10E-0 Improved Temperature Stability of One-Port SAW Resonators Achieved without Coils

The temperature stability of surface acoustic wave (SAW) resonators on ST-like quartz cuts can be increased by using double resonators. For this the turnover temperatures of the two single resonators are chosen above and below the reference (i.e. room) temperature, respectively. In the past, coils were necessary for improving temperature stability. In the present paper, solutions of temperature stable one-port double resonators without coils are described. The improvement of temperature stability is discussed in connection with the resonance type (resonance or antiresonance), the connection type of the single resonators, the use of capacitances and inductances and with the considered resonance (or antiresonance) component occurred by splitting due to resonator coupling. The parallel connection of two single resonators with different propagation directions is treated in more detail. It is shown that the temperature coefficient of frequency of 1^st order (TCF1) as well as that of 2^nd order (TCF2) can be compensated by such a circuit. For this a capacitance connected in parallel to the double resonator is not required to compensate the TCF2 but it proved to be suitable for correcting the TCF1. Finally a double one-port resonator structure on 35.5degrotY quartz is investigated experimentally.