Split-Feedback Oscillator Sensor Interface for EMI-Stable Readout
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Solution Overview
Problem
Existing sensor interface circuits are vulnerable to electromagnetic interference (EMI) and suffer from instability when low-pass filters are added to combat EMI, which affects noise reduction and overall system stability.
Innovation Solution
A closed-loop oscillator-based sensor interface circuit design that splits the feedback path into two parts, with one part converting the digital comparator output into a feedback signal for the oscillation means and the other part feeding a filtered signal back to the input nodes through an analog low-pass filter, ensuring loop stability and robustness against EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an analog low-pass filter is added to reduce EMI, then noise reduction and EMI robustness are improved, but loop stability deteriorates
Solution Approach 1:
The feedback path is segmented into two separate paths: one path feeds the digital comparator output directly to the oscillation means without analog filtering, while the other path applies analog low-pass filtering before feedback. This segmentation allows the system to benefit from EMI filtering in one path while maintaining loop stability through the unfiltered path.
Solution Approach 2:
The digital comparator output serves as an intermediary signal that is distributed to two different feedback paths. This intermediary signal allows the system to selectively apply filtering only where beneficial while maintaining the stability-critical feedback path unfiltered.
2Measurement precision
If analog filtering is applied to the oscillator input signal, then noise reduction is improved, but the accuracy of the physical quantity measurement deteriorates due to delayed feedback
Solution Approach 1:
The feedback signal is segmented into two components: one that has been analog filtered for noise reduction and another that remains unfiltered to provide accurate, timely feedback for maintaining oscillation frequency accuracy. Both components are combined to achieve both noise reduction and measurement accuracy.
3Device complexity
If a conventional single feedback path is used, then device complexity is reduced, but the ability to simultaneously achieve noise reduction and loop stability deteriorates
Solution Approach 1:
The single feedback path is segmented into two parallel paths with different filtering characteristics. This segmentation increases structural complexity but enables the system to simultaneously achieve noise reduction through the filtered path and loop stability through the unfiltered path.
Solution Approach 2:
The dual feedback path structure serves multiple functions: one path handles noise filtering while the other maintains stability, allowing the system to achieve both objectives simultaneously that would be impossible with a single-purpose feedback path.
Data Source
AI summary
An oscillator-based sensor interface circuit includes first and second input nodes arranged to receive first and second electrical signals representative of an electrical quantity, respectively; an analog filter; 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; a comparator arranged to compare signals coming from the first and second oscillators; a first feedback element 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; a digital filter arranged to yield an output signal, being an filtered version of the digital comparator output signal; a second feedback element arranged to receive the output signal and to convert the output signal into a second feedback signal.