WO2015172530A1

WO2015172530A1 - Interference elimination method for electronic compass

Info

Publication number: WO2015172530A1
Application number: PCT/CN2014/090071
Authority: WO
Inventors: 张绍磊; 童向杰; 刘玉鹏
Original assignee: 中兴通讯股份有限公司
Priority date: 2014-05-12
Filing date: 2014-10-31
Publication date: 2015-11-19
Also published as: CN105091872B; CN105091872A

Abstract

An interference elimination method for an electronic compass, comprising the following steps: 1. Checking an interference current in the PCB wiring of a terminal in real time after calibrating a geomagnetic sensor; 2. if the interference current is detected, then utilizing the current value of the interference current to obtain a geomagnetic data compensation value; 3. utilizing the geomagnetic data compensation value to compensate the geomagnetic data outputted by the geomagnetic sensor so as to obtain the geomagnetic data with the interference current eliminated. Also disclosed is an interference elimination device of the electronic compass. The interference elimination method and device of the electronic compass avoid the interference of large-current PCB wiring with the geomagnetic sensor.

Description

Electronic compass elimination interference method

Technical field

The present invention relates to electronic compass technology, and more particularly to a method for eliminating interference by an electronic compass.

Background technique

Geomagnetic sensors can be used for electronic compass functions, assisted navigation and other applications. With the continuous development of microelectronic integration technology and processing technology and material technology, the research, manufacture and application of geomagnetic sensors have reached an unprecedented level. At present, geomagnetic sensors can be divided into planar electronic compasses and three-dimensional electronic compasses according to the presence or absence of tilt compensation. They can also be divided into magnetoresistance effect sensors, Hall effect sensors and fluxgate sensors according to different sensors. Magnetoresistive sensors have been fabricated on silicon wafers to form products. The geomagnetic sensor for mobile phones is mainly a magnetoresistive effect sensor. The magnetoresistance effect sensor is made based on the magnetoresistance effect of the magnetic material. A magnetic material (such as permalloy) has an anisotropy, and when it is magnetized, its magnetization direction will depend on the axis of easy magnetization of the material, the shape of the material, and the direction of the magnetizing magnetic field. As shown, when the current is given to the banded permalloy material, the electrical resistance of the material depends on the angle between the direction of the current and the direction of magnetization. If a magnetic field (the measured magnetic field) is applied to the material, the original magnetization direction is rotated. If the direction of magnetization turns in a direction perpendicular to the current, the resistance of the material will decrease; if the direction of magnetization turns parallel to the direction of the current, the resistance of the material will increase. Magnetoresistive effect sensors typically have four such resistors and connect them into a bridge. Under the action of the measured magnetic field, the resistance values of the two resistors located at opposite positions in the bridge increase, and the resistance values of the other two resistors decrease. In its linear range, the output voltage of the bridge is proportional to the measured magnetic field.

Many smart phones now have an electronic compass function. The electronic compass mainly calculates the direction of the magnetic north pole by sensing the existence of the earth's magnetic field. However, since the earth's magnetic field is generally only a weak 0.5 Gauss, an ordinary mobile phone horn will still have a magnetic field of about 4 gauss when it is 2 cm apart. A mobile phone motor will have a magnetic field of about 6 gauss when it is 2 cm apart. This feature makes electronic devices' measurement of the magnetic field on the earth's surface very susceptible to interference from electronic devices, such as earpieces, speakers, metal sheets, vibration motors, NFC antennas, and high current traces. The interference of the earpiece, the horn, the metal piece, the vibration motor and the NFC antenna can be circumvented by the fixed compensation method, and the large current flowing in the power supply trace of the PCB is changed in real time, and cannot be circumvented by the fixed compensation method, so the mobile phone The geomagnetic needle sensor will be placed away from the power supply wiring. For example, the safety distance of the 1A power cable is 1000 (mA)/10=100 (mm). Under the trend that mobile phone motherboards are getting smaller and smaller, and the functions are more and more complicated, this condition is difficult to meet. The invention mainly aims to avoid the interference of the high current PCB trace to the geomagnetic sensor through the software and hardware method.

