Magnetic sensor and magnetic measuring device

Abstract

This magnetic sensor comprises: a magnetism detecting unit that outputs a detection signal corresponding to external magnetism; a signal processing unit that generates an output signal by subjecting the detection signal to prescribed signal processing; a current generating unit that generates a bias current; and a conduction limiting unit that limits conduction of the bias current to the magnetism detecting unit for a predetermined time.

Description

Magnetic sensor and magnetic measurement device

[0001] This application claims priority to Japanese Patent Application No. 2023-144686, filed on September 6, 2023, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 listed below discloses a magnetic sensor and a biomagnetic measurement device that generates a bias magnetic field in a pickup coil in order to suppress sensitivity variations caused by environmental changes such as temperature, manufacturing variations, etc. In this magnetic sensor and biomagnetic measurement device, a bias magnetic field is generated in the pickup coil by passing a current generated by a constant current source circuit or a current proportional to the output signal of the magnetic sensor through the pickup coil.

[0003] Japanese Patent Application Laid-Open No. 2022-100055

[0004] In the background art, a current (constant current) generated by a constant current source circuit or a current (feedback current) proportional to the output signal of a magnetic sensor is passed through a pickup coil as a bias current. In this background art, the bias current generates a magnetic field in the pickup coil that is opposite in phase to the external magnetic field that is the target of detection.

[0005] However, in order to suppress variations in sensitivity of the magnetic sensor, the bias current needs to be set to a relatively large current value. That is, the background art has a problem of relatively large power consumption. For example, when applying the background art to a device that requires multiple magnetic sensors, the large power consumption of the magnetic sensors becomes an important technical issue that needs to be resolved.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a magnetic sensor and a magnetic measurement device that can reduce power consumption more than conventional ones.

[0007] In order to achieve the above object, the present invention adopts, as a first solution relating to a magnetic sensor, a means comprising a magnetic detection unit that outputs a detection signal according to an external magnetic field, a signal processing unit that generates an output signal by performing predetermined signal processing on the detection signal, a current generation unit that generates a bias current, and a current limiting unit that limits the supply of the bias current to the magnetic detection unit for a predetermined time.

[0008] The present invention employs, as a second solution relating to the magnetic sensor, the solution of the first solution, in which the signal processing unit includes a correlated double sampling circuit that performs sample-and-hold processing on the detection signal.

[0009] The present invention employs, as a third solution related to a magnetic sensor, the second solution described above, wherein the correlated double sampling circuit includes a sample-and-hold circuit that acquires and holds two sample values ​​by sampling the detection signal at different timings, and an integration circuit that integrates the difference between the two sample values.

[0010] The present invention employs, as a fourth solution relating to the magnetic sensor, the solution according to the third solution, in which the integrating circuit is configured as a zero-drift amplifier.

[0011] The present invention employs, as a fifth solution relating to a magnetic sensor, a solution in which, in any of the first to fourth solutions above, the current generating unit includes a resistor that generates the bias current based on the output signal, and the current limiting unit includes an open / close switch provided between the signal processing unit and the current generating unit or between the current generating unit and the magnetic detection unit.

[0012] The present invention employs a sixth solution relating to a magnetic sensor, in which, in any of the first to fourth solutions described above, the magnetic detection unit includes a magnetic impedance element and a drive unit that applies a drive voltage to the magnetic impedance element.

[0013] The present invention provides a seventh solution related to the magnetic sensor, which is the sixth solution, in which the drive unit limits the application of the drive voltage in synchronization with the current limiting unit limiting the current.

[0014] In the present invention, as a first solution relating to a magnetic measurement device, a means is adopted in which the magnetic measurement device is provided with a magnetic sensor relating to any one of the first to fourth solutions and a magnetic measurement unit that measures magnetism using the output signal.

[0015] The present invention employs, as a second solution relating to the magnetic measurement device, the solution of the first solution relating to the magnetic measurement device, in which the external magnetic field is biomagnetism generated in a living body.

[0016] According to the present invention, it is possible to provide a magnetic sensor and a magnetic measurement device that can reduce power consumption more than conventional ones.

[0017] Fig. 1 is a block diagram showing an overview of a magnetic sensor A1 according to a first embodiment of the present invention. Fig. 2 is a circuit diagram showing a detailed configuration of the magnetic sensor A1 according to the first embodiment of the present invention. Fig. 3 is a block diagram showing a configuration of a magnetic measurement device B1 according to the first embodiment of the present invention. Fig. 4 is a timing chart showing the operation of the magnetic sensor A1 according to the first embodiment of the present invention. Fig. 5 is a circuit diagram showing a detailed configuration of a magnetic sensor A2 according to a second embodiment of the present invention.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [First Embodiment] First, a first embodiment of the present invention will be described with reference to Figures 1 to 5. As shown in Figure 1, a magnetic sensor A1 according to the first embodiment includes a sensor head 1, a drive unit 2, a pickup coil 3, a signal processing unit 4, a high-voltage side current limiting unit 5H, a high-voltage side current generating unit 6H, a low-voltage side current limiting unit 5L, and a low-voltage side current generating unit 6L.

[0019] Here, as will be described in detail later, R in FIG. Ｐ is the parasitic resistance of the pickup coil 3. The pickup coil 3 has a parasitic resistance R Ｐ In addition, the sensor head 1 and the pickup coil 3 (parasitic resistance RＰ ) constitutes the magneto-impedance element S.

[0020] The sensor head 1 is a two-terminal element with one end connected to the output terminal of the driver 2 and the other end grounded. This sensor head 1 is made of a magnetic material whose magnetic properties change when a drive voltage is applied from the driver 2 while an external magnetic field G is acting on it. That is, a change in magnetization, i.e., a change in magnetic flux, occurs in the sensor head 1 according to the strength (magnitude) of the external magnetic field G.

[0021] The sensor head 1 is, for example, an amorphous wire. When a drive voltage is applied from the drive unit 2 to the sensor head 1 while an external magnetic field G is acting on it, the impedance of the sensor head 1 changes, and the magnetic flux penetrating the inside of the sensor head 1 also changes. The amount of change in this impedance depends on the magnitude of the external magnetic field G.

[0022] The driver 2 has an output terminal connected to one end of the sensor head 1, and applies a predetermined drive voltage from the output terminal to one end of the sensor head 1. This driver 2, together with the magnetic impedance element S, constitutes the magnetic comparison unit of the present invention. The driver 2 is a voltage source that generates a fluctuating voltage such as a pulse voltage or a high-frequency voltage, and outputs this fluctuating voltage to the sensor head 1 as a drive voltage MIE.

[0023] The pickup coil 3 is a winding wound around the sensor head 1. One end of the pickup coil 3 is connected to one input end (first input end) of the signal processing unit 4 and the output end of the high-voltage side current generating unit 6H, and the other end is connected to the other input end (second input end) of the signal processing unit 4 and the output end of the low-voltage side current generating unit 6L.

