A signal acquisition system for surface acoustic wave magnetic sensor

Abstract

A signal acquisition system for a surface acoustic wave magnetic sensor includes a first oscillation circuit, a second oscillation circuit, a frequency mixing circuit, an amplification and shaping circuit, and a single-chip computer frequency measurement circuit; the first input end of the frequency mixing circuit is connected to the first oscillation circuit, and the second input end of the frequency mixing circuit 3 is connected to the second oscillation circuit; the amplification and shaping circuit is connected to the signal output end IF of the frequency mixing circuit; the frequency measurement circuit is mainly connected to the signal output end of the amplification and shaping circuit; the first oscillation circuit and the second oscillation circuit are both used to output the SAW sensor measurement frequency signal. The present invention adopts a Pierce type oscillation circuit, and the SAW sensor is easy to self-excite and oscillate to output a sinusoidal signal of a specific frequency. Further, the magnetic field strength can be measured by a single difference, that is, the change in the frequency of the measurement branch signal. High precision, wide detection range, and no test blind area.

Description

Technical Field

[0001] The invention belongs to the technical field of signal acquisition systems, and in particular relates to a signal acquisition system for a surface acoustic wave magnetic sensor. Background Art

[0002] Surface acoustic wave (SAW) is an elastic wave that propagates along the surface of a solid. Through the interdigital transducer structure, surface acoustic waves can be excited and detected on the surface of piezoelectric materials. When magnetostrictive films (FeCo, NiFe, Metglas, etc.) are introduced into the interdigital transducer, the Young's modulus of the magnetostrictive material changes under the action of an external magnetic field, and the velocity of the surface acoustic wave also changes accordingly, thereby achieving the purpose of detecting weak magnetic fields. The reported magnetic field sensitivity of high-Q SAW resonators can reach more than 150Hz / μT, and the detection limit can reach nT / Hz 1 / 2 Compared with other magnetic field sensors, SAW sensors can directly output specific frequency signals without analog-to-digital conversion, which is convenient for information processing. At the same time, it has the advantages of being passive, easy to oscillate, easy to integrate, and mass-producible, and has potential application value in geomagnetic navigation, biomagnetic signal detection, smart grid and other fields.

[0003] The change of SAW wave velocity induced by the external environment can be reflected as the change of sensor output signal (frequency, phase, amplitude). To obtain this information change, a matching signal acquisition system is required. The SAW sensor is directly connected to the vector network analyzer, and the S parameters of the SAW are analyzed to easily achieve the detection purpose. However, due to the high power consumption and non-portability of the instrument, this method is limited to laboratory use. In order to reduce the power consumption and volume of the test system, an open-loop detection system can be formed by a signal generator and a phase detector / amplitude comparator. The phase / amplitude detection of the SAW sensor is realized. In the phase detection method, a signal close to the center frequency of the SAW sensor is used to excite the device to output a feedback signal. The phase detector compares the phase of the excitation signal and the feedback signal, and represents the phase difference of the two signals in the form of a voltage signal. This method must ensure that the frequency of the excitation signal is consistent with that of the feedback signal, otherwise the dual-channel phase difference cannot be stable. The amplitude detection method (DDS detection method) is similar to the detection of the vector network analyzer. The DDS generates a swept frequency signal to excite the SAW sensor, and the amplitude comparator obtains the amplitude of the feedback signal. The frequency corresponding to the minimum amplitude attenuation is the sensor resonant frequency. In this method, due to the fluctuation of the DDS excitation signal frequency, the slight change of the SAW resonant frequency is sometimes difficult to detect, that is, there is a blind spot for sensor signal detection. Although the phase / amplitude detection method does not involve frequency measurement, the output frequency range of the signal generator is limited, making it difficult for high-frequency SAW devices to oscillate, and the range of detection signals is limited. In addition, the circuit structure of this method is complex, which is not conducive to sensor array detection and is difficult to apply in practice. Summary of the invention

[0004] The object of the present invention is to provide a signal acquisition system for a surface acoustic wave magnetic sensor to solve the above-mentioned problem.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A signal acquisition system for a surface acoustic wave magnetic sensor comprises a first oscillation circuit, a second oscillation circuit, a frequency mixing circuit, an amplification and shaping circuit and a single-chip computer frequency measurement circuit; the first input end of the frequency mixing circuit is connected to the first oscillation circuit, and the second input end of the frequency mixing circuit 3 is connected to the second oscillation circuit; the amplification and shaping circuit is connected to a signal output end IF of the frequency mixing circuit; the frequency measurement circuit is mainly connected to the signal output end of the amplification and shaping circuit; the first oscillation circuit and the second oscillation circuit are both used to output a SAW sensor measurement frequency signal.

