Design considerations of vacuum-sealed OCXO´s for high reliability applications

It is well known that the use of a vacuum sealed enclosure which contains the crystal and oscillator circuitry can be of significant value in enhancing the performance of OCXO´s. This paper reports on the design of a new vacuum sealed OCXO termed the EMXO having the design objectives of (1) a design which allows for the use of several different crystal enclosures, including the standard TO-8, (2) a parts count reduction of approximately 50% over previous designs and (3) a provision to utilize high reliability components such as class “S” on ceramic construction. The resulting oven thermal resistance measured approximately 180°C/W thereby yielding a steady state power dissipation of less than 1 W at -55°C