Surface acoustic wave temperature sensor test system based on FPGA

Abstract

The utility model belongs to the technical field of temperature sensor testing, and aims to solve the problems that excitation signals in a transmitting circuit are unstable and echo signals in a receiving circuit are low in signal-to-noise ratio in an existing testing system, so that the measurement progress is influenced. According to the surface acoustic wave temperature sensor testing system based on the FPGA, the output end of a microcontroller is connected with a sweep frequency excitation signal transmitting module, and the sweep frequency excitation signal transmitting module is used for transmitting a high-frequency sweep frequency signal covering the resonant frequency of a temperature sensor; the echo signal receiving module is used for receiving an echo signal sent by the temperature sensor after the temperature sensor is activated; an echo signal processing module connected with the output end of the echo signal receiving module is arranged in the microcontroller, and the echo signal processing module is used for acquiring the resonant frequency of the temperature sensor based on the echo signal. According to the utility model, the accurate resonant frequency of the SAW temperature sensor can be obtained.

Description

TECHNICAL FIELD

[0001] The utility model belongs to temperature sensor test technical field especially based on FPGA's surface acoustic wave temperature sensor test system. BACKGROUND

[0002] Surface acoustic wave (SAW) sensor is the sensor that the information of measured quantity is reflected through the change of the velocity or frequency of surface acoustic wave in surface acoustic wave device and is converted into electric signal output, and its test system is responsible for converting the physical quantity perceived by the sensor into electric signal, and collecting and analyzing the signal to extract useful information and carry out subsequent processing and analysis.

[0003] Compared with the traditional wired sensor test system, the surface acoustic wave temperature sensor test system has many advantages. First, the wireless sensor system is no longer limited by wiring and can be flexibly deployed in various environments, greatly improving the scalability and applicability of the system. Moreover, when the number of required sensors is large, the large number of cables will inevitably make the test system too complex, difficult to layout and wire, and difficult to troubleshoot and maintain after failure. Second, the wireless passive sensor system eliminates the need for power supply, greatly reducing the maintenance and operating costs of the system.

[0004] The existing test system is difficult to send stable and effective excitation signals in the transmission link to activate the sensor and make it feedback accurate temperature information. In addition, in actual application, the signals received by the test system not only contain sensor echo signals, but also mix a large number of noise signals from different sources. These noise signals bring great difficulty to the system to extract sensor information. Therefore, accurately extracting useful sensor signals from these complex mixed noise signals is crucial for the application of passive wireless SAW temperature sensors. UTILITY MODEL CONTENTS

[0005] The utility model provides a surface acoustic wave temperature sensor test system based on FPGA in order to solve at least one technical problem existing in prior art.

[0006] The utility model adopts the following technical scheme realization: a surface acoustic wave temperature sensor test system based on FPGA, including sweep frequency excitation signal transmission module, echo signal receiving module and microcontroller;

[0007] The output end of the microcontroller is connected with a sweep excitation signal transmitting module, and the sweep excitation signal transmitting module is used for transmitting a high-frequency sweep signal covering the resonant frequency of the temperature sensor; the sweep excitation signal transmitting module comprises a DDS signal generating module, a digital-to-analog conversion module, a phase-locked loop module, a power amplifier and a radio frequency switch I connected in sequence; the DDS signal generating module is built-in in the microcontroller, the low-frequency digital sweep signal generated by the DDS signal generating module is generated based on the master control chip of the microcontroller, the digital-to-analog conversion module is used for carrying out digital-to-analog conversion on the low-frequency digital sweep signal, the master control chip of the microcontroller is connected with the phase-locked loop module through an SPI interface, and the phase-locked loop module and the power amplifier are used for frequency conversion and amplification of the low-frequency sweep signal; the radio frequency switch I is controlled by the TTL square wave signal generated by the master control chip of the microcontroller; a band-pass filter is connected between the radio frequency switch I and the power amplifier;

