Active electrode with feedback

Abstract

In order to record physiological electrical signals with high quality, two feedback active electrode circuit schemes are proposed, both of which include electrode power supply, main operational amplifier, "virtual ground" circuit, "virtual ground" feedback circuit, main operational amplifier bias network, shielding circuit and other parts. The difference from the basic feedback active electrode circuit is that a complex bias network and shielding network are introduced to improve the stability of the circuit. Physiological electrical signals can be effectively detected in scenarios of direct contact with the skin and indirect contact with the skin through clothing, and interference and noise are not easily introduced.

Description

Technical Field

[0001] The present application relates to an active electrode with feedback for detecting physiological electrical signals.

[0002] Physiological electrical signals refer to electrical signals that carry physiological information, such as electrocardiogram, electroencephalogram, electromyography, and electrooculography. Active electrodes (AE), that is, electrodes with built-in detection circuits, are increasingly used in physiological signal detection, especially in wearable applications. The reason is that active electrodes achieve impedance conversion near the measurement point through their built-in circuits, and their low output impedance is not easy to introduce 50Hz or 60Hz AC interference, and is not easy to produce cable motion artifacts, which can improve the accuracy of the detection circuit. Background Art

[0003] A document discloses an active electrode with feedback for physiological electrical signal detection, which includes a voltage follower basic circuit, a "virtual ground" feedback circuit, a shielding circuit, an electrode DC power supply, etc. Figure 3 shown. Figure 3 In, V + and V- are the positive and negative ends of the electrode DC power supply; the potential v at the surface measuring point A in Input operational amplifier A1, its output v out Connected to the back-end circuit to form the voltage follower basic circuit of the active electrode; the positive and negative ends of the DC power supply V + and V - The bypass circuit is connected in series with two equal value resistors R. The potential of the connection point G between the two resistors R is (V + +V - ) / 2, that is, the midpoint potential point of both ends of the power supply, forms a "virtual ground", and then the "virtual ground" potential is input into the voltage follower A2 based on the operational amplifier, and its output is fed back to another point F near the body surface through the current limiting resistor r, forming a "virtual ground" feedback circuit. Figure 3 The active electrode circuit shown, due to the introduction of the feedback circuit, plays a role similar to the right leg driving circuit in physiological electrical signal detection. When the electrode contacts the skin for detection, it is very effective in suppressing 50Hz or 60Hz AC interference and reducing cable motion artifacts.

[0004] Figure 3 The disadvantage of the active electrode with feedback shown is that in the scenario of non-contact detection of physiological electrical signals through clothing, its voltage follows the bias current of the operational amplifier A1 in the basic circuit and is not easy to release, which can easily cause saturation of the detection electrode circuit and unstable operation of the circuit.

[0005] References:

[0006] 1. Jiawei Xu, Srinjoy Mitra, Chris Van Hoof, Refet Firat Yazicioglu and Kofi AA Makinwa, Active Electrodes for Wearable EEG Acquisition: Review and Electronics Design Methodology, DOI 10.1109 / RBME.2017.2656388, IEEE Reviews in Biomedical Engineering 2. Liu Hongxing, Qu Yongdong, Liu Lesi, Junfeng: An Active Electrode for Detecting Physiological Electrical Signals, 201810180948.8,

[0007] Application date 20180302

[0008] 3. Liu Hongxing, Liu Le, Qu Yongdong, Si Junfeng: A multifunctional ECG detection limb clamp for active electrodes, 201810370809.1, application date 20180424

[0009] 4. Liu Hongxing, Qu Yongdong, Liu Le: A shielded active electrode for physiological electrical detection, 201811199712.5, application date, application date

[0010] October 11, 2018

[0011] 5. Liu Hongxing, Qu Yongdong, Liu Le: A shielded active electrode forming bio-potential signals, application number PCT / CN2019 / 110533, mailing date October 11, 2019 (278753), application file number G19674514PCT, mailing date: 22.10.2019 Summary of the invention

[0012] Purpose of the invention.

