Resonant Impedance Sensing Loop for Stable Oscillation Amplitude
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Resonant sensors face challenges in maintaining steady-state oscillation and accurately sensing changes in resonant impedance due to variations in conductive targets, which affects their ability to accurately measure position, proximity, or physical states.
Innovation Solution
A resonant impedance sensing system incorporating a class D negative impedance stage with a comparator and a control loop stage, utilizing an inductance-to-digital conversion circuit to synchronize drive current with resonator oscillation voltage, ensuring constant resonator oscillation amplitude by canceling resonant impedance through a negative impedance control loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resonant sensor is used to sense changes in resonant impedance, then sensing capability is improved, but maintaining steady-state oscillation becomes difficult due to impedance variations
Solution Approach 1:
The patent implements a feedback control system where the resonator output is fed back through a negative impedance converter (NIC) to compensate for impedance changes. The NIC generates a compensating signal that counteracts the impedance variations caused by conductive targets, thereby maintaining steady-state oscillation while preserving sensing capability. The feedback loop continuously adjusts the negative impedance to match the changing resonant impedance.
Solution Approach 2:
The patent dynamically changes the negative impedance parameter to compensate for resonant impedance variations. By adjusting the NIC output impedance based on the detected resonant impedance changes, the system maintains constant oscillation amplitude. This parameter adaptation allows the sensor to operate in steady-state despite varying load conditions from different conductive targets.
2Stability of the object's composition
If negative impedance control loop is implemented, then resonator oscillation amplitude stability is improved, but device complexity increases
Solution Approach 1:
The patent combines the resonator and negative impedance converter into an integrated circuit where the NIC is directly coupled to the resonator output. This merging eliminates the need for separate feedback components and reduces the overall circuit complexity. The integrated design allows the negative impedance control to be implemented with minimal additional components while maintaining oscillation amplitude stability.
Solution Approach 2:
The resonator itself serves as part of the control loop by providing the oscillation signal that is fed back through the NIC. The system uses its own output to generate the compensating signal, eliminating the need for external sensing elements or additional control circuits. This self-service approach reduces device complexity while achieving the desired amplitude stability.
3Use of energy by moving object
If class D comparator is used for synchronization, then power efficiency is improved, but measurement precision may be affected by quantization
Solution Approach 1:
The patent uses a class D comparator that operates in a switched mode, providing sufficient synchronization precision for the application without the continuous operation of linear comparators. The quantization effect is acceptable because the negative impedance control loop compensates for measurement errors, and the application requires adequate rather than absolute precision. This partial action approach achieves power efficiency while maintaining sufficient measurement accuracy.
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 maintains constant resonator oscillation amplitude, enhancing the accuracy and stability of resonant impedance sensing, allowing for precise detection of changes in resonant impedance caused by conductive targets, thereby improving position and proximity sensing capabilities.
Implementation Method 1
A resonant sensor includes a resonator configured for operation in a resonance state (resonant frequency and amplitude)
Implementation Method 2
The negative impedance circuitry is configured to generate a negative impedance signal, so that the negative impedance substantially cancels resonant impedance
Implementation Method 3
Resonance is affected by a storage or loss in projected magnetic flux energy output from the inductive sensing coil, such as caused by the eddy current effect associated with a conductive target
Implementation Method 4
The H-bridge circuitry is controlled by D_clk to synchronize the discrete drive current with the resonator oscillation voltage
Data Source
Figure 1
Figure 2
AI summary
In described examples, a resonant impedance sensing system (200) includes a negative impedance control loop incorporating the resonator (210) as a loop filter, and including a class D negative impedance stage (221) implemented with a class D comparator (232), and a loop control stage (223) implemented with an output comparator (244) clocked (D clk) by the class D comparator (232). The class D comparator (232) receives resonator oscillation voltage, and generates a class D switching output synchronized with resonator oscillation frequency. A discrete current source (such as a current DAC 233) drives the resonator (210) through an H-bridge (S1/S2) switched by the class D switching output, so that the time average of the discrete drive current corresponds to resonator oscillation amplitude (215 A). Based on resonator oscillation amplitude, the output comparator (244) provides a discrete loop control signal (229) to the discrete current source (233), driving the resonator (210) with a negative impedance that balances resonant impedance, thereby maintaining constant resonator oscillation amplitude corresponding to steady-state oscillation.