[0007] Furthermore, the first oscillation circuit includes capacitors C1, C2, C3, C4, C5, C6, C7, C8, C9 and C10, inductors L1, L2, L3, L4, L5 and L6, resistors R1, R2 and R3, a 5V DC power supply, a high-frequency transistor 2SC3357, and a 4-pin SAW sensor; capacitors C1 / C2 are connected in series to the resonant circuit of the SAW sensor, inductor L1 is connected in parallel with the SAW sensor, capacitor C3 is connected between the resonant network and the amplifier circuit, and resistor R2 is connected between the base of the high-frequency transistor 2SC3357 and ground. , resistor R3 and capacitor C4 are connected in parallel between the emitter of high-frequency transistor 2SC3357 and ground, inductor L2, resistor R1, and inductor L3 are connected in series between the collector and base of high-frequency transistor 2SC3357 in sequence, capacitor C5 / C6 are connected in parallel between the negative electrode of 5V DC power supply and ground, capacitor C7, inductor L4, capacitor C8, inductor L6, and capacitor C10 are connected in series between the connection end of SAW sensor and inductor L1 and output end Net1 in sequence, inductor L5 and capacitor C9 are connected in parallel between C8 and L6; the SAW sensor is plated with a magnetic sensitive film.

[0008] Furthermore, the second oscillation circuit includes capacitors C11, C12, C13, C14, C15, C16, C17, C18, C19 and C20, inductors L7, L8, L9, L10, L11 and L12, resistors R4, R5 and R6, a 5V DC power supply, a high-frequency transistor 2SC3357, and a 4-pin SAW sensor; capacitors C11 / C12 are connected in series to the resonant circuit of the SAW sensor, inductor L7 is connected in parallel with the SAW sensor, capacitor C13 is connected between the resonant network and the amplifier circuit, and resistor R5 is connected to the high-frequency transistor 2SC3 357 base and ground, resistor R6 and capacitor C14 are connected in parallel between the emitter of high-frequency transistor 2SC3357 and ground, inductor L9, resistor R4, and inductor L8 are connected in series between the collector and base of high-frequency transistor 2SC3357 in turn, capacitor C15 / C16 are connected in parallel between the negative electrode of 5V DC power supply and ground, capacitor C17, inductor L10, capacitor C18, inductor L12, and capacitor C20 are connected in series between the connection end of SAW sensor and inductor L7 and output end Net2 in turn, and inductor L11 and capacitor C19 are connected in parallel between C18 and L12.

[0009] Further, the mixing circuit includes a mixer AD831 and a low-pass filter LFCN-255+; the first pin of the mixer AD831 is connected to the positive electrode of the power supply +5V, the second and third pins of the mixer AD831 are connected to the positive electrode of the power supply +5V through a capacitor C21 and are grounded through capacitors C21 and C34 connected in series, the fourth pin of the mixer AD831 is grounded, the fifth pin of the mixer is connected to the negative electrode of the power supply -5V and is grounded through a capacitor C22, and the sixth pin of the mixer is connected to the first oscillation circuit through a capacitor C23. The output terminal Net1 of the mixer is connected to the ground through the resistor R7, the 7th pin of the mixer is grounded through the capacitor C24, the 8th pin of the mixer is connected to the negative pole of the power supply -5V and is grounded through the capacitor C25, the 9th pin of the mixer is connected to the positive pole of the power supply +5V and is grounded through the capacitor C26, the 10th pin of the mixer is connected to the output terminal Net2 of the second oscillation circuit through the capacitor C27 and is grounded through the resistor R8, the 11th pin of the mixer is grounded and connected to the output terminal Net2 of the second oscillation circuit through the resistor R8, and the 11th pin of the mixer is connected to the ground and is connected to the output terminal Net2 of the second oscillation circuit through the resistor R8. Pin 2 is connected to the positive pole of the power supply +5V and grounded through capacitor C28, pin 13 of the mixer is grounded and connected to the output terminal Net2 of the second oscillation circuit through resistor R8, pin 14 of the mixer is connected to the positive pole of the power supply +5V through resistor R9 and grounded through resistor R9 and capacitor C29 connected in series, pin 15 of the mixer is connected to the negative pole of the power supply -5V and grounded through capacitor C30, pin 16 of the mixer is connected to pin 0 of the low-pass filter LFCN-255+ through resistor R10 and capacitor C31 connected in series , the 1st and 3rd pins of the low-pass filter LFCN-255+ are grounded, the 2nd pin is the mixing signal output terminal IF, the 17th pin of the mixer is connected to the 16th pin through the resistor R11 and to the 18th pin through the resistor R12, the 18th pin of the mixer is connected to the positive electrode of the power supply +5V through the resistor R14 and to the ground through the parallel capacitor C32 and the resistor R13, the 19th and 20th pins of the mixer are connected to the positive electrode of the power supply +5V through the capacitor C33 and to the ground through the series capacitors C33 and C34.

