Brief history of the development of ultra-precise oscillators for ground and space applications

The evolution of today´s ultra-precise oscillators is presented beginning with their origins, which were directly related to the development of the 2.5and 5-MHz AT-cut resonator, designed by Warner at Bell Laboratories in 1952 and the introduction of the first all-transistorized frequency standard by Sulzer Laboratories in 1958. Ultra-precise oscillator performance is ultimately dominated by the quartz resonator, and quartz resonator performance has improved dramatically since the original Warner resonator design. The improvements were achieved by refinements to the initial Warner design and improved resonator fabrication techniques, the development of a new SC-cut resonator, and a new resonator design, the BVA. The size reduction of resonators and the ability of the resonators to survive harsh environments has allowed the size of ultra-precise oscillators to be greatly reduced while still retaining excellent frequency stability. The relationship between resonator development and oscillator development is presented. Ultra-precise quartz oscillators have demonstrated 24-hour aging rates of <1×10^-12 and Allan variances of <6×10^-14 at 10 and 100 s. Oscillators with a £(f) phase noise floor of <-175 dBc and <-135 dBc 1 Hz from the carrier have been reported. Environmentally induced changes in the oscillator output frequency are as low as <1×10^-12 per unit measure with the exception of acceleration and ionizing radiation. The physical parameters of ultra-precise oscillators have been reduced to a volume of <300 cm ³ and a mass of <300 g. DC input power for an ultra-precise oscillator can be <0.5 W at 25°C. All of these performance parameters probably cannot be achieved in one oscillator but many of them can, and the performance parameters illustrate the capability of today´s oscillators