Biological signal measurement system

Abstract

To provide a biological signal measurement system capable of both suppressing attenuation of a biological signal and reducing an output offset voltage.SOLUTION: A capacitance amplifier circuit 3 amplifies the coupling capacitances C1 and CGC between a human body and electrodes 21 and 22. The inverting input and output of an amplifier 31 are connected, and the non-inverting input is connected to the electrode 21. Resistors R1 and R2 are connected in series between the non-inverting input and output of the amplifier 31. An output terminal T1 is connected to the connection point of the resistors R1 and R2, and is connected to the electrode 21 via the resistor R1. The output terminal T2 is connected to the electrode 22. A load resistor RL is connected between the output terminal T1 and the output terminal T2. A capacitor C3 is connected in series with the resistor R1 between the output of the amplifier 31 and the resistor R1 and the output terminal T1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biological signal measurement system. [Background technology]

[0002] BACKGROUND ART Conventionally, a biosignal measurement system has been proposed in which a person lies on a sheet provided with electrodes, and biosignals are input and measured from the electrodes (Patent Documents 1 and 2).

[0003] In the biosignal measurement system described above, the human body and electrodes are capacitively coupled via an insulator such as clothing or a sheet. The biosignal, which is an alternating current, is transmitted to the electrodes via this capacitance. However, the coupling capacitance between the human body and the electrodes is small, resulting in a high coupling impedance. Therefore, when the coupling impedance is greater than the input impedance of the biosignal processing circuit connected downstream of the electrodes, the biosignal may be attenuated below the noise level and input to the biosignal processing circuit, making it impossible to measure the biosignal accurately.

[0004] Therefore, a capacitance amplifier circuit 300 shown in Fig. 4 has been devised, which artificially increases the coupling capacitance and reduces the coupling impedance. The capacitance amplifier circuit 300 described above includes an amplifier 31, resistors R1 and R2, and a load resistor R L It is equipped with the following.

[0005] 4, by setting the resistance value αR0 of the resistor R1 to α times (α>1) the resistance value R0 of the resistor R2, the coupling capacitance can be multiplied by 1 / (α+1) to reduce the coupling impedance. However, in the capacitance amplifier circuit 300 shown in FIG. 4, the bias current of the amplifier 31 is multiplied by (α+1) to reduce the load resistance R L This causes a problem of high output offset voltage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-82938 [Patent Document 2] Special Publication No. 2005-511174 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a biological signal measurement system that can suppress attenuation of biological signals and reduce output offset voltage at the same time. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the biosignal measuring system according to the present invention has the following features. a first electrode and a second electrode that are capacitively coupled to a human body; a biosignal processing circuit that processes the biosignals of the human body input from the first electrode and the second electrode; a capacitance amplifier circuit provided between the first electrode, the second electrode and the biological signal processing circuit, The capacitance amplifier circuit includes: an amplifier having an inverting input connected to an output and a non-inverting input connected to the first electrode; a first resistor and a second resistor connected in series between the non-inverting input and the output of the amplifier; a first output terminal connected to a connection point of the first resistor and the second resistor and connected to the first electrode via the first resistor; a second output terminal connected to the second electrode; a load connected between the first output terminal and the second output terminal; a capacitor connected in series with the second resistor between the output of the amplifier and the first resistor and the first output terminal; It is a biosignal measurement system. [Effects of the Invention]

[0009] The biological signal measuring system according to the present invention has the effect of being able to suppress attenuation of the biological signal and reduce the output offset voltage at the same time.

