JP2012205632A - Contact state detecting circuit, biological signal acquisition device, and health equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological signal acquisition device which can evaluate the contact state of an electrode more promptly than before, and which can record a biological signal with a high quality.SOLUTION: An impedance measurement circuit 20 measures a contact impedance by adding a current to the electrode 10, and outputs a voltage Vimp. An impedance calculation circuit 40 calculates the value of the contact impedance from the voltage Vimp, and outputs a voltage Vcal corresponding to the value of impedance. A reference voltage-generating circuit 50 supplies a voltage Vref based on a reference value of the contact impedance. A comparator 60 compares those 2 voltages Vcal and Vref, and determines the contact state of the electrode. As a result, the fluctuation of the contact state of the electrode is promptly detected.

Description

  The present invention relates to a biological signal acquisition apparatus that acquires a biological signal by bringing a contact-type electrode into contact with a predetermined part of a human body, and more particularly to a circuit that detects a contact state between an electrode and skin.

  Biological signal acquisition devices that measure and record electrical signals of living bodies such as electroencephalograms and electrocardiograms are widely used. When using such a biological signal acquisition device, in order to reduce the contact impedance between the electrode attached to the living body and the skin and to record a high-quality signal, the electrode is often attached via a conductive gel or the like.

  However, when measuring a biological signal only for a short time in a hospital or the like, the measurement can be performed by a stationary biological signal acquisition device using an electrode through a conductive gel. In the case of measuring a biological signal while feeding a contact-type electrode (also called a dry electrode) that does not use a conductive gel or the like is used from the viewpoint of ease of use and is often measured by a portable biological signal measurement device. .

  The quality of biological signals collected using contact-type electrodes varies greatly depending on the degree of adhesion between the electrodes and the skin. Generally, in order to detect the contact state between the contact-type electrode and the skin, the contact impedance of the electrode is measured, and the contact state is determined based on the measured contact impedance value.

  FIG. 13 shows the configuration of the biological signal acquisition apparatus described in Patent Document 1. The biological signal acquisition apparatus 900 includes an electrode unit 910 and a main body 920. The main body 920 includes an AD conversion unit 921, an impedance measurement unit 922, a display unit 923, an input unit 924, an output unit 925, a CPU 926, a ROM 927, a RAM 928, a biological signal recording unit 929, and an external I / O. Each component is connected to each other by a CPU bus 931.

  The biological signal acquired by the electrode unit 910 is amplified to a predetermined voltage range by the AD conversion unit 921 and converted into digital data under a predetermined sampling condition. Digital data for a section T1 (for example, t1 = 10 seconds) shown in FIG. 14 is temporarily stored in a buffer which is a predetermined area of the RAM 928 of FIG. The impedance measuring unit 922 measures the contact impedance based on the digital data for 10 seconds stored in the buffer, and determines the contact state between the electrode and the skin. If it is determined that the contact state is good, the biological signal data for the subsequent section T2 (for example, t2 = 50 seconds) is recorded in an area different from the buffer of the RAM 128, and the biological signal acquisition process is terminated. To do.

JP 2003-102695 A

  However, when the contact state of the electrode is poor, external noise such as radio waves is mixed and the signal acquired by the electrode becomes unstable, so that the quality of the signal acquired by the biological signal acquisition device is deteriorated. The conventional biological signal acquisition apparatus has a configuration in which the impedance measurement unit 922 is disposed after the biological signal amplification integrated circuit (AD conversion unit 921), and thus has a problem that it cannot cope with a sudden change in the contact state. . For example, since the AD converter 921 itself cannot determine the quality of the signal even if the electrode suddenly changes to a state where it is separated from the skin at time t = tx during the recording of the biological signal of the section T2, It continued to output digital data of erroneous measurements. As a result, the “invalid” biological signal is erroneously recognized as “valid” and recorded in the RAM 928 and the biological signal recording unit 929, resulting in deterioration of the signal quality to be acquired.

  Accordingly, the present invention solves the above-described conventional problems, and an object thereof is to provide a biological signal acquisition apparatus capable of recording a high-quality biological signal.

