Inductive Sensing PLL Circuit With Fixed-Frequency Control
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Solution Overview
Problem
Conventional inductive sensing technologies face challenges in detecting different types of objects using a single device due to the need for different sense elements and circuits, which is not feasible in terms of cost or space, especially in small form factor devices, and suffer from limitations such as temperature drift, sensitivity issues, and the requirement for additional components like reference coils.
Innovation Solution
The implementation of an inductance-sensing circuit with a digital control loop that maintains a fixed frequency, allowing the resonant circuit to operate at a constant frequency regardless of object proximity, using an inductance detection method that measures changes in the frequency of an LC tank, and eliminating the need for a reference sensor electrode, thus improving sensitivity and reducing component requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional inductive sensing technologies use different sense elements and circuits for different objects, then detection capability for various objects is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a universal inductive sensing circuit that can detect multiple types of objects (ferrous metals, non-ferrous metals, and non-metallic objects) using a single sense element and circuit configuration. The system achieves multi-functionality by processing different response characteristics from the same hardware, eliminating the need for separate sense elements for different object types.
Solution Approach 2:
The patent changes the operating parameters of the resonant circuit, specifically maintaining a fixed frequency operation mode and measuring amplitude/phase changes rather than frequency changes. This parameter change allows the single circuit to differentiate between various object types based on their unique electromagnetic responses at the fixed frequency.
2Measurement precision
If conventional inductive sensing uses reference coils and additional components, then measurement accuracy is improved, but form factor increases
Solution Approach 1:
The patent extracts and eliminates the reference coil component from the traditional inductive sensing system. Instead of using a separate reference coil for comparison, the system uses the same sense element operating at a fixed frequency, measuring amplitude and phase changes directly. This extraction reduces component count and form factor while maintaining measurement capability.
Solution Approach 2:
The sense element serves multiple functions: it acts as both the sensing element and the reference element simultaneously. By operating the resonant circuit at a fixed frequency and measuring the response characteristics, the system achieves self-comparison capability without requiring separate reference components, thereby reducing form factor.
3Device complexity
If conventional inductive sensing operates without fixed frequency control, then circuit simplicity is maintained, but temperature drift increases
Solution Approach 1:
The patent implements a feedback control mechanism that maintains the resonant circuit at a fixed operating frequency. The system continuously monitors the resonant frequency and adjusts the circuit parameters to compensate for temperature-induced frequency shifts. This feedback control stabilizes the operating point, reducing temperature drift while maintaining reasonable circuit complexity.
4Device complexity
If inductive sensing measures frequency changes, then detection method is simplified, but sensitivity decreases
Solution Approach 1:
The patent changes the measurement parameter from frequency detection to amplitude and phase detection at a fixed frequency. By operating the resonant circuit at a predetermined fixed frequency and measuring the amplitude and phase of the response signal, the system achieves higher sensitivity because these parameters exhibit larger changes in response to object proximity than frequency alone.
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 enables high dynamic range inductance sensing with improved electromagnetic compliance, reduced temperature drift, and a smaller form factor, while maintaining sensitivity and accuracy without the need for additional components, making it suitable for various electronic devices.
Implementation Method 1
measuring changes in the frequency of an LC tank
Implementation Method 2
inductive sensing circuitry may detect the presence and location of an object
Data Source
AI summary
One inductive sensor is configured to maintain a fixed frequency in a resonant circuit. One apparatus includes an inductance-to-digital converter (LDC). The LDC includes a digital filter to measure an inductance change of a sensor and convert the inductance change to a digital value. The LDC further includes a digital control loop to maintain a fixed frequency in the sensor. The sensor forms an oscillator in the digital control loop. An output of the digital control loop is representative of the inductance change of the sensor.