Summary of the invention

It is an object of the present invention to provide a method of eliminating varying current disturbances in real time as large and constantly varying current flows around the local magnetic sensor are disturbed.

The solution to solve the above problems of the present invention includes the following steps:

Find the correction coefficient of geomagnetic interference by experiment, or make a correction database;

Calibrate the geomagnetic sensor. When the calibration current exists, if the interference current exists, measure the magnitude of the interference current. Calculate the correction coefficient or find the correction data of the three axes. Obtain the magnetic data compensation values of X, Y and Z for the geomagnetic sensor output data. Make correction, then jump to step 3; if the interference current does not exist, jump directly to step 3;

Obtain geomagnetic calibration data without interference current;

After calibration, the geomagnetic sensor enters normal operation. If there is interference current, go to step 5; if there is no interference current, directly output geomagnetic data;

The detection circuit detects the magnitude of the interference current in real time, calculates or searches the correction database according to the correction coefficient to obtain the compensation values of the three magnetic axes of the geomagnetic sensor in X, Y, and Z, and uses the obtained compensation value to correct the data output by the geomagnetic sensor, and then outputs the data. Geomagnetic data.

The electronic compass elimination interference method embodying the invention has the following beneficial effects: the real-time detection is used to obtain the magnitude of the interference current, and the geomagnetic sensor data pair is corrected, thereby overcoming the interference of the changed current on the electronic compass, so that the pointing of the electronic compass is more To be accurate, at the same time, the position of the geomagnetic sensor on the PCB is more flexible.

DRAWINGS

The invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a hardware circuit intent of the present invention;

2 is a flow chart of an electronic compass elimination interference method.

detailed description

The invention will be described in detail below with reference to the drawings and specific embodiments.

As shown in FIG. 1 , it is a method for obtaining a PCB trace current in the present invention. Connect a milliohm-level power resistor in the PCB trace, and draw the differential trace from both ends of the resistor to the ADC1 and AD2 of the ADC module to obtain the voltage difference across the resistor. Calculate the current according to the formula: current=voltage/resistance. value.

In order to eliminate the interference caused by these large currents, the present invention provides an electronic compass cancellation interference method as shown in FIG. 2. Specific steps are as follows:

1. Calibrate the geomagnetic sensor and detect whether there is interference current present;

2. If the interference current exists, the current value is Ia (see Figure 1 for current acquisition method), go to step 3; if the interference current does not exist, go to step 4;

3. Calculate the correction coefficient or obtain the correction data of the three axes of X, Y and Z by the correction coefficient T1, T2, T3, and correct the geomagnetic output data;

4. Complete the geomagnetic sensor calibration and the geomagnetic sensor begins to work normally;

5. If there is interference current Ib, go to step 6; if there is no interference current, jump directly to step 9;

6. Real-time detection of the magnitude of the interference current Ib by the detection circuit;

7. Calculated by the correction coefficient or by looking up the correction database, the magnetic data correction values T1', T2', T3' of the X, Y, Z axes are obtained;

8. Using the correction values T1', T2', T3' obtained in step 7, correcting the raw data output by the geomagnetic sensor;

9. Output geomagnetic data;

If you continue to output geomagnetic data, go to step 5; otherwise, end the data output.

Industrial applicability

As described above, the method for eliminating interference by the electronic compass provided by the embodiment of the present invention has the following beneficial effects: the real-time detection is used to obtain the magnitude of the interference current, and the geomagnetic sensor data pair is corrected to overcome the interference of the changed current on the electronic compass. The orientation of the electronic compass is more accurate, and the position of the geomagnetic sensor on the PCB is more flexible.