[0024] Such a pickup coil 3 is wound around the sensor head 1, and a change in magnetic flux on the surface of the sensor head 1 in response to an external magnetic field appears as an induced voltage at both ends of the coil through the pickup coil 3.

[0025] This induced voltage corresponds to the detection signal of the present invention, and as shown in the figure, a high-voltage side detection voltage V Ｐand the low-voltage side detection voltage V generated at the other end of the pickup coil 3. Ｎ This induced voltage is the difference voltage between the input voltage V ｉｎ The signal is input to the signal processing unit 4 as

[0026] As described above, the pickup coil 3 has a predetermined parasitic resistance R Ｐ This parasitic resistance R Ｐ As shown in the figure, functions as a resistor connected in series to the pickup coil 3 and has a predetermined resistance value (parasitic resistance value). That is, when a current is passed through the pickup coil 3, the parasitic resistance R Ｐ A parasitic voltage V corresponding to the parasitic resistance value is applied to both ends of Ｐ occurs.

[0027] This parasitic voltage V Ｐ As described in a well-known document (JP 2022-100055 A), the parasitic voltage V Ｐ is the input voltage V input to the signal processing unit 4 ｉｎ Preferably, it is subtracted from

[0028] As shown in the figure, signal processing unit 4 is a two-input, two-output electronic circuit. A first input terminal of signal processing unit 4 is connected to one end of pickup coil 3 and the output terminal of high-voltage current generator 6H, and a second input terminal is connected to the other end of pickup coil 3 and the output terminal of low-voltage current generator 6L.

[0029] The first output terminal of the signal processing unit 4 is connected to an external device (not shown) and the high-voltage side current limiting unit 5H, and outputs a positive-phase output signal V ｏｕｔ Furthermore, the second output terminal of the signal processing unit 4 is connected to the external device and the low-voltage side current limiting unit 5L, and outputs a negative phase output signal V ｏｕｔ Outputs (-).

[0030] Such a signal processing unit 4 detects the input voltage V ｉｎBy performing predetermined signal processing on the ｏｕｔ (+) and inverted output signal V ｏｕｔ (-) are generated. That is, these positive phase output signals V ｏｕｔ (+) and inverted output signal V ｏｕｔ (-) is an analog signal indicating the strength (magnitude) of the external magnetic field G detected by the pickup coil 3 (magnetic impedance element S).

[0031] The output signal of the signal processing unit 4 may be either an analog signal or a digital signal, but in the first embodiment, it is an analog signal. ｏｕｔ (+) is a positive-phase analog voltage signal that indicates the strength (magnitude) of the external magnetic field G. In contrast, the negative-phase output signal V ｏｕｔ (-) is an analog voltage signal of opposite phase that indicates the strength (magnitude) of the external magnetic field G. ｏｕｔ (+) and inverse phase output signal V ｏｕｔ (-) means that the amplitude is the same but the phase is reversed.

[0032] The input terminal of the high-voltage side current limiting unit 5H is connected to the first output terminal of the signal processing unit 4, and the output terminal is connected to the input terminal of the high-voltage side current generating unit 6H. ｏｕｔ Supply / non-supply of (+) current to the high-voltage side current generating unit 6H is set based on a switching signal input from a control device (not shown).

[0033] That is, the high-voltage side current limiting unit 5H controls the positive phase output signal V ｏｕｔ By setting the supply / non-supply of (+) to the high-voltage side current generating unit 6H, the magnetic feedback current I generated by the high-voltage side current generating unit 6H is ｆｂ The bias current is limited to a predetermined time.

[0034] The magnetic feedback current I ｆｂ generates a magnetic field corresponding to the magnitude of the current through the pickup coil 3 to the nearby sensor head 1. That is, the magnetic feedback current I ｆｂ is the positive phase output signal Vｏｕｔ (+) and inverse phase output signal V ｏｕｔ Since it is proportional to the difference with (-), the magnetic feedback current I ｆｂ The generated magnetic field is also proportional to this difference and is in opposite phase to the external magnetic field G, which acts as a magnetic feedback and solves problems such as the nonlinearity of the magnetic impedance element S.

[0035] High-voltage side current generator 6H has an input terminal connected to the output terminal of high-voltage side current limiter 5H, and an output terminal connected to one end of pickup coil 3 and a first input terminal of signal processor 4. High-voltage side current generator 6H receives positive-phase output signal V ｏｕｔ (+) based on the magnetic feedback current I ｆｂ (bias current).

[0036] The low-voltage side current limiting unit 5L has an input terminal connected to the second output terminal of the signal processing unit 4 and an output terminal connected to the input terminal of the low-voltage side current generating unit 6L. ｏｕｔ Supply / non-supply of (-) to the low-voltage side current generating section 6L is set based on the above-mentioned switching signal.

[0037] That is, the low-voltage side current limiting unit 5L generates the negative-phase output signal V ｏｕｔ By setting the supply / non-supply of (-) to the low-voltage side current generating unit 6L, the magnetic feedback current I generated by the low-voltage side current generating unit 6L is ｆｂ The bias current is limited to a predetermined time.

[0038] Here, as will be described in detail later, the driving unit 2 described above controls the magnetic feedback current I ｆｂ In synchronization with the limiting of the current (bias current) flowing through the pickup coil 3, the application of the drive voltage to the sensor head 1 is limited.

[0039] The low-voltage side current generating unit 6L has an input terminal connected to the output terminal of the low-voltage side current limiting unit 5L, and an output terminal connected to the other end of the pickup coil 3 and the second input terminal of the signal processing unit 4. The low-voltage side current limiting unit 5L converts the negative-phase output signal V ｏｕｔ (-) based on the magnetic feedback current I ｆｂ (bias current).

[0040] Next, a specific circuit configuration of the magnetic sensor A1 will be described with reference to Fig. 2. As shown in Fig. 2, the signal processing unit 4 of the magnetic sensor A1 includes a first switch 4a, a second switch 4b, a third switch 4c, a fourth switch 4d, a first capacitor 4e, a second capacitor 4f, a fifth switch 4g, a sixth switch 4h, a seventh switch 4i, an eighth switch 4j, a ninth switch 4k, a tenth switch 4m, a third capacitor 4n, a fourth capacitor 4p, an eleventh switch 4q, a twelfth switch 4r, a differential amplifier 4s, a fifth capacitor 4t, and a sixth capacitor 4u.

[0041] That is, the signal processing unit 4 includes 12 on-off switches, six capacitors, and one differential amplifier. The first switch 4a is an on-off switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this first switch 4a is connected to one end of the pickup coil 3 and the first contact of the second switch 4b, and the second contact is connected to the first contact of the third switch 4c and one end of the first capacitor 4e.

[0042] The control terminal of the first switch 4a is connected to a control device (not shown). The control device is an electronic device that comprehensively controls the magnetic sensor A1 shown in Fig. 2. The open / closed state of the first switch 4a is set based on a first sampling signal SMPL input from the control device.

