Special amplitude-frequency effects in VHF quartz resonators

High drive levels of the fundamental mode of a quartz shear-mode resonator can result not only in a frequency shift of the fundamental mode (amplitude-frequency effect) but also in nonlinear interactions with the third overtone mode. One such interaction reported here is a frequency shift of the third overtone mode. In addition, the third harmonic of the fundamental driving signal is generated which can appear close to, or directly at the third overtone resonance, depending on the relationship between the fundamental mode and third overtone mode frequencies. We examine these effects in 33-MHz fundamental mode AT-cut and SC-cut quartz resonators in which the fundamental mode and third overtone mode frequencies were closely matched by design.