JP2016077580A - Biological signal amplifying device and biological signal transmitting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological signal amplifying device capable of removing a hum noise without using a notch filter.SOLUTION: A biological signal amplifying device 2 comprises: first and second terminals 12 that receive input of biological signals; a voltage divider 13 that divides voltage between the first and second terminals 12 at a prescribed rate; a differential amplifier 14 that uses ground voltage being the voltage divided by the voltage divider 13 to amplify a difference between the biological signals input into the first and second terminals 12; and an adjustment part 15 that adjusts the ground voltage divided by the voltage divider 13, so as to cancel out noises to be input into the first and second terminals 12.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a biological signal amplification device that amplifies biological signals such as brain waves, cardiac potentials, and myoelectric potentials.

  Conventionally, a biological signal such as an electroencephalogram, an electrocardiogram, or an electromyogram is acquired and amplified using an electroencephalograph, an electrocardiograph, an electromyograph, or the like. In such a biological signal measuring device or the like, hum noise derived from the power supply frequency has been removed. For example, hum noise has been removed by using a ground electrode (see, for example, Patent Document 1). Specifically, as shown in FIG. 10, three electrodes are attached to the subject, two electrodes are connected to a terminal for amplification, and the remaining one electrode is connected to the ground of the apparatus. Being connected was done. Further, for example, hum noise has been removed by using a filter such as a notch filter or a band elimination filter (see, for example, Patent Document 2).

JP 2005-296214 A JP 2005-124903 A

However, when noise of a specific frequency is removed by using a filter as in the conventional example, a biological signal of that frequency is also removed. In addition, when a ground electrode (indifferent electrode) is used as in the above-described conventional example, since a current flows through the living body, there is a possibility that the living body (for example, a human or a laboratory animal) may receive an electric shock from the measuring device. was there. In particular, when the earth wire of the measuring device is disconnected, there is a problem that the risk of electric shock increases.
Therefore, it has been desired to develop a biological signal amplifying device that removes hum noise and does not remove biological signals without using a ground electrode.

  The present invention has been made to solve the above-described problem, and a biological signal amplification apparatus capable of reducing the influence on a biological signal by removing hum noise according to the frequency of a commercial power supply without using a ground electrode. The purpose is to provide.

In order to achieve the above object, a biological signal amplifying apparatus according to the present invention divides a voltage between a first terminal and a second terminal to which a biological signal is input and a first terminal and a second terminal at a predetermined ratio. A differential amplifier that amplifies the difference between the biological signal input to the voltage divider and the first and second terminals using a ground voltage that is a voltage divided by the voltage divider, and the first and second terminals. And an adjustment unit that adjusts a ground voltage that is divided by the voltage divider so that the input hum noise is canceled.
With such a configuration, it is possible to cancel the hum noise input to the first and second terminals without using a notch filter. As a result, noise removal according to the frequency of the commercial power supply can be realized without damaging the biological signal in that frequency band. In addition, since the ground electrode is not necessary, for example, it is possible to prevent the subject or the subject from being electrocuted. In addition, for example, by providing two electrodes to the subject or the test animal, the burden on the subject or the test animal can be reduced.

In the biological signal amplifying device according to the present invention, the adjustment unit includes a bandpass filter that extracts a signal having a frequency component corresponding to hum noise from the output of the differential amplifier, and a rectifier that rectifies the signal extracted by the bandpass filter; An extractor that extracts a DC component of the signal rectified by the rectifier, and a controller that adjusts the ground voltage so that the DC component extracted by the extractor is reduced. Amplification of the signal may be performed using a ground voltage adjusted by the controller.
With such a configuration, it is possible to know whether or not noise is appropriately canceled using the output of the extractor. Therefore, the output of the extractor can be used to adjust the voltage divider so that noise is appropriately canceled.

In the biological signal amplifying apparatus according to the present invention, the adjustment unit is configured to extract the first band-pass filter that extracts a frequency component signal corresponding to the hum noise from the output of the differential amplifier, and the signal input to the first terminal. Synchronous detection of the signal extracted by the first band-pass filter using the second band-pass filter that extracts the signal of the frequency component corresponding to the hum noise and the signal extracted by the second band-pass filter Using the detector, the extractor that extracts the DC component of the signal synchronously detected by the synchronous detector, and the DC component extracted by the extractor, the output of the differential amplifier corresponding to hum noise is reduced. A controller for adjusting the ground voltage, and the differential amplifier performs amplification related to the biological signal using the ground voltage adjusted by the controller. It may be.
With such a configuration, it is possible to know whether or not noise is appropriately canceled using the output of the extractor. Therefore, the output of the extractor can be used to adjust the voltage divider so that noise is appropriately canceled.

In the biological signal amplifying device according to the present invention, the first terminal is connected to the electrode, the length of the wiring from the first electrode that is in contact with the living body to the differential amplifier, and the second terminal The length of the wiring from the second electrode, which is an electrode that is connected to the living body, to the differential amplifier may be 1 meter or less.
The longer the wire length, the easier it is for hum noise to mix, but with such a configuration, the possibility of hum noise mixing can be reduced.