[0010] Furthermore, the amplification and shaping circuit includes an operational amplifier LM318 and a voltage comparator LM311; the signal output terminal IF of the mixing circuit is connected to the third pin of the operational amplifier LM318 through a capacitor C35 and a resistor R15 connected in series, the second pin of the operational amplifier LM318 is grounded through a resistor R16, the fourth pin of the operational amplifier LM318 is connected to the negative pole of the power supply -5V, the fourth pin of the operational amplifier LM318 is connected to the third pin of the voltage comparator LM311 through a resistor R18, and is grounded through a resistor R16 and a resistor R17 connected in series, the seventh pin of the operational amplifier LM318 is connected to the positive pole of the power supply +5V, the second pin of the voltage comparator LM311 is grounded through a resistor R19, the fourth pin of the voltage comparator LM311 is grounded, the seventh pin of the voltage comparator LM311 is connected to the power supply +5V through a resistor R20, and the sixth pin of the voltage comparator LM311 is the signal output terminal Net3 of the amplification and shaping circuit.

[0011] Furthermore, the frequency measurement circuit includes a chip STM32F103C8T6; the first pin of the chip is connected to a 3.3V level through a resistor R21, the second pin of the chip is connected to an LED through a resistor R22, the other end of the LED is connected to a 3.3V level, the third pin and the fourth pin of the chip are connected to a 32.768KHz crystal oscillator circuit; the eighth pin of the chip is grounded, the ninth pin of the chip is connected to a 3.3V level through a resistor R24, the sixteenth pin of the chip is connected to a signal output terminal Net3 of the amplification and shaping circuit, the twenty-third pin of the chip is grounded through a resistor R25, the twenty-third pin of the chip is grounded, the twenty-fourth pin of the chip is connected to a 3.3V level, the thirty-second pin and the thirty-third pin of the chip are respectively connected to the second pin and the third pin of the USB interface, and the first pin of the USB interface is connected to a 5V level through a resistor R26. , pin 3 of the USB interface is connected to a 3.3V level through resistor R29, pin 5 of the USB interface is grounded, pin 35 of the chip is grounded, pin 36 of the chip is connected to a 3.3V level, pin 7, pin 34, pin 37, pin 38, pin 39, and pin 40 of the chip are connected to pin 15, pin 7, pin 9, pin 5, pin 13, and pin 3 of the JTAG interface respectively, pin 1 and pin 2 of the JTAG interface are connected to a 3.3V level, pin 4, pin 6, pin 8, pin 10, pin 12, pin 14, pin 16, pin 18, and pin 20 of the JTAG interface are all grounded, pin 44 of the chip is grounded through resistor R30, pin 47 of the chip is grounded, and pin 48 of the chip is connected to a 3.3V level.

[0012] Furthermore, the 32.768KHz crystal oscillator circuit includes a crystal oscillator Y1, a capacitor C37 and a capacitor C38; the crystal oscillator Y1 is connected to the 3rd and 4th pins of the chip, one end of the capacitor C37 and the capacitor C38 are connected to the crystal oscillator Y1, and the other end is grounded together, the 5th and 6th pins of the chip are connected to the 8MHz crystal oscillator circuit, the crystal oscillator circuit includes a crystal oscillator X1, a resistor R23, a capacitor C39 and a capacitor C40, the crystal oscillator X1 is connected to the 5th and 6th pins of the chip, the resistor R23 is connected in parallel between the crystal oscillator X1 and the 5th and 6th pins of the chip, the capacitor C39 and the capacitor C40 are connected to the crystal oscillator X1 at one end, and the other end is grounded together.

