CN114779132A - Digital GMI sensor and signal processing method thereof - Google Patents
Digital GMI sensor and signal processing method thereof Download PDFInfo
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- CN114779132A CN114779132A CN202210451708.3A CN202210451708A CN114779132A CN 114779132 A CN114779132 A CN 114779132A CN 202210451708 A CN202210451708 A CN 202210451708A CN 114779132 A CN114779132 A CN 114779132A
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
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- G01R33/063—Magneto-impedance sensors; Nanocristallin sensors
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Abstract
The invention discloses a digital GMI sensor and a signal processing method thereof, wherein the digital GMI sensor comprises a GMI unit, an analog-to-digital conversion unit and a processing unit, wherein the GMI unit is used for inducing an external magnetic field and generating an analog output signal under the action of an excitation signal; the analog-to-digital conversion unit is used for converting the analog output signal into a digital signal; and the processing unit is used for multiplying the equidirectional reference signal and the orthogonal reference signal with the digital signal respectively to generate an equidirectional output signal and an orthogonal output signal, squaring and then squaring the equidirectional output signal and the orthogonal output signal to generate a voltage signal. The invention adopts a digital signal processing method to replace an analog circuit for conditioning, has larger detection frequency range of the sensor, can reduce the temperature drift and zero drift effects of the sensor, and increases the linearity; due to the adoption of a digital interface and digital conditioning, the system has the advantages of stable performance, flexible programming, high response speed and the like.
Description
Technical Field
The invention belongs to the technical field of weak magnetic field detection sensors, and particularly relates to a digital GMI sensor and a signal processing method thereof.
Background
The information acquisition becomes an indispensable important part for social development, and simultaneously drives the rapid development of the related information acquisition technology (sensor technology). With the further popularization and use of computer applications and networks, various electronic components tend to be developed toward integration, automation, intellectualization, networking and the like, and especially, the design of sensors is more biased toward the requirements of miniaturization, low power consumption and high sensitivity.
As an important component of a sensor family, magnetic sensors have played an indispensable role in human life, and there are many types of magnetic sensors based on different principles, including a detection coil, a hall element, a magnetoresistance effect device, a giant magneto-impedance device, a flux gate magnetometer, a superconducting quantum interferometer, and the like. The GMI effect has a series of advantages of high sensitivity, no magnetic hysteresis, good stability and the like, and the novel magnetic sensor manufactured by using the GMI effect has the advantages which cannot be compared with various magnetic sensors widely applied at present.
For GMI (giant magneto-impedance effect) magnetic sensors, a CMOS (Complementary Metal Oxide Semiconductor) gate circuit is generally used to form an oscillator to generate a voltage signal, and a circuit is used to convert the voltage oscillation signal into a current signal to excite a GMI material, as shown in fig. 1, when an external magnetic field changes, the impedance characteristic of the GMI material changes with the magnetic field, and the response voltage at two ends of a detection material can be converted into the magnitude of the external magnetic field under the condition that the excitation signal is input, and an amplitude detector is generally used to complete the operation, wherein the output signal of the amplitude detector is the output signal of the magnetic field sensor.
Because GMI effect is the characteristic exhibited by high-frequency current signals passing through sensitive materials, a high-performance conditioning scheme is required to be used for demodulating response signals in a GMI probe in order to obtain high-precision magnetic signals, but because a conditioning circuit of the GMI sensor is complex, the prepared sensor cannot reach theoretical sensitivity, and meanwhile, because an analog device is used for building the conditioning circuit, the output of the sensor is greatly influenced by the characteristics of noise, nonlinearity, temperature drift and the like of analog circuit components.
In the GMI signal conditioning circuit constructed by the analog circuit shown in fig. 2, the switching characteristics of the transistor are mainly used to realize the functions of phase-sensitive detection, including multiplication, detection, and the like. The analog phase-sensitive detection algorithm principle is simple and easy to implement, but the influence caused by the factors such as the voltage drop of the triode in the measurement process is not negligible compared with the measured signal, and in addition, the triode can introduce certain other noises, so that the useless and useful signals are not thoroughly separated, and the factors seriously influence the resolution ratio and the measurement precision of the instrument.
In summary, the current analog demodulation type GMI magnetic field measurement sensor mainly has the following two defects: the analog conditioning circuit has a complex structure and high working frequency, the heating of components can cause the problems of temperature drift, null drift and the like, and the output of the sensor is greatly influenced by the components of the demodulation circuit; the analog type conditioning circuit has a plurality of noise coupling points, the output is analog quantity, and the sensor is limited to be used in an environment with digital quantity requirements due to a signal output mode.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a digital GMI sensor based on orthogonal locking amplification, and aims to improve the linearity of the GMI magnetic field measuring sensor during measurement, reduce the temperature drift and null drift effects and enlarge the application range of the sensor.