Claims

A method of calibrating an electronic compass, comprising:

Detecting interference current in the terminal PCB trace;

If an interference current is detected, the ground magnetic data compensation value is obtained by using the current value of the interference current;

Using the geomagnetic data compensation value, the geomagnetic data output by the geomagnetic sensor is compensated to obtain geomagnetic data for eliminating current interference;

Using the geomagnetic data from which current interference has been eliminated, calibration data that has eliminated current interference is obtained.
The method of claim 1 wherein said step of detecting an interference current in a terminal PCB trace comprises:

Collecting voltage values across the sense resistors connected in series with the terminal PCB traces;

The current value of the interference current in the terminal PCB trace is obtained by using the voltage value across the sense resistor and the resistance value of the sense resistor.
The method according to claim 1 or 2, wherein said step of obtaining a geomagnetic data compensation value using said current value of said interference current comprises:

The geomagnetic data compensation value is calculated by using the current value of the interference current and the pre-stored geomagnetic interference correction coefficient, or the geomagnetic data compensation value corresponding to the current value is found by searching the pre-stored correction database.
An electronic compass for eliminating interference includes:

After the geomagnetic sensor is calibrated by the method according to any one of claims 1 to 3, the interference current in the terminal PCB trace is detected in real time;

If an interference current is detected, the ground magnetic data compensation value is obtained by using the current value of the interference current;

The geomagnetism data outputted by the geomagnetic sensor is compensated by the geomagnetic data compensation value to obtain geomagnetic data for eliminating current interference.
The method according to claim 4, wherein said step of detecting the interference current in the terminal PCB trace in real time comprises:

Collecting voltage values across the sense resistors connected in series with the terminal PCB traces;

The current value of the interference current in the terminal PCB trace is obtained by using the voltage value across the sense resistor and the resistance value of the sense resistor.
The method according to claim 4 or 5, wherein said step of obtaining a geomagnetic data compensation value using said current value of said interference current comprises:

The geomagnetic data compensation value is calculated by using the current value of the interference current and the pre-stored geomagnetic interference correction coefficient, or the geomagnetic data compensation value corresponding to the current value is found by searching the pre-stored correction database.
A calibration device for an electronic compass, comprising:

a first detecting module configured to detect an interference current in a terminal PCB trace;

a first compensation value acquisition module is configured to obtain a geomagnetic data compensation value by using a current value of the interference current if an interference current is detected;

The first compensation module is configured to perform compensation processing on the geomagnetic data output by the geomagnetic sensor by using the geomagnetic data compensation value to obtain geomagnetic data for eliminating current interference;

A calibration module is configured to utilize the geomagnetic data from which the current interference has been removed to obtain calibration data that has eliminated current interference.
The device according to claim 7, wherein the first detecting module collects a voltage value across the detecting resistor connected in series in the terminal PCB trace, and utilizes a voltage value across the detecting resistor and a resistance of the detecting resistor The value of the current of the interference current in the terminal PCB trace is obtained.
The apparatus according to claim 7 or 8, wherein the first compensation value acquisition module calculates a geomagnetic data compensation value by using a current value of the interference current and a pre-stored geomagnetic interference correction coefficient, or by searching for a pre-stored correction The database finds a geomagnetic data compensation value corresponding to the current value.
An electronic compass device for eliminating interference, comprising:

a second detecting module configured to detect the interference current in the terminal PCB trace in real time after calibrating the geomagnetic sensor by using the device according to any one of claims 7 to 9;

a second compensation value acquisition module is configured to obtain a geomagnetic data compensation value by using a current value of the interference current if an interference current is detected;

The second compensation module is configured to perform compensation processing on the geomagnetism data output by the geomagnetic sensor by using the geomagnetic data compensation value to obtain geomagnetic data for eliminating current interference.
The device according to claim 10, wherein the second detecting module collects a voltage value across the detecting resistor connected in series in the terminal PCB trace, and utilizes a voltage value across the detecting resistor and a resistance of the detecting resistor The value of the current of the interference current in the terminal PCB trace is obtained.
The apparatus according to claim 10 or 11, wherein said second compensation value acquisition module calculates a geomagnetic data compensation value by using a current value of said interference current and a pre-stored geomagnetic interference correction coefficient, or by searching for a pre-stored correction The database finds a geomagnetic data compensation value corresponding to the current value.