[0013] Compared with the prior art, the present invention has the following technical effects:

[0014] The present invention adopts a Pierce type oscillation circuit, and the SAW sensor is easy to self-oscillate and output a sinusoidal signal of a specific frequency. Further, the magnetic field strength can be measured by a single difference, that is, the change in the frequency of the measuring branch signal. It has high accuracy, a wide detection range, and no test blind area;

[0015] The frequency mixing method is used to maintain the signal to be detected in the low frequency band, which reduces the difficulty of system frequency measurement and acquisition;

[0016] The introduction of the filter circuit ensures that the signal in the resonant frequency band of the SAW sensor can pass effectively, thus increasing the reliability of the circuit.

[0017] In summary, the present invention has a simple structure, small size, easy operation, low cost, high circuit stability, high magnetic field detection accuracy, wide range, and high speed, and can be extended to other types of SAW sensor signal acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a circuit principle block diagram of the present invention;

[0019] Figure 2 is a circuit schematic diagram of a first oscillator circuit of the present invention;

[0020] Figure 3 is a circuit schematic diagram of a second oscillator circuit of the present invention;

[0021] Figure 4 It is a circuit principle diagram of the frequency mixing circuit of the present invention;

[0022] Figure 5 It is a circuit principle diagram of the amplifying and shaping circuit of the present invention;

[0023] Figure 6 It is a circuit principle diagram of the frequency measurement circuit of the present invention.

[0024] Description of reference numerals:

[0025] 1-first oscillation circuit; 2-second oscillation circuit; 3-mixing circuit; 4-amplification and shaping circuit; 5-frequency measurement circuit. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings:

[0027] like Figure 1 As shown, the present invention includes oscillation circuits 1 and 2, a mixing circuit 3, an amplifying and shaping circuit 4 and a frequency measuring circuit 5 which are connected in sequence; the first input end of the mixing circuit 3 is connected to the oscillation circuit 1 which outputs the SAW sensor measurement frequency signal, and the second input end of the mixing circuit 3 is connected to the oscillation circuit 2 which outputs the SAW sensor reference frequency signal; the amplifying and shaping circuit 4 is connected to the signal output end IF of the mixing circuit 3; the frequency measuring circuit 5 is mainly composed of a chip STM32F103C8T6, the 16th pin of the chip STM32F103C8T6 is connected to the signal output end of the amplifying and shaping circuit 4, and the chip STM32F103C8T6 can communicate with a PC end, and the sensing information is recorded on the PC end through a data acquisition program.

[0028] In actual use, the SAW sensor in the oscillation circuit 1 is coated with a magnetically sensitive film. When the external magnetic field changes, the Young's modulus of the sensitive film changes greatly, causing the frequency of the output signal of the oscillation circuit 1 to change. The SAW sensor in the oscillation circuit 2 has no magnetically sensitive film, and the frequency of the output signal of the oscillation circuit 2 is not affected by the external magnetic field. The difference frequency signal formed by the measurement branch and the reference branch enters the back-end signal processing and acquisition circuit.

[0029] like Figure 2 and Figure 3As shown, the oscillation circuit 1 includes capacitors C1, C2, C3, C4, C5, C6, C7, C8, C9 and C10, inductors L1, L2, L3, L4, L5 and L6, resistors R1, R2 and R3, a 5V DC power supply, a high-frequency transistor 2SC3357, and a 4-pin SAW sensor; the capacitors C1 and C2 are connected in series to the resonant circuit of the SAW sensor to adjust the resonant frequency of the circuit; the inductor L1 is connected in parallel with the SAW sensor to offset the parallel equivalent capacitance in the SAW sensor, the capacitor C3 is connected between the resonant network and the amplifier circuit as a feedback capacitor, the resistor R2 is connected between the base of the transistor 2SC3357 and the ground, and the resistor R3 and the capacitor C4 are connected in parallel between the emitter of the transistor 2SC3357 and the ground. The inductor L2, the resistor R1, and the inductor L3 are sequentially connected in series between the collector and the base of the transistor 2SC3357, wherein the resistors R1, R2, and R3 are used to set the static operating point of the high-frequency transistor 2sc3357, C4 is a bypass capacitor, L2 and L3 are chokes, and the capacitors C5 and C6 are connected in parallel between the negative electrode of the 5V DC power supply and the ground as filter capacitors. To suppress the high-frequency harmonic components of the SAW sensor, the capacitor C7, the inductor L4, the capacitor C8, the inductor L6, and the capacitor C10 are sequentially connected in series between the connection end of the SAW sensor and the inductor L1 and the output end Net1, and the inductor L5 and the capacitor C9 are connected in parallel between the capacitor C8 and the inductor L6 to form a bandpass filter network, so that the signal of the oscillation frequency band passes through, and the signals of other bands are filtered out or attenuated. The oscillation circuit 2 includes capacitors C11, C12, C13, C14, C15, C16, C17, C18, C19 and C20, inductors L7, L8, L9, L10, L11 and L12, resistors R4, R5 and R6, a 5V DC power supply, a high-frequency transistor 2SC3357, and a 4-pin SAW sensor. The connection method is exactly the same as that of the oscillation circuit 1, and will not be repeated here;