[0043] The second switch 4b is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this second switch 4b is connected to one end of the pickup coil 3 and the first contact of the first switch 4a, and the second contact is connected to the first contact of the fourth switch 4d and one end of the second capacitor 4f. The control terminal of the second switch 4b is connected to the above-mentioned control device (not shown), and the open / close state of the second switch 4b is set based on the second sampling signal CDS input from the control device.

[0044] The third switch 4c is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this third switch 4c is connected to the second contact of the first switch 4a and one end of the first capacitor 4e, and the second contact is grounded. The control terminal of the third switch 4c is connected to the above-mentioned control device (not shown), and the open / close state of the third switch 4c is set based on a timing signal Tx input from the control device.

[0045] The fourth switch 4d is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this fourth switch 4d is connected to the second contact of the second switch 4b and one end of the second capacitor 4f, and the second contact is grounded. The control terminal of the fourth switch 4d is connected to the above-mentioned control device (not shown), and the open / close state of the fourth switch 4d is set based on the timing signal Tx, similar to the third switch 4c.

[0046] The first capacitor 4e is a two-terminal element having a predetermined capacitance. One end of the first capacitor 4e is connected to the second contact of the first switch 4a and the first contact of the third switch 4c, and the other end is connected to the first contact of the fifth switch 4g and the first contact of the sixth switch 4h. The other end of the first capacitor 4e is also connected to one end of the third capacitor 4n.

[0047] The second capacitor 4f is a two-terminal element having a predetermined capacitance, and one end of the second capacitor 4f is connected to the second contact of the second switch 4b and the first contact of the fourth switch 4d, and the other end is connected to one end of the fourth capacitor 4p, the first contact of the eleventh switch 4q, and the first contact of the twelfth switch 4r.

[0048] The fifth switch 4g is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this fifth switch 4g is connected to the other end of the first capacitor 4e, the first contact of the sixth switch 4h, and one end of the third capacitor 4n, and the second contact is grounded. The control terminal of this fifth switch 4g is connected to the above-mentioned control device (not shown), and the open / close state of this fifth switch 4g is set based on the first sampling signal SMPL, similar to the first switch 4a.

[0049] The sixth switch 4h is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The sixth switch 4h has a first contact connected to the other end of the first capacitor 4e, the first contact of the fifth switch 4g, and one end of the third capacitor 4n, and a second contact connected to the positive phase input terminal of the differential amplifier 4s and one end of the fifth capacitor 4t. The control terminal of the sixth switch 4h is connected to the above-mentioned control device (not shown), and the open / close state of the sixth switch 4h is set based on a timing signal Tx input from the control device, similar to the third switch 4c and the fourth switch 4d.

[0050] The seventh switch 4i is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The seventh switch 4i has a first contact connected to the other end of the pickup coil 3 and the first contact of the eighth switch 4j, and a second contact connected to the first contact of the ninth switch 4k and the other end of the third capacitor 4n. The control terminal of the seventh switch 4i is connected to the control device (not shown), and the open / close state of the seventh switch 4i is set based on the first sampling signal SMPL, similar to the first switch 4a and the fifth switch 4g.

[0051] The eighth switch 4j is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this eighth switch 4j is connected to the other end of the pickup coil 3 and the first contact of the seventh switch 4i, and the second contact is connected to the first contact of the tenth switch 4m and the other end of the fourth capacitor 4p. The control terminal of the eighth switch 4j is connected to the above-mentioned control device (not shown), and the open / close state of the eighth switch 4j is set based on the second sampling signal CDS, similar to the above-mentioned second switch 4b.

[0052] The ninth switch 4k is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this ninth switch 4k is connected to the second contact of the seventh switch 4i and the other end of the third capacitor 4n, and the second contact is grounded. The control terminal of the ninth switch 4k is connected to the above-mentioned control device (not shown), and the open / close state of the ninth switch 4k is set based on the timing signal Tx, similar to the third switch 4c, the fourth switch 4d, and the sixth switch 4h.

[0053] The tenth switch 4m is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this tenth switch 4m is connected to the second contact of the eighth switch 4j and the other end of the fourth capacitor 4p, and the second contact is grounded. The control terminal of the tenth switch 4m is connected to a control device (not shown), and the open / close state of the tenth switch 4m is set based on the timing signal Tx, similar to the third switch 4c, the fourth switch 4d, the sixth switch 4h, and the ninth switch 4k.

[0054] The third capacitor 4n is a two-terminal element having a predetermined capacitance, and one end of the third capacitor 4n is connected to the other end of the second capacitor 4f, the first contact of the eleventh switch 4q, and the first contact of the twelfth switch 4r, and the other end of the third capacitor 4n is connected to the second contact of the seventh switch 4i and the first contact of the ninth switch 4k.

[0055] The fourth capacitor 4p is a two-terminal element having a predetermined capacitance, and one end of the fourth capacitor 4p is connected to the other end of the first capacitor 4e, the first contact of the fifth switch 4g, and the first contact of the sixth switch 4h, and the other end of the fourth capacitor 4p is connected to the second contact of the eighth switch 4j and the first contact of the tenth switch 4m.

[0056] The eleventh switch 4q is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this eleventh switch 4q is connected to the other end of the third capacitor 4n, the first contact of the twelfth switch 4r, and the other end of the second capacitor 4f, and the second contact is grounded. The control terminal of the eleventh switch 4q is connected to a control device (not shown), and the open / close state of the eleventh switch 4q is set based on the first sampling signal SMPL, similar to the first switch 4a, the fifth switch 4g, and the seventh switch 4i described above.

[0057] The twelfth switch 4r is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this twelfth switch 4r is connected to the other end of the third capacitor 4n, the first contact of the eleventh switch 4q, and the other end of the second capacitor 4f, and the second contact is connected to the negative-phase input terminal of the differential amplifier 4s and one end of the sixth capacitor 4u. The control terminal of the twelfth switch 4r is connected to a control device (not shown), and the open / close state of the twelfth switch 4r is set based on the timing signal Tx, similar to the third switch 4c, the fourth switch 4d, the sixth switch 4h, the ninth switch 4k, and the tenth switch 4m.

[0058] The differential amplifier 4s is a two-input, two-output integrated circuit as shown in the figure, and has a positive input terminal connected to the second contact of the sixth switch 4h and one end of the fifth capacitor 4t, and a negative input terminal connected to the second contact of the twelfth switch 4r and one end of the sixth capacitor 4u.

[0059] The positive-phase output terminal of differential amplifier 4s is connected to the other end of fifth capacitor 4t and the input terminal of high-voltage side current limiting unit 5H, and is also connected to the above-mentioned external device. The negative-phase output terminal of differential amplifier 4s is connected to the other end of sixth capacitor 4u and the input terminal of low-voltage side current limiting unit 5L, and is also connected to the above-mentioned external device.

