JP4418042B2 - Magnetic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor using a magneto-impedance effect element (hereinafter abbreviated as MI element). For example, a first MI element and a second MI element are arranged in parallel to each other, and the first MI element is arranged. The present invention relates to a magnetic sensor including an excitation coil that applies a bias magnetic field to the element and the second MI element.
[0002]
[Prior art]
The magnetic impedance effect (hereinafter abbreviated as the MI effect) is a phenomenon in which the impedance of a magnetic material is changed by an external magnetic field due to the skin effect when a high-frequency current is passed through a magnetic material having high permeability.
[0003]
FIG. 6 is a drive circuit diagram of a conventional MI element utilizing this MI effect. The first linear magnetic body 51 and the second linear magnetic body 52 are arranged in parallel to each other, and a first exciting coil 53 for adding a DC bias magnetic field is wound around the first linear magnetic body 51. The second exciting coil 54 is wound around the second linear magnetic body 52. The direction of the coil current flowing through the first exciting coil 53 and the second exciting coil 54 is configured such that one is counterclockwise and the other is clockwise with respect to the wire current flowing through the linear magnetic bodies 51 and 52. ing. Thus, by using a plurality (two in this example) of the linear magnetic bodies 51 and 52, it is possible to improve the sensitivity and temperature characteristics of the sensor.
[0004]
In the figure, 55 is a clock generator, 56 is an element drive for passing a pulse current to the first linear magnetic body 51 and the second linear magnetic body 52 based on a clock signal from the clock generator 55, respectively. A circuit 57 is a detection circuit, and includes a smoothing circuit 58 and an operational amplifier 59. The smoothing circuit 58 includes a diode (SBD Schottky Barrier Diode), a smoothing capacitor, and a resistor. FIG. 7 is a waveform diagram of each part of the drive circuit.
[0005]
[Problems to be solved by the invention]
In this conventional MI element driving circuit, the pulse voltage applied to the linear magnetic bodies 51 and 52 is smoothed by the smoothing circuit 58 and input to the operational amplifier 59. By the way, since there is a voltage drop of the diode (SBD) constituting the smoothing circuit 58, the height of the waveform (3) (see FIG. 7) cannot be maintained by the smoothing circuit 58. As a result, the waveform (4) in FIG. Thus, the pulse voltage cannot be accurately detected, and an error occurs. Further, when the pulse driving frequency is changed, there is a disadvantage that the values of the smoothing capacitor and the resistor need to be changed.
[0006]
The object of the present invention is to provide a magnetic sensor that eliminates the disadvantages of the prior art, can accurately detect the pulse voltage of the MI element, and does not require adjustment of the time constant even when the pulse drive frequency is changed. There is to do .
[0007]
[Means for Solving the Problems]
To achieve the above object, the present invention provides one or a plurality of magneto-impedance effect elements made of, for example, a linear magnetic material, an excitation coil for applying a bias magnetic field to the magneto-impedance effect element, and energizing the excitation coil. A detection circuit having a coil drive circuit for driving, an element drive circuit for driving the magneto-impedance effect element with pulses, and a sample-and-hold circuit for holding the pulse voltage of the magneto-impedance effect element in synchronization with the element drive circuit It is characterized by that.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is configured as described above. Since the sample-and-hold circuit or peak-hold circuit is used as the detection circuit in place of the conventional smoothing circuit, the pulse voltage of the MI element can be held and accurately detected. Therefore, the detection error is small and the reliability can be improved. Even if the pulse driving frequency is changed, it is not necessary to adjust the time constant as in the prior art, and the handling is convenient.
[0009]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a drive circuit diagram of an MI element according to the first embodiment, and FIG. 2 is a waveform diagram of each part of the drive circuit.
[0010]
The first linear magnetic body 1 and the second linear magnetic body 2 are arranged in parallel to each other, and the linear magnetic bodies 1 and 2 include, for example, zero magnetostriction made of an Fe—Co—Si—B alloy composition. Amorphous wire is preferred. A first exciting coil 3 and a second exciting coil 4 for applying a DC bias magnetic field are individually wound around the linear magnetic bodies 1 and 2 by several tens of turns.
[0011]
In the figure, 5 is a clock generator, and 6 is an element driving circuit for passing a pulse train current to the first linear magnetic body 1 and the second linear magnetic body 2. This element driving circuit 6 is a current output type whose current value is set to 10 mA or more, and the element driving circuit 6 has a resistance R at least 10 times the impedance of the linear magnetic bodies 1 and 2 at the gate of the digital circuit. Is connected.
[0012]
Reference numeral 7 denotes a detection circuit, a first sample and hold circuit 8 that samples and holds the peak voltage across the first linear magnetic body 1 at a predetermined timing, and both ends of the second linear magnetic body 2. It comprises a second sample and hold circuit 9 that samples and holds the peak voltage at a predetermined timing, and an operational amplifier 10 that differentially amplifies the output signals of both sample and hold circuits 8 and 9. The hold timing of the sample and hold circuits 8 and 9 is configured to be performed at the trailing edge of the pulse of the element driving circuit 6.
[0013]