[0013] A new solution with feedback active electrodes is proposed, which can effectively detect physiological electrical signals in non-skin contact detection scenarios. Of course, it can also be used for effective detection of physiological electrical signals in skin contact scenarios.

[0014] Technical solution.

[0015] A feedback active electrode for physiological electrical signal detection, comprising an electrode power supply ( Figure 1 , V + and V - ), Main Operational Amplifier ( Figure 1 , A1), "virtual ground" circuit ( Figure 1 , R and R), "virtual ground" feedback circuit ( Figure 1 , auxiliary operational amplifier A2 and current limiting resistor r), main operational amplifier bias network ( Figure 1 , R1, R2 and R3), shielding circuit ( Figure 1 , current limiting resistor R7 and shielding layer Shield), characterized in that the electrode is from the skin ( Figure 1 , Skin) directly or indirectly through fabric ( Figure 1 , Cloth, point A) to obtain the electrode input potential Vin, Vin and the main operational amplifier ( Figure 1 , A1) is connected to the inverting terminal; the main operational amplifier ( Figure 1 , A1) output ( Figure 1 , Vout) through the current limiting resistor ( Figure 1 , R7) and electrode shielding layer ( Figure 1 , Shield) connected; the main operational amplifier ( Figure 1 , A1) output ( Figure 1 , Vout) and the main operational amplifier ( Figure 1 , A1) inverting terminal is connected; the positive and negative ends of the electrode power supply ( Figure 1 , V + and V - ) bypass, connect two equal value resistors in series ( Figure 1 , R and R), forming a "virtual ground" circuit, the potential of the connection point G between the two resistors R is (V + +V - ) / 2, called the midpoint potential point of the power supply, that is, the "virtual ground"; "virtual ground" ( Figure 1 , G) potential input based on operational amplifier ( Figure 1 , A2) is the non-inverting end of the voltage follower, and its output passes through the current limiting resistor ( Figure 1 , r) feedback to another point on the body surface (direct contact or through fabric, Figure 1 , F), forming a "virtual ground" feedback circuit; the main operational amplifier ( Figure 1 , A1) input Vin is connected in series with two resistors ( Figure 1 , R1 and R3) and then to the auxiliary operational amplifier ( Figure 1 , A2) output, the main operational amplifier ( Figure 1 , A1) through the inverting terminal resistor ( Figure 1 , R2) is connected to the connection point of the two series resistors R1 and R3 to form the bias network of the main operational amplifier.

[0016] According to the above feedback active electrode for physiological electrical signal detection, it is characterized in that the main operational amplifier bias network ( Figure 1, R1, R2 and R3) are determined by solving the following optimization problem, where V I The main operational amplifier ( Figure 1 , A1) Input voltage noise, I N1 The main operational amplifier ( Figure 1 , A1) Bias current at the in-phase terminal, E nf and E nB The main operational amplifier ( Figure 1 , A1) Electrical characteristic parameters of input 1 / f noise density and broadband white noise density (unit V / √Hz), T is the absolute temperature of the resistor (unit K), k is the Boltzmann constant 1.38×10 -23 J / K, C eq For the body surface ( Figure 1 , A), Rset is the minimum value of the set input resistance:

[0017]

[0018] The objective function in the above optimization problem is It is a measure of the total output noise produced by voltage noise, current noise, and thermal noise of each resistor. The unit is V 2 / Hz, each frequency point corresponds to a noise function value.

