Investigation of amplitude effects on higher overtones in stress compensated quartz resonators

In this paper we illustrate our experimental investigations of amplitude effects on two higher overtones (the 5th and the 7th ones), as well as on the main mode (the 3rd overtone) of different stress compensated (SC) quartz resonators. The impact of amplitude of vibrations to basic parameters in the simple Butterworth-Van Dyke one-port equivalent circuit of the particular mode were derived from the impedance vs. frequency responses measured in the vicinity of the particular modes, while temperature of the investigated resonator was maintained approximately at the lower turnover point temperature of the main mode. In the 3rd overtone 10-MHz SC quartz resonators, for example, the 5th overtone or the 7th overtone (the c modes, i.e. the slow thickness-shear modes of vibration) can be excited simultaneously along with the main c mode, with assistance of an appropriate dual-mode or multi-mode crystal oscillator (MMXO); and the resonator self-temperature-sensing can be reliably implemented [1], [2], [3]. Amplitudes of particular modes, which are simultaneously excited, have impact on short-term, as well as on long-term frequency instabilities of generated signals; hence, drive levels of individual c modes have to be set up properly in the oscillator circuit.