Capacitive Touch Matrix Layout for Two-Touch Ghosting Suppression
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Solution Overview
Problem
Capacitive touch input devices face the challenge of 'ghosting' when attempting to distinguish between two diagonally opposed touches in a capacitive touch matrix, as existing row and column scanning methods cannot differentiate between equally likely solutions, particularly in less expensive devices without advanced hardware and processing power.
Innovation Solution
The implementation of additional electrodes positioned at opposite corners and point symmetrical to the center of the capacitive sensor matrix, coupled to the measuring circuitry, allows for the correct determination of multi-touch positions by measuring capacitance differences between these electrodes and the capacitive sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If row and column scanning is used to detect multi-touch, then the device can detect multiple touches, but ghosting occurs where diagonally opposed touches cannot be distinguished
Solution Approach 1:
The patent introduces additional measurement dimensions by adding corner electrodes beyond the standard row and column scanning. These electrodes provide extra capacitance measurement points that create additional equations, allowing the system to resolve the ambiguity of ghosting by measuring capacitance from multiple angular perspectives around the touch matrix.
Solution Approach 2:
Corner electrodes are introduced as intermediary sensing elements that mediate between the row/column scanning system and the ghosting problem. These electrodes act as additional observers that provide independent capacitance measurements, enabling the system to distinguish between true and false touch positions through comparative analysis.
2Measurement precision
If advanced hardware and processing power are used to eliminate ghosting, then ghosting can be eliminated, but device cost increases
Solution Approach 1:
The sensing system is segmented into multiple independent measurement channels: standard row lines, column lines, and corner electrodes. Each segment provides independent capacitance measurements that can be processed through simple comparative logic rather than requiring complex algorithms, thus eliminating ghosting without increasing processing power requirements.
Solution Approach 2:
The corner electrodes create additional copies of the capacitance measurement function at strategic positions around the matrix perimeter. These copied sensing points provide redundant information that simplifies the detection logic, allowing the system to identify true touches through pattern matching rather than complex computation.
3Adaptability or versatility
If more sensors are added to detect two-finger touches, then input options increase, but device cost and complexity increase
Solution Approach 1:
The corner electrodes serve multiple functions: they detect touches at the corners, provide additional measurement points for resolving ghosting, and contribute to overall touch pattern recognition. This multi-functionality allows the system to maintain enhanced input capabilities without proportionally increasing the total sensor count.
Solution Approach 2:
The corner electrodes are merged with the existing row and column scanning infrastructure, sharing the same capacitance measurement circuitry and processing logic. This integration allows the system to achieve enhanced multi-touch capability while reusing existing hardware resources, thereby avoiding proportional increases in 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
This configuration effectively eliminates ghosting by accurately discerning between true and false multi-touch inputs, enabling reliable detection of two-finger touches and increasing input options without the need for costly or high-processing devices.
Implementation Method 1
A capacitive touch pad includes a plurality of capacitive sensors arranged in a matrix on a substrate. A measuring circuitry measures the capacitance of each of a plurality of row lines and a plurality of column lines in the matrix coupled to the capacitive sensors.
Implementation Method 2
A first electrode is on the substrate on a first edge of the matrix and is proximal to a first corner of the matrix. The first electrode is coupled to the measuring circuitry. A second electrode is on the substrate on the first edge of the matrix and is proximal to a second corner of the matrix, the second corner opposing the first corner on the first edge. The second electrode is coupled to the measuring circuitry.
Data Source
AI summary
An apparatus includes a plurality of capacitive sensors arranged in a matrix on a substrate. A measuring circuitry measures the capacitance of each of a plurality of row lines and a plurality of column lines in the matrix coupled to the capacitive sensors. A first electrode is on the substrate on a first edge of the matrix and is proximal to a first corner of the matrix. The first electrode is coupled to the measuring circuitry. A second electrode is on the substrate on the first edge of the matrix and is proximal to a second corner of the matrix, the second corner opposing the first corner on the first edge. The second electrode is coupled to the measuring circuitry. The measuring circuitry determines the positions of two touches to the touch pad. Methods are disclosed.