JP2003167037A - Magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein since the magnetic sensor outputs a signal to a change in magnetic field as an analog signal, an A/D converter is needed for obtaining a digital signal, so that the circuit scale is increased to constitute an obstacle to reducing the size of the magnetic sensor. <P>SOLUTION: This magnetic sensor is formed by an oscillating circuit including a magnetic sensor element and a counter circuit connected to the oscillating circuit, and the signal of magnetic field change detected by the magnetic sensor element is converted to a digital signal. Thus, the output signal of the magnetic sensor can be output as a digital signal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetic sensor for detecting changes in a magnetic field.

[0002]

2. Description of the Related Art A magnetic sensor is used as a means for detecting a change in magnetic field. In the magnetic sensor, a Hall element, a magnetic resistance element, a loop coil, or a magnetic impedance element is used as a magnetic sensor that can obtain a change in magnetic field as a change in resistance value or impedance. The magnetic sensor is configured by combining these magnetic sensor elements alone or a circuit that performs signal processing.

These magnetic sensors obtain an output signal as an analog signal with respect to a change in magnetic field. A magnetic sensor in which an oscillation circuit is composed of a magnetic sensor element is disclosed in, for example, Japanese Patent Application Laid-Open No. 08-075835, but the output signal is an analog signal.

[0004]

The digitization of electronic devices has rapidly spread, and the driving force behind this is microcomputers and their applied product products. phenomenon,
Various sensors are used as means for detecting a state and converting it into an electric signal, but in the conventional magnetic sensor, the output signal is an analog signal, and an A / D converter must be added. There is difficulty connecting with digital devices.

In order to convert the output signal of the magnetic sensor from an analog signal to a digital signal, the A / D converter is generally used, but the scale of the circuit becomes large, which hinders the miniaturization of the magnetic sensor. There is.

Further, when the output of the magnetic sensor element is amplified by an operational amplifier or the like, an offset voltage, a temperature characteristic, etc. cause an error, which causes a decrease in detection accuracy.

When the magnetic sensor is used as an azimuth sensor, a coordinate X-axis and Y-axis are used to detect a two-dimensional magnetic field change.
A method of arranging the magnetic sensor element in a direction corresponding to the axis is used. Further, there is also a mode in which a posture correction function is added to the direction sensor in consideration of the inclination of the ground and the direction sensor, for example, a direction sensor for detecting a three-dimensional magnetic field change. These azimuth sensors are difficult to miniaturize because the circuit scale increases according to the number of magnetic sensor elements to be attached, and many portable devices are not able to receive signal from various sensors including magnetic sensors. Since it is a digital signal, it is an obstacle to mounting it on a mobile device.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and provides a magnetic sensor capable of outputting a signal of a magnetic field change as a digital signal, and using the magnetic sensor. It is intended to provide an orientation sensor.

[0009]

According to the present invention, a magnetic sensor is constituted by an oscillation circuit including a magnetic sensor element and a counter circuit connected to the oscillation circuit, and a magnetic field change signal detected by the magnetic sensor element is converted into a digital signal. As a result, the output signal of the magnetic sensor can be output as a digital signal, and a magnetic sensor that can provide a preferable output signal as an output signal to a digital device can be obtained.

Since the output signal of the magnetic sensor element is digitally converted from the oscillator circuit by the counter circuit, it is not necessary to amplify the analog signal by an operational amplifier or the like.

Since it is unnecessary to amplify the analog signal, the influence of an error on the magnetic sensor output signal such as the offset voltage of the operational amplifier, which is one of the causes of the deterioration of accuracy, and the temperature characteristic or the variation of the parts used for the amplification, is considered. Can be excluded.

Further, since a digital signal can be obtained without using an A / D converter, the circuit scale becomes small, which contributes to downsizing of the magnetic sensor.

The azimuth sensor using the magnetic sensor according to the configuration of the present invention requires at least two magnetic sensor elements to be mounted, and thus contributes greatly to the reduction of the circuit scale. Contributes to miniaturization.

