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; and a stabilizing unit that is provided with a current generating unit for generating a feedback current on the basis of the output signal and outputting the feedback current to the magnetism detecting unit, the stabilizing unit suppressing fluctuations in a conversion gain from the external magnetism to the output signal.

Description

Magnetic sensor and magnetic measurement device

[0001] This application claims priority to Japanese Patent Application No. 2023-144681, filed on September 6, 2023, the contents of which are incorporated herein by reference.

[0002] The following Patent Document 1 discloses a magnetic sensor and a biomagnetic measurement device that can accurately detect an induced voltage corresponding to an external magnetic field when detecting an induced voltage and generating a bias magnetic field using a single pickup coil.

[0003] This background art employs a solution comprising a sensor head having a magnetic material, a drive unit that applies current to the sensor head, a pickup coil located close to the sensor head, and an information processing unit that generates a bias magnetic field by applying current to the pickup coil and detects a signal corresponding to the voltage generated in the pickup coil, wherein the information processing unit generates a differential signal that indicates the difference between a first signal corresponding to the voltage generated in the pickup coil when the sensor head is in an energized state, and a second signal corresponding to the voltage generated in the pickup coil when the sensor head is not in an energized state.

[0004] Japanese Patent Application Laid-Open No. 2022-100056

[0005] The background art employs a magnetic feedback method for generating a bias magnetic field, in which a current corresponding to an output signal is fed back to a pickup coil to generate a bias magnetic field that is opposite in phase to the external magnetic field. Specifically, the background art converts the output signal into a current using a resistor that functions as a current generator, and feeds the current back to the pickup coil.

[0006] When using such magnetic feedback, the conversion gain from the magnetic signal to the electric signal, from the detection of the external magnetic field (external magnetism) by the pickup coil to the generation of the output signal, is determined mainly by the accuracy of the current generator (current generating unit) provided in the feedback path. However, this current generator has a problem in that the output current fluctuates due to manufacturing variations, temperature, etc., and therefore the conversion gain of the magnetic measurement device fluctuates.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a magnetic sensor and a magnetic measurement device that can suppress fluctuations in the conversion gain from external magnetism to an output signal.

[0008] In order to achieve the above object, the present invention adopts, as a first solution relating to a magnetic sensor, a magnetic detection unit that outputs a detection signal corresponding 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 feedback current based on the output signal and outputs it to the magnetic detection unit, and a stabilization unit that suppresses fluctuations in the conversion gain from the external magnetic field to the output signal.

[0009] The present invention employs, as a second solution related to a magnetic sensor, a solution in which, in the first solution described above, the stabilization unit includes a comparison unit that compares the feedback current with a predetermined reference current, and a correction signal generation unit that generates a correction signal that suppresses fluctuations in the conversion gain based on the comparison result of the comparison unit.

[0010] The present invention provides a third solution related to the magnetic sensor, which is the second solution, in which the stabilization unit controls the current generating unit based on the correction signal so that the feedback current is equal to the reference current.

[0011] The present invention provides a fourth solution related to a magnetic sensor, which is the second solution, in which the stabilization unit performs a correction process on the output signal based on the correction signal so that the feedback current becomes equal to the reference current.

[0012] The present invention employs, as a fifth solution related to a magnetic sensor, a solution in which, in any of the first to fourth solutions above, the current generating unit includes a high-voltage side current generator connected to the high-voltage side of the magnetic detection unit and generating the feedback current based on the output signal, and a low-voltage side current generator connected to the low-voltage side of the magnetic detection unit and generating the feedback current based on the output signal.

[0013] The present invention employs, as a sixth solution related to a magnetic sensor, a solution in which, in any one of the first to fifth solutions described above, the output signal is a digital signal, and the current generating unit generates the feedback current by digital-to-analog converting the output signal.

[0014] The present invention employs, as a seventh solution related to a magnetic sensor, a solution in which, in any one of the first to sixth solutions described above, the comparison unit has a hysteresis characteristic in the comparison between the feedback current and the reference current.

[0015] The present invention employs, as an eighth solution related to a magnetic sensor, a solution in which, in any one of the first to seventh solutions above, the magnetic detection unit includes a pickup coil that detects the external magnetic field and a magnetic feedback coil through which the feedback current is passed.

[0016] The present invention employs, as a ninth solution relating to the magnetic sensor, any one of the first to eighth solutions, in which the magnetic detection portion is a magnetic impedance element.

[0017] 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 eighth solutions and a magnetic measurement unit that measures magnetism using the output signal.

[0018] 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.

[0019] According to the present invention, it is possible to provide a magnetic sensor and a magnetic measurement device that can suppress fluctuations in the conversion gain from an external magnetism to an output signal due to manufacturing variations and environmental changes.

[0020] FIG. 1 is a block diagram showing the configuration of a magnetic sensor A1 according to a first embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a main part of the first embodiment of the present invention, that is, the configuration of a stabilizing unit B1. FIG. 3 is a block diagram showing the configuration of a magnetic measuring device C1 according to the first embodiment of the present invention. FIG. 4 is a timing chart showing the operation of the main part of the magnetic sensor A1 according to the first embodiment of the present invention, that is, the operation of the stabilizing unit B1. FIG. 5 is a block diagram showing the configuration of a magnetic sensor A2 according to a second embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of a magnetic sensor A3 according to a third embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of a current generating unit in a first modified example of the present invention. FIG. 8 is a block diagram showing the configuration of a stabilizing unit B4 in a first modified example of the present invention. FIG. 9 is a block diagram showing the configuration of a stabilizing unit B5 in a second modified example of the present invention. FIG. 10 is a block diagram showing the configuration of a current generating unit B6 in a second modified example of the present invention.

[0021] 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 Figs. 1 to 4. As shown in Fig. 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 current generating unit 5, a comparison unit 6, and a correction signal generating unit 7. Of these components, the current generating unit 5, the comparison unit 6, and the correction signal generating unit 7 form a stabilization unit B1 in the first embodiment.

[0022] 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.

[0023] Here, the sensor head 1 constitutes a magnetic impedance element together with a pickup coil 3, which will be described later. That is, the sensor head 1 in the first embodiment is, for example, an amorphous wire. When a drive voltage is applied to the sensor head 1 from the drive unit 2 while an external magnetic field G is acting on it, the impedance of the sensor head 1 changes, and the magnetic flux penetrating the interior of the sensor head 1 also changes. The amount of change in this impedance depends on the magnitude of the external magnetic field G.

[0024] 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 above-mentioned magnetic impedance element (sensor head 1 and pickup coil 3), constitutes the magnetic detection 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 applies the fluctuating voltage to the sensor head 1 to drive it.

[0025] 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 an output end of the current generating unit 5, and the other end is connected to the other input end (second input end) of the signal processing unit 4 and the first input end of the current generating unit 5.

[0026] 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 pickup coil 3. 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 Ｐ and 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

[0027] In FIG. 1, a resistor R ｐ This resistor R ｐis a parasitic resistance that inevitably exists in 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 resistor R ｐ A parasitic voltage corresponding to the parasitic resistance value is generated across both ends of the resistor.

[0028] As described in a well-known document (JP 2022-100055 A), this parasitic voltage is a cause of error in the detection of the external magnetic field G by the sensor head 1, drive unit 2, and pickup coil 3. In other words, as described in the above-mentioned well-known document, it is preferable that this parasitic voltage be subtracted from the induced voltage induced in the pickup coil 3.

[0029] The signal processing unit 4 has a first input terminal connected to one end of the pickup coil 3 and an output terminal of the current generating unit 5, and a second input terminal connected to the other end of the pickup coil 3 and a first input terminal of the current generating unit 5. The output terminal of the signal processing unit 4 is also connected to the second input terminal of the current generating unit 5 and the first input terminal of the correction signal generating unit 7.

[0030] The signal processing unit 4 converts the induced voltage in the pickup coil 3 into an input voltage V ｉｎ and this input voltage V ｉｎ By subjecting the signal to predetermined signal processing, an output signal D ０ That is, this output signal D ０ is a signal indicating the strength (magnitude) of the external magnetic field G. The signal processing unit 4 outputs the output signal D ０ and outputs it to the outside and to the second input terminal of the current generating unit 5.

[0031] This output signal D ０ may be either an analog signal or a digital signal, but in the first embodiment it is a digital signal. That is, the output signal D0 is a binary code of N bits (N: natural number) that indicates the strength (magnitude) of the external magnetic field G, and is configured as a bit string from the 0th bit to the N-1th bit. Note that such an output signal D ０ More precisely, in addition to the above binary code, it also includes a binary code obtained by inverting the phase of the binary code (inverted binary code).

[0032] In addition to the first and second input terminals, current generator 5 also has a third input terminal. The first input terminal of current generator 5 is connected to the other end of pickup coil 3 and the second input terminal of signal processor 4, the second input terminal is connected to the output terminal of signal processor 4 and the first input terminal of correction signal generator 7, and the third input terminal is connected to the output terminal of correction signal generator 7.

[0033] The current generating section 5 receives the output signal D input from the signal processing section 4 to the second input terminal. ０ (digital signal) based on the magnetic feedback current I ｆｂ The current generating unit 5 is a D / A converter (digital / analog converter) that generates an output signal D ０ The magnetic feedback current I generated based on ｆｂ The correction signal D is adjusted so that it is stably maintained at a predetermined value. ｃｔｒｌ and the magnetic feedback current I ｆｂ Fine-tune the.

[0034] The comparator 6 has an input terminal connected to the output terminal of the current generator 5, the pickup coil 3, and a first input terminal of the signal processor 4, and an output terminal connected to the input terminal of the correction signal generator 7. The comparator 6 converts the magnetic feedback current I ｆｂ Feedback voltage V based on Ｐ and the internally generated reference current I ＲＥＦ Reference voltage V based on ｒ Compare with.

[0035] Here, the comparison unit 6 in the first embodiment calculates the magnetic feedback current I ｆｂ and the reference current I ＲＥＦ Instead of directly comparing with the feedback voltage V Ｐ and the reference voltage V ｒ and based on the magnetic feedback current I ｆｂ and the reference current I ＲＥＦ That is, the comparison unit 6 indirectly compares the magnetic feedback current I ｆｂ The feedback voltage V is based on the voltage drop across the resistor caused by the current flowing through the resistor. Ｐ and the reference current IＲＥＦ A reference voltage V is based on the voltage drop across another resistor caused by the current flowing through the resistor. ｒ This is a comparison with.

[0036] In addition, the comparison unit 6 detects the feedback voltage V Ｐ and the reference voltage V ｒ That is, the comparison unit 6 has a hysteresis characteristic in comparison with the feedback voltage V Ｐ and the reference voltage V ｒ In order to prevent the output from repeatedly switching between "H (high level)" and "L (low level)" when the values ​​are close to each other, the first threshold voltage when the output transitions from "H (high level)" to "L (low level)" is different from the second threshold voltage when the output transitions from "L (low level)" to "H (high level)."

