JP2019211450A5 - - Google Patents

Description

Current supply device and magnetic field sensor

The present invention relates to a magnetic field sensor that uses an exciting current in which an alternating current is superimposed on a direct current bias current, and more particularly to a magnetic field sensor that makes an offset zero.

  For example, it is known that the fundamental wave type orthogonal flux gate can improve the resolution at a noise density of about 3 pT / √Hz at 10 Hz. However, it is difficult to measure a small magnetic field that changes only slowly with a time of 0.1 Hz or less. Therefore, a method of switching the polarity of the DC bias current at a frequency lower than the excitation frequency and inverting the polarity of the output at the time of the positive bias and the output at the time of the negative bias and averaging them (see Patent Document 1), A method is disclosed in which the polarity of a current in which the AC excitation current and the AC excitation current are integrated is switched, and the output before the switching and the output after the switching are averaged to cancel the offset (see Non-Patent Document 1). .

  In particular, in the technique disclosed in Non-Patent Document 1, a method of incorporating a feedback circuit as shown in FIG. 12 has been proposed. Since the offset characteristics of a sensor head having an amorphous magnetic ribbon or an amorphous magnetic wire as a core are not always equal between positive and negative bias DC currents, the sensor output (= offset) at a magnetic field input of 0 when the positive bias is applied. The offset at the magnetic field input 0 at the time of the negative bias is different. The circuit shown in FIG. 12 solves the problem that excessive magnetic noise is generated from the sensor head in the process in which the sensor always converges from its different operating point to its own stable point immediately after the switching of the bias DC current polarity. is there. The method is to provide two stable points after the switching of the polarity of the bias DC current. For this reason, a method of adding the difference voltage at the convergence point as necessary at the subsequent stage of the processing of the error amplifier is adopted. ing.

JP-A-2003-215220

Naofumi Murata, Hikaru Karo, Ichiro Sasada and Takafumi Shimizu, “Fundamental Mode Orthogonal Fluxgate Magnetometer Applicable for Mesurements of DC and Low-Frequency Magnet Fields”, IEEE SENSORS JORNAL, VOL. 18, No. 7, April 1, 2018

  However, in the technique disclosed in Patent Document 1, it is difficult to set the offset to 0 because the offset at the magnetic field input 0 at the time of the positive bias is different from the offset at the magnetic field input 0 at the time of the negative bias. Therefore, there is a problem that the output fluctuates.

  Also, as shown in FIG. 12, the technology disclosed in Non-Patent Document 1 has a configuration in which a voltage is added at the subsequent stage of the error amplifier to pursue a stabilizing operation. There is a problem that the offset does not become 0 depending on the degree (as shown in FIG. 7, this figure is a description relating to noise, but it is shown that an offset of about −22 nT occurs as a whole). Another problem is that the circuit configuration becomes very complicated as shown in FIG.

The present invention provides a magnetic field sensor capable of supplying an exciting current in which a DC bias current and an AC current are superimposed with a simple circuit and making the offset zero.

The current supply device according to the present invention is configured such that a transistor to which a pulse generated by a pulse generation unit is input, and a transistor and a ground disposed at a subsequent stage of the transistor, and a capacitor and a coil are connected in parallel. An LC resonance circuit, a first terminal for connection to a subsequent stage of the coil in the LC resonance circuit, and a second terminal for connection to the ground, between the first terminal and the second terminal. Is supplied with a current obtained by superimposing an alternating current and a direct current having a value larger than the amplitude of the alternating current to the resistor connected to the resistor.

As described above, in the current supply device according to the present invention, the transistor to which the pulse generated by the pulse generation means is input, and the capacitor and the coil are disposed between the transistor and the ground at the subsequent stage of the transistor. Are connected in parallel, a first terminal for connection to a subsequent stage of the coil in the LC resonance circuit, and a second terminal for connection to the ground. Since a current obtained by superimposing an AC current and a DC current having a value larger than the amplitude of the AC current is supplied to the resistor connected between the second terminals, the DC bias current and the AC current can be reduced with a simple circuit configuration. There is an effect that a superimposed excitation current can be supplied.

