Biological signal acquisition system and biological signal acquisition method

Abstract

This biological signal acquisition system comprises: a first detection electrode and a second detection electrode capable of coming into contact with a living body; a differential amplification circuit having a first input line to which the first detection electrode is connected and a second input line to which the second detection electrode is connected; a first variable capacitance element connected between the first input line and the reference potential; and a second variable capacitance element connected between the second input line and the reference potential.

Description

Biological signal acquisition system and biological signal acquisition method

[0001] The present invention relates to a biological signal acquisition system and a biological signal acquisition method.

[0002] Patent Document 1 describes a biosignal detection system in which a variable resistance element such as a CdS cell is provided between each of two detection electrodes and a differential amplifier, with the aim of reducing common-mode noise when two biosignals obtained from two detection electrodes in contact with a living body are differentially amplified. In this system, the resistance value of one variable resistance element is controlled to be greater than the resistance value of the other variable resistance element, so that the magnitudes of the biosignals output from the variable resistance elements connected in series to each detection electrode are the same.

[0003] JP 2018-94412 A

[0004] From the viewpoint of ensuring a good SNR (signal-to-noise ratio) of the biosignal after amplification, it is preferable to input the biosignal acquired from the detection electrode to the amplifier with as little attenuation as possible. While the configuration of inserting a variable resistance element in series with the detection electrode as in the above-mentioned conventional technology can reduce common-mode noise, it attenuates the biosignal by at least the minimum resistance value that can be achieved by the variable resistance element, which may lead to SNR degradation due to other white noise, etc. Furthermore, since resistive elements can generate thermal noise that cannot be ignored for minute biosignals such as electroencephalograms, it is preferable to avoid using them as much as possible in the front end of the amplifier circuit.

[0005] An object of the present invention is to reduce common-mode noise in biosignals obtained from multiple detection electrodes in contact with a living body without increasing other types of noise components, thereby achieving good detection of the biosignals.

[0006] One aspect of the present invention is a biosignal acquisition system comprising: a differential amplifier circuit having first and second detection electrodes contactable with a living body, a first input line to which the first detection electrode is connected and a second input line to which the second detection electrode is connected, a first variable capacitance element connected between the first input line and a reference potential, and a second variable capacitance element connected between the second input line and the reference potential. Another aspect of the present invention is a biosignal acquisition method executed by a computer for a biosignal acquisition system comprising: a differential amplifier circuit having a first input line to which the first detection electrode contactable with a living body is connected and a second input line to which the second detection electrode contactable with the living body is connected, the first variable capacitance element connected between the first input line and a reference potential, and a second variable capacitance element connected between the second input line and the reference potential, the method comprising: a noise measurement step of measuring a noise level in a predetermined frequency range included in an output of the differential amplifier circuit; and a capacitance setting step of setting the capacitances of the first and second variable capacitance elements so as to minimize the noise level in the predetermined frequency range. Another aspect of the present invention is a biosignal acquisition method executed by a computer in a biosignal acquisition system including a differential amplifier circuit having a first input line to which a first detection electrode contactable with a living body is connected and a second input line to which a second detection electrode contactable with the living body is connected, a first variable capacitance element connected between the first input line and a reference potential, and a second variable capacitance element connected between the second input line and the reference potential, and a resistance measurement circuit for measuring the contact resistance of each of the first detection electrode and the second detection electrode with the living body, the biosignal acquisition method comprising: a resistance measurement step of measuring a first contact resistance between the first detection electrode and the living body and a second contact resistance between the second detection electrode and the living body using the resistance measurement circuit; and a capacitance setting step of setting the capacitance of the first variable capacitance element and the second variable capacitance element to a value calculated using the measured values ​​of the first contact resistance and the second contact resistance. This specification is intended to include the entire contents of Japanese Patent Application No. 2024-069891, filed on April 23, 2024.

[0007] According to the present invention, it is possible to reduce common mode noise in biological signals obtained from multiple detection electrodes in contact with a living body without increasing other types of noise components such as thermal noise, thereby achieving good detection of biological signals.

[0008] FIG. 1 is a diagram showing an example of a biosignal measurement system to which a biosignal acquisition system according to the present invention is applied. FIG. 2 is a diagram showing the overall configuration of a biosignal acquisition system according to a first embodiment. FIG. 3 is a diagram showing the configuration of a signal acquisition circuit and a control device of the biosignal acquisition system according to the first embodiment. FIG. 4 is an equivalent circuit for explaining common-mode noise in the biosignal acquisition system according to the first embodiment. FIG. 5 is a flowchart of a biosignal acquisition method in the biosignal acquisition system according to the first embodiment. FIG. 6 is a flowchart of a biosignal acquisition method in the biosignal acquisition system according to the first embodiment. FIG. 7 is a flowchart of a biosignal acquisition method according to a modified example of the biosignal acquisition system according to the first embodiment. FIG. 8 is a flowchart of a biosignal acquisition method according to a modified example of the biosignal acquisition system according to the first embodiment. FIG. 9 is a diagram showing the overall configuration of a biosignal acquisition system according to a second embodiment. FIG. 10 is a diagram showing the configuration of a signal acquisition circuit and a control device of the biosignal acquisition system according to the second embodiment. FIG. 11 is a flowchart of a biosignal acquisition method in the biosignal acquisition system according to the first embodiment.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [1. First Embodiment] First, a first embodiment of the present invention will be described. [1.1. Overall Configuration] Fig. 1 is a diagram showing an example of the configuration of a biosignal measurement system 2 in which a biosignal acquisition system 1 according to a first embodiment of the present invention is used. The biosignal measurement system 2 is, for example, an electroencephalogram (EEG) measurement system that measures electroencephalograms as biosignals of a subject P. The biosignal measurement system 2 includes the biosignal acquisition system 1 and a processing device 3. The biosignal acquisition system 1 is realized, for example, as an ear-hook type device that is worn on the ear of the subject P to acquire the electroencephalogram signal of the subject P.

[0011] Here, the term "living body" refers to a part or the whole of the body of the subject P, and the term "biological signal" refers to an electrical signal generated by the body of the subject P.

[0012] The processing device 3 performs signal processing on the EEG signals acquired from the biosignal acquisition system 1 and performs EEG analysis on the processed EEG signals. The signal processing includes, for example, filtering, averaging, noise reduction, etc. on the EEG signals, and these signal processing processes improve the signal quality of the EEG signals. These signal processing processes may be executed in the biosignal acquisition system 1. The processing device 3 may be, for example, a desktop PC or a mobile PC such as a notebook PC or tablet PC. The results of the EEG analysis in the processing device 3 are output to, for example, an output device such as a display device provided in the processing device 3.

[0013] 2 and 3 are diagrams showing an example of the configuration of a biosignal acquisition system 1 according to this embodiment. Referring to FIG. 2 , the biosignal acquisition system 1 includes, for example, a wearing device 4 attached to the ear of the subject P, and a plurality of electrodes attached in contact with the skin of the subject P, which is a living body. The electrodes include, for example, a pair of a first detection electrode 5a and a second detection electrode 5b, and a bias electrode 6 that applies a bias voltage to the living body. The bias electrode 6 is attached, for example, so as to contact the skin of the earlobe of the subject P, and the pair of the first detection electrode 5a and the second detection electrode 5b are attached in close proximity to the scalp of the subject P. Hereinafter, when there is no need to distinguish between the first detection electrode 5a and the second detection electrode 5b, they will be referred to as detection electrodes 5.

