A new kind of view for a Double oven Crystal Oscillator

New demands for minimizing space and increasing frequency stability bring us to consider a new approach on double oven Oscillators. Main application of high performance oscillators are in "GNSS disciplined" applications. To allow the assembly on a board of 4TE width, the height of the OCXO is limited to 19 mm. A major requirement is in the micro second range at 1 day holdover. Ageing and thermally induced frequency drift are to be compensated. The frequency stability <6.10
^-10
in a wide temperature range -20degC to + 70degC as well as a waterproof ness to minimize the influences of humidity. The reproducibility of the frequency change must be as low as possible in the several repetitive thermal gradients to minimize the frequency hysteresis effect. The demand of synchronization networks for a daily frequency drift of <1.10
^-10
/ day in holdover mode ask for the construction of a new mechanical-thermal structure to house the SCp3 10 MHz resonator. Various oscillator diagrams have been compared (such as Clapp and Hartley-Colpitts) by simulation. The Clapp diagram is considered as being easier for adjustment, and needing fewer components. Design and simulation of thermal structure will be described. In order to decrease the total height of the internal structure to <11 mm, the traditional internal oven is replaced by a quartz plated on one side of the specific board that represents the mass of thermal inertia. All oscillator components and crystals are heated from the other side of this board by a proportional integrated thermostat. This board becomes an "inner ovenised oscillator" and is integrated in an outer temperature stabilized structure. This structure is hermetically sealed to minimize variation induced by humidity variation that interacts as a capacity effect. This second structure is thermally controlled by another proportional integrated thermostat. Thermal and mechanical designs are described in details and main results (ageing, thermal drift, thermal hysteresis ...) as long as holdover performances are provided.