JP2012055588A - Bioelectric signal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bioelectric signal detector which removes noise from a bioelectric signal, while making a dynamic range small.SOLUTION: The bioelectric signal detector includes a plurality of detecting means 100 (such as 100a, 100b, 100c) which include electrodes E (such as ch1, GND, REF) detecting electric signals generated in a user and amplification means 101 (such as 101c) for amplifying the electric signals detected by the electrodes, and one or a plurality of differential amplification means 110 (such as 110a) which differentially amplify two of signals output from the detecting means 100. The amplification means 101 have input impedance higher than contact impedance of the user with the electrodes and are provided between the electrodes E and the differential amplification means 110.

Description

  The present invention relates to a bioelectric signal detection device.

  Conventionally, human brain waves and myoelectricity are detected. For example, an apparatus for operating a computer based on an electrical signal obtained from an electrode brought into contact with a human head (hereinafter referred to as a bioelectric signal) is known (Patent Document 1). Also, a method (Patent Document 2) for measuring the user's concentration based on the detected bioelectric signal is known.

JP 2002-166050 A Special table 2002-503505 gazette

  In the above-described technique, various noises are generated in the user's body, and thus noise components must be removed from the bioelectric signal. Although it is possible to remove noise by applying a filtering process that removes a predetermined frequency component to the bioelectric signal, the noise component has a larger amplitude than the signal component due to the user's biological activity, and thus has a high dynamic range and high cost. Circuit is required.

  The present invention has been made in view of the above problems, and an object thereof is to provide a bioelectric signal detection device capable of removing noise from a bioelectric signal while reducing the dynamic range. That is.

  In order to solve the above problems, a bioelectric signal detection device according to the present invention includes a plurality of electrodes that detect an electric signal generated by a user, and amplification means that amplifies the electric signal detected by the electrode. Detecting means, and one or a plurality of differential amplifying means for differentially amplifying two of the signals output from the plurality of detecting means, wherein the amplifying means comprises a contact impedance of the user and the electrode It has a higher input impedance and is provided between the electrode and the differential amplification means.

  According to the present invention, it is possible to remove noise from a bioelectric signal while reducing the dynamic range.

  In the aspect of the invention, the amplifying unit may be provided at a position where a distance between the electrode and the amplifying unit is shorter than a distance between the amplifying unit and the differential amplifying unit.

In one aspect of the present invention, the bioelectric signal detection device includes an A / D converter for converting an output signal of the differential amplification means into a digital signal, and the plurality of detection means includes the first detection means, First detection means including a first electrode and first amplification means, and second detection means including a second electrode and second amplification means, and an input voltage range of the A / D converter Is V _{min to} V _max , the input impedance of the first amplifying means is R _ia , the input impedance of the second amplifying means is R _ic , and the contact impedance between the first electrode and the user is R and _t1, the contact impedance between the user and the second electrode and R _t2, the distance between said first electrode said first amplifying means and L _1, and said second electrode the second the distance between the amplifying means L ₂ And, the first a noise generated in the circuit including the detection means, the distance L ₁ is increased the larger the noise voltage and V _{TOTAL1 (L 1),} generating a circuit including said second detecting means the noise, the distance L ₂ is increased the larger the noise voltage and V _{Total2 (L 2),} the amplification degree of the differential amplifier means and a _v, the amplification degree of said first amplifying means a for is _a, the amplification degree of the second amplifying means and a _c, wherein the voltage of the detected electrical signal by the first electrode and V _ch1, a voltage of the electrical signal detected by said second electrode V _In the case of _ref , the position and input impedance of the first amplifying unit, the position and input impedance of the second amplifying unit, so as to satisfy the relational expressions (1) to (5) described in the claims, Set It is characterized in that is.

  In one aspect of the present invention, the amplifying means is an amplifier having an amplification factor of one.

  In the aspect of the invention, the plurality of detection units may include a first detection unit including a first electrode that contacts the user's forehead and a second electrode that contacts the user's ear. Including at least a second detecting means, wherein the one or more differential amplifying means differentially amplifies the output signals of the first detecting means and the second detecting means. .

It is a figure which shows a mode that a bioelectric signal detection apparatus is used. It is an external appearance perspective view of a bioelectric signal detection apparatus. It is a figure which shows the measurement waveform of the bioelectric signal which an electrode detects. It is a figure which shows the measurement waveform which was saturated. It is a figure which shows the bioelectric signal which an electrode detects. It is a figure which shows the waveform of the differential voltage of an electrode. It is a schematic diagram of the circuit structure of the bioelectric signal detection apparatus in this embodiment. It is a figure for demonstrating an example of the circuit structure of a differential input part. It is a figure which shows the relationship between the noise component of output signal voltage, and contact impedance. It is a circuit diagram which shows an electromagnetic induction voltage. It is a figure which shows an example of the circuit structure containing the buffer amplifier which concerns on this invention.

  Hereinafter, an example of an embodiment according to the present invention will be described in detail with reference to the drawings. First, the bioelectric signal detection apparatus 1 according to the present invention will be described.

  FIG. 1 is a diagram illustrating a state in which the bioelectric signal detection device 1 is used. As shown in FIG. 1, the bioelectric signal detection device 1 is mounted on the head of a user H, for example. The bioelectric signal detection device 1 detects a bioelectric signal indicating the life activity of the user H.

  The cable C is for inputting the bioelectric signal output from the bioelectric signal detection device 1 to the game device 200. The bioelectric signal detected by the bioelectric signal detection device 1 may be sent to the game device 200 by wireless communication.

