Capacitive Touch Sensing Circuit for Accurate Multi-Touch Detection
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Solution Overview
Problem
Existing capacitive sensing technologies in user interfaces, such as touch screens and pads, cannot resolve multiple presses or simultaneous touches, limiting their ability to accurately detect multiple input points on a touch panel.
Innovation Solution
The implementation of a capacitive sensing apparatus with interpolating circuitry, multiplexing circuitry, and a pseudo random signal generator to detect changes in capacitance across capacitors, allowing for the identification of multiple touch points by selectively charging electrodes and using a demodulator to filter and convert signals, enabling multi-touch sensing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitive sensing circuits are used to detect touch positions, then single touch detection is achieved, but multiple simultaneous touches cannot be resolved
Solution Approach 1:
The touch sensing array is segmented into multiple independently controllable capacitor groups, allowing individual addressing and measurement of each capacitor. This segmentation enables the system to distinguish between multiple simultaneous touch points by measuring capacitance changes in different capacitor groups separately, thereby resolving the limitation of traditional circuits that could only detect single touches.
Solution Approach 2:
The patent employs periodic charging and discharging cycles of capacitors through multiplexing circuitry, where capacitors are charged in sequential time divisions. By periodically switching between different capacitor groups and measuring their capacitance changes at different time intervals, the system can resolve multiple simultaneous touches that occur at different positions on the touch panel.
2Adaptability or versatility
If all electrodes are charged simultaneously to detect multiple touch points, then multi-touch capability is improved, but power consumption increases
Solution Approach 1:
Instead of charging all electrodes simultaneously, the patent uses periodic action by charging capacitor groups in sequential time divisions through multiplexing circuitry. Only one capacitor group is charged at any given time, and the system measures capacitance changes before moving to the next group. This approach maintains multi-touch detection capability while significantly reducing power consumption compared to simultaneous charging of all electrodes.
Solution Approach 2:
The system dynamically switches between different capacitor groups using multiplexing circuitry, activating only the necessary capacitor group for measurement at any given moment. This dynamic approach allows the system to maintain multi-touch capability by sequentially measuring different regions of the touch panel, while minimizing power consumption by keeping most capacitors in a low-power state rather than charging all electrodes continuously.
3Device complexity
If standard signal generation is used, then circuit simplicity is maintained, but interference from neighboring devices increases
Solution Approach 1:
The patent changes the signal generation parameter by using pseudo-random binary sequences (PRBS) instead of standard sinusoidal or square wave signals. This parameter change in signal type provides spectral spreading and unique identification codes for different capacitor groups, which reduces electromagnetic interference from neighboring devices while maintaining circuit implementation feasibility through digital logic circuits that generate PRBS signals.
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
Enables accurate detection of multiple simultaneous touches, improves accuracy over previous sensing methods, reduces power consumption by charging only one set of electrodes, and minimizes interference from neighboring devices through the use of a pseudo random signal generator.
Implementation Method 1
sensing circuitry configured to detect changes in capacitance across the capacitors responsive to movement of an input object relative to the apparatus
Implementation Method 2
The pseudo random signal generator provides a reference signal to a demodulator that is connected to the second electrodes. The demodulator demodulates a signal corresponding to the second electrodes according to the reference frequency generated by the pseudo random signal generator.
Data Source
AI summary
In one embodiment, an apparatus comprises a plurality of capacitors, each having a first electrode and a second electrode. The apparatus includes charging circuitry coupled to the first electrodes and sensing circuitry coupled to the second electrodes, the sensing circuitry configured to detect changes in capacitance across the capacitors responsive to movement of an input object relative to the apparatus. Interpolating circuitry identifies which one of the capacitors is nearest to the input object according to the detected capacitance changes.