Closed-Loop Oscillator Sensor Interface With Split Feedback for EMI Stability
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Solution Overview
Problem
Existing closed-loop oscillator-based sensor interface circuits are vulnerable to electromagnetic interference (EMI) and suffer from instability when low-pass filters are added to combat EMI, leading to reduced robustness and increased noise.
Innovation Solution
The proposed sensor interface circuit splits the feedback path into two parts, with one part comprising a digital feedback signal converted into a first feedback signal and fed to the oscillation means, and the other part comprising a second feedback signal fed to the input nodes after passing through an analog filter, ensuring loop stability while reducing EMI interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an analog filter is added to combat EMI interference, then EMI robustness is improved, but loop stability deteriorates
Solution Approach 1:
The feedback path is segmented into two separate paths: a first feedback path that bypasses the analog filter to maintain loop stability, and a second feedback path that passes through the analog filter to reduce EMI interference. This segmentation allows each path to serve its specific function without compromising the other.
Solution Approach 2:
A selector mechanism acts as an intermediary to choose between different feedback sources. The selector can switch between the first feedback signal (from the stable path) and the second feedback signal (from the filtered path), or combine them, thereby mediating between the conflicting requirements of stability and EMI robustness.
2Object-generated harmful factors
If a low-pass filter is added between sensor and oscillators, then noise is reduced, but circuit stability deteriorates
Solution Approach 1:
The feedback system is divided into two independent paths: one path maintains the filtering function for noise reduction, while the other path provides the stability function by bypassing the filter. This segmentation resolves the contradiction between noise reduction and stability.
Solution Approach 2:
The system uses dual feedback paths where the first feedback path provides stability by bypassing the filter, while the second feedback path provides noise filtering. The combination of these feedback paths allows the system to achieve both noise reduction and stability simultaneously.
3Object-affected harmful factors
If feedback is applied after the analog filter, then EMI robustness is improved, but loop stability deteriorates
Solution Approach 1:
The feedback path is segmented into two separate paths: a first feedback path that bypasses the analog filter to maintain loop stability, and a second feedback path that passes through the analog filter to improve EMI robustness. This segmentation allows each path to serve its specific function without compromising the other.
Solution Approach 2:
A selector mechanism acts as an intermediary to choose between different feedback sources. The selector can switch between the first feedback signal (from the stable path) and the second feedback signal (from the filtered path), or combine them, thereby mediating between the conflicting requirements of stability and EMI robustness.
Data Source
Figure 1~2b
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Figure 6~7
AI summary
The present invention relates to an oscillator-based sensor interface circuit comprising - a first and a second input node arranged to receive a first and a second electrical signal representative of an electrical quantity, respectively, - an analog filter (170) arranged to filter at least the first electrical signal, - oscillation means (110,120) comprising at least a first oscillator arranged to receive a first oscillator input signal and a second oscillator different from the first oscillator and arranged to receive a second oscillator input signal, said first oscillator input signal being the filtered first electrical signal and said second oscillator input signal being the second electrical signal or a filtered version thereof, said first and second oscillator input signal impacting the oscillators' frequency, - comparator means (130) arranged to compare signals coming from the first and second oscillators and for outputting a digital comparator output signal in accordance with said comparing, - a first feedback element (180) arranged to receive a representation of the digital comparator output signal and to convert the representation into a first feedback signal to be applied to the oscillation means, either directly or combined with the first and/or second oscillator input signal, respectively, - a digital filter (142) arranged to yield an output signal, being an filtered version of the digital comparator output signal, - a second feedback element (150) arranged to receive the output signal and to convert the output signal into a second feedback signal, said second feedback signal to be combined with the electrical signal at the at least first and/or second input nodes, respectively.