JP2007085824A - Magnetism detection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetism detection system which can be configured without the use of a high-frequency power source and without the use of a complex designed MI element, and that is small, and has the same sensitivity as those of conventional magnetism detection systems that use high-frequency power sources. <P>SOLUTION: The magnetism detection system 10 comprises a pulse generation section 1 for generating a rectangular-wave pulse voltage, a magnetism detection section 2 having a circuit which electrically responds to an external magnetic field independently in the three-axial directions, a differential amplifier section 3 for outputting the difference, with respect to the output of the magnetism detection section 2, and a peak hold section 4 having the function of maintaining the peak of the output of the differential amplifier section 3 for a certain period of time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic detection device including a magnetoresistive element and a measurement unit that detects its impedance.

  As a conventional technique, a magnetic detection device using an MI (Magneto-Impedance) element is known. The MI element has a characteristic that the impedance changes based on a minute change in the external magnetic field, and is a small geomagnetic detection direction sensor or attitude control sensor as a magnetoresistive element that detects the change in the external magnetic field as a voltage output signal. Applications are expected (for example, Patent Document 1).

This magnetic detection device includes an MI element that exhibits an impedance based on an external magnetic field, a bias coil for applying an AC magnetic bias to the MI element, and a high-frequency drive current of 10 to 100 MHz for measuring an impedance change of the MI element. A Colpitts oscillation circuit, a detection circuit, and a comparator.
JP-A-9-127218

  However, according to the conventional magnetic detection device, a high-frequency power source is required for magnetic detection, and both the detection circuit and the comparator require complicated circuits, which makes it difficult to reduce the size of the device. Further, due to the characteristics of the MI element, there is a problem that the design and the manufacturing process become complicated when a high frequency is used.

  Accordingly, an object of the present invention is to be configured without using a high-frequency power supply or without using a MI element with a complicated design, and is small in size and has the same sensitivity as a magnetic detection device using a conventional high-frequency power supply. The object is to provide a highly sensitive magnetic detection device.

  In order to achieve the above object, the present invention includes a pulse generator that generates a pulse voltage, an MI (Magneto-Impedace) element that detects an external magnetic field, and a resistor that is insensitive to the external magnetic field. A magnetic detection unit configured to form a bridge circuit with at least one pair of the MI elements arranged opposite to each other and a pair of the resistors arranged opposite to each other, and a change in the external magnetic field; And a differential amplifying unit for detecting the output of the magnetic detection unit according to the above.

  In order to achieve the above object, the present invention achieves the above-mentioned object, a pulse generator for generating a pulse voltage having a rise time of 2 to 10 ns, a pulse width of 10 to 100 ns and a frequency of 1 kHz to 10 MHz, an MI element for detecting an external magnetic field, and the external A resistance insensitive to a magnetic field, detecting the external magnetic field in at least one axial direction, and forming a bridge circuit with at least a pair of the opposed MI elements and a pair of the opposed resistors per axis. There is provided a magnetic detection device comprising: a magnetic detection unit configured; and a differential amplification unit that detects an output of the magnetic detection unit according to a change in the external magnetic field.

  In order to achieve the above object, the present invention achieves the above-mentioned object, a pulse generator for generating a pulse voltage having a rise time of 2 to 10 ns, a pulse width of 10 to 100 ns and a frequency of 1 kHz to 10 MHz, an MI element for detecting an external magnetic field, and the external A resistance insensitive to a magnetic field, detecting the external magnetic field in at least one axial direction, and forming a bridge circuit with at least a pair of the opposed MI elements and a pair of the opposed resistors per axis. A magnetic detection unit configured; a differential amplification unit that detects an output of the magnetic detection unit according to a change in the external magnetic field; and a peak hold unit for peak-holding the output of the differential amplification unit. There is provided a magnetic detection device characterized by comprising:

  The peak hold unit is preferably configured using BiCMOS (Bipolar Complementary Metal Oxide Semiconductor).

  According to the present invention, it is possible to configure without using a high-frequency power source or without using a complicatedly designed MI element, and it is small in size and has a sensitivity equivalent to that of a magnetic detection device using a conventional high-frequency power source. A simple magnetic detection device can be configured.

  Embodiments of a magnetic detection device of the present invention will be described below in detail with reference to the drawings.

(Configuration of magnetic detection device)
FIG. 1 is a schematic configuration diagram of a magnetic detection device according to an embodiment of the present invention.

