Iridium-next master clock

A high resolution, digitally tuned quartz oscillator with excellent phase noise and temperature stability has been developed for space applications and is being utilized in the Iridium NEXT constellation, the largest commercial satellite constellation in the world. Significant effort has been expanded to optimize the quartz resonator design, the double oven circuitry and the digital tuning scheme. The oscillator is implemented using readily available space qualified parts. The best results have been achieved with 5 MHz, third overtone, SC cut resonators multiplied by a factor of two to provide the Iridium NEXT frequency of 10 MHz. A temperature coefficient of 5E-12/10OC-interval has been realized, and single sideband phase noise of -115 dBC/Hz at offset of 1 Hz. has been achieved on the 10 MHz output. Allan deviation performance of 5E-13 for averaging times of 1 to 100 seconds has also been demonstrated. Digital tuning from the ground is accomplished by commanding a custom 16 bit DAC, implemented in a space qualified FPGA. The DAC architecture provides for high resolution ( <; 1E-11) tuning, with spurious outputs below -125 dBC. Unique features of resonator design, and oscillator circuitry are discussed, and data are presented.