  The bioelectric signal detected from the bioelectric signal detection device 1 is used in the game device 200 for various purposes. For example, the game device 200 stores the bioelectric signal change characteristic and the game operation in association with each other so that the bioelectric signal detected by the bioelectric signal detection device 1 is used for the game operation. You can do it. Further, for example, the game music may be changed according to a change in the bioelectric signal.

[Configuration of Bioelectric Signal Detection Device]
FIG. 2 is an external perspective view of the bioelectric signal detection device 1. As shown in FIG. 2, the bioelectric signal detection device 1 includes a substrate box 10, a battery box 20, a frontal band 30, a backal belt 40, and an earphone 50.

  In addition, the bioelectric signal detection device 1 of the present embodiment includes four electrodes that are brought into contact with the user H. These electrodes include, for example, a contact surface made of silver chloride and a conductive material made of silver, and detect a bioelectric signal generated by the user H. In the present embodiment, a dry electrode in which the contact surface between the user H and the electrode is in direct contact is assumed instead of the wet electrode in contact with the user H through the conductive gel. The electrode material is not limited to the above example, and various materials can be applied.

  Hereinafter, these four electrodes are referred to as electrodes ch1, ch2, GND, and REF, respectively. In addition, these four electrodes are collectively referred to as an electrode E. Electrodes ch1 and ch2 (one of which is the first electrode) are arranged on the forehead band 30 and come into contact with the skin on the frontal region of the user H. Electrodes GND and REF (second electrodes) are arranged on the earphone 50 and come into contact with the skin of the ear of the user H.

  The board | substrate box 10 is located in the user's H right side head, for example, when the user H wears the bioelectric signal detection apparatus 1. FIG. A substrate including a microcomputer unit (not shown in FIG. 2; see FIG. 7) that controls the bioelectric signal detection device 1 in an integrated manner is stored in the substrate box 10.

  The bioelectric signal detection device 1 performs noise removal processing, amplification processing, A / D conversion processing, frequency analysis processing, and the like on the bioelectric signal detected from the electrode E by the control of the microcomputer unit inside the board box 10. To the external device (for example, game device 200).

  The battery box 20 is located on the left side of the user H when the user H wears the bioelectric signal detection device 1, for example. The battery box 20 supplies power to each part of the bioelectric signal detection device 1. The battery box 20 is openable and closable. For example, a plurality of dry batteries can be stored therein.

  The battery box 20 includes, for example, a power switch 21, a power lamp 22, and a communication lamp 23. The power switch 21 is a switch for switching on / off of power supply. When the power switch 21 is operated and power is supplied, the power lamp 22 is turned on. Further, when the supply of power is finished by operating the power switch 21, the power lamp 22 is turned off. The communication lamp 23 is used to indicate whether the microcomputer unit of the board box 10 is communicating with an external terminal (for example, the game device 200).

  The forehead band 30 is located on the forehead of the user H when the user H wears the bioelectric signal detection device 1, for example. Two electrodes ch1 and ch2 are arranged inside the frontal band 30 (that is, the side in contact with the forehead of the user H).

  For example, the electrode ch1 is in contact with the right forehead of the user H (for example, the skin on the right eyebrow) and detects the bioelectric signal. On the other hand, for example, the electrode ch2 is in contact with the forehead on the left side of the user H (for example, the skin on the left eyebrow) and detects the bioelectric signal.

  The electrodes ch1 and ch2 and the microcomputer unit stored in the substrate box 10 are electrically connected. That is, the bioelectric signal detected by the electrodes ch1 and ch2 is sent to the microcomputer unit of the substrate box 10. Note that wiring (electrode code) for electrically connecting the electrodes ch1 and ch2 and the microcomputer unit of the substrate box 10 may be stored in the frontal band 30.

  The occipital belt 40 is located at the occipital region of the user H when the user H wears the bioelectric signal detection device 1, for example. The occipital belt 40 includes a buckle 41 and is adjustable in length.

  The user H adjusts the length of the occipital belt 40 so that the electrodes ch1, ch2 and the forehead come into contact with no gap. That is, the user H can wear the bioelectric signal detection device 1 according to the size of the head, and can prevent the positions of the electrodes ch1 and ch2 arranged on the frontal region from being shifted.

  Earphone 50 is attached to the ear of user H. Earphone 50 includes electrodes REF and GND and amplifier substrate 51. The electrode REF and the electrode GND are arranged at a position where they come into contact with the skin of the ear of the user H when the user H wears (inserts) the earphone 50.

  For example, the electrode REF contacts the skin of the right ear of the user H and detects a bioelectric signal around the right ear. Further, for example, the electrode GND is in contact with the skin of the left ear of the user H and detects a bioelectric signal around the left ear.

  The amplifier board 51 includes a sound buffer and the like, and controls the output of music and voice. For example, music or audio data output from the earphone 50 may be acquired from the game apparatus 200 under the control of the microcomputer unit of the board box 10.

  In addition, the microcomputer unit of the substrate box 10 is electrically connected to the electrodes REF and GND and the amplifier substrate 51. Note that wiring (electrode code) for electrically connecting the microcomputer unit of the board box 10 and the electrode GND may be stored in the battery box 20 and the frontal band 30.

[Bioelectric signals obtained from electrodes]
Next, a bioelectric signal obtained from the electrode E will be described. The electrode E is in contact with the skin of the user H and detects a potential change around the contact location.

  In the present embodiment, the electrodes ch1 and ch2 detect a total of potentials of nerve cells in the brain of the user H and muscles around the forehead by contacting the forehead of the user H. For example, when the user H moves his eyes or blinks his eyes, a bioelectric signal having a predetermined frequency component is strongly detected from the electrodes ch1 and ch2. Further, for example, when the user H is excited, the nerve cells in the brain are activated, so that a larger potential change in the bioelectric signal is detected than at rest.

