Respiratory Impedance Circuit EFT Interference Suppression
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Solution Overview
Problem
Existing methods for measuring respiratory waveforms with impedance methods face challenges in effectively suppressing electrical fast transient interference (EFT) due to high frequency and voltage characteristics of EFT signals, which interfere with respiratory detection circuits, requiring high amplification and precise impedance matching, but current solutions are limited in effectiveness and complexity.
Innovation Solution
A circuit with a peak detector circuit, comparator circuit, and electronic switch is used to detect EFT interference and disconnect the filter capacitor during interference persistence, protecting subsequent stages from interfering signals by switching the electronic switch based on signal comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amplitude of stimulating signal is increased to suppress EFT interference, then the signal-to-noise ratio is improved, but the power range of amplifier circuit and safe current via human body are exceeded
Solution Approach 1:
The patent applies periodic action by using a mechanical switch to periodically connect and disconnect the stimulating signal based on the detection of EFT interference. When EFT is detected, the switch disconnects the signal; when no EFT is present, the switch connects the signal. This periodic switching allows the system to operate at high amplitude when safe and suppress interference when needed, resolving the contradiction between maintaining high signal-to-noise ratio and staying within safe power limits
Solution Approach 2:
The patent implements feedback by using a detection circuit to monitor the presence of EFT interference and automatically control the mechanical switch to adjust the stimulating signal amplitude. The detection circuit provides feedback about interference conditions, which triggers the switch to adjust the signal level accordingly. This closed-loop feedback mechanism enables dynamic adjustment of signal amplitude to maintain optimal signal-to-noise ratio while preventing dangerous power levels
2Measurement precision
If the amplification factor of measurement circuit is increased to detect respiratory signal, then the detecting sensibility is improved, but the effect of slight interference at preceding stage is greatly amplified
Solution Approach 1:
The patent applies preliminary action by detecting EFT interference before it reaches the high-gain amplification stage and preemptively disconnecting the stimulating signal using a mechanical switch. This preliminary detection and interruption prevents the interference from being amplified along with the respiratory signal, allowing the measurement circuit to maintain high amplification factor for improved sensitivity without suffering from amplified interference
3Object-affected harmful factors
If low-pass filtering is used to eliminate EFT pulses from respiratory detection signal, then the interference is reduced, but high frequency interference pulses cannot be effectively eliminated due to their transient nature
Solution Approach 1:
The patent applies the taking out principle by physically extracting or removing the EFT interference from the signal path using a mechanical switch that disconnects the stimulating signal when EFT is detected. Instead of attempting to filter the interference while it passes through the circuit, the system extracts or removes the interfering signal component by opening the circuit switch, thereby eliminating the interference source rather than trying to separate it from the respiratory signal
4Object-affected harmful factors
If mechanical structure is adjusted to reduce distributed capacitance between power supply and floating circuit, then EFT coupling is reduced, but the power line distance from electro cardiac leads cannot be increased indefinitely
Solution Approach 1:
The patent introduces an intermediary element - a mechanical switch - that mediates between the power supply and the floating circuit. This switch acts as a controllable intermediary that can disconnect the circuit when EFT interference is detected, providing a more effective solution than merely adjusting the physical layout. The mechanical switch serves as an active intermediary that dynamically controls the connection based on interference conditions
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 effectively suppresses EFT interference by disconnecting the circuit during interference periods, ensuring accurate respiratory waveform detection and reducing the need for high amplification and precise impedance matching, thus enhancing the reliability of respiratory measurement circuits.
Implementation Method 1
a peak detector circuit, a comparator circuit and an electronic switch. The peak detector circuit is provided for receiving an interfering signal
Implementation Method 2
an output thereof and a reference signal are input to two input terminals of the comparator circuit; and an output terminal of the comparator circuit is connected to a control terminal of the electronic switch
Implementation Method 3
switching the electronic switch based on signal comparisons... disconnecting the circuit during interference periods
Implementation Method 4
disconnecting the filter capacitor in filter/demodulator circuit
Data Source
AI summary
A circuit for measuring respiratory waveform with impedance method and a method and device for resisting electrical fast transient interference are provided, and wherein an output from the peak detector circuit and a reference signal are input to two input terminals of the comparator circuit, an output terminal of the comparator circuit is connected to a control terminal of the electronic switch, and one terminal of the electronic switch is connected to an output terminal of the signal amplifier circuit and the other to an input terminal of the demodulator/amplifier circuit. If a level of the output signal of the peak detector circuit is greater than the level of the reference signal, the electronic switch is switched off in response to an inversion of the output of the comparator circuit so that the interference is isolated from the next stage circuit. The present invention is prone to be implemented with significant effect.