In the biological signal amplifying device according to the present invention, the voltage divider is configured to apply one of the first and second voltages obtained by dividing the voltage between the first and second terminals at a frequency higher than the frequency of the biological signal. By alternately selecting, the voltage between the first and second terminals may be divided.
With such a configuration, for example, the circuit scale of the voltage divider can be reduced.

In the biological signal amplification device according to the present invention, the biological signal may be any one of an electroencephalogram, a cardiac potential, and a myoelectric potential.
With such a configuration, it is possible to realize appropriate amplification with reduced hum noise for a minimal signal such as an electroencephalogram.

The biological signal transmission device according to the present invention includes a biological signal amplification device and a transmission unit that wirelessly transmits a transmission signal that is an output signal of the differential amplifier.
With such a configuration, it is possible to make it less susceptible to hum noise after amplification than in the case of wired transmission.

In the biological signal transmission apparatus according to the present invention, the transmission unit performs a PFM modulator that performs pulse frequency modulation on the transmission signal, a differentiator that differentiates the pulse frequency modulated signal, and performs ASK modulation on the differentiated signal. An ASK modulator, and an ASK modulated signal may be transmitted wirelessly.
With such a configuration, transmission power can be reduced.

  According to the biological signal amplifying apparatus and the like according to the present invention, it is possible to reduce the influence on the biological signal when noise corresponding to the frequency of the commercial power supply is removed.

The figure which shows the structure of the biosignal transmitter by Embodiment 1 of this invention. The figure for demonstrating adjustment of the voltage divider in the same embodiment Waveform diagram showing an example of a signal in the same embodiment The block diagram which shows the structure of the transmission part in the embodiment Waveform diagram showing an example of a signal in the same embodiment The figure which shows another example of a structure of the biosignal transmitter by the embodiment The figure which shows an example of the experimental result using the biological signal amplifier by the same embodiment The figure which shows another example of the voltage divider in the same embodiment Waveform diagram showing an example of the control signal of the voltage divider in the same embodiment The figure which shows an example of the position of the electrode with which a subject is mounted | worn in a prior art example

  Hereinafter, a biological signal transmission apparatus according to the present invention will be described using embodiments. Note that, in the following embodiments, the components given the same reference numerals are the same or equivalent, and repetitive description may be omitted.

(Embodiment 1)
A biological signal transmission apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings. The biological signal transmission apparatus according to the present embodiment removes hum noise according to the frequency of the commercial power supply by automatically adjusting the ground voltage.

FIG. 1 is a block diagram showing a configuration of a biological signal transmitter 1 according to this embodiment. The biological signal transmission device 1 according to the present embodiment includes a biological signal amplification device 2 and a transmission unit 16.
The biological signal amplification device 2 includes a first terminal 11, a second terminal 12, a voltage divider 13, a differential amplifier 14, and an adjustment unit 15.

The 1st terminal 11 is electrically connected with the 1st electrode which is an electrode which contacts a living body. Then, a biological signal from the first electrode is input. The living body may be a human or an animal other than a human. The animal may be a vertebrate or an invertebrate. The vertebrates may be mammals such as mice, rats, guinea pigs, and rabbits, and may be reptiles, amphibians, fish, and birds. Further, the biological signal may be any one of an electroencephalogram, a cardiac potential, and a myoelectric potential. The myoelectric potential may be an ocular myoelectric potential (ocular potential) or may be another myoelectric potential.
The 2nd terminal 12 is electrically connected with the 2nd electrode which is an electrode which contacts a living body. Then, a biological signal from the second electrode is input. In addition, the living body which the 1st and 2nd electrode contacts is the same normally.

  Note that the contact of the first and second electrodes with the living body may be direct contact or contact via an electrode glue or the like. For example, when the living body is an animal other than a human being, the electrode may be a needle, a bolt, or the like embedded in the living body. Further, it is preferable that the first and second electrodes are attached to appropriate portions of the living body in accordance with a biological signal to be amplified (for example, an electroencephalogram, a cardiac potential, etc.). In addition, the first and second electrodes and the first and second terminals 11 and 12 are each connected by a conductive cable, and it is preferable that the length of the cable is short. This is to reduce the influence of hum noise received from the commercial power supply. For example, the length of the wiring from the first electrode to the differential amplifier 14 and the length of the wiring from the second electrode to the differential amplifier 14 are preferably 1 meter or less, respectively. More preferably, it is centimeters or less, and further preferably 30 centimeters or less.

