JP4281380B2 - Biological signal measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological signal measuring apparatus that measures myoelectricity, brain waves, nerve action potentials, and the like of a living body such as a human being.
[0002]
[Prior art]
FIG. 6 is a diagram showing a configuration of a conventional biological signal measuring apparatus. This prior art shows an example of a myoelectric potential measuring device, and a pair of detection electrodes 51 for inputting myoelectric potential and a measurement for amplifying myoelectric potential input from the detection electrode 51 disposed on the electrode back surface 52 of the detection electrode 51. An amplifier 53 (shown in detail in FIG. 7), and a shield line 54 that outputs the myoelectric potential amplified by the measurement amplifier 53 to the battery box 55 and conversely supplies power and a reference voltage from the battery box 55 to the measurement amplifier 53. And a battery box 55 for supplying electric power and a reference voltage to the measurement amplifier 53 and supplying a measured and amplified myoelectric potential to a main amplifier of a biological signal measuring device main body (not shown).
[0003]
The detection electrode 51 has a diameter of 22 to 25 mm as a whole suitable for measuring myoelectric potential, and is arranged concentrically so that myoelectric potential can be measured without considering directivity. In this respect, it has a function as a spatial filter.
[0004]
FIG. 7 is a diagram showing a detailed configuration of the measurement amplifier. The measurement amplifier 53 includes a non-inverting amplifier 542 and a differential amplifier 543. The non-inverting amplifier 542 includes an external resistor R11 and a capacitor C11, operational amplifiers 533 and 534, and resistors 535 and 536. The differential amplifier 543 includes resistors 537, 538, 540, 541 and an operational amplifier 539.
[0005]
Here, when the resistance value of the resistors 535 and 536 is Rf = 25 kΩ, the gain G of the measurement amplifier 53 is
G = 1 + 2Rf / R11
= 1 + 50 [kΩ] / R11
The low cut-off frequency fc is
fc = 1 / 2πC11R11
(See Patent Document 1).
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 10-276995
[Problems to be solved by the invention]
Since the resistance due to the contact between the detection electrode 51 and the skin is large and unstable, measurement is also performed by applying a paste (conductive electrode glue) and reducing the resistance with the skin, but the input impedance is high. By performing impedance conversion by the amplifier 53, it is not necessary to apply paste. In addition, since the measurement amplifier 53 amplifies the myoelectric potential, there is an advantage that the SN ratio does not deteriorate even if noise due to shaking of the shield wire 54 is applied. However, the polarization voltage due to the contact between the detection electrode 51 and the skin is about +70 mV even if a silver-silver chloride electrode, which is supposed to be small, is used. Although it is necessary to cut a frequency region below a predetermined low-frequency cutoff frequency fc, in order to measure myoelectric potential, for example, this low-frequency cutoff frequency fc = 5 [Hz] must be set, and a gain G = 100 When designed as [double], R11 = 500 [Ω] and C11 = 64 [μF], but it is difficult to obtain a nonpolar electrolytic capacitor of 64 μF, and when it is arranged on the back surface of the electrode, the detection electrode 51 is It must be large and thick. Therefore, it can be dealt with by increasing the value of the resistor R11, lowering the gain G, lowering the capacitor C11 to a certain capacity of the chip capacitor lineup, and raising the low cut-off frequency fc. This not only impairs the advantage as an electrode, but also cuts off the band required as a myoelectric potential measuring device. At present, this is the case, and the advantages of the active electrode are not fully utilized.
[0008]
Also, since the filter circuit for measuring myoelectric potential (low cut-off frequency fc = 5 to 500 [Hz]) is incorporated on the back surface of the electrode, the size and shape of the detection electrode, the low cut-off frequency, etc. are used. The purpose is limited. That is, this myoelectric potential measuring apparatus using a large concentric electrode uses a dish electrode to measure an electroencephalogram with a low cut-off frequency fc = 0.3 to 20 [Hz] (depending on the type of electroencephalogram) or a small concentric electrode. Nerve action potential measurement using a low cut-off frequency fc = 1 to 3 [kHz] cannot be performed. In addition, even when limited to the measurement of myoelectric potential, according to the Japanese Industrial Standard (JIS standard), as conditions to be provided as an electromyograph, a standard that a common mode rejection ratio is 60 dB or more, noise is less than 10 μVp-p, and minimum sensitivity is 10 μV. In addition to the above, it is one of the standards to have a built-in bandwidth (low cut-off frequency) variable filter, but the conventional method does not satisfy the standard.