  The magnetic detection device 10 includes a pulse generator 1 that generates a pulse voltage of a rectangular wave, a magnetic detector 2 having a circuit that electrically responds to an external magnetic field independently in three axial directions, and for each axial direction. A differential amplifying unit 3 that is provided and outputs a difference between the two outputs of the magnetic detection unit 2, and a peak hold having a function of maintaining a peak of the output with respect to the output of each differential amplifying unit 3 for a predetermined time. Part 4. A signal processing unit 5 that converts the output of the peak hold unit 4 into a desired output corresponding to an electronic device on which the magnetic detection device 10 is mounted is installed outside the magnetic detection device 10.

  The peak hold unit 4 is configured using a BiCMOS (Bipolar Complementary Metal Oxide Semiconductor) that can sufficiently respond to the output from the differential amplifier unit 3 in terms of time.

  FIG. 2 is a circuit diagram of a magnetic detection unit of the magnetic detection device according to the embodiment of the present invention. FIG. 2 relates to one of the three axes, and the same circuit is applied to the remaining two axes.

  The magnetic detection unit 2 includes two MI elements 20 arranged opposite to each other and two resistors 21 arranged opposite to each other, and is configured by a bridge circuit. Iin is connected to the pulse generator 1, and V1 and V2 are connected to the differential amplifier 3.

  FIG. 3A is a plan view showing the configuration of the MI element according to the present invention. (B) is an equivalent circuit diagram of the MI element in (a).

  As shown in FIG. 3A, the MI element 20 includes a planar substrate 200 made of a material such as silicon, and a sensor element made of a high permeability material such as NiFe formed on the surface of the substrate 200 by high-frequency sputtering. 201, an element joint portion 202 made of Cu that electrically connects the sensor elements 201, and an electrode 203 made of Cu that electrically connects the sensor element 201 to the outside.

  As shown in FIG. 3B, the MI element 20 constitutes an equivalent circuit in which an inductor 204 and a resistor 205 are connected in series, and a capacitor 206 is connected in parallel.

(Operation of magnetic detector)
The operation of the magnetic detection device according to the embodiment of the present invention will be described below with reference to FIGS.

  The impedance of the MI element 20 changes in proportion to the strength of the external magnetic field. In the equivalent circuit of FIG. 3B, the characteristics of the inductor 204 and the capacitor 206 do not change based on the magnetic field, and the characteristic of the resistor 205 changes based on the magnetic field. As a result, the impedance of the entire MI element 20 changes.

  The pulse voltage is input from the pulse generator 1, and in the magnetic detector 2 shown in FIG. 2, a current based on the pulse voltage flows on the right side and the left side of the bridge circuit. The current flowing on the right side of the bridge circuit has a phase difference based on the impedance of the MI element 20 with respect to the current flowing on the left side. As a result, the voltage V1 on the left side of the bridge circuit has a smoother rise than the voltage V2 on the right side.

  FIG. 4 is a schematic diagram of the input and output waveforms of the magnetic detection unit and the output waveform of the differential amplification unit according to the embodiment of the present invention. (A) shows a case where the external magnetic field B is weak, and (b) shows a case where the external magnetic field B is strong.

  When a rectangular wave pulse voltage is input to the magnetic detection unit 2, the output voltages V 1 and V 2 become rectangular waves having a gentle rise in proportion to the impedance of the MI element 20. For example, as shown in FIGS. 4A and 4B, when the magnetic detection unit 2 is in a magnetic field of different strength, the output voltages V1 and V2 of (b) are more gentle than (a). A square wave with a large rise is shown.

  Based on the characteristics of the magnetic detection unit 2 described above, the difference between V1 and V2 output from the differential amplification unit 3 is large when the magnetic field is strong and small when the magnetic field is weak, as shown in FIG.

  The output of the differential amplifying unit 3 has a small energy because the peak width is short. Therefore, the peak hold unit 4 maintains the output peak of the differential amplification unit 3 for a certain period of time and outputs it to the signal processing unit 5 as a signal having sufficient energy. The signal processing unit 5 converts the signal received from the peak hold unit 4 into a desired command signal.

  FIG. 5 is a schematic diagram showing a general rectangular wave.

  Based on the characteristics of the magnetic detection unit 2, the linearity of the magnetic detection device 10 with respect to the external magnetic field is as follows: Tr = 2-10 ns, Tw = It is good when 10 to 100 ns, and is particularly optimal when Tr = 5 ns and Tw = 30 ns. In this embodiment, the frequency of the pulse signal is 250 kHz, and it has been confirmed that good linearity can be obtained without using a high frequency.

