JP3216182B2 - Electronic compass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic compass.

[0002]

2. Description of the Related Art A magnetoresistive element is applied to a non-contact switch, a displacement sensor, a compass, and the like by utilizing a characteristic that a resistance value changes according to the strength of a magnetic field. Since the change in the resistance value of the magnetoresistive element is small in a range where the magnetic field applied to the magnetoresistive element is weak, a constant bias magnetic field is applied so that a weak magnetic field can be detected.

[0003]

In order to measure the azimuth of terrestrial magnetism, it is necessary to detect magnetic field components in two orthogonal directions. Therefore, two magnetic resistance elements are used and their magnetic detection directions are orthogonal. So that

However, even if a magnetic field having the same strength is applied, a difference occurs between the outputs of the two magnetoresistive elements due to variations in the resistance values of the individual magnetoresistive elements, and an error occurs in the azimuth measurement. There was a problem.

Therefore, conventionally, it is necessary to adjust the current flowing through the magnetoresistive element in order to correct the variation in the characteristics of each magnetoresistive element, and there has been a problem that the adjustment is troublesome.

An object of the present invention is to make it possible to easily correct variations in characteristics among a plurality of magnetic sensors.

[0007]

A magnetic sensor is a magnetoresistive element or the like whose resistance changes according to the strength of a magnetic field.
In order to detect the direction and strength of the earth's magnetism, for example, two magnetoresistive elements are arranged so that the magnetism detection directions are orthogonal to each other.

The bias magnetic field applying means applies a predetermined bias magnetic field to the plurality of magnetic sensors. The reference value detecting means detects a reference value among the output values of the magnetic sensor when the bias magnetic field applying means changes the bias magnetic field.

[0009] The value to be the standard, the extremes of the output of the magnetic sensor in a state in which bias applying means is changing a bias magnetic field, or, which is the output value when the magnetic sensor is in the saturated state.

The correction means corrects the output value of the magnetic sensor in a state where a predetermined bias magnetic field is applied, based on a reference value detected by the reference value detection means. The calculating means calculates the azimuth from the outputs of the plurality of magnetic sensors corrected by the correcting means.

[0011]

According to the present invention, the output of each magnetic sensor when a predetermined bias magnetic field is applied is corrected by the output of the reference magnetic sensor. Measurement error can be reduced. Accordingly, there is no need to correct variations in the characteristics of the magnetic sensor, variations in the bias magnetic field, and the like, so that adjustment work is not required.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an electronic compass according to a first embodiment of the present invention.

The detecting section 1 is composed of two magnetoresistive elements arranged orthogonally and a voltage detecting circuit for extracting a change in resistance value when a predetermined bias magnetic field is applied to the magnetoresistive element as a voltage change. I have.

The analog voltage value detected by the detection unit 1 is converted into a digital value by an A / D conversion unit 2 and is calculated / calculated.
Output to the control unit 3. The arithmetic / control unit 3 obtains the output voltages of the two magnetoresistive elements when a predetermined bias magnetic field is applied and the output voltages of the two magnetoresistive elements when the magnetic field is set to 0, and calculates those data. The data is stored in the register of the RAM 4.

The arithmetic / control section 3 corrects the output voltage of the magnetoresistive element when an external magnetic field is applied from the above data stored in the RAM 4, and calculates the azimuth of the geomagnetism from the corrected output voltage. An arrow indicating the direction of the direction of the compass with respect to magnetic north, or an arrow indicating the direction of magnetic north is displayed on the display unit 5 composed of a liquid crystal display device or the like. The operations of the detection unit 1, the A / D conversion unit 2, and the like are controlled by the calculation / control unit 3.

FIG. 2 is a diagram showing an example of the configuration of the magnetoresistive element substrate of the detecting section 1. The magnetoresistive elements 6, 7 such as permalloy are formed on the substrate so that the magnetic detection directions are orthogonal to each other. I have.

Next, FIG. 3 is a specific circuit configuration diagram of the detection section 3. As shown in FIG. The bias voltage _Vb is directly applied to one end of the bias coil L2 wound around the magnetoresistive element 7, and the resistor R1 and the inverter INV1 are connected to one end of the bias coil L1 wound around the magnetoresistive element 6. and bias voltage V _b is applied through the other end of the bias coil L1, L2 are connected to each other. Note that the bias voltage _Vb is a voltage having a constant cycle in which a high level and a low level are alternately repeated.