  The voltage divider 13 divides the voltage between the first and second terminals 11 and 12 at a predetermined ratio. The divided voltage is used as the ground voltage of the differential amplifier 14 as will be described later. The voltage divider 13 may be realized by, for example, a variable resistor, an electronic volume, an attenuator, or the like. Further, the voltage divider 13 may be capable of dividing the voltage between the first and second terminals 11 and 12 at an arbitrary ratio, or a plurality of predetermined ratios (usually, jumping off). It may be one that can be divided in pressure). The ratio of the partial pressure is adjusted by the adjusting unit 15.

  The differential amplifier 14 amplifies the difference between the biological signals input to the first and second terminals 11 and 12. At the time of amplification, the differential amplifier 14 performs amplification using a ground voltage that is a voltage divided by the voltage divider 13. Although FIG. 1 shows a case where the signal 101 from the first terminal 11 is a positive input and the signal 102 from the second terminal 12 is a negative input, the reverse may be possible. The frequency band of the signal amplified by the differential amplifier 14 does not matter. When a signal in a specific frequency band is amplified, a filter that allows a signal in a desired frequency band to pass therethrough may be provided before the differential amplifier 14, and only the signal in that frequency band may be amplified. The frequency band may include a frequency corresponding to hum noise, for example, 50 Hz or 60 Hz.

  The adjustment unit 15 adjusts the ground voltage divided by the voltage divider 13 so that the hum noise input to the first and second terminals 11 and 12 is canceled out. The adjustment unit 15 includes a differential amplifier 21, a BPF 22, 23, a synchronous detector 24, an extractor 25, and a controller 26. The ground voltage is adjusted by adjusting a voltage dividing ratio in the voltage divider 13.

  The differential amplifier 21 amplifies the difference between the signal 101 input to the first terminal 11 and the ground voltage signal 103 divided by the voltage divider 13. In the differential amplifier 21, the signal 101 from the first terminal 11 is a positive input, and the divided signal 103 is a negative input.

  The BPFs 22 and 23 are band pass filters that allow only certain frequency component signals to pass through. The frequency is a frequency according to the frequency of the commercial power source, that is, hum noise. Therefore, each of the BPFs 22 and 23 inputs a noise component corresponding to the frequency of the commercial power supply to the synchronous detector 24. For example, the BPFs 22 and 23 may extract a signal with a frequency component of 50 Hz, may extract a signal with a frequency component of 60 Hz, may extract a signal with a frequency component of both 50 Hz and 60 Hz, A signal having a frequency band of 50 to 60 Hz may be extracted. The BPF 22 extracts a signal having a frequency component corresponding to hum noise from the signal input to the first terminal 11. In FIG. 1, the output of the differential amplifier 21 is used as a signal input to the first terminal 11. The BPF 23 extracts a signal having a frequency component corresponding to the hum noise from the output signal of the differential amplifier 14. The BPFs 22 and 23 may both extract signals having the same frequency component.

  The synchronous detector 24 uses the signal extracted by the BPF 22 to synchronously detect the signal extracted by the BPF 23. The noise component of the signal extracted by the BPF 22, that is, the signal input to the first terminal 11 is used as a reference signal. For example, the synchronous detector 24 may multiply the reference signal by a signal that has passed through the BPF 23.

  The extractor 25 extracts the direct current component of the signal 107 synchronously detected by the synchronous detector 24. For example, the extractor 25 may be a low-pass filter that allows only the DC component of the signal 107 to pass therethrough or may be a circuit that performs a moving average process. By using this extractor 25, even if a signal that has passed through the BPFs 22 and 23 contains a component of a biological signal, adjustment according to the component can be prevented. Even if a component of a biological signal is included in a signal that has passed through the BPFs 22 and 23, it is not considered to be a signal with a constant period like hum noise. This is because the signal component can be removed.

  The controller 26 uses the DC component extracted by the extractor 25 to adjust the ground voltage so that the output of the differential amplifier 14 corresponding to the hum noise becomes small. That is, the controller 26 adjusts the ratio of the partial pressure of the voltage divider 13 so that the noise component corresponding to the frequency of the commercial power supply is reduced. Specifically, the controller 26 adjusts the ground voltage so that the DC component extracted by the extractor 25 approaches zero. The differential amplifier 14 amplifies the biological signal using the adjusted ground voltage. The adjustment is performed so that the hum noise component approaches 0. However, for example, when the ratio of the partial pressure by the voltage divider 13 can only take a discrete value, the hum noise component may not become 0. possible. Therefore, the adjustment unit 15 adjusts the ratio of the voltage divider 13 to cancel the hum noise input to the first and second terminals 11 and 12. It may be cancellation or cancellation in the sense of reducing the output hum noise component. A specific control method will be described later.

The adjustment by the adjustment unit 15 is normally performed dynamically when a biological signal is input to the first and second terminals 11 and 12. This is because, as will be described later, the ratio of the partial pressure suitable for canceling the hum noise components input from the first and second terminals 11 and 12 can constantly change.
In addition, among the configurations included in the adjustment unit 15, a configuration that can be realized by an MCU (microcontroller) may be realized by the MCU.

