Ultralow Phase Noise 10-MHz Crystal Oscillators

This paper describes the design and implementation of low phase noise 10-MHz crystal oscillators [using stress compensated (SC) cut crystal resonators] which are being used as a part of the chain of a local oscillator for use in compact atomic clocks. The design considerations and phase noise measurements are presented. The design includes a low-noise transformer coupled differential amplifier, spurious resonance rejection filter, and electronically tuned phase shifter. Phase noise measurements demonstrate a performance of −122 dBc to −123 dBc/Hz at 1-Hz offsets and −148 dBc/Hz at 10-Hz offsets. The phase noise at 1-Hz offset is very similar to the phase noise produced by the low-noise version of a doubled 5-MHz BVA resonator-based oscillators (model number 8607) previously produced by Oscilloquartz. The noise floor of the oscillators presented in this paper is around −161 dBc/Hz. These designs can be used as the reference oscillator to control the timing of many modern electronics systems.