[0008] A radio frequency switch II is connected between the sweep excitation signal transmitting module and the echo signal receiving module, the radio frequency switch II is connected with the antenna, and the radio frequency switch II is used for isolating the high-frequency sweep signal and the echo signal and controlling the transceiving state; the echo signal receiving module is used for receiving the echo signal emitted by the temperature sensor after being activated, and the echo signal receiving module comprises a low-noise amplifier, a mixer and an analog-to-digital conversion module connected in sequence; the low-noise amplifier and the mixer are used for amplifying and frequency-converting the echo signal, the analog-to-digital conversion module is used for carrying out analog-to-digital conversion on the processed echo signal, a band-pass filter is connected between the low-noise amplifier and the mixer, and a low-pass filter is arranged between the mixer and the analog-to-digital conversion module; a echo signal processing module connected with the output end of the echo signal receiving module is built-in in the microcontroller, and the echo signal processing module is used for obtaining the resonant frequency of the temperature sensor based on the echo signal; the echo signal processing module comprises an LMS adaptive filter integrated on the master control chip of the microcontroller, and the LMS adaptive filter is connected with the analog-to-digital conversion module.

[0009] Preferably, the model of the master control chip of the microcontroller is XC7A35T, and the output end of the microcontroller is connected with an upper computer.

[0010] Preferably, the antenna adopts a spiral antenna and is composed of a spiral metal.

[0011] Compared with the prior art, the utility model has the advantages of:

[0012] The utility model discloses a stable low frequency sweep signal is produced by DDS signal generation module, and after frequency conversion of phase-locked loop and power amplifier amplification, the high frequency sweep signal covering the resonant frequency of sensor is obtained, when the sensor is activated and sends echo signal, echo signal is captured, and after low noise amplifier amplification and frequency converter down conversion, becomes the low frequency signal that can be received by analog-digital conversion module, and the echo signal of conversion digital signal is filtered after adaptive digital filter, and its frequency spectrum is analyzed by main control chip, and the resonant frequency of SAW temperature sensor is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical scheme in the embodiments of the utility model or prior art, the drawings needed in the embodiments will be briefly introduced as follows, and obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other drawings can be obtained according to these drawings without creative labor.

[0014] Figure 1 It is the overall structure schematic diagram of SAW temperature sensor test system based on FPGA;

[0015] Figure 2 It is the echo signal processing process schematic diagram;

[0016] Figure 3 It is the LMS multistage processing structure schematic diagram;

[0017] Figure 4 It is the FPGA and phase-locked loop module connection schematic diagram;

[0018] Figure 5 It is the radio frequency power amplification circuit schematic diagram;

[0019] Figure 6 It is the frequency mixing module circuit structure schematic diagram. DETAILED DESCRIPTION

[0020] The technical scheme in the embodiments of the utility model is clearly and completely described in conjunction with the drawings in the embodiments of the utility model, and obviously, the described embodiments are only some embodiments of the utility model, not all embodiments. Based on the embodiments of the utility model, all other embodiments obtained by those skilled in the art without creative labor belong to the range protected by the utility model.

[0021] It should be understood that the structure, proportion, size and the like shown in the drawings of the specification are only used to cooperate with the disclosed content, to be understood and read by those skilled in the art, and are not used to limit the implementation conditions of the utility model, so they do not have technical significance. Any modification of structure, change of proportion relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the utility model, should fall within the scope of the disclosed technology, it should be noted that in the specification, relationship terms such as first and second are only used to distinguish one entity from another, and do not necessarily require or imply any actual relationship or order between the entities.

[0022] The utility model provides an embodiment:

[0023] A kind of based on FPGA's surface acoustic wave temperature sensor test system, including sweep frequency excitation signal transmitting module, echo signal receiving module and microcontroller;The output of microcontroller is connected with sweep frequency excitation signal transmitting module, and sweep frequency excitation signal transmitting module is used to emit high frequency sweep signal covering temperature sensor resonance frequency;Echo signal receiving module is used to receive echo signal that temperature sensor is activated and emits;Microcontroller is built-in with the output of echo signal receiving module and is connected with echo signal processing module, and echo signal processing module is used to obtain the resonance frequency of temperature sensor based on echo signal.

[0024] In the embodiment, sweep frequency excitation signal transmitting module generates 9-10MHz sweep signal by DDS technology, is up-converted to 260-450MHz by phase-locked loop module, is amplified by power amplifier, and is emitted by antenna;Echo signal receiving module first amplifies the received echo signal by low-noise amplifier, and then is down-converted to 1-10MHz by mixer to meet the sampling signal frequency requirement of ADC module;Microcontroller issues instructions to the whole test system, and returns sensor resonance frequency information to host computer;Echo signal processing module filters and analyzes the collected down-converted signal to obtain the resonance frequency of SAW temperature sensor.

