How Does Ambient Temperature Fluctuation Influence the Short-Term Frequency Stability of OCXO?

Short-term frequency stability (STFS) is one of the most important specification of oven-controlled crystal oscillators (OCXOs). Although numerous studies have investigated factors that influence STFS, research on the impact of ambient temperature fluctuation is rare. This work investigates the relationship between the ambient temperature fluctuation and the STFS by introducing a model of the OCXO’s short-term frequency–temperature characteristic (STFTC), which considers the transient thermal response of the quartz resonator, the thermal structure, and the oven control system. According to the model, an electrical–thermal co-simulation is adopted to determine the temperature rejection ratio of the oven control system and estimates the phase noise and Allan deviation (ADEV) that caused by fluctuations in ambient temperature. As a verification, a 10-MHz single-oven oscillator is designed. From the measured results, the estimated phase noise near the carrier agrees well with the measured results, and it can be seen that only when the temperature fluctuation is less than 10 mK at 1–100 s, the oscillator can maintain the characteristics of flicker frequency noise at the offset frequency from 10 mHz to 1 Hz, and the ADEV is possible to reach at the order of E −13 in 100 s. Thus, the model proposed in this study effectively predicts the impact of ambient temperature fluctuation on the STFS of an OCXO.