FIG. 2 is a circuit block diagram illustrating a configuration of a magnetic field sensor according to the first embodiment. FIG. 3 is a first diagram illustrating offset characteristics of the magnetic field sensor according to the first embodiment. FIG. 2 is a second diagram illustrating offset characteristics of the magnetic field sensor according to the first embodiment. FIG. 7 is an overall circuit block diagram of a magnetic field sensor according to a second embodiment. FIG. 9 is a circuit block diagram of a current supply unit of the magnetic field sensor according to the second embodiment. It is a figure showing an example of the concrete circuit composition of the current supply part of the magnetic field sensor concerning a 2nd embodiment. It is a diagram showing the results of simulation of the magnetizing current when changing the duty ratio of the pulse waveform in the circuit of FIG. FIG. 7 is a diagram showing a result of simulating changes in a bias DC current and an AC exciting current with respect to a duty ratio of a pulse waveform in the circuit of FIG. 6. FIG. 7 is a diagram showing a timing chart when a pulse waveform is generated in the circuit of FIG. 6. FIG. 7 is a diagram illustrating a sine wave when a high level and a low level of a pulse waveform are inverted in the circuit of FIG. 6. FIG. 10 is a diagram illustrating a waveform of an exciting current when the duty ratio of the waveform corresponding to FIG. 9D is 0.33 and the duty ratio of the waveform corresponding to E ′ is 0.67. FIG. 3 is a diagram illustrating a circuit configuration of a conventional technique.

  Hereinafter, embodiments of the present invention will be described. The same elements are denoted by the same reference numerals throughout the embodiment.

(First embodiment of the present invention)
The magnetic field sensor according to the present embodiment will be described with reference to FIGS. In the magnetic field sensor according to the present embodiment, the polarity of the bias DC current is switched in the fundamental wave type orthogonal flux gate, and the bias DC current according to the switching of the polarity is applied to make the offset zero. In the present embodiment, when the polarity of the bias DC current is switched, the offset characteristic becomes as shown in FIG. The characteristics are as shown in FIG. In the case of such a characteristic, it is possible to cancel the offset by multiplying the output of the half cycle by -1 and adding the result.

  FIG. 1 is a circuit block diagram illustrating a configuration of the magnetic field sensor according to the present embodiment. In FIG. 1, a magnetic field sensor 1 includes a current supply unit 41 that supplies an exciting current, a magnetic core 15 that is energized by superimposing an AC exciting current and a bias DC current that constitute the exciting current, and a coil wound around the magnetic core 15. It includes a sensor head 14 composed of a rotating detection coil 13 and a detection circuit 16 having a negative feedback configuration connected to one end of the detection coil 13 which is not on the ground side. The current supply unit 41 includes a bias DC power supply 10 including a DC power supply 10a that supplies a bias DC current for the positive electrode to the magnetic core 15 and a DC power supply 10b that supplies a bias DC current for the negative electrode to the magnetic core 15. Switch 11 that periodically switches which of the DC power supply 10a for power supply and the DC power supply 10b for negative power supply to the energized state is connected in series with the DC power supply 10 via the first switch 11, and is used for excitation. And an AC power supply 12 for supplying the AC exciting current to the magnetic core 15.

Incidentally, the magnetic field sensor 1 according to this embodiment, the amorphous magnetic wire-free magnetostrictive composition as the magnetic core 15, or using amorphous magnetic ribbon of fine long free magnetostrictive compositions, alternating excitation current direct wire or magnetic thin The magnetic field is applied to the magnetic core 15, and the detection signal is detected as an induced voltage of the detection coil 13 wound around the magnetic core 15. This is an orthogonal fluxgate sensor in which the direction or the detection magnetic field that is the longitudinal direction of the ribbon is orthogonal.

  Further, the magnetic field sensor 1 according to the present embodiment has a fundamental wave type orthogonal flux in which the output of the detection coil is obtained by the output of the fundamental wave having the same AC excitation frequency by superimposing a bias DC current larger than the amplitude of the AC excitation current. It is a gate sensor. In other words, a bias DC current having a value larger than the amplitude of the AC exciting current supplied from the AC power supply 12 (in the case of negative polarity, larger than its absolute value) is output from the DC power supply 10 to the magnetic core 15, and It is supplied superimposed on the exciting current. Further, a phase adjusting means for adjusting the phase of the AC current supplied by the AC power supply 12 may be provided at the subsequent stage of the AC power supply 12.