[0019] A feedback active electrode for physiological electrical signal detection, comprising an electrode power supply ( Figure 2 , V + and V - ), Main Operational Amplifier ( Figure 2 , A1), "virtual ground" circuit ( Figure 2 , R and R), "virtual ground" feedback circuit ( Figure 2 , auxiliary operational amplifier A2 and current limiting resistor r), main operational amplifier bias network ( Figure 2 , R2, R3, R4, R5 and R6), shielding circuit ( Figure 2 , current limiting resistor R7 and shielding layer Shield), characterized in that the electrode is from the skin ( Figure 2 , Skin) directly or indirectly through fabric ( Figure 2 , Cloth, point A) to obtain the electrode input potential Vin, Vin and the main operational amplifier ( Figure 2 , A1) is connected to the inverting terminal; the main operational amplifier ( Figure 2 , A1) output ( Figure 2 , Vout) through the current limiting resistor ( Figure 2 , R7) and electrode shielding layer ( Figure 2 , Shield) connected; the main operational amplifier ( Figure 2 , A1) output ( Figure 2 , Vout) and the main operational amplifier ( Figure 2 , A1) inverting terminal is connected; the positive and negative ends of the electrode power supply ( Figure 2 , V + and V - ) bypass, connect two equal value resistors in series ( Figure 2 , R and R), forming a "virtual ground" circuit, the middle connection point of the two resistors R ( Figure 2 , G) has a potential of (V + +V - ) / 2, called the midpoint potential point of the power supply, that is, the "virtual ground"; "virtual ground" ( Figure 2 , G) potential input based on operational amplifier ( Figure 2 , A2) is the non-inverting end of the voltage follower, and its output passes through the current limiting resistor ( Figure 2 , r) feedback to another point on the body surface (direct contact or through fabric, Figure 2 , F), forming a "virtual ground" feedback circuit; the main operational amplifier ( Figure 2 , A1) input Vin is connected in series with three resistors ( Figure 1 , R4, R6 and R3) and then to the auxiliary operational amplifier ( Figure 2 , A2) output, the main operational amplifier ( Figure 2 , A1) through the inverting terminal resistor ( Figure 2 , R2) is connected to the connection point of the two series resistors R6 and R3, and the middle connection point of the two resistors R4 and R6 is connected to the auxiliary operational amplifier ( Figure 2 , A2) output terminals, together forming the bias network of the main operational amplifier.

[0020] According to the above feedback active electrode for physiological electrical signal detection, it is characterized in that the main operational amplifier bias network ( Figure 2 , R2, R3, R4, R5 and R6) are determined by solving the following optimization problem, where I N1 The main operational amplifier ( Figure 2 , A1) Bias current at the in-phase terminal, E nf and E nB The main operational amplifier ( Figure 2 , A1) Electrical characteristic parameters of input 1 / f noise density and broadband white noise density (unit V / √Hz), T is the absolute temperature of the resistor (unit K), k is the Boltzmann constant 1.38×10 -23 J / K, C eq For the body surface ( Figure 2 , A), Rset is the minimum value of the set input resistance:

[0021]

[0022] The objective function in the above optimization problem is

[0023] V total 2 =V 0_n 2 +V 0_R4 2 +V 0_R5 2 +V 0_R6 2 +V 0_R3 2 +V 0_R2 2 +V 0_in1 2 +V 0_in2 2 It is a measure of the total output noise produced by voltage noise, current noise, and thermal noise of each resistor. The unit is V 2 / Hz, each frequency point corresponds to a noise function value.

[0024] Beneficial effects.

[0025] Compared with the basic circuit with active electrode with feedback, the above two solutions of active electrode with feedback arrange a special bias network and propose a solution to determine the bias network parameter value with the goal of minimizing the electrode output noise and the input resistance greater than the set value as the constraint, aiming to minimize the impact of the operational amplifier bias current on the stability of the circuit. The effectiveness of the solution is verified by experiment below.

[0026] The inventors made two active electrodes according to the two proposed technical solutions, and also made existing basic active electrodes with feedback, as shown in the examples, and conducted comparative tests. The core module of the test device is the PCI 4461 card of NI. It is inserted into the industrial computer and the corresponding software is written to build a high-precision 2-way voltage synchronous acquisition system with signal processing function. This system is used to synchronously acquire two voltage signals, such as Figure 4 As shown, one is based on Figure 3 A pair of control electrodes in the scheme shown is used to test the voltage signal from a point on the left arm to a point on the right arm ( Figure 4 The other is based on the present invention Figure 1 A pair of electrodes or Figure 2 The pair of electrodes shown is used to test the voltage signal from one point on the left arm to one point on the right arm ( Figure 4 two electrodes away from the wrist).