  The operations described above can be similarly applied to the x-axis, y-axis, and z-axis in the triaxial space.

  Further, the MI element is given a magnetic bias by a direct current with a coil or the like (not shown) in order to obtain good sensitivity and to determine the direction of the magnetic field.

  Further, the signal processing unit 5 may be installed in the magnetic detection device 10 or in an electronic device to be mounted.

(Effect of magnetic detector)
According to the above-described embodiment, in the magnetic detection device 10, the output from the magnetic detection unit 2 depends on the rise time and pulse width of the input pulse voltage, and does not depend on the waveform. In the description of the embodiment, a pulse voltage of 250 kHz is used. However, if the pulse voltage has a frequency of about 1 kHz to 10 MHz, a minute change in the magnetic field can be detected based on the input, so a high frequency is not required. The pulse generator 1 can be configured without using a high-performance one.

  In addition, since it is configured without using a high-frequency power supply, it is not necessary to use an MI element with a complicated design corresponding to a high frequency, and a detection circuit, a comparator corresponding to a high frequency, and the like are not required. As a result, restrictions on the design of the magnetic detection device 10 are reduced, and it is easy to design a small size, and at the same time, the cost can be reduced.

  In addition, since the MI element is configured as a bridge, a minute response to the magnetic field of the MI element can be detected with high accuracy, and sensitivity equivalent to that of a magnetic detection device using a conventional high-frequency power source can be obtained.

It is a schematic block diagram of the magnetic detection apparatus which concerns on embodiment of this invention. It is a circuit diagram of the magnetic detection part of the magnetic detection apparatus regarding embodiment of this invention. (A) is a top view which shows the structure of MI element based on this invention. (B) is an equivalent circuit diagram of the MI element in (a). It is a schematic diagram of the input and output waveforms of the magnetic detection unit and the output waveform of the differential amplification unit according to the embodiment of the present invention. (A) shows a case where the external magnetic field is weak, and (b) shows a case where the external magnetic field is strong. It is a schematic diagram which shows a general rectangular wave.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pulse generation part, 2 ... Magnetic detection part, 3 ... Differential amplification part, 4 ... Peak hold part,
DESCRIPTION OF SYMBOLS 5 ... Signal processing part, 10 ... Magnetic detection apparatus, 20 ... MI element, 21 ... Resistance, 200 ... Substrate,
DESCRIPTION OF SYMBOLS 201 ... Sensor element 202 ... Element junction part 203 ... Electrode 204 ... Inductor 205 ... Resistance, 206 ... Capacitor

Claims (4)

A pulse generator for generating a pulse voltage;
An MI (Magneto-Impedace) element for detecting an external magnetic field and a resistance insensitive to the external magnetic field, the external magnetic field is detected in at least one axial direction, and at least a pair of opposingly arranged MI per axis A magnetic detection unit comprising a bridge circuit with the element and a pair of opposed resistors,
And a differential amplifying unit that detects an output of the magnetic detection unit according to a change in the external magnetic field. A pulse generator for generating a pulse voltage having a frequency of 1 kHz to 10 MHz with a rise time of 2 to 10 ns and a pulse width of 10 to 100 ns;
An MI element for detecting an external magnetic field; a resistance insensitive to the external magnetic field; detecting the external magnetic field in at least one axial direction; and at least a pair of opposingly arranged MI elements per axis; A magnetic detection unit comprising a bridge circuit with the resistors arranged opposite to each other;
And a differential amplifying unit that detects an output of the magnetic detection unit according to a change in the external magnetic field. A pulse generator for generating a pulse voltage having a frequency of 1 kHz to 10 MHz with a rise time of 2 to 10 ns and a pulse width of 10 to 100 ns;
An MI element for detecting an external magnetic field; a resistance insensitive to the external magnetic field; detecting the external magnetic field in at least one axial direction; and at least a pair of opposingly arranged MI elements per axis; A magnetic detection unit comprising a bridge circuit with the resistors arranged opposite to each other;
A differential amplifier for detecting the output of the magnetic detector in response to a change in the external magnetic field;
And a peak hold unit for peak-holding the output of the differential amplifier.   The magnetic detection device according to claim 3, wherein the peak hold unit is configured using a BiCMOS (Bipolar Complementary Metal Oxide Semiconductor).