Multi-Touch Sensor System Using Self and Mutual Capacitance
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately detecting multiple simultaneous touches due to ambiguity in self-capacitance measurements and increased response time in mutual capacitance measurements, which affects the system's response to touch actions.
Innovation Solution
A multi-touch sensor system that performs initial self-capacitance measurements on each electrode and then conducts mutual capacitance measurements only on the nodes corresponding to the touched electrodes or their adjacent nodes, reducing the total number of measurements required to determine touch positions, thereby improving response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If self-capacitance measurements are performed on all electrodes, then system response time is fast, but multi-touch position accuracy deteriorates due to ambiguity
Solution Approach 1:
The patent segments the measurement process into two phases: first performing self-capacitance measurements on all electrodes to quickly identify potentially touched electrodes, then performing mutual capacitance measurements only on specific nodes formed by these electrodes. This segmentation resolves the contradiction by dividing the measurement task to achieve both speed and accuracy.
Solution Approach 2:
The patent applies partial action by performing mutual capacitance measurements only on a subset of nodes rather than all possible electrode pairs. Specifically, it measures nodes involving potentially touched electrodes from self-capacitance measurements, which is fewer than exhaustive mutual capacitance measurements but sufficient to resolve position ambiguity.
2Measurement precision
If mutual capacitance measurements are performed on all nodes, then multi-touch position accuracy is improved, but system response time deteriorates
Solution Approach 1:
The patent performs preliminary self-capacitance measurements on all electrodes before performing mutual capacitance measurements. This preliminary action identifies which electrodes are potentially touched, allowing the system to skip unnecessary mutual capacitance measurements on nodes that would not provide useful information, thus improving response time while maintaining accuracy.
Solution Approach 2:
The patent performs mutual capacitance measurements only on a partial set of nodes - specifically those involving electrodes that showed capacitance changes in self-capacitance measurements - rather than performing exhaustive measurements on all possible electrode pairs. This partial measurement approach maintains position accuracy while reducing measurement time.
3Productivity
If self-capacitance measurements are used, then measurement speed is fast, but multi-touch detection capability deteriorates due to inability to disambiguate positions
Solution Approach 1:
The patent segments the detection capability into two complementary measurement types: self-capacitance for fast initial detection of touched electrodes, and mutual capacitance for accurate determination of touch positions. This segmentation enables the system to maintain high measurement speed while achieving full multi-touch detection capability.
Solution Approach 2:
The patent merges self-capacitance and mutual capacitance measurement approaches into a unified multi-touch detection system. The self-capacitance measurements identify which electrodes are touched, and the mutual capacitance measurements resolve the positions, combining both methods to achieve both speed and multi-touch capability.
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 enhances the system's ability to accurately detect multiple simultaneous touches while reducing measurement time, resulting in faster response times compared to full mutual capacitance systems.
Implementation Method 1
The capacitive touch sensors are activated (controls a signal indicating activation) by a change in capacitance of the capacitive touch sensor when an object, e.g., a user's finger tip, causes the capacitance thereof to change.
Implementation Method 2
In the X-Y grid touch sensor, for example, mutual capacitance may refer to the capacitive coupling between an X-axis and Y-axis electrode. One set of electrodes on the touch screen may serve as receivers and the electrodes in the other set may serve as transmitters.
Data Source
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AI summary
Systems and methods for determining multiple touch events in a multi-touch sensor system are provided. The system may have a touch sensor including nodes defined by a plurality of electrodes, which may comprise a first and second set. The method may include measuring self capacitance for at least two electrodes, detecting a touched electrode, and measuring the mutual capacitance for only a subset of the nodes (e.g., fewer than all of the nodes and including at least the nodes corresponding to the touched electrodes) resulting in the detection of two or more touched nodes. The self capacitance measurements may be performed on each of the electrodes, and the touched electrodes may comprise electrodes from both the first and second sets. Alternatively, the self capacitance measurements may be performed only on electrodes in the first set, and the touched electrodes may comprise electrodes from only the first set.