[0025] Since the control instructions of the test system are complex, and the signal processing rate requirement of echo signal processing module is high, the model of the main control chip of microcontroller adopts Artix7 series XC7A35T, and the output of microcontroller is connected with host computer.

[0026] The sweep excitation signal transmitting module comprises a DDS signal generating module, a digital-to-analog conversion module, a phase-locked loop module, a power amplifier and a radio frequency switch I connected in sequence. A band-pass filter is connected between the radio frequency switch I and the power amplifier. The DDS signal generating module is built in a microcontroller. The low-frequency digital sweep signal generated by the DDS signal generating module is generated based on a master control chip of the microcontroller. The digital-to-analog conversion module is used for digital-to-analog conversion of the low-frequency digital sweep signal. The master control chip of the microcontroller is connected with the phase-locked loop module through an SPI interface. The phase-locked loop module and the power amplifier are used for frequency conversion and amplification of the low-frequency sweep signal. The radio frequency switch I is controlled by a TTL square wave generated by the master control chip of the microcontroller.

[0027] The DDS signal generating module adopts an FPGA design scheme and can be realized by only controlling a DDS IP. The digital-to-analog conversion module adopts AD9767 of ADI Company, which has a highest conversion rate of 125 MSPs, a double-port interface, allows double or staggered input data, a highest resolution of 14 bits, supports 3.3V or 5V single power supply, etc. The phase-locked loop module adopts ADF4351 chip of ADI Company, which integrates an integer and fractional frequency synthesizer of a low-phase-noise voltage-controlled oscillator, is controlled through a three-wire SPI serial interface, can set a center frequency through an external inductor, has an output frequency range of 35MHz to 4400MHz, and controls the output frequency by changing the internal register storage value to control the frequency multiplication. The power amplification module adopts SBB5089Z of Qorvo Company, which has a working bandwidth of 50MHz to 4000MHz, a noise coefficient of 1.1dB, and can provide a gain of 20.8dB in a working frequency range of 200MHz to 500MHz. The radio frequency switch adopts HMC349 radio frequency switch chip of Analog Devices, which can work in a range of 100MHz to 4000MHz, has a 50-ohm matching integrated inside, has a low insertion loss of 1.0dB and an isolation of 60dB in a range of 100MHz to 1000MHz.

[0028] The sweep excitation signal transmitting module and the echo signal receiving module are connected with a radio frequency switch II, the radio frequency switch II is connected with an antenna, and the radio frequency switch II is used for isolating the high-frequency sweep signal and the echo signal and controlling the transceiving state. The antenna adopts a spiral antenna composed of a spiral metal, the radiation characteristic of which is determined by the ratio of the spiral diameter to the wavelength, and the frequency response characteristic is wide.

[0029] The echo signal receiving module comprises a low-noise amplifier, a mixer and an analog-to-digital conversion module connected in sequence, wherein the low-noise amplifier and the mixer amplify and frequency-convert the echo signal, and the analog-to-digital conversion module analog-to-digital converts the processed echo signal.

[0030] The low-noise amplification module selects a SPF5189Z low-noise amplification chip of Qorvo Company, which has a working frequency of 50MHz to 4000MHz, supports 3V-5V single power supply, and provides ultra-low noise coefficient and high linearity performance in the gain block configuration, and has a gain of 18.7dB and a noise coefficient of 0.60dB at a working frequency of 900MHz at the output end; the mixer adopts an ADI Company AD831 active mixer, which is configured to include a mixer, a limiting amplifier, a low-noise output amplifier, a low-pass filter and a bias circuit, the local oscillator and the radio frequency input frequency can reach 500MHz, and the intermediate frequency output mode includes differential current output and single-ended voltage output; the analog-to-digital conversion module adopts an ADI Company AD9226 chip, which is a 12-bit, 65MSPS analog-to-digital converter (ADC) powered by a 5V single power supply, and has a built-in high-performance sampling holding amplifier and a reference voltage source.

[0031] The echo signal processing module comprises an LMS adaptive filter integrated on a main control chip of a microcontroller, and the LMS adaptive filter is connected with the analog-to-digital conversion module. A digital LMS adaptive filter is integrated in an FPGA as a core to filter and process the signals collected by a receiving circuit after frequency conversion and to perform spectrum analysis.

