CN106026966A - Notch filtering method and circuit for GMI magnetic sensor - Google Patents
Notch filtering method and circuit for GMI magnetic sensor Download PDFInfo
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- H—ELECTRICITY
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Abstract
The invention discloses a notch filtering method for GMI magnetic sensors, and a circuit thereof. The notch filtering method comprises steps of performing amplitude phase transforming on input signals and only keeping the amplitude and phase of to-be-filtered interference signals unchanged, and performing differential synthesizing on the signals after amplitude phase transforming and original input signals and then outputting. The notch filtering circuit comprises an amplitude phase transforming module and a differential synthesizing module. The amplitude phase transforming module only keeps the amplitude and the phase of to-be-filtered interference signals unchanged, while the differential synthesizing module performs differential synthesizing on the signals after amplitude phase transforming and the original input signals, and then outputting. The notch filtering method and circuit can effectively filter out power frequency electromagnetic interference signals in the fields such as biological weak current and magnetic detection by using the amplitude phase transforming and differential synthesizing of signals. The method and the circuit can be widely applied to application occasions with high requirement of high notch filtering attenuation times in actual projects and low matching degree of used resistor capacitors, with advantages of high attenuation times and allowing slight mismatching of the resistor capacitors.
Description
Technical field
The present invention relates to the signal detection technique of GMI Magnetic Sensor, be specifically related to a kind of trap for GMI Magnetic Sensor and filter
Wave method and circuit.
Background technology
GMI effect, i.e. passes to alternating current I when silk or the band of soft magnetic material (mostly being Co base amorphous and Fe base nanometer crystal)ac
Time, the alternating voltage U at material two endswAlong with external magnetic field H added by silk longitudinal directionexChange and the phenomenon of sensitive change, its essence
It it is the impedance sensitive change with externally-applied magnetic field of amorphous wire self.
GMI Magnetic Sensor based on the design of GMI effect comprises soft magnetic material (mostly being Co base amorphous and Fe base nanometer crystal)
The induction coil that silk or band are constituted, by induction coil, can be converted into material two ends by the impedance variation value of soft magnetic material
Alternating voltage Uw, thus realize external magnetic field HexMeasurement.Sensor based on the design of GMI effect has the most weak
Magnetic detection performance, its detectivity, up to 1pT, may be used for the detection in extremely weak biological magnetic field under unshielded environments, than
Such as core field, lung magnetic field, brain magnetic field etc..But, in the environment of our at present life, electromagnetic pollution is extremely serious, common all
City's electromagnetic noise all reaches nT rank, and this partial noise is mainly power frequency and the disturbance of its each harmonic that power device produces
Magnetic field, therefore when GMI Magnetic Sensor pT detection of magnetic field under unshielded environments, it is necessary to carry out city noise effectively
Filter, i.e. mainly Hz noise is filtered.
Filtering for Hz noise, traditional method is to use double-T shaped topological structure notch filter to characteristic frequency
Signal filters, but double-T shaped topological structure notch filter has extremely strict requirements to the matching degree of resistor, electricity
The most not coupling of resistance capacitor will make notch depth rapid decrease, even if using accurate capacitance-type resistor, it is also difficult to
Reach preferable filter effect, be therefore normally used for the less demanding occasion of attenuation multiple.But GMI Magnetic Sensor is for non-
When carrying out pT magnetic field detection under shielding environment, the strictest to the attenuation requirement of set specific frequency signal, it is desirable to attenuation multiple need to reach
1000 times (-60dB), it is contemplated that engineer applied need for environment allows resistor-capacitor not mate, precision capacitance resistor is i.e.
Can meet requirement, the most traditional double T topological structure notch filters are extremely difficult to requirement.
Summary of the invention
The technical problem to be solved in the present invention: for surrounding electromagnetic pollution extremely serious in the case of, when use GMI magnetic pass
The sensor technology that power frequency and each harmonic signal disturbing thereof are particularly acute in the biological magnetic field detection of unshielded environments hypodermis tesla is asked
Topic, it is provided that power frequency electromagnet is disturbed signal cancellation to fall by a kind of mode utilizing two paths of differential signals to carry out synthesizing, and can be widely applied to
In engineering reality, trap circuit attenuation multiple requires the application scenario that resistor-capacitor matching degree high, used is the highest, and attenuation multiple is high,
And allow the most unmatched notch filter method for GMI Magnetic Sensor of capacitance-type resistor and circuit.