  The detection circuit 16 transmits a voltage induced in the detection coil 13 by application of an external magnetic field to the synchronous rectifier (PSD) 17 without changing the polarity, a circuit 19 that reverses the polarity and transmits the same, and a DC power supply. There is provided a second switch 20 for selecting in synchronization with the first switch 11 for switching the polarity of 10a, 10. A third switch 21 for shutting off the detection circuit 16 at a predetermined timing, a low-pass filter 22 connected downstream of the third switch 21, an error amplifier 23 connected downstream of the low-pass filter 22, A feedback resistor 24 is connected to the subsequent stage of the error amplifier 23 and the other end is connected to one end of the detection coil 13 which is not the ground side. Note that a preamplifier may be inserted after the high-pass filter as necessary. Further, the synchronization pulse to the PSD 17 may be inverted (the phase is shifted by 180 degrees) without using the circuit 19.

  When the polarity of the bias DC current is periodically switched, the domain wall movement of the magnetic core 15 occurs in the switching cycle, so that noise increases compared to the case where the switching is not performed. However, since noise generated due to domain wall movement is concentrated in a certain period immediately after switching, excellent noise characteristics can be obtained except for this portion. That is, the signal is temporarily cut off at the moment when the first switch 11 (switching frequency: fs) is switched using the third switch 21 (switching frequency: 2 fs), for example, immediately after the switching of the first switch 11. The detection circuit 16 is cut off for one-fourth of the switching cycle of the first switch 11 (one-half of the switching cycle of the third switch 21) to cut off the signal, and the next one-fourth cycle ( By returning the remaining １ ／ cycle of the switching cycle of the third switch 21) to the feedback circuit, it is possible to reduce noise due to the polarity switching of the bias DC current.

In the closed loop circuit of the detection circuit 16, since the error amplifier 23 always feeds a feedback current that minimizes the magnetic flux linked to the detection coil 13, the linearity error of the sensor input / output characteristics is reduced. In addition, it has been reported that the optimum operating point of the sensor can be searched for by adjusting the phase of the synchronous rectifier 17 in the feedback loop, and the noise of the sensor can be reduced under the best phase conditions (Reference 1: H. Karo). , K. Shimoda, Y. Maeda and I. Sasada: “The First 36 Channel Fluxgate-Sensor-Array for the MCG Measurement”, IE EJ Transactions on Sensors and Micromachines. 136, No. 6, pp. 224-228, DOI : 10.1541 / ieejsmas.136.224, 2016).

  On the other hand, in the conventional circuit as shown in FIG. 12, since the offset when a positive bias DC current is applied is different from the offset when a negative bias DC current is applied, the bias DC current is switched. The offset cannot be zeroed.

  The reason why the offset characteristics differ between the case where the bias DC current is positive and the case where the bias DC current is negative is that the offset characteristics of the sensor head 14 are not symmetrical between the positive region and the negative region of the bias DC current. As an example, FIG. 2 shows offset values A and B for bias DC currents of 0.05 A and −0.05 A. As described above, generally, in the bias DC current having the same absolute value, each offset has a different value.

  To solve this problem, as shown in FIG. 3, positive and negative bias DC currents having equal offset values (= A) (in FIG. 3, idc1 = 0.05A and idc2 = −0.03A). ), The convergence point becomes the same by switching the polarity of the bias DC current, so that the addition of the voltage value after the error amplification as shown in FIG. 12 becomes unnecessary. That is, in the magnetic field sensor 1 of FIG. 1, the DC power supplies 10a and 10b that supply the bias DC current have their voltage values set so that the offsets shown in FIG. 3 are equivalent.

  For example, in the case of FIG. 3, when the bias DC current is idc1 = 0.05 A in the positive region and the bias DC current is idc2 = −0.03 A in the negative region, the respective offsets (= A) are equivalent. Become. Therefore, in the magnetic field sensor 1 of FIG. 1, the voltage value is set such that the DC power supply 10a that supplies the positive bias DC current supplies the magnetic core 15 with idc1 = 0.05 A during the calibration. Similarly, the voltage value is set so that the DC power supply 10b that supplies the negative bias DC current supplies the magnetic core 15 with idc2 = −0.03A.