[0030] In actual use, the oscillation circuit is powered by a 5V DC regulated power supply. By introducing closed-loop positive feedback, the circuit can start to oscillate at the resonance point of the sensor, self-oscillate and output a sine wave signal. Through the signal screening of the bandpass filter network, the effective signal in the oscillation frequency range can pass.

[0031] like Figure 4As shown, the mixer circuit 3 mainly includes a mixer AD831 and a low-pass filter LFCN-255+; the first pin of the mixer AD831 is connected to the positive electrode of the power supply +5V, the second / third pins of the mixer AD831 are connected to the positive electrode of the power supply +5V through a capacitor C21 and are grounded through capacitors C21 and C34 connected in series, the fourth pin of the mixer AD831 is grounded, the fifth pin of the mixer is connected to the negative electrode of the power supply -5V and is grounded through a capacitor C22, and the sixth pin of the mixer is connected to the oscillation circuit through a capacitor C23. 1 is connected to the output terminal Net1 of the oscillation circuit 2 and is grounded through a resistor R7, the 7th pin of the mixer is grounded through a capacitor C24, the 8th pin of the mixer is connected to the negative electrode of the power supply -5V and is grounded through a capacitor C25, the 9th pin of the mixer is connected to the positive electrode of the power supply +5V and is grounded through a capacitor C26, the 10th pin of the mixer is connected to the output terminal Net2 of the oscillation circuit 2 through a capacitor C27 and is grounded through a resistor R8, the 11th pin of the mixer is grounded and connected to the output terminal Net2 of the oscillation circuit 2 through a resistor R8, and the mixer The 12th pin of the mixer is connected to the positive electrode of the power supply +5V and is grounded through a capacitor C28, the 13th pin of the mixer is grounded and connected to the output terminal Net2 of the oscillation circuit 2 through a resistor R8, the 14th pin of the mixer is connected to the positive electrode of the power supply +5V through a resistor R9 and is grounded through a series resistor R9 and a capacitor C29, the 15th pin of the mixer is connected to the negative electrode of the power supply -5V and is grounded through a capacitor C30, the 16th pin of the mixer is connected to the 0th pin of the low-pass filter LFCN-255+ through a series resistor R10 and a capacitor C31. The 1st and 3rd pins of the low-pass filter LFCN-255+ are grounded, and the 2nd pin is the mixing signal output terminal IF. The 17th pin of the mixer is connected to the 16th pin through the resistor R11 and to the 18th pin through the resistor R12. The 18th pin of the mixer is connected to the positive electrode of the power supply +5V through the resistor R14 and to the ground through the parallel capacitor C32 and the resistor R13. The 19th and 20th pins of the mixer are connected to the positive electrode of the power supply +5V through the capacitor C33 and to the ground through the capacitors C33 and C34 connected in series.

[0032] In actual use, the mixer circuit 3 is powered by a ±5V dual power supply. The output signal of the mixer circuit 3 contains sum frequency components and difference frequency components. The low-pass filter LFCN-255+ can filter out the high-frequency sum frequency signal and retain the difference frequency signal reflecting the magnetic field strength, thereby ensuring the stability of the output low-frequency signal and facilitating the counting and frequency measurement.

[0033] like Figure 5As shown, the amplification and shaping circuit 4 mainly includes an operational amplifier LM318 and a voltage comparator LM311; the signal output terminal IF of the mixing circuit is connected to the third pin of the operational amplifier LM318 through a capacitor C35 and a resistor R15 connected in series, the second pin of the operational amplifier LM318 is grounded through a resistor R16, the fourth pin of the operational amplifier LM318 is connected to the negative electrode of the power supply -5V, the fourth pin of the operational amplifier LM318 is connected to the third pin of the voltage comparator LM311 through a resistor R18, and is grounded through a resistor R16 and a resistor R17 connected in series, the seventh pin of the operational amplifier LM318 is connected to the positive electrode of the power supply +5V, the second pin of the voltage comparator LM311 is grounded through a resistor R19, the fourth pin of the voltage comparator LM311 is grounded, the seventh pin of the voltage comparator LM311 is connected to the power supply +5V through a resistor R20, and the sixth pin of the voltage comparator LM311 is the signal output terminal Net3 of the amplification and shaping circuit.