In order to solve above-mentioned technical problem, the technical solution used in the present invention is:
A kind of notch filter method for GMI Magnetic Sensor, step includes:
1) input signal is carried out width phase inversion, and only keep treating that filtering interfering signal amplitude is constant, phase invariant；
2) export after the signal after width phase inversion and original input signal being carried out difference synthesis.
Preferably, described step 1) specifically refer to, by Two-orders Butterworth band filter, input signal is carried out width phase
Conversion, the mid frequency of described Two-orders Butterworth band filter is to treat that the frequency of filtering interference signals, gain are 1.
Preferably, described Two-orders Butterworth band filter includes the two-stage circuit of cascade arrangement, in two-stage circuit first
Level circuit includes resistance R1, resistance R2, resistance R3, electric capacity C1, electric capacity C2 and operational amplifier U1, operational amplifier
The negative input of U1 connects reference voltage, electrode input end passes sequentially through electric capacity C1, resistance R1 is connected with signal to be filtered, electricity
R2 one end is connected between electric capacity C1 and resistance R1, another terminates reference voltage in resistance, and resistance R3 concatenation is arranged in computing and puts
Between electrode input end and the outfan of big device U1, electric capacity C2 one end is connected between electric capacity C1 and resistance R1, the other end
It is connected with the outfan of operational amplifier U1；In two-stage circuit second level circuit include resistance R4, resistance R5, resistance R6,
Electric capacity C3, electric capacity C4 and operational amplifier U2, the negative input of operational amplifier U2 connects reference voltage, electrode input end
Pass sequentially through electric capacity C3, resistance R4 is connected with the outfan of operational amplifier U1, resistance R5 one end be connected to electric capacity C3 and
Between resistance R4, another terminate reference voltage, resistance R6 concatenation is arranged in electrode input end and the output of operational amplifier U2
Between end, electric capacity C4 one end is connected between electric capacity C3 and resistance R4, the other end and the outfan phase of operational amplifier U2
Even.
Preferably, described step 2) specifically refer to passing ratio computing circuit by the signal after width phase inversion and original input signal
Both export after carrying out difference synthesis.
Preferably, described scaling circuit includes resistance R7, resistance R8, resistance R9 and operational amplifier U3, and computing is put
The negative input of big device U3 is connected with the signal after width phase inversion by resistance R7, electrode input end and original input signal phase
Even, resistance R9 concatenation is arranged between electrode input end and the outfan of operational amplifier U3.
A kind of notch filter circuit for GMI Magnetic Sensor, including width phase inversion module and difference synthesis module, input letter
Number being divided into two-way, a road input signal exports to difference synthesis module after carrying out width phase inversion by width phase inversion module
Input, another road input signal are directly output to another input of difference synthesis module, and described width phase inversion module is only protected
Hold and treat that filtering interfering signal amplitude is constant, phase invariant, described difference synthesis module by the signal after width phase inversion be originally inputted
Both signals export after carrying out difference synthesis.
Preferably, described width phase inversion module is Two-orders Butterworth band filter, described Two-orders Butterworth band
The mid frequency of bandpass filter is to treat that the frequency of filtering interference signals, gain are 1.
Preferably, described Two-orders Butterworth band filter includes the two-stage circuit of cascade arrangement, in two-stage circuit first
Level circuit includes resistance R1, resistance R2, resistance R3, electric capacity C1, electric capacity C2 and operational amplifier U1, operational amplifier
The negative input of U1 connects reference voltage, electrode input end passes sequentially through electric capacity C1, resistance R1 is connected with signal to be filtered, electricity
Resistance R2 one end is connected between electric capacity C1 and resistance R1, other end ground connection, and resistance R3 concatenation is arranged in operational amplifier U1
Electrode input end and outfan between, electric capacity C2 one end is connected between electric capacity C1 and resistance R1, the other end and computing are put
The outfan of big device U1 is connected；In two-stage circuit second level circuit include resistance R4, resistance R5, resistance R6, electric capacity C3,
Electric capacity C4 and operational amplifier U2, the negative input of operational amplifier U2 connects reference voltage, electrode input end passes sequentially through
Electric capacity C3, resistance R4 are connected with the outfan of operational amplifier U1, and resistance R5 one end is connected to electric capacity C3 and resistance R4
Between, another terminate reference voltage, resistance R6 concatenation is arranged between electrode input end and the outfan of operational amplifier U2,
Electric capacity C4 one end is connected between electric capacity C3 and resistance R4, the other end is connected with the outfan of operational amplifier U2.