In order to achieve the purpose, the invention provides the following technical scheme:
a digital GMI sensor comprising a GMI unit, an analog-to-digital conversion unit, and a processing unit,
the GMI unit is used for inducing an external magnetic field under the action of an excitation signal and generating an analog output signal;
the analog-to-digital conversion unit is used for converting the analog output signal into a digital signal;
and the processing unit is used for multiplying the equidirectional reference signal and the orthogonal reference signal with the digital signal respectively to generate an equidirectional output signal and an orthogonal output signal, and squaring and adding the quadrate output signal and the orthogonal output signal and squaring to generate a voltage signal.
Specifically, the processing unit includes a numerically controlled oscillator, a first multiplication unit, a second multiplication unit, a first digital low-pass filtering unit, a second digital low-pass filtering unit, and a square sum processing unit,
the digital controlled oscillator is used for generating the cocurrent reference signal and the orthogonal reference signal;
the first multiplication unit is used for multiplying the equidirectional reference signal and the digital signal;
the second multiplication unit is used for multiplying the orthogonal reference signal and the digital signal;
the first digital low-pass filtering unit is used for extracting direct current quantity obtained by multiplying the equidirectional reference signal and the digital signal;
the second digital low-pass filtering unit is used for extracting direct current quantity obtained after multiplication of the orthogonal reference signal and the digital signal;
and the square sum processing unit is used for summing after the direct current quantity square operation of the first digital low-pass filtering unit and the second digital low-pass filtering unit, and then squaring to obtain the digital quantity amplitude of the modulation signal.
Specifically, the cocurrent reference signal and the orthogonal reference signal are digital sinusoidal signals which are orthogonal signed numbers, and the frequency of the digital sinusoidal signals is consistent with that of the digital signals.
Specifically, the processing unit is connected to the digital-to-analog conversion unit, and is configured to convert the voltage signal into an analog voltage signal;
specifically, the first digital low-pass filtering unit and the second digital low-pass filtering unit are both digital FIR filters.
In particular, the processing unit further comprises an excitation circuit, wherein,
the excitation circuit is used for generating an excitation signal for exciting the GMI unit;
the excitation signal is a sinusoidal signal or a narrow pulse signal.
Specifically, the excitation circuit includes an accumulator register, a waveform data look-up table, a synchronization register, a D/a converter, and a voltage-to-current converter, wherein,
the accumulation register is used for outputting an accumulation result as an address line of the waveform data lookup table;
the waveform data lookup table is used for outputting corresponding waveform data according to the address line;
the synchronous register is used for storing the waveform data and outputting a waveform signal with continuous period;
the D/A converter is used for converting the waveform signal of the output continuous period into an analog voltage excitation signal;
the voltage-current converter is used for converting the voltage excitation signal into a current excitation signal.
Specifically, the GMI unit comprises a GMI element, a bias power supply, a current limiting resistor, a bias coil, a low pass filter and a low noise amplifier, wherein,
the bias power supply is connected to the bias coil after passing through the current-limiting resistor to provide a bias magnetic field for the GMI element, and the bias power supply is used for controlling the magnitude of the bias magnetic field by changing the magnitude of the current-limiting resistor;
the GMI element is connected with the low-pass filter and the low-noise amplifier in turn.
Specifically, the GMI element is an amorphous soft magnetic thin strip material.
A method of signal processing for a digital GMI sensor, the method comprising the steps of:
the GMI unit generates an analog output signal according to the excitation signal;
the analog output signal is converted into a digital signal through an analog-to-digital conversion unit;
the processing unit sends out a syntropy reference signal and an orthogonal reference signal, and the syntropy reference signal and the orthogonal reference signal are respectively multiplied with the digital signal to generate a syntropy output signal and an orthogonal output signal, and the syntropy output signal and the orthogonal output signal are squared and squared to generate a voltage signal.
Specifically, the processing unit sends out a syntropy reference signal and a quadrature reference signal, and performs multiplication operation with the digital signal respectively to generate a syntropy output signal and a quadrature output signal, and performs square sum operation and square opening on the syntropy output signal and the quadrature output signal to generate a voltage signal, specifically,
a digital controlled oscillator generating the co-directional reference signal and a quadrature reference signal;
a first multiplication unit configured to multiply the homodromous reference signal and the digital signal;
a second multiplication unit configured to multiply the orthogonal reference signal and the digital signal;
the first digital low-pass filtering unit is used for extracting direct current quantity obtained by multiplying the homodromous reference signal by the digital signal;
the second digital low-pass filtering unit extracts the direct current quantity obtained by multiplying the orthogonal reference signal by the digital signal;
and the square sum processing unit sums the direct current quantity square operation of the first digital low-pass filtering unit and the second digital low-pass filtering unit and then performs square opening to obtain a voltage signal.
Specifically, the cocurrent reference signal and the orthogonal reference signal are orthogonal sine signals with signed numbers, and the frequency of the signals is consistent with the digital signals.
Specifically, the equidirectional component output signal converts an equidirectional component output digital signal into an analog equidirectional component voltage signal through an analog-digital unit;
and the quadrature component output signal converts a quadrature component output digital signal into an analog quadrature component voltage signal through an analog-to-digital unit.
