hardware and reducing device complexity
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 and efficiently eliminates ghost points in multi-touch devices, balancing speed and cost by leveraging the rapid detection of the projective sensing method with the accuracy of the matrix sensing method.
Implementation Method 1
The sensing elements are usually implemented by resistors or capacitors, for example
Data Source
AI summary
A ghost cancellation method for the multi-touch sensitive device is disclosed. The multi-touch sensitive device includes a sensing array having multiple lines of a first axis and multiple lines of a second axis intersecting with each other. All the lines of the sensing array are scanned to determine which ones of the lines are touched, so as to determine touch point candidates. For each touch point candidate, a driving signal is applied to the line of the first axis, and the line of the second axis is detected to check if the touch point candidate is actually touched.