Inductive Sensing Circuit Using Fly-Back Sigma-Delta Conversion
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Solution Overview
Problem
Conventional inductive sensing systems face limitations in sensing resolution and flexibility due to dependencies on oscillator frequency, which is affected by PCB inductor self-resonance frequency and component tolerances, making them inflexible and unsuitable for multi-sensor scanning applications.
Innovation Solution
The proposed solution involves generating fly-back currents from sensed inductance to induce a voltage that can be sigma-delta modulated into a digital value, allowing for single-ended or pseudo-differential sensing configurations that are not limited by oscillator frequency and provide improved flexibility and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional oscillator-based inductive sensing is used, then the system can provide basic sensing functionality, but the sensing resolution is limited due to dependencies on oscillator frequency and component tolerances
Solution Approach 1:
The patent extracts the oscillator frequency dependency from the sensing system by using a voltage source that operates independently of any oscillator. The sensing is performed by measuring the fly-back current directly through a balance capacitor, eliminating the need for oscillator-based frequency measurement and its associated component tolerances.
Solution Approach 2:
The patent changes the fundamental sensing parameter from frequency-based measurement to voltage-based measurement. By measuring the voltage across a balance capacitor during a fixed time period and comparing it to a reference voltage, the system achieves higher resolution without being constrained by oscillator frequency stability or component tolerances.
2Adaptability or versatility
If oscillator-based sensing is implemented, then the system can operate with standard components, but the flexibility for multi-sensor scanning is reduced due to component tolerances and self-resonance frequency limitations
Solution Approach 1:
The patent creates a universal sensing architecture that can scan multiple sensors using a single voltage source and switching network. The system uses a multiplexer to selectively connect different sensors to the same measurement circuitry, eliminating the need for separate oscillator circuits for each sensor and enabling flexible multi-sensor scanning applications.
Solution Approach 2:
The patent uses a reference capacitor that is identical in structure and value to the balance capacitor, creating a reference measurement that compensates for variations in capacitor tolerances. This copying approach allows the system to achieve high accuracy despite using standard components with typical tolerances.
3Measurement precision
If fixed time-period voltage measurement is used, then the system achieves improved resolution independent of clock frequency, but requires precise timing control
Solution Approach 1:
The patent incorporates feedback logic that uses the measured voltage to control the switching timing and duration. The system adjusts the measurement parameters based on previous measurements to optimize the fixed time period, making the timing control more precise and easier to implement while maintaining independence from clock frequency variations.
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 inductive sensing systems to achieve higher sensitivity and resolution, independent of clock frequencies and supply voltages, thereby enhancing the flexibility and accuracy of inductive sensing, particularly in multi-sensor scanning applications.
Implementation Method 1
A sensor inductance can be energized by coupling the sensor inductance across a potential
Data Source
AI summary
A method can include in a first phase of a sensing operation, controlling at least a first switch to energize a sensor inductance; in a second phase of the sensing operation that follows the first phase, controlling at least a second switch to couple the sensor inductance to a first modulator capacitance to induce a first fly-back current from the sensor inductance, the first fly-back current generating a first modulator voltage at the first modulator capacitance, and in response to the first modulator voltage, controlling at least a third switch to generate a balance current that flows in an opposite direction to the fly-back current at the first modulator node. The first and second phases can be repeated to generate a first modulator voltage at the first modulator capacitance. the modulator voltage can be converted into a digital value representing the sensor inductance. Related devices and systems are also disclosed.