Specifically, the first digital low-pass filtering unit and the second digital low-pass filtering unit are both digital FIR filters.
In particular, the processing unit further comprises an excitation circuit, wherein,
the excitation circuit generates an excitation signal for exciting the GMI unit, wherein the excitation signal is a sinusoidal signal or a narrow pulse signal.
Specifically, the excitation circuit generates an excitation signal for exciting the GMI unit, and specifically, the accumulation register outputs an accumulation result as an address line of the waveform data lookup table;
the waveform data lookup table outputs corresponding waveform data according to the address line;
the synchronous register stores the waveform data and outputs a waveform signal with continuous periods;
the D/A converter converts the waveform signal of the output continuous period into an analog voltage excitation signal;
the voltage-current converter converts the voltage excitation signal into a current excitation signal.
Specifically, the current excitation signal sequentially enters a low-pass filter and a low-noise amplifier through a GMI element to obtain an analog output signal, wherein a bias power supply is connected to a bias coil to provide a bias magnetic field for the GMI element after passing through a current-limiting resistor, and the magnitude of the bias magnetic field is controlled by controlling the magnitude of the current-limiting resistor. The invention has the technical effects and advantages that:
the digital GMI sensor based on orthogonal locking amplification adopts a digital signal processing method to replace an analog circuit for conditioning, has a larger detection frequency range, can reduce the temperature drift and null drift effects of the sensor and increase the linearity; due to the adoption of the digital interface, the application range of the sensor is further expanded.
The analog voltage quantity is directly output, and meanwhile, due to the programmable characteristic of the FPGA, relevant adjustment CAN be performed according to a digital interface of a user, wherein the relevant adjustment includes but is not limited to IIC, SPI, CAN bus, private protocol bus and the like, and the application range is wider compared with that of an analog sensor.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
FIG. 1 is a graph of the rate of change of impedance of a GMI material of the present invention as a function of magnetic field magnitude at 5MHz excitation;
FIG. 2 is a block diagram of a demodulation architecture for a typical diagonal GMI sensor;
FIG. 3 is a block diagram of a digital GMI sensor according to the present invention;
FIG. 4 is a schematic diagram of digital GMI sensor excitation signal generation according to the present invention;
fig. 5 is a graph of the output characteristics of the digital GMI sensor of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
In order to solve the defects of the prior art, the invention discloses a digital GMI sensor and a signal processing method thereof, the digital GMI sensor comprises a GMI unit, an analog-to-digital conversion unit, a processing unit and a digital-to-analog conversion unit, wherein,
the GMI unit is used for inducing an external magnetic field under the action of an excitation signal and generating an analog output signal; the GMI unit comprises a GMI element, a bias power supply, a current-limiting resistor, a bias coil, a low-pass filter and a low-noise amplifier, wherein the bias power supply is connected to the bias coil after passing through the current-limiting resistor to provide a bias magnetic field for the GMI element and is used for controlling the magnitude of the bias magnetic field by changing the magnitude of the current-limiting resistor; the GMI element is sequentially connected with the low-pass filter and the low-noise amplifier and is made of soft magnetic thin strip materials.
The analog-to-digital conversion unit comprises a D/A converter and is used for converting the analog output signal into a digital signal;
the processing unit is controlled by the FPGA platform and is used for respectively carrying out multiplication operation on the equidirectional reference signal and the orthogonal reference signal and the digital signal to generate an equidirectional output signal and an orthogonal output signal, and carrying out square sum operation and square opening on the equidirectional output signal and the orthogonal output signal to generate a digital magnitude;
further, as can be seen from fig. 3, the processing unit includes a numerically controlled oscillator, a first multiplication unit, a second multiplication unit, a first digital low-pass filtering unit, a second digital low-pass filtering unit, and a square sum processing unit, where the numerically controlled oscillator is configured to generate the co-directional reference signal and the quadrature reference signal; the first multiplication operation unit is used for performing multiplication operation on the equidirectional reference signal and the digital signal; the second multiplication unit is used for multiplying the orthogonal reference signal and the digital signal; the first digital low-pass filtering unit is used for extracting direct current quantity obtained by multiplying the equidirectional reference signal and the digital signal; the second digital low-pass filtering unit is used for extracting direct current quantity after multiplication of the orthogonal reference signal and the digital signal; and the square sum processing unit is used for summing after the direct current quantity square operation of the first digital low-pass filtering unit and the second digital low-pass filtering unit, and then squaring to obtain the digital quantity amplitude of the modulation signal.
The same-direction reference signal and the orthogonal reference signal are mutually orthogonal sine signals with signed numbers, and the frequency of the sine signals is consistent with that of the digital signals.
Furthermore, the homodromous component output signal is connected with an analog-to-digital unit and used for converting a homodromous component output digital signal into an analog homodromous component voltage signal; the orthogonal component output signal is connected with the analog-digital unit and used for converting the orthogonal component output digital signal into an analog orthogonal component voltage signal.