In order to solve the above-described problem, a contact state detection circuit according to the invention of claim 1 includes:
A contact state detection circuit for detecting a contact state between an electrode and skin,
An impedance measurement circuit for measuring a contact impedance of the electrode, comprising a measurement current source for applying an alternating current to the electrode;
An impedance calculation circuit that outputs a first voltage corresponding to the contact impedance to a first node based on an output signal of the impedance measurement circuit;
A reference voltage generation circuit that outputs a second voltage corresponding to an impedance threshold for detecting the contact state to a second node;
A comparator for comparing the first voltage and the second voltage is provided.

  Thus, by measuring the contact impedance of the electrode and calculating the impedance, it is possible to quickly detect the contact state between the electrode and the skin, and the advantage that the quality of the acquired biosignal data can be ensured. is there.

The contact state detection circuit according to claim 2,
The contact state detection circuit according to claim 1,
The current source for measurement is characterized in that the frequency of the alternating current can be adjusted.

  As a result, in the configuration of claim 1, by further adjusting the frequency of the alternating current in claim 2, it is possible to measure the contact impedance even at different frequencies and to obtain the frequency characteristic of the contact impedance. is there.

The contact state detection circuit according to claim 3,
The contact state detection circuit according to claim 1,
The impedance calculation circuit includes an absolute value calculation circuit.

  Thereby, in the structure of Claim 1, it has the advantage that the value of an impedance can be obtained easily by having an absolute value calculation circuit further in Claim 3.

The contact state detection circuit according to claim 4,
The reference voltage generation circuit includes:
A first resistance element having one end connected to a power supply voltage and the other end connected to the second node;
And a second resistance element having one end connected to the second node and the other end connected to a ground voltage.

  Thus, in the configuration of claim 1, the reference voltage can be easily generated using the resistance voltage dividing configuration of claim 4.

The contact state detection circuit according to claim 5,
In the contact state detection circuit according to claim 4,
The reference voltage generation circuit includes:
The resistance value of the first or second resistance element is adjustable.

  Thus, in the configuration of claim 4, the threshold value for determining the contact state can be made variable by changing the resistance value of the resistance element in claim 5, so that the contact state detection can be performed for more electrodes. There is an advantage that it can be applied to a circuit.

The contact state detection circuit according to claim 6 comprises:
The contact state detection circuit according to claim 1,
The reference voltage generation circuit includes:
A first current source having one end connected to the power supply voltage and the other end connected to the second node;
And a third resistance element having one end connected to the second node and the other end connected to a ground voltage.

  Thus, in the configuration of claim 1, the reference voltage can be easily generated by providing the constant current source and the resistance element in claim 6.

The contact state detection circuit according to claim 7,
The reference voltage generation circuit includes:
The current value of the first current source or the resistance value of the third resistance element can be adjusted.

  Thereby, in the configuration of claim 6, the threshold value for determining the contact state can be made variable by changing the resistance value of the resistance element in claim 7, so that the contact state detection can be performed for more electrodes. There is an advantage that it can be applied to a circuit.

The contact state detection circuit according to claim 8,
A contact state detection circuit for detecting a contact state between n electrodes (n is an integer of 2 or more) and skin,
A selection circuit for selecting one of the n electrodes;
An impedance measurement circuit for measuring a contact impedance of the electrode, comprising a measurement current source for applying an alternating current to the electrode;
An impedance calculation circuit that outputs a first voltage corresponding to the contact impedance to a first node based on an output signal of the impedance measurement circuit;
A reference voltage generation circuit that outputs a second voltage corresponding to an impedance threshold for detecting the contact state to a second node;
A comparator for comparing the first voltage and the second voltage is provided.

  Thus, when it is desired to detect the contact state of a plurality of electrodes, the contact state of all the electrodes can be examined by providing one contact state detection circuit that can select the electrode for measuring the contact impedance.

The contact state detection circuit according to claim 9,
In the contact state detection circuit according to claim 8,
The current source for measurement is characterized in that the frequency of the alternating current can be adjusted.

  Thus, in the configuration of claim 8, by making it possible to adjust the frequency of the alternating current in claim 9, it is possible to measure the contact impedance even at different frequencies and to obtain the frequency characteristic of the contact impedance. is there.

The contact state detection circuit according to claim 10,
In the contact state detection circuit according to claim 8,
The impedance calculation circuit includes an absolute value calculation circuit.

  Thus, the configuration of claim 8 has the advantage that the impedance value can be easily obtained by further including the absolute value calculation circuit of claim 10.