Here, a method of adjusting the partial pressure ratio of the voltage divider 13 will be described with reference to FIGS. FIG. 2 is a diagram illustrating a circuit configuration related to voltage division. In FIG. 2, wiring related to the transmission unit 16 and the differential amplifier 21 is omitted. FIG. 3 is a waveform diagram showing each signal in the biological signal amplifying apparatus 2. In FIG. 2, there are resistances related to electrode contact points, electrode glue, and the like between the portion where the biological signal of the subject is generated and the first and second terminals 11 and 12. The resistance value is not known, but those that can vary according to the motion, temperature, etc. of the subject (or a test animal), where, as shown in Figure 2, they each R _1, and R _2. The voltage divider 13 divides the voltage between the first and second terminals 11 and 12 in a ratio of R ₃ : R ₄ . Further, the voltage of the biological signal that is input to the first electrode side (the first terminal 11 side) V _1, the voltage of hum an e _n1, inputted to the second electrode side (the second terminal 12 side) _{V 2} the voltage of the biological signal that is, when the voltage of hum an _{e n2,} GND reference voltage of the signal _{101, (V 1 + e n1)} × R 3 / (R 1 + R 3) next, GND signal 102 The reference voltage is (V ₂ + en ₂ ) × R ₄ / (R ₂ + R ₄ ). When the amplification factor of the differential amplifier 14 is K, the voltage of the signal 105 is K × {(V ₁ + en ₁ ) × R ₃ / (R ₁ + R ₃ ) − (V ₂ + en ₂ ) × R ₄ / (R ₂ + R ₄ )}. Here, the hum noise components input from the first and second terminals 11 and 12 are considered to have the same phase. This will be briefly described. Since the frequency of hum noise is usually 50 Hz or 60 Hz, the wavelength is about 5000 to 6000 km. Compared to such a very long wavelength, the distance between the two electrodes is sufficiently negligible. Therefore, it is considered that there is no problem even if the hum noise components input from the first and second electrodes (first and second terminals 11 and 12) are considered to be in phase. Therefore, in order to component hum is canceled _{out, e n1 × R 3 / (} R 1 + R 3) = e n2 × R 4 / (R 2 + R 4) and may be so. As described above, the resistances R ₁ and R ₂ are unknown, and normally, e _n1 ≠ en ₂ , but the voltage dividing ratio is adjusted so that the hum noise output from the differential amplifier 14 is reduced. by _{a e n1 × R 3 / (R} 1 + R 3), e n2 × R 4 / (R 2 + R 4) and to match, or can be approximated, hum inputted from the terminals Can be offset. Next, specific processing will be described.

FIG. 3A is a waveform diagram showing the hum noise component of the signal 101 input to the first terminal 11 and the hum noise component of the signal 102 input to the second terminal 12. The differential amplifier 21 receives the signals 101 and 103 and outputs a signal corresponding to the difference between the two signals. A signal 104 obtained by extracting a frequency component corresponding to hum noise from the output of the differential amplifier 21 (GND reference signal 101) is output from the BPF 22. Note that the hum noise component of the signal 103 is obtained by dividing the hum noise component of the signals 101 and 102 shown in FIG. 3A by a ratio of R ₃ : R ₄ , so that the signals 101 and 103 are differentially amplified. The signal 104 from which the hum noise component has been extracted is as shown in FIG. Further, the signals 101 to 103 are input to the differential amplifier 14, and a signal 105 proportional to the difference between the signal 101 based on the signal 103 and the signal 102 based on the signal 103 is output. A signal 106 obtained by extracting a frequency component corresponding to hum noise from the signal 105 is output from the BPF 23. FIG. 3C is a waveform diagram showing the signal 106. Further, the signals 104 and 106 are multiplied by the synchronous detector 24, and the signal 107 shown in FIG. 3D is output. Then, the extractor 25 extracts a signal 108 that is a DC component of the signal 107. FIG. 3E is a waveform diagram showing the signal 108. As can be seen from the above description, when the voltages of the hum noise components of the signals 101 and 102 match, the hum noise input from the first and second terminals 11 and 12 is canceled, and the signal 108 is 0. Therefore, when the voltage of the signal 108 is positive, the controller 26 only needs to adjust the voltage dividing ratio of the voltage divider 13 so that R ₃ becomes smaller and R ₄ becomes larger. With that adjustment, the signal 108 becomes smaller. On the other hand, when the voltage of the signal 108 becomes negative, the controller 26 may adjust the voltage dividing ratio of the voltage divider 13 so that R ₃ becomes larger and R ₄ becomes smaller. In this way, the voltage division ratio can be adjusted so that the hum noise components input to the first and second terminals 11 and 12 are canceled out.

Note that the resistances R ₁ and R ₂ of the electrodes vary depending on the type of electrode and the like, but are, for example, about 1 kΩ to several MΩ. Therefore, the resistance (R ₃ + R ₄ ) of the voltage divider 13 may be set to a value sufficiently larger than them. For example, the resistance (R ₃ + R ₄ ) of the voltage divider 13 may be set to 10 MΩ or more, may be set to 100 MΩ or more, or may be set to another value that can appropriately remove hum noise. .

