Saw Sensor Transmission Circuit Design

Surface acoustic wave (SAW) sensor has been more and more widely used in many domains such as environmental monitoring, chemical disposal controlling, and clinical analyzing because of its small size, high sensitivity, and low price.SAW sensing signal is mainly detected via measuring the changes in frequency, phase and amplitude of SAW sensors. In this thesis, three different SAW sensor measurement circuits are designed.For SAW delay line (SAWDL) sensors, a phase lock loop (PLL) circuit is designed. The SAW sensor is placed between Voltage Controlled Oscillator (VCO) and Frequency Phase Detector (PFD). The PLL works at the central frequency of SAW sensor.For one port SAW resonator (SAWR) sensors, frequency detecting circuit and phase detecting circuit are designed respectively. The frequency detecting circuit is constructed based on dual channel structure. One channel is coated by sensing film as sensing channel. The other is reference channel without film. The frequency signals of the two channels are inputed into the mixer to get the frequency difference. The output signal from the mixer is low pass filtered, reshaped and amplified, then measured by frequency counter. The result is displayed on a LCD.In phase detecting circuit, a SAW oscillator takes place of a signal generator. The oscillating signal is sent to a phase detector by two routines. For the first routine, the signal is sent to the phase detector via SAW sensor. While for the second routine, the signal is directly send to the phase detector. Therefore, the phase detecting capability is realized by comparing the difference between the two routines.In this thesis, the test results of these three circuits are also reported. The frequency detecting circuit is applied to humidity detecting as well as DMMP vapor detecting. In these two cases, Copper phthalocyanine (CuPc) doped polyvinylpyrrolidone (PVP) and PVDF are coated on the sensing channel as sensing films, respecitively. The capability of the circuits is demonstrated. In comparison with the phase detecting circuit, the sensitivity of frequency detecting circuit is much higher.