CN109541272B - Analog signal isolation method and isolation circuit based on transformer coupling - Google Patents

Analog signal isolation method and isolation circuit based on transformer coupling Download PDF

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CN109541272B
CN109541272B CN201811576261.2A CN201811576261A CN109541272B CN 109541272 B CN109541272 B CN 109541272B CN 201811576261 A CN201811576261 A CN 201811576261A CN 109541272 B CN109541272 B CN 109541272B
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resistor
capacitor
diode
power supply
electrode
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CN109541272A (en
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乔爱民
罗少轩
李瑜庆
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Bengbu College
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
    • G01R1/30—Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses an analog signal isolation method and an isolation circuit based on transformer coupling, which are characterized in that an analog signal is used as a modulation signal, a square wave signal with higher frequency is used as a carrier signal, a high-frequency transformer is used as an analog multiplier, the analog signal and the square wave signal are subjected to time domain multiplication through the analog multiplier to obtain an amplitude modulation wave, and then the amplitude modulation wave is demodulated by a synchronous demodulation method and then subjected to low-pass filtering to restore the original analog signal. The invention adopts the transformer coupling isolation to play the role of blocking the propagation path of the interference signal, is different from the photoelectric coupling analog signal isolation circuit which has the defect of poor temperature stability, has better temperature stability, combines the modulation and demodulation of signals, and can conveniently realize the isolation of analog signals by taking the transformer as an analog multiplier in a time domain.

Description

Analog signal isolation method and isolation circuit based on transformer coupling
Technical Field
The invention relates to the field of analog signal isolation transformation application, in particular to an analog signal isolation method and an isolation circuit based on transformer coupling.
Background
In many application occasions, especially in application sites with strong interference sources, analog signals, especially low-frequency analog signals, are easy to be interfered by other interference signals such as electromagnetic signals, high-frequency digital signals and the like, so that useless various interference signals are often overlapped in the transmission process of the analog signals, the signal to noise ratio is low, the acquisition precision of the analog signals of a detection system is affected, and the overall precision of the analog signal detection system is reduced. In general, cutting off the propagation path of an interference signal and pushing an analog signal of a relatively low frequency to a high frequency region are effective methods of removing the interference signal and improving the signal-to-noise ratio. At present, the following methods are commonly used for removing interference signals: 1) The frequency selection network is adopted simply, and the filter circuits such as bandpass, bandstop, low pass, high pass and the like are designed through the spectrum analysis of the useful signals and the interference signals, but the practicability is limited by the diversity of frequency components of the interference signals, and the effect is limited; 2) The photoelectric coupling analog isolation circuit is adopted to isolate analog signals, and the method is widely applied at present, but has relatively poor temperature stability; 3) The method has the advantages that the microcontroller is adopted as a core, analog signals are subjected to analog-to-digital conversion, then digital photoelectric isolation is carried out on digital quantities, the isolation method has a certain effect in some application occasions with low interference intensity, however, in a stronger interference environment, in the analog-to-digital conversion process, the converted analog signals are very likely to be overlapped with a considerable part of interference signals, and certain distortion exists between the converted digital quantities and useful analog signals; 4) The integrated analog signal isolation chip with high price is adopted, the isolation effect is good, but the cost is high, so that the application prospect is limited.
Disclosure of Invention
The invention aims to provide an analog signal isolation method and an isolation circuit based on transformer coupling, which can also play a role in blocking the propagation path of an interference signal compared with a method for isolating an analog signal by photoelectric coupling, and the transformer coupling analog signal isolation circuit has better temperature stability and can conveniently realize the isolation of the analog signal.
The technical scheme of the invention is as follows:
An analog signal isolation method based on transformer coupling uses an analog signal as a modulation signal, a higher-frequency square wave signal as a carrier signal, a high-frequency transformer is used as an analog multiplier, the analog signal and the square wave signal are subjected to time domain multiplication through the analog multiplier to obtain an amplitude-modulated wave, and then the amplitude-modulated wave is demodulated by a synchronous demodulation method and then subjected to low-pass filtering to restore the original analog signal;
The analog signal isolation circuit based on the analog signal isolation method comprises an amplitude conversion circuit, a modulation and synchronous demodulation filter circuit and an amplitude inverse conversion circuit;
The amplitude conversion circuit comprises a sensor interface JP1, a zero adjusting circuit, an instrument amplifier U1, a precision operational amplifier U2, a potentiometer RG, a resistor R5, a resistor R6, a resistor R9, a resistor R10, a resistor R11, a resistor R13, a resistor R27, a capacitor C1 and a capacitor C2, wherein the zero adjusting circuit is connected to an IN+ pin of the sensor interface JP1, one end of the resistor R9 and one end of the capacitor C1 are connected with an IN+ pin of the sensor interface JP1, the other end of the resistor R9 and one end of the resistor R5 are connected with an IN-phase input end of the instrument amplifier U1, the other end of the resistor C1 and the other end of the resistor R5 are grounded, a GND pin of the sensor interface JP1 is connected with one end of the resistor R10, the other end of the resistor R10 and one end of the resistor R6 are connected with an output end of the instrument amplifier U1, the other end of the resistor R13 and one end of the capacitor C2 are connected with an output end of the resistor R2, one end of the resistor R2 is connected with an IN series connection of the input end of the precision operational amplifier U2, and the output end of the precision operational amplifier RG 2 is connected with the output end of the precision amplifier U2 is connected with the input end of the precision amplifier U2, and the input end of the precision amplifier is connected with the input end of the precision amplifier, and the precision amplifier is connected with the input end of the precision amplifier input end of the resistor input end;