  The transmitter 16 wirelessly transmits a transmission signal that is the output signal 105 of the differential amplifier 14. As shown in FIG. 4, the transmitter 16 includes a PFM modulator 31, a differentiator 32, an ASK modulator 33, and a power amplifier 34. The transmitter 16 may transmit radio waves or infrared light. In the present embodiment, the former case will be mainly described. In addition, the transmission signal to be transmitted may be a digital signal after AD conversion, or an analog signal before AD conversion. Moreover, when the transmission part 16 transmits a transmission signal by radio | wireless, the biosignal transmitter 1 may operate | move with the electric power supplied from the battery which is not shown in figure. Further, when the biological signal is transmitted wirelessly, the influence of hum noise can be reduced as compared with the case where the biological signal is transmitted. This is because a biological signal can be transmitted without using a wired cable that is affected by hum noise. It is preferable that the wiring from the differential amplifier 14 to the transmission unit 16, the wiring in the transmission unit 16, and the wiring from the transmission unit 16 to the antenna are also short. This is to reduce the influence of hum noise.

  The PFM modulator 31 performs pulse frequency modulation on the transmission signal that is the output of the biological signal amplification device 2. By the pulse frequency modulation, for example, as shown in FIG. 5A, the transmission signal is converted into a signal 201 having a constant pulse width and changing the transmission interval (frequency) of the pulse.

  The differentiator 32 differentiates the pulse frequency modulated signal. By the differentiation, for example, the pulse 201 modulated by the pulse frequency is converted into a signal 202 shown in FIG.

  The ASK modulator 33 performs ASK modulation (amplitude shift keying) on the differentiated signal. By the ASK modulation, for example, as shown in FIG. 5C, the differentiated signal 202 is converted into a signal 203 in which a carrier wave exists only during a period in which the signal 202 is high (a period equal to or greater than a threshold). The Specifically, the carrier wave may be transmitted using a switch that is turned on only when the signal 202 is high. With this ASK modulation, no signal is transmitted during a period when the signal 202 is not high, and transmission power can be reduced.

  The power amplifier 34 amplifies the power of the signal 203 after ASK modulation, and sends the amplified signal to the antenna. In this way, the transmission signal after ASK modulation corresponding to the biological signal is wirelessly transmitted from the biological signal transmitting apparatus 1.

  In addition, when demodulating the transmission signal transmitted from the biological signal transmission apparatus 1, the signal 201 after PFM modulation can be reproduced by performing processing opposite to that at the time of modulation. Specifically, the rising point of the signal after PFM modulation can be known from the position where the carrier wave exists in the received signal, and the pulse width in PFM modulation is known, so that the signal 201 after PFM modulation can be reproduced. . Then, an amplified biological signal can be obtained by performing PFM demodulation on the signal 201.

  Further, in the biological signal amplifying apparatus 2 in FIG. 1, the case of performing synchronous detection or the like has been described, but this need not be the case. For example, the voltage dividing ratio by the voltage divider 13 may be adjusted so that the hum noise component in the output signal of the amplifier becomes small. FIG. 6 is a diagram illustrating a configuration of such a biological signal transmission device 1. In the biological signal transmission device 1 of FIG. 6, the configuration and operation other than the adjustment unit 15 of the biological signal amplification device 2 are the same as those described above, and the description thereof is omitted. In FIG. 6, the adjustment unit 15 included in the biological signal amplifying apparatus 2 includes a BPF 23, a rectifier 41, an extractor 42, and a controller 43. The BPF 23 is the same as that described above, and extracts a hum noise component from the output signal of the differential amplifier 14.

The rectifier 41 rectifies the signal extracted by the BPF 23. The rectification may be, for example, full wave rectification or half wave rectification.
The extractor 42 extracts a DC component of the signal rectified by the rectifier 41. The extractor 42 is the same as the extractor 25 described above. For example, the extractor 42 may be a low-pass filter that passes only the DC component of the rectified signal, or may be a circuit that performs moving average processing. .