[0009]
In view of the above problems, the present invention provides a biological signal measuring apparatus capable of arbitrarily setting a low cut-off frequency even if the detection electrode is made small and the gain of a measurement amplifier mounted on the back surface is increased. The purpose is to provide.
[0010]
It is another object of the present invention to provide a biological signal measuring apparatus that can be used for a plurality of applications by changing the low cut-off frequency of the measurement amplifier.
[0011]
[Means for Solving the Problems]
The biological signal measuring apparatus of the present invention transmits a first amplifier and a second electrode arranged on the skin surface, a measurement amplifier to which a signal between the first electrode and the second electrode is input, and an output of the measurement amplifier. An active shield line and an output of the active shield line are integrated and fed back as a reference voltage of the measurement amplifier via the active shield line to obtain a signal in a frequency region below a predetermined low-frequency cutoff frequency of the measurement amplifier. And a capacitor for determining a low cut-off frequency is not connected to the measurement amplifier .
[0012]
Further, the integration circuit can be applied to bioelectric measurements for a plurality of uses by making the circuit constant for integration variable and making the low-frequency cutoff frequency variable.
[0013]
Further, the integration circuit can reduce artifacts due to stimulation by dynamically changing the low cut-off frequency by controlling the change of the circuit constant by a signal.
[0014]
In addition, since the first electrode and the second electrode have the same area in contact with the skin, it is possible to reduce in-phase noise due to impedance imbalance.
[0015]
In addition, the measurement amplifier can use electrodes for a plurality of applications by connecting a plurality of types of electrodes to its input in a switchable manner.
[0016]
In addition, by being a myoelectric potential measuring device that measures myoelectric potential, it is possible to amplify without missing the frequency region required for myoelectric potential measurement by setting a low low-frequency cutoff frequency while having a high amplification gain. Can do.
[0017]
Moreover, since it is an electroencephalogram measurement apparatus that measures electroencephalograms, it is not necessary to maintain a resting posture, and electroencephalograms can be measured with good S / N ratio while living daily.
[0018]
In addition, since it is a nerve action potential measuring device that measures the nerve action potential, it may be placed on a finger or the like with a fast conduction speed, and even if it is a nerve action potential measurement that requires a small detection electrode, the detection electrode It is possible to realize an active electrode in which a measurement amplifier is mounted on the back surface of the substrate.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0020]
FIG. 1 is a diagram showing the configuration of the biological signal measuring apparatus according to the first embodiment of the present invention. The detection electrode 11, the electrode back surface 12, the measurement amplifier 13, the active shield line 14, and the battery box 15 are respectively the detection electrode 51, the electrode back surface 52, the measurement amplifier 53, and the shield line 54 of the conventional biological signal measurement device shown in FIG. Corresponding to the battery box 55, the biological signal measuring apparatus of the present embodiment omits the capacitor C11 external to the measurement amplifier 53, integrates the measured and amplified myoelectric potential in the battery box 15, and measures the measurement amplifier 13. A circuit that feeds back as a reference voltage is provided. Specifically, the myoelectric potential output from the active shield line 14 is integrated by the resistor R3, the capacitor C1, and the operational amplifier 16 and used as the reference voltage of the measurement amplifier 13 via the active shield line 14. As a result, the capacitor is eliminated from the electrode back surface 12, so that the weight can be reduced and the detection electrode 11 can be made small. The active shield line 14 is preferably a flexible cord such as a stereo earphone cord (parallel wire of a single core shield).
