CN112869749A - Non-contact electrocardio detection circuit - Google Patents
Non-contact electrocardio detection circuit Download PDFInfo
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- CN112869749A CN112869749A CN202110055486.9A CN202110055486A CN112869749A CN 112869749 A CN112869749 A CN 112869749A CN 202110055486 A CN202110055486 A CN 202110055486A CN 112869749 A CN112869749 A CN 112869749A
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Abstract
The invention provides a non-contact electrocardio detection circuit, which adopts a differential input mode and consists of two sets of same circuits, wherein any one set of circuits consists of a resistance-capacitance coupling circuit, a voltage follower, a bootstrap circuit and a virtual earth circuit. The invention greatly improves the input resistance of the detection circuit in a bootstrap mode, improves the resistance value of the input resistance to controllable multiple of the actual resistance value, avoids the bootstrap circuit from enabling the whole circuit to enter a self-oscillation state by utilizing resistance voltage division, solves the problem that ultrahigh input impedance is needed in a non-contact electrocardio detection circuit, and realizes non-contact electrocardio detection.
Description
Technical Field
The invention relates to the technical field of medical signal detection, in particular to a non-contact electrocardiogram monitoring method.
Background
The main reasons for traffic accidents are the bad physical and mental states of drivers such as drunk driving, fatigue driving, emotional abnormality, sudden diseases and the like; the aerospace medicine guarantee technology becomes an important foundation for promoting the development of manned aerospace engineering, and a new technology and new equipment for monitoring the health condition of astronauts become problems to be solved urgently; daily electrocardiographic monitoring of heart disease patients is more indispensable. The electrocardio is the most important index for judging the physical and mental states, is an important basis for clinical diagnosis and disease condition evaluation, and can reflect the physical and mental states of a person through long-term real-time electrocardio monitoring. Therefore, it is very necessary to perform electrocardiographic monitoring on the above-mentioned personnel. However, drivers, astronauts and patients with heart disease require continuous electrocardiographic monitoring for a long time and certain freedom of movement, so that a non-contact non-inductive measurement is more preferred in electrocardiographic monitoring.
Conventional wet electrodes require the use of hydrogels to increase the conductivity of the signal path between the skin and the electrode, are prone to skin irritation, and are not suitable for long-term use. Dry electrodes, like wet electrodes, also require direct electrical contact with the skin, and furthermore, dry electrodes without a conductive gel are much more sensitive to skin conditions and are very susceptible to body movement. Compared with the traditional wet electrode and dry electrode, the non-contact electrode does not need to be in direct contact with the body of a patient when in use, does not need to be prepared in advance, does not need to consider the body surface state of a user, and can enable the user to detect electrocardiosignals through an insulating layer material. However, because the capacitance value formed by coupling the collecting electrode and the human body is very low, and is in pF magnitude, the input resistance of the detection circuit at least should be in T omega magnitude to obtain the electrocardio voltage through voltage division. This requires the input impedance of the back-end acquisition circuit to be very high. Because the gate of the field effect transistor at the input end of the high input impedance operational amplifier is charged by leakage current without an input bias network and the amplifier is saturated in a short time, the high input impedance of the operational amplifier cannot be directly used for the capacitive coupling type acquisition of human body bioelectricity signals.
Aiming at the existing application requirements and the defects of the prior art, the invention provides a bootstrap method for greatly improving the input resistance of the detection circuit, improving the resistance value of the input resistance to controllable multiple of the actual resistance value, and utilizing resistance voltage division to avoid the bootstrap circuit to enable the whole circuit to enter a self-oscillation state, thereby solving the problem that the circuit in a non-inductive non-contact electrocardio detection circuit needs ultrahigh input impedance, and further realizing non-contact electrocardio detection.
Reference documents:
[1]Jin Chun，Zeng Wei.Fatigue monitor algorithm research based on EEG[J].Science Technology and Engineering，2015，15(34):231-234
[2]Jia Haijiang，Liu Zhiqiang，Wang Peng，et al.A distinction method for drowsy driving based on human-vehicle features[J].China Sci-encepaper，2016，11(7):751-753.
[3] lixiaqiong, clown, Zhuyunban, Li 22531Jie, Fan Yulong, Gao Bin, Dengylin biosensor technology in aerospace medicine Protection [ J ] Life sciences instruments 2018,16(Z1): 127-.
[4]Lin C T,Ko L W,Chiou J C,et al.Noninvasive Neural Prostheses Using Mobile and Wireless EEG.Proc IEEE,2008,96:1167–1183
[5]Sumit M,Leon C,Ognian M,et al.Non-Contact Wearable Wireless ECG Systems for Long Term Monitoring[J].IEEE Reviews in Biomedical Engineering,2018:1-1.
[6]Chi Y M,Cauwenberghs G.Wireless Non-contact EEG/ECG Electrodes for Body Sensor Networks[C]//International Conference on Body Sensor Networks.2010:297-301.