Preferably, described difference synthesis module is scaling circuit.
Preferably, described scaling circuit includes resistance R7, resistance R8, resistance R9 and operational amplifier U3, and computing is put
The negative input of big device U3 is connected with the signal after width phase inversion by resistance R7, electrode input end and original input signal phase
Even, resistance R9 concatenation is arranged between electrode input end and the outfan of operational amplifier U3.
For the notch filter method of GMI Magnetic Sensor, the present invention has an advantage that first input signal is carried out width by the present invention
Phase inversion, and only keep treating that filtering interfering signal amplitude is constant, phase invariant, by the signal after width phase inversion be originally inputted letter
Export after carrying out difference synthesis both number, so that the signal after width phase inversion is constant with amplitude in original input signal, phase place
Constant treats that filtering interference signals is eliminated during difference synthesizes, it is possible to disturb signal cancellation to fall power frequency electromagnet, can be wide
General it is applied to the application scenario that in engineering reality, trap circuit attenuation multiple requirement resistor-capacitor matching degree high, used is the highest, tool
There is attenuation multiple high, and allow the slight unmatched advantage of capacitance-type resistor.
The present invention is the present invention notch filter method for GMI Magnetic Sensor for the notch filter circuit of GMI Magnetic Sensor
Corresponding circuit structure, the most also has above-mentioned advantage, does not repeats them here.
Accompanying drawing explanation
Fig. 1 is the electrical block diagram of embodiment of the present invention notch filter circuit.
Fig. 2 is width phase inversion module amplitude characteristic analog result in the embodiment of the present invention.
Fig. 3 is width phase inversion module phase characteristic analog result in the embodiment of the present invention.
Detailed description of the invention
The present embodiment includes for the step of the notch filter method of GMI Magnetic Sensor:
1) input signal is carried out width phase inversion, and only keep treating that filtering interfering signal amplitude is constant, phase invariant；
2) export after the signal after width phase inversion and original input signal being carried out difference synthesis.
In the present embodiment, step 1) specifically refer to, by Two-orders Butterworth band filter, input signal is carried out width phase
Conversion, the mid frequency of Two-orders Butterworth band filter is to treat that the frequency of filtering interference signals, gain are 1, so
Can be by the Phase advance 360 ° of mid frequency (treating filtering interference signals).The quality of Two-orders Butterworth band filter
Factor preferably employs 2 or 5 or 10.
In the present embodiment, step 2) specifically refer to passing ratio computing circuit by the signal after width phase inversion and original input signal
Both export after carrying out difference synthesis.
As it is shown in figure 1, the present embodiment includes width phase inversion module and difference synthesis for the notch filter circuit of GMI Magnetic Sensor
Module, input signal is divided into two-way, and a road input signal exports after carrying out width phase inversion by width phase inversion module to difference conjunction
An input of module, another road input signal is become to be directly output to another input of difference synthesis module, described width phase
Conversion module only keeps treating that filtering interfering signal amplitude is constant, phase invariant, and described difference synthesis module is by the letter after width phase inversion
Number carry out exporting after difference synthesis with original input signal.
In the present embodiment, width phase inversion module is Two-orders Butterworth band filter, described Two-orders Butterworth band
The mid frequency of bandpass filter is to treat that the frequency of filtering interference signals, gain are 1, so can (wait to filter dry by mid frequency
Disturb signal) Phase advance 360 °.Additionally, width phase inversion module can also use other kinds of width phase inversion electricity as required
Road, as long as only keeping treating that filtering interfering signal amplitude is constant, phase invariant, can realize the signal after width phase inversion with original
Input signal between the two treat that filtering interfering signal amplitude is constant, phase invariant, thus by the signal after width phase inversion with original
Both input signals carry out can filtering during difference synthesis therein treating filtering interference signals.As it is shown in figure 1, Two-orders Bart
Butterworth band filter includes the two-stage circuit of cascade arrangement, in two-stage circuit first order circuit include resistance R1, resistance R2,
Resistance R3, electric capacity C1, electric capacity C2 and operational amplifier U1, the negative input of operational amplifier U1 connect reference voltage,
Electrode input end passes sequentially through electric capacity C1, resistance R1 is connected with signal to be filtered, and resistance R2 one end is connected to electric capacity C1 and electricity
Between resistance R1, other end ground connection, resistance R3 concatenation is arranged between electrode input end and the outfan of operational amplifier U1,
Electric capacity C2 one end is connected between electric capacity C1 and resistance R1, the other end is connected with the outfan of operational amplifier U1；Two-stage
In circuit, second level circuit includes resistance R4, resistance R5, resistance R6, electric capacity C3, electric capacity C4 and operational amplifier U2,
The negative input of operational amplifier U2 connects reference voltage, electrode input end passes sequentially through electric capacity C3, resistance R4 and computing are put
The outfan of big device U1 is connected, and resistance R5 one end is connected between electric capacity C3 and resistance R4, another terminates reference voltage,
Resistance R6 concatenation is arranged between electrode input end and the outfan of operational amplifier U2, and electric capacity C4 one end is connected to electric capacity C3
And between resistance R4, the other end is connected with the outfan of operational amplifier U2.It should be noted that Two-orders Butterworth
The reference voltage of band filter can be with ground connection (being equivalent to 0V), it is also possible to uses other reference voltages (such as 2.5V as required
Deng).
