Capacitive Key Detection Under Common-Mode Interference
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Solution Overview
Problem
Current touch sensing technologies face challenges in accurately detecting the operating state of capacitive touch keys due to common-mode interference, particularly when a mobile phone is connected to a charger, leading to unstable key detection and errors, which is difficult and costly to resolve using frequency hopping methods.
Innovation Solution
A key detecting method and apparatus that samples output signal values, calculates noise and signal variations, and determines the key's operating state by comparing these variations to predefined thresholds, eliminating the need for complex auxiliary circuits by using real-time sampling and peak-to-peak calculations to differentiate between key-pressed and key-released states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency hopping method is used to handle common-mode interference, then key detection accuracy is improved, but device complexity and cost increase due to complex circuits needed for fast and reliable frequency conversion
Solution Approach 1:
The patent changes the detection parameter from frequency domain (frequency hopping) to time domain (temporal pattern recognition). By monitoring the time sequence of sampling values and recognizing specific temporal patterns that indicate touch events, the system achieves accurate key detection without requiring complex frequency conversion circuits. This parameter transformation resolves the contradiction by maintaining detection accuracy while simplifying the hardware architecture.
2Reliability
If frequency hopping method is used to handle common-mode interference, then key detection reliability is improved, but manufacturing cost increases due to complex auxiliary circuits
Solution Approach 1:
The patent replaces the mechanical/electrical frequency hopping system with a software-based temporal pattern recognition system. Instead of physically switching frequencies using complex circuits, the system processes the existing signal in the time domain by analyzing sequences of sampling values. This substitution dramatically reduces manufacturing complexity and cost while maintaining reliable touch detection through intelligent signal processing.
3Device complexity
If conventional sampling method is used without noise separation, then device complexity is reduced, but measurement precision deteriorates due to inability to distinguish noise from signal under common-mode interference
Solution Approach 1:
The patent segments the sampling process into distinct phases: collecting multiple sampling values over time, identifying temporal patterns that represent genuine touch events versus random noise, and making detection decisions based on these patterns. This temporal segmentation allows the system to distinguish signal from noise without requiring complex noise separation circuits, resolving the contradiction between algorithmic simplicity and detection accuracy.
Data Source
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AI summary
A key detecting method and apparatus, which relate to touch sensing technologies, where the key detecting method includes: sampling an output signal value, and calculating a current noise value and a current signal value respectively according to the sampling result (S101); determining, according to the current noise value and the current signal value, whether a noise variation and a signal variation reach a corresponding noise variation threshold and signal variation threshold, respectively (SI02); and determining an operating state of a key according to the determination result (S103). With the above method and apparatus, there is no need to additionally provide a complex auxiliary circuit to realize detection of a state of the key, instead, a state of a smart terminal is determined by correspondingly sampling and calculating the signal value, thereby reducing the cost and meanwhile improving the accuracy of the detection of the state of the key, enabling user to obtain better user experience.