[0037] Such a comparison unit 6 calculates the feedback voltage V Ｐ and the reference voltage V ｒ The comparison result with the magnetic feedback current I ｆｂ and the reference current I ＲＥＦ A step signal indicating the magnitude relationship with the comparison signal V ｃｏｍｐ The comparison signal V ｃｏｍｐ is the output voltage V Ｐ and the reference voltage V ｒ The signal changes to "H (high level)" or "L (low level)" depending on the magnitude relationship between the signal and the output.

[0038] The correction signal generating unit 7 has a first input terminal connected to the output terminal of the signal processing unit 4 and a second input terminal of the current generating unit 5, a second input terminal connected to the output terminal of the comparing unit 6, and an output terminal connected to the third input terminal of the current generating unit 5. The correction signal generating unit 7 converts, for example, the output signal D ０ (digital signal) and the comparison signal V input from the comparison unit 6 to the second input terminal. ｃｏｍｐ By performing predetermined logic processing on each of them, the correction signal D ｃｔｒｌ Generate.

[0039] That is, the correction signal generator 7 generates the correction signal D ｃｔｒｌBy controlling the current generating unit 5 using ０ (digital signal) to magnetic feedback current I ｆｂ Correction signal D ｃｔｒｌ is the comparison signal V input from the comparator 6 to the correction signal generator 7. ｃｏｍｐ Since the feedback voltage V Ｐ is the reference voltage V ｒ That is, the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ The current generating unit 5 is controlled so that the current becomes equal to the above.

[0040] The current generating section 5, the comparing section 6, and the correction signal generating section 7 described above constitute the stabilizing section B1 in the first embodiment. ０ (digital signal) is used as the input signal, and the magnetic feedback current I ｆｂ That is, the stabilization unit B1 outputs the output signal D ０ (digital signal) based on a constant value (reference current I ＲＥＦ ) the magnetic feedback current I ｆｂ is generated and output to the pickup coil 3.

[0041] Next, the specific configuration of the stabilization unit B1 will be described with reference to Fig. 2. As shown in the figure, the stabilization unit B1 includes N high-voltage side resistance cells 10, N low-voltage side resistance cells 11, two reference cells 12, a constant current source 13, a comparator 14, and a logic circuit 15.

[0042] Of these components, the N high-voltage side resistor cells 10 and the N low-voltage side resistor cells 11 constitute the above-mentioned current generating unit 5. The N high-voltage side resistor cells 10 correspond to the high-voltage side current generators of the present invention, and the N low-voltage side resistor cells 11 correspond to the low-voltage side current generators of the present invention. Furthermore, the two reference cells 12, the constant current source 13, and the comparator 14 constitute the above-mentioned comparing unit 6. Furthermore, the logic circuit 15 corresponds to the above-mentioned correction signal generating unit 7.

[0043] The high-voltage side resistor cell 10 and the low-voltage side resistor cell 11 output the above-mentioned output signal D ０ That is, N high-voltage side resistor cells 10 are provided corresponding to the bit string from the 0th bit to the (N-1)th bit. ０ The zeroth-order high-voltage side resistor cell corresponding to the zeroth-order bit of the output signal D ０ The first high-voltage side resistor cell corresponding to the first bit of the output signal D ０ The N-1th high-voltage side resistor cell corresponds to the N-1th bit of the N-1th high-voltage side resistor cell.

[0044] The N high-voltage side resistance cells 10 all have the same circuit configuration, and as shown in the figure, include a high-voltage side switch 10a, a low-voltage side switch 10b, a variable resistor 10c, and an enable switch 10d. The N low-voltage side resistance cells 11 all have the same circuit configuration, and as shown in the figure, include a high-voltage side switch 11a, a low-voltage side switch 11b, a variable resistor 11c, and an enable switch 11d.

[0045] The high-voltage side switch 10a is a two-contact open / close switch, with the first contact connected to the DC power supply, the second contact connected to the first contact of the low-voltage side switch 10b and one end of the variable resistor 10c, and the control end connected to the control end of the high-voltage side switch 11a and the control end of the low-voltage side switch 11b in the low-voltage side resistance cell 11 and the first input end of the logic circuit 15.

[0046] The control terminal of the high-voltage side switch 10a is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B1. The high-voltage side switch 10a receives the output signal D ０ is input, and the output signal D ０ The open / closed state is controlled by

[0047] That is, the high-voltage side switch 10a of the first high-voltage side resistor cell receives the output signal D ０ The high-voltage side switch 10a of the first high-voltage side resistor cell is controlled by the 0th bit of the output signal D ０The open / close state of the high-voltage side switch 10a of the (N-1)th high-voltage side resistor cell is controlled by the (N-1)th bit of the output signal D0.

[0048] Like high-voltage-side switch 10a, low-voltage-side switch 10b is a two-contact open / close switch. A first contact of low-voltage-side switch 10b is connected to the second contact of high-voltage-side switch 10a and one end of variable resistor 10c, a second contact is grounded, and a control terminal is connected to the control terminal of high-voltage-side switch 11a and the control terminal of low-voltage-side switch 11b in low-voltage-side resistor cell 11 and a first input terminal of logic circuit 15.

[0049] The control terminal of the low-voltage side switch 10b is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B1. ０ (digital signal) is input, and the output signal D ０ The open / closed state is controlled inversely to that of high-voltage side switch 10a by the inverted sign of the digital signal.

[0050] That is, the low-voltage side switch 10b of the first high-voltage side resistor cell receives the output signal D ０ The open / close state is controlled by the inverted code of the 0th bit in the low-voltage side switch 10b of the first high-voltage side resistor cell, and the low-voltage side switch 10b of the first high-voltage side resistor cell is controlled by the inverted code of the 0th bit in the low-voltage side resistor cell. ０ The open / close state is controlled by the inverted sign of the most significant bit in (omitted), and the low-voltage side switch 10b of the N-1th high-voltage side resistor cell ... ０ The open / close state is controlled by the inverted sign of the (N-1)th bit in

[0051] Variable resistor 10c is a three-terminal resistive element having a predetermined resistance variable range, and one end of variable resistor 10c is connected to the second contact of high-voltage side switch 10a and the first contact of low-voltage side switch 10b, and the other end is connected to the first contact of enable switch 10d.

[0052] The control terminal of the variable resistor 10c is commonly connected to the control terminal of the variable resistor 11c in the low-voltage side resistance cell 11 and the control terminal of the variable resistor 12a in the reference cell 12. The variable resistor 10c is connected to the control terminal of the correction signal D ｃｔｒｌ The resistance value is set variably and discretely by the

[0053] The enable switch 10d is a two-contact open / close switch, with a first contact connected to the other end of the variable resistor 10c and a second contact serving as an input / output terminal for connecting to the outside of the high-voltage side resistor cell 10. The second contact (input / output terminal) of the enable switch 10d is commonly connected to the input / output terminals of all the high-voltage side resistor cells 10 as shown in the figure.

[0054] In addition, the second contact (input / output terminal) of the enable switch 10d is also connected to one end of the pickup coil 3, a first input terminal of the signal processing unit 4, and a first input terminal of the comparator 14. The open / closed state of the enable switch 10d is controlled by an enable signal EN (not shown).

[0055] This enable signal EN is connected to the magnetic feedback current I ｆｂ The enable signal EN is a control signal that turns on (power supply) / off (power non-supply) the power supply to the pickup coil 3. In a normal state, the enable signal EN sets the enable switch 10d to the ON state (closed state), and the magnetic feedback current I ｆｂ The high-voltage side resistor cell 10 is set to a state in which power is supplied to the pickup coil 3.

[0056] On the other hand, the N low-voltage side resistor cells 11 output the output signal D ０ The 0th bit of the low-voltage-side resistor cell LS ０ , output signal D ０ The first low-voltage side resistor cell LS corresponding to the first bit of １ , (omitted), output signal D ０ The N-1th low-voltage side resistor cell LS corresponding to the N-1th bit of Ｎ－１ It consists of:

[0057] In the N low-voltage side resistor cells 11, the high-voltage side switch 11a is a two-contact open / close switch, similar to the high-voltage side switch 10a of the high-voltage side resistor cell 10. The first contact of this high-voltage side switch 11a is connected to the DC power supply, and the second contact is connected to the first contact of the low-voltage side switch 11b and one end of the variable resistor 11c.

[0058] The control terminal of the high-voltage side switch 11a is connected to the control terminal of the high-voltage side switch 10a and the control terminal of the low-voltage side switch 10b in the high-voltage side resistor cell 10, and to the first input terminal of the logic circuit 15. The high-voltage side switch 11a is connected to the first high-voltage side resistor cell HS １ Similarly to the low-voltage side switch 10b in ０ The open / closed state is controlled by the inverted sign of

[0059] That is, the first low-voltage side resistance cell LS １ The high-side switch 11a in ０ The open / close state is controlled by the inverted code of the 0th bit of the first low-voltage side resistor cell HS １ The high-voltage side switch 11a outputs the output signal D ０ The open / close state is controlled by the inverted code of the first bit of the (N-1)th low-voltage side resistor cell HS Ｎ－１ The high-voltage side switch 11a outputs the output signal D ０ The open / close state is controlled by the inverted sign of the (N-1)th bit.

[0060] Like the high-voltage side switch 11a, the low-voltage side switch 11b is a two-contact open / close switch. The first contact of the low-voltage side switch 11b is connected to the second contact of the high-voltage side switch 11a and one end of the variable resistor 11c, and the second contact is grounded.

[0061] The control terminal of the low-voltage side switch 11b is connected to the control terminal of the high-voltage side switch 10a and the control terminal of the low-voltage side switch 10b in the high-voltage side resistor cell 10, and to the first input terminal of the logic circuit 15. The low-voltage side switch 11b is connected to the first high-voltage side resistor cell HS １Similarly to the high-voltage side switch 10a in ０ The open / closed state is controlled by

[0062] That is, the first low-voltage side resistance cell LS １ The low-voltage side switch 11b of the output signal D ０ The open / close state is controlled by the 0th bit in the １ The low-voltage side switch 11b of the output signal D ０ The open / close state is controlled by the first bit in the (Omitted) N-1th low-voltage side resistor cell LS Ｎ－！ The low-voltage side switch 11b of the output signal D ０ The open / close state is controlled by the N-1th bit in

[0063] Variable resistor 11c is a two-terminal resistive element having a predetermined resistance variable range, and one end of variable resistor 11c is connected to the second contact of high-voltage side switch 11a and the first contact of low-voltage side switch 11b, and the other end is connected to the first contact of enable switch 11d.