The contact state detection circuit according to claim 11 comprises:
In the contact state detection circuit according to claim 8,
The reference voltage generation circuit includes:
A first resistance element having one end connected to a power supply voltage and the other end connected to the second node;
And a second resistance element having one end connected to the second node and the other end connected to a ground voltage.

  Thus, in the configuration of claim 1, the reference voltage can be easily generated using the resistance voltage dividing configuration of claim 4.

The contact state detection circuit according to claim 12,
The contact state detection circuit according to claim 11,
The reference voltage generation circuit includes:
The resistance value of the first or second resistance element is adjustable.

  Thus, in the configuration of claim 11, the threshold value for determining the contact state can be made variable by changing the resistance value of the resistance element in claim 12. There is an advantage that it can be applied to a circuit.

The contact state detection circuit according to claim 13,
In the contact state detection circuit according to claim 8,
The reference voltage generation circuit includes:
A first current source having one end connected to the power supply voltage and the other end connected to the second node;
And a third resistance element having one end connected to the second node and the other end connected to a ground voltage.

  Thus, in the configuration of claim 1, the reference voltage can be easily generated by providing the constant current source and the resistance element in claim 6.

The contact state detection circuit according to claim 14,
In the contact state detection circuit according to claim 13,
The reference voltage generation circuit includes:
The current value of the first current source or the resistance value of the third resistance element can be adjusted.

  Thus, in the configuration of claim 13, the threshold value for determining the contact state can be made variable by changing the resistance value of the resistance element in claim 14. There is an advantage that it can be applied to a circuit.

The biological signal acquisition apparatus according to claim 15,
A biological signal acquisition device for acquiring a biological signal,
The contact state detection circuit according to any one of claims 1 to 14,
An AD converter that converts an analog signal obtained by the contact state detection circuit into a digital code;
And a recording unit for recording the digital code obtained by the AD converter.

  Accordingly, in the biological signal acquisition device in which it is important to ensure that the electrode is in contact with the skin, the contact state detection circuit can be used to quickly detect the contact state, and the biological signal with high signal quality. The signal can be acquired.

The health device according to claim 16,
In any one of Claims 1-14,
Each of the n electrodes (n is an integer of 1 or more) is attached to the tip, and n pressing bodies that move forward and backward with respect to the skin,
The contact state detection circuit;
And a control unit that sends a control signal for controlling the forward / backward movement to each of the n pressing bodies.

  As a result, not only the state in which the electrode and the skin are in contact but also the health device in which the separated state is important, the contact state detection circuit can be used to quickly detect the operating state of the pressing body. There is an advantage that the device can be easily controlled.

  According to the contact state detection circuit of the present invention, even if the contact state between the electrode and the skin changes suddenly, the effectiveness of the biological signal to be acquired can be quickly detected before AD conversion is performed. Therefore, a high-quality and highly reliable biological signal can be acquired.

The figure which shows the structural example of the contact state detection circuit which concerns on Embodiment 1 of this invention. Diagram showing a configuration example of an impedance measurement circuit The figure which shows the structural example of the impedance calculation circuit The figure which shows the structural example of a reference voltage generation circuit The figure which shows another structural example of a reference voltage generation circuit Diagram showing a specific example of contact impedance measurement The figure for demonstrating operation | movement of the contact state detection circuit shown in FIG. The figure which shows the structural example of the contact state detection circuit which concerns on Embodiment 2 of this invention. The figure explaining the modification of FIG. The figure which shows the structural example of a biosignal acquisition apparatus. Diagram showing a configuration example of a health device The figure for demonstrating operation | movement of the health equipment shown in FIG. The figure which shows the structure of the conventional biosignal acquisition apparatus. The figure for demonstrating operation | movement of the conventional biosignal acquisition apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected about the component which has the same function through each following embodiment, and description is abbreviate | omitted again.

<< First Embodiment >>
FIG. 1 shows a configuration example of a contact state detection circuit 100 according to the first embodiment. The contact state detection circuit 100 applies an impedance measurement current to the electrodes, and outputs an analog signal Vimp indicating an impedance signal superimposed on the biological signal and a contact failure detection signal Vdet in which the contact state is determined based on the analog signal Vimp. To do. The contact state detection circuit 100 includes an impedance measurement circuit 20 and a contact state evaluation circuit 30.

