Research On The Wireless Test System Of Passive Wireless SAW Sensor Based On FPGA

Sensor technology has been widely used in many fields such as automotive and aerospace. However surface acoustic wave(SAW) sensor has smaller size, lower power consumption, higher quality factor and better repeatability compared with traditional sensors. SAW sensor is also a wireless passive sensor, which enables it be detected in high temerature, high pressure, high speed and many other harsh environment. As a result, SAW sensor draw much attention by researchers in recent years. And the wireless test system of SAW sensor plays a particularly important role.Firstly, this paper tested two kinds of SAW sensors resonant type and delay-line type by vector network analyzer to obtain their time domain signals and frequency domain signals. By comparing the characteristics of two sensor signals,we chose the resonant-type SAW sensor as our object.Secondly, this paper proposed an overal plan of test system based-on FPGA after analyzing the characteristics of resonat-type SAW sensor’s feedback signal. The transmitting unit used DDS+PLL+PA architecture, and the receiving unit used superheterodyne receiver architectrue. The DSP was depended on FFT IP core that can get the resonance frequency of the SAW sensor which was about 433.855 MHz.Then according to the test system design, this paper selected and tested the circuit modules including FPGA chip, ADC and DAC chip, PLL, LNA, RF switches and so on. Also we complete the impedance matching of the SAW sensor to antenna by ADS. Each circuit module met the test requirements well. The DDS module can generate stable and high power low-frequency signal. The PLL module enables frequency multiplication function of 32 times well. The gain of LNA module is20.667 dB near the resonant frequency of SAW sensor and the noise figure is only0.4dB. The isolation of RF switch module is higher than 80 dB near the resonant frequewncy of SAW sensor. The frequency-mixer and low-pass filter can run well too.Finally, this paper tested the temperature respectively by a vector network analyzer and the designed FPGA-base wireless test system from room temperature to150 ℃. The results verified the Stability and reliability of the designed FPGA-based test system.