[0060] The fifth capacitor 4t is a two-terminal element having a predetermined capacitance, and one end of the fifth capacitor 4t is connected to the second contact of the sixth switch 4h and the positive-phase input terminal of the differential amplifier 4s, and the other end is connected to the positive-phase input terminal of the differential amplifier 4s and the external device.

[0061] The sixth capacitor 4u is a two-terminal element having a predetermined capacitance, and one end of the sixth capacitor 4u is connected to the second contact of the twelfth switch 4r and the negative-phase input terminal of the differential amplifier 4s, and the other end is connected to the negative-phase input terminal of the differential amplifier 4s and the external device.

[0062] Here, among the components of the magnetic sensor A1, the first switch 4a, the second switch 4b, the third switch 4c, the fourth switch 4d, the first capacitor 4e, the second capacitor 4f, the fifth switch 4g, the seventh switch 4i, the eighth switch 4j, the ninth switch 4k, the tenth switch 4m, the third capacitor 4n, the fourth capacitor 4p and the eleventh switch 4q constitute the sample-and-hold circuit Ka in the first embodiment.

[0063] In this sample-and-hold circuit Ka, the first capacitor 4e and the fourth capacitor 4p are connected together such that the other end of the first capacitor 4e is connected to one end of the fourth capacitor 4p. These first capacitors 4e and 4p form a first series circuit. Furthermore, the second capacitor 4f and the third capacitor 4n are connected together such that the other end of the second capacitor 4f is connected to one end of the third capacitor 4n. These second capacitors 4f and third capacitors 4n form a second series circuit.

[0064] As will be described in detail later, this sample-and-hold circuit Ka detects the high-voltage side detection voltage V at different timings based on the well-known correlated double sampling method.Ｐ and low voltage side detection voltage V Ｎ It is a correlated double sampling circuit that acquires and holds two sample values ​​by performing sample-and-hold processing on the (detection signal).

[0065] The differential amplifier 4s, the fifth capacitor 4t, and the sixth capacitor 4u constitute the integrating circuit Kb in the first embodiment. The integrating circuit Kb integrates the difference between the high-voltage detection voltage VH input from the sample-and-hold circuit Ka via the sixth switch 4h and the low-voltage detection voltage VL input from the sample-and-hold circuit Ka via the twelfth switch 4r, thereby generating the positive-phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ Generates (-).

[0066] Here, the integrating circuit Kb may be configured as a well-known zero-drift amplifier. Zero-drift amplifiers are known to have several circuit configurations, including a chopper type or chopper-type auto-zero type. Alternatively, a circuit configuration in which a correlated double sampling technique other than the above is applied to the differential amplifier may be used.

[0067] By configuring the integrating circuit Kb as a zero-drift amplifier, it is possible to suppress drift due to input offset voltage and 1 / f noise caused by variations in the characteristics of the transistors that make up the differential amplifier 4s. In other words, by employing a zero-drift amplifier as the integrating circuit Kb, it is possible to improve the accuracy of the magnetic sensor A1.

[0068] 2, high-voltage side current limiting unit 5H includes switch 5a. Switch 5a is an electronically controlled switch with two contacts and a control terminal. One terminal of switch 5a is connected to the positive-phase output terminal of differential amplifier 4s and the other terminal of fifth capacitor 4t, and the other terminal is connected to the input terminal of high-voltage side current generating unit 6H.

[0069] The control terminal of the open / close switch 5a is connected to the control device (not shown). That is, the open / close switch 5a is an electronically controlled switch whose open / close state is set based on a switching signal EN input from the control device to the control terminal, and the positive phase output signal V ｏｕｔ Supply / non-supply of (+) current to the high voltage side current generating section 6H is set based on the above-mentioned switching signal.

[0070] As shown, high-voltage side current generating unit 6H includes resistor 6a, which is a two-terminal element having a predetermined resistance value, one end of which is connected to the second contact of open / close switch 5a in high-voltage side current limiting unit 5H, and the other end of which is connected to one end of pickup coil 3, the first contact of first switch 4a, and the first contact of second switch 4b.

[0071] The resistor 6a has a positive phase output signal V applied to one end via the open / close switch 5a. ｏｕｔ (+) is the magnetic feedback current I ｆｂ That is, the high-voltage side current generating unit 6H shown in FIG. ｆｂ This is the simplest circuit in the current generating section of the present invention that generates a bias current.

[0072] The low-voltage side current limiting unit 5L includes an open / close switch 5b. This open / close switch 5b is an electronically controlled switch with two contacts and a control terminal. One terminal of this open / close switch 5b is connected to the negative-phase output terminal of the differential amplifier 4s and the other terminal of the sixth capacitor 4u, and the other terminal is connected to the input terminal of the low-voltage side current generating unit 6L.

[0073] Similarly to the switch 5a of the high-voltage side current limiting unit 5H, the switch 5b has a control terminal connected to the control device (not shown). That is, the switch 5a is set to an open or closed state based on the switching signal EN input to the control terminal, and the negative-phase output signal V ｏｕｔ Supply / non-supply of (-) to the low-voltage side current generating section 6L is set based on the above-mentioned switching signal.

[0074] As shown in the figure, low-voltage side current generating unit 6L includes resistor 6b, which is a two-terminal element having a predetermined resistance value, one end of which is connected to the second contact of open / close switch 5b in low-voltage side current limiting unit 5L, and the other end of which is connected to the other end of pickup coil 3, the first contact of seventh switch 4i, and the first contact of eighth switch 4j.

[0075] Such a resistor 6b is connected to one end of the resistor 6b via the open / close switch 5b to receive the inverted output signal V ｏｕｔ (-) is the magnetic feedback current I ｆｂ That is, the low-voltage side current generating unit 6L shown in FIG. 2 functions as a voltage / current converter that converts the magnetic feedback current I ｆｂ This is the simplest circuit in the current generating section of the present invention that generates a bias current.

[0076] Next, the magnetic measurement device C1 according to the first embodiment will be described with reference to Fig. 3. As shown in Fig. 3, the magnetic measurement device C1 includes a plurality of magnetic sensors A1 according to the first embodiment and positive-phase output signals V ｏｕｔ (+) and inverted output signal V ｏｕｔ The device is equipped with four magnetic measurement units E1 to E4 that measure the magnetism (biomagnetism) emitted by a living body using (-).

[0077] The magnetic sensors A1 detect biomagnetic fields emitted by various organs in the human body, such as magnetism emitted by the brain (cerebromagnetism), nerves (neuromagnetism), the heart (cardiac magnetism), and muscles (muscle magnetism).

[0078] The magnetic sensor A1 for detecting brain magnetism is connected to the first magnetic measurement unit E1, and outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ The magnetic sensor A1 for detecting neuromagnetism is connected to the second magnetic measurement unit E2, and outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ Outputs (-).

[0079] The magnetic sensor A1 for detecting cardiac magnetism is connected to a third magnetic measurement unit E3, and outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ The magnetic sensor A1 for detecting muscle magnetism is connected to the fourth magnetic measurement unit E4, and outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ Outputs (-).