[Impedance measurement circuit]
FIG. 2 shows a configuration example of the impedance measurement circuit 20. The impedance measurement circuit 20 includes a measurement current source 21. When an alternating current I is applied to the electrode side (node N1), the voltage V2 at the node N2 on the contact state detection circuit side is superimposed on the biological signal by a voltage represented by the product of the current I and the value (Z) of the contact impedance. Value. Since the voltage V2 is output as the analog signal Vimp of the contact state detection circuit 100, V2 = Vimp. Further, as shown in FIG. 2, the nodes N1 and N2 may be the same node, that is, V1 = V2.

  The frequency of the alternating current is preferably set to a frequency (for example, 1 kHz) higher than the frequency band of the biological signal (for example, 0.01 to 200 Hz). This is because the biological signal and the contact impedance signal are separated after the contact state detection circuit 100 for analysis and recording.

  When the contact impedance is measured in the frequency band of the biological signal, only the contact impedance signal can be acquired. The reason is that the contact impedance signal (for example, 100 mV) is much larger than the biological signal (for example, several tens of μV), and the biological signal is buried in the contact impedance signal.

  The measurement current source 21 can change the measurement frequency of the contact impedance by changing the frequency of the alternating current I (for example, changing to 10 Hz). By measuring for a plurality of frequencies, the frequency characteristics of the contact impedance can be obtained.

  Further, it is desirable that the measurement current source 21 has a configuration in which the amplitude Ia of the current I can be adjusted. Even if the measurement conditions such as the type of electrode, the surface state of the skin, and the type of biological signal to be acquired are different, the voltage generated in the impedance measurement can be appropriately adjusted. In addition, it is desirable that the electrode used as the reference electrode has a function capable of setting the direction of the current in the alternating current I to be opposite.

[Contact state evaluation circuit]
The contact state evaluation circuit 30 shown in FIG. 1 is a circuit that compares the contact impedance of the electrode 10 with a predetermined reference impedance and determines the contact state of the electrode. The contact state evaluation circuit 30 includes an impedance calculation circuit 40, a reference voltage generation circuit 50, and a comparator 60.

<Impedance calculation circuit>
The impedance calculation circuit 40 is a circuit that converts the voltage V2 measured and output by the impedance measurement circuit 20 into a voltage Vcal corresponding to the contact impedance value of the electrode 10. The configuration of the impedance calculation circuit 40 is shown in FIG. The impedance calculation circuit 40 includes an absolute value circuit 41 and a constant multiplication circuit 42. As described above, since the value of the contact impedance Z is represented by a complex number, the magnitude of the contact impedance can be easily calculated by performing an operation for obtaining the absolute value of the complex number Z. The constant multiplication circuit 42 is a circuit that performs a constant multiplication based on the value of the amplitude Ia of the current I applied by the impedance measurement circuit 20.

  Usually, the equivalent circuit of the electrode and the skin is represented by a series-parallel circuit of a resistor R and a capacitor C, and the contact impedance Z is represented by a complex impedance including a real component and an imaginary component. Therefore, the contact impedance depends on the frequency of the current I. In order to determine the magnitude of the contact impedance Z, the absolute value (| Z |) of the complex impedance is calculated.

  The absolute value of the complex number may be extracted in advance by the impedance measurement circuit 20 from the real component and the imaginary component of the voltage V2, and the absolute value circuit 41 may calculate the absolute value of the complex number. If it is known that one of the real component and the imaginary component of the contact impedance is an extremely large signal, the calculation of the impedance calculation circuit 40 can be simplified. For example, when the real component of the contact impedance is much larger than the imaginary component (for example, 100 times or more), the impedance signal of the imaginary part is ignored and only the real component is input to the constant multiplier 42 and the voltage Vcal is output. May be.

<Reference voltage generation circuit>
The reference voltage generation circuit 50 is a circuit that generates a reference voltage Vref based on a threshold value of contact impedance. A configuration example of the reference voltage generation circuit 50 is shown in FIG. Two resistance elements R1 and R2 are connected in series between the power supply voltage Vdd and the ground voltage Vss. The resistance element R2 corresponds to the reference value of the contact impedance. The reference voltage Vref is a voltage obtained by dividing the power supply voltage Vdd by resistance, and can be expressed as the following equation.

