An experimental study of frequency jumps during the aging of quartz oscillators

The cause of sudden frequency jumps during the aging of high-stability quartz oscillators has been investigated using an accurate method of measuring the resonant frequency versus drive current for AT-cut crystal resonators. In some cases, a change in the crystal current is accompanied by a jump in the resonance frequency. This is attributed to spurious resonances near the fundamental mode. The current which causes coupling between the spurious and fundamental modes shifts with the crystal driving time. This shift in the current is responsible for the abrupt frequency jumps observed.