[0021]
Here, the gain G and the low-frequency cutoff frequency fc will be described. Since C11 in FIG. 6 is eliminated and the resistors 535 and 536 are each 25 kΩ, the gain of the non-inverting amplifier is 1 + 50 k / R1, the gain of the differential amplifier is 1, and the integrator of FIG. 1 is −1 / (jωC1R3). Since the feedback is negatively fed to the input of the dynamic amplifier, the overall gain G is
G = (1 + 50k / R1) × 1 / {1-1 / (jωC1R3)}
It becomes. At this time,
At ω → ∞, G = 1 + 50k / R1
ω → 0, G = 0 (G = 1 in the conventional example)
It becomes. The low cut-off frequency fc (= ω / 2π) is
ωC1R3 = 1
When
fc = 1 / 2πC1R3
It becomes. Therefore, the gain G of the measurement amplifier 13 can be adjusted independently by the resistor R1, and the low-frequency cutoff frequency fc can be adjusted independently by the capacitor C1 and the resistor R3. Since the capacitor C1 and the resistor R3 are not restricted by physical size or gain G in designing their values, the value of the low-frequency cutoff frequency fc can be freely selected. If the resistance R3 is a variable resistance, depending on the measurement object such as myoelectric potential (5 to 500 Hz), brain wave (0.3 to 20 Hz: depending on the type of brain wave), and nerve action potential (1 k to 3 kHz), The low cut-off frequency fc of the measurement amplifier 13 can be set freely. Further, the low-frequency cutoff frequency fc can be dynamically switched by switching the resistor R3 to the resistor R2 by the photo moss relay 17 or the like. By dynamically switching the resistor R2, the low cut-off frequency fc is selectively set high only when the artifact due to the stimulus is mixed, and the artifact by the stimulus is reduced as a whole by quickly returning to the base line. be able to. Further, when the power source is not a bipolar power source but a single power source, the non-inverting input of the operational amplifier 16 may be connected to an intermediate potential obtained by dividing the power source potential V + by the resistors R4 and R5 instead of the ground.
[0022]
FIG. 2 is a diagram illustrating a configuration example of a general-purpose detection electrode. FIG. 2 (a) shows an electrode 21a, 22b (dish) having a diameter of about 15 mm, which is bonded to an electrode 21 having the same shape as that of a concentric detection electrode 11 for measuring a nerve action potential. An example of connecting to an electrode or a disposable electrode is shown. Alternatively, a lead wire may be attached to the detection electrode 11 in advance, and an electrode having another shape may be connected. FIG. 2 (b) shows an example in which the electrode 21 to be bonded and the dish electrode or disposable electrode 22a, 22b are connected to the electrode 21 via a lead wire. FIG. 2 (c) shows an electrode 23 to be bonded and a snap (a pair of concave and convex fasteners) 24a and 24b connected to this via a lead wire, and another electrode (from the other side of the snap via a lead wire). An example of connection is shown. FIG. 2 (d) shows a flexible electrode 25 having a concentric electrode having a diameter of 15 mm on the surface and a concentric electrode for measuring myoelectric potential having a diameter of about 25 mm on the back surface. An example of conversion to concentric electrodes is shown. By making the electrode flexible, the entire electrode surface is in close contact with the skin, so that the electrodes are concentrically contacted, and the characteristics as a spatial filter can be utilized. Note that, by setting both electrodes of the concentric electrodes to have the same area, it is possible to reduce the occurrence of common-mode noise due to impedance imbalance.
[0023]
FIG. 3 is a diagram illustrating another configuration example of the general-purpose detection electrode. FIG. 3A shows an example in which female snaps 32a and 32b are connected to the detection electrode 11 via a connector 31, and the plate electrodes 33a and 33b having male snaps 33c and 33d are snapped. The connector 31 can be configured by connecting the concentric electrodes of the detection electrode 11 and the female snaps 32a and 32b with enamel wires, and fixing the measurement amplifier 13 and the enamel wires with epoxy. In FIG. 3 (b), a connector 38 to which male snaps 37a and 37b are fixed is snapped to the female snaps 32a and 32b shown in FIG. 3 (a), and the connector 38 is further extended via a lead wire 39. The example which connects the detection electrode 40 of the concentric circle of a diameter is shown. FIG. 3 (c) shows an example in which a stereo earphone socket 34 is connected to the detection electrode 11, a stereo earphone jack 35 is inserted, and a detection electrode (not shown) is connected via a lead wire 36.