The controller 43 adjusts the ground voltage so that the DC component extracted by the extractor 42 becomes small. Therefore, the controller 43 may hold the output voltage from the extractor 42 before adjustment. Then, the controller 43 changes the partial pressure ratio in a certain direction, and if the change causes the output voltage of the extractor 42 to approach 0 compared to before the adjustment, the partial pressure ratio continues in that direction. If the change causes the output voltage of the extractor 42 to be far from 0 compared to before adjustment, the partial pressure ratio may be changed in the opposite direction. Specifically, the controller 43 first adjusts the partial pressure ratio so that R ₃ becomes larger (or smaller). Next, the output voltage from the extractor 42 after the adjustment is compared with the output voltage that has been held before the adjustment, and if the adjusted output voltage is closer to 0, the same adjustment is performed. That is, the adjustment for increasing R ₃ (or the adjustment for decreasing R ₃ ) is repeated. On the other hand, if the adjusted output voltage is away from 0, the hum noise component has increased due to the adjustment, and therefore the controller 43 adjusts the voltage dividing ratio in the opposite direction. That is, the controller 43 performs adjustment to reduce the _{R 3} (or _{R 3} a larger adjustment). By such feedback control, the voltage dividing ratio of the voltage divider 13 can be adjusted so that the hum noise components input to the first and second terminals 11 and 12 are canceled out, and the hum noise can be reduced. it can. In order to prevent the feedback control from diverging, for example, the amount of change in the voltage dividing ratio (for example, the amount of change in the resistance R ₃ ) is adjusted according to the absolute value of the output voltage from the extractor 42. May be. That is, the controller 43 may perform feedback control in which the amount of change per time decreases as the absolute value of the output voltage from the extractor 42 decreases.

(Experimental example)
An experiment for confirming the reduction of hum noise was performed using the biological signal amplifying apparatus 2 shown in FIG. In the experiment, two electrodes connected to the first and second terminals 11 and 12 are mounted on the thigh of the subject, and an electric cord is wound around the knee of the same leg several times. An AC current was passed through the electrical cord. The electric cord reproduces the same situation as when the electric blanket is hung down from the knee. FIG. 7 is a waveform diagram showing an output signal of the differential amplifier 14 in such a situation. In this experiment, the amplification factor by the differential amplifier 14 was set to 2000 times. Before the “adjustment start” time point in FIG. 7 (on the left side), since the adjustment unit 15 is not operated, a lot of hum noise is observed. On the other hand, when the adjustment unit 15 is operated at the “adjustment start” time point, it is understood that the hum noise is reduced by the adjustment. That is, it was confirmed that the hum noise can be appropriately removed from the biological signal by the biological signal amplifying apparatus 2 according to the present embodiment.

  As described above, according to the biological signal transmission device 1 according to the present embodiment, the hum noise input to the first and second terminals 11 and 12 is canceled by adjusting the partial pressure ratio of the voltage divider 13. You can make it. As a result, hum noise contained in the biological signal can be reduced, and the biological signal can be analyzed with higher accuracy. In particular, since the electroencephalogram and the myoelectric potential of the eyeball are weak, the influence of hum noise is increased. However, hum noise can be appropriately removed even in such a situation. For example, when measuring a biological signal of a subject using an electric blanket, the influence of hum noise increases, but even in such a situation, the biological signal can be appropriately measured. Conventionally, by using a notch filter or the like, the frequency component corresponding to the hum noise is removed from the biological signal, so that the information of the biological signal of the frequency component is impaired. On the other hand, in the biological signal amplifying apparatus 2 according to the present embodiment, hum noise can be removed without using such a notch filter or the like, so that a biological signal corresponding to the frequency band of hum noise can also be used for analysis or the like. . Further, since the biological signal can be amplified without using the ground electrode, it is possible to prevent electric shock of the subject or the subject animal. In addition, since the number of electrodes attached to the subject or the test animal can be reduced, the stress on the subject or the like can be reduced. As a result, the measurement of the biological signal in a more natural state can be performed. It becomes possible. In addition, when PFM modulation, differentiation, and ASK modulation are performed in the transmission unit 16, transmission power can be reduced. As a result, it is possible to realize transmission of a biological signal for a longer period without replacing the battery.

  In the present embodiment, the case where the transmission unit 16 has the configuration shown in FIG. 4 has been described, but this need not be the case. When it is not so important to reduce the transmission power, the transmission of the biological signal may be realized using a transmission unit having another configuration.

  In the present embodiment, the case where a biological signal is transmitted wirelessly has been described, but this need not be the case. It goes without saying that the biological signal may be transmitted by wire. Therefore, the biological signal amplifying apparatus 2 may be used other than the biological signal transmitting apparatus 1.

  Further, in the present embodiment, the case where the adjustment unit 15 has the configuration shown in FIGS. 1 and 6 has been described, but as a result, the hum noise input to the first and second terminals 11 and 12 is canceled. Needless to say, the adjustment unit 15 may have a configuration other than those as long as it can be adjusted.