[0080] The first magnetic measurement unit E1 outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ The second magnetic measurement unit E2 measures the intensity and distribution of the brain magnetism based on the (-) and outputs the result to the outside. ｏｕｔ (+) and inverted output signal V ｏｕｔ The third magnetic measurement unit E3 measures the intensity and distribution of neuromagnetic fields based on the (-) and outputs the results to the outside. The third magnetic measurement unit E3 outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ The fourth magnetic measurement unit E4 measures the strength and distribution of cardiac magnetism based on the (-) and outputs the result to the outside. The fourth magnetic measurement unit E4 outputs a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ Based on (-), the strength and distribution of muscle magnetism are measured and output to the outside.

[0081] The magnetic measurement device C1 described above can realize a stable, high-resolution (picotesla level) biomagnetic measurement device that is small in size and consumes low power. That is, the magnetic measurement device C1 does not require the use of a well-known magnetic sensor head (SQUID, etc.) for biomagnetic measurement, and can achieve significant miniaturization and cost reduction.

[0082] Next, the operations of the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment will be described in detail with reference to the timing chart shown in FIG.

[0083] This timing chart shows the various signals described above, namely, the switching signal EN that controls the open / close switch 5a (high-voltage side current limiting unit 5H) and the open / close switch 5b (low-voltage side current limiting unit 5L), the drive voltage MIE of the sensor head 1, the first sampling signal SMPL that controls the first switch 4a, the fifth switch 4g, the seventh switch 4i, and the eleventh switch 4q, the second sampling signal CDS that controls the second switch 4b and the eighth switch 4j, the timing signal Tx that controls the third switch 4c, the fourth switch 4d, the sixth switch 4h, the ninth switch 4k, the tenth switch 4m, and the twelfth switch 4r, and the input voltage V ｉｎ and output signal D ｏｕｔ This shows the relationship between

[0084] First, the switching signal EN transitions from L (Low level) to H (Hi level) at time t1, causing the magnetic feedback current I ｆｂ The magnetic feedback current I (bias current) starts to flow through the pickup coil 3. ｆｂ As a result of the current flow, the input voltage V ｉｎ rises from 0V to the bias voltage Vb.

[0085] At this time t1, the drive voltage MIE is not input to the sensor head 1, so the pickup coil 3 (magnetic impedance element S) is not in a state where it can detect the external magnetic field G. The bias voltage Vb is Ｐ The magnetic feedback current I ｆｂ is the voltage resulting from the flow of

[0086] Here, at time t1, in addition to the transition of the switching signal EN from "L" to "H," the first sampling signal SMPL and the second sampling signal CDS also transition from "L" to "H." Due to these transitions of the first sampling signal SMPL and the second sampling signal CDS, the first switch 4a, the fifth switch 4g, the seventh switch 4i, the eleventh switch 4q, the second switch 4b, and the eighth switch 4j are set from "open" (open state) to "closed" (closed state).

[0087] Also, at time t1, the timing signal Tx transitions from "H" to "L." This transition of the timing signal Tx sets the third switch 4c, the fourth switch 4d, the sixth switch 4h, the ninth switch 4k, the tenth switch 4m, and the twelfth switch 4r from "closed" to "open."

[0088] That is, at time t1, a high-voltage side detection voltage VB corresponding to the bias voltage Vb is applied to one end of the first capacitor 4e and the second capacitor 4f. Ｐ The other ends of the first capacitor 4e and the second capacitor 4f are grounded. The other ends of the third capacitor 4n and the fourth capacitor 4p are applied with a low-voltage detection voltage VB corresponding to the bias voltage Vb. Ｎ is applied to the third capacitor 4n, and one end of the fourth capacitor 4p is grounded.

[0089] As a result, the first capacitor 4e and the second capacitor 4f are connected to the high-voltage side detection voltage VB Ｐ The third capacitor 4n and the fourth capacitor 4p are charged by the low-voltage side detection voltage VB Ｎ is charged by

[0090] Then, at time t2, when a predetermined time has elapsed since time t1, the second sampling signal CDS transitions from "H" to "L." That is, at this time t2, the high-voltage side detection voltage VB Ｐ The application of the high voltage detection voltage VB Ｐ At time t2, the low-voltage side detection voltage VB Ｎ The application of the low voltage side detection voltage VB Ｎ is held.

[0091] Then, at time t3, a predetermined time after time t2, the drive voltage MIE is supplied to the sensor head 1, and the pickup coil 3 (magnetic impedance element S) is ready to detect the external magnetic field G. As a result, the input voltage V ｉｎ is the magnetic feedback current I ｆｂWhen the external magnetic field G is detected with the bias current (bias current) flowing and the drive voltage MIE being supplied to the sensor head 1, the voltage rises above the bias voltage Vb and reaches a peak voltage Vm at time t4.

[0092] A high-voltage side detection voltage VM corresponding to the peak voltage Vm is applied to one end of the first capacitor 4e. Ｐ The other end of the fourth capacitor 4p is applied with a low-voltage detection voltage VM corresponding to the peak voltage Vm. Ｎ As a result, the first capacitor 4e is charged with the high-voltage side detection voltage VM Ｐ The fourth capacitor 4p is charged by the low-voltage side detection voltage VM Ｎ is charged by

[0093] At time t4, the first sampling signal SMPL transitions from "H" to "L." That is, at time t4, the high-voltage side detection voltage VM Ｐ The application of the high voltage detection voltage VM Ｐ The low-voltage side detection voltage VM at one end of the fourth capacitor 4p is held. Ｎ The application of the low voltage detection voltage VM Ｎ is held.

[0094] Then, at time t5, when a predetermined time has elapsed since time t4, the switching signal EN and the drive voltage MIE transition from "H" to "L." That is, the application of the drive voltage by the drive unit 2 to the sensor head 1 is controlled by the magnetic feedback current I ｆｂ The bias current is limited in synchronization with the current flow to the pickup coil 3.

[0095] As a result, at time t5, the magnetic feedback current I ｆｂ The supply of the bias current (bias current) to the pickup coil 3 is terminated, and the supply of the drive voltage MIE to the sensor head 1 is also terminated. That is, the magnetic feedback current I ｆｂAt the same time that the supply of the bias current to the pickup coil 3 is terminated, the application of the drive voltage MIE to the sensor head 1 is terminated.

[0096] Then, at time t6, when a predetermined time has elapsed since time t5, the timing signal Tx transitions from "L" to "H." That is, the third switch 4c, the fourth switch 4d, the sixth switch 4h, the ninth switch 4k, the tenth switch 4m, and the twelfth switch 4r are set from "open" to "closed" at time t6.

[0097] As a result, the fourth capacitor 4p in the first series circuit is connected in parallel to the first capacitor 4e with a polarity opposite to that during charging, and the third capacitor 4n in the second series circuit is connected in parallel to the second capacitor 4f with a polarity opposite to that during charging.