[0032] In the transmitting stage, first, a direct digital frequency synthesis (DDS) technology of a field programmable gate array (FPGA) of a microcontroller is used to design and generate a digital sweep signal with an increasing frequency in a range of 9~10MHz, which is sent to a phase-locked loop (PLL) module through a digital-to-analog conversion circuit. The PLL module frequency-multiplies the signal, and the FPGA controls the PLL module to change the frequency multiplication number through an SPI interface, so that in a frequency range of 260.00~450.00MHz, a specific sweep interval can be set according to the resonant frequency of a SAW temperature sensor to be measured, and linear sweep with a bandwidth of not less than 10MHz is realized.

[0033] The radio frequency switch 1 is controlled by the TTL square wave signal generated by the FPGA, and determines the action of the frequency multiplied signal. The local oscillator signal (LO) of the mixer is provided by the PLL. When the PLL finishes transmitting the frequency sweeping excitation signal of a SAW temperature sensor, it starts to transmit the local oscillator signal. At this time, the 9MHz digital sine signal output by the DDS corresponds to the signal stabilized at the starting value of the frequency sweeping signal after being multiplied by the PLL. In order to improve the temperature measurement distance, a power amplification circuit is designed to amplify the power of the frequency sweeping signal. The radio frequency switch 2 plays a role in isolating the frequency sweeping excitation signal and the echo signal and controlling the transmitting and receiving states. In the receiving stage, the echo signal generated by the sensor is received through the electromagnetic coupling of the test system antenna, and the received echo signal is amplified in power by the low-noise amplifier. The amplified signal is down-converted and filtered by the mixer, and then collected by the analog-to-digital conversion circuit. In the echo signal processing stage, the FPGA controls the ADC module to collect the signal after mixing and filtering. Then, LMS adaptive filtering and spectrum analysis are performed in the FPGA, and the resonant frequency of the resonant SAW temperature sensor can be obtained, so as to measure the temperature of the position to be measured.

[0034] As shown in Figure 2 In order to obtain accurate temperature information, the collected digital signal should be filtered to improve the signal-to-noise ratio. Considering that the noise characteristics of the signal are unknown and constantly changing, the filter should track the changes of the noise and continuously adjust the filter parameters to optimize the filtering effect. Considering the implementation of the overall system and the filtering algorithm, the FPGA is taken as the core, the LMS adaptive filter is integrated, the down-converted signal collected by the receiving circuit is filtered and analyzed, and the resonant frequency of the SAW temperature sensor is obtained.

[0035] The digital signal collected by the ADC module is first stored in the internal resource FIFO1 of the FPGA. After being full, LMS adaptive filtering is started, the data in FIFO1 is read out, and the data in FIFO2 is stored. When the next echo signal processing is performed, the data in FIFO2 is read out. In this way, the echo signal is processed in a loop, and the signal processing time is shortened.

[0036] After the adaptive filtering is completed, the frequency information of the down-converted signal is obtained by performing spectrum analysis on the digital signal through the FFT IP core. The LMS adaptive filter used in this paper can eliminate noise without knowing the characteristics of the original echo signal. It has better filtering performance, low computational complexity, good convergence, and is easy to implement, which meets the requirements of digital filtering in this paper.

[0037] As shown in Figure 3As shown, the modular design of the LMS adaptive filter in FPGA design is based on the unique hardware language design features of FPGA to ensure processing speed while making more efficient use of FPGA logic resources. To clearly illustrate the specific modular design scheme, the LMS adaptive filter can be divided into three main modules: error calculation, weight update, and FIR filter. The algorithms for these three modules include addition, subtraction, shifting, and multiplication operations, which can be implemented using Verilog programming language. To further clarify the specific design scheme of the three modules, the FPGA first stores the acquired down-converted signal in synchronous FIFO1. When FIFO1 is full, the LMS adaptive filter is started. FIFO1 begins reading data, while FIFO2 begins acquiring waveforms. FIFO1 and FIFO2 have a depth of 4096 and a bit width of 16 bits. The digital signal acquired by the AD converter is placed in the lower 12 bits, and the clock is connected to the top-level clock signal, thus allowing the LMS adaptive filter module to operate cyclically. The desired signal of the module is generated by the DDS IP inside the FPGA, with a bit width of 16 bits, and the frequency can be changed through the frequency control word.