[0014] The biosignal acquisition system 1 includes a signal acquisition circuit 7 and a control device 8. The signal acquisition circuit 7 and the control device 8 are housed inside a housing 9 attached to the wearing device 4. The detection electrodes 5 and the bias electrodes 6 are connected to the signal acquisition circuit 7 and / or the control device 8 via wiring provided inside the wearing device 4. The control device 8 performs operation settings for the signal acquisition circuit 7 and acquires the biosignals input from the detection electrodes 5 via the signal acquisition circuit 7.

[0015] Fig. 3 is a diagram showing the configuration of the signal acquisition circuit 7 and the control device 8. Fig. 3 shows the first detection electrode 5a, the second detection electrode 5b, and the bias electrode 6 attached so as to be in contact with the skin SK (shown as a dashed line) of the living body LB of the subject P. Contact resistances 50a, 50b, and 51 of the first detection electrode 5a, the second detection electrode 5b, and the bias electrode 6 are shown in the living body LB. Hereinafter, the resistance values ​​of the contact resistances 50a, 50b, and 51 will be referred to as R ＣＰ , R ＣＮ , and R ＢＩＡＳ Let's say.

[0016] The living body LB also contains a biological signal V obtained by the first detection electrode 5a and the second detection electrode 5b. ｅｅｇｐ and V ｅｅｇｎ In addition, a first signal source 52a and a second signal source 52b are shown, which are equivalent signal sources of the biological signal V. ｅｅｇｐ , V ｅｅｇｎ Common mode noise V that can be superimposed on ｃｍ An equivalent noise source 53 is shown.

[0017] The signal acquisition circuit 7 includes a differential amplifier circuit 11 having a first input line 10a to which the first detection electrode 5a is connected and a second input line 10b to which the second detection electrode 5b is connected. For example, the first input line 10a and the second input line 10b are the non-inverting input and inverting input lines, respectively, of the differential amplifier circuit 11. The differential amplifier circuit 11 can be realized as a circuit block including an operational amplifier (op-amp) or the like, or as a single integrated circuit.

[0018] The differential amplifier circuit 11 differentially amplifies and outputs the biological signals input from the first detection electrode 5 a and the second detection electrode 5 b. The amplified biological signals output from the differential amplifier circuit 11 are converted into digital data by an ADC (A / D converter) 12 and output to the control device 8.

[0019] The signal acquisition circuit 7 also includes a first variable capacitance element 13a connected between the first input line 10a and a reference potential Vr, and a second variable capacitance element 13b connected between the second input line 10b and the reference potential Vr. In this embodiment, the reference potential Vr is a bias voltage V generated by a bias voltage generation circuit 24 of the control device 8 (described later). ＢＩＡＳ In the present embodiment, as an example, a reference potential line 16 to which the first variable capacitance element 13 a and the second variable capacitance element 13 b are connected and which applies a reference potential Vr is connected to the bias voltage line 14. The bias voltage line 14 is connected to the bias voltage generating circuit 24 to transmit the bias voltage V ＢＩＡＳ This is the supply line.

[0020] Alternatively, the reference potential Vr may be the circuit ground voltage V supplied by the ground voltage supply circuit 23 of the control device 8. ＧＮＤ In this case, for example, the reference potential line 16 may not be connected to the bias voltage line 14, but may be connected to the circuit ground as shown by the dotted line in Fig. 3. The same applies to Fig. 10.

[0021] In this embodiment, the first variable capacitance element 13 a and the second variable capacitance element 13 b are electrically controlled variable capacitance elements whose capacitance is set by an electric signal. The electrically controlled variable capacitance element may be an element in which the distance between electrodes is controlled using, for example, MEMS technology or a piezoelectric element, thereby controlling the capacitance between the electrodes.

[0022] The contact resistance 50a and the first variable capacitance element 13a of the first detection electrode 5a, and the contact resistance 50b and the second variable capacitance element 13b of the second detection electrode 5b each constitute a low-pass filter. In this embodiment, as will be described later, the time constant of the low-pass filter constituted by the contact resistance 50a and the first variable capacitance element 13a and the time constant of the low-pass filter constituted by the contact resistance 50b and the second variable capacitance element 13b are controlled by the capacitances of the first variable capacitance element 13a and the second variable capacitance element 13b, respectively. As a result, in this embodiment, the time constant of the low-pass filter constituted by the contact resistance 50a and the first variable capacitance element 13a and the time constant of the low-pass filter constituted by the contact resistance 50b and the second variable capacitance element 13b are adjusted to control the biosignal V input to the differential amplifier circuit 11. ｅｅｇｐ , V ｅｅｇｎ Common mode noise V ｃｍ Suppress.

[0023] The control device 8 includes a processor 20, a memory 21, a communication device 22, a ground voltage supply circuit 23, a bias voltage generation circuit 24, and a power supply circuit 25. The power supply circuit 25 may include, for example, a battery and a power supply monitoring IC that monitors the output of the battery. The bias voltage generation circuit 24 receives power from the power supply circuit 25 and generates a bias voltage V ＢＩＡＳ The ground voltage supply circuit 23 receives power from the power supply circuit 25 and generates a circuit ground voltage V ＧＮＤ Generates the circuit ground voltage V ＧＮＤ is the bias voltage V ＢＩＡＳ The potential may be different from the bias voltage V ＢＩＡＳ The potential may be the same as that of the

[0024] The communication device 22 includes a transceiver for the biological signal acquisition system 1 to perform wireless or wired communication with the processing device 3. In the present embodiment, the communication device 22 includes, for example, a wireless transceiver for performing wireless communication with the processing device 3 in accordance with the Bluetooth (registered trademark) communication standard.

[0025] The memory 21 is a volatile and / or non-volatile storage device, and may be configured, for example, as a semiconductor memory. The memory 21 stores the program 33 executed by the processor 20 and / or various parameters used in the execution of the processes. The memory 21 may also temporarily store data generated during the execution of the processes.

[0026] The processor 20 is a computer including, for example, a CPU, an MPU, or an MCU. The processor 20 may include a ROM in which a program is written, a RAM for temporarily storing data, etc. The processor 20 includes, as functional elements or units, a signal acquisition unit 30, a noise measurement unit 31, and a setting unit 32.

[0027] These functional elements of the processor 20 are realized, for example, by the processor 20, which is a computer, executing a program 33. The program 33 can be stored in any computer-readable storage medium. Alternatively, all or part of the functional elements of the processor 20 can be configured by hardware, each of which includes one or more electronic circuit components.

[0028] After the capacitances of the first variable capacitance element 13 a and the second variable capacitance element 13 b are set by a setting unit 32 described later, the signal acquiring unit 30 acquires the biosignals acquired from the first detection electrode 5 a and the second detection electrode 5 b and amplified by the differential amplifier circuit 11 as digital data using the ADC 12. The signal acquiring unit 30 transmits the digital data of the acquired biosignals to the processing device 3 via the communication device 22.

[0029] The noise measurement unit 31 and the setting unit 32 cooperate to set the capacitances of the first variable capacitance element 13a and the second variable capacitance element 13b so as to suppress noise contained in the biosignals acquired from the first detection electrode 5a and the second detection electrode 5b prior to acquisition of the biosignals by the signal acquisition unit 30. The setting operation is performed, for example, when the control device 8 receives a measurement start instruction from the processing device 3. In this embodiment, the noise is common-mode noise that is superimposed on the biosignals acquired from the first detection electrode 5a and the second detection electrode 5b and is in phase with each other.