  Note that, in the peak region S where the bias DC current idc shown in FIG. 3 is close to 0, the condition of bias DC current idc> AC excitation current iac, which is a condition necessary for performing the operation of the fundamental wave type orthogonal flux gate, is satisfied. Since there is no region, the power supply to the magnetic core 15 is performed based on at least the condition of the current value outside the region S.

  In this way, by adjusting the respective voltage values of the DC power supplies 10a and 10b in advance so that a bias DC current having an offset equivalent to a positive bias DC current and a negative bias DC current value is supplied. Even when the polarity of the bias DC current is switched, the offset can be made zero and the stable magnetic field sensor 1 having no fluctuation can be realized, and it is not necessary to have a complicated circuit as shown in FIG. A high-performance magnetic sensor can be realized with a simple circuit.

(Second embodiment of the present invention)
The magnetic field sensor according to the present embodiment will be described with reference to FIGS. In the magnetic field sensor according to the present embodiment, similarly to the magnetic field sensor according to the first embodiment, even when the polarity of the bias DC current is switched, the bias DC current is supplied with a value corresponding to the polarity. However, the polarity of the bias DC current is switched by performing the polarity switching on the excitation current in which the bias DC current and the AC excitation current are superimposed. In the present embodiment, when the polarity is switched with respect to the exciting current in which the bias DC current and the AC exciting current are superimposed, the offset characteristics are shown in FIG. The characteristics are as shown in FIG. In the case of such a characteristic, the offset can be canceled as a result by simply adding the positive offset and the negative offset. That is, as in the case of the first embodiment, the voltage value is set so that the offset is equivalent. In the present embodiment, a duplicate description of the first embodiment will be omitted.

  FIG. 4 is an overall circuit block diagram of the magnetic field sensor according to the present embodiment, and FIG. 5 is a circuit block diagram of a current supply unit of the magnetic field sensor according to the present embodiment. In FIG. 4, the magnetic field sensor 1 switches a polarity of a current supply unit 41 that supplies a bias DC current and an AC excitation current and a polarity of an excitation current supplied from the current supply unit 41 on which the bias DC current and the AC excitation current are superimposed. A fourth switch 42, a sensor head 14 including a magnetic core 15 to which the exciting current is supplied and a detection coil 13 wound around the magnetic core 15, and a negative feedback detection circuit 16 connected to the detection coil 13 And

  The detection circuit 16 is connected to the detection coil 13, receives a signal from the detection coil 13, converts the impedance of the buffer circuit 43, amplifies the signal, and connects to a subsequent stage of the preamplifier circuit 44. A synchronous rectifier (PSD) 17 for performing synchronous rectification on a signal from the coil 13, a third switch 21 for cutting off the detection circuit 16 at a predetermined timing, and a low-pass filter connected to a stage subsequent to the third switch 21 22, an error amplifier 23 connected downstream of the low-pass filter 22, and a feedback resistor 24 connected downstream of the error amplifier 23 and having the other end connected to one end of the detection coil 13 that is not the ground side. . After the signal is amplified by the buffer circuit 43 and the preamplifier circuit 44, the configuration is the same as that described in the first embodiment.

  FIG. 5 is a diagram illustrating the principle of the configuration of the current supply unit 41 in FIG. 4. The DC power supply 10 a supplies a bias DC current for the positive electrode to the magnetic core 15 and the DC power supply supplies a bias DC current for the negative electrode to the magnetic core 15. A bias DC power supply 10 comprising a bias DC power supply 10b, a first switch 11 for periodically switching which one of a positive DC power supply 10a and a negative DC power supply 10b is turned on, and an excitation AC excitation current An AC power supply 12 that supplies the magnetic core 15, a phase shifter 51 that adjusts the phase of the AC exciting current, and an adder 52 that adds DC and AC are provided.

  The switching operation of the first switch 11 and the fourth switch 42 is synchronized, and the fourth switch 42 is connected to the positive pole (the terminals P1 and P2 are connected in FIG. When the first switch 11 is connected to the DC power supply 10a and the fourth switch 42 is connected to the negative electrode (the terminals N1 and N2 are connected in FIG. The first switch 11 is connected to the DC power supply 10b when the first switch 11 is connected to the DC power supply 10b. The state in which the fourth switch 42 is connected to the positive electrode corresponds to the plus area in FIG. 3, and the state in which the fourth switch 42 is connected to the negative electrode corresponds to the minus area in FIG. doing. That is, the respective voltage values of the DC power supplies 10a and 10b are controlled such that a bias DC current in which the offset at the positive polarity and the offset at the negative polarity are equivalent as shown in FIG.