Thus, by providing the first sample-and-hold circuit 8 and the second sample-and-hold circuit 9 instead of the conventional smoothing unit, the clock signal input to the first sample-and-hold circuit 8 can be obtained as shown in FIG. The peak value of the waveform can be accurately held.
[0014]
3 is a drive circuit diagram of the MI element according to the second embodiment, FIG. 4 is a configuration diagram of the MI element used in the drive circuit, and FIG. 5 is a timing chart of each part of the drive circuit. In the MI element according to this embodiment, one exciting coil 13 is wound around the first linear magnetic body 11 and the second linear magnetic body 12 arranged in parallel as shown in FIG. Has been. Therefore, the first linear magnetic body 11 and the second linear magnetic body 12 are arranged at the core of the exciting coil 13.
[0015]
In FIG. 3, 14 is a clock generator, 15 is a frequency divider, 16 is a first AND gate, 17 is a second AND gate, 18 is an element drive circuit, and 19 is an on / off control of energization to the excitation coil 13. A coil drive circuit including a switching element is configured such that the direction of the bias magnetic field generated by the exciting coil 13 is periodically reversed (see arrows Y1 and Y2 in FIG. 4). Indicates the direction of current flowing through the linear magnetic bodies 11 and 12).
[0016]
Reference numeral 20 denotes a detection circuit, a switching circuit 21, a first sample and hold circuit 22 that samples and holds the peak voltage across the first linear magnetic body 11 at a predetermined timing, and the second linear shape. It comprises a second sample and hold circuit 23 that samples and holds the peak voltage at both ends of the magnetic body 12 at a predetermined timing, and an operational amplifier 24 that differentially amplifies the output signals of both sample and hold circuits 22 and 23. Has been. The switching circuit 21 is synchronized with the coil driving circuit 19.
[0017]
FIG. 5 is a timing chart of each part of this drive circuit diagram. The direction of the bias magnetic field generated by the exciting coil 12 is periodically reversed at CK2 and CK4 in the figure. In synchronism with this coil drive, the first linear magnetic body 11 and the second linear magnetic body 12 are sequentially driven by the MI drive pulse.
[0018]
In the above-described embodiment, the first linear magnetic body and the second linear magnetic body are both arranged in parallel, but both may be arranged at a fixed angle such as a right angle. In the above embodiment, two linear magnetic bodies are used, but a plurality of three or more may be used.
[0019]
Although the sample and hold circuit is used in the above embodiment, a peak hold circuit can be used instead.
[0020]
The MI element driving circuit of the present invention can be applied to a driving circuit such as a magnetic sensor or a magnetic azimuth sensor that detects and measures the strength, direction, distribution, and the like of a magnetic field.
[0021]
【The invention's effect】
The present invention according to claim 1 is configured as described above. Since the sample-and-hold circuit is used in the detection circuit instead of the conventional smoothing circuit, the pulse voltage of the MI element is held and accurately detected. Therefore, the detection error is small and the reliability can be improved. Even if the pulse driving frequency is changed, it is not necessary to adjust the time constant as in the prior art, and the handling is convenient.
[0022]
The present invention according to claim 3 is configured as described above. Since only one excitation coil for applying a bias magnetic field to the MI element is required, the excitation coils can be connected between the excitation coils as in the case of using a plurality of excitation coils. There is no need to adjust the characteristics, making assembly work easier. Further, since the number of exciting coils is one, the size and weight can be reduced.
[Brief description of the drawings]
FIG. 1 is a drive circuit diagram of a magneto-impedance effect element according to a first embodiment of the invention.
FIG. 2 is a waveform diagram of each part of the drive circuit of the magneto-impedance effect element according to the first embodiment.
FIG. 3 is a drive circuit diagram of a magneto-impedance effect element according to a second embodiment of the present invention.
FIG. 4 is a configuration diagram of a magneto-impedance effect element according to a second embodiment.
FIG. 5 is a timing chart of the drive circuit according to the second embodiment.
FIG. 6 is a drive circuit diagram of a conventional magneto-impedance effect element.
FIG. 7 is a waveform diagram of each part of a driving circuit of a conventional magneto-impedance effect element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,11 1st linear magnetic body 1,12 2nd linear magnetic body 3 1st excitation coil 4 2nd excitation coil 5,14 Clock generator 6,18 Element drive circuit 7,20 Detection circuit 8 , 22 First sample-and-hold circuit 9, 23 Second sample-and-hold circuit 10, 24 Operational amplifier 13 Excitation coil 15 Frequency divider 16 First AND gate 17 Second AND gate 19 Coil drive circuit 21 Switching circuit

Claims (3)

A magneto-impedance effect element;
An exciting coil for applying a bias magnetic field to the magneto-impedance effect element;
A coil drive circuit for energizing the excitation coil;
An element driving circuit for driving the magneto-impedance effect element with a pulse;
A magnetic sensor comprising a detection circuit having a sample-and-hold circuit for holding a pulse voltage of the magneto-impedance effect element in synchronization with the element driving circuit. 2. The magnetic sensor according to claim 1, wherein the hold timing of the sample and hold circuit is configured to be performed at the trailing edge of the pulse of the element driving circuit. 2. The excitation coil according to claim 1, wherein one excitation coil is provided, and the coil drive circuit is configured to alternately reverse the direction of the current supplied to the excitation coil, and the magnetic field is synchronized with the coil drive circuit. A magnetic sensor configured to drive an impedance effect element .

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