[7] Zhanglin, Severe floods, Zhai Jie non-contact electrodes in the detection of cardiac electrical signals and research progress [ J ] aerospace medicine and medical engineering, 2014,27(02): 152-.
Disclosure of Invention
The invention designs a non-contact electrocardio detection circuit based on a capacitive coupling principle, as shown in figure 1, the non-inductive measurement is realized, the input resistance of the detection circuit is greatly improved in a bootstrap mode, the resistance value of the input resistance is improved to a controllable multiple of the actual resistance value, the bootstrap circuit is prevented from enabling the whole circuit to enter a self-excited oscillation state by utilizing resistance voltage division, and the problem of ultrahigh input impedance of the circuit can be solved. See the description below for details:
a non-contact electrocardio detection circuit is characterized in that the circuit adopts a differential input mode and consists of two sets of same circuits, wherein any one set of circuit consists of a resistance-capacitance coupling circuit, a voltage follower, a bootstrap circuit and a virtual earth circuit. Electrocardiosignals are input from IN1 and IN2, the electrocardiosignals are connected with the positive input end of the voltage follower through the output of the resistance-capacitance coupling circuit, the output end of the voltage follower is connected with the bootstrap circuit and the signal output ends OUT1 and OUT2, the bootstrap circuit feeds back the signals to the positive input end of the voltage follower through resistance voltage division, and the resistance-capacitance coupling circuit and the bootstrap circuit are both connected with a reference ground AGND provided by a virtual ground circuit.
The resistance-capacitance coupling circuit is composed of a capacitor C1 and resistors R3 and R4. The human body and the collecting electrode form a coupling capacitor C1, and the coupling capacitor C1 and the resistors R3 and R4 form a resistance-capacitance coupling circuit.
The voltage follower is composed of an operational amplifier A1 and resistors R3 and R4. The resistors R3, R4 provide a bias current path for the operational amplifier a 1.
The bootstrap circuit consists of resistors R3, R4, R7, R8 and a capacitor C4, after a signal output by the voltage follower is subjected to voltage division through resistors R7 and R8, the capacitor C4 is coupled to the resistor R4 to form bootstrap of a resistor R3, so that the equivalent resistance of the resistor R3 subjected to bootstrap is greatly improved, the (R7+ R8)/R7 times are improved, and the resistance-capacitance coupling circuit is further enabled to obtain electrocardiosignals of a human body more easily. The voltage division function of the resistors R7 and R8(R7< < R8) enables the voltage division coefficient to be smaller than 1 but close to 1, so that the effect of the bootstrap circuit is guaranteed, and the circuit is prevented from entering a self-oscillation state.
The resistance-capacitance coupling circuit is composed of a capacitor C2 and resistors R5 and R6. The human body and the collecting electrode form a coupling capacitor C2, and the coupling capacitor C2 and the resistors R5 and R6 form a resistance-capacitance coupling circuit.
The voltage follower is composed of an operational amplifier A2 and resistors R5 and R6. The resistors R5, R6 provide a bias current path for the operational amplifier a 2.
The bootstrap circuit consists of resistors R5, R6, R9, R10 and a capacitor C5, after a signal output by the voltage follower is subjected to voltage division through resistors R9 and R10, the capacitor C5 is coupled to the resistor R5 to form bootstrap of a resistor R6, so that the equivalent resistance of the resistor R6 subjected to bootstrap is greatly improved, the (R10+ R9)/R10 times are improved, and the resistance-capacitance coupling circuit is further enabled to obtain electrocardiosignals of a human body more easily. The voltage division function of the resistors R10 and R8(R10< < R9) enables the voltage division coefficient to be smaller than 1 but close to 1, so that the effect of the bootstrap circuit is guaranteed, and the circuit is prevented from entering a self-oscillation state.
The virtual ground circuit is composed of a power supply Vcc, a power ground GND, resistors R1, R2 and a capacitor C3. The voltage dividing circuit formed by the resistors R1 and R2 provides a reference ground AGND of the whole circuit, and the capacitor C3 plays a role in filtering.
The technical scheme provided by the invention has the beneficial effects that:
1. the invention improves the input resistance of the detection circuit to controllable multiple of the actual resistance through the resistance voltage division characteristic in the bootstrap circuit, avoids the circuit from entering a self-excited oscillation state, and ensures the stability of the circuit.
2. The portable non-contact electrocardio detection circuit is simple and feasible, small in size and convenient to carry, and is suitable for special applications such as daily electrocardio monitoring of astronauts, automobile drivers and heart disease patients;
3. the invention solves the problem that non-contact electrocardio detection needs ultrahigh input impedance, avoids the use of ultrahigh resistance, improves the operation precision of a circuit and reduces noise;
4. the invention has lower requirement on the precision degree of components and reduces the circuit cost.