The first digital low-pass filtering unit and the second digital low-pass filtering unit are both digital FIR filters.
Further, the processing unit further comprises an excitation circuit, wherein the excitation circuit is configured to generate an excitation signal for exciting the GMI unit, and the excitation signal is a sinusoidal signal or a narrow pulse signal.
Further, fig. 4 shows a schematic diagram of generation of an excitation signal of the Digital GMI sensor, and a signal excitation portion of the present invention adopts a DDS (Direct Digital Synthesis) principle to complete output of an analog voltage signal with adjustable frequency, phase and amplitude according to a DDS schematic block diagram. As can be seen from fig. 4, the excitation circuit includes an accumulation register, a waveform data look-up table, a synchronization register, a D/a converter and a voltage-current converter (not shown), wherein the accumulation register outputs the accumulation result as an address line of the waveform data look-up table, and the waveform data look-up table outputs corresponding waveform data according to the address line, and the process is repeated so as to output a continuous cycle sine waveform. The synchronous register is used for storing the waveform data and outputting a sine waveform signal with continuous period; the D/A converter is used for converting the waveform signal of the output continuous period into an analog voltage excitation signal; the voltage-current converter is used for converting the voltage excitation signal into a current excitation signal.
And the digital-to-analog conversion unit comprises an A/D converter and is used for converting the digital magnitude into an analog voltage.
Furthermore, the digital-to-analog conversion unit has two paths, one path is used for converting the digital magnitude into an analog voltage signal, and the other path is used for generating an analog voltage excitation signal required by the GMI unit.
A method of signal processing for a digital GMI sensor, the method comprising the steps of:
the GMI unit generates an analog output signal according to the excitation signal;
the analog output signal is converted into a digital signal through an analog-to-digital conversion unit;
a digital control oscillator in the processing unit generates the syntropy reference signal and the orthogonal reference signal, and after the syntropy reference signal and the digital signal are subjected to multiplication operation through a first multiplication operation unit and a second multiplication operation unit respectively, an alternating current component is filtered and a direct current quantity is reserved through a first digital low-pass filtering unit and a second digital low-pass filtering unit respectively to obtain a syntropy output signal and an orthogonal output signal, and the syntropy output signal and the orthogonal output signal are subjected to square sum operation and square opening to generate a digital quantity amplitude;
and the digital magnitude is converted into an analog voltage signal through the digital-to-analog conversion unit and is output.
Further, the cocurrent reference signal and the orthogonal reference signal are sinusoidal signals with orthogonal signed numbers, and the frequency of the sinusoidal signals is consistent with that of the digital signals.
Further, the first digital low-pass filtering unit and the second digital low-pass filtering unit are both digital FIR filters.
An excitation signal to excite the GMI unit is generated by an excitation circuit, wherein the excitation signal is a sinusoidal signal or a narrow pulse signal.
Further, the excitation circuit generates an excitation signal for exciting the GMI unit, specifically, the accumulation register outputs an accumulation result as an address line of a waveform data lookup table; the waveform data lookup table outputs corresponding waveform data according to the address line; the synchronous register stores the waveform data and outputs a waveform signal with continuous period; the D/A converter converts the waveform signal of the output continuous period into an analog voltage excitation signal; the voltage-current converter converts the voltage excitation signal into a current excitation signal.
Fig. 3 is a block diagram of a digital GMI sensor according to the present invention, which is mainly divided into three parts, the first part is an ADC signal acquisition part, which acquires a response voltage of a GMI element by using an ADC chip and inputs the acquired response voltage to an FPGA for processing, the second part is an FPGA signal processing part, which is designed to implement a DDS signal generator and a digital quadrature locking and amplifying algorithm to complete measurement of a signal amplitude, and the third part is a DAC output part, which outputs a calculation result by using a DAC chip.
Further, with reference to fig. 3, the digital GMI sensor in this embodiment is designed based on the principle of quadrature lock amplification, and its operation mode is as follows: the FPGA controls a DDS (direct Digital frequency synthesizer) to output a sinusoidal voltage signal with specific frequency, and the voltage signal is subjected to Digital to Analog (DA) conversion and a voltage-current converter to obtain a sinusoidal current excitation signal with constant frequency and constant amplitude; a sinusoidal current excitation signal is input from one end of the GMI element, the other end of the GMI element is output to be grounded, and response voltage signals at two ends of the GMI element are used as output; analog response voltage signals at two ends of the GMI element are converted into Digital signals which can be processed by an FPGA (field programmable gate array) through an LPF (Low Pass Filter), an LNA (Low Noise Amplifier) and an AD converter (Analog to Digital ); the signal detection algorithm based on the orthogonal locking amplification principle realized by the FPGA is used for detecting useful voltage signals in the acquired response voltage signals, wherein two paths of reference signals which have the same frequency with the excitation signal and are orthogonal to each other are generated by a numerical control oscillator in the FPGA; the digital magnitude is converted to an analog voltage via an analog voltage output channel (DA converter).