  In the present embodiment, the voltage divider 13 selects the voltage drop between the first and second terminals 11 and 12 by selecting the position of the voltage drop as shown in FIG. Although the case where the partial pressure is divided has been described, this need not be the case. As long as the voltage between the first and second terminals 11 and 12 can be divided, the configuration of the voltage divider 13 is not limited thereto. For example, the voltage divider 13 may have the configuration shown in FIG. In FIG. 8, the voltage divider 13 divides the voltage between the first and second terminals 11, 12 and the resistors R 11, R 12, R 13 connected in series and the voltage of the node 121 after the voltage division (hereinafter, referred to as “voltage divider”). Switches SW1 and SW2 that alternately select one of the “first voltage” and the voltage of the node 122 after voltage division (hereinafter sometimes referred to as “second voltage”); Is provided. The voltage selected by the switches SW1 and SW2 is obtained by dividing the voltage between the first and second terminals 11 and 12, and is used as the ground voltage of the differential amplifier 14. The magnitudes (resistance values) of the resistors R11 and R13 may or may not be the same. Here, the case where both are the same is mainly described. Further, the resistance value of the resistor R12 may be smaller than that of the resistors R11 and R13, or may not be so. Here, the former case will be mainly described. Since the resistances R11 and R13 are larger than the resistance R12, it is possible to reduce the influence of noise generated by switching the switches SW1 and SW2 on the biological signal. For example, the resistors R11 and R13 may be 10 MΩ, and the resistor R12 may be 2 MΩ. Strictly speaking, the voltage divider 13 shown in FIG. 8 cannot divide the voltage between the first and second terminals 11 and 12 at an arbitrary ratio, and the first and second voltages can be divided. The pressure will be divided. That is, the range in which voltage division is possible is narrower than the voltage between the first and second terminals 11 and 12. The range in which the voltage can be divided is determined according to the sizes of the resistors R11 and R13 and the resistor R12. Therefore, when the range in which the voltage can be divided is increased, for example, the resistance value of the resistor R12 is increased. Or the resistance values of the resistors R11 and R13 may be reduced. For example, semiconductor switches such as FETs are preferably used as the switches SW1 and SW2. Further, FIG. 8 shows the case where voltage division is performed using two switches SW1 and SW2, but as a result, the number of switches is not limited as long as the first and second voltages can be divided. Absent.

  Next, a method for alternately selecting one of the first and second voltages by the switches SW1 and SW2 of the voltage divider 13 shown in FIG. 8 will be described. As shown in the waveform diagram of FIG. 9, when the switch SW1 is ON, the switch SW2 is OFF, and when the switch SW1 is OFF, the switches SW1 and SW2 are controlled so that the switch SW2 is ON. And As a result, the ground voltage of the differential amplifier 14 becomes the first or second voltage selected by the switches SW1 and SW2. Note that one cycle “T3 (s)” of ON and OFF of the switches SW1 and SW2 is constant, and the frequency (= 1 / T3) corresponding to the cycle T3 is the first and second terminals 11 and 12. It is assumed that the frequency is higher than the frequency of the biological signal input to. For example, when the biological signal is an electroencephalogram, the frequency is about 0.5 to 100 Hz. Therefore, the switching frequency (= 1 / T3) of the switches SW1 and SW2 may be about 10 kHz, for example. By doing so, it is possible to realize a partial pressure according to the ratio of ON and OFF in one cycle. For example, as shown in FIG. 9, assuming that the OFF period in one cycle of the switch SW1 is T1 (s) and the ON period is T2 (s), the voltage after voltage division (= ground voltage) Is a value obtained by dividing the first and second voltages at a ratio of T2: T1. As shown in FIG. 9, the switch controller (not shown) that controls the switches SW <b> 1 and SW <b> 2 may be included in the voltage divider 13 or may be included in the adjustment unit 15. In the former case, the adjustment unit 15 outputs an instruction regarding the increase or decrease of the ground voltage to the voltage divider 13, and the switch control unit controls each of the switches SW1 and SW2 according to the instruction. Become. On the other hand, in the latter case, a switch control unit (for example, which may be included in the controllers 26 and 43) included in the adjustment unit 15 is input to the first and second terminals 11 and 12. The switches SW1 and SW2 are controlled so that the hum noise is canceled out. The ground voltage divided by the voltage divider 13 is adjusted by changing the periods T1 and T2. Although the case where the period T3 (= T1 + T2) is unchanged has been described here, this need not be the case. For example, the divided voltage may be adjusted by making one of the periods T1 and T2 constant and changing the other. In that case, T3 will change. As described above, when the voltage divider 13 is configured by the resistors R11, R12, and R13 and the switches SW1 and SW2, the circuit scale is reduced to, for example, 1 / compared to the voltage divider 13 configured by a variable resistor, an electronic volume, or the like. The biological signal amplification device 2 can be downsized.

  In the above embodiment, each process or each function may be realized by centralized processing by a single device or a single system, or may be distributedly processed by a plurality of devices or a plurality of systems. It may be realized by doing.

  In the above embodiment, the information exchange between the components is performed by one component when, for example, the two components that exchange the information are physically different from each other. It may be performed by outputting information and receiving information by the other component, or when two components that exchange information are physically the same, one component May be performed by moving from the phase of the process corresponding to to the phase of the process corresponding to the other component.

  In the above embodiment, information related to processing executed by each component, for example, information received, acquired, selected, generated, transmitted, or received by each component In addition, information such as threshold values, mathematical formulas, setting values, and the like used by each component in processing may be temporarily or over a long period of time in a recording medium (not shown), even if not specified in the above description. . Further, the storage of information on the recording medium (not shown) may be performed by each component or a storage unit (not shown). Further, reading of information from the recording medium (not shown) may be performed by each component or a reading unit (not shown).