[0064] The control terminal of the variable resistor 11c is commonly connected to the control terminal of the variable resistor 10c in the high-voltage side resistor cell 10 and the control terminal of the variable resistor 12a in the reference cell 12. The variable resistor 11c is connected to the control terminal of the correction signal D ｃｔｒｌ The resistance value is variably set by

[0065] The enable switch 11d is a two-contact open / close switch, with a first contact connected to the other end of the variable resistor 11c and a second contact serving as an input / output terminal for connecting to the outside of the low-voltage side resistor cell 11. The second contact (input / output terminal) of the enable switch 11d is commonly connected to the input / output terminals of all the low-voltage side resistor cells 11 as shown in the figure.

[0066] The second contact (input / output terminal) of the enable switch 11d is also connected to the other end of the pickup coil 3 and the second input terminal of the signal processing unit 4. The open / close state of the enable switch 11d is controlled by the enable signal EN described above. This enable signal EN is used to control the magnetic feedback current I for the purpose of power saving, etc. ｆｂ is provided to energize the pickup coil 3 for a specific period of time.

[0067] The two reference cells 12 have the same circuit configuration and each includes a variable resistor 12a. The variable resistor 12a is a two-terminal resistor element having a predetermined resistance variable range. One end of the variable resistor 12a is connected to a DC power supply, and the other end is connected to the input terminal of the constant current source 13 and the second input terminal of the comparator 14.

[0068] The variable resistor 12a has a control terminal commonly connected to the control terminal of the variable resistor 10c in the high-voltage side resistor cell 10 and the control terminal of the variable resistor 11c in the low-voltage side resistor cell 11. The variable resistor 12a, like the variable resistor 10c in the high-voltage side resistor cell 10 and the variable resistor 11c in the low-voltage side resistor cell 11, receives the correction signal D input to its control terminal from the logic circuit 15 (correction signal generator 7). ｃｔｒｌ The resistance value is variably set by

[0069] The constant current source 13 is a two-terminal element having an input terminal and an output terminal. The input terminal of this constant current source 13 is connected to the other terminal of the variable resistor 12a and the second input terminal of the comparator 14, and the output terminal is grounded. The constant current source 13 has a reference voltage V ｒ is applied, a constant reference current I flows from the input terminal to the output terminal. ＲＥＦ Forcefully flow.

[0070] Here, the reference voltage V ｒ is the power supply voltage V of the DC power supply ｃｃ , the set resistance value R of the variable resistor 12a ｒ and the reference current I, which is the characteristic value of the constant current source 13 ＲＥＦThat is, the reference voltage Vr is determined by the power supply voltage V applied to one end of the variable resistor 12a. ｃｃ is the set resistance value R of the variable resistor 12a ｒ and the reference current I ＲＥＦ This is the voltage drop obtained by multiplying

[0071] The comparator 14 is a three-terminal element having a pair of input terminals (first and second input terminals) and one output terminal. Of the first and second input terminals, the first input terminal is a negative-phase input terminal (-) as shown in the figure, and the second input terminal is a positive-phase input terminal (+) as shown in the figure.

[0072] The comparator 14 receives a feedback voltage V Ｐ and a reference voltage V applied to the second input terminal. ｒ and a comparison signal V ｃｏｍｐ The comparison signal V ｃｏｍｐ is the feedback voltage V Ｐ is the reference voltage V ｒ In the above cases, the voltage becomes L level (low voltage), and the feedback voltage V Ｐ is the reference voltage V ｒ If the signal is smaller than 1, it is a binary signal that is at H level (high potential).

[0073] Logic circuit 15 corresponds to the correction signal generator 7 and is a two-input, one-output logic circuit. A first input terminal of logic circuit 15 is connected to the control terminal of high-voltage-side switch 10a and the control terminal of low-voltage-side switch 10b in high-voltage-side resistor cell 10, and to the control terminal of high-voltage-side switch 11a and the control terminal of low-voltage-side switch 11b in low-voltage-side resistor cell 11.

[0074] A first input terminal of the logic circuit 15 is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B1. A second input terminal of the logic circuit 15 is connected to the output terminal of the comparator 14. An output terminal of the logic circuit 15 is connected to the control terminal of the variable resistor 10c in the high-voltage side resistance cell 10, the control terminal of the variable resistor 11c in the low-voltage side resistance cell 11, and the control terminal of the variable resistor 12a in the reference cell 12.

[0075] The logic circuit 15 receives the output signal D input from the signal processing unit 4 to the first input terminal. ０ and the comparison signal V input from the comparator 14 to the first input terminal. ｃｏｍｐ By performing predetermined logical processing on the ｃｔｒｌ This correction signal D ｃｔｒｌ is the feedback current I ｆｂ is a digital signal indicating the amount of correction.

[0076] The above-mentioned comparator 14 has a hysteresis characteristic as explained in the comparison unit 6. In contrast, the logic circuit 15 (correction signal generating unit 7) is configured so as to function even if the comparator 14 (comparison unit 6) does not have a hysteresis characteristic. In other words, the logic circuit 15 has a dead band over a predetermined period, and even if the comparison result of the comparator 14 (comparison unit 6) changes, the correction signal D ｃｔｒｌ Do not update.

[0077] This correction signal D ｃｔｒｌ is output to the current generating unit 5 as a control signal for controlling the current generating unit 5. That is, the correction signal D ｃｔｒｌ is the feedback voltage V Ｐ and the reference voltage V ｒ Based on the magnitude relationship with the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ The current generating unit 5 is feedback controlled so that the current becomes equal to the current.

[0078] Here, the current generating unit 5 in the first embodiment is provided with N high-voltage side resistance cells 10 functioning as D / A converters on one end side of the pickup coil 3, and N low-voltage side resistance cells 11 also functioning as D / A converters on the other end side of the pickup coil 3. That is, the stabilizing unit B1 in the first embodiment generates a feedback current I ｆｂ The circuit configuration used is to correct the above.

[0079] 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 output signals D ０ The device includes four magnetic measurement units E1 to E4 that measure the magnetism (biomagnetism) emitted by a living body using the magnetic sensors A1. The magnetic sensors A1 detect the biomagnetism emitted by various organs in the human body, for example, and detect the magnetism emitted by the brain (cerebromagnetism), the magnetism emitted by nerves (neuromagnetism), the magnetism emitted by the heart (cardiac magnetism), and the magnetism emitted by muscles (muscle magnetism).

[0080] The magnetic sensor A1 for detecting the brain magnetism is connected to the first magnetic measurement unit E1, and outputs an output signal D indicative of the brain magnetism to the first magnetic measurement unit E1. ０ The magnetic sensor A1 for detecting neuromagnetism is connected to the second magnetic measurement unit E2, and outputs an output signal D indicating neuromagnetism to the second magnetic measurement unit E2. ０ Output.

[0081] The magnetic sensor A1 for detecting cardiac magnetism is connected to a third magnetic measurement unit E3, and outputs an output signal D indicative of cardiac magnetism to the third magnetic measurement unit E3. ０ The magnetic sensor A1 for detecting muscle magnetism is connected to the fourth magnetic measurement unit E4, and outputs an output signal D indicating muscle magnetism to the fourth magnetic measurement unit E4. ０ Output.

[0082] The first magnetic measurement unit E1 outputs an output signal D indicative of brain magnetism. ０ The second magnetic measurement unit E2 measures the intensity and distribution of the brain magnetism based on the signal D ０The third magnetic measurement unit E3 measures the intensity and distribution of neuromagnetism based on the signal D and outputs the signal D to the outside. ０ The fourth magnetic measurement unit E4 measures the strength and distribution of cardiac magnetism based on the signal D and outputs the signal D to the outside. ０ Based on this, the strength and distribution of muscle magnetism are measured and output to the outside.

[0083] 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.

[0084] 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.

[0085] The first embodiment aims to suppress fluctuations in the conversion gain of the magnetic sensor A1, thereby improving the measurement accuracy of the magnetic measurement device C1. ｃｃ If fluctuations in the ambient temperature or the like occur, the conversion gain of the magnetic sensor A1 may fluctuate due to these variations and fluctuations. When the conversion gain of the magnetic sensor A1 fluctuates, the output current D ０ fluctuates, making it impossible to realize stable magnetic detection and measurement.

[0086] In the first embodiment, the stabilization unit B1 having the above-described configuration is provided in the magnetic sensor A1, thereby suppressing fluctuations in the conversion gain of the magnetic sensor A1 and achieving stable magnetic detection and measurement. The timing chart in Figure 4 shows the time-series operation of the stabilization unit B1.

[0087] For example, as shown in the top row of FIG. ｃｃ When the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ At this time, the output signal D ０is "2" as shown in the figure, that is, when it matches the number of cells of the reference cell 12, the comparison signal V ｃｏｍｐ The resistance value of the variable resistor 10c in the high-voltage side resistance cell 10, the resistance value of the variable resistor 11c in the low-voltage side resistance cell 11, and the resistance value of the variable resistor 12a in the reference cell 12 are controlled in accordance with the correction signal D ｃｔｒｌ Update.

[0088] For example, the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ In the following case, the feedback voltage V Ｐ is the reference voltage V ｒ Therefore, the comparison signal V ｃｏｍｐ As shown in the figure, the correction signal D ｃｔｒｌ When the resistance value of the variable resistor 10c in the high-voltage side resistance cell 10, the resistance value of the variable resistor 11c in the low-voltage side resistance cell 11, and the resistance value of the variable resistor 12a in the reference cell 12 also decrease, resulting in a decrease in the magnetic feedback current I ｆｂ increases.

[0089] That is, in the stabilization section B1, the output signal D ０ Whenever the number of reference cells 12 becomes "2", the comparison signal V ｃｏｍｐ The resistance value of the variable resistor 10c in the high-voltage side resistance cell 10, the resistance value of the variable resistor 11c in the low-voltage side resistance cell 11, and the resistance value of the variable resistor 12a in the reference cell 12 are controlled by the magnetic feedback current I ｆｂ and the reference current I ＲＥＦ The value is automatically corrected so that it is equal to the value of the

[0090] In addition, in this stabilization section B1, the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ When the feedback voltage V Ｐ is the reference voltage V ｒ Since the comparison signal V ｃｏｍｐ changes to H level (high potential) as shown in the figure.

[0091] Even in this state, as described above, every time the output signal D0 becomes "2" which matches the number of the reference cells 12, the comparison signal V ｃｏｍｐ In response to this, the resistance value of the variable resistor 10c in the high-voltage side resistance cell 10, the resistance value of the variable resistor 11c in the low-voltage side resistance cell 11, and the resistance value of the variable resistor 12a in the reference cell 12 are automatically corrected so that the magnetic feedback current Ifb and the reference current IREF are equal.

[0092] 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 corresponding to an external magnetic field G, and an output signal D ０ a signal processing unit 4 for generating an output signal D ０ Based on the feedback current I ｆｂ and generates the feedback current I ｆｂ and a stabilization unit B1 that stabilizes the signal and outputs it to the pickup coil 3 (magnetic detection unit).

[0093] Therefore, according to the first embodiment, since the stabilization unit B1 is provided, the output signal D ０ It is possible to provide a magnetic sensor A1 and a magnetic measurement device C1 that can suppress fluctuations in the conversion gain to the input signal.

