A comparative analysis of one-port Colpitt and two-port Pierce SAW oscillators for DMMP vapor sensing

This paper reports an experimental study on chemical sensitivity and noise behavior of Colpitt and Pierce SAW oscillators based on 433.92 MHz one-port and two-port SAW resonator devices, respectively. The oscillators are characterized for phase noise as well as Allan variance. The sensitivity for DMMP (di-methyl methyl phosphonate) vapor is imparted by providing a diallyl-bisphenol polymer precursor as a selective interface coated on to both the SAW devices in an identical manner. Comparative vapor sensing experiments are carried out under simultaneous exposure to the same DMMP vapor stream in different ranges of vapor concentration and duration. A new data acquisition method is employed which is wireless and automated. It uses an antenna pickup at the input of a spectrum analyzer with PC control interface. The results show that the two-port Pierce oscillator is more stable but less sensitive than the one-port Colpitt oscillator. It is found that under the conditions of analyte exposure durations longer than 30 s the one-port Colpitt oscillator yields higher signal to noise ratios. The results are interpreted in terms of phase response characteristics and different sensitivities of the one-port and two-port SAW devices towards mass loading and viscoelastic effects.