Drawings
FIG. 1 is a circuit diagram of a non-contact electrocardiographic measurement;
FIG. 2 is a diagram of the electrocardiographic waveform measured by the vehicle-mounted non-contact electrocardiographic detection system。
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Application example: vehicle-mounted non-contact electrocardiogram detection system
Application scenarios: the vehicle-mounted non-contact electrocardio detection system is carried in an automobile and is used for detecting electrocardiosignals of a driver.
The system comprises the following components: the vehicle-mounted non-contact electrocardio detection system comprises an electrocardio acquisition circuit module, a signal processing module, a transmission module,
The display module is composed of a central electricity acquisition circuit module, namely the invention.
Introduction of modules:
electrocardio acquisition circuit module (invention): the system is used for collecting electrocardiosignals, and conductive fibers are selected as collecting electrodes. The signal processing module: the method is used for processing the electrocardiosignals.
The signal transmission module: adopt bluetooth as transmission module, realize uploading the electrocardio waveform after signal processing module handles to display module.
And the display module is used for displaying the electrocardiographic waveform in real time.
Actual test conditions:
fig. 2 shows a waveform of the electrocardiograph measured by the vehicle-mounted non-contact electrocardiograph detection system.
Claims (8)
1. A non-contact electrocardio detection circuit is characterized IN that the circuit adopts a differential input mode and consists of two sets of same circuits, wherein any one set of circuits consists of a resistance-capacitance coupling circuit, a voltage follower, a bootstrap circuit and a virtual ground circuit, electrocardio signals are input by IN1 and IN2, the output of the resistance-capacitance coupling circuit is connected with the positive input end of the voltage follower, the output end of the voltage follower is connected with the bootstrap circuit and signal output ends OUT1 and OUT2, the bootstrap circuit feeds back signals to the positive input end of the voltage follower through resistance voltage division, and the resistance-capacitance coupling circuit and the bootstrap circuit are both connected with a reference ground AGND provided by the virtual ground circuit.
2. The bootstrap circuit of claim 1, characterized in that, the bootstrap circuit is composed of resistors R3, R4, R7, R8 and a capacitor C4, after the voltage division of the signal output by the voltage follower is performed by resistors R7, R8, the capacitor C4 is coupled to the resistor R4 to form bootstrap of the resistor R3, so that the equivalent resistance of the resistor R3 after bootstrap is greatly increased, which is increased by (R7+ R8)/R7 times, further making the rc-coupled circuit more easily obtain the signal of the human body, wherein, the voltage division function of the resistors R7, R8(R7< < R8) makes the voltage division coefficient smaller than 1 but close to 1, thus not only ensuring the effect of the bootstrap circuit, but also ensuring that the self-excited oscillation state of the electrocardiograph circuit is not entered.
3. The RC coupling circuit of claim 1, wherein the human body and the collecting electrode form a coupling capacitor C1, and the coupling capacitor C1 and the resistors R3 and R4 form the RC coupling circuit.
4. The voltage follower of claim 1, wherein the voltage follower comprises an operational amplifier a1 and resistors R3 and R4, and the resistors R3 and R4 provide a bias current path for the operational amplifier a 1.
5. The bootstrap circuit of claim 1, characterized in that, the bootstrap circuit is composed of resistors R5, R6, R9, R10 and a capacitor C5, after the voltage division of the signal output by the voltage follower is performed by resistors R9, R10, the capacitor C5 is coupled to the resistor R5 to form bootstrap of the resistor R6, so that the equivalent resistance of the resistor R6 after bootstrap is greatly increased, which is increased by (R10+ R9)/R10 times, further making the rc-coupled circuit more easily obtain the signal of the human body, wherein, the voltage division function of the resistors R10, R9(R10< < R9) makes the voltage division coefficient smaller than 1 but close to 1, thus not only ensuring the effect of the bootstrap circuit, but also ensuring that the self-excited oscillation state of the electrocardiograph circuit is not entered.
6. The RC coupling circuit of claim 1, wherein the human body and the collecting electrode form a coupling capacitor C2, and the coupling capacitor C2 and the resistors R5 and R6 form the RC coupling circuit.
7. The voltage follower of claim 1, wherein the voltage follower comprises an operational amplifier a2 and resistors R5 and R6, and the resistors R5 and R6 provide a bias current path for the operational amplifier a 2.
8. The virtual ground circuit of claim 1, wherein the virtual ground circuit is composed of a power supply Vcc, a power supply ground GND, resistors R1, R2 and a capacitor C3, a voltage dividing circuit composed of resistors R1 and R2 provides a reference ground AGND of the whole circuit, and the capacitor C3 plays a role in filtering.
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| CN202110055486.9A CN112869749A (en) | 2021-01-15 | 2021-01-15 | Non-contact electrocardio detection circuit |
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