  FIG. 6 is a diagram illustrating an example of a specific circuit configuration of the current supply unit 41 in FIG. The circuit shown in FIG. 6 supplies a pulse waveform generated by the pulse generation means to the base of the transistor (supply) when supplying an excitation current in which an AC excitation current is superimposed on a bias DC current to the magnetic core 15 of the sensor head 14. B), an excitation current is generated in which the AC excitation current is superimposed on the bias DC current. At this time, the pulse generating means can control the value of the bias DC current by adjusting the duty ratio of the pulse waveform.

  FIG. 7 is a diagram illustrating a simulation result when an exciting current is generated by the circuit of FIG. FIG. 7A shows a simulation result when the duty ratio is set to 50%, and FIG. 7B shows a simulation result when the duty ratio is set to 32%. It is a waveform. The repetition frequency f of the pulse waveform is 31.25 kHz, and the resonance frequency fr of the LC resonance circuit is 15.65 kHz. In this manner, by supplying pulse waveforms having different duty ratios to the base of the transistor in FIG. 6, it is possible to generate an exciting current in which the value of the bias DC current is controlled.

  FIG. 8 is a diagram showing a result of simulating the bias DC current and the AC exciting current when the duty ratio of the pulse waveform is changed in the circuit of FIG. As shown in FIG. 8, the bias DC current increases as the duty ratio increases. In other words, it is clear that by adjusting the duty ratio of the pulse waveform in the circuit of FIG. 6, a bias DC current that can make the offset zero can be supplied. In the graph of FIG. 8, the AC exciting current is kept almost constant.

  From the simulation results of FIGS. 7 and 8, it is understood that the values of the bias DC current and the AC exciting current can be controlled by the duty ratio of the pulse waveform with the circuit configuration shown in FIG. By supplying the bias DC current and the AC exciting current whose current values are controlled in such a manner as to cancel the positive offset value and the negative offset value at the timing of the polarity switching, the offset is reduced to zero and the high-performance magnetic field is supplied. A sensor can be realized.

  In the circuit of FIG. 6, it is possible to control the increase or decrease of the exciting current by adjusting the values of the resistors R1 and R2. Further, it is desirable that the repetition frequency of the pulse waveform is 1.5 times or more, preferably 2 to 3 times the resonance frequency of the LC resonance circuit in the circuit.

  Processing for controlling the duty ratio of a pulse waveform in the circuit of FIG. 6 will be described in more detail. FIG. 9 is a diagram showing a timing chart when a pulse waveform is generated in the circuit of FIG. In FIG. 9A, a pulse is output by the timer IC at a repetition frequency twice the frequency of the AC exciting current. The pulse generating means generates a rectangular wave according to the output of the timer IC, as shown in FIG. At this time, for example, a rectangular wave can be generated using a T flip-flop that changes in synchronization with the rise of the waveform in FIG. Also, as shown in FIG. 9C, a ramp wave (saw wave) is generated from the rectangular wave generated in FIG. 9B. The ramp wave can be generated by, for example, charging a capacitor with a constant current circuit and discharging the capacitor at the rising timing in FIG. 9B. A threshold value Th is set for the ramp wave generated in FIG. 9C, and rectangular waves having different duty ratios are generated based on the threshold value Th (FIGS. 9D and 9E).

  Note that, in the circuit diagram of FIG. 4, the synchronization signal input to the PSD 17 has the pulse waveform generated in FIG. 9B. If it is necessary to shift the phase at this time, the waveform of FIG. 9B is temporally delayed while maintaining the duty ratio D = 0.5. For example, the waveform of FIG. 9A may be input to the monostable multivibrator, the second T flip-flop may be driven at the rear end of the output of the monostable multivibrator, and the output may be applied to the PSD 17.

  For example, in the case of FIG. 9 (D), the threshold value Th is set to a high value, and a high level is obtained when the threshold value Th is higher than the ramp waveform by using a comparator that inputs the threshold value Th and the ramp wave. A square wave has been generated. The case of FIG. 9 (E) is the same as that of FIG. 9 (D) except that the threshold value Th is set lower than in the case of FIG. 9 (D), so that the duty ratio of the pulse waveform is different. Has become. By adjusting the threshold value Th in this manner, the duty ratio of the pulse waveform can be easily adjusted with a simple circuit.