A constant current is supplied to one end of each of the magnetoresistive elements 6 and 7 from DC current sources 8 and 9, and the other end is grounded. Magnetoresistive element 6 and DC current source 8
Are connected to capacitors C ₁ and C ₂ via gates 10 and 11, respectively, and connected to gates 10 and 11 and capacitors C ₁ and C ₂ via resistors R 2 and R 3. The negative input terminal and the positive input terminal of the operational amplifier 13 are connected to each other.

Similarly, the magnetic resistance element 7 and the DC current source 9
A capacitor is connected to the connection point through gates 12 and 13.
C_Three, C_FourAre connected to the gates 12 and 13 and
Densa C _Three, C_FourIs connected through resistors R4 and R5.
The-input terminal and the + input terminal of the operational amplifier 14 are respectively
Connected.

The control terminals of the gates 10 and 12 and the gates 11 and 13 are supplied with signals I and NI having a phase difference of 180 ° as shown in FIG. gate 10 and 12 is turned on, a positive output voltage of the magnetoresistive element 6 when the bias magnetic field is applied is held in the capacitor C _1, C _3. The gate 11 and 13 when the signal NI is high is turned on, the output voltage of the magnetoresistive element 6 when the negative bias magnetic field is applied is held in the capacitor C _2, C _4. The magnetic field generated when the bias voltage _Vb is positive is defined as a positive bias magnetic field.

The voltage difference between these capacitors C ₁ and C ₂ ,
That positive, the output voltage difference of the magnetoresistive element 6 when the negative bias magnetic field is applied is output to the A / D converter 2 as a voltage V _X is amplified by the operational amplifier 14.

Further, the voltage difference between the capacitor C _3, C _4, or positive, the output voltage difference of the magnetic resistance element 7 when the negative bias magnetic field is applied is amplified by the operational amplifier 15 by the voltage V _y as A / It is output to the D conversion unit 2.

Further, the output voltages of the magnetoresistive elements 6 and 7 are input to the + input terminals of the operational amplifiers 16 and 17, respectively, and the output of the operational amplifiers 16 and 17 is a diode D.
1, and are fed back to each negative input terminal via D2.

The output terminal of the operational amplifier 16 is connected to the cathode of a diode D1.
The + input terminal of the operational amplifier 18 is connected to the anode of. Furthermore, between the + input terminal and the supply voltage + V of the operational amplifier 18, resistor R10 and capacitor C ₅ is connected in series, the transistor TR1 is connected in parallel to its resistor R10 and the capacitor C ₅ .

The base of the transistor TR1 is the rise of the bias voltage V _b as shown in FIG. 4, and the signal V _r to the low level is applied prior to the fall, when the signal V _r is low Transistor TR
1 is adapted to discharge the voltage of the capacitor C ₅ is turned on.

The circuit consisting operational amplifiers 16, 18 and the capacitor C _5, etc. is a circuit for holding the minimum value of the output voltage of the magnetoresistive element 6, the minimum voltage V that is held
_my is output to the A / D converter 2.

Similarly, the output terminal of the operational amplifier 17 is
The cathode of the diode D2 is connected to the diode D2.
The + input terminal of the operational amplifier 19 is connected to the anode of
ing. Furthermore, the + input terminal of the operational amplifier 19 and the power supply
Between the resistor R11 and the capacitor C₆Directly
Connected to the column, the resistor R11 and the capacitor C ₆
And a transistor TR2 is connected in parallel. Tiger
The signal V is applied to the base of the transistor TR2._rIs given
You.

[0028] constitute a Pikuhorudo circuit 21 for detecting a negative peak value of the output voltage of the operational amplifier 16 to 19, capacitors C _5, C _6, the magnetoresistive element 6, 7 by transistors TR1, TR2, and the like.

Next, the operation of the above circuit will be described with reference to the time chart of FIG. 4 and the diagram showing the relationship between the magnetoresistive element and the magnetic field of FIG. The magnetoresistive elements 6 and 7 of this embodiment are:
As shown in FIG. 5, the output voltage, that is, the magnetic resistance decreases as the magnetic field decreases.

When the bias voltage _Vb changes from a low level to a high level, the bias magnetic field applied to the magnetoresistive elements 6 and 7 changes from negative to positive. At this time, the output voltage E of the magnetoresistive elements 6, 7 becomes a constant value determined by the positive bias magnetic field B and the external magnetic field at that time after passing through the minimum value as shown in FIG.

When the positive bias magnetic field is applied, the output voltage E of the magnetoresistive elements 6 and 7 changes when the signal I goes high and the gates 10 and 12 are turned on, and the capacitors C ₁ and C ₃ are turned on. , And is held as it is while the signal I is at the low level and the gates 10 and 12 are off.

