Variable Profile Common Mode Filter for Touch Sensing
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Solution Overview
Problem
Touch-sensing devices experience noise interference due to direct coupled noise when a touch object completes a circuit connection with external noise sources, such as charging devices, which affects the accuracy of capacitance measurements and contact detection.
Innovation Solution
A method and apparatus that estimate and subtract direct coupled noise from capacitance values using noise estimation techniques, allowing for the removal of noise interference and improving contact detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a touch object completes a circuit connection with external noise sources, then the touch-sensing device can detect contact, but direct coupled noise interferes with capacitance measurement accuracy
Solution Approach 1:
The patent segments the capacitance measurement into two components: the total measured capacitance and the estimated direct-coupled noise capacitance. By separating these components and subtracting the noise estimate from the total measurement, the system isolates the true touch signal from noise interference, thereby maintaining both contact detection reliability and measurement precision
Solution Approach 2:
The patent introduces an intermediary noise estimation process that measures the direct-coupled noise component separately through dedicated noise estimation circuits. This intermediary measurement acts as a mediator between the noisy touch signal and the final processed output, allowing the system to compensate for noise effects without losing the ability to detect actual contacts
2Measurement precision
If noise estimation and subtraction techniques are applied, then capacitance measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary noise estimation before the final capacitance measurement and processing stages. By pre-characterizing the direct-coupled noise properties and storing noise profiles in memory, the system prepares noise compensation data in advance, reducing the computational burden during real-time operation and simplifying the overall device architecture
Solution Approach 2:
The patent creates a copy or model of the noise characteristics through noise estimation circuits that replicate the noise behavior. This noise model is stored in memory and used for compensation during touch detection, allowing the system to handle complex noise patterns without requiring equally complex real-time processing circuitry
Data Source
AI summary
A method and apparatus to remove direct coupled noise caused by a contact between a touch object and a capacitive sense array.