  The reference voltage generation circuit 50 in FIG. 4 can adjust the voltage Vref expressed by Equation 1 by controlling the resistance value of the resistance element R2. The reference voltage Vref is adjusted when the contact impedance shows different characteristics by changing the type of electrode or the location where the electrode is attached. The reference voltage generation circuit 50 may have a configuration in which the resistance value of the resistance element R1 can be adjusted.

  Further, the reference voltage generation circuit may have the circuit configuration shown in FIG. In the reference voltage generation circuit 50a shown in FIG. 5, a current source 51 and a resistance element R3 are connected in series between a power supply voltage Vdd and a ground voltage Vss. The resistance value of the resistance element R3 corresponds to the reference value of the contact impedance. The reference voltage Vref can be expressed by the following equation when the current value of the current source 51 is Iref.

  In the reference voltage generation circuit 50a, the voltage Vref expressed by Equation 1 can be adjusted by controlling the resistance value of the resistance element R3. The reference voltage generation circuit 50a may be configured to control the current value Iref of the current source 51.

<Comparator>
The comparator 60 compares the voltage Vcal corresponding to the contact impedance with the voltage Vref corresponding to the reference impedance. For example, the output Vdet of the comparator 60 is at a low level when the voltage Vcal is lower than the voltage Vref, and is at a high level when the voltage Vcal is not lower than the voltage Vref. The output Vdet is output as a contact failure detection signal of the contact state detection circuit 100 as it is. Therefore, when the contact impedance of the electrode is larger than the reference impedance value, it is understood that the contact failure detection signal Vdet is at a high level, and the contact failure of the electrode occurs. At this time, information such as prompting the user to reattach the electrode can be sent to the user via the device.

〔Concrete example〕
Next, the operation characteristics of the contact state detection circuit 100 will be described with specific examples with reference to FIGS. 6 and 7.

  FIG. 6 shows a measurement example of the frequency characteristics of the contact impedance when the contact-type electrode and the contact state detection circuit 100 are used. The contact impedance is calculated by the impedance calculation circuit 40. The reference value of impedance is determined by the user based on the impedance characteristics shown in FIG. 6 (for example, 2 MΩ). The value of the resistor R2 of the reference voltage generation circuit 50 can be adjusted.

  FIG. 7 shows a time chart when a biological signal is acquired using the contact state detection circuit 100. Impedance measurement is started with the electrodes in contact at time t = t0. Since the calculation result of the impedance is equal to or less than a reference value (for example, 2 MΩ), the contact failure detection signal Vdet indicates a low level (ground voltage Vss), which indicates that the electrodes are in contact.

  Assume that the contact state suddenly deteriorated at time t = tx. The impedance calculation result exceeds the reference value (2 MΩ), and the contact failure detection signal Vdet changes to the high level (power supply voltage Vdd). As a result, the user can immediately grasp that the electrode has left the skin.

  Thus, when the contact state detection circuit 100 is used, even if the contact state of the electrode changes suddenly, the effectiveness of the acquired biological signal can be quickly determined. Therefore, it is possible to perform control so that an invalid biological signal is not recorded when the recording unit is disposed after the contact state detection circuit 100 and the contact failure detection signal Vdet indicates a high level.

  In addition, since the contact state detection circuit 100 can always monitor the contact impedance, it is not subject to the restriction that the time T1 for temporarily monitoring the contact impedance and the subsequent measurement time T2 are set as in the prior art. There is an effect that the flexibility of time increases.

  As described above, by using the contact state detection circuit 100 of the present invention, there is an effect that recording of a high quality biological signal can be realized.

<< Second Embodiment >>
FIG. 8 shows a configuration of a contact state detection circuit 200 according to the second embodiment. The contact state detection circuit 200 uses the selection circuit 70 and the selection signal SEL to select one electrode (referred to as the kth electrode) from among the n electrodes 10 (n is an integer of 2 or more), Impedance measurement is performed to determine the contact state of the electrode. An analog voltage Vimpk corresponding to the contact impedance of the k-th electrode selected by the selection circuit 70 and a contact failure detection signal Vdetk are output. As shown in FIG. 8, the selection signal SEL may be a control signal composed of a plurality of bits. For example, when the contact state detection circuit 200 detects the contact state of the eight electrodes 10 (n = 8), the selection signal SEL requires 3 bits. If it is desired to detect the contact state of all the eight electrodes 10, all eight combinations of the 3-bit selection signal SEL may be switched in a time-sharing manner, and each contact failure detection signal Vdetk may be monitored.

