Physiological Signal Circuit With Pre-Amplification Noise Suppression
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Solution Overview
Problem
Existing physiological signal monitoring devices face challenges in effectively processing weak physiological signals, such as myoelectric signals, due to noise interference, which can lead to signal saturation and loss of the target signal during amplification.
Innovation Solution
A signal processing circuit comprising an analog circuit with a first processing circuit that enhances the signal-to-noise ratio through common mode signal suppression, low-pass filtering, and notch filtering, followed by a second processing circuit that amplifies the signal with a frequency-dependent gain, effectively isolating the target signal from noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the signal is amplified directly without preprocessing, then the amplification gain can be increased to enhance the weak physiological signal, but the noise signal is also amplified and may cause signal saturation and loss of the target signal
Solution Approach 1:
The signal processing circuit is divided into multiple functional modules: a first processing circuit for initial signal conditioning (including common mode rejection and filtering), and a second processing circuit for amplification. This segmentation allows each module to perform its specific function optimally without interfering with others, resolving the contradiction by structuring the complex circuit into manageable, functionally-separated units.
Solution Approach 2:
The first processing circuit performs preliminary signal conditioning before the main amplification stage. This includes common mode rejection to eliminate interference signals, low-pass filtering to remove high-frequency noise, and high-pass filtering to eliminate low-frequency drift. By performing these actions preliminarily, the signal is prepared for optimal amplification without noise saturation, resolving the contradiction between measurement precision and device complexity.
2Object-affected harmful factors
If a general signal processing circuit is used to remove noise, then the noise can be reduced, but the weak physiological signal may also be lost or distorted
Solution Approach 1:
The circuit employs frequency-selective filtering with different characteristics for different frequency ranges. The low-pass filter preserves frequencies below a certain threshold while attenuating higher frequencies, the high-pass filter preserves frequencies above a threshold while attenuating lower frequencies, and the notch filter specifically targets power frequency interference. This local quality approach ensures that noise removal is selective rather than blanket, preserving the physiological signal while removing specific noise components.
Solution Approach 2:
The filter cutoff frequencies and notch frequencies are specifically tuned to match the characteristics of physiological signals and common noise sources. By adjusting these parameters, the circuit optimizes the balance between noise rejection and signal preservation for specific application scenarios, resolving the contradiction between removing harmful factors and maintaining reliability.
3Power
If the amplification gain is increased to process weak signals, then the signal strength can be enhanced, but the processing margin is reduced and signal saturation occurs
Solution Approach 1:
The first processing circuit performs preliminary signal conditioning to remove noise and interference before the main amplification stage. This preliminary action increases the effective processing margin by eliminating noise components that would otherwise consume dynamic range, allowing the second processing circuit to amplify the signal with higher gain without causing saturation, thus resolving the contradiction between signal strength enhancement and processing margin preservation.
Data Source
AI summary
The embodiments of the present disclosure are for a signal processing circuit. The signal processing circuit includes an analog circuit. The analog circuit is used for processing an initial signal it receives. The initial signal includes a target signal and a noise signal. The analog circuit includes a first processing circuit and a second processing circuit. The first processing circuit is used to increase a ratio of the target signal to the noise signal, and output a first processed signal. The second processing circuit is used to amplify the first processed signal. A gain multiple of the second processing circuit to the first processed signal varies with a frequency of the first processed signal. The first processing circuit includes a common mode signal suppression circuit used to suppress a common mode signal in the initial signal, a low-pass filter circuit, and a high-pass filter circuit.