The technical solution of the present invention will be further described with reference to specific examples.
Fig. 2 shows a block diagram of a demodulation structure of a typical diagonal GMI sensor, the GMI sensor of the present invention is in a diagonal excitation mode, as shown in the figure, a signal output by a DDS signal generator passes through a voltage-current converter to obtain a current excitation signal with constant amplitude and frequency, the current excitation signal is applied to a GMI material, and a response voltage at two ends of the GMI material is output to an amplitude detection circuit for detection. The GMI signal conditioning circuit constructed in the analog circuit shown in FIG. 2 comprises an excitation circuit, a GMI element and a detection circuit, wherein the excitation circuit comprises a DDS (Direct Digital Synthesis) and a V-i (voltage-current) converter, and the detection circuit comprises amplitude detection, wherein V isdrIndicating the analogue voltage, V, emitted by the DDSgWhich represents the response voltage of the GMI,igrepresenting GMI drive current, RoffetDenotes the feedback resistance, RgionIndicating the zeroing amplifying resistance. The output signal of the DDS signal generator passes through a voltage-current converter to obtain a current excitation signal with constant amplitude and frequency, the current excitation signal is applied to the GMI material, and the response voltage at two ends of the GMI material is output to an amplitude detection circuit for detection. The typical diagonal GMI sensor mainly utilizes the switching characteristics of a triode to realize the functions of phase-sensitive detection, including multiplication, detection and the like, the principle of an analog phase-sensitive detection algorithm is simpler and easier to realize, but the influence caused by the factors such as the voltage drop of the triode in the measurement process is not negligible compared with the measured signal, and in addition, the triode can introduce certain other noises, so that the useless and useful signals are not thoroughly separated, and the factors seriously influence the resolution and the measurement precision of the instrument. In summary, the current analog demodulation type GMI magnetic field measurement sensor mainly has the following two defects:
firstly, the analog conditioning circuit is relatively complex in structure and relatively high in working frequency, the heating of components can cause the problems of temperature drift, null drift and the like, and the sensor output is greatly influenced by the components of the demodulation circuit.
Secondly, the analog conditioning circuit has a plurality of noise coupling points, and the output is analog quantity, and the sensor is limited to be used in the environment with digital quantity requirements due to the signal output mode.
Based on the structure, the invention completes the collection and processing of the material response voltage and the generation of the excitation signal by using an FPGA (Field-Programmable Gate Array). Meanwhile, in the digital GMI sensor based on orthogonal locking amplification, the data processing is carried out in a digital mode, and appropriate correction can be carried out on the interference of nonlinearity, temperature drift and the like of an external element. As can be known from fig. 3, the GMI sensor of the present invention is in a diagonal excitation mode, the FPGA controls the DDS (direct digital frequency synthesizer) to output a sinusoidal voltage signal with a specific frequency, and the voltage signal is input to the voltage-current converter and then converted to obtain a sinusoidal current signal with a constant frequency and a constant amplitude;
the GMI probe adopts a diagonal driving mode, namely a sine current excitation signal is input from one end of the GMI element, the sine current excitation signal is output from the other end of the GMI element and is grounded, and response voltage signals at two ends of the GMI element are used as output;
a high-speed ADC (Analog-to-Digital Converter) signal acquisition channel for converting Analog response voltage signals at two ends of the GMI element into Digital signals which can be processed by the FPGA;
the signal detection algorithm based on the orthogonal locking amplification principle and realized by the FPGA is used for detecting useful voltage signals in the acquired response voltage signals, wherein two paths of reference signals which have the same frequency with the excitation signal and are orthogonal to each other are generated by a numerical control oscillator in the FPGA, and the reference signals comprise sin reference signals and cos reference signals;
further, after multiplication operation is performed on the sin reference signal and the cos reference signal and the Response voltage signal respectively, filtering an alternating current component by using an FIR (Finite Impulse Response, non-recursive filter) low-pass filter to obtain two paths of direct current quantities, performing square operation on the two paths of direct current quantities respectively, summing, flattening, and calculating to obtain a digital quantity amplitude of the signal;
further, the digital magnitude is converted into an analog voltage through an analog voltage output channel.
Further, according to a schematic diagram generated by an excitation signal of the digital GMI sensor based on quadrature locking amplification in fig. 4, a signal excitation part in the embodiment of the present invention adopts a DDS principle, and completes output of an analog voltage signal with adjustable frequency, phase and amplitude according to the DDS principle. In the embodiment, the DDS signal generator and the voltage-current converter designed by the FPGA are used for generating the sinusoidal current excitation signal, the frequency range of the output signal is 0.1-65 MHz, the excitation frequency change can be completed by only adjusting one parameter, and the GMI sensitive materials with different frequency characteristics can be conveniently tested.
