Differential Inductive Sensing with Shared LC-Resonator Capacitor
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Solution Overview
Problem
Inductive proximity sensors face limitations in switching accuracy due to temperature drift and component tolerances, especially when using resonant inductive sensing with LC tank circuits, where even small capacitor mismatches can result in significant distance errors.
Innovation Solution
The implementation of differential inductance readout based on sense/reference LC-ring oscillators with a shared resonator capacitor, where the Lsense and Lref resonators are time-multiplexed to operate with a common capacitor, enabling accurate inductance measurements by converting analog resonance measurements into digital signals using a Schmitt trigger, and suppressing parasitic capacitance effects through shorting or bootstrapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resonant inductive sensing with LC tank circuits is used, then sensing capability is achieved, but temperature drift and component tolerances cause switching accuracy limitations
Solution Approach 1:
The patent merges the sense resonator and reference resonator into a differential pair that shares a common capacitor. This combination allows the system to measure the difference between the two resonators, thereby canceling out common-mode temperature drift effects and improving switching accuracy despite temperature variations and component tolerances.
Solution Approach 2:
The patent implements a feedback mechanism where the differential output from the sense and reference resonators is continuously monitored and used to adjust the switching threshold. This feedback approach compensates for temperature drift by dynamically adapting to changing conditions, maintaining accurate switching detection across varying temperatures.
2Measurement precision
If resonant sensing with separate capacitors is used, then inductance measurement is achieved, but capacitor mismatch results in significant distance errors
Solution Approach 1:
The patent combines the sense and reference resonators to share a single common capacitor. This eliminates the capacitor mismatch problem entirely since both resonators use the exact same capacitor component, ensuring that manufacturing tolerances do not cause distance measurement errors. The differential measurement approach then focuses solely on detecting actual target proximity rather than capacitor variations.
3Device complexity
If time-multiplexed operation with shared capacitor is implemented, then component count is reduced, but parasitic capacitance effects increase
Solution Approach 1:
The patent extracts and separately manages parasitic capacitance effects by implementing switching mechanisms that isolate the shared capacitor from inactive resonator paths. During time-multiplexed operation, when one resonator is inactive, its path is opened or disconnected to prevent parasitic capacitance from affecting the active resonator's measurement, thereby maintaining measurement accuracy while still reducing overall component count.
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 enhances the accuracy and reliability of inductive sensing by eliminating the need for precisely matched resonator capacitors, reducing temperature drift, and minimizing noise, while maintaining low phase jitter and accurate differential inductance readouts.
Implementation Method 1
resonant sensing in which the inductive sensor is a resonator with a inductor coil and a series/parallel capacitor (LC tank circuit)... The IDC drives the sensor resonator to maintain a resonance state (sustained oscillation)
Implementation Method 2
converting analog resonance measurements from the resonators into digital resonator excitation signals
Implementation Method 3
Inductive sensors are used to detect/measure events/conditions based on changes in a sensing B-field... measuring changes in sensor resonator losses due to eddy current losses in the target
Data Source
Figure 1A~1B
Figure 2A~3
Figure 4
AI summary
For inductive sensing (such as for proximity switching), differential inductance readout (141) is based on Sense/Reference resonators implemented as LC-ring oscillators, with Ls/LR inductor coils and a shared (time-multiplexed) resonator capacitor Cc. The ring oscillators include matched Lsense/Lref drivers (124, 126) time-multiplexed (by out enable signals OEsense/OEref), to provide Lsense/Lref resonator excitation signals to the Lsense/Lref resonators (LS/LR, Cc), based on resulting Lsense/Lref resonance measurements (such as of resonance state) acquired by the ring oscillators from the Lsense/Lref resonators. Differential readout data is based on the time-multiplexed Lsense/Lref resonance measurements, corresponding respectively to LS/LR coil inductances (such as based on Lsense/Lref resonator oscillation frequency). The ring oscillators can be implemented with a Schmitt trigger (122), converting analog resonance measurements into digital input to the Lsense/Lref drivers. Driver matching and layout matching can be used to improve accuracy. Effects of parasitic capacitance at the driver outputs can be suppressed by shorting or bootstrapping across the inactive LS/LR coil inductances.