In the present embodiment, electric capacity C1, electric capacity C2, electric capacity C3, electric capacity C4 value is identical (is all Cf), according to cascade
Type Butterworth filter normalization table, it may be determined that Two-orders Butterworth band filter parameter at different levels is as follows:
In two-stage circuit, transmission function and the mid frequency such as formula (1) of first order circuit are shown；
In formula (1), A1S () represents the transmission function of first order circuit, f in two-stage circuit0Lead to for Two-orders Butterworth band
The mid frequency of wave filter, S is Laplace operator, C1Represent the capacitance of electric capacity C1, C2Represent the electric capacity of electric capacity C2
Value, R1Represent the resistance value of resistance R1, R2Represent the resistance value of resistance R2, R3Represent the resistance value of resistance R3.
If Cf=C1=C2, then have formula (2)；
In formula (2), R1Represent the resistance value of resistance R1, R2Represent the resistance value of resistance R2, R3Represent the electricity of resistance R3
Resistance, Q is the quality factor (typically taking 2 or 5 or 10) of Two-orders Butterworth band filter, f0For Two-orders
The mid frequency (frequency of power frequency interference signals to be filtered) of Butterworth band filter, A1For first order circuit in two-stage circuit
Gain (amplification), CfFor electric capacity C1 and the capacitance of electric capacity C2.
In two-stage circuit, transmission function and the mid frequency such as formula (3) of first order circuit are shown；
In formula (3), A2S () represents the transmission function of second level circuit, f in two-stage circuit0Lead to for Two-orders Butterworth band
The mid frequency of wave filter, S is Laplace operator, C3Represent the capacitance of electric capacity C3, C4Represent the electric capacity of electric capacity C4
Value, R4Represent the resistance value of resistance R4, R5Represent the resistance value of resistance R5, R6Represent the resistance value of resistance R6.
If Cf=C3=C4, then have formula (4)；
In formula (4), R4Represent the resistance value of resistance R4, R5Represent the resistance value of resistance R5, R6Represent the electricity of resistance R6
Resistance Q is the quality factor of Two-orders Butterworth band filter, f0For in Two-orders Butterworth band filter
Frequency of heart, A2For the gain (amplification) of second level circuit, C in two-stage circuitfFor electric capacity C3 and the capacitance of electric capacity C4.
Owing to Two-orders Butterworth band filter gain is 1, then understand the gain A of first order circuit in two-stage circuit1And two-stage
The gain A of second level circuit in circuit2Meet following relation: A1·A2=1.So can be by logical for Two-orders Butterworth band filter
The output of ripple device is as an input of difference synthesis module, and another input of difference synthesis module is the defeated of primary signal
Enter end.So, resistance R7 end input signal is that the power frequency interference signals of primary signal is constant, and other signals have and to a certain degree decline
The signal subtracted, when poor with primary signal, power frequency interference signals just can be cancelled.
The amplitude characteristic analog result of the present embodiment Two-orders Butterworth band filter shown in Figure 2, by two classes
After connection Butterworth band filter carries out width phase inversion, the mid frequency f of Two-orders Butterworth band filter0(to be filtered
Frequency except interference signal) corresponding gain G is 1.The present embodiment Two-orders Butterworth bandpass filtering shown in Figure 3
The phase characteristic analog result of device, after carrying out width phase inversion by Two-orders Butterworth band filter, the phase of input signal
Position is switched between-180 °～180 °, and the mid frequency f of wherein Two-orders Butterworth band filter0(wait to filter dry
Disturb the frequency of signal) corresponding phase place is 0.Therefore, visible according to above-mentioned analog result, the logical filter of Two-orders Butterworth band
Input signal can be carried out width phase inversion by ripple device, and only keeps treating that filtering interfering signal amplitude is constant, phase invariant.