[0024]
FIG. 4 is a diagram illustrating a configuration example in which a dedicated detection electrode is not provided. 2 and 3 are provided with versatility so that a certain detection electrode can be used and another detection electrode can be used. In particular, a plurality of types can be used without connecting a predetermined detection electrode. A connector for connecting the detection electrodes may be provided. That is, in this example, the female snap 42 is fitted and fixed to the lower surface of the double-sided substrate 41, the IC 43 of the measurement amplifier 13 is mounted on the upper surface, and each is connected by the copper foil 44. According to this, a plurality of detection electrodes can be used without worrying about the existence of the dedicated detection electrodes.
[0025]
FIG. 5 is a diagram illustrating a connection example of detection electrodes when measuring an electroencephalogram. Measuring amplifiers 13a, 13b, 13c, 13d are connected between the detection electrodes 11a, 11b, between the detection electrodes 11b, 11c, between the detection electrodes 11c, 11d, and between the detection electrodes 11d, 11e, respectively. , 11c, 11d, and 11e can be measured.
[0026]
The present invention is not limited to the above embodiment.
[0027]
The present invention may be a myoelectric potential measurement device dedicated to myoelectric potential measurement, an electroencephalogram measurement device dedicated to electroencephalogram measurement, or a neural action potential measurement device dedicated to nerve action potential measurement. .
[0028]
【The invention's effect】
As described above, according to the present invention, an active electrode having a high gain and an arbitrary low cutoff frequency can be realized. In addition, the low cut-off frequency can be made variable and used for a plurality of uses such as myoelectric potential measurement, nerve action potential measurement, and electroencephalogram measurement.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a biological signal measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of a general-purpose detection electrode.
FIG. 3 is a diagram showing another configuration example of a general-purpose detection electrode.
FIG. 4 is a diagram illustrating a configuration example in which a dedicated detection electrode is not provided.
FIG. 5 is a diagram showing a connection example of detection electrodes when measuring an electroencephalogram.
FIG. 6 is a diagram showing a configuration of a conventional biological signal measuring apparatus.
FIG. 7 is a diagram showing a detailed configuration of a measurement amplifier.
[Explanation of symbols]
11, 51 Detection electrodes 13, 53 Measuring amplifier 14 Active shield line 16 Operational amplifier 17 Photo MOS relays 22a, 22b Disposable electrodes 24a, 24b Snap 31 Connectors 32a, 32b Female snaps 33c, 33d Male snaps 33a, 33b Dish electrodes 34 Stereo earphone socket 35 Stereo earphone jack 36 Lead wire 37a, 37b Male snap 38 Connector 39 Lead wire 40 Detection electrode 41 Double-sided substrate 42 Female snap 43 IC
44 Copper foil 54 Shielded wire

Claims (8)

A first electrode and a second electrode disposed on the skin surface;
A measurement amplifier to which a signal between the first electrode and the second electrode is input;
An active shield line for transmitting the output of the measurement amplifier;
An integrating circuit for blocking a signal in a frequency region below a predetermined low cut-off frequency of the measurement amplifier by integrating an output of the active shield line and feeding back as a reference voltage of the measurement amplifier via the active shield line; And a capacitor for determining a low cut-off frequency is not connected to the measurement amplifier . The biological signal measuring apparatus according to claim 1, wherein the integrating circuit makes the low-frequency cutoff frequency variable by making a circuit constant for integration variable. The biological signal measuring apparatus according to claim 2, wherein the integration circuit dynamically changes the low-frequency cutoff frequency by controlling a change in the circuit constant with a signal. The biological signal measuring device according to claim 1, wherein the first electrode and the second electrode have the same area in contact with the skin. The biological signal measuring device according to claim 1, wherein a plurality of types of electrodes are switchably connected to the input of the measurement amplifier. The biosignal measuring device according to claim 1, wherein the biosignal measuring device measures myoelectric potential. The biological signal measuring apparatus according to claim 1, wherein the biological signal measuring apparatus is an electroencephalogram measuring apparatus that measures an electroencephalogram. 5. The biological signal measuring device according to claim 1, wherein the biological signal measuring device is a nerve action potential measuring device for measuring a nerve action potential.

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