Development and Performance of the Timing Unit Rubidium Oscillator (TURbO) as a Compact, High Performance Atomic Clock for Dynamic Environments

As threats to the accessibility of position navigation and time (PNT) systems continue to increase, the availability of atomic clocks that can operationally support functions in GNSS denied applications becomes increasingly critical. Selecting an atomic clock for GNSS denied applications includes trade-offs between size, weight and power (SWaP), and holdover performance in the target environment; for the lowest cost. By combining a SWaP reduced physics package with a high-performance silicon MEMs flywheel oscillator and full digital control of environmental parameters, FEI has achieved performance better than 1E-11 / sqrt tau out to 1,000 seconds. The TURbO is a small, lamp based, double resonance rubidium clock. To achieve vibration performance and SWaP, FEI has integrated a 10MHz silicon oscillator in place of the traditional quartz oscillator. The silicon oscillator technology is mature enough for TURbO to achieve good phase noise performance and be virtually vibration insensitive while improving SWaP as compared to quartz. The TURbO also incorporates full digital control for the physics package, environmental and clock control loop electronics, allowing miniaturization and further SWaP improvements. TURbO is engineered to be manufacturable and we anticipate cost reduction at scale. At a volume of less than 150????, a 2.54 ???? maximum profile height and a weight of < 0.5 ????, the TURbO is designed to provide high performance output, including frequency stability and phase noise, while subjected to dynamic environments. The target TURbO frequency stability is 5E-12 / sqrt tau to 10,000 seconds, and a drift rate of less than 1E-12 per day. The target phase noise at 10MHz is better than -90 dBc at 1Hz, with a floor of better than -150 dBc. TURbO measured performance shown in this presentation is achieved while subjected to typical airborne platform levels of vibration, and over a temperature range of -40C to +60C, with a target range of -55C to +71C.