[0098] That is, the voltage at the junction between first capacitor 4e and fourth capacitor 4p is high-voltage side detection voltage VH, which is obtained by subtracting bias voltage Vb from peak voltage Vm at high-voltage side detection voltage VH, and the voltage at the junction between second capacitor 4f and third capacitor 4n is low-voltage side detection voltage VL, which is obtained by subtracting bias voltage Vb from peak voltage Vm at low-voltage side detection voltage VL.

[0099] Here, the high-voltage side detection voltage VB held in the first capacitor 4e and the second capacitor 4f during the period from time t1 to t2 is Ｐ and the low-voltage side detection voltage VL held in the third capacitor 4n and the fourth capacitor 4p. Ｐ is the first sample value. Also, the high-voltage side detection voltage VM held in the first capacitor 4e during the period from time t3 to t4 is Ｐ and the low-voltage side detection voltage VM held in the fourth capacitor 4p. Ｐ is the second sample value.

[0100] Of these first and second sample values, the high-voltage side detection voltage VB Ｐ and high voltage side detection voltage VM Ｐ is the high voltage side detection voltage V Ｐare two sample values ​​(high-voltage side sample values) sampled at different times for the low-voltage side detection voltage VL Ｐ and the low voltage side detection voltage VM Ｐ is the low voltage side detection voltage V Ｎ are two sample values ​​(low-voltage side sample values) sampled at different times.

[0101] The high-voltage side detection voltage VH and the low-voltage side detection voltage VL generated by the operation of the sample-and-hold circuit Ka from time t1 to time t5 are output from the sample-and-hold circuit Ka to the integrating circuit Kb at time t5. The integrating circuit Kb then differentially amplifies the high-voltage side detection voltage VH and the low-voltage side detection voltage VL to generate the positive-phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ Outputs (-).

[0102] The magnetic sensor A1 and magnetic measurement device C1 according to the first embodiment include a pickup coil 3 (magnetic detection unit) that outputs a detection signal in response to an external magnetic field G, and an input voltage V ｉｎ (detection signal) is subjected to predetermined signal processing to generate a positive phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ a signal processing unit 4 that generates a magnetic feedback current I ｆｂ The magnetic detection unit includes a high-voltage side current generating unit 6H and a low-voltage side current generating unit 6L that generate a bias current, and a high-voltage side current limiting unit 5H and a low-voltage side current limiting unit 5L that limit the flow of the bias current to the magnetic detection unit for a predetermined time.

[0103] That is, according to the first embodiment, by providing the high-voltage side current limiting unit 5H and the low-voltage side current limiting unit 5L, the magnetic feedback current I ｆｂ By limiting the period during which the bias current (bias current) is applied to the pickup coil 3 (magnetic detection unit), it is possible to provide a magnetic sensor A1 and a magnetic measurement device C1 that can reduce power consumption more than before.

[0104] In addition, in the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the signal processing unit 4 detects the input voltage V ｉｎSince the pickup coil 3 (magnetic detection unit) is provided with a correlated double sampling circuit that performs sample-and-hold processing on the detection signal, the parasitic resistance R Ｐ Therefore, according to the first embodiment, it is possible to detect the external magnetic field G with high accuracy.

[0105] In addition, in the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the correlated double sampling circuit detects the input voltage V ｉｎ The first embodiment includes a sample-and-hold circuit Ka that acquires and holds two sample values ​​by sampling the detection signal at different times, and an integration circuit Kb that integrates the difference between the two sample values. According to this first embodiment, it is possible to suppress the influence of the parasitic resistance RP with a simple circuit configuration.

[0106] Furthermore, in the magnetic sensor A1 and magnetic measurement device C1 according to the first embodiment, the differential amplifier Kb is configured as a zero-drift amplifier, so that it is possible to detect the external magnetic field G with high accuracy.

[0107] In the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the high-voltage side current generating unit 6H and the low-voltage side current generating unit 6L generate a positive-phase output signal V ｏｕｔ (+) and inverted output signal V ｏｕｔ (-) based on the magnetic feedback current I ｆｂ The high-voltage side current limiting unit 5H and the low-voltage side current limiting unit 5L are provided with open / close switches 5a and 5b arranged between the signal processing unit 4 and the current generating unit.

[0108] According to the first embodiment, it is possible to configure the high-voltage side current generating unit 6H, the low-voltage side current generating unit 6L, the high-voltage side current limiting unit 5H, and the low-voltage side current limiting unit 5L with a simple circuit configuration.

[0109] Furthermore, in the magnetic sensor A1 and magnetic measuring device C1 of the first embodiment, the magnetic detection unit includes a magnetic impedance element S and a driving unit 2 that applies a driving voltage MIE to the magnetic impedance element S, so that it is possible to detect external magnetic fields G with high sensitivity.

[0110] According to the first embodiment, the driving unit 2 controls the magnetic feedback current I ｆｂ Since the application of the drive voltage MIE to the sensor head 1 is limited in synchronization with the current limit of the bias current, it is possible to reduce the power consumption of the drive unit 2. Therefore, this also reduces the power consumption of the magnetic sensor A1 and the magnetic measurement device C1.

[0111] Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. 5. As shown in the figure, a magnetic sensor A2 according to the second embodiment is configured as a single-ended circuit. In FIG. 5, the same components as those in FIGS. 1 and 2 according to the first embodiment are denoted by the same reference numerals. The following description will mainly focus on differences from the first embodiment.

[0112] The magnetic sensor A2 includes a pickup coil 3 (magnetic detection unit) that outputs a detection signal in response to an external magnetic field G, and an input voltage V ｉｎ (detection signal) is subjected to predetermined signal processing to generate an output signal V ｏｕｔ a signal processing unit 7 that generates a magnetic feedback current I ｆｂ (bias current), and a magnetic feedback current I ｆｂ and a current limiting unit 8 that limits the supply of current (bias current) to the pickup coil 3 (magnetic detection unit) for a predetermined time.

[0113] In the second embodiment, the signal processing unit 7 includes a first switch 7a, a second switch 7b, a third switch 7c, a fourth switch 7d, a first capacitor 7e, a second capacitor 7f, a fifth switch 7g, a sixth switch 7h, a differential amplifier 7i, and a third capacitor 7j, as shown in the figure.

[0114] Among these components, the first switch 7a, the second switch 7b, the third switch 7c, the fourth switch 7d, the first capacitor 7e, the second capacitor 7f, and the fifth switch 7g constitute a sample-and-hold circuit Kc, while the differential amplifier 7i and the third capacitor 7j constitute an integrating circuit.

[0115] The first switch 7a is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of the first switch 7a is connected to one end of the pickup coil 3 and the first contact of the second switch 7b, and the second contact is connected to the first contact of the third switch 7c and one end of the first capacitor 7e.

[0116] The control terminal of the first switch 7a is connected to a control device (not shown). The control device is an electronic device that comprehensively controls the magnetic sensor A2 shown in Fig. 5. The open / closed state of the first switch 7a is set based on a first sampling signal SMPL input from the control device.