  As described above, according to this embodiment, there is an effect that the contact state of a plurality of electrodes can be monitored by one contact state detection circuit 200. In particular, the contact state detection circuit 200 is useful because it is not necessary to constantly monitor the contact state of all the electrodes when a biological signal is measured in a stationary state such as when the user is sitting on a chair.

  The present embodiment is also useful when the calculation of contact impedance is expressed by a complicated expression. Only one impedance measurement circuit 20 and one contact state evaluation circuit 30 are required, and a contact state detection circuit with a small area and low cost can be realized.

<< Modification of Second Embodiment >>
FIG. 9 shows a contact state detection circuit 200a according to a modification of the second embodiment. An impedance measurement circuit 20 is provided for each of the electrodes 10, and one electrode (referred to as the kth electrode) for which an impedance value is to be calculated is selected while constantly measuring contact impedance for all the electrodes. The contact state is determined.

  The contact state detection circuit 200a outputs an analog voltage Vimpk corresponding to the contact impedance of the kth electrode selected by the selection circuit 70 and a contact failure detection signal Vdetk.

  In the present embodiment, when the number of impedance measurements frequently occurs per unit time, or when the positions of electrodes to be arranged are separated, the circuit scale of the contact state detection circuit 200a can be kept relatively small. Useful in that it can.

<< Biological signal acquisition device >>
As shown in FIG. 10, the contact state detection circuit 100 can be applied to the biological signal acquisition apparatus 300. In the biological signal acquisition apparatus 300 of this embodiment, the contact state of the three electrodes is detected. The biological signal acquisition device 300 includes an electrode 10, a contact state detection circuit 100, an output control unit 180, a contact failure display unit 181, an AD converter 190, and a main body 320 of the biological signal acquisition device.

(Operation from electrode to AD conversion)
The operation from the kth electrode 10 to the AD converter 190 will be described. The kth contact state detection circuit 100 outputs the analog signal Vimpk and the contact failure detection signal Vdetk of the kth electrode unit 10. The output control unit 180 performs control to output actual measurement data only when the analog signal Vimpk is valid according to the contact state. For example, when the contact failure detection signal Vdetk is at a low level (in a contact state), the output Vimpk ′ outputs the input data Vimpk as it is. On the other hand, when Vdetk is at a high level (separated state), the output Vimpk ′ outputs the ground voltage Vss (or the power supply voltage Vdd). The AD converter 190 converts the analog data of Vimpk ′ into a digital code IMPk at a predetermined sampling time.

  The contact failure display unit 181 is configured with a display element such as an LED to transmit the contact failure of the electrode to the user and prompt the user to reattach the electrode. The LED is turned off when the contact failure detection signal output Vdet is at a low level, and the LED is turned on when it is at a high level.

(Operation of the biological signal acquisition device main body)
The main body 320 of the biological signal acquisition apparatus includes an input unit 321, an output unit 322, a DSP 323, a RAM 324, a waveform display unit 325, a recording unit 326, and an external interface 327.

  The input unit 321 includes buttons, function keys, and the like, and is used to input various settings and events of the biological signal acquisition apparatus 300. The output unit 322 is a speaker, for example, and is used for notifying various kinds of information to the user of the device by sound when a contact failure occurs.

  The DSP 323 controls each component and realizes various operations necessary for the biological signal acquisition apparatus 300. Also, signal analysis algorithms such as fast Fourier transform and digital filtering are executed, and post-processing of biosignal data analysis is also performed.

  The RAM 324 is used not only as an area for the DSP 323 to work but also as a temporary storage area for various data.

  The waveform display unit 325 has the same function as the contact failure display unit 181 on the main body side, in addition to displaying raw data of biological signals, analysis results of operations performed by the DSP, and the like.

  The recording unit 326 is configured by a non-volatile memory such as a flash memory, and stores acquired biological waveform data, various information related to data acquisition (acquisition time, user personal information, etc.), and the like. The recording unit 326 may be detachably connected to the main body 320.

  The external I / F 327 is an interface circuit for connecting an external device or the like that analyzes a biological signal, for example, and is configured by a well-known serial interface (RS-232C, USB, IEEE 1394, etc.). The external interface is where the same image as the display unit is sent to an external device via a specific interface such as an external monitor.

