CTXO, CLEVER TIME CRYSTAL OSCILLATOR

摘要

The short-term frequency stability of quartz crystal oscillators is of great importance. Because of current high-level need, we show how this may be extended to the long-term in an oven-less, low-power configuration, by surmounting the basic problems due to temperature, adverse effects due to shock, vibration and general acceleration effects, inherent frequency inaccuracy, and lastly, oscillator frequency and time jumps, activity dips and drop outs - categorically called abnormal behavior. We desire to reduce the size of all of these effects by one to two orders of magnitude. This may be accomplished using an ensemble of inexpensive oscillators, such as TCXOs or MCXOs. Properly configured and properly measured, most of the important characterization parameters can be learned for each member of the ensemble and for the ensemble as a whole. The lead or lag hysteresis effects in TCXOs seem to be ameliorated in this approach. In addition, the use of TCXOs reduce the temperature compensation to a second order fit problem. The design goal is to have a oscillator which will be inexpensive, environmentally insensitive, robust, adaptive and small. The performance goal is of order 1 X 10~(-8) from -35 to 85 degrees Celsius. The analysis shows that with a good choice of optimization routine that it indeed is possible to get excellent temperature compensation using a multiplicity of oscillators, a generic TXCO (or DTCXO) compensation, followed by good second-order compensation. A Monte Carlo analysis resulted in 1 X 10~(-8) total frequency change as a function of 120℃ change in temperature, 99.9% of the time if the orientation spread of the crystals is less than 2 minutes of arc.