The modulation and synchronous demodulation filter circuit comprises a reverse protection diode D11, a self-recovery fuse F1, a primary low-pass filter circuit, a resistor R20, a resistor R22, a capacitor C11, a capacitor C12, an NPN triode Q4, an NPN triode Q5, a high-frequency transformer T1, a diode D5, a field effect transistor Q6, a high-frequency transformer T2, a diode D10, a field effect transistor Q7 and a secondary low-pass filter circuit, wherein the positive electrode of the reverse protection diode D11 is connected with a 24V direct current power supply, the positive electrode of the reverse protection diode D11 is connected with one end of the self-recovery fuse F1, the other end of the self-recovery fuse F1 is connected with the input end of the primary low-pass filter circuit, one end of the resistor R20 and one end of the resistor R22 are connected with the output end of the primary low-pass filter circuit, the other end of the resistor R20 is connected with the base electrode of the NPN triode Q4, the other end of the resistor R22 is connected with the base electrode of the NPN triode Q5, the collector of NPN triode Q4 is connected with the base of NPN triode Q5 through a capacitor C11, the collector of NPN triode Q5 is connected with the base of NPN triode Q4 through a capacitor C12, the emitter of NPN triode Q4 and the emitter of NPN triode Q5 are grounded, the collector of NPN triode Q4 is connected with one end of the primary coil of high-frequency transformer T1, the collector of NPN triode Q5 is connected with the other end of the primary coil of high-frequency transformer T1, the output end of the primary low-pass filter circuit is connected with the primary coil of high-frequency transformer T1 as an excitation power supply, the secondary of high-frequency transformer T1 generates three paths of mutually isolated and independent positive and negative symmetrical power supplies, the first path of secondary of high-frequency transformer T1 forms 8V positive and negative symmetrical power supplies, the second path of high-frequency transformer T1 forms 14V positive and negative symmetrical power supplies, the positive pole of the first path of secondary is connected with the negative pole of diode D5, the positive electrode of the diode D5 is connected with the grid electrode of the field effect tube Q6, the source electrode of the field effect tube Q6 is connected with the negative electrode of the first path secondary, the drain electrode of the field effect tube Q6 is connected with one end of the high-frequency transformer T2, the other end of the high-frequency transformer T2 is connected with the output end of the amplitude conversion circuit, one end of the secondary side of the high-frequency transformer T2 is connected with the drain electrode of the field effect tube Q7, the source electrode of the field effect tube Q7 is grounded, the grid electrode of the field effect tube Q7 is connected with the positive electrode of the diode D10, the negative electrode of the diode D10 is connected with a +14V power supply, the second low-pass filter circuit consists of a resistor R12, a capacitor C22, a capacitor C23, a resistor R26 and a capacitor C28, one end of the capacitor C28 is connected with one end of the secondary side of the high-frequency transformer T2, one end of the other end of the capacitor C28 is connected with the other end of the secondary side of the high-frequency transformer T2 through the resistor R26, one end of the capacitor C22 is connected with the other end of the secondary side of the high-frequency transformer T2, one end of the resistor R12 and one end of the capacitor C22 is connected with the other end of the secondary side of the high-frequency transformer C2, the other end of the capacitor C12 is connected with one end of the filter voltage and the other end of the capacitor C23 is connected with the other end of the filter voltage;
The amplitude inverse transformation circuit selects a voltage amplitude inverse transformation circuit or a current amplitude inverse transformation circuit; the voltage amplitude inverse transformation circuit comprises an operational amplifier U3A, a socket P1A, a socket P2A, a resistor R7A, a resistor R24A, a capacitor C21A, a resistor R18A, a resistor R15A, a diode D1A, a capacitor C17A, a capacitor C18A and a resistor R14A, wherein a pin 3 of the socket P1A is a filter voltage input end, a pin 1 is a grounding end, a pin 1 of the socket P1A is a filter voltage input end, a pin 3 is a grounding end, pins 2 and 3 of the socket P1A are in short circuit, pins 2 and 3 of the socket P2A are in short circuit, the pin 2 of the socket P1A is connected with the non-inverting input end of the operational amplifier U3A through the resistor R7A, the pin 2 after the short circuit of the socket P2A is connected with the inverting input end of the operational amplifier U3A through the resistor R24A, one end of the capacitor C21A is connected with the inverting input end of the operational amplifier U3A in parallel, the other end of the capacitor C21A is connected with the resistor R18A in parallel, the other end of the capacitor C18A is connected with the other end of the capacitor C18A, the output end of the capacitor D1A is connected with the output end of the resistor C14A, and the other end of the capacitor C14A is connected with the output end of the resistor C14A is connected with the positive end of the resistor C14A, and the output end of the resistor C is connected with the resistor C17A, and the signal of the output end of the resistor is connected with the resistor C is a standard;
The current amplitude inverse transformation circuit comprises an operational amplifier U3B, a socket P1B, a socket P2B, a socket P3B, a resistor R7B, a resistor R24B, a capacitor C21B, a resistor R18B, a resistor R15B, a diode D1B, a capacitor C17B, a capacitor C18B, a resistor R8B, a resistor R25B, a resistor R17B, a diode D2B, PNP triode Q1B, PNP Q2B and an NPN triode Q3B, a pin 3 of the socket P1B is a filter voltage input end, a pin 1 is a grounding end, a pin 1 of the socket P1B is a filter voltage input end, a pin 3 is a grounding end, pins 2 and 1 of the socket P1B are in short circuit, a pin 2 of the socket P1B is connected with the in-phase input end of the operational amplifier U3B through the resistor R7B, a pin 2 of the socket P2B is connected with the in parallel with the inverting end of the operational amplifier U3B through the resistor R24B, a pin 21B is connected with the inverting end of the operational amplifier U18B, the other end of the parallel connection of the capacitor C21B and the resistor R18B, the emitter of the PNP triode Q2B are connected with the pin 2 of the socket P3B, the output end of the operational amplifier U3B, the positive electrode of the diode D1B and the pin 1 of the socket P3B are connected with one end of the resistor R15B, the negative electrode of the diode D1B is connected with a +14V power supply, one end of the capacitor C17B, one end of the capacitor C18B, the base of the PNP triode Q1B, the collector of the PNP triode Q2B, the negative electrode of the diode D2B and the other end of the resistor R15B are connected as current transmission signal output ends, the other end of the capacitor C17B and the other end of the capacitor C18B are grounded, one end of the resistor R8B is connected with the in-phase input end of the operational amplifier U3B, the other end of the resistor R8B is connected with a +14V power supply, one end of the resistor R25B is connected with a +14V power supply, one end of the resistor R17B is connected with a +14V power supply, the other end of the resistor R25B is connected with the PNP triode Q2B, the other end of the resistor R17B, the base electrode of the PNP triode Q2B and the emitter electrode of the PNP triode Q1B are connected with the collector electrode of the NPN triode Q3B, the collector electrode of the PNP triode Q1B is connected with the base electrode of the NPN triode Q3B, and the collector electrode of the NPN triode Q3B is connected with the anode of the diode D2B.