  As described in the simulation result of FIG. 7, the magnitude of the bias DC current can be controlled by adjusting the duty ratio of the pulse waveform in the circuit of FIG. That is, as shown in FIG. 3, since the positive bias DC current and the negative bias DC current having the equivalent offset have different absolute values, a current is supplied so as to cancel the offset in each polarity. Next, the pulse generation means of FIG. 6 generates a pulse waveform. At this time, as shown in FIG. 9, the duty ratio of the pulse waveform is adjusted by adjusting the threshold value Th to be compared with the ramp waveform, and the current value having a magnitude corresponding to the duty ratio is adjusted to the positive polarity and the negative polarity. , It is possible to realize a very high performance magnetic field sensor having an offset of zero.

  Note that the ramp wave shown in FIG. 9 is not limited to this, and any waveform may be used as long as the output changes with time during one cycle, that is, a waveform that can be converted from the threshold value Th to time. For example, it is possible to use a waveform that monotonically increases or decreases with time or a waveform that has a monomodal property that changes with time.

  In the present embodiment, an offset value generated when a positive bias DC current is supplied and an offset value generated when a negative bias DC current is supplied are equivalent to positive and negative bias DC current values. The current supply unit 41 may be configured to automatically adjust the value of the bias DC current to the positive and negative bias DC current values measured by the measurement unit.

  As described above, in the magnetic field sensor according to the present embodiment, the alternating voltage waveform biased with the DC current is generated based on the rectangular pulse waveform, and the bias DC current is generated according to the duty ratio of the rectangular pulse waveform. Since the value is controlled, the offset can be made zero and the circuit configuration can be simplified.

  In addition, other embodiments than the configuration shown in each of the above embodiments will be described below. For example, a combination of the detection circuit 16 in the circuit diagram of FIG. 1 shown in the first embodiment and the circuit of the current supply unit 41 shown in FIGS. It is possible to realize a sensor.

  Specifically, first, the waveform of FIG. 9E is inverted between a high level and a low level. FIG. 10 is a diagram showing a sine wave when the high level and the low level of the pulse waveform are inverted in the circuit of FIG. As shown in FIG. 10, by inverting the high level and the low level of the pulse waveform, the sine wave component is also inverted according to the pulse waveform.

  Then, in the inverted pulse waveform, the duty ratio is adjusted so as to be equal to the magnitude of the bias DC current supplied by the voltage of the DC power supply 10a. The waveform adjusted in this manner is temporarily assumed to be E ', and the polarity of the bias DC current is switched by using the switching method of FIG. 4 for the waveform of FIG. 9D and the waveform of E'. FIG. 11 is a diagram showing the waveform of the exciting current when the duty ratio of the waveform corresponding to FIG. 9D is 0.33 and the duty ratio of the waveform corresponding to E ′ is 0.67. Thus, it can be seen that when the pulse waveform is inverted in the waveform of E ', the phase of the sine wave is also inverted. That is, the bias DC current can be adjusted without affecting the AC exciting current.

In another embodiment, by adopting such a configuration, necessary bias DC currents idc1 and idc2 are supplied to the magnetic core 15, and the inversion of the AC excitation current is performed by using E ′ in which the sine wave component has been inverted in advance. Inversion occurs twice by using the waveform, and the operation of the magnetic field sensor according to the present invention can be performed.

Hereinafter, additional notes according to the present invention will be shown. The magnetic field sensor according to the present invention supplies a sensor head formed by winding a detection coil around a magnetic core, and an excitation AC current and a bias DC current superimposed on the magnetic core, if necessary. Current supply means, switching means for switching at least the polarity of the DC current for bias, and a detection circuit connected to the detection coil and detecting a magnetic field measured by the sensor head with a feedback current, the switching means When the polarity of the DC current is switched to a positive polarity, an offset value generated when a positive bias DC current is applied is equal to an offset value generated when a negative bias DC current is applied. Of the bias DC current value and the negative bias DC current value, the positive bias DC current value is supplied to the magnetic core by the current supply means. Is, when the switching means switches the polarity of the direct current negative polarity is to the negative bias DC current value is supplied to the magnetic core by the current supply means.