[0034] In actual use, the mixer circuit 3 outputs a sinusoidal signal with a small amplitude, which cannot be directly counted and measured. The amplification and shaping circuit 4 transforms the low-frequency sinusoidal waveform, the operational amplifier LM318 is powered by a ±5V dual power supply, and the voltage comparator LM311 is powered by a 5V single power supply. The circuit outputs a pulse square wave signal with high and low levels. After that, the counting method can be used to measure its frequency through the single-chip microcomputer / FPGA.

[0035] like Figure 6As shown, the frequency measurement circuit 4 is mainly composed of a chip STM32F103C8T6; the first pin of the chip is connected to the 3.3V level through a resistor R21, the second pin of the chip is connected to the LED through a resistor R22, the other end of the LED is connected to the 3.3V level, the third pin and the fourth pin of the chip are connected to a 32.768KHz crystal oscillator circuit, the crystal oscillator circuit includes a crystal oscillator Y1, a capacitor C37 and a capacitor C38, the crystal oscillator Y1 and the third pin and the fourth pin of the chip are connected to the 32.768KHz crystal oscillator circuit. The pins of the chip are connected, one end of the capacitor C37 and the capacitor C38 are connected to the crystal oscillator Y1, and the other end is grounded together. The 5th and 6th pins of the chip are connected to the 8MHz crystal oscillator circuit, which includes a crystal oscillator X1, a resistor R23, a capacitor C39 and a capacitor C40. The crystal oscillator X1 is connected to the 5th and 6th pins of the chip, the resistor R23 is connected in parallel between the crystal oscillator X1 and the 5th and 6th pins of the chip, and one end of the capacitor C39 and the capacitor C40 is connected to the crystal oscillator X1, and the other end is grounded together. The 8th pin of the chip is grounded, the 9th pin of the chip is connected to a 3.3V level through a resistor R24, the 16th pin of the chip is connected to the signal output terminal Net3 of the amplifying and shaping circuit, the 20th pin of the chip is grounded through a resistor R25, the 23rd pin of the chip is grounded, the 24th pin of the chip is connected to a 3.3V level, the 32nd pin and the 33rd pin of the chip are respectively connected to the 2nd pin and the 3rd pin of the USB interface, the 1st pin of the USB interface is connected to a 5V level through a resistor R26, the 3rd pin of the USB interface is connected to a 3.3V level through a resistor R29, the 5th pin of the USB interface is grounded, the 35th pin of the chip is grounded, and the Pin 36 is connected to a 3.3V level, pin 7, pin 34, pin 37, pin 38, pin 39 and pin 40 of the chip are respectively connected to pin 15, pin 7, pin 9, pin 5, pin 13 and pin 3 of the JTAG interface, pin 1 and pin 2 of the JTAG interface are connected to a 3.3V level, pin 4, pin 6, pin 8, pin 10, pin 12, pin 14, pin 16, pin 18 and pin 20 of the JTAG interface are all grounded, pin 44 of the chip is grounded through resistor R30, pin 47 of the chip is grounded, and pin 48 of the chip is connected to a 3.3V level.

[0036] In actual use, the chip STM32F103C8T6 is powered by a 5V DC regulated power supply. After power-on, the LED lights up to indicate that the power supply is normal. Among them, the crystal oscillator circuit provides a reference clock for the chip. The frequency measurement program can be written into the chip STM32F103C8T6 through the JTAG interface, and the program can be debugged in real time. Through the input capture function of the chip's internal timer, the frequency difference representing the external magnetic field strength can be measured. The program written in Labview collects the frequency difference sent by the chip to the PC via the USB communication interface, thus realizing the measurement of the magnetic field strength by the SAW magnetic field sensor.