Firstly, a unipolar signal and a square wave carrier signal of an analog signal after amplitude conversion enter a modulator to be modulated to obtain an amplitude-modulated wave; the amplitude modulated wave is synchronously demodulated by a demodulator, the amplitude modulated wave after synchronous demodulation is filtered by a low-pass filter circuit, a low-frequency signal similar to the spectrum of the original analog signal is remained, and finally the low-frequency signal similar to the spectrum of the original analog signal is restored to the original analog signal through amplitude conversion.
The zero adjusting circuit consists of a potentiometer RZ, a resistor R4, a resistor R1 and a resistor R2, wherein one end of the resistor R1 is grounded, the other end of the resistor R1 is connected with a fixed end of the potentiometer RZ, the other fixed end of the potentiometer RZ is connected with one end of the resistor R2, the other end of the resistor R2 is connected with a regulated power supply E+, and the adjustable end of the potentiometer RZ is connected with an IN+ pin of a sensor interface JP1 through the resistor R4.
The first secondary of the high-frequency transformer T1 forms an 8V positive-negative symmetrical power supply through a circuit formed by a diode D3, a diode D4, an electrolytic capacitor E1, an electrolytic capacitor E2, a capacitor C9 and a capacitor C10, the negative electrode of the diode D3 and the positive electrode of the diode D4 are connected with one end of the first secondary, the positive electrode of the diode D3, the negative electrode of the electrolytic capacitor E1 and one end of the capacitor C9 are connected to serve as-8V power supply output ends, the negative electrode of the diode D4, the positive electrode of the electrolytic capacitor E2 and one end of the capacitor C10 are connected to serve as +8V power supply output ends, and the positive electrode of the electrolytic capacitor E1, the negative electrode of the electrolytic capacitor E2, the other end of the capacitor C9 and the other end of the capacitor C10 are connected to serve as a grounding end GND; the positive power supply input ends of the instrument amplifier U1 and the precise operational amplifier U2 are connected with the +8V power supply output end, and the positive power supply input ends and the negative power supply input ends of the instrument amplifier U1 and the precise operational amplifier U2 are connected with the-8V power supply output end.
The second secondary of the high-frequency transformer T1 forms a 14V positive-negative symmetrical power supply through a circuit formed by a diode D7, a diode D9, an electrolytic capacitor E4, an electrolytic capacitor E6, a capacitor C14 and a capacitor C16, the anode of the diode D7 and the cathode of the diode D9 are connected with one end of the first secondary, the cathode of the diode D7, the anode of the electrolytic capacitor E4 and one end of the capacitor C14 are connected to serve as +14V power supply output ends +14V1, the anode of the diode D9, the cathode of the electrolytic capacitor E6 and one end of the capacitor C16 are connected to serve as-14V power supply output ends-14V 1, and the cathode of the electrolytic capacitor E4, the anode of the electrolytic capacitor E6, the other end of the capacitor C14 and the other end of the capacitor C16 are connected to serve as a grounding end GND1; the +14V power supply output end +14V1 outputs a stabilized voltage power supply E+ through a stabilized voltage chip U4, the second path secondary of the transformer T1 is coupled with the auxiliary primary coil of the transformer T1, the auxiliary primary coil of the transformer T1 forms a 14V positive and negative symmetrical power supply through a circuit composed of a diode D6, a diode D8, an electrolytic capacitor E3, an electrolytic capacitor E5, a capacitor C13 and a capacitor C15, the positive electrode of the diode D6 and the negative electrode of the diode D8 are connected with one end of the auxiliary primary coil of the transformer T1, the negative electrode of the diode D6, the positive electrode of the electrolytic capacitor E3 and one end of the capacitor C13 are connected to serve as +14V power supply output end +14V2, the positive electrode of the diode D8, the negative electrode of the electrolytic capacitor E5 and one end of the capacitor C15 are connected to serve as-14V power supply output end-14V 2, and the negative electrode of the electrolytic capacitor E3, the positive electrode of the electrolytic capacitor E5, the other end of the capacitor C13 and the other end of the capacitor C15 are connected to serve as a grounding end GND2; the positive power input end of the operational amplifier U3 of the voltage amplitude inverse transformation circuit or the current amplitude inverse transformation circuit is connected with the +14V power output end +14V2, and the negative power input end of the operational amplifier U3 of the voltage amplitude inverse transformation circuit or the current amplitude inverse transformation circuit is connected with the-14V power output end-14V 2.
The principle of the invention is as follows:
the reason why the carrier signal of the present invention adopts square wave instead of simple harmonic as the modulation signal is that: in practical application circuits, square wave signals are easy to obtain and have strong carrying capacity, and according to the spectrum analysis of the square wave signals, the square wave signals are formed by superposition of infinite simple harmonic signals with single frequency, and as the center frequency of the square wave signals is equal to the fundamental frequency of multiple harmonics, the cut-off frequency of the last low-pass filter circuit can be conveniently determined only by determining that the center frequency of the square wave signals is far higher than the frequency of the analog signals, so that the original analog signals are finally restored.
Let x (t) be the analog signal, its highest frequency is f m, P (t) be the square wave carrier signal, its center frequency is f o,fo>>fm, and the transformer isolation process of the analog signal is as shown in fig. 1.
The modulator and the demodulator are respectively realized by a high-frequency isolation transformer combined with a related circuit, and according to the related theory of Fourier series and Fourier transformation, the process frequency spectrum of the transformer analog signal isolation based on the square wave carrier signal can be obtained as follows:
Let X '(f) of amplitude spectrum of the analog signal X' (t) after amplitude conversion be fig. 2, and double-side amplitude spectrum of harmonic components of the square wave carrier signal with amplitude of 1 and the synchronous square wave demodulation signal be fig. 3.