Thus, in the magnetic field sensor according to the present invention, when the polarity of the bias DC current is switched to the positive polarity, the offset value generated when the positive bias DC current is applied and the negative bias DC current are applied. Of the positive bias DC current value and the negative bias DC current value that are equivalent to the offset value that occurs when the positive bias DC current value is supplied to the magnetic core, the polarity of the bias DC current is switched to negative polarity In such a case, since the negative bias DC current value is supplied to the magnetic core, the offset is equal between the case where the bias DC current is positive and the case where the bias DC current is negative, and either the output when the bias current is positive or negative is output. When the polarity is inverted and added in the smoothing filter, the bias DC current value is controlled so that the offset is subtracted, and the offset is reduced. An effect that can be filtered.

In the magnetic field sensor according to the present invention, if necessary, the current supply means supplies a first DC power supply for supplying the positive bias DC current, a second DC power supply for supplying the negative bias DC current, An excitation current is generated by adding an AC power supply that supplies an AC current, a positive bias DC current supplied by the first DC power supply or a negative bias DC current supplied by the second DC power supply, and the AC current. And second switching means for switching the polarity of the exciting current.

As described above, in the magnetic field sensor according to the present invention, the current supply unit includes the first DC power supply that supplies the positive bias DC current, the second DC power supply that supplies the negative bias DC current, An AC power supply that supplies an AC current; and an adding unit that generates an exciting current by adding the positive bias DC current or the negative bias DC current and the AC current. Since the second switching means for switching the polarity is provided, a positive or negative bias DC current can be switched and supplied to the magnetic core so as to cancel the offset in accordance with the positive or negative offset, and the offset can be made zero. This has the effect that it can be performed.

In the magnetic field sensor according to the present invention, if necessary, the current supply unit generates an alternating voltage waveform biased with a DC current based on a rectangular pulse waveform, and the bias is generated according to a duty ratio of the rectangular pulse waveform. To control the value of the DC current for use.

As described above, in the magnetic field sensor according to the present invention, the alternating voltage waveform biased with the DC current is generated based on the rectangular pulse waveform, and the value of the bias DC current is determined according to the duty ratio of the rectangular pulse waveform. Therefore, for example, processing such as addition of a voltage value after error amplification as shown in Non-Patent Document 2 and its circuit become unnecessary, and the circuit can be simplified and the offset can be made zero. It has the effect of being able to.

In the magnetic field sensor according to the present invention, the current supply unit may generate a rectangular pulse waveform at a half cycle of an alternating current supplied to the magnetic core, if necessary. On the basis of the waveform, a periodic waveform generating means for generating a periodic waveform whose output changes with time during one cycle, and threshold adjusting means for adjusting a threshold set for the generated periodic waveform A duty ratio of the rectangular pulse waveform is controlled by an output change of the periodic waveform according to a change of the threshold value.

As described above, in the magnetic field sensor according to the present invention, the rectangular pulse waveform is generated at a half cycle of the alternating current supplied to the magnetic core, and the time change during one cycle is performed based on the generated rectangular pulse waveform. In order to control the duty ratio of the rectangular pulse waveform by adjusting the threshold set for the generated periodic waveform and controlling the duty ratio of the rectangular pulse waveform with the output change of the periodic waveform according to the change of the threshold, Only by adjusting the threshold value, it is possible to control and supply a current value corresponding to the polarity of the bias DC current, so that the circuit configuration can be simplified.

The magnetic field sensor according to the present invention, if necessary, the positive and negative offset values that occur when a positive bias DC current is applied and the offset value that occurs when a negative bias DC current is applied are equivalent Measuring means for measuring a bias DC current value is provided, and the current supply means adjusts the value of the bias DC current to positive and negative bias DC current values measured by the measuring means.

As described above, in the magnetic field sensor according to the present invention, the offset value generated when the positive bias DC current is applied is equal to the offset value generated when the negative bias DC current is applied. The bias DC current value is measured, and the current supply means adjusts the value of the bias DC current to the positive and negative bias DC current values measured by the measurement means. Thus, the operation can be significantly improved.