[0030] In the setting operation, the noise measurement unit 31 measures the noise level contained in the amplified biological signal acquired from the differential amplifier circuit 11. The noise level is, for example, the noise power contained in the amplified biological signal. Specifically, the noise measurement unit 31 performs a discrete Fourier transform on the digital data of the output (hereinafter also referred to as the amplified output) of the differential amplifier circuit 11 acquired via the ADC 12, and measures the noise level as the spectrum density of the noise contained in the amplified output in a frequency range of interest. The discrete Fourier transform can be performed, for example, by FFT (fast Fourier transform). Here, the frequency range of interest corresponds to a predetermined frequency range in the present disclosure.

[0031] The frequency range of interest may be, for example, a frequency range including the power supply frequency (50 Hz or 60 Hz) of a commercial power source. Alternatively, if the frequency range of the main environmental noise in the environment in which the biological signal measurement system 2 is used is known, the frequency range of the main environmental noise may be the frequency range of the main environmental noise. The frequency range of interest may be predetermined and stored in the memory 21, or may be specified by the processing device 3.

[0032] The setting unit 32 sets the capacitance of the first variable capacitance element 13 a and the second variable capacitance element 13 b. In this embodiment, in particular, the setting unit 32 sets the capacitance of the first variable capacitance element 13 a and / or the second variable capacitance element 13 b so that the noise level in the frequency range of interest measured by the noise measurement unit 31 is minimized.

[0033] Fig. 4 is an equivalent circuit for explaining common-mode noise input to the differential amplifier circuit 11 of the signal acquisition circuit 7 from the usage environment of the biological signal acquisition system 1. In Fig. 4, a noise source 60 is an equivalent noise source of environmental noise and corresponds to the noise source 53 shown in the biological body LB in Fig. 3. The biological body LB is coupled to the noise source 60 via a coupling capacitance 61 and to the earth ground (or ground potential) via a coupling capacitance 62. The bias voltage line 14 is also coupled to the earth ground via a coupling capacitance 63.

[0034] A first input capacitance 64a on the first input line 10a side of the differential amplifier circuit 11 exists between the first input line 10a and the bias voltage line 14. The capacitance C of the first input capacitance 64a ＩＰ is the capacitance C of the first variable capacitance element 13a. ＶＰ and the parasitic capacitance of the first input line 10a. In addition, a second input capacitance 64b exists between the second input line 10b and the bias voltage line 14. The capacitance C of the second input capacitance 64b ＩＮ is the capacitance C of the second variable capacitance element 13b. ＶＮ and the parasitic capacitance of the second input line 10b.

[0035] In FIG. 4, the environmental noise V ＮＯＩＳＥ The input voltage V of the differential amplifier circuit 11 ＩＮ The common mode rejection ratio (CMRR) of the common mode noise in is given by the following equation (1).

[0036]

[0037] In formula (1), V ＮＥ is a biological noise voltage with respect to the ground potential, and is a noise voltage with respect to the ground potential at the positions where the first detection electrode 5a, the second detection electrode 5b, and the bias electrode 6 contact the living body LB. ＮＣ is the reference potential Vr (V ＢＩＡＳ The voltages Vr and Vr are biological noise voltages with respect to the reference potential Vr at the positions where the first detection electrode 5a and the second detection electrode 5b are in contact with the living body LB. ＮＥare shown, but each V ＮＥ Since the values ​​are almost the same, in equation (1) there is approximately one V ＮＥ Similarly, in Figure 4, two V ＮＣ are shown, but each V ＮＣ Since the values ​​are almost the same, in equation (1) there is approximately one V ＮＣ It is treated as such.

[0038] In addition, in equation (1), ω is the angular frequency of the common-mode noise. For simplicity, hereinafter, angular frequencies indicated using the symbol "ω" will be referred to simply as "frequency" with the "ω" character omitted.

[0039] In equation (1), ω １ is the angular frequency of the low-pass filter formed by the contact resistor 51 and the coupling capacitance 63, which is determined by the resistance value of the contact resistor 51 and the electrostatic capacitance of the coupling capacitance 63. Ｐ is the angular frequency determined by the resistance value of the contact resistor 50a and the capacitance of the first input capacitor 64a of the low-pass filter formed on the first input line 10a by the contact resistor 50a and the first input capacitor 64a. Ｎ is an angular frequency determined by the resistance value of the contact resistor 50b and the capacitance of the second input capacitor 64b of the low-pass filter formed on the second input line 10b by the contact resistor 50b and the second input capacitor 64b.

[0040] where ω Ｐ is expressed by the formula (2). In the formula (2), τ Ｐ is the time constant of the low-pass filter formed by the contact resistance 50a and the first input capacitance 64a. ＰＰ is the parasitic capacitance of the first input line 10a.

[0041]

[0042] Also, ω Ｎ is expressed by the formula (3). In the formula (3), τ Ｎ is the time constant of the low-pass filter formed by the contact resistance 50b and the second input capacitance 64b. ＰＮ is the parasitic capacitance of the second input line 10b.

[0043]

[0044] From the equations (1), (2), and (3), the capacitance C of the first variable capacitance element 13a included in the first input capacitance 64a is ＶＰ and the capacitance C of the second variable capacitance element 13b included in the second input capacitance 64b ＶＮ By adjusting the two time constants τ Ｐ , τ Ｎ By approaching the value of ω Ｐ and ω Ｎ It can be seen that by bringing the values ​​of , , and , closer to each other, the common mode rejection ratio CMRR of the common mode noise can be increased, thereby reducing the common mode noise.

[0045] In this embodiment, specifically, the setting unit 32 sets the capacitance C of the first variable capacitance element 13a so that the noise level in the frequency range of interest measured by the noise measurement unit 31 is minimized. ＶＰ and the capacitance C of the second variable capacitance element 13b ＶＮ By adjusting the common mode rejection ratio (CMRR) of the common mode noise, the common mode noise is maximized (i.e., the common mode noise is minimized).

[0046] For example, the setting unit 32 first calculates the capacitance C ＶＰ is set to the minimum value C of the capacitance variable range of the first variable capacitance element 13a. ＶＰ _min, and the capacitance C of the second variable capacitance element 13b is set to ＶＮ is set to the minimum value C of the capacitance variable range of the second variable capacitance element 13b. ＶＮ _min, and the first variable capacitance element 13a and the second variable capacitance element 13b are set to their initial states.

[0047] In this initial state, the time constant τ Ｐ and τ Ｎ The first is that when the capacitance of either the first variable capacitance element 13a or the second variable capacitance element 13b is increased, ω Ｐ and ω Ｎ The difference between the two is a monotonically increasing pattern. In this case, the initial state is the most Ｐ and ω ＮSecondly, when the capacitance of the other of the first variable capacitance element 13a and the second variable capacitance element 13b is increased, the difference between ω Ｐ and ω Ｎ The difference between the two decreases, and when the capacitance of the other one reaches a certain value, ω Ｐ and ω Ｎ This is a pattern in which the difference between the two can be a minimum of zero.