[0027] Test experiment 1. The synchronous sampling rate is set to 100kHz, and the two synchronously collected signals are both subjected to a real-time FIR bandpass filter with a passband of 0.5-40Hz. The unit sample value response h(n) length of the filter is set to 10 seconds. The subject remains quiet and the cable does not move. The results of the two-channel signal collected and processed in this way are as follows Figure 5 As shown; Figure 5 The two figures in the middle and upper parts are based on Figure 3 The signal waveform diagram and spectrum diagram of a pair of control electrodes shown in the figure, the lower two diagrams are based on the present invention Figure 1 The signal waveform and spectrum of a pair of electrodes are shown in Figure 2. Figure 3 The detection results of the active electrode shown in the control have great interference and noise, while the detection results of the active electrode based on the present invention have great interference and noise. Figure 1 The detection results for the active pair of electrodes shown have much less interference and noise.

[0028] Test experiment 2. The synchronous sampling rate is set to 100kHz, and the two synchronously collected signals are both subjected to a real-time FIR bandpass filter with a passband of 0.5-40Hz. The unit sample value response h(n) length of the filter is set to 10 seconds. The subject remains quiet and the cable does not move. The results of the two signals collected and processed in this way are as follows Figure 6 As shown; Figure 6 The two figures in the middle and upper parts are based on Figure 3 The signal waveform diagram and spectrum diagram of a pair of control electrodes shown in the figure, the lower two diagrams are based on the present invention Figure 2 The signal waveform and spectrum of a pair of electrodes are shown in Figure 2. Figure 3 The detection results of the control active electrode shown in the figure have large interference and noise, while at this time based on the present invention Figure 2 The detection results for the active pair of electrodes shown have much less interference and noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 , Schematic diagram of the first active electrode circuit with feedback of the present invention

[0030] Figure 2 , Schematic diagram of the second active electrode circuit with feedback of the present invention

[0031] Figure 3 , compared with the basic active electrode circuit scheme with feedback

[0032] Figure 4 , Schematic diagram of comparative test scenario

[0033] Figure 5 , Schematic diagram of comparative test results

[0034] Figure 6 , Schematic diagram of comparative test results of experiment 2

[0035] Figure 7 , a schematic diagram of the active electrode body implemented according to the scheme of the present invention

[0036] Figure 8 , Bode plot test results of the two active electrodes implemented Example

[0037] Embodiment 1. Press Figure 1 The technical solution 1 shown in the figure is to make a PCB circuit board, and the active electrode body part is made as shown in the figure. Figure 7 As shown. In the implementation, the DC power supply uses a 3V battery CR2032 to supply power; as the two core devices, the two operational amplifiers, A1, choose LMP7721 with extremely low bias current, and A2 chooses OPA320; the two resistors R choose 100kΩ, the current limiting resistor r chooses 0Ω for convenience without loss of generality, and the shielding resistor R7 chooses 100Ω; at the same time, according to the optimization problem of formula (1), the optimal bias resistors R1, R2, and R3 at the 1Hz frequency point are solved, and the values ​​are 100GΩ, 1kΩ, and 100kΩ respectively. When solving the optimization problem of formula (1), Rset is set to 1×10 12 Ω,V I , I N1 It can be found in the DataSheet of the LMP7721 device, which are C eq The value is 470pF, and the optimal values ​​of R1, R2, and R3 are selected from the existing resistor values ​​in the market. Finally, the values ​​of R1, R2, and R3 are 100GΩ, 1kΩ, and 100kΩ respectively. At this time, the theoretical input resistance calculated according to the values ​​of R1, R2, and R3 can reach 10×10 12 Ω. In the comparative test experiment 1 of the beneficial effect column, the pair of electrodes of the present application is a pair of electrodes implemented in this way, which is more Figure 3 The scheme has achieved the effect of being significantly less susceptible to noise interference.