  As described above, when the biological signal acquisition device 300 is used, the contact state detection circuit 100 can detect the contact state of the electrodes in real time, and the output control unit 180 can extract only valid biological signal data. There is an advantage that a high-quality biological signal can be recorded.

《Health equipment》
As shown in FIG. 11, the contact state detection circuit 100 can be applied to a health device 400 such as a shiatsu massage machine. The health device 400 uses four compression parts instead of four fingers, arranges small electrodes 10 on the contact surface between the compression part and the skin, and in each operation mode of the compression operation and the decompression operation. Acupressure massage is performed while monitoring the contact impedance between the electrode and the skin. In a health device such as acupressure massage, it is important to control not only the state where the compression part is in contact with the skin but also the state where the compression part is separated from the skin.

  The health device 400 includes an electrode 10, a compression unit 410, a contact state detection circuit 100, a contact state display unit 420, and a control unit 430. As for a signal indicating the contact state of the kth electrode, a contact state detection signal Vdetk ′ is output instead of the contact failure detection signal Vdetk. The contact state detection signal Vdetk ′ indicates a high level when the contact impedance of the contact state detection circuit 100 is lower than the reference impedance (contact state), and indicates a low level when the contact impedance is not lower than the reference impedance (distant state).

  FIG. 12 is a diagram illustrating an example of the operation of the health device 400 used as a shiatsu massage machine. At time T1, the arm's urn is compressed with the compression part (mode T1), and at the subsequent time T2, the compression part is separated from the arm (mode T2).

  At time t = t0, the kth compression unit receives the control signal Vfk from the control unit 430, compresses the skin, and shifts to mode T1. During this time, the contact state detection signal Vdetk ′ of the contact state detection circuit 100 indicates a high level and is sent to the control unit 430. When the mode transitions to mode T2 after the elapse of T1 seconds, the control unit 430 sends a control signal Vfk to the compression unit 410 to perform a decompression operation, and the compression unit and the skin are separated. Here, the contact state detection signal Vdetk ′ of the contact state detection circuit 100 indicates a low level and is sent to the control unit 430.

  As described above, when the health device 400 of the present invention is used, it is possible to detect in real time both the state in which the electrode and the skin are in contact with each other, and therefore it is possible to accurately control compression and decompression. it can.

  Note that the electrode impedance measurement need not always be performed. In particular, since the electrode is pressed against the skin in the compression mode, the impedance measurement may be performed intermittently. There is an effect that power consumed in the contact state detection circuit 100 and the health device 400 can be saved.

  The contact state detection circuit according to the present invention is useful for a biological signal acquisition apparatus such as a portable electroencephalogram measurement apparatus that acquires a biological signal by bringing an electrode into contact with a predetermined part of a human body. It is also useful for health equipment such as a portable massage machine in which the compression operation is controlled according to the contact state.

Vdd Power supply voltage Vss Ground voltage Vcal Impedance voltage conversion value (calculated value)
Vref Reference voltage Vimp Impedance signal analog data Vdet Contact failure detection signal Vimpk Impedance signal analog data Vimp1 to Vimp3 Impedance signal analog data Vimp1 'to Vimp3' Impedance signal analog data Vdtk Contact failure detection signals Vdet1 to Vdet3 Contact failure detection signal Vdetk ′ Contact state detection signals Vdet1 ′ to Vdet3 ′ Contact state detection signals Vf1 to Vf4 Control signal I Current value Ia of current source for measurement Ia Amplitude of current I for measurement IMP1 to IMP3 Digital data of impedance signal N1 Electrode side of impedance measurement circuit Node N2 Contact state evaluation circuit side node V1 of impedance measurement circuit Voltage V2 of node N1 of impedance measurement circuit Voltage of de N2 R1, R2, R3 resistor element

DESCRIPTION OF SYMBOLS 10 Electrode 20 Impedance measurement circuit 21 Current source 30 for measurement Contact state determination circuit 40 Impedance calculation circuit 41 Absolute value circuit 42 Constant multiplication circuit 50 Reference voltage generation circuit 51 Current source 60 Comparator 70 Selection circuit 100 Contact state detection circuit 180 Output control Unit 181 contact failure display unit 190 AD converter 200, 200a contact state detection circuit 300 biological signal acquisition device 320 biological signal acquisition device body 321 input unit 322 output unit 323 DSP
324 RAM
325 Waveform display unit 326 Recording unit 327 External I / F
330 DSP Bus 400 Health Equipment 410 Pressure Unit 420 Contact State Display Unit 430 Control Unit