[0048] Therefore, the setting unit 32 can suppress common-mode noise by, for example, starting from the above-mentioned initial state and adjusting the capacitance of at least one of the first variable capacitance element 13a and the second variable capacitance element 13b so that the noise level measured by the noise measurement unit 31 is minimized.

[0049] 5 and 6 are flowcharts showing the procedure of the processing of the biosignal acquisition method performed by the processor 20 of the control device 8, which is the computer of the biosignal acquisition system 1.

[0050] The processing shown in Figures 5 and 6 begins, for example, when the first detection electrode 5a, the second detection electrode 5b, and the bias electrode 6 are attached so as to contact the skin SK of the living body LB of the subject P, the power of the biological signal acquisition system 1 is turned on, and the control device 8 receives a measurement start instruction from the processing device 3.

[0051] When the process starts, the setting unit 32 first calculates the capacitance C of the first variable capacitance element 13a. ＶＰ is set to the minimum value C of the capacitance variable range of the first variable capacitance element 13a. ＶＰ _min, and the capacitance C of the second variable capacitance element 13b is set to ＶＮ is set to the minimum value C of the capacitance variable range of the second variable capacitance element 13b. ＶＮ Next, the noise measurement unit 31 measures the noise level in the frequency range of interest of the amplified output of the differential amplifier circuit 11 acquired from the ADC 12, and the setting unit 32 stores the measured noise level in the memory 21 as a noise level NLa (S102).

[0052] Next, the setting unit 32 calculates the current capacitance C of the first variable capacitance element 13a. ＶＰ Specifically, the setting unit 32 determines whether the current capacitance C ＶＰ The value obtained by adding ΔCp to the maximum value C of the capacitance variable range of the first variable capacitance element 13a ＶＰ Then, it is determined whether the current capacitance C ＶＰ The value obtained by adding ΔCp to the maximum value C ＶＰ If it does not exceed _max (S104, NO), the setting unit 32 sets the capacitance C of the first variable capacitance element 13a ＶＰ the current capacitance C ＶＰ That is, the capacitance C of the first variable capacitance element 13a is set to a value obtained by adding ΔCp to the capacitance C ＶＰ Next, the noise measurement unit 31 measures the noise level in the target frequency range of the amplified output of the differential amplifier circuit 11 acquired from the ADC 12, and the setting unit 32 stores the measured noise level in the memory 21 as the noise level NLb (S108).

[0053] The setting unit 32 determines whether the noise level NLb is greater than the noise level NLa (S110). ＶＰ It is then determined whether the noise level has increased as a result of increasing the capacitance C of the first variable capacitance element 13a by ΔCp. ＶＰ When the noise level does not increase as a result of increasing the noise level NLb by ΔCp, that is, when the noise level NLb is equal to or lower than the noise level NLa (S110, NO), the setting unit 32 sets the noise level NLb measured by the noise measurement unit 31 in step S108 as the noise level NLa (S112). Specifically, the setting unit 32 overwrites the noise level NLa stored in the memory 21 with the noise level NLb stored in the memory 21. Thereafter, the setting unit 32 returns to step S104 and repeats the process.

[0054] On the other hand, when the noise level NLb is greater than the noise level NLa in step S110 (S110, YES), the setting unit 32 determines whether the capacitance C ＶＰ the current capacitance C ＶＰ On the other hand, in step S104, the current capacitance C ＶＰ The value obtained by adding ΔCp to the maximum value C ＶＰ If it exceeds _max (YES in S104), the setting unit 32 proceeds to step S114.

[0055] 5, for example, in step S106, the capacitance C ＶＰ is the minimum value C ＶＰ After the noise level is increased by ΔCp from the capacitance C_min, when the noise level increases in step S110, the noise level is ＶＰ , the capacitance C of the first variable capacitance element 13a is assumed to increase monotonically with respect to ＶＰ is the minimum value C ＶＰ On the other hand, in step S106, the capacitance C ＶＰ The minimum value C ＶＰ When the noise level is increased from _min by ΔCp, if it is detected in step S110 that the noise level has changed from a decrease to an increase, the capacitance C ＶＰ is returned to the value that minimizes the noise level.

[0056] If the answer to step S104 is YES, that is, if the noise level is less than the capacitance C ＶＰ When the capacitance C ＶＰ When the capacitance C of the first variable capacitance element 13a monotonically decreases without having a minimum value, ＶＰ In step S114, the maximum value C ＶＰ For example, the resistance value R of the contact resistors 50a and 50b is set to the largest value that does not exceed the resistance value R ＣＰ and R ＣＮSince the difference between the time constant τ Ｐ and τ Ｎ If the difference between the contact resistances 50a and 50b cannot be minimized, the determination in step S104 may be YES. In this case, the first detection electrode 5a and / or the second detection electrode 5b may be reattached to the living body LB to reduce the resistance value R ＣＰ and R ＣＮ By making these values ​​equal, the noise level can be made to have a minimum value within the variable range of the capacitance of the first variable capacitance element 13a.

[0057] After executing step S114, the setting unit 32 executes the processes of step S116 and subsequent steps in FIG. 6 to set the capacitance C ＶＮ First, the setting unit 32 sets the noise level NLb measured by the noise measurement unit 31 in step S108 as the noise level NLa (S116). Specifically, the setting unit 32 overwrites the noise level NLa stored in the memory 21 with the noise level NLb stored in the memory 21.

[0058] Next, the setting unit 32 calculates the current capacitance C of the second variable capacitance element 13b. ＶＮ Specifically, the setting unit 32 determines whether the current capacitance C ＶＮ The value obtained by adding ΔCn to the maximum value C of the capacitance variable range of the second variable capacitance element 13b ＶＮ Then, it is determined whether the current capacitance C ＶＮ The value obtained by adding ΔCn to the maximum value C ＶＮ If it does not exceed _max (S118, NO), the setting unit 32 sets the capacitance C of the second variable capacitance element 13b ＶＮ the current capacitance C ＶＮ That is, the capacitance C of the second variable capacitance element 13b is set to a value obtained by adding ΔCn to the capacitance C ＶＮNext, the noise measurement unit 31 measures the noise level in the target frequency range of the amplified output of the differential amplifier circuit 11 acquired from the ADC 12, and the setting unit 32 stores the measured noise level in the memory 21 as the noise level NLb (S122).

[0059] The setting unit 32 determines whether the noise level NLb is greater than the noise level NLa (S124). ＶＮ It is then determined whether the noise level has increased as a result of increasing the capacitance C of the second variable capacitance element 13b by ΔCn. ＶＮ If the noise level does not increase as a result of increasing ΔCn, that is, if the noise level NLb is equal to or lower than the noise level NLa (S124, NO), the setting unit 32 returns to step S116 and repeats the process.

[0060] On the other hand, when the noise level NLb is greater than the noise level NLa in step S124 (S124, YES), the setting unit 32 determines whether the capacitance C ＶＮ the current capacitance C ＶＮ On the other hand, in step S118, the current capacitance C ＶＮ The value obtained by adding ΔCn to the maximum value C ＶＮ If it exceeds _max (YES in S118), the setting unit 32 proceeds to step S126.

[0061] 5, in the process of FIG. 6, the noise level is calculated based on the capacitance C ＶＮ When the capacitance increases monotonically with respect to ＶＮ is the minimum value C ＶＮ _min, and the noise level is set to the capacitance C ＶＮ When the capacitance C ＶＮ is set to a value that minimizes the noise level. As a result, after the process of step S126, the capacitance C of the first variable capacitance element 13a is set to a value that minimizes the noise level. ＶＰ and the capacitance C of the second variable capacitance element 13bＶＮ Both of these are set.