When the signal _Vr goes low before a certain time before the bias voltage _Vb goes low, the transistor T
R1, TR2 is turned on capacitor C _5, a peak C ₆ is discharged hold circuit 21 enters a standby state. Thereafter, when the signal _Vr goes high, the transistor TR
1, TR2 is turned off, and the output voltages of the magnetoresistive elements 6, 7 are input to the negative peak hold circuit 21.

Bias voltage V_bIs high level to low level
Applied to the magnetoresistive elements 6, 7 when changing to a bell
When the bias magnetic field changes from positive to negative,
Since the output voltages of the elements 6 and 7 become minimum, the minimum value is
Each capacitor C_Five, C ₆Is held.

When the bias voltage _Vb is at a low level, that is, when a negative bias magnetic field is applied, the output voltage E of each of the magnetoresistive elements 6 and 7 is, as shown in FIG. The constant value is determined by B and the external magnetic field at that time.

When the negative bias magnetic field is applied, the output voltage E of the magnetoresistive elements 6 and 7 changes when the signal NI goes high and the gates 11 and 13 are turned on.
₂ and C ₄ , and are held as they are while the signal NI goes low and the gates 11 and 13 are off.

The operational amplifiers 14 and 15 detect the voltage difference between the capacitors C ₁ and C ₂ and the capacitors C ₃ and C ₄ , respectively. The magnetoresistive elements 6 and 7 when the positive and negative bias magnetic fields are applied, respectively. output voltage difference voltage V _X, V _y of
Is output to the A / D converter 2.

These voltages V _X and V _y are _supplied to the A / D converter 2
In it is converted into digital values, (T _0, T ₃ in FIG. 4) to the low-level bias voltage B _b from the high level, or at the transition from the low level to the high level RA
It is stored in the registers H ₀ and H ₁ of M4.

Further, when the magnetic field held by the capacitors C ₅ and C ₆ is zero, the output voltages V _mx ,
V _my is converted to a digital value by the A / D converter 2 while the signals I and NI are at the high level, and the RAM 4 is output at the timing when each signal changes from the high level to the low level.
In the registers R ₀ and R ₁ .

The arithmetic / control section 3 applies the voltages V _X , V _y proportional to the external magnetic field to the magnetoresistive element 6,
7 is normalized by the output voltages V _mx and V _my , and the direction is calculated from them. By repeating these calculations, the azimuth at that time can always be calculated and displayed.

As a result, even when the characteristics of the two magnetoresistive elements 6 and 7 vary, an accurate azimuth can be calculated by correcting the output voltages of both. Next, a second embodiment of the present invention will be described. In this embodiment, the output voltage when a saturation magnetic field is applied to the magnetoresistive element is used to correct the output voltage of the magnetoresistive element when an arbitrary external magnetic field is applied.

FIG. 6 is a circuit block diagram of an electronic compass in the second embodiment. A common bias coil L3 is wound around two magnetoresistive elements 6, 7 patterned on the substrate so that the magnetic detection directions are orthogonal to each other. One end of the bias coil L3 is connected to the output of the operational amplifier 41. Connected, and the other end is grounded via a resistor R14.

The + input terminal of the operational amplifier 41 is connected to the gate 4
2 and 43 are connected to two output terminals of the reference voltage generating circuit 44, and the-input terminal is connected to a connection point between the resistor R14 and the bias coil L3.
Supplies a voltage substantially equal to the voltage input to the + input terminal to the bias coil L3.

From two output terminals of the reference voltage generating circuit 44, a voltage V _ref1 for generating a magnetic field for saturating the magnetoresistive elements 6 and 7 in the bias coil L3 and a voltage V _ref2 for generating a predetermined bias magnetic field are provided. Are output, respectively.
One of these output voltages is selected by the gates 42 and 43 and output to the + input terminal of the operational amplifier 41.

The gate switching circuit 45 outputs a signal to the gate 4 based on a signal a output from an arithmetic / control unit 57 described later.
This circuit generates signals b and c for turning on and off the switches 2 and 43. Note that the signal b is a signal having the same phase as the signal a as shown in FIG. 7, and the signal c is a signal having the opposite phase to the signal b.

Therefore, when the signal b is at the high level, the gate 42 is turned on, the voltage _Vref1 is applied to the + input terminal of the operational amplifier 41, and a saturation magnetic field is generated in the bias coil L3. On the other hand, when the signal c is at a high level, the gate 43 is turned on and the voltage V is applied to the + input terminal of the operational amplifier 41.
_ref2 is given, and a predetermined bias magnetic field is generated in the bias coil L3.