After modulation and synchronous demodulation, the amplitude spectrum of the convolution result of the X' (f) and each harmonic component of the periodic square wave can be obtained according to the property of the delta function, and the amplitude spectrum is shown in fig. 4 and 5.
Let X m "(f) be the Fourier transform of X m" (t), the amplitude spectrum of which is FIG. 6.
Comparing fig. 1 and fig. 6, it can be seen that the difference between the X m "(f) spectrum and the X' (f) spectrum of the original signal is mainly that the amplitudes are different in the effective frequency band of the original analog signal, meanwhile, the X m" (f) also has other high-frequency signals, the high-frequency partial signals can be filtered by low-pass filtering, only the low-frequency signals similar to the spectrum of the original analog signal are left after filtering, and the original analog signal can be restored by amplitude transformation.
The invention has the advantages that:
Compared with the method for isolating the analog signals by photoelectric coupling, the method has the advantages that the transformer coupling isolation is adopted to play a role in blocking the propagation paths of the interference signals, and the method is different from the photoelectric coupling analog signal isolation circuit which has the defect of poor temperature stability, has better temperature stability, combines the modulation and demodulation of signals, and can conveniently realize the isolation of the analog signals by taking the transformer as an analog multiplier in a time domain.
Drawings
FIG. 1 is a flow chart of the analog signal isolation method of the present invention.
Fig. 2 is a graph of the amplitude spectrum of x' (t) in fig. 1.
Fig. 3 is a bilateral amplitude spectrum diagram of the harmonic components of the square wave carrier signal P (t) and the synchronous square wave demodulation signal P' (t) with amplitude 1.
Fig. 4 is a graph of the amplitude spectrum of the convolution result of the amplitude spectrum X '(f) of X' (t) in fig. 1.
Fig. 5 is a graph of the amplitude spectrum of the convolution result of each harmonic component of the periodic square wave.
FIG. 6 is a graph of the amplitude spectrum of the Fourier transform of x m "(t) in FIG. 1.
Fig. 7 is a circuit diagram of an amplitude conversion circuit of the present invention.
Fig. 8 is a circuit diagram of a modulation and synchronous demodulation filter circuit of the present invention.
Fig. 9 is a circuit diagram of the voltage amplitude inverse transformation circuit of the present invention.
Fig. 10 is a circuit diagram of an inverse current amplitude transformation circuit of the present invention.
Fig. 11 is a voltage stabilizing circuit diagram of the voltage stabilizing chip U4 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Firstly, a unipolar signal and a square wave carrier signal of an analog signal after amplitude conversion enter a modulator for modulation to obtain an amplitude modulation wave; the amplitude modulated wave is synchronously demodulated by a demodulator, the amplitude modulated wave after synchronous demodulation is filtered by a low-pass filter circuit, a low-frequency signal similar to the spectrum of the original analog signal is remained, and finally the low-frequency signal similar to the spectrum of the original analog signal is restored to the original analog signal through amplitude conversion.
An analog signal isolation circuit based on transformer coupling comprises an amplitude conversion circuit, a modulation and synchronous demodulation filter circuit and an amplitude inverse conversion circuit;
Referring to fig. 7, the amplitude conversion circuit comprises a sensor interface JP1, a zero adjusting circuit, an instrument amplifier U1, a precision operational amplifier U2, a potentiometer RG, a resistor R5, a resistor R6, a resistor R9, a resistor R10, a resistor R11, a resistor R13, a resistor R27, a capacitor C1 and a capacitor C2, wherein the zero adjusting circuit comprises a potentiometer RZ, a resistor R4, a resistor R1 and a resistor R2, one end of the resistor R1 is grounded, the other end of the resistor R1 is connected with a fixed end of the potentiometer RZ, the other fixed end of the potentiometer RZ is connected with one end of the resistor R2, the other end of the resistor R2 is connected with a regulated power supply E+, the adjustable end of the potentiometer RZ is connected with an IN+ pin of the sensor interface JP1 through the resistor R4, one end of the resistor R9 and one end of the capacitor C1 are connected with an IN+ pin of the sensor interface JP1, the other end of the resistor R9 and one end of the resistor R5 are connected with the IN-phase input end of the instrument amplifier U1, the other end of the capacitor C1 and the other end of the resistor R5 are grounded, the GND pin of the sensor interface JP1 is connected with one end of the resistor R10, the other end of the resistor R10 and one end of the resistor R6 are connected with the anti-phase input end of the instrument amplifier U1, the other end of the resistor R6 and one end of the resistor R13 are connected with the output end of the instrument amplifier U1, the other end of the resistor R13 and one end of the capacitor C2 are connected with the IN-phase input end of the precision operational amplifier U2, the other end of the capacitor C2 is grounded, the anti-phase input end of the precision operational amplifier U2 is connected with the sliding end of the potentiometer RG, one fixed end of the potentiometer RG is connected with the resistor R11 IN series, the other fixed end of the potentiometer RG is connected with the output end of the precision operational amplifier U2 IN series, the output end of the precision operational amplifier U2 is used as the output end of the amplitude conversion circuit to output a unipolar signal Vin1 after amplitude conversion; the analog signal can be connected into unipolar and differential signals, taking differential analog small signals output by a sensor as an example, the instrument amplifier U1 and the precision operational amplifier U2 realize amplitude transformation of the differential analog signals, the potentiometers RZ, R4, R1 and R2 form a zero-setting circuit, zero adjustment of the differential signals is realized, and the amplitude adjustment can be realized through the potentiometer RG;
