CN109932670B - Closed-loop TMR magnetic field measuring device based on power-on position - Google Patents
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Abstract
A closed-loop TMR magnetic field measuring device based on a power-on set comprises a TMR magnetic sensor, a differential-to-single-ended chip, an integrating circuit, a V/I conversion circuit, an exciting circuit and a feedback lead. The feedback lead is arranged below the TMR magnetic sensor, and a magnetic field generated by the feedback lead is parallel to a sensitive axis of the TMR magnetic sensor; the signal output end of the TMR magnetic sensor is connected with a differential-to-single-ended chip, the differential-to-single-ended chip is connected with an integrating circuit, and the output end of the integrating circuit is connected to a feedback wire after being converted by a V/I conversion circuit to form a closed loop; the V/I conversion circuit comprises a feedback resistor and a feedback resistor, wherein the feedback resistor is used for adjusting the magnitude of feedback current in a closed loop; the feedback lead and the V/I conversion circuit are both connected with the exciting circuit. The device adopts a closed loop structure, and performs magnetic field compensation on the TMR sensor from hardware by designing a feedback wire and arranging the feedback wire under the TMR sensor chip as a setting and feedback element, thereby inhibiting hysteresis of the sensor and improving the sensitivity of the sensor.
Description
Technical Field
The invention relates to the technical field of magnetic field measurement, in particular to a closed-loop TMR magnetic field measuring device based on a power-on position.
Background
The geomagnetic field is a weak vector field, is used as a natural magnetic source existing on the earth surface, has wide application range, and has irreplaceable effect in various fields such as military affairs, aviation and the like. For weak magnetic field measurement, a high-precision magnetic field measurement device is indispensable, and the device is mainly made by taking a magnetic field sensor as a sensitive element and combining a corresponding signal conditioning circuit, so that a proper magnetic field sensor is selected, and a simple and effective signal conditioning circuit is designed to optimize the magnetic field sensor, thereby being an important guarantee for developing a high-performance magnetic field measurement device.
At present, the commonly used magnetic field sensors include Anisotropic Magnetoresistive (AMR) sensors, Giant Magnetoresistive (GMR) sensors, Tunneling Magnetoresistive (TMR) sensors, Giant Magnetoresistive (GMI) sensors, fluxgate sensors, etc., which have respective advantages, but the TMR sensors have great advantages in terms of sensor sensitivity, for example, a sensor manufactured by multidimensional companies and having the model of TMR9001, the sensitivity of which reaches 300mV/V/Oe, is ten times or even tens times higher than that of other sensors. In contrast, a high-sensitivity sensor can output a voltage signal meeting the measurement condition of the circuit without amplifying the signal, so that the introduction of amplifier noise in a traditional signal conditioning circuit can be reduced, and therefore, if a high-precision magnetic field measuring device is designed, the TMR sensor is a good choice as a sensitive element. In practical application, a magnetic field measuring device using a TMR sensor as a sensitive element usually adopts a signal conditioning circuit with an open-loop structure, which has the advantages of small volume, simple structure and the like, but the TMR sensor is made of a magnetic multilayer thin film material, and the characteristics of the material determine that the TMR sensor has large hysteresis, for example, a TMR9001 sensor has hysteresis up to 0.1Oe within a magnetic field range of ± 0.5Oe, which has a great influence on the performance of the magnetic field measuring device designed by using the TMR sensor as a sensitive element, and the signal conditioning circuit with the open-loop structure can only simply process a sensor output signal but cannot solve the hysteresis problem.
Firstly, on the basis of physical or mathematical principles, a corresponding sensor output hysteresis model is established to obtain a local hysteresis curve of the sensor, and then the local hysteresis curve is compensated through an algorithm. And from the internal reason of hysteresis generation, the hysteresis of the sensor is fundamentally reduced by developing a novel sensitive material or the hysteresis is changed by adopting a novel production process, for example, the hysteresis of the material can be changed by finding out different annealing temperatures through research in documents, but the method often causes the loss of other performances of the sensor while reducing the hysteresis of the sensor.
Disclosure of Invention
In order to solve the technical problem, the invention provides a closed-loop TMR magnetic field measuring device based on a power-on setting, which adopts a closed-loop structure, and performs magnetic field compensation on a TMR sensor from hardware by designing a feedback wire and arranging the feedback wire under a TMR sensor chip to be used as a setting and feedback element, thereby inhibiting hysteresis of the sensor and improving the sensitivity of the sensor.