  Further, in the above embodiment, when the information used by each component etc., for example, information such as threshold values and various set values used by each component may be changed by the user, the above explanation is given. Even if not specified, the user may be able to change the information as appropriate, or may not be so. If the information can be changed by the user, the change is realized by, for example, a not-shown receiving unit that receives a change instruction from the user and a changing unit (not shown) that changes the information in accordance with the change instruction. May be. The change instruction received by the receiving unit (not shown) may be received from an input device, information received via a communication line, or information read from a predetermined recording medium, for example. .

  In the above-described embodiment, each component may be configured by dedicated hardware, or a component that can be realized by software may be realized by executing a program. For example, each component can be realized by a program execution unit such as a CPU reading and executing a software program recorded on a recording medium such as a hard disk or a semiconductor memory. At the time of execution, the program execution unit may execute the program while accessing the storage unit or the recording medium. The program may be executed by reading a program recorded on a predetermined recording medium (for example, a magnetic disk or a semiconductor memory). Further, the computer that executes the program may be singular or plural. That is, centralized processing may be performed, or distributed processing may be performed.

  Further, the present invention is not limited to the above-described embodiment, and various modifications are possible, and it goes without saying that these are also included in the scope of the present invention.

  As described above, according to the biological signal transmitting apparatus and the like according to the present invention, an effect that the influence of hum noise can be reduced is obtained.

DESCRIPTION OF SYMBOLS 1 Biosignal transmitter 2 Biosignal amplifier 11 1st terminal 12 2nd terminal 13 Voltage divider 14, 21 Differential amplifier 15 Adjustment part 16 Transmission part 22, 23 BPF (band pass filter)
24 Synchronous detector 25, 42 Extractor 26, 43 Controller 31 PFM modulator 32 Differentiator 33 ASK modulator 34 Power amplifier 41 Rectifier

Claims (8)

First and second terminals to which a biological signal is input;
A voltage divider that divides the voltage between the first and second terminals at a predetermined rate;
A differential amplifier that amplifies a difference between the biological signals input to the first and second terminals using a ground voltage that is a voltage divided by the voltage divider;
A biological signal amplifying apparatus comprising: an adjustment unit that adjusts a ground voltage divided by the voltage divider so that hum noise input to the first and second terminals is canceled. The adjustment unit is
A bandpass filter for extracting a signal of a frequency component corresponding to hum noise from the output of the differential amplifier;
A rectifier that rectifies the signal extracted by the bandpass filter;
An extractor for extracting a DC component of the signal rectified by the rectifier;
A controller that adjusts the ground voltage so that the direct current component extracted by the extractor is reduced, and
The biological signal amplification device according to claim 1, wherein the differential amplifier performs amplification related to the biological signal using a ground voltage adjusted by the controller. The adjustment unit is
A first bandpass filter that extracts a signal of a frequency component corresponding to hum noise from the output of the differential amplifier;
A second band-pass filter that extracts a signal having a frequency component corresponding to hum noise from the signal input to the first terminal;
A synchronous detector for synchronously detecting the signal extracted by the first bandpass filter using the signal extracted by the second bandpass filter;
An extractor for extracting a DC component of the signal synchronously detected by the synchronous detector;
A controller that adjusts the ground voltage so that the output of the differential amplifier corresponding to hum noise is reduced using the DC component extracted by the extractor;
The biological signal amplification device according to claim 1, wherein the differential amplifier performs amplification related to the biological signal using a ground voltage adjusted by the controller. The electrode to which the first terminal is connected, the length of the wiring from the first electrode which is an electrode in contact with a living body to the differential amplifier, and the electrode to which the second terminal is connected, The biological signal amplification device according to any one of claims 1 to 3, wherein the length of the wiring from the second electrode, which is an electrode in contact with the living body, to the differential amplifier is 1 meter or less. The voltage divider alternately selects one of the first and second voltages obtained by dividing the voltage between the first and second terminals at a frequency higher than the frequency of the biological signal. The biological signal amplifying device according to claim 1, wherein the voltage between the first and second terminals is divided. The biological signal amplifying apparatus according to claim 1, wherein the biological signal is one of an electroencephalogram, a cardiac potential, and a myoelectric potential. The biological signal amplifying device according to any one of claims 1 to 6,
A biological signal transmission apparatus comprising: a transmission unit that wirelessly transmits a transmission signal that is an output signal of the differential amplifier. The transmitter is
A PFM modulator for performing pulse frequency modulation on the transmission signal;
A differentiator for differentiating the pulse frequency modulated signal;
An ASK modulator that performs ASK modulation on the differentiated signal;
The biological signal transmission apparatus according to claim 7, wherein the ASK modulated signal is wirelessly transmitted.