Referring to fig. 8, the modulation and synchronous demodulation filter circuit comprises a reverse protection diode D11, a self-recovery fuse F1, a primary low-pass filter circuit, a resistor R20, a resistor R22, a capacitor C11, a capacitor C12, an NPN triode Q4, an NPN triode Q5, a high-frequency transformer T1, a diode D5, a field effect transistor Q6, a high-frequency transformer T2, a diode D10, a field effect transistor Q7 and a secondary low-pass filter circuit, wherein the positive electrode of the reverse protection diode D11 is connected with a 24V dc power supply, the positive electrode of the reverse protection diode D11 is connected with one end of the self-recovery fuse F1, the other end of the self-recovery fuse F1 is connected with the input end of the primary low-pass filter circuit, one end of the resistor R20 and one end of the resistor R22 are connected with the output end of the primary low-pass filter circuit, the other end of the resistor R20 is connected with the base of the NPN triode Q4, the other end of the resistor R22 is connected with the base of the NPN triode Q5, the collector of NPN triode Q4 is connected with the base of NPN triode Q5 through a capacitor C11, the collector of NPN triode Q5 is connected with the base of NPN triode Q4 through a capacitor C12, the emitter of NPN triode Q4 and the emitter of NPN triode Q5 are grounded, the collector of NPN triode Q4 is connected with one end of the primary coil of high-frequency transformer T1, the collector of NPN triode Q5 is connected with the other end of the primary coil of high-frequency transformer T1, the output end of the primary low-pass filter circuit is connected with the primary coil of high-frequency transformer T1 as an excitation power supply, the secondary of high-frequency transformer T1 generates three paths of mutually isolated and independent positive and negative symmetrical power supplies, the first path of secondary of high-frequency transformer T1 forms 8V positive and negative symmetrical power supplies, the second path of high-frequency transformer T1 forms 14V positive and negative symmetrical power supplies, the positive electrode of the first path of secondary is connected with the negative electrode of diode D5, the positive electrode of diode D5 is connected with the gate of field effect transistor Q6, the source electrode of the field effect tube Q6 is connected with the cathode of the first path of secondary, the drain electrode of the field effect tube Q6 is connected with one end of the high-frequency transformer T2, the other end of the high-frequency transformer T2 is connected with the output end of the amplitude conversion circuit, one end of the secondary of the high-frequency transformer T2 is connected with the drain electrode of the field effect tube Q7, the source electrode of the field effect tube Q7 is grounded, the grid electrode of the field effect tube Q7 is connected with the anode of the diode D10, the cathode of the diode D10 is connected with a +14V power supply, the second low-pass filter circuit is composed of a resistor R12, a capacitor C22, a capacitor C23, a resistor R26 and a capacitor C28, one end of the capacitor C28 is connected with one end of the secondary of the high-frequency transformer T2, one end of the other end of the capacitor C28 is connected with the other end of the secondary of the high-frequency transformer T2 through a resistor R26, one end of the capacitor C22 is connected with the other end of the secondary of the high-frequency transformer T2, the other end of the resistor R12 and one end of the capacitor C23 are connected with the other end of the capacitor C23 as filter voltage output ends, and the other end of the capacitor C22 is connected with the other end of the capacitor C23; the push-pull circuit consisting of R20, R22, C11, C12, Q4 and Q5 and the primary of the high-frequency transformer T1 generates a 40KHz square wave signal for exciting the primary of the T1, and three paths of mutually isolated and independent positive and negative symmetrical power supplies are generated at the secondary of the T1; modulating a square wave carrier signal and an analog signal Vin1 subjected to amplitude conversion by D5, a field effect transistor Q6 and a primary implementation of a high-frequency transformer T2; the primary to secondary turns ratio of T2 is 1:1, a synchronous demodulation circuit is formed by a primary side of T2, D10 and a field effect transistor Q7, and a low-pass filter circuit formed by R12, C22, C23, R26 and C28 is used for filtering amplitude modulation waves after synchronous demodulation to obtain a unipolar voltage signal Vo1.
The first secondary of the high-frequency transformer T1 forms an 8V positive-negative symmetrical power supply through a circuit formed by a diode D3, a diode D4, an electrolytic capacitor E1, an electrolytic capacitor E2, a capacitor C9 and a capacitor C10, wherein the cathode of the diode D3 and the anode of the diode D4 are connected with one end of the first secondary, the anode of the diode D3, the cathode of the electrolytic capacitor E1 and one end of the capacitor C9 are connected to serve as-8V power supply output ends, the cathode of the diode D4, the anode of the electrolytic capacitor E2 and one end of the capacitor C10 are connected to serve as +8V power supply output ends, and the anode of the electrolytic capacitor E1, the cathode of the electrolytic capacitor E2, the other end of the capacitor C9 and the other end of the capacitor C10 are connected to serve as a grounding end GND; the positive power supply input ends of the instrument amplifier U1 and the precise operational amplifier U2 are connected with the +8V power supply output end, and the positive power supply input ends and the negative power supply input ends of the instrument amplifier U1 and the precise operational amplifier U2 are connected with the-8V power supply output end; the second secondary of the high-frequency transformer T1 forms a 14V positive-negative symmetrical power supply through a circuit formed by a diode D7, a diode D9, an electrolytic capacitor E4, an electrolytic capacitor E6, a capacitor C14 and a capacitor C16, wherein the anode of the diode D7 and the cathode of the diode D9 are connected with one end of the first secondary, the cathode of the diode D7, the anode of the electrolytic capacitor E4 and one end of the capacitor C14 are connected to be used as +14V power supply output ends +14V1, the anode of the diode D9, the cathode of the electrolytic capacitor E6 and one end of the capacitor C16 are connected to be used as-14V power supply output ends-14V 1, and the cathode of the electrolytic capacitor E4, the anode of the electrolytic capacitor E6, the other end of the capacitor C14 and the other end of the capacitor C16 are connected to be used as a grounding end GND1; the +14V power supply output end +14V1 outputs a stabilized voltage power supply E+ through a stabilized voltage chip U4 (see FIG. 11), the second path secondary of the transformer T1 is coupled with the auxiliary primary coil of the transformer T1, the auxiliary primary coil of the transformer T1 forms a 14V positive and negative symmetrical power supply through a circuit composed of a diode D6, a diode D8, an electrolytic capacitor E3, an electrolytic capacitor E5, a capacitor C13 and a capacitor C15, the anode of the diode D6 and the cathode of the diode D8 are connected with one end of the auxiliary primary coil of the transformer T1, the cathode of the diode D6, the anode of the electrolytic capacitor E3 and one end of the capacitor C13 are connected to serve as +14V power supply output end +14V2, the anode of the diode D8, the cathode of the electrolytic capacitor E5 and one end of the capacitor C15 are connected to serve as-14V power supply output end-14V 2, and the cathode of the electrolytic capacitor E3, the anode of the electrolytic capacitor E5, the anode of the capacitor C13 and the other end of the capacitor C13 are connected to serve as a grounding end GND2; the positive power input end of the operational amplifier U3 of the voltage amplitude inverse transformation circuit or the current amplitude inverse transformation circuit is connected with the +14V power output end +14V2, and the negative power input end of the operational amplifier U3 of the voltage amplitude inverse transformation circuit or the current amplitude inverse transformation circuit is connected with the-14V power output end-14V 2;
