Saw resonators for temperature stable oscillators

A double two-port resonator by means of which the compensation of the TCF1 as well as the TCF2 is possible is presented. The double resonator is composed of two coupled two-port single SAW resonators. The propagation directions are characterized by opposite and equal signs of TCF1 and TCF2, respectively. The coupling is realized by cascading and using a coupling inductance. In order to explain the TC compensation qualitatively a simple coupled spring resonator is treated analytically. An example of a double two-port resonator is studied by means of model calculations and experiments. 35.5 degrees rotY quartz is used as a wafer material. The propagation angles (angle between the propagation direction and the X axis) of the single resonators are chosen to be larger and smaller, respectively, than the angle in vicinity of 45 degrees whose TCF1 is zero. The frequency whose temperature stability is studied is defined as frequency belonging to a fixed phase. This phase is kept constant within the entire temperature range. The frequency and vertical bar S21 vertical bar are calculated and measured as functions of temperature. Not only the theoretical but also the experimental results express the temperature shift of frequency from -30 degrees C until 70 degrees C to be essentially smaller than that in the case TCF1=0 in vicinity of 45 degrees.