The technical scheme adopted by the invention is as follows:
a closed-loop TMR magnetic field measuring device based on a power-on set comprises a TMR magnetic sensor, a differential-to-single-ended chip, an integrating circuit, a V/I conversion circuit, an exciting circuit and a feedback lead.
The feedback lead is arranged below the TMR magnetic sensor, and a magnetic field generated by the feedback lead is parallel to a sensitive axis of the TMR magnetic sensor;
the signal output end of the TMR magnetic sensor is connected with a differential-to-single-ended chip, the differential-to-single-ended chip is connected with an integrating circuit, and the output end of the integrating circuit is connected to a feedback wire after being converted by a V/I conversion circuit to form a closed loop;
the V/I conversion circuit comprises a feedback resistor and a feedback resistor, wherein the feedback resistor is used for adjusting the magnitude of feedback current in a closed loop;
the feedback lead and the V/I conversion circuit are both connected with the exciting circuit.
The feedback lead is arranged below the TMR magnetic sensor chip in a PCB wiring mode, when the magnetic field measuring device is electrified, a pulse current is given out from the exciting circuit, the TMR magnetic sensor is set, and the output voltage of the TMR magnetic sensor is changed along a fixed output curve.
After the TMR magnetic sensor is electrified and set, a bridge of the TMR magnetic sensor can output a voltage signal which is in direct proportion to an external magnetic field to be measured, the voltage is integrated by an integrating circuit and then outputs an gradually increased integrating voltage, and the integrating voltage is subjected to V/I conversion by a V/I conversion circuit and then can generate a feedback current to be sent to a feedback wire.
The invention discloses a closed-loop TMR magnetic field measuring device based on a power-on position, which has the following technical effects:
1. the TMR sensor is combined, the output curve of the sensor is controlled by using the set pulse generated by the exciting circuit, and the sensor works under a stable zero magnetic field condition through closed-loop feedback, so that the output voltage of the sensor is kept at a zero point, the hysteresis problem of the TMR sensor is effectively inhibited, and the performance of the sensor is improved.
2. The sensitivity is adjustable: the sensitivity of the magnetic field measuring device can be freely adjusted according to the required magnetic field measuring range in practical application by adjusting the resistance value of the feedback resistor R in the V/I conversion circuit, and if the required magnetic field measuring range is very small, the sensitivity of the device can be adjusted to a very large value.
3. The noise performance is good: the TMR sensor with high sensitivity is used as a sensitive element, and the output voltage signal of the TMR sensor can meet the detection requirement of a subsequent circuit, so that a signal amplification circuit is omitted, and the introduction of noise of an amplifier is avoided; the output voltage of the invention is obtained by integrating the integrating circuit, and the integrating circuit can not generate noise; in addition, the invention adopts a closed loop feedback structure, so that the sensitivity of the output voltage of the device is irrelevant to the sensitivity of the sensor, and is determined by the resistance value of the feedback resistor, therefore, when the sensitivity of the device is very high, the actual noise is very small after conversion, for example: assuming that the input noise of the magnetic field measuring device is
Then the theoretical noise power spectral density is 50 muV/nT
When the sensitivity is set to 100 muV/nT, the theoretical noise power spectral density is
Drawings
The invention is further illustrated by the following figures and examples.
Fig. 1 is a layout of the feedback element of the present invention.
Fig. 2 is an overall structural view of the present invention.
FIG. 3 is a schematic diagram of the V/I conversion circuit of the present invention.
FIG. 4(1) is a schematic diagram of the operation of the sensor according to the present invention when the sensor is subjected to a set pulse (before set);
fig. 4(2) is a schematic diagram of the operation of the sensor (after setting) when receiving the set pulse.
Detailed Description
A closed-loop TMR magnetic field measuring device based on a power-on set comprises a TMR magnetic sensor 1, a differential-to-single-ended chip 2, an integrating circuit 3, a V/I conversion circuit 4, an exciting circuit 5 and a feedback lead 6.
