Acoustic surface-wave oscillator system for gas sensor

The disclosed system comprises two groups of acoustic surface wave oscillator composed of acoustic surface wave delay line, radio frequency amplifier and phasing network, and one group of mixer circuit composed of mixer, low frequency amplifier and low pass filter. Outputs of two groups of oscillator are connected to the mixer. The output of the mixer passing through low pass filter and low frequency amplifier outputs signal of difference frequency between two groups of oscillator. Two groups of delay line are fabricated on same substrate. Single-phase unidirectional transducer (SPUDT) structure is adopted in delay line so as to reduce insertion loss. Length of the long transducer is equal to distance between geometric centers of transducers. Comb structure is adopted, and gap between combs is equal to length of the short transducer in order to restrain unwanted mode of oscillation. The oscillator is operated at single mode so as to raise frequency stability (0.07 ppm).