One end of each of the magnetoresistive elements 6 and 7 is connected to V
Is connected to the _DD, the other end is connected to V _SS through respective constant current circuits 46 and 47. Constant current circuits 46, 47
Is a circuit for supplying a constant current to the magnetoresistive elements 6 and 7.

The magnetoresistive elements 6, 7 and the constant current circuits 46, 4
7 is connected to an A / D converter 52 via gates 50 and 51. The output voltages of the magnetoresistive elements 6 and 7 selected by the gates 50 and 51 are output from the A / D converter. 52
Is converted into a digital value and output to the arithmetic / control unit 57.

The gate switching circuit 55 includes gates 50 and 51 based on a signal d output from the arithmetic / control unit 57.
Is a circuit for generating signals e and f for turning on and off.
Note that the signals e and f are output from the arithmetic / control unit 57 as shown in FIG.
Is a signal having a cycle twice as long as the signal d output from the signal e, and the signal e and the signal f have a 180 ° phase difference from each other.

The magnetoresistive elements 6 and 7 and the constant current circuit 4
At the connection point with the magnetic resistance elements 6 and 47, the peak value of the resistance value of the magnetic resistance elements 6 and 7, ie, in this case, the positive peak value of the output voltage of the magnetic resistance elements 6 and 7 when a saturation magnetic field is applied is set. Resistance value detection circuits 48 and 49 for detecting are connected,
The output voltage of these resistance value detection circuits 48 and 49 is
The signals are output to the A / D converter 52 via the reference numerals 3 and 54.
Incidentally resistance value detecting circuit 48 and 49, a peak hold circuit 21 in FIG. 3 is similar to that controlled by the signal V _r, computing / control unit 57 is controlled by a signal j to be output.

FIG. 8 is a diagram showing the relationship between the strength of the magnetic field and the output voltage of the magnetoresistive element. The output voltage U indicates the output voltage of the magnetoresistive element when a certain external magnetic field is applied in a state where the bias magnetic field B is applied. The output voltage is substantially constant above the saturation magnetic field H at which the magnetoresistive element is saturated. Becomes

The gate switching circuit 56 includes the arithmetic control unit 5
7 is a circuit for generating signals i and h for turning on and off the gates 53 and 54 based on the signal g output from the gate 7. The signals i and f are calculated by the arithmetic / control unit 57 as shown in FIG.
Is a signal having a cycle twice as long as the signal g output from the signal i, and the signal i and the signal h are 180 ° out of phase with each other.

The arithmetic / control unit 57 corrects the output voltages of the magnetoresistive elements 6 and 7 when the external magnetic field is measured with the output voltages of the two magnetoresistive elements 6 and 7 when the saturation magnetic field is applied. Then, an error of the output voltage caused by a variation in the characteristics of the individual magnetoresistive elements 6 and 7 is corrected, and an accurate azimuth of the geomagnetism is calculated. Then, the calculated azimuth is displayed on the display unit 58 with an arrow or the like indicating the direction of magnetic north.

Next, the operation of the above circuit will be described with reference to the time chart of FIG. When the signal a as shown in FIG. 7 is output from the arithmetic / control unit 57, the signal c having the same phase as the signal a and the signal b having the opposite phase to the signal a are output from the gate switching circuit 45 to the control terminals of the gates 42 and 43. Is done.

When the signal c is at a high level, the gate 43 is turned on and the voltage _Vref2 is supplied to the bias coil L3. A predetermined bias magnetic field is generated in the bias coil L3 by the voltage V _ref2, and a voltage proportional to the strength of the terrestrial magnetism at that time is output from the magnetoresistive elements 6 and 7.

When the signal c is at a high level, the gate switching circuit 55 outputs signals e and f which have a period twice as long as the signal c, and which are at a high level for a certain period when the signal c is at a high level.
Is output, the output voltages of the two magnetoresistive elements 6 and 7 when a predetermined bias magnetic field is applied are applied to the gate 5.
0 and 51 are alternately selected and output to the A / D converter 52.

Next, when the signal b goes high, the gate 42 is turned on during that time, and the voltage V is applied to the bias coil L3.
_ref1 is supplied. A saturation magnetic field is generated in the bias coil L3 by the voltage _Vref1, and a constant voltage is output from the magnetoresistive elements 6, 7.