The amplitude inverse transformation circuit selects a voltage amplitude inverse transformation circuit or a current amplitude inverse transformation circuit;
Referring to fig. 9, the voltage amplitude inverse transformation circuit includes an operational amplifier U3A, a socket P1A, a socket P2A, a resistor R7A, a resistor R24A, a capacitor C21A, a resistor R18A, a resistor R15A, a diode D1A, a capacitor C17A, a capacitor C18A and a resistor R14A, a pin 3 of the socket P1A is a filter voltage input terminal, a pin 1 is a ground terminal, a pin 1 of the socket P1A is a filter voltage input terminal, a pin 3 is a ground terminal, pins 2 and 3 of the socket P1A are shorted, pins 2 and 3 of the socket P2A are connected with an in-phase input terminal of the operational amplifier U3A through the resistor R7A, the pin 2 after shorting of the socket P2A is connected with an inverting input terminal of the operational amplifier U3A through the resistor R24A, one end of the capacitor C21A and the resistor R18A is connected with the inverting input terminal of the operational amplifier U3A in parallel, the other end of the capacitor C21A and the resistor R18A is connected with the other end of the capacitor C1A parallel with the resistor R1A, the other end of the output terminal of the operational amplifier U3A is grounded, the other end of the capacitor C1A is connected with the other end of the resistor C14A and the other end of the resistor C14A is connected with the output terminal of the resistor C17A, and the other end of the resistor C1A is connected with the output terminal of the resistor C14A and the resistor b is connected with the output end of the resistor b 2;
Referring to fig. 10, the inverse current amplitude transformation circuit includes an operational amplifier U3B, a socket P1B, a socket P2B, a socket P3B, a resistor R7B, a resistor R24B, a capacitor C21B, a resistor R18B, a resistor R15B, a diode D1B, a capacitor C17B, a capacitor C18B, a resistor R8B, a resistor R25B, a resistor R17B, a diode D2B, PNP, a transistor Q1B, PNP Q2B, and an NPN transistor Q3B, a pin 3 of the socket P1B is a filtered voltage input terminal, a pin 1 is a ground terminal, a pin 1 of the socket P1B is a filtered voltage input terminal, a pin 3 is a ground terminal, pins 2 and 1 of the socket P1B are shorted, a pin 2 of the socket P2B is shorted to an in-phase input terminal of the operational amplifier U3B through the resistor R7B, a pin 2 of the socket P2B is shorted to an inverting input terminal of the operational amplifier U3B through the resistor R24B, a capacitor C21B is connected to an inverting terminal of the operational amplifier U3B in parallel, the other end of the capacitor C21B and the resistor R18B after being connected in parallel, the emitter of the PNP triode Q2B is connected with the pin 2 of the socket P3B, the output end of the operational amplifier U3B, the positive electrode of the diode D1B and the pin 1 of the socket P3B are connected with one end of the resistor R15B, the negative electrode of the diode D1B is connected with the +14V power supply, one end of the capacitor C17B, one end of the capacitor C18B, the base of the PNP triode Q1B, the collector of the PNP triode Q2B, the negative electrode of the diode D2B and the other end of the resistor R15B are connected as current transmission signal output ends, the other end of the capacitor C17B and the other end of the capacitor C18B are grounded, one end of the resistor R8B is connected with the in-phase input end of the operational amplifier U3B, the other end of the resistor R8B is connected with the +14V power supply, one end of the resistor R25B is connected with the +14V power supply, one end of the resistor R17B is connected with the +14V power supply, the other end of the resistor R25B is connected with the PNP triode Q2B, the other end of the emitter of the resistor R17B is grounded, the base electrode of the PNP triode Q2B and the emitter electrode of the PNP triode Q1B are connected with the collector electrode of the NPN triode Q3B, the collector electrode of the PNP triode Q1B is connected with the base electrode of the NPN triode Q3B, and the collector electrode of the NPN triode Q3B is connected with the anode electrode of the diode D2B.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (5)

1. An analog signal isolation method based on transformer coupling is characterized in that: taking the analog signal as a modulation signal, taking a square wave signal with higher frequency as a carrier signal, taking a high-frequency transformer as an analog multiplier, performing time domain multiplication on the analog signal and the square wave signal through the analog multiplier to obtain an amplitude-modulated wave, demodulating the amplitude-modulated wave by using a synchronous demodulation method, and then performing low-pass filtering to restore the original analog signal;
The analog signal isolation circuit based on the analog signal isolation method comprises an amplitude conversion circuit, a modulation and synchronous demodulation filter circuit and an amplitude inverse conversion circuit;
The amplitude conversion circuit comprises a sensor interface JP1, a zero adjusting circuit, an instrument amplifier U1, a precision operational amplifier U2, a potentiometer RG, a resistor R5, a resistor R6, a resistor R9, a resistor R10, a resistor R11, a resistor R13, a resistor R27, a capacitor C1 and a capacitor C2, wherein the zero adjusting circuit is connected to an IN+ pin of the sensor interface JP1, one end of the resistor R9 and one end of the capacitor C1 are connected with an IN+ pin of the sensor interface JP1, the other end of the resistor R9 and one end of the resistor R5 are connected with an IN-phase input end of the instrument amplifier U1, the other end of the resistor C1 and the other end of the resistor R5 are grounded, a GND pin of the sensor interface JP1 is connected with one end of the resistor R10, the other end of the resistor R10 and one end of the resistor R6 are connected with an output end of the instrument amplifier U1, the other end of the resistor R13 and one end of the capacitor C2 are connected with an output end of the resistor R2, one end of the resistor R2 is connected with an IN series connection of the input end of the precision operational amplifier U2, and the output end of the precision operational amplifier RG 2 is connected with the output end of the precision amplifier U2 is connected with the input end of the precision amplifier U2, and the input end of the precision amplifier is connected with the input end of the precision amplifier, and the precision amplifier is connected with the input end of the precision amplifier input end of the resistor input end;