[0062] After step S126, the signal acquisition unit 30 starts acquiring the biosignal using the signal acquisition circuit 7 (S128). After step S126, step S127 may be added to determine whether the noise level NLa is within a range small enough to acquire the biosignal. If step S127 determines that the noise level NLa is not suitable for measuring the biosignal, a notification may be sent indicating that the detection electrodes need to be reattached. Alternatively, if step S127 determines that the noise level NLa is suitable for measuring the biosignal, the process may proceed to step S128 and start acquiring the biosignal. After step S128, the signal acquisition unit 30 determines whether a measurement end instruction has been received from the processing device 3 (S130). If the measurement end instruction has not been received (NO in S130), the signal acquisition unit 30 returns to step S128 and continues acquiring the biosignal. On the other hand, if the measurement end instruction has been received (YES in S130), the signal acquisition unit 30 ends this process.

[0063] 5 and 6, steps S102, S108, and S122 correspond to the noise measurement step in the present disclosure, and steps S114 and S126 correspond to the capacitance setting step in the present disclosure.

[0064] As a modified example, the biosignal acquisition system 1 can execute the processes shown in Figures 7 and 8 instead of the processes shown in Figures 5 and 6. Figures 7 and 8 are flowcharts showing the procedure of a process that is a modified example of the biosignal acquisition method, which is performed by the processor 20 of the control device 8, which is the computer of the biosignal acquisition system 1.

[0065] The processing shown in Figures 7 and 8 begins, for example, when the detection electrode 5 and bias electrode 6 are attached so as to contact the skin SK of the living body LB of the subject P, the power of the biological signal acquisition system 1 is turned on, and the control device 8 receives a measurement start instruction from the processing device 3.

[0066] In the process shown in FIG. 7, the setting unit 32 calculates the capacitance C ＶＮThe minimum value C ＶＮ _min, the capacitance C of the first variable capacitance element 13a ＶＰ The noise level NLc for the capacitance C ＶＰ 8, the setting unit 32 measures the capacitance C of the first variable capacitance element 13a. ＶＰ The minimum value C ＶＰ _min, the capacitance C of the second variable capacitance element 13b ＶＮ The noise level NLd for the capacitance C ＶＮ The measurement is carried out over the entire variable range.

[0067] The setting unit 32 then adjusts the capacitance C of the first variable capacitance element 13a so as to achieve the minimum noise level of the noise levels NLc and NLd. ＶＰ and the capacitance C of the second variable capacitance element 13b ＶＮ Set.

[0068] 7, when the process starts, the setting unit 32 first initializes the index i to 0 (S200). The index i is stored in the array C ＶＰ _m and the noise level NLc are used as an index to an array NLc_m that stores the noise level NLc.

[0069] Next, the setting unit 32 sets the minimum value C of the capacitance variable range of the first variable capacitance element 13a. ＶＰ _min to C ＶＰ _m(i), and the capacitance C of the second variable capacitance element 13b ＶＮ is set to the minimum value C of the capacitance variable range of the second variable capacitance element 13b. ＶＮ Next, the setting unit 32 sets the capacitance C ＶＰ , C ＶＰ _m(i) is set to the value stored therein (S204).

[0070] Next, the noise measurement unit 31 measures the noise level NLc and stores the measurement value in NLc_m(i) (S206). ＶＰ The value obtained by adding the above-mentioned predetermined value ΔCp to the value stored in _m(i) is the maximum value C of the capacitance variable range of the first variable capacitance element 13a.ＶＰ It is then determined whether or not the value exceeds C_max (S104). ＶＰ The value stored in _m(i) plus ΔCp is the maximum value C ＶＰ If the value does not exceed C_max (NO in S208), the setting unit 32 ＶＰ The value stored in _m(i) plus ΔCp is defined as C ＶＰ _m(i+1) (S210). Then, the setting unit 32 increments the value of i by +1 (S212), and returns to step S204 to repeat the process.

[0071] On the other hand, C ＶＰ The value stored in _m(i) plus ΔCp is the maximum value C ＶＰ 8. When the capacitance C_max of the second variable capacitance element 13b is exceeded (YES in S208), the setting unit 32 proceeds to step S214 in FIG. ＶＮ The minimum value C ＶＮ The capacitance C of the first variable capacitance element 13a when set to ＶＰ The noise level NLc for the capacitance C ＶＰ The results of measurements over the entire variable range of ＶＰ _m and stored in the array NLc_m.

[0072] Next, in step S214 of FIG. 8, the setting unit 32 initializes the index j to 0 (S214). The index j is stored in the array C ＶＮ _m and the noise level NLd are used as an index to an array NLd_m that stores the noise level NLd.

[0073] Next, the setting unit 32 calculates the capacitance C of the first variable capacitance element 13a. ＶＰ is set to the minimum value C of the capacitance variable range of the first variable capacitance element 13a. ＶＰ _min, and the minimum value C of the capacitance variable range of the second variable capacitance element 13b is set to ＶＮ _min to array C ＶＮ _m(j) (S216). Next, the setting unit 32 stores the capacitance C ＶＮ , array C ＶＮ_m(j) is set to the value stored in (S218).

[0074] Next, the noise measurement unit 31 measures the noise level NLd and stores the measurement value in the array NLd_m(j) (S220). ＶＮ The value stored in the variable capacitance element 13b_m(j) plus the predetermined value ΔCn is the maximum value C of the variable capacitance range of the second variable capacitance element 13b. ＶＮ It is then determined whether the value exceeds _max (S222). ＶＮ The value stored in _m(j) plus ΔCn is the maximum value C ＶＮ If it does not exceed _max (S222, NO), the setting unit 32 ＶＮ The value stored in _m(j) plus ΔCn is stored in the array C ＶＮ _m(j+1) (S224). Then, the setting unit 32 increments the value of j by +1 (S226), and returns to step S218 to repeat the process.

[0075] On the other hand, array C ＶＮ The value stored in _m(i) plus ΔCn is the maximum value C ＶＮ When it exceeds _max (YES in S222), the setting unit 32 proceeds to step S228. ＶＰ The minimum value C ＶＰ The capacitance C of the second variable capacitance element 13b when set to ＶＮ The noise level NLd for C ＶＮ The results of measurements over the entire variable range of ＶＮ _m and stored in the array NLd_m.

[0076] Next, the setting unit 32 sets the array NLc_m and the array C ＶＰ _m, the noise level NLc is calculated based on the capacitance C ＶＰ Then, it is determined whether the noise level NLc increases monotonically with respect to the capacitance C of the first variable capacitance element 13a (S228). ＶＰWhen the capacitance C of the first variable capacitance element 13a increases monotonically (YES in S228), the setting unit 32 ＶＰ The minimum value C ＶＰ _min (S230). In addition, the setting unit 32 sets the array NLd_m and the array C ＶＮ _m, the capacitance C of the second variable capacitance element 13b ＶＮ is the noise level NLd_m at its minimum. ＶＮ _m (S232).