[0038] Embodiment 2. Figure 2 The second technical solution shown in FIG. 1 is to manufacture a PCB circuit board, and the active electrode body part is as shown in FIG. Figure 7As shown. In the implementation, the DC power supply uses a 3V battery CR2032 to supply power; as the two core devices, the operational amplifiers A1 uses the LMP7721 with extremely low bias current, and A2 uses the OPA320; the two resistors R use 100kΩ, the current limiting resistor r uses 0Ω for convenience without loss of generality, and the shielding resistor R7 uses 100Ω; at the same time, according to the optimization problem of formula (2), the optimal bias resistors R2, R3, R4, R5, and R6 at the 1Hz frequency point are solved, and the values ​​are 20kΩ, 1GΩ, 1GΩ, 1GΩ, and 680kΩ, respectively. When solving the optimization problem of formula (2), Rset is set to 1×10 12 Ω,V I , I N1 The datasheet of LMP7721 device can be found as follows: C eq The value is 470pF, and the obtained R2, R3, R4, R5, and R6 are selected from the existing market resistance values, and the final values ​​are 20kΩ, 1GΩ, 1GΩ, 1GΩ, and 680kΩ. At this time, the calculated theoretical input resistance can reach 1.39×10 12 Ω. In the comparative test experiment 2 of the beneficial effect column, the pair of electrodes of the present application is a pair of electrodes implemented in this way, which is more Figure 3 The scheme has achieved the effect of being significantly less susceptible to noise interference.

[0039] Figure 8 The Bode plot test results of the two active electrodes with feedback in the present application are shown above. The 3dB attenuation frequencies are approximately 0.00045Hz and 0.003Hz respectively (It should be noted that when testing the Bode plot, for convenience, a 20pF capacitor C was soldered to the electrode input end, and the equivalent capacitance value C used in the previous calculation was not used. eq =470pF). If both electrodes are considered as first-order systems, then The actual input resistances of the two electrodes were calculated to be 17.68TΩ and 2.65TΩ respectively. Although there are certain errors between the two measured values ​​and the two theoretically calculated input resistances, they are of the same order of magnitude and are both relatively large. Both electrodes have achieved obvious anti-noise interference effects.

[0040] 1. When applying for an invention patent or utility model patent, you must submit a description in duplicate (one original and one copy).

[0041] 2. The manual should be typed or printed, the handwriting should be neat and clear, black, meet the requirements of plate making, the height of the characters should be between 3.5 mm and 4.5 mm, and the line spacing should be between 2.5 mm and 3.5 mm. The first page of the manual should be on this page, and the continuation pages can be written on white paper of the same size and quality. The paper should be used vertically, only the front side should be used, and there should be blank space around: 25 mm on the left and top, 15 mm on the right and bottom.

[0042] 3. Application documents sent by mail must not be folded.

[0043] 4. The first line of the first page of the specification shall state the title of the invention, which shall be consistent with the title in the application and centered on the left and right. There shall be a blank line between the title of the invention and the body of the specification. The specification format shall include the following five parts, and the title shall be stated in front of each part: Technical field (body content)

[0044] Background technology (text content)

[0045] Summary of the invention (content)

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[0047] Specific implementation method (text content)