[0094] In the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the stabilization unit B1 outputs the output signal D ０ Based on the feedback current I ｆｂ a current generating unit 5 that generates a feedback voltage V Ｐ and the reference voltage V ｒ and based on the feedback current I ｆｂ and the reference current I ＲＥＦ and a comparison signal V ｃｏｍｐ Based on the feedback current I ｆｂ is the reference current I ＲＥＦ and a correction signal generating unit 7 that controls the current generating unit 5 so that the current is equal to the

[0095] According to the first embodiment, the feedback current Iｆｂ is the reference current I ＲＥＦ Since the current generating unit 5 is feedback-controlled by the correction signal generating unit 7 so that the reference current I ＲＥＦ The feedback current I is equal to ｆｂ It is possible to stabilize the

[0096] In the magnetic sensor A1 and magnetic measurement device C1 according to the first embodiment, the stabilization unit B1 has a pair of current generators 5 provided on both ends of the pickup coil 3 (magnetic detection unit). Therefore, according to the first embodiment, the feedback current I is much larger than when the current generators 5 are provided on only one side of the pickup coil 3 (magnetic detection unit). ｆｂ It is possible to stabilize the temperature with high precision.

[0097] In the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the comparison unit 6 controls the feedback current I ｆｂ and the reference current I ＲＥＦ According to the first embodiment, the feedback current I ｆｂ and the reference current I ＲＥＦ When the values ​​are close to each other, the comparison signal V ｃｏｍｐ It is possible to suppress fluctuations in the

[0098] That is, according to the first embodiment, the correction signal D ｃｔｒｌ Therefore, according to the first embodiment, it is possible to stably control the current generating unit 5 by the comparing unit 6, and therefore, the feedback current I ｆｂ It is possible to further stabilize the

[0099] In the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the logic circuit 15 (correction signal generator 7) has a dead zone over a predetermined period. ｆｂ and the reference current I ＲＥＦ When the values ​​are close to each other, the comparison signal V ｃｏｍｐ It is possible to suppress fluctuations in the

[0100] Furthermore, in the magnetic sensor A1 and the magnetic measurement device C1 according to the first embodiment, the output signal is a digital signal, and the current generating unit 5 outputs the output signal D ０ (digital signal) based on the feedback current I ｆｂ Therefore, according to the first embodiment, the output signal D ０ (digital signal) based on the feedback current I ｆｂ It is possible to generate with high accuracy.

[0101] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 5. In Fig. 5, the same components as those in the first embodiment are denoted by the same reference numerals. The following mainly describes the differences from the first embodiment.

[0102] 5, the magnetic sensor A2 according to the second embodiment includes the sensor head 1, drive unit 2, pickup coil 3, signal processing unit 4, current generating unit 5, comparison unit 6, and correction signal generating unit 7 of the magnetic sensor A1 according to the first embodiment, as well as a digital filter 20 and a digital multiplier 21. Of these components, the comparison unit 6, correction signal generating unit 7, digital filter 20, and digital multiplier 21 form a stabilization unit B2 in the second embodiment.

[0103] In the magnetic sensor A2 according to the second embodiment, the correction signal D ｃｔｒｌ is supplied to the digital multiplier 21, rather than to the current generating unit 5 as in the first embodiment. In the magnetic sensor A1 according to the first embodiment, the D / A conversion characteristic (conversion coefficient) of the current generating unit 5 functioning as a D / A converter is calculated using the correction signal D ｃｔｒｌ The feedback current I ｆｂ was stabilized.

[0104] In contrast, the magnetic sensor A2 according to the second embodiment generates a correction signal D ｃｔｒｌ Control of the current generating unit 5 using the correction signal D ｃｔｒｌ is supplied to the current generating unit 5 to generate a feedback current I ｆｂInstead of directly regulating the feedback current I ｆｂ The output signal D due to fluctuations ０ Fluctuations in the (digital signal) are corrected by post-processing using a digital filter 20 and a digital multiplier 21 .

[0105] In the magnetic sensor A2, the input terminal of the digital filter 20 is connected to the output terminal of the signal processing unit 4, and the output terminal is connected to the first input terminal of the digital multiplier 21. The digital filter 20 multiplies the output signal D ０ A band-limited output signal D obtained by limiting the signal band of (digital signal) １ (digital signal) is output to the digital multiplier 21.

[0106] The digital multiplier 21 has a first input terminal connected to the output terminal of the digital filter 20 and a second input terminal connected to the output terminal of the correction signal generator 7. The digital multiplier 21 also has an output terminal connected to an external device. That is, the output terminal of the digital multiplier 21 is the output terminal of the magnetic sensor A2 according to the second embodiment.

[0107] This digital multiplier 21 multiplies the band-limited output signal D １ (digital signal) and correction signal D ｃｔｒｌ The corrected output signal D ｏｕｔ Correction signal D ｃｔｒｌ is the feedback current I ｆｂ Since it is a digital signal indicating the amount of correction, the correction output signal D ｏｕｔ is the feedback current I ｆｂ The output signal D due to the fluctuation ０ This suppresses fluctuations in the

[0108] That is, the stabilization unit B2 in the second embodiment uses the correction signal D ｃｔｒｌ Using the feedback current I ｆｂ Instead of directly correcting ｃｔｒｌ Based on the feedback current I ｆｂ is the reference current I ＲＥＦ The output signal D０ This is a method for performing correction processing on the image.

[0109] According to the second embodiment, the stabilization unit B2 is provided with the comparator 6, the correction signal generator 7, the digital filter 20, and the digital multiplier 21, so that the correction output signal D ｏｕｔ It is possible to provide a magnetic sensor A2 and a magnetic measurement device C2 that can suppress fluctuations in the conversion gain to the magnetic field.

[0110] Furthermore, according to the second embodiment, it is possible to simplify the analog circuit in the current generating unit 5, and therefore it is possible to reduce the area required for mounting the analog circuit compared to the first embodiment. Therefore, according to the second embodiment, it is possible to improve the degree of freedom in mounting the circuit in the current generating unit 5.

[0111] Third Embodiment Next, a third embodiment of the present invention will be described with reference to Fig. 6. In Fig. 6, the same components as those in the first embodiment are denoted by the same reference numerals. The following mainly describes the differences from the first embodiment.

[0112] 6, the magnetic sensor A3 according to the third embodiment includes a magnetic feedback coil 3a in addition to the sensor head 1, drive unit 2, pickup coil 3, signal processing unit 4, current generating unit 5, comparison unit 6, and correction signal generating unit 7 of the magnetic sensor A1 according to the first embodiment. Note that the stabilization unit B3 in the third embodiment is the same as the stabilization unit B1 in the first embodiment.

[0113] In the magnetic sensor A1 according to the first embodiment, the pickup coil 3 is supplied with a feedback current I in addition to a magnetic detection current based on an external magnetic field G. ｆｂ The feedback current I ｆｂ generates a feedback magnetic field in the pickup coil 3, improving the linearity of the detection characteristics of the external magnetic field G. That is, in the magnetic sensor A1, the pickup coil 3 is used both for detecting the external magnetic field G and for generating the feedback magnetic field.

[0114] In contrast, in the magnetic sensor A2 according to the second embodiment, the feedback current I generated by the current generating unit 5ｆｂ Unlike the first embodiment, power is supplied to the pickup coil 3, but to the magnetic feedback coil 3a. In the magnetic sensor A2 according to the second embodiment, the pickup coil 3 is dedicated to detecting the external magnetic field G, and a feedback magnetic field is generated by the magnetic feedback coil 3a provided separately from the pickup coil 3.

[0115] In this magnetic sensor A2, the magnetic feedback coil 3a is provided in close proximity to the pickup coil 3 and the sensor head 1. That is, the magnetic feedback coil 3a is a winding that is magnetically coupled with the pickup coil 3.

[0116] One end of the magnetic feedback coil 3a is connected to the output terminal of the current generator 5, and the other end is connected to the first input terminal of the current generator 5. The feedback current I supplied from the current generator 5 ｆｂ A feedback magnetic field is generated in the surroundings based on the above, and this feedback magnetic field acts on the pickup coil 3.

[0117] According to the third embodiment, the stabilization unit B3 is provided, so that the correction output signal D ｏｕｔ It is possible to provide a magnetic sensor A3 and a magnetic measurement device C3 that can suppress fluctuations in the conversion gain to the magnetic field.

[0118] Furthermore, according to the third embodiment, the number of parts increases because the magnetic feedback coil 3a is provided separately from the pickup coil 3. However, because the pickup coil 3 is dedicated to detecting the external magnetic field G, the degree of freedom in selecting the pickup coil 3 is improved compared to the first embodiment. Furthermore, the problem of parasitic voltage caused by the resistor Rp (parasitic resistance) in FIG. 1 can be avoided.

[0119] Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to Fig. 2 showing the first embodiment. In the magnetic sensor according to the fourth embodiment, the low-voltage side resistive cell 11 of the current generating unit 5 in the first embodiment is omitted, and the other end of the pickup coil 3 (magnetic detecting unit) is grounded.

[0120] That is, the magnetic sensor according to the fourth embodiment has a single-ended circuit configuration in which a D / A converter is provided only on one side of the pickup coil 3 (magnetic detection unit). For example, the magnetic sensor described in Patent Document 1 has a single-ended circuit configuration similar to the magnetic sensor according to the fourth embodiment.

[0121] According to the fourth embodiment, the comparison unit 6, the correction signal generation unit 7, and the stabilization unit include a current generation unit from which the low-voltage side resistance cell 11 has been removed, so that it is possible to suppress fluctuations in the conversion gain in the same way as in the first to third embodiments described above.

[0122] The present invention is not limited to the first to fourth embodiments, and the following modifications are possible: (1) In the above embodiments, the high-voltage side resistor cell 10 and the low-voltage side resistor cell 11 are configured as resistor-type D / A converters as shown in FIG. 2. However, the current generating unit of the present invention is not limited to this. The high-voltage side resistor cell 10 and the low-voltage side resistor cell 11 may be configured as a conversion circuit as shown in FIG. 7, for example.

[0123] The conversion circuit shown in Fig. 7(a) is a current steering type D / A conversion circuit. The conversion circuit shown in Fig. 7(b) is a resistance type D / A converter similar to those in the first to fourth embodiments. On the other hand, the conversion circuits shown in Figs. 7(c) and 7(d) are configured to convert the output signal D ０ is an analog signal, not a digital signal, and the correction signal D ｃｔｒｌ The feedback current I ｆｂ The current value is adjustable.

[0124] The conversion circuit shown in FIG. 7(c) converts the correction signal D ｃｔｒｌ By variably setting the transfer conductance Gm by ｆｂ On the other hand, the conversion circuit shown in FIG. ｃｔｒｌ The resistance value of the resistor is variably set by the resistor value, thereby adjusting the current value of the feedback current Ifb.

