New design of low profile precision OCXO for time keeping, positioning and telecom applications

A new precision OCXO has been developed at Morion R&D laboratory. The aim of this work was to develop a relatively simple high stability low profile device based on single oven structure. To achieve high frequency stability vs. temperature SC-cut crystal in TO-8 holder was used and a radical new oven design was worked out. The main problem in the oven design is to minimize the temperature gradients over the crystal. It can be done if heat flow through the crystal is near zero. That is why in the new design the crystal is symmetrically situated relative to the heaters so that only a small part of heat flow goes through the crystal. Generally in a single oven structure with limited thermal insulation there is no possibility to have zero heat flow through the crystal. Due to this heat flow the, crystal temperature differs from the heater temperature (more exactly-the temperature of sensor) which is kept constant by thermocontroller. This difference depends on temperature difference between oven and outer space and appears as a static error of oven. To eliminate this kind of error thermal compensation was used. The theoretical thermal model of the oven was built and calculations were done to optimize the oven design and thermocontroller circuit. In the final design of OCXO mode B of the crystal\´s oscillation is used as a temperature sensor for fine tuning of thermocontroller. As a result the following parameters of OCXO were achieved: frequency range from 5 up to 16.384 MHz, frequency stability vs. temperature ±(1.0+2)·10^-9 for temperature range -40-+70°C and ±5·10^-10 for temperature range -10-+60°C, power consumption at steady state at 25°C (without air flow) <1.8 W, dimensions 41×51×19 mm or 2"×2"× 0.75"