Further, the DDS comprises an accumulation register, a waveform data lookup table, a synchronous register and a D/A converter, under the drive of a 125MHz clock, the accumulation register outputs the accumulation result as an address line of the waveform data lookup table, the waveform data lookup table outputs corresponding waveform data according to the address, and the steps are repeated, so that sine waveforms with continuous periods are output. The frequency of the output signal is controlled by the frequency word FWORD, so changing the signal frequency only requires changing the magnitude of FWORD. A D/A converter of the signal output link selects a chip AD9767, 125MHz clock signals output by a phase-locked loop are utilized to drive the AD9767 to work, and analog sinusoidal voltage excitation signals are obtained through conversion.
The analog voltage excitation signal is converted into a sinusoidal current excitation signal by a v-i converter (voltage-to-current converter).
In the acquisition design of the voltage signals at two ends of the GMI element, the excitation signal is up to 5MHz, so that the analog-to-digital conversion unit in the embodiment adopts a high-speed ADC chip, when the response voltage is demodulated in a digital quantity form, the output of the sensor is not influenced by the drift characteristic of the analog chip, and the linearity of the sensor can be improved by a method of compensating the output quantity.
FIG. 1 shows a curve of the relationship between the impedance change rate of the GMI material and the magnitude of a magnetic field under the excitation of 5MHz, the magnitude of the magnetic field of the material is changed by passing current with the frequency of 5MHz and the amplitude of 10mA, the impedance change of the material is recorded by a high-frequency impedance analyzer, and the impedance change rate of the GMI material is larger than 350 percent according to the curve.
Furthermore, in the embodiment of the invention, the ADC chip is used for collecting the GMI element response voltage, compared with an analog conditioning circuit, the main noise source of the GMI sensor is an ADC chip collecting channel, and noise of different degrees is introduced into each stage of processing circuits in the analog circuit, so that the noise source analysis of the GMI sensor is more convenient.
Furthermore, the ADC chip used in the embodiment of the present invention is AD9226, when the chip is configured as a single-ended input, the input range is 1.0V-3.0V, and the response voltage amplitude in the system can reach ± 4V after pre-amplification, so as to keep a certain margin for the sensor adjustment, and therefore, a signal attenuation circuit needs to be designed to enable the system to complete the acquisition of ± 5V external voltage signals, and the conversion formula is as follows:
wherein, VoutFor attenuating the output voltage of the circuit, VinIs the input voltage of the attenuator circuit.
When V isinWhen it is-5V, Vout1V; when V isinWhen it is 5V, Vout3V; just meets the above requirements. After the digital signal is converted, the conversion formula is subjected to inverse operation, the digital signal is amplified, and a real value of the input voltage can be obtained.
In the design of a signal measurement algorithm based on the orthogonal locking amplification principle of an FPGA platform, multiplication and filtering operations need to be carried out on acquired signals. The data collected by the ADC chip is unsigned integer data, the digital quantity range of the data is 0-4096, and the collected data value range is +/-2048 through sign conversion operation so as to meet the requirement of a subsequent conditioning algorithm. Two paths of orthogonal reference signals and acquired signals are subjected to multiplication operation, the reference signals are generated by an IP core of a numerically controlled oscillator in an FPGA, a sign number multiplier is configured to multiply the acquired signals and the reference signals, the multiplication output result is input into an FIR low-pass filter to be subjected to filtering processing, and the part is divided into two paths, namely the acquired signals are respectively multiplied by in-phase reference signals and orthogonal reference signals.
The invention uses the low-pass FIR filter designed by the window function to complete the direct current quantity extraction after multiplication, the cut-off frequency is set to be 1Hz, the cut-off frequency is 250kHz in the practical design application, and the requirement of filtering 5MHz frequency multiplication components is met. Reference signal vref(t) and a response voltage vin(t) can be written as:
vref(t)＝Vr cos(ω0t) (2)
vin(t)＝Vi cos(ω0t+θ) (3)
wherein v isrefReference signal v generated for numerically controlled oscillator in FPGAinAcquisition of a response voltage signal, V, across a GMI element for an ADCrRepresenting the amplitude of the reference signal, ViRepresenting the magnitude, omega, of a response voltage signal across an ADC-acquisition GMI element0Representing the angular frequency of the signal and theta representing the initial phase of the response voltage signal acquired by the ADC across the GMI element.
After passing through the multiplier, the result can be expressed as:
up(t)＝0.5VrVi cosθ+0.5VrVi cos(2ω0t+θ) (4)
wherein u ispThe ADC acquires an output signal V obtained by multiplying a response voltage signal at two ends of the GMI element by a reference signal through a multiplierrRepresenting the reference signal amplitude, ViRepresenting the magnitude, omega, of a response voltage signal across an ADC-acquisition GMI element0Representing the angular frequency of the signal, t representing time, and theta representing the initial phase of the response voltage signal across the ADC collecting the GMI element.