The modulation and synchronous demodulation filter circuit comprises a reverse protection diode D11, a self-recovery fuse F1, a primary low-pass filter circuit, a resistor R20, a resistor R22, a capacitor C11, a capacitor C12, an NPN triode Q4, an NPN triode Q5, a high-frequency transformer T1, a diode D5, a field effect transistor Q6, a high-frequency transformer T2, a diode D10, a field effect transistor Q7 and a secondary low-pass filter circuit, wherein the positive electrode of the reverse protection diode D11 is connected with a 24V direct current power supply, the positive electrode of the reverse protection diode D11 is connected with one end of the self-recovery fuse F1, the other end of the self-recovery fuse F1 is connected with the input end of the primary low-pass filter circuit, one end of the resistor R20 and one end of the resistor R22 are connected with the output end of the primary low-pass filter circuit, the other end of the resistor R20 is connected with the base electrode of the NPN triode Q4, the other end of the resistor R22 is connected with the base electrode of the NPN triode Q5, the collector of NPN triode Q4 is connected with the base of NPN triode Q5 through a capacitor C11, the collector of NPN triode Q5 is connected with the base of NPN triode Q4 through a capacitor C12, the emitter of NPN triode Q4 and the emitter of NPN triode Q5 are grounded, the collector of NPN triode Q4 is connected with one end of the primary coil of high-frequency transformer T1, the collector of NPN triode Q5 is connected with the other end of the primary coil of high-frequency transformer T1, the output end of the primary low-pass filter circuit is connected with the primary coil of high-frequency transformer T1 as an excitation power supply, the secondary of high-frequency transformer T1 generates three paths of mutually isolated and independent positive and negative symmetrical power supplies, the first path of secondary of high-frequency transformer T1 forms 8V positive and negative symmetrical power supplies, the second path of high-frequency transformer T1 forms 14V positive and negative symmetrical power supplies, the positive pole of the first path of secondary is connected with the negative pole of diode D5, the positive electrode of the diode D5 is connected with the grid electrode of the field effect tube Q6, the source electrode of the field effect tube Q6 is connected with the negative electrode of the first path secondary, the drain electrode of the field effect tube Q6 is connected with one end of the high-frequency transformer T2, the other end of the high-frequency transformer T2 is connected with the output end of the amplitude conversion circuit, one end of the secondary side of the high-frequency transformer T2 is connected with the drain electrode of the field effect tube Q7, the source electrode of the field effect tube Q7 is grounded, the grid electrode of the field effect tube Q7 is connected with the positive electrode of the diode D10, the negative electrode of the diode D10 is connected with a +14V power supply, the second low-pass filter circuit consists of a resistor R12, a capacitor C22, a capacitor C23, a resistor R26 and a capacitor C28, one end of the capacitor C28 is connected with one end of the secondary side of the high-frequency transformer T2, one end of the other end of the capacitor C28 is connected with the other end of the secondary side of the high-frequency transformer T2 through the resistor R26, one end of the capacitor C22 is connected with the other end of the secondary side of the high-frequency transformer T2, one end of the resistor R12 and one end of the capacitor C22 is connected with the other end of the secondary side of the high-frequency transformer C2, the other end of the capacitor C12 is connected with one end of the filter voltage and the other end of the capacitor C23 is connected with the other end of the filter voltage;
The amplitude inverse transformation circuit selects a voltage amplitude inverse transformation circuit or a current amplitude inverse transformation circuit; the voltage amplitude inverse transformation circuit comprises an operational amplifier U3A, a socket P1A, a socket P2A, a resistor R7A, a resistor R24A, a capacitor C21A, a resistor R18A, a resistor R15A, a diode D1A, a capacitor C17A, a capacitor C18A and a resistor R14A, wherein a pin 3 of the socket P1A is a filter voltage input end, a pin 1 is a grounding end, a pin 1 of the socket P1A is a filter voltage input end, a pin 3 is a grounding end, pins 2 and 3 of the socket P1A are in short circuit, pins 2 and 3 of the socket P2A are in short circuit, the pin 2 of the socket P1A is connected with the non-inverting input end of the operational amplifier U3A through the resistor R7A, the pin 2 after the short circuit of the socket P2A is connected with the inverting input end of the operational amplifier U3A through the resistor R24A, one end of the capacitor C21A is connected with the inverting input end of the operational amplifier U3A in parallel, the other end of the capacitor C21A is connected with the resistor R18A in parallel, the other end of the capacitor C18A is connected with the other end of the capacitor C18A, the output end of the capacitor D1A is connected with the output end of the resistor C14A, and the other end of the capacitor C14A is connected with the output end of the resistor C14A is connected with the positive end of the resistor C14A, and the output end of the resistor C is connected with the resistor C17A, and the signal of the output end of the resistor is connected with the resistor C is a standard;
The current amplitude inverse transformation circuit comprises an operational amplifier U3B, a socket P1B, a socket P2B, a socket P3B, a resistor R7B, a resistor R24B, a capacitor C21B, a resistor R18B, a resistor R15B, a diode D1B, a capacitor C17B, a capacitor C18B, a resistor R8B, a resistor R25B, a resistor R17B, a diode D2B, PNP triode Q1B, PNP Q2B and an NPN triode Q3B, a pin 3 of the socket P1B is a filter voltage input end, a pin 1 is a grounding end, a pin 1 of the socket P1B is a filter voltage input end, a pin 3 is a grounding end, pins 2 and 1 of the socket P1B are in short circuit, a pin 2 of the socket P1B is connected with the in-phase input end of the operational amplifier U3B through the resistor R7B, a pin 2 of the socket P2B is connected with the in parallel with the inverting end of the operational amplifier U3B through the resistor R24B, a pin 21B is connected with the inverting end of the operational amplifier U18B, the other end of the parallel connection of the capacitor C21B and the resistor R18B, the emitter of the PNP triode Q2B are connected with the pin 2 of the socket P3B, the output end of the operational amplifier U3B, the positive electrode of the diode D1B and the pin 1 of the socket P3B are connected with one end of the resistor R15B, the negative electrode of the diode D1B is connected with a +14V power supply, one end of the capacitor C17B, one end of the capacitor C18B, the base of the PNP triode Q1B, the collector of the PNP triode Q2B, the negative electrode of the diode D2B and the other end of the resistor R15B are connected as current transmission signal output ends, the other end of the capacitor C17B and the other end of the capacitor C18B are grounded, one end of the resistor R8B is connected with the in-phase input end of the operational amplifier U3B, the other end of the resistor R8B is connected with a +14V power supply, one end of the resistor R25B is connected with a +14V power supply, one end of the resistor R17B is connected with a +14V power supply, the other end of the resistor R25B is connected with the PNP triode Q2B, the other end of the resistor R17B, the base electrode of the PNP triode Q2B and the emitter electrode of the PNP triode Q1B are connected with the collector electrode of the NPN triode Q3B, the collector electrode of the PNP triode Q1B is connected with the base electrode of the NPN triode Q3B, and the collector electrode of the NPN triode Q3B is connected with the anode of the diode D2B.