The feedback wire 6 is arranged below the TMR magnetic sensor 1, and the magnetic field generated by the feedback wire 6 is parallel to the sensitive axis of the TMR magnetic sensor 1. The direction of the sensitive axis of the magnetic core of the TMR magnetic sensor 1 is found out before wiring, and then the TMR magnetic sensor is arranged around the sensitive axis, so that the feedback lead 6 is parallel to the sensitive axis, and the direction of the magnetic field generated in the feedback lead is opposite to the direction of the external magnetic field borne by the sensitive axis. When the feedback current is input into the feedback wire, a feedback magnetic field is generated in the feedback wire, and because the feedback wire is parallel to the sensitive shaft during wiring and the direction of the magnetic field generated in the feedback wire is opposite to the direction of the external magnetic field applied to the sensitive shaft, the magnetic field generated in the feedback wire can be offset with the external magnetic field applied to the sensitive shaft, so that the compensation effect is achieved, and the magnetic core of the sensor works in a zero field.
The signal output end of the TMR magneto-dependent sensor 1 is connected with a differential-to-single-ended chip 2, the differential-to-single-ended chip 2 is connected with an integrating circuit 3, and the output end of the integrating circuit 3 is connected to a feedback wire 6 after being converted by a V/I conversion circuit 4 to form a closed loop;
the V/I conversion circuit 4 includes a feedback resistor 7 for adjusting the magnitude of the feedback current in the closed loop.
The feedback lead 6 and the V/I conversion circuit 4 are both connected with the excitation circuit 5.
The TMR magneto-dependent sensor 1 is a sensor which is produced by Jiangsu multidimensional technology and technology limited and has the model of TMR9001, the chip has lower background noise, and the sensitivity reaches 300 mV/V/Oe.
The differential-to-single-ended chip 2 is a differential amplifier chip with the model number of AD 620.
The integrating circuit 3 consists of an input operational amplifier chip of type OPA4130 UA.
The exciting circuit 5 is composed of a constant current source chip with the model number of REF 200.
The resistance value of the feedback resistor 7 can be adjusted according to the use requirement, and when the required measuring range is +/-100000 nT, the resistance value of the resistor can be set to be 50 omega; when the required range is 500000nT, the resistance value of the resistor can be set to 100 omega.
The feedback lead 6 is arranged under the TMR magnetic sensor 1 chip in a PCB wiring mode, when the magnetic field measuring device is electrified, a pulse current is given out from the exciting circuit 5, the TMR magnetic sensor 1 is set, and the output voltage of the TMR magnetic sensor 1 is changed along a fixed output curve.
After the TMR magnetic sensor 1 is electrified and set, a bridge of the TMR magnetic sensor 1 can output a voltage signal which is in direct proportion to an external magnetic field to be measured, the voltage is integrated by the integrating circuit 3 and then outputs an gradually increased integrating voltage, and the integrating voltage is subjected to V/I conversion by the V/I conversion circuit 4 and then can generate a feedback current to be sent to the feedback wire 6.
The V/I conversion circuit 4 comprises an operational amplifier U1, an operational amplifier U2 and a feedback resistor 7, one end of a feedback wire 6 is connected with one end of the feedback resistor 7 and the non-inverting input end of the operational amplifier U1, the inverting input end of the operational amplifier U1 is connected with the output end of the operational amplifier U1, the output end of the operational amplifier U1 is connected with one end of a resistor R1, the other end of the resistor R1 is connected with the non-inverting input end of the operational amplifier U2 and one end of a resistor R2, the inverting input end of the operational amplifier U2 is connected with one end of a resistor R3 and the other end of a resistor R4, and one end of a; the other end of the feedback wire 6 is grounded, the other end of the resistor R3 is grounded, and the other end of the resistor R2 is connected with the integrating circuit 3.
The exciting circuit 5 is a monostable circuit and is used for generating a setting pulse to form a power-on setting circuit, the circuit can generate a setting pulse when being powered on every time, the setting pulse acts on the feedback lead 6 to generate a strong magnetic field to excite the TMR magneto-dependent sensor 1, and therefore the output of the TMR magneto-dependent sensor is kept on a fixed magnetic hysteresis loop.