Claims

1. A signal acquisition system for a surface acoustic wave magnetic sensor, characterized in that: It includes a first oscillation circuit, a second oscillation circuit, a frequency mixing circuit, an amplification and shaping circuit and a single-chip computer frequency measurement circuit; the first input end of the frequency mixing circuit is connected to the first oscillation circuit, and the second input end of the frequency mixing circuit 3 is connected to the second oscillation circuit; the amplification and shaping circuit is connected to the signal output end IF of the frequency mixing circuit; the frequency measurement circuit is mainly connected to the signal output end of the amplification and shaping circuit; the first oscillation circuit and the second oscillation circuit are both used to output the SAW sensor measurement frequency signal; The first oscillation circuit includes capacitors C1, C2, C3, C4, C5, C6, C7, C8, C9 and C10, inductors L1, L2, L3, L4, L5 and L6, resistors R1, R2 and R3, a 5V DC power supply, a high-frequency transistor 2SC3357, and a 4-pin SAW sensor; capacitors C1 / C2 are connected in series to the resonant circuit of the SAW sensor, inductor L1 is connected in parallel with the SAW sensor, capacitor C3 is connected between the resonant network and the amplifier circuit, resistor R2 is connected between the base of the high-frequency transistor 2SC3357 and ground, and resistor R3 and capacitor C4 are connected in parallel between the emitter of high-frequency transistor 2SC3357 and the ground, inductor L2, resistor R1, and inductor L3 are connected in series between the collector and base of high-frequency transistor 2SC3357 in sequence, capacitor C5 / C6 are connected in parallel between the negative electrode of 5V DC power supply and the ground, capacitor C7, inductor L4, capacitor C8, inductor L6, and capacitor C10 are connected in series between the connection end of SAW sensor and inductor L1 and output end Net1 in sequence, inductor L5 and capacitor C9 are connected in parallel between C8 and L6; the SAW sensor is plated with a magnetic sensitive film; The second oscillation circuit includes capacitors C11, C12, C13, C14, C15, C16, C17, C18, C19 and C20, inductors L7, L8, L9, L10, L11 and L12, resistors R4, R5 and R6, a 5V DC power supply, a high-frequency transistor 2SC3357, and a 4-pin SAW sensor; capacitors C11 / C12 are connected in series to the resonant circuit of the SAW sensor, inductor L7 is connected in parallel with the SAW sensor, capacitor C13 is connected between the resonant network and the amplifier circuit, and resistor R5 is connected to the high-frequency transistor 2SC335 7 base and ground, resistor R6 and capacitor C14 are connected in parallel between the emitter of high-frequency transistor 2SC3357 and ground, inductor L9, resistor R4, and inductor L8 are connected in series between the collector and base of high-frequency transistor 2SC3357 in sequence, capacitors C15 / C16 are connected in parallel between the negative electrode of 5V DC power supply and ground, capacitor C17, inductor L10, capacitor C18, inductor L12, and capacitor C20 are connected in series between the connection end of SAW sensor and inductor L7 and output end Net2 in sequence, and inductor L11 and capacitor C19 are connected in parallel between C18 and L12; The mixer circuit includes a mixer AD831 and a low-pass filter LFCN-255+; the first pin of the mixer AD831 is connected to the positive electrode of the power supply +5V, the second and third pins of the mixer AD831 are connected to the positive electrode of the power supply +5V through a capacitor C21 and are grounded through capacitors C21 and C34 connected in series, the fourth pin of the mixer AD831 is grounded, the fifth pin of the mixer is connected to the negative electrode of the power supply -5V and is grounded through a capacitor C22, and the sixth pin of the mixer is connected to the output terminal N of the first oscillation circuit through a capacitor C23. et1 and grounded through a resistor R7, the 7th pin of the mixer is grounded through a capacitor C24, the 8th pin of the mixer is connected to the negative pole of the power supply -5V and grounded through a capacitor C25, the 9th pin of the mixer is connected to the positive pole of the power supply +5V and grounded through a capacitor C26, the 10th pin of the mixer is connected to the output terminal Net2 of the second oscillation circuit through a capacitor C27 and grounded through a resistor R8, the 11th pin of the mixer is grounded and connected to the output terminal Net2 of the second oscillation circuit through a resistor R8, and the 12th pin of the mixer is connected to the positive pole of the power supply +5V and grounded through a capacitor C26. The 13th pin of the mixer is connected to the positive electrode of the power supply +5V and is grounded through the capacitor C28, the 14th pin of the mixer is connected to the positive electrode of the power supply +5V through the resistor R9 and is grounded through the series resistor R9 and capacitor C29, the 15th pin of the mixer is connected to the negative electrode of the power supply -5V and is grounded through the capacitor C30, the 16th pin of the mixer is connected to the 0th pin of the low-pass filter LFCN-255+ through the series resistor R10 and capacitor C31, The 1st and 3rd pins of the low-pass filter LFCN-255+ are grounded, the 2nd pin is the mixing signal output terminal IF, the 17th pin of the mixer is connected to the 16th pin through the resistor R11 and to the 18th pin through the resistor R12, the 18th pin of the mixer is connected to the positive electrode of the power supply +5V through the resistor R14 and to the ground through the parallel capacitor C32 and the resistor R13, the 19th and 20th pins of the mixer are connected to the positive electrode of the power supply +5V through the capacitor C33 and to the ground through the capacitors C33 and C34 connected in series; The amplification and shaping circuit includes an operational amplifier LM318 and a voltage comparator LM311; the signal output terminal IF of the mixing circuit is connected to the third pin of the operational amplifier LM318 through a capacitor C35 and a resistor R15 connected in series, the second pin of the operational amplifier LM318 is grounded through a resistor R16, the fourth pin of the operational amplifier LM318 is connected to the negative electrode of the power supply -5V, the fourth pin of the operational amplifier LM318 is connected to the third pin of the voltage comparator LM311 through a resistor R18, and is grounded through a resistor R16 and a resistor R17 connected in series, the seventh pin of the operational amplifier LM318 is connected to the positive electrode of the power supply +5V, the second pin of the voltage comparator LM311 is grounded through a resistor R19, the fourth pin of the voltage comparator LM311 is grounded, the seventh pin of the voltage comparator LM311 is connected to the power supply +5V through a resistor R20, and the sixth pin of the voltage comparator LM311 is the signal output terminal Net3 of the amplification and shaping circuit.