[0038] like Figure 4 As shown, the key hardware component of the entire transmitter circuit module is the connection between the FPGA and the phase-locked loop (PLL) module. The FPGA configures the PLL register values ​​via the DATE signal, thereby controlling the frequency of the up-converted signal on the PLL. The PLL requires a 10MHz drive clock, generated by the DDS IP core and provided by the FPGA.

[0039] like Figure 5 As shown, the power amplifier uses the Qorvo SBB5089Z to generate a drive signal with sufficient transmit power. Its operating bandwidth is 50MHz to 4000MHz, and its noise figure is 1.1dB. This amplifier supports a single 5V supply and provides 20.8dB of gain over the 200MHz to 500MHz range.

[0040] like Figure 6 As shown, the mixer circuit is powered by a dual ±5V power supply. P1 and P2 are the input ports for the RF signal and the local oscillator signal, respectively. The signals are processed by DC blocking and filtering before entering the AD831 chip. P3 is the output port for the intermediate frequency (IF) signal. In this downconversion circuit, the local oscillator signal frequency is equal to the starting value of the sweep excitation signal frequency. Therefore, theoretically, the frequency of the echo signal is always greater than the local oscillator signal frequency, ensuring that the IF signal will not have a negative frequency after downconversion.

[0041] The beneficial effects of the utility model are that: the FPGA and DAC are combined to generate a stable controllable excitation signal of 9-10MHz; the maximum gain of the power amplification circuit reaches 26.83dB; the maximum isolation of the radio frequency switch in the sweep frequency range is 71.6dB; the frequency mixer can also realize down-conversion well under the condition that the phase-locked loop provides a local oscillation signal; the LMS adaptive filtering based on the FPGA and the scheme of extracting frequency information through the FFT IP core are proposed according to the characteristics of the echo signal of the SAW temperature sensor; the overall test results show that the effective test distance of the system is 25cm, the system is good in linearity in the temperature and resonance frequency relationship curve in the temperature range of 25-140 DEG C in the temperature rise experiment, and the maximum difference between the test results of the system and the vector network analyzer at the same temperature is 0.06MHz.

[0042] The above is only the preferred specific implementation method of the utility model, but the protection scope of the utility model is not limited to this, any skilled person in the art can easily think of the changes or replacements within the technical range disclosed by the utility model, which should be covered in the protection scope of the utility model. Therefore, the protection scope of the utility model should be subject to the protection scope of the claims.

Claims

1. An FPGA-based surface acoustic wave temperature sensor test system, characterized by: The sweep excitation signal transmitting module, the echo signal receiving module and the microcontroller are included. The output end of the microcontroller is connected with the sweep excitation signal transmitting module, and the sweep excitation signal transmitting module is used for transmitting a high-frequency sweep signal covering the resonant frequency of the temperature sensor. The DDS signal generating module is built-in in the microcontroller, and the low-frequency digital sweep signal generated by the DDS signal generating module is generated based on the master control chip of the microcontroller. 2.The FPGA-based surface acoustic wave temperature sensor test system of claim 1, wherein: The sweep excitation signal transmitting module and the echo signal receiving module are connected with a radio frequency switch II, the radio frequency switch II is connected with the antenna, and the radio frequency switch II is used for isolating the high-frequency sweep signal and the echo signal and controlling the receiving and transmitting states.

3. The FPGA-based surface acoustic wave temperature sensor test system of claim 1, wherein: The echo signal receiving module is used for receiving the echo signal emitted by the temperature sensor after being activated, and the echo signal receiving module includes a low-noise amplifier, a mixer and an analog-digital conversion module connected in sequence. The low-noise amplifier and the mixer are connected with a band-pass filter, and the mixer and the analog-digital conversion module are provided with a low-pass filter. The microcontroller is built-in with an echo signal processing module connected with the output end of the echo signal receiving module, and the echo signal processing module is used for obtaining the resonant frequency of the temperature sensor based on the echo signal. The master control chip of the microcontroller is XC7A35T, and the output end of the microcontroller is connected with an upper computer. The antenna is a spiral antenna composed of a spiral metal.

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