The magnetic field measuring device controls the magnitude of the feedback current in the closed-loop circuit by setting the magnitude of the resistance value of the feedback resistor 7 in the V/I conversion circuit 4. The conversion process is as follows:
the TMR magnetic sensor 1 outputs a voltage signal which is converted into a single-ended chip 2 through a difference circuit and integrated by an integrating circuit 3, and then an integrating voltage U is output0The voltage is converted by V/I to generate a feedback current I, and the magnitude of the feedback current I is as follows:
After the magnetic field measuring device is set, the sensor bridge outputs a voltage signal which is in direct proportion to an external magnetic field to be measured, the voltage outputs an integrated voltage which is gradually increased after being integrated, and the integrated voltage can generate a feedback current to act on the feedback wire 6 after being subjected to V/I conversion. When the current outputted by the V/I conversion circuit 4 is introduced into the feedback wire 6, a feedback magnetic field B is generated in the feedback wire 6IThe formula is as follows:
in the formula, B is the compensating magnetic field intensity generated by the band-pass electrification of the bias current; mu is vacuum magnetic conductivity; i is a feedback current; r is the distance from a point in space to the bias current band. The magnetic field can be gradually offset with an external magnetic field to be measured, meanwhile, the integral output voltage is gradually increased until saturation, when the integral output voltage reaches a saturation point, the feedback magnetic field and the external magnetic field to be measured are completely offset, and at the moment, the sensor works in a zero field. Therefore, the sensor works in a stable magnetic field environment, so that the hysteresis generated by the sensor under the change of the external magnetic field environment is greatly reduced.
The output voltage sensitivity of the magnetic field measuring device can be adjusted by changing the size of the feedback resistor 7 in the V/I conversion circuit 4, but the corresponding range of the magnetic field measuring device can be reduced while the output voltage sensitivity of the magnetic field measuring device is improved. Because the magnetic field measuring device is of a closed loop structure and adopts integral feedback, the voltage finally output by the magnetic field measuring device is generated by the integral circuit 3, the voltage magnitude is independent of the sensitivity of the TMR magnetic sensor 1, and the actual output voltage sensitivity can be changed by adjusting the feedback resistor 7 in the V/I conversion circuit 4, and the principle is as follows:
the magnetic field measuring range of the magnetic field measuring device designed by the invention is assumed to be +/-50000 nT, the corresponding output voltage is +/-2.5V, and the constant of the feedback wire is 50 mA/GS. The actual voltage sensitivity of the magnetic field measuring device is obtained to be SN＝2.5V/50000nT＝50μV/nT。
In the feedback circuit, the feedback magnetic field generated by the feedback wire is: b isII/k. Wherein B isIFor the feedback magnetic field, I is the feedback current generated by the V/I conversion circuit, and k is the coil constant of the feedback wire designed by the invention. After V/I conversion, the feedback current can be expressed as: i ═ V0R, wherein V0To integrate the output voltage, R is the feedback resistance in the V/I conversion circuit. From which an integral voltage V can be derived0And a feedback magnetic field BIThe relation of (1): v0＝k·R·BI. Because the device adopts a closed loop structure, when the circuit is balanced, the sensor works in a zero magnetic field, namely BI＝BXThe actual sensitivity of the magnetic field measurement device is therefore: sNSince the feedback line constant k is a constant value, the sensitivity of the signal conditioning circuit can be adjusted by changing the resistance value of the feedback resistor R. However, increasing the resistance R increases the output voltage sensitivity of the conditioning circuit, but the output range also decreases, for example, when R is 100 Ω, the calculated voltage sensitivity is 50 μ V/nT, and the corresponding range is ± 50000 nT; when R is 200 Ω, the voltage sensitivity can reach 100 μ V/nT, but the range is only ± 25000 nT.
The implementation steps are as follows:
(1): the feedback elements are arranged, as shown in fig. 1, the feedback wire 6 is placed at the bottom of the chip of the TMR magneto sensor 1, and the direction of the magnetic field of the feedback wire 6 is parallel to the direction of the sensitive axis of the TMR magneto sensor 1.
(2): the signal output end of the TMR magnetic sensor 1 is connected with the input end of the differential-to-single-ended chip 2, and the differential signal output by the TMR magnetic sensor 1 is converted into a single-ended signal through the module and then output.
(3): the output end of the differential-to-single-ended chip 2 is connected with the input end of the integrating circuit 3, and the integrating circuit 3 is used for carrying out integration operation on the output signal, so that the signal output amplitude is improved.