[0010] The present invention has been briefly described above. The details of the present invention will become clearer by reading the following detailed description of the invention (hereinafter referred to as "embodiments") with reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a circuit diagram showing an embodiment of a biological signal measuring system of the present invention. [Figure 2] FIG. 2 is an explanatory diagram for explaining a method for measuring an electrocardiogram using the sheet-type electrode shown in FIG. [Figure 3] FIG. 3 is a diagram showing an equivalent circuit from a signal source (heart) of a biosignal to the electrodes shown in FIG. 1, and the capacitance amplifier circuit shown in FIG. [Figure 4] FIG. 4 is a circuit diagram showing an example of a conventional capacitance amplifier circuit. DETAILED DESCRIPTION OF THE INVENTION

[0012] Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0013] The biosignal measurement system 1 shown in Fig. 1 is a system for measuring biosignals generated from the human body. Examples of biosignals include an electrocardiogram, which is an electrical signal generated by the contraction and relaxation of cardiac muscles, an electromyogram, which is an electrical signal generated by muscle contraction, and an electroencephalogram, which is an electrical signal generated by nerve cells in the brain. In this embodiment, an example of measuring an electrocardiogram as a biosignal will be described.

[0014] As shown in the figure, the biosignal measurement system 1 includes a sheet-type electrode 2, a capacitance amplification circuit 3, and a biosignal processing circuit 4. As shown in Fig. 2, the sheet-type electrode 2 includes an insulating sheet 20, and electrodes 21 (first electrode) and 22 (second electrode) provided on the sheet 20, with the side with electrodes 21 and 22 serving as the backside. The biosignal measurement system 1 of this embodiment measures an electrocardiogram while a person lies on the sheet-type electrode 2 placed with the backside facing downwards. The electrodes 21 and 22 are capacitively coupled to the human body 10 via the sheet 20 or clothing 11, and are connected to both ends of a signal source 12 that generates a biosignal (the heart in the case of an electrocardiogram).

[0015] Next, an equivalent circuit from the signal source 12 to the electrodes 21 and 22 will be described with reference to Fig. 3. Since the electrodes 21 and 22 are capacitively coupled to the human body 10, there are a coupling capacitance C1, a resistance r1, and a coupling capacitance C GC and resistance r GC The coupling impedance Z C1 ,Z CG Also, the coupling impedance Z C1 Between the signal source 12 and the heart muscle, resistances rs such as internal resistance of the human body and skin resistance occur.

[0016] The above-mentioned coupling capacitances C1 and C GC is small, so the coupling impedance Z C1 ,Z CG This coupling impedance Z C1 ,Z GC >>Under certain conditions of the input impedance of the biological signal processing circuit 4, the biological signal may be attenuated to below the noise level and input to the biological signal processing circuit 4. In this embodiment, in order to suppress the attenuation of the biological signal, a capacitance amplifier circuit 3 is provided between the electrodes 21, 22 and the biological signal processing circuit 4. The biological signal processing circuit 4 is a circuit that performs processing such as amplifying the biological signal.

[0017] The capacitance amplifier circuit 3 includes coupling capacitances C1 and C GC By artificially increasing the coupling impedance Z C1,Z CG The capacitance amplifier circuit 3 is a circuit that reduces the capacitance of the amplifier 31, resistors R1 and R2, output terminals T1 and T2, and a load resistor R L (load) and a capacitor C3. The inverting input and output of the amplifier 31 are connected, and the non-inverting input is connected to the electrode 21. Resistors R1 and R2 are connected in series between the non-inverting input and output of the amplifier 31.

[0018] The output terminal T1 is connected to the connection point of the resistors R1 and R2, and is connected to the electrode 21 via the resistor R1. The output terminal T2 is connected to the electrode 22 and also to a ground potential (not shown). L is connected between the output terminal T1 and the output terminal T2. The capacitor C3 is connected in series with the resistor R2 between the output of the amplifier 31 and the connection point of the resistor R1 and the output terminal T1. In this embodiment, the capacitor C3 is connected between the resistor R2 and the output of the amplifier 31.

[0019] Now, the coupling impedance Z C1 ,Z GC , resistance R1, R2, load resistance R L , the current flowing through the resistance of resistor rs is I1, I GC , I 21 ,I 22 , I L , Irs, and the voltage of the biosignal is Es. If the bias current Ib of the amplifier 31 is ignored, when the resistance value αR0 of the resistor R1 is set to α times the resistance value R0 of the resistor R2, the coupling impedance Z C1 ,Z CG , resistance R1, resistance rs has an equal AC current Iac (i.e. I1 = I GC =I 21 =Irs=Iac) flows through resistor R2, and a current α times the current Iac (i.e., I 22 = α·Iac) flows through the load resistance R L A current (α+1) times the AC current Iac flows through the resistor.