The first term is the difference frequency component of the product, the second term is the sum frequency component, the output of the multiplier is passed through a low-pass filter, and the DC quantity u in the signal can be extractedo(t), the expression of which is:
uo(t)＝0.5VrVi cosθ (5)
wherein u isoIs the output DC signal of a low-pass filter, VrRepresenting the amplitude of the reference signal, ViRepresenting the magnitude, omega, of a response voltage signal across an ADC-acquisition GMI element0Representing the angular frequency of the signal and theta represents the initial phase of the response voltage signal across the ADC collecting the GMI element.
The output of which is proportional to the magnitude V of the response voltage signal across the ADC acquisition GMI elementi。
On the design of a signal output channel of the GMI sensor, two paths of direct current quantities are summed after square operation, then square opening is carried out to obtain a Digital quantity amplitude of a modulation signal, firstly, a six-digit nixie tube is used for displaying the Digital quantity amplitude, a calculation result is visually observed, then, a DAC (Digital-to-Analog Converter) chip is used for converting the Digital quantity into an Analog quantity, and an analysis instrument is used for conveniently analyzing parameters such as noise performance, sensitivity and the like of the sensor. Fig. 5 is an output characteristic curve of the digital GMI sensor according to the present invention, in which the sensor is placed in a shield barrel, the magnitude of the magnetic field in the shield barrel is changed, and the analog voltage value output from the sensor is recorded, and in conjunction with fig. 5, a positive direction test curve is obtained by changing the magnetic field from-100 μ T to 100 μ T and recording the analog voltage value output from the sensor, and a negative direction test curve is obtained by changing the magnetic field from 100 μ T to-100 μ T and recording the analog voltage value output from the sensor; the measuring range of the sensor is +/-100 mu T, the slope of the fitting straight line is 16.34kV/T, namely the output sensitivity corresponding to the sensor is 16.34kV/T, and the correlation coefficient of the fitting curve is 0.9993 according to the output result of a fitting tool.
The invention CAN directly output analog voltage, and CAN carry out related adjustment according to a digital interface of a user due to the programmable characteristic of the FPGA, wherein the related adjustment comprises but is not limited to IIC, SPI, CAN bus, private protocol bus and the like, and the application range is wider compared with an analog sensor.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.
Claims (10)
1. A digital GMI sensor comprising a GMI unit, an analog-to-digital conversion unit, and a processing unit, wherein,
the GMI unit is used for inducing an external magnetic field under the action of an excitation signal and generating an analog output signal;
the analog-to-digital conversion unit is used for converting the analog output signal into a digital signal;
and the processing unit is used for multiplying the equidirectional reference signal and the orthogonal reference signal with the digital signal respectively to generate an equidirectional output signal and an orthogonal output signal, and squaring and adding the quadrate output signal and the orthogonal output signal and squaring to generate a voltage signal.
2. The digital GMI sensor according to claim 1, wherein the processing unit comprises a numerically controlled oscillator, a first multiplication unit, a second multiplication unit, a first digital low pass filter unit, a second digital low pass filter unit, and a sum of squares processing unit, wherein,
the digital controlled oscillator is used for generating the cocurrent reference signal and the orthogonal reference signal;
the first multiplication unit is used for multiplying the equidirectional reference signal and the digital signal;
the second multiplication unit is used for multiplying the orthogonal reference signal and the digital signal;
the first digital low-pass filtering unit is used for extracting direct current quantity obtained by multiplying the equidirectional reference signal and the digital signal;
the second digital low-pass filtering unit is used for extracting direct current quantity after multiplication of the orthogonal reference signal and the digital signal;
the square sum processing unit is used for summing after the square operation of the direct current quantities of the first digital low-pass filtering unit and the second digital low-pass filtering unit and then squaring to obtain the digital quantity amplitude of the modulation signal; the homodromous reference signal and the orthogonal reference signal are digital sinusoidal signals which are orthogonal signed numbers, and the frequency of the digital sinusoidal signals is consistent with that of the digital sinusoidal signals;
the first digital low-pass filtering unit and the second digital low-pass filtering unit are both digital FIR filters.
3. The digital GMI sensor according to claim 1 further comprising a digital to analog conversion unit,
the digital-to-analog conversion unit is connected with the processing unit and used for converting the voltage signal into an analog voltage signal.
4. The digital GMI sensor according to claim 1, wherein the processing unit further comprises an excitation circuit, wherein,
the excitation circuit is used for generating an excitation signal for exciting the GMI unit;
the excitation signal is a sine signal or a narrow pulse signal;
the excitation circuit includes an accumulator register, a waveform data look-up table, a synchronization register, a D/a converter, and a voltage-to-current converter, wherein,
the accumulation register is used for outputting an accumulation result as an address line of the waveform data lookup table;
the waveform data lookup table is used for outputting corresponding waveform data according to the address line;
a synchronous register for storing the waveform data and outputting a waveform signal of a continuous period;
the D/A converter is used for converting the waveform signal of the output continuous period into an analog voltage excitation signal;
the voltage-current converter is used for converting the voltage excitation signal into a current excitation signal.