  On the other hand, the electrodes GND and REF detect the aggregation of the potentials of the muscles around the ears of the user H by contacting the ears of the user H. The bioelectric signal detected from the electrode GND is used to indicate the reference voltage of the user H. The bioelectric signal detected from the electrode REF is used, for example, to remove noise components from the bioelectric signal detected from the electrodes ch1 and ch2.

  Here, the noise contained in the bioelectric signal will be described. For example, the bioelectric signal includes various noises due to the surrounding environment when the user H uses the bioelectric signal detection device 1. For example, noise generated by a change in static electricity charged to the user H is an example.

  Further, for example, hum noise that is electrostatically induced in the body of the user H from a device around the user H (for example, a commercial power source) is generated. For example, when the user H is near a household electrical outlet, the user H is affected by a magnetic field generated from the household electrical outlet, and noise is generated.

  It is known that the noise as described above is almost uniformly on the entire head of the user H. That is, the bioelectric signal detected from the electrode E is the sum of the bioelectric signal component generated by the user H's life activity and the noise signal component.

  FIG. 3 is a diagram illustrating a measurement waveform of the bioelectric signal detected by the electrode E. The bioelectric signals detected by the electrode ch1 and the electrode ch2 both show the same waveform, and therefore the electrode ch1 will be described as an example here. As shown in FIG. 3, the measurement waveform (solid line in FIG. 3) of the bioelectric signal detected by the electrode ch1 is a component of the bioelectric signal (dotted line in FIG. 3) generated by the bioactivity of the user H, and the user H's This is a sum of noise signal components generated in the body (the one-dot chain line in FIG. 3).

  It is known that the signal strength of the bioelectric signal generated by the life activity of the user H is several tens of μV to several hundred μV, and the signal strength of the noise signal is about several hundred mV. In FIG. 3, for the convenience of explanation, these scales are not matched.

  In order to detect a bioelectric signal generated by the biological activity of the user H and use it for a game operation or the like of the game apparatus 200, a noise component must be removed from the bioelectric signal detected from the electrode E.

  Here, it is known that the frequency of the bioelectric signal generated by the biological activity of the user H is lower (for example, about 2 Hz to 40 Hz) than the frequency of the noise signal (for example, about 50 Hz). Therefore, the bioelectric signal detection apparatus 1 can also remove the frequency component of noise by converting the bioelectric signal detected by the electrode ch1 into digital data and performing a filtering process.

  However, as described above, since the signal strength of the noise signal is larger than the signal strength of the bioelectric signal due to the biological activity of the user H, there is a possibility that the dynamic range indicating the amplitude that can be expressed by digital data is insufficient. . If the dynamic range is insufficient when A / D conversion is performed, the measurement waveform shown in FIG. 3 is saturated, and thus the noise component cannot be removed.

  FIG. 4 shows a saturated measurement waveform. As shown in FIG. 4, when the dynamic range is insufficient compared with the amplitude of the measurement waveform, the measurement waveform is saturated and the noise component is not understood, and thus noise cannot be removed by filtering processing.

When the noise signal component is removed by a digital filter, the noise signal is about several hundred mV, and for example, A / D conversion with an input voltage range width of 500 mV (hereinafter referred to as peak-to-peak voltage V _p-p ). A vessel is required.

Further, in order to analyze the life activity of the user H, it is necessary to match the quantization width a of the A / D conversion with the signal intensity of the bioelectric signal generated by the life activity of the user H. That is, for example, it is conceivable that the quantization width a is set to 0.1 μV in accordance with the order of the signal intensity of the bioelectric signal generated by the biological activity of the user H (for example, several tens μV to several hundred μV). In this case, if the quantization width is 0.1 μV, 5 * 10 ⁶ steps are required. That is, in this case, an A / D converter with a high dynamic range in which the quantization bit number b is 23 bits or more is required.

In the case of the above example, when an A / D converter with a small dynamic range (for example, the number of quantization bits b is 10 bits), the measurement waveform is saturated as shown in FIG. become unable. For example, when the quantization width a is 0.1 μV, the peak-to-peak voltage V _p-p is 102.4 μV in an A / D converter with a relatively small dynamic range where the quantization bit number b is 10 bits. For this reason, the waveform of a noise signal having a strength of several hundred mV is saturated.

  Therefore, in this embodiment, an A / D converter with a small dynamic range is used by canceling the noise signal based on the bioelectric signal detected by the electrode ch1 and the bioelectric signal detected by the electrode REF. Even so, noise can be removed.

  FIG. 5 is a diagram illustrating a bioelectric signal detected by the electrode REF. As shown in FIG. 5, the bioelectric signal detected by the electrode REF is similar to the bioelectric signal detected by the electrode ch1, and the component of the bioelectric signal generated by the biological activity of the user H (dotted line in FIG. 5) This is a combination of a noise signal component (dotted line in FIG. 5) generated in the body of the user H.

  However, the electrode REF is disposed in the ear that is relatively less affected by muscle movement and nerve cell activity. That is, the electrode REF is disposed at a position where a change in the bioelectric signal generated by the biological activity of the user H is relatively small. In the present embodiment, the bioelectric signal component generated by the biological activity of the user H among the bioelectric signals detected by the electrode REF is regarded as substantially zero. In other words, almost all bioelectric signals detected by the electrode REF are regarded as noise components.

  Therefore, by taking the difference between the bioelectric signal detected by the electrode ch1 and the bioelectric signal detected by the electrode REF, the noise component is removed from the bioelectric signal detected by the electrode ch1. That is, it can be said that these differential voltages indicate an electrical signal due to the biological activity of the right frontal region of the user H.