[0077] Next, the signal acquiring unit 30 starts acquiring the biological signal using the signal acquiring circuit 7 (S238). Thereafter, the signal acquiring unit 30 determines whether or not a measurement end instruction has been received from the processing device 3 (S240). If the measurement end instruction has not been received (S240, NO), the signal acquiring unit 30 returns to step S238 and continues acquiring the biological signal. On the other hand, if the measurement end instruction has been received (S240, YES), the signal acquiring unit 30 ends this process.

[0078] On the other hand, in step S228, the noise level NLc is equal to the capacitance C ＶＰ When the capacitance C of the second variable capacitance element 13b does not monotonically increase (S228, NO), the setting unit 32 ＶＮ The minimum value C ＶＮ _min (S234). ＶＰ _m, the capacitance C of the first variable capacitance element 13a ＶＰ is the noise level NLc at its minimum. ＶＰ _m (S236), and the process proceeds to step S238.

[0079] In this way, by placing the first variable capacitance element 13a and the second variable capacitance element 13b between the differential line from the detection electrode 5 and the reference potential Vr and adjusting their capacitances, the influence of common-mode noise can be reduced, thereby obtaining a low-noise signal without reducing the signal level from the living body. Furthermore, since elements such as resistors are not placed in series with the signal line, the generation of thermal noise due to resistance can be prevented. Furthermore, since an increase in the resistance value of the signal line makes it more susceptible to external noise such as radio noise and commercial power noise, this embodiment, in which resistors or the like are not placed in series with the signal line, allows for the acquisition of minute signals of a few microvolts to a few millivolts, such as electroencephalograms, without reducing the signal level from the living body.

[0080] [2. Second embodiment] Next, a second embodiment of the present invention will be described. [2.1. Configuration of biosignal acquisition system] Figures 9 and 10 are diagrams showing the configuration of a biosignal acquisition system 1A according to a second embodiment of the present invention, and correspond to Figures 2 and 3 showing the biosignal acquisition system 1 according to the first embodiment. In Figures 9 and 10, the same components as those in the biosignal acquisition system 1 shown in Figures 2 and 3 are designated by the same reference numerals as in Figures 2 and 3, and the above description of each component is applicable.

[0081] The biological signal acquiring system 1A can be used in the biological signal measuring system 2 instead of the biological signal acquiring system 1.

[0082] The biosignal acquisition system 1A differs from the biosignal acquisition system 1 in that it includes a signal acquisition circuit 7A and a control device 8A instead of the signal acquisition circuit 7 and the control device 8. The signal acquisition circuit 7A has a configuration similar to that of the signal acquisition circuit 7, but differs from the signal acquisition circuit 7 in that it further includes a resistance measurement circuit 15. The resistance measurement circuit 15 measures the resistance values ​​R of the contact resistances 50a and 50b between the first detection electrode 5a and the second detection electrode 5b, respectively, and the living body LB. ＣＰ and R ＣＮThe resistance measurement circuit 15 is a circuit for measuring the voltage across the voltage divider resistor. The resistance measurement circuit 15 may include, for example, a current source, a switch, and the like that operate in response to instructions from the control device 8A, and a voltage divider resistor (neither of which is shown). In response to instructions from the control device 8A, the resistance measurement circuit 15 passes a measurement current along various current paths including the first detection electrode 5a, the second detection electrode 5b, the living body LB, and the bias electrode 6, and transmits data on the voltage across the voltage divider resistor to the control device 8A.

[0083] The control device 8A has a configuration similar to that of the control device 8, but differs in that it includes a processor 20A instead of the processor 20, and stores a program 33A in the memory 21 instead of the program 33. The processor 20A has a configuration similar to that of the processor 20, but differs in that it includes a resistance measurement unit 40 and a setting unit 32A instead of the noise measurement unit 31 and the setting unit 32.

[0084] The signal acquisition unit 30, the resistance measurement unit 40, and the setting unit 32A are functional elements realized by, for example, the processor 20A, which is a computer, executing the program 33A. The program 33A can be stored in any computer-readable storage medium. Alternatively, all or part of the functional elements of the processor 20A can be configured by hardware including one or more electronic circuit components.

[0085] The resistance measurement unit 40 controls the resistance measurement circuit 15 to measure the resistance value R of the contact resistance 50a between the first detection electrode 5a and the living body LB. ＣＰ , and the resistance value R of the contact resistance 50b between the second detection electrode 5b and the living body LB ＣＮ Here, the contact resistance 50a between the first detection electrode 5a and the living body LB corresponds to the first contact resistance in the present disclosure. Also, the contact resistance 50b between the second detection electrode 5b and the living body LB corresponds to the second contact resistance in the present disclosure.

[0086] The setting unit 32A has the same configuration as the setting unit 32, but has a capacitance C ＶＰ or the capacitance C of the second variable capacitance element 13b ＶＮis set to a value calculated using the resistance measurement value of the contact resistor 50a or 50b, the noise level of the common mode noise at the input of the differential amplifier circuit 11 is suppressed.

[0087] Specifically, for example, the setting unit 32A calculates the resistance value R of the contact resistor 50a as shown in equation (4): ＣＰ and the minimum value C of the capacitance variable range of the first variable capacitance element 13a ＶＰ The time constant τ, which is the product of ＰＭ , and the resistance value R of the contact resistor 50b ＣＮ and the minimum value C of the capacitance variable range of the second variable capacitance element 13b ＶＮ The time constant τ, which is the product of ＮＭ Calculate.

[0088]

[0089] Then, the setting unit 32A sets the time constant τ ＰＭ and τ ＮＭ The capacitance C of the first variable capacitance element 13a is ＶＰ and the capacitance C of the second variable capacitance element 13b ＶＮ is set as in equation (5) or equation (6).

[0090]

[0091] This allows τ ＰＭ and τ ＮＭ Adjust the smaller of these to the larger value, ω Ｐ and ω Ｎ This reduces the difference between the two and suppresses the common mode noise level.

[0092] 2.2 Operation of the Biosignal Acquisition System Next, a description will be given of the operation of the biosignal acquisition system 1A. Fig. 11 is a flowchart showing the procedure of the processing of the biosignal acquisition method performed by the processor 20A of the control device 8A, which is the computer of the biosignal acquisition system 1A.

[0093] The process shown in Figure 11 begins, for example, when the first detection electrode 5a, the second detection electrode 5b, and the bias electrode 6 are attached so as to contact the skin SK of the living body LB of the subject P, the power of the biological signal acquisition system 1A is turned on, and the control device 8A receives a measurement start instruction from the processing device 3.

[0094] When the process starts, first, the resistance measurement unit 40 controls the resistance measurement circuit 15 to measure the resistance value R of the contact resistance 50a between the first detection electrode 5a and the living body LB. ＣＰ and the resistance value R of the contact resistance 50b between the second detection electrode 5b and the living body LB. ＣＮ Next, the setting unit 32A measures the resistance value R of the contact resistor 50a. ＣＰ and the minimum value C of the capacitance variable range of the first variable capacitance element 13a ＶＰ Product τ with _min ＰＭ , is calculated (S302). ＣＮ and the minimum value C of the capacitance variable range of the second variable capacitance element 13b ＶＮ Product τ with _min ＮＭ is calculated (S304).

[0095] Next, the setting unit 32A sets τ ＰＭ is τ ＮＭ Then, it is determined whether τ is smaller than τ (S306). ＰＭ is τ ＮＭ If it is smaller (S306, YES), the setting unit 32A calculates the capacitance C of the first variable capacitance element 13a according to the above-mentioned equation (5). ＶＰ and the capacitance C of the second variable capacitance element 13b is set. ＶＮ The minimum value C ＶＮ _min (S308).

