Abstract
This paper reports the designing of surface acoustic wave (SAW) oscillator with varactor diode (or varicap) as a part of tuning element. A practical way to enhance sensitivity of SAW sensor oscillator is performed by tuning capacitance using varicap. The varactor diode is placed at three different locations of the oscillator circuit to realize three different configurations. The change in frequency with applied voltage to varactor diode is studied for all three configurations. Sensitivity study for the three configurations is carried out with di-methyl methyl phosphonate vapor. The sensitivity, stability, and noise of each configuration are analyzed. Using varicap, about six times enhancement in sensitivity (~1.15 kHz/ppm) could be achieved. A simple and additive electronic method of tuning is utilized to improve sensitivity as compared with other methods that involve major changes in the sensor.
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