Low phase-noise, high frequency OCXOs

June 05, 2013 // By Graham Prophet
IQD’s IQOV-200 series Oven Controlled Crystal Oscillator (OCXO) has been designed to optimise low phase noise performance. Phase noise is caused primarily by semiconductor thermal noise but noisy resistors, capacitors and inductors can all have an effect, as can poor signal transfer paths due to circuit layout and design.

Good oscillator design consideration allow the IQOV-200 series to deliver phase noise performance of -172dBc/Hz at 100kHz offset and -160dBc/Hz at 1kHz offset based on a nominal oscillating frequency of 100MHz. Available at any frequency in the range 80MHz to 130MHz, the new model is initially housed in an industry-standard 36 x 27 mm IEC C008 Euro package although other package styles including surface mount variants can be considered to suit specific customer applications. The oscillator nominally operates from a 12-V power supply and consumes 1W in steady state, incorporating a very high level of internal voltage regulation to provide immunity to external voltage variations. Drive capability is quoted at +6 dBm into 50 Ω.

Operating over a standard temperature range of -20 to 60C with an initial frequency stability of ±50 ppb (parts per billion), other temperature ranges and stabilities can be considered as required. The key component within any quartz oscillator is the quartz crystal and the IQOV-200 series’ long term aging rates are particularly low due to the very high quality and processing of the quartz crystal. IQD’s German high specification division IQD FOQ GmbH where the new model was designed, has the critical advantage of close integration between the single site in-house crystal and oscillator design and manufacturing departments. The new model incorporates a SC-cut (Stress Compensated) HC43 cold welded crystal as exhaustive research has shown that this style of package offers much less stress on the crystal than the more commonly used multiple mounting point systems. This has a direct effect in improving the oscillator’s close-in phase noise. The actual drive circuitry has its most direct influence on the far-out phase noise performance. Inevitably both aspects are somewhat interactive so a fine engineering balance has to be struck.

Applications for this high specification OCXO include ground and airborne radar equipment (both military and commercial); military digital communications systems; satellite communications such as ‘Very Small