The magnetic sensor element used in the present invention can be used by adjusting the constant of the oscillation circuit to an appropriate value as long as it is a magnetic sensor element exhibiting a change in resistance value or impedance. It is desirable to selectively use the magnetic sensor element depending on the change in the magnetic field to be detected. Particularly, a magnetic impedance element that can detect a minute magnetic field change and has a large change rate can obtain good results.

[0015]

The operation of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of the present invention. An oscillation circuit 2 including a magnetic sensor element 1 outputs a change in magnetic field around the magnetic sensor element as a change in oscillation frequency. The counter circuit 3 connected to the oscillator circuit 2 outputs the frequency change, which is the output signal of the oscillator circuit 2, as a digital signal.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. Embodiments to which the present invention is applied will be described below with reference to the drawings. Needless to say, the present invention is not limited to the following embodiments, and the configuration can be arbitrarily changed without departing from the gist of the present invention.

[0017]

Example 1 A magneto-impedance element 11 in which a CoFeB material was formed as a thin film having a pattern length of 5 mm on a glass substrate.
2 has characteristics as shown in FIG. 2 with respect to changes in the magnetic field, it is incorporated in a resin casing 5 as shown in FIG. 3, and a bias magnetic field is applied by a bias magnet 4 to operate. The magneto-impedance element 11 comprises a capacitor 7 mounted on a substrate 8 built in a resin casing 5 and a CMOS inverter IC 6 to form an oscillation circuit 2 as shown in FIG.

The output of the oscillator circuit 2 is connected to a counter circuit 3 which is mainly composed of a counter IC mounted on the substrate 8 and the output signal of the oscillator circuit 2 is converted into a digital signal. Here, an 8-BIT counter is configured, and a clock for operating the counter is given 10 KHz for operation.

The output signal of the oscillating circuit 2 oscillates at 1.8 MHz when the external magnetic field is 0, changes the external magnetic field, and changes in the oscillation frequency are obtained.

[0020]

[Embodiment 2] FIG. 5 shows an azimuth sensor using a magnetic sensor according to the present invention. As means for detecting an azimuth, a change in geomagnetism is detected, and a posture correction function is added. The magneto-impedance element 12 is arranged in the X-axis direction so as to be arranged in three directions of the axis, the Y-axis, and the Z-axis.
The magnetic impedance element 13 is mounted in the Y-axis direction and the magnetic impedance element 14 is mounted in the Z-axis direction in the resin casing 5.

The three magneto-impedance elements mounted are respectively connected to a capacitor and a CMOS inverter IC, and the X-axis, Y-axis and Z-axis at the position of the above-mentioned direction sensor.
An oscillating circuit whose oscillating frequency is changed by geomagnetism in three directions corresponding to the axis is configured. The signals output from the oscillation circuits including the magnetic sensor elements for the three directions of geomagnetism are respectively connected to a counter circuit and digitally converted to obtain the three directions of geomagnetism as digital signals, thereby functioning as an orientation sensor. You can get it.

By adding a latch circuit to the output of the counter circuit in the first or second embodiment, an output signal can be given at a timing according to the request of the external device connected to the magnetic sensor.

[0023]

According to the present invention, it is possible to provide a magnetic sensor having a high affinity with digital equipment. Furthermore, by using a magnetic sensor element such as a high-sensitivity and small-sized magnetic impedance element, the circuit configuration can be downsized and can be utilized for a direction sensor or the like mounted in a mobile device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing characteristics of a magneto-impedance element.

FIG. 3 is a diagram of a magnetic sensor showing an embodiment of the present invention.

FIG. 4 is a diagram showing an oscillator circuit according to an embodiment of the present invention.

FIG. 5 is a diagram of an orientation sensor showing an embodiment of the present invention.

[Explanation of symbols]

1 Magnetic sensor element 11, 12, 13, 14 Magneto-impedance element 2 oscillator circuits 3 counter circuit 4 bias magnet 5 Resin case 6 CMOS inverter IC 7 capacitors 8 substrates

Claims (3)

[Claims] 1. A magnetic sensor having an oscillation circuit including a magnetic sensor element and a counter circuit connected to the oscillation circuit. 2. A magnetic sensor using the magnetic sensor element according to claim 1 as a magnetic impedance sensor element. 3. A magnetic sensor using the magnetic sensor according to claim 1 or 2 as an azimuth sensor.