Digital PLL Inductive Sensing for Stable Metal Detection

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Solution Overview

Problem

Existing inductive sensing technologies face challenges in efficiently detecting both ferrous and non-ferrous metals due to sensitivity limitations, temperature drift, and the need for multiple sense elements and circuits, which are not feasible in devices with small form factors.

Innovation Solution

Implementing a digital control loop in inductance-sensing circuitry to maintain a fixed frequency in the resonant circuit, using an inductance-to-digital converter (LDC) and a digital feedback loop to improve sensitivity and reduce temperature drift, allowing detection of both ferrous and non-ferrous metals without additional components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional inductive sensing circuits are used to detect both ferrous and non-ferrous metals, then detection capability is achieved, but sensitivity is limited and temperature drift occurs

Engineering Contradiction:

ImprovesensitivityVSAvoidtemperature drift

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the operating parameters by using a digital phase-locked loop to maintain a fixed resonant frequency, allowing the circuit to compensate for temperature-induced frequency shifts. This enables stable sensing across temperature variations while maintaining high sensitivity through digital control mechanisms.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a feedback mechanism where the resonant frequency is continuously monitored and adjusted via a digital control loop. This feedback system compensates for temperature drift by dynamically tuning the resonant circuit to maintain optimal operating conditions, thereby improving both sensitivity and temperature stability.

Inventive Principle:

Principle #23Feedback

2Adaptability or versatility

If multiple sense elements and circuits are used to detect different metal types, then detection versatility is improved, but device complexity increases

Engineering Contradiction:

Improvedetection capabilityVSAvoidcircuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent makes a single inductive sensing circuit universal by enabling it to detect both ferrous and non-ferrous metals through digital signal processing and frequency modulation techniques. The same hardware circuit adapts its detection mode based on the target material, eliminating the need for separate dedicated circuits for different metal types.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent replaces complex hardware differentiation (multiple physical sense elements) with software/digital processing methods. By using a programmable digital signal processor to analyze resonant frequency responses, the system can distinguish between different metal types without requiring physically separate sensing circuits for each metal category.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If additional sensing components are added to improve detection performance, then sensing accuracy is improved, but form factor increases

Engineering Contradiction:

Improvedetection accuracyVSAvoidform factor

Core Design Contradiction:

Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent merges multiple functions into a single integrated circuit by combining the resonant sensing element, frequency modulation circuitry, and digital signal processing capabilities into one compact unit. This integration achieves high detection accuracy without requiring separate discrete components, thereby maintaining a small form factor suitable for portable devices.

Inventive Principle:

Principle #5Merging (Combining)

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

The solution provides high dynamic range inductance sensing with improved electromagnetic compliance, reduced sensitivity to thermal drift, and a smaller form factor, enabling efficient detection of various metals in devices with limited space.

Implementation Method 1

maintain a fixed frequency in the resonant circuit

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 2

inductive sensing circuitry to detect the presence and location of an object

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS12425026B2High performance inductive sensing all digital phase locked loop

Publication Date: 2025.09.23 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

Front-end circuits that combine inductive and capacitive sensing are described. In one embodiment, an apparatus includes a plurality of inductive elements, an inductive measurement circuit, and a frequency divider circuit. The inductive measurement circuit is to output a first signal with a first frequency. The first signal is associated with an inductance change of one of the inductive elements. A feedback circuit can maintain the sinusoidal operation of the first signal. The frequency divider circuit can generate a second signal with a second frequency that is lower than the first frequency.