DIGITALLY CONTROLLED RUBIDIUM OSCILLATOR

Rubidium atomic oscillator (RbOSC), which is physically compact and exhibits excellent frequency stability, has become available for various applications as a frequency standard. In most cases, such oscillators are used as "independent frequency reference sources." Recently, however, it has also become important to use them under "mutually synchronized" conditions. The authors have developed a digitally controlled rubidium oscillator (DCRO), which can synchronize another frequency source. The +/- 3.3 x 10(-8) wide frequency control range with good linearity and 1 x 10(-12) fine control step are highlighted. In order to achieve a wide frequency range with fine steps, a synthesizer was developed which has three-stage phase locked loop oscillators with variable frequency dividers. Data for controlling the frequency dividers, written in a 3 Mbit ROM, was calculated using a computer. Along with delta-y(tau) = 6 x 10(-12)/tau-1/2 fine frequency stability, a more than 20 year long life and compactness were realized, easily satisfying telecommunications and broadcasting system requirements.