[0125] The conversion circuits of FIGS. 7(a) and 7(c) can increase the output impedance, thereby reducing the induced voltage (input voltage V ｉｎ 7B and 7D have the advantage of being able to reduce noise.

[0126] (2) As a modification of the stabilization unit B1 shown in FIG. 2, for example, stabilization units B4 and B5 shown in FIG. 8 and FIG. 9 are conceivable. The stabilization unit B4 in FIG. 8 has N high-voltage side resistance cells 10 as shown in the figure. Ｈ , and N low-voltage side resistor cells 11 Ｌ , high voltage side reference cell 12 Ｈ , low-voltage side reference cell 12 Ｌ , high voltage side differential amplifier 14 Ｈ , low voltage side differential amplifier 14 Ｌ , high voltage side signal circuit 15 Ｈ , low voltage side signal circuit 15 Ｌ , constant current source 16, high voltage side enable switch 17 Ｈ and low voltage side enable switch 17 Ｌ It is equipped with:

[0127] Among these components, N high-voltage side resistor cells 10 Ｈ , N low-voltage side resistor cells 11 Ｌ , high voltage side enable switch 17 Ｈ and low voltage side enable switch 17 Ｌ constitute the current generating unit 5 in FIG. 1. N high-voltage side resistor cells 10 Ｈ corresponds to the high-voltage side current generator in the present invention, and N low-voltage side resistance cells 11 Ｌ corresponds to the low-voltage side current generator in the present invention.

[0128] Also, the high-voltage side reference cell 12 Ｈ , low-voltage side reference cell 12 Ｌ , high voltage side differential amplifier 14 Ｈ , low voltage side differential amplifier 14 Ｌ and constant current source 16 constitute the comparison unit 6 in FIG. Ｈ and low-voltage side signal circuit 15Ｌ constitutes the correction signal generating unit 7 in FIG.

[0129] High-voltage side resistor cell 10 Ｈ and low-voltage side resistor cell 11 Ｌ is the output signal D of the signal processing unit 4 ０ N high-voltage side resistor cells 10 are provided corresponding to the bit string of the digital signal. Ｈ is the output signal D ０ The zeroth-order high-voltage side resistor cell corresponding to the zeroth-order bit of the output signal D ０ The first high-voltage side resistor cell corresponding to the first bit of the output signal D ０ The N-1th high-voltage side resistor cell corresponds to the N-1th bit of the N-1th high-voltage side resistor cell.

[0130] N high-voltage side resistor cells 10 Ｈ All of the N high-voltage side resistor cells 10H have the same circuit configuration. As shown in the figure, each of the N high-voltage side resistor cells 10H includes a high-voltage side switch 10e, a low-voltage side switch 10f, a high-voltage side transistor 10g, a low-voltage side transistor 10h, and a resistor 10i.

[0131] The high-voltage side switch 10e is a two-contact open / close switch, with a first contact connected to a DC power supply, a second contact connected to the source terminal of the high-voltage side transistor 10g, and a control terminal connected to the control terminal of the low-voltage side switch 10f and the low-voltage side resistor cell 11. Ｌ the control terminal of the high-voltage side switch 11e and the control terminal of the low-voltage side switch 11f, and the high-voltage side signal circuit 15 Ｈ The first input terminal and the low-voltage side signal circuit 15 Ｌ is connected to the first input terminal of the

[0132] The control terminal of high-voltage side switch 10e is connected to the output terminal of signal processing unit 4 and the second input terminal of current generating unit 5 outside stabilization unit B4. High-voltage side switch 10e receives output signal D ０ (digital signal) is input, and the output signal D ０ The open / closed state is controlled by a digital signal.

[0133] That is, the high-voltage side switch 10e of the first high-voltage side resistor cell is connected to the output signal D ０ The high-voltage side switch 10e of the first high-voltage side resistor cell is controlled by the 0th bit of the output signal D ０ The open / close state is controlled by the first bit of (digital signal), (omitted), and the high-voltage side switch 10e of the (N-1)th high-voltage side resistor cell is controlled by the output signal D ０ The open / closed state is controlled by the (N-1)th bit of the (digital signal).

[0134] The low-voltage-side switch 10f is a two-contact open / close switch similar to the high-voltage-side switch 10e. The first contact of the low-voltage-side switch 10f is connected to the source terminal of the low-voltage-side transistor 10h, the second contact is grounded, and the control terminal is connected to the control terminal of the high-voltage-side switch 10e and the low-voltage-side resistor cell 11. Ｌ the control terminal of the high-voltage side switch 11e and the control terminal of the low-voltage side switch 11f, and the high-voltage side signal circuit 15 Ｈ The first input terminal and the low-voltage side signal circuit 15 Ｌ is connected to the first input terminal of the

[0135] The control terminal of the low-voltage side switch 10f is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B4. ０ (digital signal) is input, and the output signal D ０ The open / closed state is controlled in the opposite manner to that of high-voltage side switch 10e by the inverted sign of (digital signal).

[0136] That is, the low-voltage side switch 10f of the first high-voltage side resistor cell is connected to the output signal D ０ The open / close state is controlled by the inverted sign of the 0th bit in the (digital signal), and the low-voltage side switch 10f of the first high-voltage side resistor cell outputs the output signal D ０ The open / close state is controlled by the inverted sign of the most significant bit in the (digital signal), (omitted), and the low-voltage side switch 10f of the (N-1)th high-voltage side resistor cell outputs the output signal D ０The open / close state is controlled by the inverted sign of the (N-1)th bit in the (digital signal).

[0137] The high-voltage side transistor 10g is a P-type MOS transistor as shown in the figure. The gate terminal of this high-voltage side transistor 10g is connected to the low-voltage side resistor cell 11. Ｌ the gate terminal of the high-voltage side transistor 11g in the high-voltage side signal circuit 15 Ｈ output terminal and high voltage side reference cell 12 Ｈ The gate terminal of the high-voltage side transistor 12b in the

[0138] The source terminal of high-voltage side transistor 10g is connected to the second contact of high-voltage side switch 10e, and the drain terminal is connected to the drain terminal of low-voltage side transistor 10h and one end of resistor 10i. Ｈ The high voltage side correction signal DH is input to the gate terminal from ｃｔｒｌ The resistance between the drain and source terminals is controlled by

[0139] The low-voltage side transistor 10h is an N-type MOS transistor as shown in the figure. The gate terminal of the low-voltage side transistor 10h is connected to the low-voltage side resistor cell 11. Ｌ the gate terminal of the low-voltage side transistor 11h in the low-voltage side signal circuit 15 Ｌ output terminal and low voltage side reference cell 12 Ｌ The gate terminal of the low-voltage side transistor 12d is connected to the gate terminal of the low-voltage side transistor 12d.

[0140] The source terminal of the low-voltage side transistor 10h is connected to the drain terminal of the high-voltage side transistor 10g and one end of the resistor 10i, and the drain terminal is connected to the first contact of the low-voltage side switch 10f. Ｌ The low-voltage side correction signal DL is input to the gate terminal from ｃｔｒｌ The resistance between the drain and source terminals is controlled by

[0141] The resistor 10i is a resistive element having a predetermined resistance value. One end of the resistor 10i is connected to the drain terminal of the high-voltage side transistor 10g and the drain terminal of the low-voltage side transistor 10h, and the other end is connected to the high-voltage side enable switch 17. Ｈ The N high-voltage side resistor cells 10 are connected to the first contacts of the N high-voltage side resistor cells 10. Ｈ The other ends of the resistors 10i in are all connected together as shown in the figure.

[0142] Such a resistor 10i is connected to the output signal D ０ Depending on the open / closed states of high-voltage side switch 10e and low-voltage side switch 10f, which are turned ON (closed) / OFF (open) by a digital signal, one end is connected to a DC power supply via high-voltage side transistor 10g or to ground potential (GND) via low-voltage side transistor 10h.

[0143] On the other hand, N low-voltage side resistor cells 11 Ｌ All of the N low-voltage side resistor cells 11 have the same circuit configuration. Ｌ As shown in the figure, the inverter 11 includes a high-voltage side switch 11e, a low-voltage side switch 11f, a high-voltage side transistor 11g, a low-voltage side transistor 11h, and a resistor 11i.

[0144] The high-voltage side switch 11e is a two-contact open / close switch, with a first contact connected to a DC power supply, a second contact connected to the source terminal of the high-voltage side transistor 11g, and a control terminal connected to the control terminal of the low-voltage side switch 11f and the high-voltage side resistor cell 10 Ｈ the control terminal of the high-voltage side switch 10e and the control terminal of the low-voltage side switch 10f, and the high-voltage side signal circuit 15 Ｈ The first input terminal and the low-voltage side signal circuit 15 Ｌ is connected to the first input terminal of the

[0145] The control terminal of the high-voltage side switch 11e is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B4. ０ (digital signal) is input, and the output signal D ０The open / closed state is controlled by a digital signal.

[0146] That is, the high-voltage side switch 11e of the first low-voltage side resistor cell is connected to the output signal D ０ The high-voltage side switch 11e of the first low-voltage side resistor cell is controlled by the 0th bit of the output signal D ０ The open / close state is controlled by the first bit of (digital signal), (omitted), and the high-voltage side switch 11e of the (N-1)th low-voltage side resistor cell is controlled by the output signal D ０ The open / closed state is controlled by the (N-1)th bit of the (digital signal).

[0147] The low-voltage side switch 11f is a two-contact open / close switch similar to the high-voltage side switch 11e. The first contact of the low-voltage side switch 11f is connected to the source terminal of the low-voltage side transistor 11h, the second contact is grounded, and the control terminal is connected to the control terminal of the high-voltage side switch 11e and the high-voltage side resistor cell 10. Ｈ the control terminal of the high-voltage side switch 10e and the control terminal of the low-voltage side switch 10f, and the high-voltage side signal circuit 15 Ｈ The first input terminal and the low-voltage side signal circuit 15 Ｌ is connected to the first input terminal of the

[0148] The control terminal of the low-voltage side switch 11f is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B4. ０ (digital signal) is input, and the output signal D ０ The open / closed state is controlled inversely to that of the high-voltage side switch 11e by the inverted sign of the (digital signal).

[0149] That is, the low-voltage side switch 11f of the first low-voltage side resistor cell is connected to the output signal D ０ The open / close state is controlled by the inverted code of the 0th bit in the (digital signal), and the low-voltage side switch 11f of the 1st low-voltage side resistor cell outputs the output signal D ０The open / close state is controlled by the inverted sign of the most significant bit in the (digital signal), (omitted), and the low-voltage side switch 11f of the (N-1)th low-voltage side resistor cell outputs the output signal D ０ The open / close state is controlled by the inverted sign of the (N-1)th bit in the (digital signal).