(4): the output of the integrating circuit 3 is connected to the input of the V/I conversion circuit 4. The integrated output voltage is processed using a V/I conversion circuit 4 by which the circuit output voltage is converted to a feedback current and input to a feedback conductor 6.
(5): and a drive circuit 5 consisting of a monostable circuit is connected with a feedback lead 6 to form an electrifying setting circuit. When the equipment is powered on, the feedback wire 6 generates a strong magnetic field after being subjected to a pulse signal sent by the excitation circuit, and a voltage output curve of the TMR magnetic sensor 1 is excited by the strong magnetic field to work on a hysteresis loop, as shown in FIG. 4.
(6): the input of the V/I conversion circuit 4 is connected to a feedback conductor 6. The feedback lead 6 is used to generate a compensation magnetic field to compensate the external magnetic field to which the TMR magneto sensor 1 is subjected. After the feedback current flows into the feedback wire 6, a compensation magnetic field is generated around the wire, the magnetic field is equal to the external magnetic field borne by the TMR magnetic sensor 1 in magnitude and opposite in direction, so that the compensation magnetic field can be offset with the external magnetic field, the sensor works in a stable magnetic field environment, and hysteresis generated by the sensor under the change of the external magnetic field environment is greatly reduced.
Claims (1)
1. A closed-loop TMR magnetic field measuring device based on a power-on set comprises a TMR magnetic sensor (1), a differential-to-single-ended chip (2), an integrating circuit (3), a V/I conversion circuit (4), an excitation circuit (5) and a feedback wire (6); the method is characterized in that:
the feedback lead (6) is arranged below the TMR magnetic sensor (1), and a magnetic field generated by the feedback lead (6) is parallel to a sensitive axis of the TMR magnetic sensor (1);
the signal output end of the TMR magnetic sensor (1) is connected with a differential-to-single-ended chip (2), the differential-to-single-ended chip (2) is connected with an integrating circuit (3), and the output end of the integrating circuit (3) is connected to a feedback wire (6) after being converted by a V/I conversion circuit (4) to form a closed loop;
the V/I conversion circuit (4) comprises a feedback resistor (7) for adjusting the magnitude of feedback current in a closed loop;
the feedback lead (6) and the V/I conversion circuit (4) are both connected with the exciting circuit (5);
the closed-loop TMR magnetic field measurement method comprises the following steps:
1): the feedback lead (6) is placed at the bottom of the chip of the TMR magneto-dependent sensor (1), and the direction of the magnetic field of the feedback lead (6) is parallel to the direction of the sensitive axis of the TMR magneto-dependent sensor (1);
2): connecting a signal output end of the TMR magneto-dependent sensor (1) with an input end of a differential-to-single-ended chip (2), and converting a differential signal output by the TMR magneto-dependent sensor (1) into a single-ended signal through the differential-to-single-ended chip (2) and outputting the single-ended signal;
3): the output end of the differential-to-single-ended chip (2) is connected with the input end of the integrating circuit (3), and the integrating circuit (3) is used for carrying out integration operation on the output signal, so that the signal output amplitude is increased;
4): the output end of the integrating circuit (3) is connected with the input end of the V/I conversion circuit (4); the voltage output after integration is processed by a V/I conversion circuit (4), and the circuit output voltage can be converted into feedback current and input into a feedback wire (6) through the circuit;
5): connecting an excitation circuit (5) consisting of a monostable circuit with a feedback wire (6) to form an electrifying setting circuit; when the equipment is electrified, the feedback lead (6) generates a strong magnetic field after receiving a pulse signal sent by the excitation circuit, the voltage output curve of the TMR magnetic sensor (1) is excited by the strong magnetic field to work on a hysteresis loop,
6): the output end of the V/I conversion circuit (4) is connected with a feedback lead (6), and the feedback lead (6) is used for generating a compensation magnetic field to compensate the external magnetic field borne by the TMR magnetic sensor (1); after the feedback current flows into the feedback lead (6), a compensation magnetic field is generated around the lead, the magnetic field is equal to the external magnetic field borne by the TMR magnetic sensor (1) in magnitude and opposite in direction, and therefore the compensation magnetic field can be offset with the external magnetic field, and the sensor works in a stable magnetic field environment.
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