5. The digital GMI sensor according to claim 1 wherein the GMI unit comprises a GMI element, a bias power supply, a current limiting resistor, a bias coil, a low pass filter, and a low noise amplifier, wherein,
the bias power supply is connected to the bias coil after passing through the current-limiting resistor to provide a bias magnetic field for the GMI element, and the bias power supply is used for controlling the magnitude of the bias magnetic field by changing the magnitude of the current-limiting resistor;
the GMI element is sequentially connected with the low-pass filter and the low-noise amplifier;
the GMI element is an amorphous soft magnetic thin ribbon material.
6. A method of signal processing for a digital GMI sensor, the method comprising the steps of:
the GMI unit generates an analog output signal according to the excitation signal;
the analog output signal is converted into a digital signal through an analog-to-digital conversion unit;
the processing unit sends out an equidirectional reference signal and an orthogonal reference signal, the equidirectional reference signal and the orthogonal reference signal are respectively multiplied with the digital signal to generate an equidirectional output signal and an orthogonal output signal, and the equidirectional output signal and the orthogonal output signal are subjected to square-sum operation and square-open operation to generate a voltage signal.
7. The signal processing method according to claim 6, wherein the processing unit generates a syntropic reference signal and a quadrature reference signal, and performs multiplication with the digital signal to generate a syntropic output signal and a quadrature output signal, and performs square-sum operation and square-open operation on the syntropic output signal and the quadrature output signal to generate a voltage signal, specifically,
a numerically controlled oscillator generates the co-directional reference signal and a quadrature reference signal;
a first multiplication unit multiplies the same-direction reference signal and the digital signal;
a second multiplication unit multiplies the orthogonal reference signal and the digital signal;
the first digital low-pass filtering unit extracts the direct current quantity obtained by multiplying the equidirectional reference signal by the digital signal;
the second digital low-pass filtering unit extracts the direct current quantity obtained by multiplying the orthogonal reference signal by the digital signal;
the square sum processing unit sums the direct current quantity square operation of the first digital low-pass filtering unit and the second digital low-pass filtering unit, and then square is conducted to obtain a voltage signal;
the same-direction reference signal and the orthogonal reference signal are orthogonal signed sinusoidal signals, and the frequency of the sinusoidal signals is consistent with that of the digital signals;
the first digital low-pass filtering unit and the second digital low-pass filtering unit are both digital FIR filters.
8. The signal processing method according to claim 7,
the homodromous component output signal converts a homodromous component output digital signal into an analog homodromous component voltage signal through an analog-to-digital unit;
and the quadrature component output signal converts a quadrature component output digital signal into an analog quadrature component voltage signal through an analog-to-digital unit.
9. The signal processing method of claim 6, wherein the processing unit further comprises a stimulus circuit, wherein,
the excitation circuit generates an excitation signal for exciting the GMI unit; the excitation signal is a sine signal or a narrow pulse signal;
the excitation circuit generates an excitation signal that excites the GMI cell, specifically,
the accumulation register outputs the accumulation result as an address line of the waveform data lookup table;
the waveform data lookup table outputs corresponding waveform data according to the address line;
the synchronous register stores the waveform data and outputs a waveform signal with continuous periods;
the D/A converter converts the waveform signal of the output continuous period into an analog voltage excitation signal;
and the voltage-current converter converts the voltage excitation signal into a current excitation signal.
10. The signal processing method of claim 9, wherein the current excitation signal sequentially enters a low pass filter and a low noise amplifier through the GMI element to obtain an analog output signal, wherein a bias power supply is connected to a bias coil after passing through a current limiting resistor to provide a bias magnetic field to the GMI element, and the magnitude of the bias magnetic field is controlled by controlling the magnitude of the current limiting resistor.
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| CN116128064A (en) * | 2023-04-12 | 2023-05-16 | 合肥本源量子计算科技有限责任公司 | Quantum bit state reading circuit, measurement and control circuit and quantum computer |
| CN117310303A (en) * | 2023-09-22 | 2023-12-29 | 中国科学院长春光学精密机械与物理研究所 | Charge measurement method based on digital phase-sensitive demodulation algorithm |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116128064A (en) * | 2023-04-12 | 2023-05-16 | 合肥本源量子计算科技有限责任公司 | Quantum bit state reading circuit, measurement and control circuit and quantum computer |
| CN116128064B (en) * | 2023-04-12 | 2023-12-12 | 本源量子计算科技（合肥）股份有限公司 | Quantum bit state reading circuit, measurement and control circuit and quantum computer |
| CN117310303A (en) * | 2023-09-22 | 2023-12-29 | 中国科学院长春光学精密机械与物理研究所 | Charge measurement method based on digital phase-sensitive demodulation algorithm |
| CN117310303B (en) * | 2023-09-22 | 2024-04-16 | 中国科学院长春光学精密机械与物理研究所 | Charge measurement method based on digital phase-sensitive demodulation algorithm |
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