[0150] The high-voltage side transistor 11g is a P-type MOS transistor as shown in the figure. The gate terminal of this high-voltage side transistor 11g is connected to the high-voltage side resistor cell 11. Ｈ the gate terminal of the high-voltage side transistor 10g in the low-voltage side signal circuit 15 Ｌ output terminal and low voltage side reference cell 12 Ｌ The gate terminal of the low-voltage side transistor 12d in the

[0151] The source terminal of the high-voltage side transistor 11g is connected to the second contact of the high-voltage side switch 11e, and the drain terminal is connected to the drain terminal of the low-voltage side transistor 11h and one end of the resistor 11i. Ｌ The low-voltage side correction signal DL is input to the gate terminal from ｃｔｒｌ The resistance between the drain and source terminals is controlled by

[0152] The low-voltage side transistor 11h is an N-type MOS transistor as shown in the figure. The gate terminal of this low-voltage side transistor 11h is connected to the high-voltage side resistor cell 11. Ｈ the gate terminal of the low-voltage side transistor 10h in the low-voltage side signal circuit 15 Ｌ output terminal and low voltage side reference cell 12 Ｌ The gate terminal of the low-voltage side transistor 12d in the

[0153] The source terminal of the low-voltage side transistor 11h is connected to the drain terminal of the high-voltage side transistor 11g and one end of the resistor 11i, and the drain terminal is connected to the first contact of the low-voltage side switch 11f. Ｌ The low-voltage side correction signal DL is input to the gate terminal from ｃｔｒｌThe resistance between the drain and source terminals is controlled by

[0154] The resistor 11i is a resistive element having a predetermined resistance value. One end of the resistor 11i is connected to the drain terminal of the high-voltage side transistor 11g and the drain terminal of the low-voltage side transistor 11h, and the other end is connected to the low-voltage side enable switch 17. Ｌ The N low-voltage side resistor cells 11 are connected to the first contacts of the N low-voltage side resistor cells 11. Ｌ The other ends of the resistors 11i in are all connected in common as shown in the figure.

[0155] Such a resistor 11i is connected to the output signal D ０ Depending on the open / closed states of the high-voltage side switch 11e and the low-voltage side switch 11f, which are turned ON (closed) / OFF (open) by a digital signal, one end is connected to a DC power supply via the high-voltage side transistor 11g or to ground potential (GND) via the low-voltage side transistor 11h.

[0156] High-voltage side reference cell 12 Ｈ The high-voltage side transistor 12b includes a high-voltage side transistor 12b and a resistor 12c. The high-voltage side transistor 12b is a P-type MOS transistor as shown in the figure. The gate terminal of the high-voltage side transistor 12b is connected to the high-voltage side resistor cell 10. Ｈ the gate terminal of the high-voltage side transistor 10g in the low-voltage side resistor cell 11 Ｌ the gate terminal of the high-voltage side transistor 11g and the high-voltage side signal circuit 15 Ｈ is connected to the output terminal of

[0157] The source terminal of the high-voltage side transistor 12b is connected to a DC power supply, and the drain terminal is connected to one end of a resistor 12c, which is a two-terminal element having a predetermined resistance value. One end of the resistor 12c is connected to the drain terminal of the high-voltage side transistor 12b, and the other end is connected to the high-voltage side differential amplifier 14. Ｈ and the input terminal of the constant current source 16.

[0158] Such a high-voltage side reference cell 12 ＨIn the high-voltage side transistor 12b, the high-voltage side signal circuit 15 Ｈ The high voltage side correction signal DH is input to the gate terminal from ｃｔｒｌ The resistance value between the drain and source terminals changes based on the voltage V. When the high-voltage side transistor 12b is turned on (conductive), one end of the resistor 12c is connected to the DC power supply.

[0159] Low-voltage side reference cell 12 Ｌ The low-voltage side transistor 12d includes a low-voltage side transistor 12d and a resistor 12e. As shown in the figure, the low-voltage side transistor 12d is an N-type MOS transistor. The gate terminal of the low-voltage side transistor 12d is connected to the high-voltage side resistor cell 10. Ｈ the gate terminal of the low-voltage side transistor 10h in the low-voltage side resistor cell 11 Ｌ the gate terminal of the low-voltage side transistor 11h and the low-voltage side signal circuit 15 Ｌ is connected to the output terminal of

[0160] The drain terminal of the low-voltage side transistor 12d is connected to one end of a resistor 12e, and the source terminal is grounded. The resistor 12e is a two-terminal element having a predetermined resistance value. One end of the resistor 12e is connected to the drain terminal of the low-voltage side transistor 12d, and the other end is connected to the low-voltage side differential amplifier 14. Ｌ and the output terminal of the constant current source 16.

[0161] Such a low-voltage side reference cell 12 Ｌ In the low-voltage side transistor 12d, the low-voltage side signal circuit 15 Ｌ The low-voltage side correction signal DL is input to the gate terminal from ｃｔｒｌ The resistance value between the drain and source terminals changes based on the voltage V. One end of the resistor 12e is grounded when the low-voltage side transistor 12d is turned on (conductive).

[0162] That is, in the stabilization unit B4 according to this modification, the high-voltage side reference cell 12 Ｈ The high-voltage side transistor 12b and the low-voltage side reference cell 12 ＬBy biasing both of the low-voltage side transistors 12b and 12d, a current path is created from the DC power supply to the high-voltage side transistor 12b, resistor 12c, constant current source 16, resistor 12e, low-voltage side transistor 12d, and ground potential (GND).

[0163] High-voltage side differential amplifier 14 Ｈ is a three-terminal element having a first input terminal (negative phase input terminal), a second input terminal (positive phase input terminal), and an output terminal. Ｈ is the high-voltage reference voltage VH applied to the first input terminal (negative phase input terminal). ｒ and the high-voltage feedback voltage V applied to the second input terminal (positive phase input terminal). Ｐ The error signal obtained by amplifying the difference between ｃｏｍｐ High voltage side signal circuit 15 Ｈ Output to.

[0164] Low voltage side differential amplifier 14 Ｌ is the high-voltage side differential amplifier 14 Ｈ Similarly to the above, the low-voltage side differential amplifier 14 is a three-terminal element having a first input terminal (negative phase input terminal), a second input terminal (positive phase input terminal), and an output terminal. Ｌ is the low-voltage reference voltage VL applied to the first input terminal (negative-phase input terminal). ｒ and the low-voltage side feedback voltage V applied to the second input terminal (positive phase input terminal) Ｎ The error signal obtained by amplifying the difference between ｃｏｍｐ Low voltage side signal circuit 15 Ｌ Output to.

[0165] High-voltage side signal circuit 15 Ｈ is an analog circuit with two inputs and one output. Ｈ The first input terminal is a high-voltage side resistor cell 10 Ｈ The control terminal of the high-voltage side switch 10e and the control terminal of the low-voltage side switch 10f, and the low-voltage side resistor cell 11 Ｌ The control terminal of the high-voltage side switch 11e and the control terminal of the low-voltage side switch 11f and the low-voltage side logic circuit 15 Ｌ is connected to the first input terminal of the

[0166] In addition, the high-voltage side signal circuit 15 Ｈ The first input terminal of the high-voltage side signal circuit 15 is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B4. Ｈ The second input terminal is connected to the high-voltage side differential amplifier 14 Ｈ is connected to the output terminal of

[0167] Furthermore, this high-voltage side signal circuit 15 Ｈ The output terminal is a high-voltage side resistor cell 10 Ｈ the gate terminal of the high-voltage side transistor 10g in the low-voltage side resistor cell 11 Ｌ The gate terminal of the high-voltage side transistor 11g and the high-voltage side reference cell 12 Ｈ The gate terminal of the high-voltage side transistor 12b in the

[0168] This high-voltage side signal circuit 15 Ｈ is the output signal D input from the signal processing unit 4 to the first input terminal. ０ (digital signal) and high-voltage side differential amplifier 14 Ｈ The high-voltage comparison signal VH is input to the second input terminal. ｃｏｍｐ By performing logical processing on the high voltage side correction signal DH ｃｔｒｌ This high voltage side correction signal DH ｃｔｒｌ is the feedback current I ｆｂ is an analog signal indicating the amount of correction.

[0169] This high voltage side correction signal DH ｃｔｒｌ is a control signal for controlling the high-voltage side transistor 10g, the high-voltage side transistor 11g, and the high-voltage side transistor 12b. Ｈ , low-voltage side resistor cell 11 Ｌ and high-voltage side reference cell 12 Ｈ will be output.

[0170] Low-voltage side signal circuit 15 Ｌ is the high-voltage side signal circuit 15 Ｈ This low-voltage side signal circuit 15 is an analog circuit with two inputs and one output. Ｌ The first input terminal is a high-voltage side resistor cell 10 ＨThe control terminal of the high-voltage side switch 10e and the control terminal of the low-voltage side switch 10f, and the low-voltage side resistor cell 11 Ｌ The control terminal of the high-voltage side switch 11e and the control terminal of the low-voltage side switch 11f and the high-voltage side logic circuit 15 Ｈ is connected to the first input terminal of the

[0171] In addition, the low-voltage side signal circuit 15 Ｌ The first input terminal of the low-voltage side signal circuit 15 is connected to the output terminal of the signal processing unit 4 and the second input terminal of the current generating unit 5 outside the stabilizing unit B4. Ｌ The second input terminal is the low-voltage side differential amplifier 14 Ｌ is connected to the output terminal of

[0172] Furthermore, this low-voltage side signal circuit 15 Ｌ The output terminal is a high-voltage side resistor cell 10 Ｈ the gate terminal of the low-voltage side transistor 10h in the low-voltage side resistor cell 11 Ｌ the gate terminal of the low-voltage side transistor 11h and the low-voltage side reference cell 12 Ｌ The gate terminal of the low-voltage side transistor 12d in the

[0173] This low-voltage side signal circuit 15 Ｌ is the output signal D input from the signal processing unit 4 to the first input terminal. ０ (digital signal) and low-voltage side differential amplifier 14 Ｌ The low-voltage side comparison signal VL is input to the second input terminal from ｃｏｍｐ By performing predetermined logical processing on the low voltage side correction signal DL ｃｔｒｌ This low-voltage side correction signal DL ｃｔｒｌ is the high voltage side correction signal DH ｃｔｒｌ Similarly, the feedback current I ｆｂ is an analog signal indicating the amount of correction.

[0174] This low-voltage side correction signal DL ｃｔｒｌ is a control signal for controlling the low-voltage side transistor 10h, the low-voltage side transistor 11h, and the low-voltage side transistor 12d. Ｈ , low-voltage side resistor cell 11 Ｌand low-voltage side reference cell 12 Ｌ will be output.

[0175] The constant current source 16 is a two-terminal element having an input terminal and an output terminal. The input terminal of the constant current source 16 is connected to the high-voltage side reference cell 12. Ｈ The other end of the resistor 12c and the high-voltage side differential amplifier 14 Ｈ The output terminal is connected to the first input terminal (negative phase input terminal) of the low-voltage side reference cell 12 Ｌ The other end of the resistor 12e and the low-voltage side differential amplifier 14 Ｌ The first input terminal (negative phase input terminal) of the amplifier is connected to the first input terminal (negative phase input terminal) of the amplifier.