  FIG. 6 is a diagram illustrating a waveform of a differential voltage between the electrode ch1 and the electrode REF. That is, the waveform shown in FIG. 6 is a difference waveform obtained by subtracting the solid line waveform shown in FIG. 5 from the solid line waveform shown in FIG. As shown in FIG. 6, the noise component is removed, and an electrical signal due to the biological activity of the right frontal region of the user H can be obtained.

  In the above description, the electrode ch1 has been described as an example. However, since the bioelectric signal detected by the electrode ch2 also shows a waveform similar to that in FIG. 3, the bioelectric signal detected by the electrode ch2 is also detected by the electrode REF. The noise component can be canceled using the bioelectric signal. The waveform of the bioelectric signal detected by the electrode GND is the same as the waveform of the electrode REF shown in FIG.

  As described above, the bioelectric signal detection device 1 can cancel the noise component using the bioelectric signal detected by the electrode REF. Next, the circuit configuration of the bioelectric signal detection apparatus 1 will be described.

[Circuit Configuration of Bioelectric Signal Detection Device]
FIG. 7 is a schematic diagram of a circuit configuration of the bioelectric signal detection apparatus 1 in the present embodiment. As shown in FIG. 7, the bioelectric signal detection apparatus 1 includes detection units 100a, 100b, 100c, and 100d, differential amplification units 110a and 110b, filter units 120a and 120b, amplification units 130a and 130b, and a microcomputer unit 140. . These components may be driven by dry batteries stored in the battery box 20.

  The detection units 100 a and 100 d are included in the frontal band 20, and the detection units 100 b and 100 c are included in the earphone 50. Other components are included in the substrate box 10.

  The detection units 100a, 100b, 100c, and 100d (hereinafter collectively referred to as the detection unit 100) include electrodes ch1, GND, REF, and ch2, and detect bioelectric signals generated by the user H. To do.

  The differential amplifying units 110a and 110b (hereinafter collectively referred to as the differential amplifying unit 110) differentially amplifies two of the signals output from the plurality of detecting units 100. For example, And an operational amplifier having a predetermined amplification degree.

  The differential amplification unit 110a differentially amplifies the detection signal of the detection unit 100a and the detection signal of the detection unit 100c so as to remove (cancel) the noise component from the detection signal of the detection unit 100a. The differential amplifier 110b differentially amplifies the detection signal of the detection unit 100d and the detection signal of the detection unit 100c so as to remove (cancel) the noise component from the detection signal of the detection unit 100d.

  Filter units 120a and 120b (hereinafter collectively referred to as filter unit 120) remove a predetermined frequency component (frequency component of a noise signal) of the output signal of differential amplification unit 110. The filter unit 120 may be a digital filter including an A / D converter. In other words, the filter unit 120 is for removing noise components that could not be removed by the differential amplification unit 110.

  For example, the filter unit 120 includes a low-pass filter (for example, an eighth-order multi-stage low-pass filter) for removing external electromagnetic noise (for example, noise of 40 Hz or more) induced in a cable or a human body. In addition, for example, the filter unit 120 is a high-pass filter (for example, a fourth-order multi-stage high-pass filter) for removing low-frequency noise (for example, noise of 2 Hz or less) that occurs at the location where the user H is static or the electrode E is in contact. including.

  Note that the filter unit 120 may be a band-pass filter that removes high-frequency noise and low-frequency noise and passes only a signal component (for example, a signal component of 2 Hz to 40 Hz) due to the biological activity of the user H. The frequency band of the electrical signal taken out by the filter unit 120 may be appropriately changed according to the noise frequency of the electrical signal generated by the user H.

The amplifying units 130a and 130b (hereinafter collectively referred to as the amplifying unit 130) include an operational amplifier having a predetermined amplification degree. The amplifying unit 130 amplifies the bioelectric signal that has passed through the filter unit 120 and has a predetermined frequency component cut off, and outputs the bioelectric signal to the microcomputer unit 140. The amplification degree of the electric signal in the amplification unit 130 may be an arbitrary value. For example, since the electric signal related to the living body of the user H is several μV, an amplification factor (for example, ¹⁰⁶ times) for amplifying the electric signal to several V may be set.

  The microcomputer unit 140 includes a microprocessor, a memory, an A / D converter that converts an analog output electric signal into a digital format, various input / output interfaces, and the like. The microcomputer unit 140 acquires a bioelectric signal from which noise has been removed by the differential amplification unit 110 and the filter unit 120 and has been amplified by the amplification unit 130.

  For example, the microcomputer unit 140 may perform frequency analysis on the bioelectric signal. For example, the microcomputer unit 140 measures the signal strength of the bioelectric signal for each frequency and outputs it as an output signal to the game apparatus 200 via an output terminal (not shown) and the cable C.

  The bioelectric signal detection apparatus 1 removes noise components based on the circuit configuration as described above. However, since the contact impedance generated between the electrode E and the user H differs depending on the position of the electrode E and the passage of time, the magnitude of the noise component included in the bioelectric signal input to the differential amplification unit 110 However, there is a possibility that noise cannot be completely removed by the differential voltage.

  That is, when there is a difference in the contact impedance between the plurality of electrodes E and the user H, the effect of the differential amplifier 110 removing noise components is reduced. In the present embodiment, a dry electrode is used as the electrode E included in the detection unit 100. Therefore, a larger contact impedance is generated between the electrode E and the user H than in the case where a wet electrode is used. That is, if the variation in contact impedance is not taken into account, the differential amplifier 110 cannot completely remove noise, and the waveform may be saturated as shown in FIG.