When the signal b is at the high level, the gate switching circuit 56 outputs the signals h and i, which are at the high level for a certain period when the signal g is at the high level, twice as long as the signal g. The output voltages of the two magnetoresistive elements 6 and 7 when a magnetic field is applied are alternately selected by the gates 53 and 54 and output to the A / D converter 52.

The arithmetic / control unit 57 determines the measurement voltage, that is, the respective magnetic resistance elements 6 and 7 when the bias magnetic field is applied, based on the output voltages of the magnetic resistance elements 6 and 7 when the saturation magnetic field is applied. Output voltage is being corrected. This makes it possible to calculate an accurate azimuth that does not depend on the variation in the output voltage of each of the magnetoresistive elements 6 and 7.

In this case, the dispersion of the output voltages of the magnetoresistive elements 6, 7 is automatically corrected at the time of execution of the arithmetic processing. Therefore, it is necessary to adjust the dispersion of the output voltages of the magnetoresistive elements 6, 7 at the time of manufacturing. In addition, a decrease in accuracy due to aging or the like can be prevented.

In the above embodiment, the dispersion of the output voltages of the magnetoresistive elements 6 and 7 is corrected during the arithmetic processing. For example, the output voltages V _X and V when the magnetoresistive elements 6 and 7 are saturated are corrected. _y is differentially amplified and the constant current circuit 46 or 4
7 may be subjected to negative feedback control to correct variations in output voltages of the two magnetoresistive elements 6 and 7. In this case, since it is not necessary to correct the output voltage of the magnetoresistive element for each measurement cycle, the processing load on the arithmetic / control unit 3 is reduced.

The output of the resistance values 48 and 49 for correcting the output voltages of the magnetoresistive elements 6 and 7 is not collected every cycle, but only at power-on or at regular intervals. Is also good.

Further, the present invention is not limited to the magneto-resistive element having the characteristics described in the embodiment, but may be applied to a magneto-resistive element having a characteristic that the resistance value decreases when the magnetic field becomes strong, or a magnetic sensor other than the magneto-resistive element. The invention is applicable.

Further, the present invention is not limited to a dedicated device for a compass, but can also be incorporated in electronic wristwatches, altimeters and the like, and can also be used for navigation devices for automobiles.

[0064]

According to the present invention, the output of each magnetic sensor is corrected by correcting the output voltage of the magnetic sensor when the external magnetic field is measured by the output of the magnetoresistive element serving as a reference for the plurality of magnetic sensors. Can be corrected. This eliminates the need to adjust the outputs of the plurality of magnetic sensors, and can also prevent variations in outputs due to aging.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a first embodiment.

FIG. 2 is a diagram showing a structure of a magnetoresistive element substrate.

FIG. 3 is a circuit configuration diagram of a detection unit.

FIG. 4 is a time chart illustrating an operation of each unit of the detection unit.

FIG. 5 is a diagram showing a relationship between an output voltage and a magnetic field of the magnetoresistive element of the first embodiment.

FIG. 6 is a circuit configuration diagram of a second embodiment.

FIG. 7 is a time chart showing the operation of each section of the circuit of the second embodiment.

FIG. 8 is a diagram showing a relationship between an output voltage and a magnetic field of the magnetoresistive element of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection part 2 A / D conversion part 3 Operation / control part 5 Display part 6, 7 Magnetoresistive element

Claims (2)

(57) [Claims] A plurality of magnetic sensors; a bias magnetic field applying means for applying a bias magnetic field to the magnetic sensors; and a bias magnetic field which is changed by the bias magnetic field applying means.
Reference value detecting means for detecting an extreme value of the output of the magnetic sensor in a state where the magnetic field is applied, and an output value of the magnetic sensor in a state where the bias magnetic field applying means applies a predetermined bias magnetic field to the reference value. An electronic azimuth meter comprising: correction means for correcting based on a value detected by a detection means; and azimuth calculation means for calculating an azimuth from an output of the magnetic sensor corrected by the correction means. 2. A plurality of magnetic sensors, and a bias for applying a bias magnetic field to these magnetic sensors.
The magnetic sensor is saturated by the magnetic field applying means and the bias magnetic field applying means.
A base for detecting the output value of the magnetic sensor in the sum state
The quasi-value detecting means and the bias magnetic field applying means apply a predetermined bias magnetic field
The output value of the magnetic sensor in the state where
Correction means for correcting based on the value detected by the reference value detection means
From the output of the magnetic sensor corrected by the correction means.
Electronic compass, characterized in that it comprises a bearing calculation means for calculating.