[0176] The input terminal of the constant current source 16 is connected to a DC power supply via a resistor 12c, and the output terminal is connected to a ground potential (GND) via a resistor 12e, so that a constant reference current I flows from the input terminal to the output terminal. ＲＥＦ That is, the constant current source 16 supplies the high-voltage side reference cell 12 connected in series thereto with Ｈ Resistor 12c and low-voltage side reference cell 12 Ｌ A reference current I common to the resistors 12e ＲＥＦ Apply electricity to the

[0177] As shown in the figure, the input terminal of the constant current source 16 is connected to the high-voltage reference voltage VH ｒ The output terminal of the constant current source 16 is connected to the low-voltage reference voltage VL ｒ The high-voltage reference voltage VH ｒ is the power supply voltage V ｃｃ is the resistance value R of the resistor 12c Ｈ and the resistance value of the high-voltage side transistor 12b, and the reference current I ＲＥＦ The voltage is dropped by the voltage obtained by multiplying the low-voltage side reference voltage VL ｒ is the resistance R of the resistor 12e when the ground potential (=0) is Ｌ and the sum of the resistance value of the voltage-side transistor 12d and the reference current I ＲＥＦ The voltage is increased by the voltage multiplied by .

[0178] High voltage side enable switch 17 Ｈ is a two-contact open / close switch. ＨThe first contacts are connected to N high-voltage side resistor cells 10. Ｈ The second contact is connected to the high-voltage side differential amplifier 14 Ｈ and one end of the pickup coil 3.

[0179] In addition, this high voltage side enable switch 17 Ｈ The control terminal of the high-voltage side enable switch 17 is connected to an external control device (not shown). Ｈ The open / close state of the switch is controlled by an enable signal EN input to the control terminal. As explained in the first embodiment, this enable signal EN is ｆｂ This is a control signal that turns on (power supply) / off (power non-supply) the power supply to the pickup coil 3.

[0180] Low voltage side enable switch 17 Ｌ is the high voltage side enable switch 17 Ｈ This low-voltage side enable switch 17 is a two-contact open / close switch similar to the one shown in FIG. Ｌ The first contacts are connected to N low-voltage side resistor cells 11. Ｌ The second contact is connected to the low-voltage side differential amplifier 14 Ｌ and the other end of the pickup coil 3.

[0181] In addition, this low voltage side enable switch 17 Ｌ is the high voltage side enable switch 17 Ｈ The low-voltage side enable switch 17 is connected to an external control device in the same manner as the low-voltage side enable switch 17. Ｌ The open / close state of the switch is controlled by an enable signal EN input to the control terminal. This enable signal EN is a magnetic feedback current I ｆｂ This is a control signal that turns on (power supply) / off (power non-supply) the power supply to the pickup coil 3.

[0182] In such a stabilization section B4, the high-voltage side resistor cell 10 Ｈ and low-voltage side resistor cell 11 Ｌare configured as resistance-type D / A converters similar to the high-voltage side resistor cell 10 and the low-voltage side resistor cell 11 in the stabilization unit B1 of the first embodiment.

[0183] In addition, in the stabilization section B4, the high voltage side comparison signal VH ｃｏｍｐ is the high voltage reference voltage VH ｒ and the high voltage feedback voltage V Ｐ and the low-voltage side comparison signal VL ｃｏｍｐ is the low voltage reference voltage VL ｒ and the low voltage feedback voltage V Ｎ This is the result of a comparison with

[0184] And the high voltage side comparison signal VH ｃｏｍｐ and the output signal D of the signal processing unit 4 ０ (digital signal) and the high-voltage side correction signal DH generated based on ｃｔｒｌ is the high voltage side feedback voltage V Ｐ and the high voltage reference voltage VH ｒ and the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ The high-voltage side resistance cell 10 Ｈ and low-voltage side resistor cell 11 Ｌ is feedback controlled.

[0185] In addition, the low voltage side comparison signal VL ｃｏｍｐ and the output signal D of the signal processing unit 4 ０ (digital signal) and the low-voltage side correction signal DL generated based on ｃｔｒｌ is the low voltage side feedback voltage V Ｎ and the low voltage reference voltage VL ｒ and the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ The high-voltage side resistance cell 10 Ｈ and low-voltage side resistor cell 11 Ｌ is feedback controlled.

[0186] According to such a stabilization unit B4, the number of required circuit elements (area) increases compared to the stabilization unit B1 in the first embodiment, but the output signal D ｏIt is possible to stabilize the conversion gain to with higher precision.

[0187] (3) The stabilization unit B5 in FIG. 9 stabilizes the output signal D of the signal processing unit 4. ０ This corresponds to the case where the output signal D in the stabilization section B5 is an analog signal, not a digital signal. ０ is a positive-phase analog signal, the positive-phase output signal D ０ (+) and the inverse phase analog signal D ０ (-) and is included.

[0188] As shown in FIG. 9 , the stabilization unit B5 includes an operational amplifier 30, a reference resistance transistor 31, a resistor 32, a constant current source 33, a high-voltage side resistance transistor 34, a low-voltage side resistance transistor 35, a high-voltage side resistor 36, a high-voltage side enable switch 37, a low-voltage side resistor 38, and a low-voltage side enable switch 39.

[0189] The operational amplifier 30 is a three-terminal element having a first input terminal (positive phase input terminal), a second input terminal (negative phase input terminal), and an output terminal. The first input terminal (positive phase input terminal) of this operational amplifier 30 is connected to a second reference voltage source (not shown), and the second input terminal (negative phase input terminal) is connected to one end of a resistor 32 and an input terminal of a constant current source 33. The second reference voltage source supplies a second reference voltage V ＲＥＦ２ is output to the first input terminal (positive phase input terminal) of the operational amplifier 30.

[0190] The output terminal of this operational amplifier 30 is connected to the gate terminal of the amplifying transistor 31, the gate terminal of the high-voltage side transistor 34, and the gate terminal of the low-voltage side transistor 35. Such an operational amplifier 30 amplifies the difference (error) between a first voltage applied to the first input terminal (positive phase input terminal) and a second voltage applied to the second input terminal (negative phase input terminal), and outputs an error voltage V Ｇ Output as

[0191] As shown in the figure, the amplifier transistor 31 is an N-type MOS transistor, and its gate terminal is connected to the output terminal of the operational amplifier 30, the gate terminal of the high-voltage side transistor 34, and the gate terminal of the low-voltage side transistor 35.

[0192] The drain terminal of the amplifier transistor 31 is connected to a first reference voltage source (not shown), and the source terminal is connected to the other end of the resistor 32. The first reference voltage source supplies a first reference voltage V ＲＥＦ１ is output to the drain terminal of the amplifier transistor 31. The amplifier transistor 31 amplifies the current of the output of the operational amplifier 30.

[0193] Resistor 32 is a two-terminal element having a predetermined resistance value. One end of resistor 32 is connected to the second input terminal (negative-phase input terminal) of operational amplifier 30 and the input terminal of constant current source 33, and the other end is connected to the source terminal of amplifying transistor 31. Resistor 32 is a circuit element for dropping voltage, and its resistance value is set to the same value as the resistance value of high-voltage side resistor 36 and the resistance value of low-voltage side resistor 38.

[0194] The constant current source 33 is a two-terminal element having an input terminal and an output terminal. The input terminal of this constant current source 33 is connected to the second input terminal (negative phase input terminal) of the operational amplifier 30 and one terminal of the resistor 32, and the output terminal is grounded. The input terminal of this constant current source 33 is connected to the first reference voltage source via the amplifying transistor 31 and the resistor 32, and a constant reference current I ＲＥＦ Flush.

[0195] High-voltage side transistor 34 is an N-type MOS transistor biased in the linear region, similar to amplifying transistor 31. The gate terminal of high-voltage side transistor 34 is connected to the output terminal of operational amplifier 30, the gate terminal of amplifying transistor 31, and the gate terminal of low-voltage side transistor 35. The drain terminal of high-voltage side transistor 34 is connected to the positive phase output terminal of signal processing unit 4, and the source terminal is connected to one end of high-voltage side resistor 36.

[0196] Such a high-voltage side transistor 34 receives a positive-phase output signal D ０ (+), the resistance value of the high-voltage side resistor 36 whose one end is connected to the source terminal, and the error voltage V applied to the gate terminal Ｇ based on the source current (magnetic feedback current I ｆｂ) is set.

[0197] Low-voltage side transistor 35 is an N-type MOS transistor similar to high-voltage side transistor 34. The gate terminal of low-voltage side transistor 35 is connected to the output terminal of operational amplifier 30, the gate terminal of amplifying transistor 31, and the gate terminal of high-voltage side transistor 34. The drain terminal of low-voltage side transistor 35 is connected to the negative phase output terminal of signal processing section 4, and the source terminal is connected to one end of low-voltage side resistor 38.

[0198] Such a low-voltage side transistor 35 receives an inverted output signal D ０ (-), the resistance value of the low-voltage side resistor 38 whose one end is connected to the source terminal, and the error voltage V applied to the gate terminal Ｇ based on the source current (magnetic feedback current I ｆｂ ) is set.

[0199] High-voltage side resistor 36 is a two-terminal element having a predetermined resistance value. One end of high-voltage side resistor 36 is connected to the source terminal of high-voltage side transistor 34, and the other end is connected to the first contact of high-voltage side enable switch 37. High-voltage side resistor 36 flows magnetic feedback current I as well as the source current of high-voltage side transistor 34, as described above. ｆｂ This sets the following.

[0200] High-voltage side enable switch 37 is a two-contact open / close switch as shown in the figure. High-voltage side enable switch 37 has a first contact connected to the other end of high-voltage side resistor 36 and a second contact connected to one end of pickup coil 3.

[0201] The control terminal of the high-voltage side enable switch 37 is connected to an external control device (not shown). The open / close state of the high-voltage side enable switch 37 is controlled by an enable signal EN input to the control terminal from the external control device. As described in the first embodiment, the enable signal EN is a signal that controls the magnetic feedback current I ｆｂThis is a control signal that turns on (power supply) / off (power non-supply) the power supply to the pickup coil 3.

[0202] Low-voltage side resistor 38 is a two-terminal element having a predetermined resistance value. One end of low-voltage side resistor 38 is connected to the source terminal of low-voltage side transistor 35, and the other end is connected to the first contact of low-voltage side enable switch 39. Low-voltage side resistor 38 flows magnetic feedback current I as well as the source current of low-voltage side transistor 35, as described above. ｆｂ The resistance value is set to the same value as the resistance value of resistor 32 and the resistance value of high-voltage side resistor 36.