[0117] The second switch 7b is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this second switch 7b is connected to one end of the pickup coil 3 and the first contact of the first switch 7a, and the second contact is connected to the first contact of the fourth switch 7d and one end of the second capacitor 7f. The control terminal of the second switch 7b is connected to the above-mentioned control device (not shown), and the open / close state of the second switch 7b is set based on the second sampling signal CDS input from the control device.

[0118] The third switch 7c is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this third switch 7c is connected to the second contact of the first switch 7a and one end of the first capacitor 7e, and the second contact is grounded. The control terminal of the third switch 7c is connected to the above-mentioned control device (not shown), and the open / close state of the third switch 7c is set based on a timing signal Tx input from the control device.

[0119] The fourth switch 7d is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this fourth switch 7d is connected to the second contact of the second switch 7b and one end of the second capacitor 7f, and the second contact is connected to the other end of the first capacitor 7e, one end of the fifth switch 7g, and one end of the sixth switch 7h. The control terminal of the fourth switch 7d is connected to the above-mentioned control device (not shown), and the open / close state of the fourth switch 7d is set based on the timing signal Tx, similar to the third switch 7c.

[0120] The first capacitor 7e is a two-terminal element having a predetermined capacitance, and has one end connected to the second contact of the first switch 7a and the first contact of the third switch 7c, and the other end connected to the first contact of the fifth switch 7g, the second contact of the fourth switch 7d, and the first contact of the sixth switch 7h.

[0121] The second capacitor 7f is a two-terminal element having a predetermined capacitance, and one end of the second capacitor 7f is connected to the second contact of the second switch 7b and the first contact of the fourth switch 7d, and the other end is grounded.

[0122] The fifth switch 7g is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The first contact of this fifth switch 7g is connected to the other end of the first capacitor 7e, the second contact of the fourth switch 7d, and the first contact of the sixth switch 7h, and the second contact is grounded. The control terminal of this fifth switch 7g is connected to the above-mentioned control device (not shown), and the open / close state of this fifth switch 7g is set based on the first sampling signal SMPL, similar to the first switch 4a.

[0123] The sixth switch 7h is an open / close switch (electronically controlled switch) with two contacts and a control terminal. The sixth switch 7h has a first contact connected to the other end of the first capacitor 7e, the second contact of the fourth switch 7d, and the first contact of the fifth switch 7g, and a second contact connected to the negative-phase input terminal of the differential amplifier 7i and one end of the third capacitor 7j. The control terminal of the sixth switch 7h is connected to the above-mentioned control device (not shown), and the open / close state of the sixth switch 7h is set based on the timing signal Tx, similar to the third switch 4c and the fourth switch 4d.

[0124] As shown in the figure, the differential amplifier 7i is an integrated circuit with two inputs and one output. The negative input terminal of this differential amplifier 7i is connected to the second contact of the sixth switch 7h and one end of the third capacitor 7j, and the positive input terminal is grounded. The output terminal of this differential amplifier 7i is connected to the other end of the third capacitor 7j and the input terminal of the current limiting unit 8, and is also connected to an external device.

[0125] The third capacitor 7j is a two-terminal element having a predetermined capacitance, and one end of the third capacitor 7j is connected to the second contact of the sixth switch 7h and the negative-phase input terminal of the differential amplifier 7i, and the other end is connected to the output terminal of the differential amplifier 7i and an external device.

[0126] In the sample-and-hold circuit Kc according to the second embodiment, the first capacitor 7e and the second capacitor 7f are connected in parallel via the fourth switch 7d, i.e., the other end of the first capacitor 7e is connected to the other end of the second capacitor 7f via the fourth switch 7d.

[0127] The sample-and-hold circuit Kc is a correlated double sampling circuit that acquires and holds sample values ​​by performing sample-and-hold processing on the detection voltage Vc (detection signal) at different timings based on the well-known correlated double sampling method. Also, the integrating circuit Kd in the second embodiment amplifies the detection voltage Vs input from the sample-and-hold circuit Kc via the sixth switch 7h to generate an output signal V ｏｕｔ Generate.

[0128] In the second embodiment, the current limiting unit 8 includes an open / close switch 8a. The open / close switch 8a is an electronically controlled open / close switch having two contacts and a control terminal. A first contact of the open / close switch 8a is connected to the output terminal of the differential amplifier 7i and the other terminal of the third capacitor 7j, and a second contact is connected to the input terminal of the current generating unit 9.

[0129] The control terminal of the open / close switch 8a is connected to the control device (not shown). That is, the open / close switch 8a is an electronically controlled switch whose open / close state is set based on a switching signal EN input from the control device to the control terminal, and the output signal V ｏｕｔ The supply / non-supply of the current to the current generating unit 9 is set based on the switching signal EN.

[0130] In the second embodiment, the current generator 9 also includes a resistor 9a. The resistor 9a is a two-terminal element having a predetermined resistance value, with one end connected to the second contact of the open / close switch 8a in the current limiter 8 and the other end connected to one end of the pickup coil 3, the first contact of the first switch 7a, and the first contact of the second switch 7b.

[0131] Next, the operation of the magnetic sensor A2 according to the second embodiment will be described. Note that the operation of the magnetic sensor A2 is the same as that of the first embodiment, so the operation of the magnetic sensor A2 will be described with reference to the timing chart of FIG.

[0132] This timing chart shows the relationship between the switching signal EN, the drive voltage MIE, the first sampling signal SMPL, the second sampling signal CDS, the timing signal Tx, and the input voltage V ｉｎ and output signal D ｏｕｔ This shows the relationship between

[0133] When the switching signal EN transitions from “L” to “H” at time t1, the magnetic feedback current I ｆｂ The magnetic feedback current I (bias current) starts to flow through the pickup coil 3. ｆｂ As a result of the current flow, the input voltage V ｉｎ rises from 0V to the bias voltage Vb.

[0134] At this time t1, the drive voltage MIE is not input to the sensor head 1, so the pickup coil 3 (magnetic impedance element S) is not in a state where it can detect the external magnetic field G. The bias voltage Vb is Ｐ The magnetic feedback current I ｆｂ is the voltage resulting from the flow of

[0135] Here, at time t1, in addition to the transition of the switching signal EN from "L" to "H", the first sampling signal SMPL and the second sampling signal CDS also transition from "L" to "H". Due to these transitions of the first sampling signal SMPL and the second sampling signal CDS, the first switch 7a, the second switch 7b, and the fifth switch 7g are set from "open" (open state) to "closed" (closed state).

[0136] Also, at time t1, the timing signal Tx transitions from "H" to "L." This transition of the timing signal Tx sets the third switch 7c, the fourth switch 7d, and the sixth switch 7h from "closed" to "open."

