Doubly rotated quartz crystal resonator for miniaturized VC-TCXO in mobile phone

This paper presents the development of a SMD, double rotated, [(YXwl)φ/θ] quartz crystal resonator with a first rotation angle "φ" smaller than the conventional FC, IT or SC-cut. A small voltage controlled temperature compensated crystal oscillator (VC-TCXO) at 26 MHz with dimensions of 4.0×2.5×1.5 mm can be realized using this resonator. The frequency-temperature characteristic (F-T) is 2.5 parts per million (ppm) over the temperature range -30°C to +75°C. This is achieved without an upper temperature range compensation circuit. In this paper, we have paid special attention to the double rotated quartz crystal resonators with a smaller rotation angle φ. We have fabricated double rotated quartz crystal resonators with the rotation angles of φ=7°, 9°, 12°, 14° and 16°. We have determined the optimum angle, which is smaller than that of the FC-cut. As a result, the size of a VC-TCXO can be significantly reduced since the compensation circuit for the upper temperature range may be omitted.