[0203] Low-voltage side enable switch 39 is a two-contact open / close switch similar to high-voltage side enable switch 37. This low-voltage side enable switch 39 has a first contact connected to the other end of low-voltage side resistor 38 and a second contact connected to the other end of pickup coil 3.

[0204] The control terminal of the low-voltage side enable switch 39 is connected to an external control device (not shown). Like the high-voltage side enable switch 37, the open / closed state of the low-voltage side enable switch 39 is controlled by an enable signal EN input to the control terminal from the external control device.

[0205] In this stabilization section B5, the resistance value of resistor 32, the resistance value of high-voltage side resistor 36, and the resistance value of low-voltage side resistor 38 are set to the same value, so that an appropriate error voltage V Ｇ By controlling the resistance values ​​of the amplifying transistor 31, the high-voltage side transistor 34, and the low-voltage side transistor 35 through the output voltage of the operational amplifier 30, the magnetic feedback current I ｆｂ is the reference current I of the constant current source 33 ＲＥＦ That is, the error voltage V of the operational amplifier 30 is controlled to match Ｇ is the magnetic feedback current I ｆｂ is the reference current I ＲＥＦ The gate voltages of the high-voltage side transistor 34 and the low-voltage side transistor 35 are feedback-controlled so that they coincide with each other.

[0206] According to such a stabilization unit B5, the output signal D ０ is the positive phase output signal D ０ (+) and inverse phase output signal D ０ Even in the case of a balanced analog signal consisting of (-) and (-), a relatively simple circuit configuration can be used to output a signal D from an external magnetic G. ｏ It is possible to stabilize the conversion gain to

[0207] (4) Fig. 10 shows a modification of the current generating section 5. The current generating section B6 according to this modification generates the output signal D ０ This corresponds to the case where the bit length of the digital signal is 1 bit. As shown in FIG. 10, the current generating section B6 is a high-voltage side shift register 40 Ｈ , a plurality of high-voltage side switches 41 Ｈ , a plurality of high-voltage side variable resistors 42 Ｈ , low-voltage side shift register 40 Ｌ , a plurality of low-side switches 41 Ｌ and a plurality of low-voltage side variable resistors 42 Ｌ It is equipped with:

[0208] High-voltage side shift register 40 Ｈ is a digital circuit in which a plurality of D flip-flop circuits are cascade-connected, and outputs a signal D ０ is used as an input signal. Ｈ is an output signal D based on a separately input clock signal (not shown). ０ is passed from the preceding D flip-flop circuit to the succeeding D flip-flop circuit.

[0209] FIG. 10 shows an example of a five-stage shift register in which five D flip-flop circuits are cascade-connected. Ｈ is a 1-bit output signal D ０ The high-voltage side shift register 40 has a function of converting the voltage Vcc into a 5-bit binary code. Ｈ The number of stages is not limited to five.

[0210] Multiple high-voltage side switches 41Ｈ is a two-contact open / close switch having a first contact and a second contact. Ｈ is the high-voltage side shift register 40 Ｈ The first contacts of the respective D flip-flop circuits are connected to the output terminals of the corresponding D flip-flop circuits.

[0211] In addition, a plurality of high-voltage side switches 41 Ｈ The second contacts of the plurality of high-voltage side variable resistors 42 are provided corresponding to the plurality of D flip-flop circuits. Ｈ Further, the high-voltage side switches 41 are connected to one end of the Ｈ Each control terminal has a plurality of low-voltage side switches 41 Ｌ and an enable signal EN is applied to them in common.

[0212] That is, an arbitrary D flip-flop circuit and a high-voltage side variable resistor 42 corresponding to the D flip-flop circuit Ｈ There is one high-voltage side switch 41 between Ｈ Each D flip-flop circuit and the high-voltage side variable resistor 42 Ｈ The connection relationship between them is controlled by an enable signal EN.

[0213] Multiple high-voltage side variable resistors 42 Ｈ are two-terminal resistance elements having a predetermined resistance variable range. Ｈ is the high-voltage side shift register 40 Ｈ A plurality of D flip-flop circuits and a plurality of high-voltage side switches 41 in Ｈ , and one end of each is provided corresponding to the high-voltage side switch 41 Ｈ is connected to the second contact of the

[0214] In addition, a plurality of high-voltage side variable resistors 42 Ｈ The other ends of the resistors 42 are all connected together and to one end of the pickup coil 3. Ｈ Each control terminal is a plurality of low-voltage side variable resistors 42 Ｌand the output terminal of the correction signal generating unit 7. Ｈ is the correction signal D inputted in common to each control terminal from the correction signal generating unit 7. ｃｔｒｌ The resistance value is variably set based on the above.

[0215] Low-voltage side shift register 40 Ｌ is the high-voltage side shift register 40 Ｈ This low-voltage side shift register 40 is a digital circuit in which D flip-flop circuits having the same number of stages as the low-voltage side shift register 40 are cascaded. Ｌ is the high-voltage side shift register 40 Ｈ Similarly, the output signal D ０ is the input signal. Ｌ is the high-voltage side shift register 40 Ｈ Similarly, the output signal D ０ is passed from the preceding D flip-flop circuit to the succeeding D flip-flop circuit.

[0216] A plurality of low-side switches 41 Ｌ is a two-contact open / close switch having a first contact and a second contact. Ｌ is the low-voltage side shift register 40 Ｌ The first contacts of the respective D flip-flop circuits are connected to the output terminals of the corresponding D flip-flop circuits.

[0217] In addition, a plurality of low-voltage side switches 41 Ｌ The second contacts of each of the low-voltage side shift registers 40 Ｌ A plurality of low-voltage side variable resistors 42 corresponding to the D flip-flop circuits Ｌ Further, the plurality of low-voltage side switches 41 are connected to one end of the Ｌ Each control terminal is a plurality of high-voltage side switches 41 Ｈ and an enable signal EN is applied to them in common.

[0218] That is, the low-voltage side shift register 40 ＬAny D flip-flop circuit in the above and a low-voltage side variable resistor 42 corresponding to the D flip-flop circuit Ｌ There is one low-voltage side switch 41 between Ｌ Each D flip-flop circuit and the low-voltage side variable resistor 42 Ｌ The connection relationship between them is controlled by an enable signal EN.

[0219] A plurality of low-voltage side variable resistors 42 Ｌ are two-terminal resistance elements having a predetermined resistance variable range. Ｌ is the low-voltage side shift register 40 Ｌ A plurality of D flip-flop circuits and a plurality of low-side switches 41 in Ｌ , and one end of each is provided corresponding to the low-voltage side switch 41 Ｌ is connected to the second contact of the

[0220] In addition, a plurality of low-voltage side variable resistors 42 Ｌ The other ends of the low-voltage side variable resistors 42 are all connected together and to the other end of the pickup coil 3. Ｌ Each control terminal is a plurality of high-voltage side variable resistors 42 Ｈ and the output terminal of the correction signal generating unit 7. Ｌ is the correction signal D inputted in common to each control terminal from the correction signal generating unit 7. ｃｔｒｌ The resistance value is variably set based on the above.

[0221] In such a current generating section B6, a plurality of high-voltage side variable resistors 42 Ｈ and a plurality of low-voltage side variable resistors 42 Ｌ The resistance value of the correction signal DL of the correction signal generating unit 7 ｃｔｒｌ Therefore, according to the current generating section B6, the output signal D of the signal processing section 4 ０ Even if the bit length of the output signal D ｏ It is possible to stabilize the conversion gain to

[0222] (5) 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.

[0223] A1 to A3 Magnetic sensors B1 to B5 Stabilization unit B6 Current generation unit C1 Magnetic measurement device G External magnetism 1 Sensor head 2 Driving unit 3 Pickup coil 3a Magnetic feedback coil 4 Signal processing unit 5 Current generation unit 6 Comparison unit 7 Correction signal generation unit 10, 10 Ｈ High voltage side resistance cell (high voltage side current generator) 11, 11 Ｌ Low-voltage side resistance cell (low-voltage side current generator) 12 Reference cell 12 Ｈ High voltage side reference cell 12 Ｌ Low voltage side reference cell 13 Constant current source 14 Comparator 14 Ｈ High voltage side differential amplifier 14 Ｌ Low voltage side differential amplifier 15 Logic circuit 15 Ｈ High voltage side signal circuit 15 Ｌ Low voltage side signal circuit 16 Constant current source 17 Ｈ High voltage side enable switch 17 Ｌ Low-voltage side enable switch 20 Digital filter 21 Digital multiplier 30 Operational amplifier 31 Amplifying transistor 32 Resistor 33 Constant current source 34 High-voltage side transistor 35 Low-voltage side transistor 36 High-voltage side resistor 37 High-voltage side enable switch 38 Low-voltage side resistor 39 Low-voltage side enable switch 40 Ｈ High voltage side shift register 40 Ｌ Low voltage side shift register 41 Ｈ High voltage side switch 41 Ｌ Low voltage side switch 42 Ｈ High voltage side variable resistor 42 Ｌ Low voltage side variable resistor

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 generation unit that generates a feedback current based on the output signal and outputs it to the magnetic detection unit; and a stabilization unit that suppresses fluctuations in the conversion gain from the external magnetic field to the output signal.

2. The magnetic sensor according to claim 1, characterized in that the stabilization unit comprises: a comparison unit that compares the feedback current with a predetermined reference current; and a correction signal generation unit that generates a correction signal that suppresses fluctuations in the conversion gain based on the comparison result of the comparison unit.

3. The magnetic sensor according to claim 2, wherein said stabilizing section controls said current generating section based on said correction signal so that said feedback current becomes equal to said reference current.

4. The magnetic sensor according to claim 2, wherein said stabilizing section performs a correction process on said output signal based on said correction signal so that said feedback current becomes equal to said reference current.

5. A magnetic sensor as described in claim 1 or 2, characterized in that the current generating unit comprises: a high-voltage side current generator connected to the high-voltage side of the magnetic detection unit and generating the feedback current based on the output signal; and a low-voltage side current generator connected to the low-voltage side of the magnetic detection unit and generating the feedback current based on the output signal.

6. The magnetic sensor according to claim 1 or 2, characterized in that the output signal is a digital signal, and the current generating section generates the feedback current by performing digital / analog conversion of the output signal.

7. The magnetic sensor according to claim 3 or 4, wherein the comparison section has a hysteresis characteristic in the comparison between the feedback current and the reference current.

8. The magnetic sensor according to claim 2 or 3, wherein the correction signal generating section has a dead zone spanning a predetermined period.

9. A magnetic sensor as claimed in claim 1 or 2, characterized in that the magnetic detection section comprises: a pickup coil that detects the external magnetic field; and a magnetic feedback coil through which the feedback current is passed.

10. The magnetic sensor according to claim 1 or 2, wherein the magnetic detection portion is a magnetic impedance element.

11. 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.

12. The magnetic measuring device according to claim 11, wherein the external magnetic field is biomagnetic field generated in a living body.

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