Reference Signs List 1 magnetic field sensor 10 (10a, 10b) DC power supply 11 first switch 12 AC power supply 13 detection coil 14 sensor head 15 magnetic core 16 detection coil 17 synchronous rectifier 18, 19 circuit 20 second switch 21 third switch 22 low-pass filter 23 error Amplifier 24 Feedback resistor 41 Current supply unit 42 Fourth switch 43 Buffer circuit 44 Preamplifier circuit 51 Phase shifter

Claims (9)

A transistor to which a pulse generated by the pulse generating means is input;
An LC resonance circuit disposed between the transistor and the ground at a subsequent stage of the transistor, wherein a capacitor and a coil are connected in parallel;
A first terminal for connection to a subsequent stage of the coil in the LC resonance circuit;
A second terminal for connecting to the ground,
A current supply device, wherein a current obtained by superimposing an alternating current and a direct current having a value larger than the amplitude of the alternating current is supplied to a resistor connected between the first terminal and the second terminal. The current supply device according to claim 1,
A current supply device wherein a pulse frequency generated by the pulse generation means is higher than a resonance frequency of the LC resonance circuit. A current supply device according to claim 1 or 2,
A magnetic field sensor comprising: a fundamental wave type orthogonal flux gate to which a magnetic core constituting a sensor head is connected between the first terminal and the second terminal . The magnetic field sensor according to claim 3,
The fundamental wave type orthogonal flux gate,
A sensor head formed by winding a detection coil around the magnetic core;
Switching means for switching at least the polarity of the DC current for bias,
A detection circuit connected to the detection coil and detecting a magnetic field measured by the sensor head by a feedback current ,
When the switching unit switches the polarity of the DC current to a positive polarity, an offset value generated when a positive bias DC current is applied is equivalent to an offset value generated when a negative bias DC current is applied. Among the positive bias DC current value and the negative bias DC current value, the positive bias DC current value is supplied to the magnetic core by the current supply device,
The magnetic field sensor according to claim 1, wherein when the switching unit switches the polarity of the DC current to a negative polarity, the negative bias DC current value is supplied to the magnetic core by the current supply device . The magnetic field sensor according to claim 4 ,
A magnetic field sensor , wherein the current supply device generates an alternating voltage waveform biased with a DC current based on a rectangular pulse waveform, and controls a value of the DC current for bias according to a duty ratio of the rectangular pulse waveform . The magnetic field sensor according to claim 5,
The current supply device,
Rectangular pulse waveform generating means for generating a rectangular pulse waveform with a half cycle of the alternating current supplied to the magnetic core,
A periodic waveform generating unit that generates a periodic waveform whose output changes with time during one cycle based on the generated rectangular pulse waveform;
Threshold adjusting means for adjusting a threshold set for the generated periodic waveform,
A magnetic field sensor for controlling a duty ratio of the rectangular pulse waveform by an output change of the periodic waveform according to a change of the threshold value. The magnetic field sensor according to any one of claims 1 to 6,
Measuring means for measuring a positive and negative bias DC current value in which an offset value generated when a positive bias DC current is supplied and an offset value generated when a negative bias DC current is supplied are equivalent,
A magnetic field sensor, wherein the current supply device adjusts the value of the bias DC current to positive and negative bias DC current values measured by the measuring unit. A sensor head formed by winding a detection coil around a magnetic core;
Current supply means for supplying an alternating current for excitation and a direct current for bias superimposed on the magnetic core;
Switching means for switching at least the polarity of the DC current for bias,
A detection circuit connected to the detection coil and detecting a magnetic field measured by the sensor head by a feedback current,
When the switching unit switches the polarity of the DC current to a positive polarity, an offset value generated when a positive bias DC current is applied is equivalent to an offset value generated when a negative bias DC current is applied. Among the positive bias DC current value and the negative bias DC current value, the positive bias DC current value is supplied to the magnetic core by the current supply unit,
The magnetic field sensor according to claim 1, wherein when the switching unit switches the polarity of the DC current to a negative polarity, the negative bias DC current value is supplied to the magnetic core by the current supply unit. The magnetic field sensor according to claim 8,
The current supply means,
A first DC power supply that supplies the positive bias DC current;
A second DC power supply that supplies the negative bias DC current;
An AC power supply for supplying the AC current;
A positive bias DC current supplied by the first DC power supply or a negative bias DC current supplied by the second DC power supply, and an adding means for adding the AC current to generate an exciting current; Yes,
A magnetic field sensor comprising second switching means for switching the polarity of the exciting current.

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