2. The method for isolating analog signals based on transformer coupling according to claim 1, wherein: firstly, a unipolar signal and a square wave carrier signal of an analog signal after amplitude conversion enter a modulator to be modulated to obtain an amplitude-modulated wave; the amplitude modulated wave is synchronously demodulated by a demodulator, the amplitude modulated wave after synchronous demodulation is filtered by a low-pass filter circuit, a low-frequency signal similar to the spectrum of the original analog signal is remained, and finally the low-frequency signal similar to the spectrum of the original analog signal is restored to the original analog signal through amplitude conversion.
3. The transformer coupling-based analog signal isolation method of claim 1, wherein: the zero adjusting circuit consists of a potentiometer RZ, a resistor R4, a resistor R1 and a resistor R2, wherein one end of the resistor R1 is grounded, the other end of the resistor R1 is connected with a fixed end of the potentiometer RZ, the other fixed end of the potentiometer RZ is connected with one end of the resistor R2, the other end of the resistor R2 is connected with a regulated power supply E+, and the adjustable end of the potentiometer RZ is connected with an IN+ pin of a sensor interface JP1 through the resistor R4.
4. The transformer coupling-based analog signal isolation method of claim 1, wherein: the first secondary of the high-frequency transformer T1 forms an 8V positive-negative symmetrical power supply through a circuit formed by a diode D3, a diode D4, an electrolytic capacitor E1, an electrolytic capacitor E2, a capacitor C9 and a capacitor C10, the negative electrode of the diode D3 and the positive electrode of the diode D4 are connected with one end of the first secondary, the positive electrode of the diode D3, the negative electrode of the electrolytic capacitor E1 and one end of the capacitor C9 are connected to serve as-8V power supply output ends, the negative electrode of the diode D4, the positive electrode of the electrolytic capacitor E2 and one end of the capacitor C10 are connected to serve as +8V power supply output ends, and the positive electrode of the electrolytic capacitor E1, the negative electrode of the electrolytic capacitor E2, the other end of the capacitor C9 and the other end of the capacitor C10 are connected to serve as a grounding end GND; the positive power supply input ends of the instrument amplifier U1 and the precise operational amplifier U2 are connected with the +8V power supply output end, and the positive power supply input ends and the negative power supply input ends of the instrument amplifier U1 and the precise operational amplifier U2 are connected with the-8V power supply output end.
5. A transformer coupling based analog signal isolation method according to claim 3, wherein: the second secondary of the high-frequency transformer T1 forms a 14V positive-negative symmetrical power supply through a circuit formed by a diode D7, a diode D9, an electrolytic capacitor E4, an electrolytic capacitor E6, a capacitor C14 and a capacitor C16, the anode of the diode D7 and the cathode of the diode D9 are connected with one end of the first secondary, the cathode of the diode D7, the anode of the electrolytic capacitor E4 and one end of the capacitor C14 are connected to serve as +14V power supply output ends +14V1, the anode of the diode D9, the cathode of the electrolytic capacitor E6 and one end of the capacitor C16 are connected to serve as-14V power supply output ends-14V 1, and the cathode of the electrolytic capacitor E4, the anode of the electrolytic capacitor E6, the other end of the capacitor C14 and the other end of the capacitor C16 are connected to serve as a grounding end GND1; the +14V power supply output end +14V1 outputs a stabilized voltage power supply E+ through a stabilized voltage chip U4, the second path secondary of the transformer T1 is coupled with the auxiliary primary coil of the transformer T1, the auxiliary primary coil of the transformer T1 forms a 14V positive and negative symmetrical power supply through a circuit composed of a diode D6, a diode D8, an electrolytic capacitor E3, an electrolytic capacitor E5, a capacitor C13 and a capacitor C15, the positive electrode of the diode D6 and the negative electrode of the diode D8 are connected with one end of the auxiliary primary coil of the transformer T1, the negative electrode of the diode D6, the positive electrode of the electrolytic capacitor E3 and one end of the capacitor C13 are connected to serve as +14V power supply output end +14V2, the positive electrode of the diode D8, the negative electrode of the electrolytic capacitor E5 and one end of the capacitor C15 are connected to serve as-14V power supply output end-14V 2, and the negative electrode of the electrolytic capacitor E3, the positive electrode of the electrolytic capacitor E5, the other end of the capacitor C13 and the other end of the capacitor C15 are connected to serve as a grounding end GND2; the positive power input end of the operational amplifier U3 of the voltage amplitude inverse transformation circuit or the current amplitude inverse transformation circuit is connected with the +14V power output end +14V2, and the negative power input end of the operational amplifier U3 of the voltage amplitude inverse transformation circuit or the current amplitude inverse transformation circuit is connected with the-14V power output end-14V 2.
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