  Therefore, the bioelectric signal detection device 1 according to the present embodiment has a configuration in which the effect of removing the noise component by the differential amplifier 110 does not decrease even if the contact impedances of the plurality of electrodes E vary in magnitude. ing. Hereinafter, this configuration will be described in detail.

  First, the relationship between the contact impedance and the noise removal capability of the differential amplifier 110 will be described. Since the differential amplifier 110a and the differential amplifier 110b have the same configuration, the differential amplifier 110a will be described below as an example.

[Noise removal capability of differential amplifier]
FIG. 8 is a diagram for explaining an example of a circuit configuration of the differential amplifier 110a. The electrode E in contact with the skin of the user H generates contact impedance due to the user's sweat, sebum, and the like. 8, the electrode ch1, GND, the contact impedance between the REF and the user H, respectively contact impedance _{R t1,} R _tg, and _{R t2.} It is generally known that the contact impedances R _t1 , R _tg , and R _t2 are about several tens of kΩ to several MΩ.

In FIG. 8, noise generated in the body of the user H is referred to as generated noise V _noise0 . As described above, since the external electromagnetic noise is generated almost uniformly over the entire head of the user H, the generated noise V _noise0 is shown at positions corresponding to the electrodes ch1, GND, and REF as shown in FIG. _Further, the voltage of the generated noise V _noise0 is _assumed to be a noise voltage V _comm (common mode noise voltage). In addition, although the electrode GND detects the electrical signal by the user's H biological activity, this component is set to substantially zero and description is abbreviate | omitted.

Further, here, for convenience of explanation, it is assumed that electromagnetic induction noise (details will be described later) does not occur in the circuit. An input impedance R _i of the operational amplifier 111a included in the differential amplifier 110a is schematically shown in FIG.

As described with reference to FIGS. 3 to 6, the voltage _{V ch1} bioelectric signals electrode ch1 is detected, the bioelectrical signal (signal _{V Creature1} by the biological activities of the user H, for the voltage and _{V Create1} )) And a noise component (for example, voltage V _com ) are added together.

Further, the voltage _{V ref} of the bioelectrical signal electrode REF is detected, (a signal _{V Creature2,} this voltage is _{V Create2.)} Bioelectric signal by the biological activities of the user H and a noise component, both the sum of It has been done.

The operational amplifier 111a detects a differential voltage between the electrode ch1 and the electrode REF and removes a noise component. Here, the current I ₁ flowing from the electrode ch1 to the operational amplifier 111a and the negative input signal voltage V ₁ of the operational amplifier 111a are expressed by the following equations.
(1) I ₁ = V ₁ / R _{i1
(2) V 1 = V comm} + V create1 -R t1 * I 1

From the above formulas (1) and (2), the negative input signal voltage V ₁ is expressed by the following formula.
_{(3) V 1 = R i1} * (V comm + V create1) / (R i1 + R t1)

On the other hand, the current I ₂ flowing from the electrode REF to the operational amplifier 111a and the positive input signal voltage V ₂ of the operational amplifier 111a are expressed by the following equations.
(4) I ₂ = V ₂ / R _{i1
(5) V 2 = V comm} + V create2 -R t2 * I 2

From the above equations (4) and (5), the positive side input signal voltage V ₂ is expressed by the following equation.
_{(6) V 2 = R i1} * (V comm + V create2) / (R i1 + R t2)

The output signal voltage V ₀₁ of the operational amplifier 111a is expressed by the following expression based on the amplification degree A _v of the operational amplifier 111a, expressions (3), and (6).
(7) V ₀₁ = A _v * (V ₂ −V ₁ ) = A _v * R _i1 * (1 / (R _i1 + R _t2 ) −1 / (R _i1 + R _t1 )) * V _com + A _v * R _i1 * (V _create2 / (R _i1 + R _t2 ) − (V _create1 / (R _i1 + R _t1 ))

As shown in the equation (7), the output signal voltage V ₀₁ has a noise component (“A _v * R _{i1 in the} equation (7) becomes smaller as the difference between the contact impedance R _t1 and the contact impedance R _t2 is smaller. The absolute value of * (1 / (R _i1 + R _t2 ) −1 / (R _i1 + R _t1 )) * V _comm “)” becomes smaller. That is, the smaller the difference between the contact impedance R _t1 and the contact impedance R _t2 , the better the noise component removal performance of the differential amplifier 110.

FIG. 9 is a diagram illustrating the relationship between the noise component of the output signal voltage V ₀ and the contact impedance. Example shown in FIG. 9, for example, 100 mV noise voltage _{V comm,} the amplification degree _{A v} 2 * 10 ^4, and the contact impedance _{R t2} and ¹⁰⁴ Omega, varying input impedance _{R i} and contact impedance _{R t1} In this case, the noise component of the output signal voltage V ₀₁ obtained by the equation (7) is shown.

As shown in FIG. 9, the smaller the difference between the values of the contact impedance R _t1 and the contact impedance R _t2 (in the case of FIG. 9, the closer to 10 ⁴ Ω), the smaller the noise component of the output signal voltage V ₀₁ . Further, the noise component of the output signal voltage V ₀₁ becomes smaller as the input impedance R _i1 becomes larger than the contact impedance R _t1 and the contact impedance R _t2 .

Accordingly, if the input impedance R _i1 is extremely large (eg, 1 GΩ or more) compared to the order of contact impedance (several tens of kΩ to several MΩ), the noise is not affected by the difference between the contact impedance R _t1 and the contact impedance R _t2. The ability to remove components is guaranteed. For example, if the input impedance R _{i1 is set} to 100 times or more of the contact impedances R _t1 and R _t2 , even if the contact impedance R _t1 is twice the contact impedance R _t2 , as shown in the equation (7), the operational amplifier The amplitude of noise can be reduced to several tenths by the differential input of 111a.