[0020] According to Kirchhoff's law, the AC current Iac is expressed by the following equation (1).

[0021]

number

[0022] The output voltage Vo of the capacitance amplifier circuit 3 is expressed by the following equation (2).

[0023]

number

[0024] R0< <R L In this case, the output voltage Vo is expressed by the following equation (3).

[0025]

number

[0026] As is clear from equation (3), the capacitance amplifier circuit 3 has coupling capacitances C1 and C GC Multiply by (α+1) to get the coupling impedance Z C1 ,Z CG can be multiplied by 1 / (α+1), which can suppress the attenuation of biological signals.

[0027] According to this embodiment, a capacitor C3 is provided between the resistor R2 and the output of the amplifier 31. A DC bias current Ib flows through the amplifier 31. Therefore, the current I 21 is the sum of the AC current Iac and the bias current Ib (I 21 If there is no capacitor C3, the current I 22 is the current (Iac+Ib) flowing through resistor R1 multiplied by α (I 22 = α (Iac + Ib)) Load resistance R L The current I L is the current I flowing through resistor R1 21 = Iac+Ib (α+1) times (I L =(α+1)·(Iac+Ib)), and the output voltage Vo is Ib(α+1)×R L An offset voltage of

[0028] In this embodiment, the DC component (bias current Ib) is cut by the capacitor C3. L The current I L is expressed by the following equation (4). I L =(α+1)·Iac+Ib …(4)

[0029] That is, the load resistance R L The current I L In this case, only the AC signal Iac is multiplied by (α+1), and the bias current Ib, which is a DC component, is not multiplied by (α+1). This makes it possible to reduce the output offset voltage of the output voltage Vo. In other words, the capacitance amplifier circuit 3 of this embodiment can suppress the attenuation of the biological signal and reduce the output offset voltage at the same time.

[0030] The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, etc. Furthermore, the material, shape, size, number, location, etc. of each component in the above-described embodiments are arbitrary and not limited as long as they can achieve the present invention.

[0031] In the above-described embodiment, the capacitor C3 is connected between the output of the amplifier 31 and the resistor R2, but this is not limiting. The capacitor C3 may be connected between the output of the amplifier 31 and the connection point between the resistor R1 and the output terminal T1, or may be connected between the resistor R2 and the connection point between the output terminal T1 and the resistor R1.

[0032] According to the above-described embodiment, the load resistor R L However, the load is not limited to this, and a capacitor, a coil, or the like may be used as the load. [Explanation of symbols]

[0033] 1. Biosignal measurement system 3. Capacitance amplifier circuit 4. Biosignal processing circuit 21 electrode (first electrode) 22 electrode (second electrode) 31 Amplifier C3 capacitor R1 Resistor (First Resistor) R2 resistor (second resistor) T1 output terminal (first output terminal) T2 output terminal (second output terminal) R L Load resistance (load)

Claims

[Claim 1] a first electrode and a second electrode that are capacitively coupled to a human body; a biosignal processing circuit that processes biosignals of the human body input from the first electrode and the second electrode; a capacitance amplifier circuit provided between the first electrode, the second electrode and the biological signal processing circuit, The capacitance amplifier circuit includes: an amplifier having an inverting input connected to an output and a non-inverting input connected to the first electrode; a first resistor and a second resistor connected in series between the non-inverting input and the output of the amplifier; a first output terminal connected to a connection point of the first resistor and the second resistor and connected to the first electrode via the first resistor; a second output terminal connected to the second electrode; a load connected between the first output terminal and the second output terminal; a capacitor connected in series with the second resistor between the output of the amplifier and the first resistor and the first output terminal; Biosignal measurement system.

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