Multi-mode crystal oscillator for simultaneous excitation of three thickness-shear modes in stress compensated resonator

This paper deals with evaluation of self-temperature-sensing of stress compensated (SC) quartz resonator with simultaneous excitation of three higher overtones - the slow thickness-shear modes (i.e. the c-modes) in multi-mode crystal oscillator (MMXO). We have designed the MMXO especially for excitation of three c-modes in standard 10-MHz 3^rd overtone SC resonators: the 3^rd overtone, the 5^th overtone and the 7^th overtone. Each excited mode has its own frequency vs. temperature characteristic that can be measured and approximated as well. Simultaneous excitation of the three modes of vibrations in the volume of the resonator enables us to enhance the self-temperature-sensing. Consequently, in addition to compensation for frequency shifts due to variations of the resonator´s temperature, also frequency shifts caused by different aging rates of the particular modes can be identified autonomously (without necessity for any external frequency reference).