However, since the differential amplifying unit 110 is housed in the board box 10, the wiring connecting the electrode E and the input impedance R _i1 shown in FIG. 8 has a certain distance (for example, the board box 10 and the frontal region). Distance to the band 30 or the earphone 50). Therefore, external noise (for example, noise due to electromagnetic induction) may occur in the circuit shown in FIG.

For example, the region surrounded by the wiring for transmitting the detection signal of the electrode ch1 shown in FIG. 8 to the differential amplifier 110a and the wiring for transmitting the detection signal of the electrode GND to the differential amplifier 110a is externally provided. When the electromagnetic wave from pierces, electromagnetic induction noise (external noise) is generated in this region. For example, as the distance L ₀ between the electrode ch1 and the differential amplifier 110 increases, the area of this region (hereinafter referred to as area S (L ₀ )) increases.

Here, when the magnetic flux density of the external electromagnetic wave from the device (for example, commercial power source) around the user H is B (T), the electromagnetic induction voltage V (L ₀ ) generated by the wiring of the electrode ch1 and the wiring of the electrode GND. Is expressed by the following formula based on the time change of the magnetic flux.
(8) V (L ₀ ) = − d (B * S (L ₀ )) / dt

From the above equation (8), when the distance L ₀ between the electrode ch1 and the input impedance R _i is increased, the area S (L ₀ ) is increased, so that the electromagnetic induction voltage V (L ₀ ) is increased.

FIG. 10 is a circuit diagram showing the electromagnetic induction voltage. FIG. 10 shows only the contact impedance R _t1 and the input impedance R _{i1 in} the circuit of FIG. As shown in FIG. 10, the voltage across the input impedance R _i is expressed by (R _i1 / (R _t1 + R _i1 )) * V (L ₀ ). That is, when the input impedance _Ri increases, the influence of the electromagnetic induction voltage V (L ₀ ) on the negative input signal voltage V ₁ increases.

In addition, when the wiring from the electrode E to the differential amplifier 110 has a certain length, electrostatic coupling noise or the like is generated between the wiring and the user H. That is, noise may be picked up like a highly sensitive antenna due to the high input impedance R _i1 . Therefore, the bioelectric signal detection device 1 according to the present invention suppresses the generation of this noise.

[Buffer amplifier to reduce generated noise]
The detection unit 100 of the bioelectric signal detection apparatus 1 according to the present invention includes a buffer amplifier (amplifying means) in order to prevent the occurrence of noise based on the high input impedance as described above. As with the operational amplifier 111a in FIG. 8, this buffer amplifier is based on the contact impedance (for example, several tens of kΩ) of the user H and the electrodes ch1, ch2, and REF so that the effect of noise removal by the differential amplifier 110 is not reduced. It has a high input impedance (eg, 1 GΩ or more).

  The buffer amplifier amplifies the electric signal detected by the electrode E. In addition, the buffer amplifier is disposed between the electrode E and the differential amplifier 110. For example, the buffer amplifier is provided at a position where the distance between the electrode E and the buffer amplifier is shorter than the distance between the buffer amplifier and the differential amplification beauty 110. In other words, for example, the buffer amplifier has a position where the output voltage of the differential amplifying unit 110 is not saturated by the component of the external noise generated in the circuit including the input impedance of the buffer amplifier (for example, the electrode E (Just after).

  FIG. 11 is a diagram showing an example of a circuit configuration including the buffer amplifier according to the present invention. As shown in FIG. 11, buffer amplifiers 101a and 101c (hereinafter, the buffer amplifiers arranged immediately after the electrode E are collectively referred to as buffer amplifiers 101) are arranged between the electrodes ch1 and REF and the operational amplifier 101. Has been.

  The amplification degrees of the buffer amplifiers 101a and 101c are set to, for example, substantially the same level (for example, 1). The amplification factors of the buffer amplifiers 101a and 101c may be set within a range in which an input impedance higher than the contact impedance can be obtained.

In FIG. 11, the input impedance of the buffer amplifier 101a is R _ia (> contact impedance R _1t ), and the input impedance of the buffer amplifier 101c is R _ic (> contact impedance R _2t ). Also, the voltages of electromagnetic induction noise generated in the circuit shown in FIG. 11 are referred to as noise voltage V _ei1 and noise voltage V _ei2 . In addition, noise V _noise1 and noise V _noise2 including noise generated in the circuit, such as electromagnetic induction noise and electrostatic coupling noise, are used.

For example, the noise voltage V _ei1 is represented by −d (B * S (L ₁ )) / dt based on the distance L ₁ between the electrode ch1 and the buffer amplifier 101a. Further, for example, based on the distance L ₂ between the electrode REF and the buffer amplifier _{101 c} , the noise voltage V _ei2 is expressed by −d (B * S (L ₂ )) / dt.

