Capacitive Sensor Noise Mitigation Using Comb Filter Zero Alignment
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Solution Overview
Problem
Capacitive sensing devices face interference from noise signals, such as ambient and device-generated signals, which can lead to incorrect identification of input objects, necessitating effective noise mitigation techniques.
Innovation Solution
A processing system for capacitive sensing devices incorporates a sensor module with a receiver and filters to remove interference frequencies, utilizing a comb filter to align 'zeroes' with noise harmonics and preserve sensing signals, thereby reducing noise impact and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple filters are used to remove interference frequencies, then noise mitigation is improved, but device complexity increases
Solution Approach 1:
The filtering process is divided into multiple stages: a first filter removes interference at a first frequency, and a second filter removes interference at a second frequency. This segmented approach allows each filter to target specific noise components independently, improving overall noise mitigation while keeping individual filter designs relatively simple.
Solution Approach 2:
The filter module is designed to handle multiple types of interference frequencies using the same basic filtering architecture. By reusing the filter structure for different frequency targets, the design achieves multi-functionality without proportionally increasing complexity.
2Measurement precision
If filter zeroes are aligned with noise harmonics, then measurement precision is improved, but sensitivity to frequency variations worsens
Solution Approach 1:
The system adjusts filter parameters, specifically the positioning of zeroes in the frequency domain, to align with identified noise harmonics. This parameter optimization maximizes measurement precision by placing filter nulls at problematic frequencies while maintaining the ability to adapt to different operating conditions.
Data Source
AI summary
Disclosed herein are techniques for reducing certain types of noise in capacitive sensing devices. The techniques generally comprise utilizing a low-pass filter in conjunction with a comb filter to “zero out” frequency components associated with certain types of noise. More specifically, the comb filter is configured to zero out noise associated with the fundamental frequency and harmonics of noise that approximates a square wave or an impulse train. The frequency of the sensing signal for capacitive sensing is chosen such that the comb filter does not zero out such frequency.