Monopolar Physiological Signal Detection Device Common-Mode Interference
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Solution Overview
Problem
Current heart rate monitoring devices using optical pulse sensors are affected by ambient light, posture, skin color, wrist size, and electromagnetic interference from supply mains, making it difficult to obtain precise and reliable heart rate data, especially in real-world settings where maintaining stillness is challenging.
Innovation Solution
A monopolar physiological signal detection device comprising a detection area, differential amplifier, delay circuit, driven-body circuit, and band-pass filter, which separates and suppresses common-mode interference, allowing for accurate heart rate measurement using a single electrode contact point, even in the presence of electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If optical pulse sensor module is used for heart rate monitoring, then the device can be made wearable and portable, but the measurement precision is severely degraded due to ambient light, posture, skin color, wrist size, and electromagnetic interference
Solution Approach 1:
The patent replaces the optical pulse sensor module with a monopolar electrocardiogram (ECG) detection system. Instead of using optical mechanisms that are sensitive to ambient light and physical contact conditions, the invention uses electrical signal detection through a single electrode, fundamentally substituting the sensing mechanism to achieve better performance in wearable applications.
Solution Approach 2:
The invention extracts and eliminates the common-mode interference signals (50Hz/60Hz electromagnetic interference) from the detected physiological signals using a differential amplifier configuration. By separating the useful heart rate signal from the harmful interference, the system achieves accurate measurements despite the presence of electromagnetic fields from power supplies.
2Measurement precision
If user maintains stillness during measurement, then the measurement precision improves, but the ease of operation deteriorates because it limits real-world application
Solution Approach 1:
The patent substitutes the optical sensing system with an electrical sensing system that is inherently less sensitive to motion artifacts. The monopolar ECG detection with differential amplification and common-mode rejection can accurately capture heart rate signals even when the user is moving or in various postures, eliminating the need for stillness requirements.
3Measurement precision
If two contact sites are required for accurate measurement, then the measurement precision improves, but the device complexity and ease of operation worsen due to requiring user to touch additional sites
Solution Approach 1:
The invention segments the body into two parts: a single active electrode placed on the chest and a reference electrode placed on a limb. This segmentation allows the system to measure heart rate signals unilaterally without requiring the user to actively touch additional contact sites, simplifying the user interface while maintaining measurement accuracy through the differential amplification of the two electrode signals.
4Ease of operation
If electromagnetic interference from supply mains is present, then the ease of operation improves (no shielding needed), but the measurement precision deteriorates due to common-mode interference
Solution Approach 1:
The patent uses a differential amplifier with high common-mode rejection ratio to extract the useful heart rate signal from the mixed signal containing 50Hz/60Hz electromagnetic interference. The differential amplifier rejects the common-mode interference components while amplifying the differential heart rate signal, allowing accurate measurements even in environments with power supply electromagnetic fields without requiring electromagnetic shielding.
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
Enables precise and reliable heart rate monitoring without the need for stillness or additional contact points, effectively filtering out common-mode interference to provide accurate heart rate data in various environments.
Implementation Method 1
a differential amplifier (301), a delay circuit (302), a driven-body circuit (303), a band-pass filter (304), and an output (400)... The differential amplifier accordingly amplifies the electrical heartbeat signal, the delayed electrical heartbeat signal, the common-mode interference signal, and the suppressed common-mode interference signal
Implementation Method 2
a time delay is generated by the delay circuit and introduced the time delay into the electrical heartbeat signal to form a delayed electrical heartbeat signal
Implementation Method 3
the differential amplifier accordingly amplifies the electrical heartbeat signal, the delayed electrical heartbeat signal, the common-mode interference signal, and the suppressed common-mode interference signal and then transmits them to the band-pass filter to obtain a resulted heartbeat signal
Implementation Method 4
The detection area is configured to be in contact with a detectable site... A detection area on the monopolar physiological signal detection device subsequently obtains an electrical heartbeat signal and a common-mode interference signal from a detectable site
Data Source
AI summary
A monopolar physiological signal detection device and a method of operating the monopolar physiological signal detection device are provided. With a differential amplifier, a delay circuit, a driven-body circuit, and a band-pass filter, the monopolar physiological signal detection device can reduce the common-mode interference induced by supply mains. Moreover, the monopolar physiological signal detection device employs a single electrode to generate electric potentials with different time factors from the same skin surface. Accordingly, consecutive heartbeat related information of a user can be collected even when the user is under natural and comfortable postures.