Optimization of drive-level in high stability low-noise OCXOs

This paper describes results of an experimental study of the influence of driving current on aging rate and noise properties of OCXOs, based on SC-cut 3rd overtone crystals. During the study, two groups of 12 and 30 samples were tested under different conditions: first at a driving current raised step-by-step from 1.5 up to 3.0 mA; second at 3.0 mA sustained constant during the experiment. The tests did not show noticeable impact on aging using a driving current up to 2.5 mA, while the 3.0 mA current produced aging degradation for most units. The phase noise level at close-to-the carrier offset is not sensitive to drive level while the noise floor can be reduced to about -170 dBc at 3.0 mA exciting current.