900 Biosignal acquisition apparatus 910 Electrode unit 920 Main body 921 AD conversion unit 922 Impedance measurement unit 923 Display unit 924 Input unit 925 Output unit 926 CPU
927 ROM
928 RAM
929 biological signal recording unit 930 external I / F
931 CPU bus

Claims (16)

A contact state detection circuit for detecting a contact state between an electrode and skin,
An impedance measurement circuit for measuring a contact impedance of the electrode, comprising a measurement current source for applying an alternating current to the electrode;
An impedance calculation circuit that outputs a first voltage corresponding to the contact impedance to a first node based on an output signal of the impedance measurement circuit;
A reference voltage generation circuit that outputs a second voltage corresponding to an impedance threshold for detecting the contact state to a second node;
A contact state detection circuit comprising a comparator for comparing the first voltage and the second voltage. In claim 1,
The contact state detection circuit, wherein the measurement current source is capable of adjusting a frequency of the alternating current. In claim 1,
The impedance calculation circuit includes an absolute value calculation circuit. In claim 1,
The reference voltage generation circuit includes:
A first resistance element having one end connected to a power supply voltage and the other end connected to the second node;
A contact state detection circuit comprising: a second resistance element having one end connected to the second node and the other end connected to a ground voltage. In claim 4,
The reference voltage generation circuit includes:
A contact state detection circuit, wherein a resistance value of the first or second resistance element is adjustable. In claim 1,
The reference voltage generation circuit includes:
A first current source having one end connected to the power supply voltage and the other end connected to the second node;
A contact state detection circuit comprising: a third resistance element having one end connected to the second node and the other end connected to a ground voltage. In claim 6,
The reference voltage generation circuit includes:
The contact state detection circuit, wherein a current value of the first current source or a resistance value of the third resistance element is adjustable. A contact state detection circuit for detecting a contact state between n electrodes (n is an integer of 2 or more) and skin,
A selection circuit for selecting one of the n electrodes;
An impedance measurement circuit for measuring a contact impedance of the electrode, comprising a measurement current source for applying an alternating current to the electrode;
An impedance calculation circuit that outputs a first voltage corresponding to the contact impedance to a first node based on an output signal of the impedance measurement circuit;
A reference voltage generation circuit that outputs a second voltage corresponding to an impedance threshold for detecting the contact state to a second node;
A contact state detection circuit comprising a comparator for comparing the first voltage and the second voltage. In claim 8,
The contact state detection circuit, wherein the measurement current source is capable of adjusting a frequency of the alternating current. In claim 8,
The impedance calculation circuit includes an absolute value calculation circuit. In claim 8,
The reference voltage generation circuit includes:
A first resistance element having one end connected to a power supply voltage and the other end connected to the second node;
A contact state detection circuit comprising: a second resistance element having one end connected to the second node and the other end connected to a ground voltage. In claim 11,
The reference voltage generation circuit includes:
A contact state detection circuit, wherein a resistance value of the first or second resistance element is adjustable. In claim 8,
The reference voltage generation circuit includes:
A first current source having one end connected to the power supply voltage and the other end connected to the second node;
A contact state detection circuit comprising: a third resistance element having one end connected to the second node and the other end connected to a ground voltage. In claim 13,
The reference voltage generation circuit includes:
The contact state detection circuit, wherein a current value of the first current source or a resistance value of the third resistance element is adjustable. A biological signal acquisition device for acquiring a biological signal,
The contact state detection circuit according to any one of claims 1 to 14,
An AD converter that converts an analog signal obtained by the contact state detection circuit into a digital code;
A biosignal acquisition apparatus comprising: a recording unit that records a digital code obtained by the AD converter. In any one of Claims 1-14,
Each of the n electrodes (n is an integer of 1 or more) is attached to the tip, and n pressing bodies that move forward and backward with respect to the skin,
The contact state detection circuit;
A health device comprising: a control unit that sends a control signal for controlling the advance / retreat movement to each of the n pressing bodies.

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