Mutual Capacitance Frequency Switching for Charger Noise Rejection

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Solution Overview

Problem

Capacitance sensing systems face challenges in accurately distinguishing touch events from noise, particularly due to external noise sources like chargers and environmental electrical fields, which can lead to erroneous touch detections or missed touches.

Innovation Solution

The implementation of a noise listening circuit that dynamically adjusts filtering based on detected noise levels, using techniques such as median filtering and frequency hopping to differentiate between common mode and localized noise, thereby enhancing the system's ability to filter out external noise and improve touch event detection accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional capacitance sensing is used without advanced noise filtering, then the system structure remains simple, but noise from external sources like chargers causes erroneous touch detections

Engineering Contradiction:

Improvetouch detection accuracyVSAvoidnoise filtering system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system dynamically switches between two frequency sets (first and second frequency sets) based on detected noise levels. When noise is detected, the system transitions to the second frequency set which operates at frequencies less susceptible to the detected noise, thereby adaptively maintaining reliable touch detection without requiring permanently complex filtering hardware

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the operating frequency parameter of the capacitance sensing system. By switching between different frequency sets, the system alters its operational characteristics to avoid noise interference, resolving the contradiction between maintaining simple structure and achieving reliable detection in noisy environments

Inventive Principle:

Principle #35Parameter changes

2Reliability

If frequency hopping is implemented to switch between multiple operating frequencies, then noise filtering effectiveness improves, but system complexity and processing requirements increase

Engineering Contradiction:

Improvenoise rejection capabilityVSAvoidfrequency management complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The frequency spectrum is segmented into two distinct frequency sets. The first frequency set operates at higher frequencies while the second frequency set operates at lower frequencies. This segmentation allows the system to divide and conquer different noise scenarios by selecting the appropriate frequency set, improving noise rejection without requiring management of a large number of frequencies

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system implements partial frequency hopping by maintaining only two frequency sets rather than continuously sweeping through many frequencies. This partial action approach provides sufficient noise rejection capability for charger noise and environmental interference while keeping the frequency management complexity manageable

Inventive Principle:

Principle #16Partial or excessive action

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 effectively reduces noise interference, leading to more reliable touch event detection and reduced false positives or negatives, even in environments with significant external noise sources.

Implementation Method 1

A voltage source VTX can be a transmit signal generated on a TX electrode... Cm can be a mutual capacitance between a TX electrode and a receive (RX) electrode

Methodology Applied

Scientific EffectMutual capacitance coupling: Capacitance

Implementation Method 2

A noise listening circuit can be provided that can listen for the presence of noise on a channel

Methodology Applied

Scientific EffectElectrical field detection: Electric Field

Data Source

PatentUS9209802B1Frequency selection with two frequency sets of multiple operating frequencies in a mutual capacitance sensing devices

Publication Date: 2015.12.08 PARADE TECHNOLOGIES LTD

AI summary

Apparatuses and methods of frequency selection algorithms and frequency set selection are described. One method monitors a signal on the electrodes of a sense network, determine a first group of noise metrics of noise in the signal, determine a second group of noise metrics. The method switches from a first operating frequency in a first set to a second operating frequency in the first frequency set based on the first group of noise metrics and switches from the first operating frequency in the first set to a third operating frequency in a second frequency set based on the second group of noise metrics.