In the present embodiment, difference synthesis module is scaling circuit.As it is shown in figure 1, scaling circuit include resistance R7,
Resistance R8, resistance R9 and operational amplifier U3, the negative input of operational amplifier U3 passes through resistance R7 and width phase inversion
After signal be connected, electrode input end is connected with original input signal, resistance R9 concatenates and is arranged in the positive pole of operational amplifier U3
Between input and outfan.In scaling circuit shown in Fig. 1, the resistance sizes of resistance R7 will be by resistance R8 and resistance
R9 determines, formula is R7=R8//R9, and amplification G is determined by R8 and R9, and formula is G=1+R9/R8.Additionally, difference
Synthesis module can also use other kinds of difference combiner circuit as required.
The above is only the preferred embodiment of the present invention, and protection scope of the present invention is not limited merely to above-described embodiment, all
The technical scheme belonged under thinking of the present invention belongs to protection scope of the present invention.It should be pointed out that, for the art is common
For technical staff, some improvements and modifications without departing from the principles of the present invention, these improvements and modifications also should be regarded as this
The protection domain of invention.
Claims (10)
1. the notch filter method for GMI Magnetic Sensor, it is characterised in that step includes:
1) input signal is carried out width phase inversion, and only keep treating that filtering interfering signal amplitude is constant, phase invariant；
2) export after the signal after width phase inversion and original input signal being carried out difference synthesis.
Notch filter method for GMI Magnetic Sensor the most according to claim 1, it is characterised in that described step 1)
Specifically referring to, by Two-orders Butterworth band filter, input signal is carried out width phase inversion, described Two-orders Bart irrigates
The mid frequency of this band filter is to treat that the frequency of filtering interference signals, gain are 1.
Notch filter method for GMI Magnetic Sensor the most according to claim 2, it is characterised in that: described second order
Cascade Butterworth band filter includes the two-stage circuit of cascade arrangement, and in two-stage circuit, first order circuit includes resistance R1, electricity
Resistance R2, resistance R3, electric capacity C1, electric capacity C2 and operational amplifier U1, the negative input of operational amplifier U1 connects reference
Voltage, electrode input end pass sequentially through electric capacity C1, resistance R1 is connected with signal to be filtered, and resistance R2 one end is connected to electric capacity
Between C1 and resistance R1, another terminate reference voltage, resistance R3 concatenation be arranged in operational amplifier U1 electrode input end and
Between outfan, electric capacity C2 one end is connected between electric capacity C1 and resistance R1, the other end and the output of operational amplifier U1
End is connected；In two-stage circuit, second level circuit includes resistance R4, resistance R5, resistance R6, electric capacity C3, electric capacity C4 and computing
Amplifier U2, the negative input of operational amplifier U2 connects reference voltage, electrode input end passes sequentially through electric capacity C3, resistance
R4 is connected with the outfan of operational amplifier U1, and resistance R5 one end is connected between electric capacity C3 and resistance R4, another termination
Reference voltage, resistance R6 concatenation is arranged between electrode input end and the outfan of operational amplifier U2, and electric capacity C4 one end is even
Be connected between electric capacity C3 and resistance R4, the other end is connected with the outfan of operational amplifier U2.
Notch filter method for GMI Magnetic Sensor the most according to claim 1, it is characterised in that described step 2)
Specifically refer to export after the signal after width phase inversion and original input signal are carried out difference synthesis by passing ratio computing circuit.
Notch filter method for GMI Magnetic Sensor the most according to claim 4, it is characterised in that: described ratio
Computing circuit includes resistance R7, resistance R8, resistance R9 and operational amplifier U3, the negative input of operational amplifier U3
Be connected by the signal after resistance R7 and width phase inversion, electrode input end is connected with original input signal, and resistance R9 concatenates layout
Between the electrode input end and outfan of operational amplifier U3.