The current I ₁₁ flowing from the electrode ch1 to the buffer amplifier 101a side and the positive input signal voltage V ₁₁ of the buffer amplifier 101a are expressed by the following equations. Note that V _total1 (L ₁ ) shown below is noise generated in a circuit including the first detection means (detection unit 100a), and increases as the distance L ₁ increases. For example, V _total1 (L ₁ ) is obtained by adding a noise voltage V _el1 and a voltage of electrostatic coupling noise. The voltage V _ch1 is a voltage of an electric signal detected by the electrode ch1. That is, the voltage _{V ch1} is obtained by summing the voltage _{V comm} and the voltage _{V Create1.}
(9) V ₁₁ = I ₁₁ * R _ia
(10) V ₁₁ = V _total1 (L ₁ ) + V _ch1 −R _t1 * I ₁₁

From equations (9) and (10), the positive input signal voltage _{V 11} of the buffer amplifier 101a is represented by the following equation.
(11) V ₁₁ = R _ia * (V _total1 (L ₁ ) + V _ch1 ) / (R _ia + R _t1 )

On the other hand, the current I ₂₁ flowing from the electrode REF to the buffer amplifier 101c side and the positive input signal voltage V ₂₁ of the buffer amplifier 101c are expressed by the following equations. Note that V _total2 (L ₂ ) shown below is noise generated in a circuit including the second detection means (detection unit 100c), and increases as the distance L ₂ increases. For example, V _total2 (L ₂ ) is obtained by adding a noise voltage V _el2 and a voltage of electrostatic coupling noise. The voltage V _ref is a voltage of an electric signal detected by the electrode REF. That is, the voltage _{V ref} is obtained by summing the voltage _{V comm} and the voltage _{V Create2.}
(12) V ₂₁ = I ₂₁ * R _ic
(13) V ₂₁ = V _total2 (L ₂ ) + V _ref −R _t2 * I ₂₁

From the equations (12) and (13), the positive input signal voltage V ₂₁ of the buffer amplifier 101a is expressed by the following equation.
(14) V ₂₁ = R _ic * (V _total2 (L ₂ ) + V _ref ) / (R _ic + R _t2 )

The amplification degree of the buffer amplifier 101a _{A a} result, the negative-side input voltage _{V 12} of the operational amplifier 111a _is a A a _{* V 11.} Further, when the amplification degree of the buffer amplifier 101c and _{A c,} positive input voltage _{V 22} of the operational amplifier 111c _is a A c _{* V 21.}

Therefore, the output signal voltage V ₀₂ of the operational amplifier 111a is expressed by the following equation based on the amplification degree A _v , the equations (11) and (14).
_{(15) V 02 = A v} * (V 21 -V 11) = A v * (A c * R ic * (V total2 (L 2) + V ref) / (R ic + R t2) -A a * R ia * (V _total1 (L ₁ ) + V _ch1 ) / (R _ia + R _t1 ))

If the output signal voltage V ₀₂ falls within the input voltage range V _{min to} V _max of the A / D converter of the bioelectric signal detection device 1, the residual noise is generated in the filter unit 120 without saturating the waveform. Can be removed. As described above, the input voltage range V _{min to} V _max of the A / D converter is, for example, the quantization width a and the quantization bit number b of the A / D converter included in the bioelectric signal detection device 1. , And a predetermined minimum input voltage.

Therefore, the position and input impedance R _ia of the buffer amplifier 101a and the position and input impedance R _{ic of} the buffer amplifier 101c are set so as to satisfy the following expression.
(16) V _min <A _v * (V ₂₂ −V ₁₂ ) <V _max
(17) V ₂₂ = A _c * R _ic * (V _total2 (L ₂ ) + V _ch1 ) / (R _ic + R _t2 )
(18) V ₁₂ = A _a * R _ia * (V _total1 (L ₁ ) + V _ref ) / (R _ia + R _t1 )

  By satisfying the relational expressions (16) to (18), the output signal of the differential amplifier 110 falls within the input voltage range. Therefore, when this output signal is converted by the A / D converter at the subsequent stage, the waveform is not saturated, so that residual noise can be reliably removed by the filtering process.

Incidentally, the amplification degree _{A v, A a, A c} may have been set so as to satisfy the above equation (16) to (18). In addition, “R _ic / (R _ic + R _t2 )” in the equation (17) and “R _ia / (R _ia + R _t1 )” in the equation (18) are approximated by 1 and the distance L ₁ or the distance, respectively. L ₂ may be determined.

Further, since the buffer amplifiers 101a and 101c are arranged immediately after the electrodes ch1 and REF, respectively, the input impedance _Ria and the input impedance _Ric are immediately after the electrodes ch1 and REF. That is, since the distance L ₁ and the distance L ₂ is substantially zero, it is possible to reduce the generation of electromagnetic induction noise or capacitive coupling noise.

To explain with numerical examples, the distance L ₁ and the distance L ₂ are substantially zero,
Amplification degree A _v = A _a = A _c = 1
V _total1 (L ₁ ) = 1.2 mV
V _total1 (L ₂ ) = 1 mV
R _t1 = 10 kΩ
R _t2 = 15 kΩ
V _comm = 300 mV
V _create1 = 500μV
V _create2 = _100μV
In this case, when the input impedance R _ic and the input impedance R _ia are set to 100 MΩ, the voltage A _v * (V ₂₂ −V ₁₂ ) output from the differential amplifier 110 is about 615 μV. This magnitude is on the same order as V _create1 and V _create2 . Therefore, even if the size of the input voltage range is several hundred μV, the voltage output from the differential amplifier 110 does not saturate.

  The operational amplifier 111a differentially amplifies two output electric signals of the buffer amplifier 101a and the buffer amplifier 101c. Although the input impedance of the operational amplifier 111a is not shown in FIG. 11, it may be smaller than the input impedance of the buffer amplifier 101. That is, since the buffer amplifier 101 can prevent the noise removal performance from being lowered due to the contact impedance, it is not necessary to set the input impedance of the operational amplifier 111a high. When the input impedance of the operational amplifier 111a is high as shown in FIG. 8, the influence of electromagnetic induction noise and electrostatic coupling noise generated in the circuit including this input impedance is greatly affected. However, in the circuit of FIG. Can be reduced.

