Capacitance Measurement with Variable-Cycle EMI Rejection

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Solution Overview

Problem

Existing capacitance measurement methods are susceptible to interference from electromagnetic waves, leading to reduced accuracy and reliability in capacitance determination and touch recognition.

Innovation Solution

The method involves alternating measurement cycles with different periods and transferring charge to a further capacitive element, determining capacitance based on the total charge transferred over multiple cycles, thereby reducing interference by detuning the sampling frequency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If charge transfer is performed repeatedly at a fixed frequency, then measurement speed and productivity are improved, but susceptibility to electromagnetic interference increases

Engineering Contradiction:

Improvemeasurement speedVSAvoidelectromagnetic interference susceptibility

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies dynamics by making the measurement frequency variable rather than fixed. The control unit dynamically adjusts the frequency of charge transfer operations based on detected interference conditions, allowing the system to adapt to changing electromagnetic environments while maintaining measurement functionality

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent utilizes periodic action by performing repeated charge transfer cycles at varying frequencies. By modulating the period of measurement cycles and using different duty cycles for charging and discharging phases, the system achieves interference rejection while maintaining productive measurement throughput

Inventive Principle:

Principle #19Periodic action

2Object-affected harmful factors

If analog low-pass filters are used to counter interference, then interference above Shannon frequency is reduced, but device complexity and loss of information increase

Engineering Contradiction:

Improvehigh-frequency interference reductionVSAvoidfiltering circuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical/analog filtering system with a digital signal processing approach. Instead of using analog low-pass filters that require physical components and circuitry, the system uses digital correlation methods and software-based frequency analysis to achieve interference rejection, thereby reducing hardware complexity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an intermediary computational process (cross-correlation analysis) between the raw measurement signal and the final capacitance determination. This intermediary step allows for selective frequency component analysis and interference identification without requiring physical filtering components

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If fixed-frequency measurement cycles are used, then measurement process simplicity is maintained, but accuracy under interference conditions deteriorates

Engineering Contradiction:

Improvemeasurement process simplicityVSAvoidcapacitance determination accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent changes the frequency parameter of measurement cycles dynamically based on detected interference conditions. By varying the measurement frequency away from interfering signals while maintaining the periodic measurement structure, the system preserves operational simplicity while improving measurement accuracy under interference

Inventive Principle:

Principle #35Parameter changes

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 significantly enhances capacitance measurement accuracy by minimizing the influence of external electromagnetic interference, ensuring reliable capacitance determination and touch recognition.

Implementation Method 1

the capacitive element is charged and an amount of charge is subsequently transferred from the capacitive element to a further capacitive element

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

an amount of charge is subsequently transferred from the capacitive element to a further capacitive element

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS12487261B2Interference-insensitive determination of a capacitance

Publication Date: 2025.12.02 VALEO SCHALTER & SENSOREN GMBH

AI summary

According to a method for determining the capacitance of a capacitive element (3), during each measurement cycle of a plurality of successive measurement cycles, the capacitive element (3) is charged, and then a charge quantity is transferred to a further capacitive element (5). After the plurality of measurement cycles, a measurement value relating to the total charge quantity transferred is determined, and the capacitance of the capacitive element (3) is determined as a function of the measurement value. A first duration is defined for a first subset of the plurality of measurement cycles, and a different second duration is defined for a second subset of the plurality of measurement cycles.