[0096] Next, the signal acquiring unit 30 starts acquiring the biological signal using the signal acquiring circuit 7A (S312). Thereafter, the signal acquiring unit 30 determines whether or not a measurement end instruction has been received from the processing device 3 (S314). If the measurement end instruction has not been received (S314, NO), the signal acquiring unit 30 returns to step S312 and continues acquiring the biological signal. On the other hand, if the measurement end instruction has been received (S314, YES), the signal acquiring unit 30 ends this process.

[0097] On the other hand, in step S306, τ ＰＭ is τ ＮＭ If it is equal to or greater than this (S306, NO), the setting unit 32A calculates the capacitance C of the second variable capacitance element 13b according to the above-mentioned equation (6). ＶＮ and the capacitance C of the first variable capacitance element 13a is set. ＶＰ The minimum value C ＶＰ _min (S310). After that, the setting unit 32A moves the process to step S312.

[0098] 11, step S300 corresponds to the resistance measurement step in the present disclosure, and steps S308 and S310 correspond to the capacitance setting step in the present disclosure.

[0099] 3. Other Embodiments

[0100] The biosignal acquisition system 1 of the first embodiment described above includes one pair of detection electrodes 5, but may include multiple pairs of detection electrodes 5. In this case, the biosignal acquisition system 1 includes one signal acquisition circuit 7 for each pair of detection electrodes 5, and one control device 8 controls the capacitance C of the first variable capacitance element 13 a of each signal acquisition circuit 7. ＶＰ and the capacitance C of the second variable capacitance element 13b ＶＮ The control device 8 can acquire biosignals from the corresponding sets of detection electrodes 5 via the respective signal acquisition circuits 7. The same applies to the biosignal acquisition system 1A of the second embodiment.

[0101] The setting unit 32A of the biosignal acquisition system 1A of the second embodiment calculates the capacitance C of the first variable capacitance element 13a according to the formulas (5) and (6). ＶＰ and the capacitance C of the second variable capacitance element 13b ＶＮ However, instead of the equations (5) and (6), an equation in which terms indicating the frequency characteristics of the input resistances and the contributions of the parasitic capacitances of the first input line 10 a and the second input line 10 b of the differential amplifier circuit 11 are added to the equations (5) and (6) may be used.

[0102] Although the biosignal acquisition system 1, 1A is realized as a single device, the functional elements may be divided into multiple devices. For example, the control device 8, 8A may be provided in another device (e.g., the processing device 3). In this case, the entire biosignal acquisition system 1, 1A, including the parts of the biosignal acquisition system 1, 1A excluding the control device 8, 8A and the control device 8, 8A provided in the other device, can be considered to constitute the biosignal acquisition system 1, 1A.

[0103] Furthermore, although the biosignal acquisition system 1, 1A is an ear-hook type in the above-described embodiment, it may be any type of device equipped with electrodes that can come into contact with a living body, such as a hat type that is worn on the head.

[0104] In the above-described embodiment, the biosignal acquisition systems 1 and 1A are applied to the biosignal measurement system 2, which is an electroencephalogram (EEG) measurement system, but they may be applied to any biosignal measurement system that uses multiple electrodes that can come into contact with a living body. Such a biosignal measurement system may be an electrocardiogram measurement system, an electromyogram measurement system, or the like.

[0105] In the biosignal acquisition systems 1 and 1A, the capacitance of each of the first variable capacitance element 13a and the second variable capacitance element 13b (hereinafter collectively referred to as the variable capacitance element 13) is increased at regular intervals. However, the capacitance may be first changed at wide intervals to set a range in which the noise level in the frequency range of interest is minimized, and then the capacitance of the variable capacitance element 13 may be changed at small intervals within the set range to set the capacitance of the variable capacitance element 13 so as to minimize the noise level in the frequency range of interest. This two-stage processing allows the variable capacitance element 13 to be optimized accurately in a short time. Based on the same idea, the interval at which the capacitance of the variable capacitance element 13 is changed may be divided into three stages.

[0106] The present invention is not limited to the configurations of the above-described embodiments, and can be implemented in various forms without departing from the spirit of the invention.

[0107] 4. Configurations Supported by the Above-described Embodiments The above-described embodiments and modifications support the following configurations.

[0108] (Configuration 1) A biosignal acquisition system comprising: first and second detection electrodes contactable with a living body; a differential amplifier circuit having a first input line to which the first detection electrodes are connected and a second input line to which the second detection electrodes are connected; a first variable capacitance element connected between the first input line and a reference potential; and a second variable capacitance element connected between the second input line and the reference potential. According to Configuration 1, by adjusting the capacitance of the first variable capacitance element and the second variable capacitance element, common-mode noise of biosignals acquired from a plurality of detection electrodes in contact with a living body can be reduced without increasing other types of noise components such as thermal noise, thereby achieving good detection of biosignals.

[0109] (Configuration 2) The biosignal acquisition system according to Configuration 1, wherein the capacitance of the first variable capacitance element and the capacitance of the second variable capacitance element are set to values ​​that minimize a noise level in a predetermined frequency range included in the output of the differential amplifier circuit within a variable range of the capacitance of the first variable capacitance element and the variable range of the capacitance of the second variable capacitance element, respectively. According to Configuration 2, by adjusting the capacitances of the first variable capacitance element and the second variable capacitance element, it is possible to minimize common-mode noise in the biosignal within the variable range of the capacitance of the first variable capacitance element and the second variable capacitance element.

[0110] (Configuration 3) The biosignal acquisition system according to Configuration 1 or 2, wherein the first variable capacitance element and the second variable capacitance element are electrically controlled variable capacitance elements whose capacitances are set by an electric signal, and further comprising a setting unit that sets the capacitances of the first variable capacitance element and the second variable capacitance element. According to Configuration 3, the capacitances of the first variable capacitance element and the second variable capacitance element can be automatically adjusted by an electric signal, thereby reducing common-mode noise in the biosignal.

[0111] (Configuration 4) The biological signal acquisition system according to Configuration 3, further comprising a noise measurement unit that measures a noise level in a predetermined frequency range included in the output of the differential amplifier circuit, and the setting unit sets the capacitances of the first variable capacitance element and the second variable capacitance element so as to minimize the noise level in the predetermined frequency range. According to Configuration 4, the capacitances of the first variable capacitance element and the second variable capacitance element can be automatically adjusted so that the noise level included in the output of the differential amplifier circuit is minimized at a frequency at which common-mode noise is generated.

[0112] (Configuration 5) The biological signal acquisition system according to claim 4, wherein the setting unit measures a noise level in the predetermined frequency range while changing the capacitance of at least one of the first variable capacitance element and the second variable capacitance element at regular intervals, sets a capacitance range of the at least one variable capacitance element in which the noise level in the predetermined frequency range is minimized, measures the noise level in the predetermined frequency range while changing the capacitance of the at least one variable capacitance element at intervals smaller than the regular intervals within the set capacitance range, and sets the capacitance of the at least one variable capacitance element so as to minimize the noise level in the predetermined frequency range. According to Configuration 5, the capacitance of the first variable capacitance element and / or the second variable capacitance element can be set accurately in a short time so as to minimize the noise level in the predetermined frequency range.