  In addition, it is considered that external noise is also generated in the circuit on the output impedance side of the buffer amplifier 101. However, by increasing the amplification factor of the buffer amplifier 101 by one, the input impedance is increased and the output impedance is decreased. Therefore, the generation of this noise can be reduced.

  In the above description, the configurations of the detection units 100a, 100b, and 100c and the differential amplification unit 110a have been described as examples. However, similar noise removal processing is performed on the bioelectric signal detected by the detection unit 100d. That is, the buffer amplifier 101 having a high input impedance is disposed immediately after the electrode ch2 of the detection unit 100d, and the bioelectric signal is differentially amplified by the differential amplification unit 100b. As a result, the noise component detected by the detection unit 100d can be canceled by the component of the detection unit 100c, and noise caused by the high input impedance of the buffer amplifier 101 can be suppressed.

[Summary of Embodiment]
As described above, the bioelectric signal detection device 1 can remove noise generated in the body of the user H because the differential amplifier 110 outputs the differential voltage of the electrode E. In addition, since the input impedance of the buffer amplifier 101 arranged immediately after the electrodes ch1, ch2, and REF is higher than the contact impedance, it is possible to suppress a decrease in noise removal performance by the differential amplifier 110 due to variations in contact impedance. it can. Further, by arranging the buffer amplifier 101 immediately after the electrode E, it is possible to suppress the generation of noise even when the high input impedance R _i2 is used.

  Therefore, even if an A / D converter having a relatively small dynamic range is used, residual noise can be reliably removed by the filter unit 120 without saturating the measurement waveform. In addition, a dry electrode that is easy to handle can be used instead of a wet electrode that requires time and effort to wipe off the conductive gel.

  The present invention is not limited to the embodiment described above, and can be appropriately changed without departing from the spirit of the present invention. For example, in the above embodiment, the number of electrodes (detectors) is four, but a plurality of electrodes may be arranged in the bioelectric signal detector 1 in order to detect a differential voltage. The number of is not limited to four. The number of the differential amplifiers may be arranged according to the number of detection units.

  Further, for example, the case where the bioelectric signal detection device is mounted on the head has been described, but any device that contacts the user's body and the electrode may be used, and the device may be mounted on the hand or foot.

  DESCRIPTION OF SYMBOLS 1 Bioelectric signal detection apparatus, 10 board box, 20 battery box, 21 power switch, 22 power lamp, 23 communication lamp, 30 frontal band, 40 occipital belt, 41 buckle, 50 earphone, 51 amplifier board, E, ch1 , Ch2, GND, REF electrode, 100, 100a, 100b, 100c, 100d detector, 101a, 101c buffer amplifier, 110, 110a, 110b differential amplifier, 111a operational amplifier, 120, 120a, 120b filter, 130, 130a , 130b amplifying unit, 140 microcomputer unit.

Claims (5)

A plurality of detecting means including an electrode for detecting an electric signal generated by a user, and an amplifying means for amplifying the electric signal detected by the electrode;
One or more differential amplifying means for differentially amplifying two of the signals output from the plurality of detecting means;
Including
The bioelectric signal detection apparatus according to claim 1, wherein the amplification means has an input impedance higher than a contact impedance of the user and the electrode, and is provided between the electrode and the differential amplification means.   2. The bioelectric signal detection according to claim 1, wherein the amplifying means is provided at a position where a distance between the electrode and the amplifying means is shorter than a distance between the amplifying means and the differential amplifying means. apparatus. The bioelectric signal detection device includes an A / D converter for converting an output signal of the differential amplification means into a digital signal,
The plurality of detection means include at least a first detection means including a first electrode and a first amplification means, and a second detection means including a second electrode and a second amplification means,
The input voltage range of the A / D converter is V _{min to} V _max ,
Let R _{ia be} the input impedance of the first amplification means,
Let R _{ic be} the input impedance of the second amplification means,
The contact impedance between the first electrode and the user is R _t1 ,
The contact impedance between the second electrode and the user is R _t2 ,
The distance between the said first electrode first amplifying means and L _1,
The distance between the second amplifying means and the second electrode is L _2,
A noise generated in the circuit including the first detecting means, the distance _{L 1} is increased the larger the noise voltage and _{V TOTAL1 (L 1),}
A noise generated in the circuit including the second detecting means, a distance voltage noise L ₂ increases with increasing the V _{Total2 (L 2)} the amplification degree of the differential amplifier means and A _v,
The amplification degree of said first amplifying means and A _a,
The amplification factor of the second amplifying means and A _c,
The voltage of the electrical signal detected by the first electrode is _Vch1 ,
When the voltage of the electrical signal detected by the second electrode is V _ref ,
The position and input impedance of the first amplifying means and the position and input impedance of the second amplifying means are set so as to satisfy the following relational expressions (1) to (5). The bioelectric signal detection device according to claim 1 or 2.
(1) R _ia > R _t1
(2) R _ic > R _t2
(3) V _min <A _v * (V ₁₂ −V ₂₂ ) <V _{max
(4) V 12 = A c} * R ic * (V total2 (L 2) + V ch1) / (R ic + R t2)
(5) V ₂₂ = A _a * R _ia * (V _total1 (L ₁ ) + V _ref ) / (R _ia + R _t1 )   The bioelectric signal detection apparatus according to any one of claims 1 to 3, wherein the amplifying means is an amplifier having an amplification factor of one. The plurality of detection means include: a first detection means including a first electrode that contacts the user's forehead; and a second detection means including a second electrode that contacts the user's ear. Including at least
5. The one or more differential amplifying means differentially amplifies output signals from the first detecting means and the second detecting means. 6. Bioelectric signal detection device.

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