Oscilent Corporation - Technical References
Introduction to Quartz Frequency Standards

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Introduction to Quartz Frequency Standards - Warmup

When power is applied to a frequency standard, it takes a finite amount of time before the equilibrium frequency stability is reached. Figure 22, discussed above, illustrates the warmup of two OCXOs. The warmup time of an oscillator is a function of the thermal properties of the resonator, the oscillator circuit and oven construction, the input power, and the oscillator's temperature prior to turn-on. Typical warmup time specifications of OCXOs (e.g., from a 0°C start) range from 3 minutes to 10 minutes. Even TCXOs, MCXOs, and simple XOs take a few seconds to "warm up," although these are not ovenized. The reasons for the finite warmup, i.e., stabilization, periods are that it takes a finite amount of time for the signal to build up in any high-Q circuit, and the few tens of milliwatts of power which are dissipated in these oscillators can change the thermal conditions within the oscillators.