[0137] That is, at time t1, the high-voltage side detection voltage VB corresponding to the bias voltage Vb is applied to one end of the first capacitor 7e and the second capacitor 7f. Ｐ is applied to the first capacitor 7e and the second capacitor 7f, and the other ends of the first capacitor 7e and the second capacitor 7f are grounded. As a result, the first capacitor 7e and the second capacitor 7f are connected to the input voltage V ｉｎ and the input voltage V ｉｎ Hold.

[0138] Then, at time t2, when a predetermined time has elapsed since time t1, the second sampling signal CDS transitions from "H" to "L." That is, at this time t2, the input voltage V ｉｎ The application of is interrupted.

[0139] Then, at time t3, a predetermined time after time t2, the drive voltage MIE is supplied to the sensor head 1, and the pickup coil 3 (magnetic impedance element S) is ready to detect the external magnetic field G. As a result, the input voltage V ｉｎ is the magnetic feedback current I ｆｂ When the external magnetic field G is detected with the bias current (bias current) flowing and the drive voltage MIE being supplied to the sensor head 1, the voltage rises above the bias voltage Vb and reaches a peak voltage Vm at time t4.

[0140] One end of the first capacitor 7e is connected to a high-voltage side detection voltage VM corresponding to the peak voltage Vm. Ｐ As a result, the first capacitor 7e is charged by the input voltage V ｉｎ and the input voltage V ｉｎ Hold.

[0141] At time t4, the first sampling signal SMPL transitions from "H" to "L." That is, at time t4, the input voltage V ｉｎ The application of is interrupted.

[0142] Then, at time t5, when a predetermined time has elapsed since time t4, the switching signal EN and the driving voltage MIE transition from "H" to "L." That is, at time t5, the magnetic feedback current I ｆｂ The supply of the bias current to the pickup coil 3 is terminated, and the supply of the drive voltage MIE to the sensor head 1 is also terminated.

[0143] Then, at time t6, which is a predetermined time after time t5, the timing signal Tx transitions from "L" to "H." That is, the third switch 7c, the fourth switch 7d, and the sixth switch 7h are set from "open" to "closed" at time t6.

[0144] As a result, the second capacitor 7f is connected in series with the first capacitor 7e with the polarity opposite to that during charging, so that the voltage at the connection point between the first capacitor 7e and the second capacitor 7f becomes the detection voltage Vc, which is the peak voltage Vm minus the bias voltage Vb.

[0145] The detection voltage Vc generated by the operation of the sample-and-hold circuit Kc over the period from time t1 to time t5 is output from the sample-and-hold circuit Kc to the integrating circuit Kd at time t5. The integrating circuit Kd then differentially amplifies the detection voltage Vc to generate an output signal V ｏｕｔ Generate.

[0146] The magnetic sensor A2 and the magnetic measurement device C2 according to the second embodiment include a pickup coil 3 (magnetic detection unit) that outputs a detection signal in response to an external magnetic field G, and an input voltage V ｉｎ(detection signal) is subjected to predetermined signal processing to generate an output signal V ｏｕｔ a signal processing unit 7 that generates a magnetic feedback current I ｆｂ The magnetic sensor includes a current generating unit 9 that generates a bias current, and a current limiting unit 8 that limits the bias current flow to the magnetic detection unit for a predetermined time.

[0147] Therefore, according to the second embodiment, since the current limiting unit 8 is provided, the magnetic feedback current I ｆｂ Therefore, according to the second embodiment, it is possible to provide a magnetic sensor A2 and a magnetic measurement device C2 that can reduce power consumption more than conventional ones.

[0148] The present invention is not limited to the above embodiment, and the following modifications are possible: (1) In the above embodiment, the bias current is generated based on the magnetic feedback current I ｆｂ However, the present invention is not limited to this. A constant current generated independently of the output signal may be used as the bias current.

[0149] (2) In the above embodiment, the magnetic feedback current I ｆｂ However, the present invention is not limited to this. A magnetic feedback current I is passed through a coil (magnetic feedback coil) provided separately from the pickup coil 3. ｆｂ (bias current) may be passed through.

[0150] (3) In the above embodiment, a magnetic measurement device that measures biomagnetism as an external magnetic field G has been described, but the present invention is not limited to this. The magnetic measurement device according to the present invention can detect various external devices other than biomagnetism with low power consumption and high accuracy.

[0151] A1, A2 Magnetic sensor C1 Magnetic measurement device E1 Magnetic measurement section G External magnetic Ka, Kc Sample and hold circuit Kb, Kd Integration circuit S Magnetic impedance element 1 Sensor head 2 Drive section 3 Pickup coil 4 Signal processing section 4a First switch 4b Second switch 4c Third switch 4d Fourth switch 4e First capacitor 4f Second capacitor 4g Fifth switch 4h Sixth switch 4i Seventh switch 4j Eighth switch 4k Ninth switch 4m Tenth switch 4n Third capacitor 4p Fourth capacitor 4q Eleventh switch 4r Twelfth switch 4s Differential amplifier 4t Fifth capacitor 4u Sixth capacitor 5L Low-voltage side current limiting section 5H High-voltage side current limiting section 6L Low-voltage side current generating section 6H High-voltage side current generating section 7 Signal processing section 7a First switch 7b Second switch 7c Third switch 7d Fourth switch 7e First capacitor 7f Second capacitor 7g Fifth switch 7h Sixth switch 7i Differential amplifier 7j Third capacitor 8 Current limiting unit 9 Current generating unit

Claims

1. A magnetic sensor comprising: a magnetic detection unit that outputs a detection signal in response to an external magnetic field; a signal processing unit that generates an output signal by performing predetermined signal processing on the detection signal; a current generating unit that generates a bias current; and a current limiting unit that limits the supply of the bias current to the magnetic detection unit for a predetermined period of time.

2. The magnetic sensor according to claim 1, wherein the signal processing section includes a correlated double sampling circuit.

3. The magnetic sensor according to claim 2, characterized in that the correlated double sampling circuit comprises: a sample-and-hold circuit that obtains and holds two sample values ​​by sampling the detection signal at different timings; and an integration circuit that integrates the difference between the two sample values.

4. The magnetic sensor according to claim 3, wherein the integrating circuit is configured as a zero drift amplifier.

5. The magnetic sensor according to claim 1 or 2, characterized in that the current generating unit includes a resistor that generates the bias current based on the output signal, and the current limiting unit includes an open / close switch provided between the signal processing unit and the current generating unit or between the current generating unit and the magnetic detection unit.

6. A magnetic sensor according to any one of claims 1 to 3, characterized in that the magnetic detection section comprises: a magnetic impedance element; and a drive section that applies a drive voltage to the magnetic impedance element.

7. The magnetic sensor according to claim 6, wherein the drive section limits the application of the drive voltage in synchronization with the current limiting section limiting the current.

8. A magnetic measurement device comprising: a magnetic sensor according to claim 1 or 2; and a magnetic measurement unit that measures the external magnetic field using the output signal.

9. The magnetic measuring device according to claim 8, wherein the external magnetic field is biomagnetic field generated in a living body.

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