6. the notch filter circuit for GMI Magnetic Sensor, it is characterised in that: include that width phase inversion module and difference are closed
Becoming module, input signal is divided into two-way, and a road input signal exports to difference after carrying out width phase inversion by width phase inversion module
One input of synthesis module, another road input signal are directly output to another input of difference synthesis module, described width
Phase inversion module only keeps treating that filtering interfering signal amplitude is constant, phase invariant, and described difference synthesis module is by after width phase inversion
Signal and original input signal export after carrying out difference synthesis.
Notch filter circuit for GMI Magnetic Sensor the most according to claim 6, it is characterised in that: described width phase
Conversion module is Two-orders Butterworth band filter, and the mid frequency of described Two-orders Butterworth band filter is
Treat that the frequency of filtering interference signals, gain are 1.
Notch filter circuit for GMI Magnetic Sensor the most according to claim 7, it is characterised in that: described second order
Cascade Butterworth band filter includes the two-stage circuit of cascade arrangement, and in two-stage circuit, first order circuit includes resistance R1, electricity
Resistance R2, resistance R3, electric capacity C1, electric capacity C2 and operational amplifier U1, the negative input of operational amplifier U1 connects reference
Voltage, electrode input end pass sequentially through electric capacity C1, resistance R1 is connected with signal to be filtered, and resistance R2 one end is connected to electric capacity
Between C1 and resistance R1, other end ground connection, resistance R3 concatenation is arranged in electrode input end and the outfan of operational amplifier U1
Between, electric capacity C2 one end is connected between electric capacity C1 and resistance R1, the other end is connected with the outfan of operational amplifier U1；
In two-stage circuit, second level circuit includes resistance R4, resistance R5, resistance R6, electric capacity C3, electric capacity C4 and operational amplifier
U2, the negative input of operational amplifier U2 connects reference voltage, electrode input end passes sequentially through electric capacity C3, resistance R4 and fortune
The outfan calculating amplifier U1 is connected, and resistance R5 one end is connected between electric capacity C3 and resistance R4, another termination reference electricity
Pressure, resistance R6 concatenation is arranged between electrode input end and the outfan of operational amplifier U2, and electric capacity C4 one end is connected to electricity
Hold between C3 and resistance R4, the other end is connected with the outfan of operational amplifier U2.
Notch filter circuit for GMI Magnetic Sensor the most according to claim 6, it is characterised in that: described difference
Synthesis module is scaling circuit.
Notch filter circuit for GMI Magnetic Sensor the most according to claim 9, it is characterised in that: described ratio
Computing circuit includes resistance R7, resistance R8, resistance R9 and operational amplifier U3, the negative input of operational amplifier U3
Be connected by the signal after resistance R7 and width phase inversion, electrode input end is connected with original input signal, and resistance R9 concatenates layout
Between the electrode input end and outfan of operational amplifier U3.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108008205A (en) * | 2017-12-07 | 2018-05-08 | 中国电子科技集团公司第四十研究所 | A kind of self-adapting signal modulate circuit and method applied to electromagnetic field detection |
| CN109407157A (en) * | 2018-12-05 | 2019-03-01 | 中国科学院地质与地球物理研究所 | A kind of induction type magnetic sensor and electromagnetic survey equipment |
| CN109709500A (en) * | 2019-02-28 | 2019-05-03 | 青岛海月辉科技有限公司 | Low-intensity magnetic field signal acquisition circuit |
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| CN101001481A (en) * | 2006-01-14 | 2007-07-18 | 三星电子株式会社 | Apparatus and method of reducing noise of earphones, noise reducing earphones, and a portable audio reproducing apparatus |
| CN201001101Y (en) * | 2007-02-05 | 2008-01-02 | 青岛海信电器股份有限公司 | Universal interfere cancelling circuit |
| CN101656901A (en) * | 2008-08-21 | 2010-02-24 | 欧力天工股份有限公司 | Noise-canceling system |
| CN102480280A (en) * | 2010-11-23 | 2012-05-30 | 上海诚佳电子科技有限公司 | Signal simulated arbitrary waveform generator |
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| CN108008205A (en) * | 2017-12-07 | 2018-05-08 | 中国电子科技集团公司第四十研究所 | A kind of self-adapting signal modulate circuit and method applied to electromagnetic field detection |
| CN109407157A (en) * | 2018-12-05 | 2019-03-01 | 中国科学院地质与地球物理研究所 | A kind of induction type magnetic sensor and electromagnetic survey equipment |
| CN109709500A (en) * | 2019-02-28 | 2019-05-03 | 青岛海月辉科技有限公司 | Low-intensity magnetic field signal acquisition circuit |
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