2. A signal acquisition system for a surface acoustic wave magnetic sensor according to claim 1, characterized in that: The frequency measurement circuit includes a chip STM32F103C8T6; the first pin of the chip is connected to a 3.3V level through a resistor R21, the second pin of the chip is connected to an LED through a resistor R22, the other end of the LED is connected to a 3.3V level, the third pin and the fourth pin of the chip are connected to a 32.768KHz crystal oscillator circuit; the eighth pin of the chip is grounded, the ninth pin of the chip is connected to a 3.3V level through a resistor R24, the sixteenth pin of the chip is connected to a signal output terminal Net3 of an amplifying and shaping circuit, the twenty-third pin of the chip is grounded through a resistor R25, the twenty-third pin of the chip is grounded, the twenty-fourth pin of the chip is connected to a 3.3V level, the thirty-second pin and the thirty-third pin of the chip are respectively connected to the second pin and the third pin of a USB interface, the first pin of the USB interface is connected to a 5V level through a resistor R26, and the US Pin 3 of the B interface is connected to a 3.3V level through resistor R29, pin 5 of the USB interface is grounded, pin 35 of the chip is grounded, pin 36 of the chip is connected to a 3.3V level, pin 7, pin 34, pin 37, pin 38, pin 39 and pin 40 of the chip are connected to pin 15, pin 7, pin 9, pin 5, pin 13 and pin 3 of the JTAG interface respectively, pin 1 and pin 2 of the JTAG interface are connected to a 3.3V level, pin 4, pin 6, pin 8, pin 10, pin 12, pin 14, pin 16, pin 18 and pin 20 of the JTAG interface are all grounded, pin 44 of the chip is grounded through resistor R30, pin 47 of the chip is grounded, and pin 48 of the chip is connected to a 3.3V level.

3. A signal acquisition system for a surface acoustic wave magnetic sensor according to claim 2, characterized in that: The 32.768KHz crystal oscillator circuit includes a crystal oscillator Y1, a capacitor C37 and a capacitor C38; the crystal oscillator Y1 is connected to the 3rd and 4th pins of the chip; one end of the capacitor C37 and the capacitor C38 are connected to the crystal oscillator Y1, and the other end is grounded; the 5th and 6th pins of the chip are connected to the 8MHz crystal oscillator circuit, and the crystal oscillator circuit includes a crystal oscillator X1, a resistor R23, a capacitor C39 and a capacitor C40; the crystal oscillator X1 is connected to the 5th and 6th pins of the chip; the resistor R23 is connected in parallel between the crystal oscillator X1 and the 5th and 6th pins of the chip; one end of the capacitor C39 and the capacitor C40 is connected to the crystal oscillator X1, and the other end is grounded.

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