[0113] (Configuration 6) The biosignal acquisition system according to Configuration 3, further comprising: a resistance measurement circuit for measuring the contact resistance of each of the first detection electrode and the second detection electrode with the living body; and a resistance measurement unit for controlling the resistance measurement circuit to measure a first contact resistance between the first detection electrode and the living body and a second contact resistance between the second detection electrode and the living body, wherein the setting unit sets the capacitances of the first variable capacitance element and the second variable capacitance element to values ​​calculated using measured values ​​of the first contact resistance and the second contact resistance. According to Configuration 6, the capacitances of the first variable capacitance element and the second variable capacitance element are determined from the values ​​of the contact resistance between the detection electrode and the living body without measuring a noise level, thereby reducing common-mode noise in the biosignal without using complex processing.

[0114] (Configuration 7) A biosignal acquisition method executed by a computer in a biosignal acquisition system including a differential amplifier circuit having a first input line to which a first detection electrode contactable with a living body is connected and a second input line to which a second detection electrode contactable with the living body is connected, and a first variable capacitance element connected between the first input line and a reference potential and a second variable capacitance element connected between the second input line and the reference potential, the biosignal acquisition method comprising: a noise measurement step of measuring a noise level in a predetermined frequency range included in an output of the differential amplifier circuit; and a capacitance setting step of setting the capacitance of the first variable capacitance element and the second variable capacitance element so as to minimize the noise level in the predetermined frequency range. The biosignal acquisition method of Configuration 7 achieves the same effects as Configuration 4.

[0115] (Configuration 8) A biosignal acquisition method executed by a computer in a biosignal acquisition system including a differential amplifier circuit having a first input line connected to a first detection electrode contactable with a living body and a second input line connected to a second detection electrode contactable with the living body, a first variable capacitance element connected between the first input line and a reference potential and a second variable capacitance element connected between the second input line and the reference potential, and a resistance measurement circuit for measuring the contact resistance of the first detection electrode and the living body, respectively, the biosignal acquisition method comprising: a resistance measurement step of measuring a first contact resistance between the first detection electrode and the living body and a second contact resistance between the second detection electrode and the living body using the resistance measurement circuit; and a capacitance setting step of setting the electrostatic capacitance of the first variable capacitance element and the second variable capacitance element to values ​​calculated using measured values ​​of the first contact resistance and the second contact resistance. The biosignal acquisition method of Configuration 8 achieves the same effects as Configuration 5.

[0116] REFERENCE SIGNS LIST 1...biological signal acquisition system, 2...biological signal measurement system, 3...processing device, 4...wearing device, 5...detection electrode, 5a...first detection electrode, 5b...second detection electrode, 6...bias electrode, 7, 7A...signal acquisition circuit, 8, 8A...control device, 9...casing, 10a...first input line, 10b...second input line, 11...differential amplifier circuit, 12...ADC, 13a...first variable capacitance element, 13b...second variable capacitance element, 14...bias voltage line, 15...resistance measurement circuit, 16...reference potential line 16, 20, 20A...processor, 21...memory ri, 22...communication device, 23...ground voltage supply circuit, 24...bias voltage generation circuit, 25...power supply circuit, 30...signal acquisition unit, 31...noise measurement unit, 32, 32A...setting unit, 33, 33A...program, 40...resistance measurement unit, 50a...contact resistance (first contact resistance), 50b...contact resistance (second contact resistance), 51...contact resistance, 52a...first signal source, 52b...second signal source, 53, 60...noise source, 61, 62, 63...coupling capacitance, 64a...first input capacitance, 64b...second input capacitance, LB...living body, P...subject, SK...skin.

Claims

1. A biosignal acquisition system comprising: a first detection electrode and a second detection electrode that can be brought into contact with a living body; a differential amplifier circuit having a first input line to which the first detection electrode is connected and a second input line to which the second detection electrode is connected; a first variable capacitance element connected between the first input line and a reference potential; and a second variable capacitance element connected between the second input line and the reference potential.

2. The biosignal acquisition system according to claim 1, wherein the capacitance of the first variable capacitance element and the capacitance of the second variable capacitance element are set to values ​​that minimize the noise level in a predetermined frequency range included in the output of the differential amplifier circuit within the variable range of the capacitance of the first variable capacitance element and the variable range of the capacitance of the second variable capacitance element, respectively.

3. The biosignal acquisition system according to claim 1 or 2, wherein the first variable capacitance element and the second variable capacitance element are electrically controlled variable capacitance elements whose capacitance is set by an electrical signal, and further comprising a setting unit that sets the capacitance of the first variable capacitance element and the second variable capacitance element.

4. The biosignal acquisition system according to claim 3, further comprising a noise measurement unit that measures the noise level in a predetermined frequency range contained in the output of the differential amplifier circuit, and the setting unit sets the capacitance of the first variable capacitance element and the second variable capacitance element so as to minimize the noise level in the predetermined frequency range.

5. The biological signal acquisition system of claim 4, wherein the setting unit measures the noise level in the specified frequency range while changing the capacitance of at least one of the first variable capacitance element and the second variable capacitance element at regular intervals, and sets a capacitance range of the at least one variable capacitance element in which the noise level in the specified frequency range is minimized; and measures the noise level in the specified frequency range while changing the capacitance of the at least one variable capacitance element at intervals smaller than the regular intervals within the set capacitance range, and sets the capacitance of the at least one variable capacitance element so that the noise level in the specified frequency range is minimized.

6. A biosignal acquisition system as described in claim 3, comprising: a resistance measurement circuit for measuring the contact resistance of each of the first detection electrode and the second detection electrode with the living body; and a resistance measurement unit that controls the resistance measurement circuit to measure the first contact resistance between the first detection electrode and the living body and the second contact resistance between the second detection electrode and the living body, wherein the setting unit sets the capacitance of the first variable capacitance element and the second variable capacitance element to a value calculated using the measured values ​​of the first contact resistance and the second contact resistance.

7. A biosignal acquisition method executed by a computer in a biosignal acquisition system comprising: a differential amplifier circuit having a first input line to which a first detection electrode contactable with a living body is connected and a second input line to which a second detection electrode contactable with the living body is connected; a first variable capacitance element connected between the first input line and a reference potential; and a second variable capacitance element connected between the second input line and the reference potential, the biosignal acquisition method comprising: a noise measurement step of measuring the noise level in a predetermined frequency range included in the output of the differential amplifier circuit; and a capacitance setting step of setting the capacitance of the first variable capacitance element and the second variable capacitance element so that the noise level in the predetermined frequency range is minimized.

8. A biosignal acquisition method executed by a computer in a biosignal acquisition system comprising: a differential amplifier circuit having a first input line to which a first detection electrode contactable with a living body is connected and a second input line to which a second detection electrode contactable with the living body is connected; a first variable capacitance element connected between the first input line and a reference potential and a second variable capacitance element connected between the second input line and the reference potential; and a resistance measurement circuit for measuring the contact resistance of each of the first detection electrode and the second detection electrode with the living body, the biosignal acquisition method comprising: a resistance measurement step of measuring a first contact resistance between the first detection electrode and the living body and a second contact resistance between the second detection electrode and the living body using the resistance measurement circuit; and a capacitance setting step of setting the electrostatic capacitance of the first variable capacitance element and the second variable capacitance element to values ​​calculated using measured values ​​of the first contact resistance and the second contact resistance.

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