CTXO, clever time crystal oscillator (clock)

The short-term frequency stability of quartz crystal oscillators is of great importance. We show how this can 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. The design goal is to reduce the size of all of these effects by one to two orders of magnitude. This is accomplished by using an ensemble of inexpensive oscillators, such as TCXOs or MCXOs. The lead or lag hysteresis effects in TCXOs seem to be ameliorated in this approach. In addition, the use of TCXOs reduces the temperature compensation to a second order fit problem. The CTXO oscillator (clock) is designed to be inexpensive, environmentally insensitive, robust, adaptive and small. The performance goal is about 10^-8 from -35 to 85°C, and analysis shows that, with a good choice of optimization routine, it is possible to get excellent temperature compensation using a multiplicity of oscillators, a generic TCXO (or DTCXO) compensation, followed by good second-order compensation