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Claims

1. A feedback active electrode for physiological electrical signal detection, comprising an electrode power supply, a main operational amplifier, a "virtual ground" circuit, a "virtual ground" feedback circuit, a main operational amplifier bias network, and a shielding circuit, characterized in that: The electrode receives the electrode input potential V directly from the skin or indirectly through the cloth in , V in Connected to the in-phase terminal of the main operational amplifier; the output of the main operational amplifier is connected to the electrode shielding layer through a current limiting resistor; the output of the main operational amplifier is connected to the inverting terminal of the main operational amplifier; the bypass of the positive and negative ends of the electrode power supply, two equal value resistors are connected in series to form a "virtual ground" circuit, and the potential of the connection point G between the two resistors R is (V + +V - ) / 2, called the midpoint potential point of the power supply, that is, the "virtual ground"; the "virtual ground" potential input is based on the in-phase end of the voltage follower of the operational amplifier, and its output is fed back to another point on the body surface through a current limiting resistor, forming a "virtual ground" feedback circuit; the input V in The two resistors are connected in series in sequence and then connected to the output end of the auxiliary operational amplifier. The inverting end of the main operational amplifier is connected to the connection point of the two series resistors R1 and R3 through a resistor to form a bias network of the main operational amplifier.

2. A feedback active electrode for physiological electrical signal detection according to claim 1, characterized in that: The values ​​of R1, R2, and R3 in the main op amp bias network are determined by solving the following optimization problem, where V I is the voltage noise at the main op amp input, I N1 is the bias current of the non-inverting terminal of the main operational amplifier, E nf and E nB The electrical characteristic parameters of the 1 / f noise density and broadband white noise density at the input of the main operational amplifier, in V / √Hz, T is the absolute temperature of the resistor, in K, and k is the Boltzmann constant 1.38×10 -23 J / K, C eq is the equivalent input capacitance at the body surface, and Rset is the minimum value of the set input resistance: The objective function in the above optimization problem is It is a measure of the total output noise produced by voltage noise, current noise, and thermal noise of each resistor. The unit is V 2 / Hz, each frequency point corresponds to a noise function value.

3. A feedback active electrode for physiological electrical signal detection, comprising an electrode power supply, a main operational amplifier, a "virtual ground" circuit, a "virtual ground" feedback circuit, a main operational amplifier bias network, and a shielding circuit, characterized in that: The electrode receives the electrode input potential V directly from the skin or indirectly through the cloth in , V in Connected to the in-phase terminal of the main operational amplifier; the output of the main operational amplifier is connected to the electrode shielding layer through a current limiting resistor; the output of the main operational amplifier is connected to the inverting terminal of the main operational amplifier; the bypass of the positive and negative ends of the electrode power supply, two equal value resistors are connected in series to form a "virtual ground" circuit, and the potential of the middle connection point of the two resistors R is (V + +V - ) / 2, called the midpoint potential point of the power supply, that is, the "virtual ground"; the "virtual ground" potential input is based on the in-phase end of the voltage follower of the operational amplifier, and its output is fed back to another point on the body surface through a current limiting resistor, forming a "virtual ground" feedback circuit; the input V in The three resistors are connected in series in sequence and then connected to the output end of the auxiliary operational amplifier. The inverting end of the main operational amplifier is connected to the connection point of the two series resistors R6 and R3 through a resistor. At the same time, the middle connection point of the two resistors R4 and R6 is connected to the output end of the auxiliary operational amplifier through the resistor group R5, together forming the bias network of the main operational amplifier.

4. The feedback active electrode for physiological electrical signal detection according to claim 3, characterized in that: The values ​​of R2, R3, R4, R5, and R6 in the main op amp bias network are determined by solving the following optimization problem, where I N1 is the bias current of the non-inverting terminal of the main operational amplifier, E nf and E nB The electrical characteristic parameters of the 1 / f noise density and broadband white noise density at the input of the main operational amplifier, in V / √Hz, T is the absolute temperature of the resistor, in K, and k is the Boltzmann constant 1.38×10 - 23 J / K, C eq is the equivalent input capacitance at the body surface, and Rset is the minimum value of the set input resistance: The objective function in the above optimization problem is V total 2 =V 0_n 2 +V 0_R4 2 +V 0_R5 2 +V 0_R6 2 +V 0_R3 2 +V 0_R2 2 +V 0_in1 2 +V 0_in2 2 It is a measure of the total output noise produced by voltage noise, current noise, and thermal noise of each resistor. The unit is V 2 / Hz, each frequency point corresponds to a noise function value.

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