Design and Development of RF Synthesizer for Rubidium Atomic Clock

In this study, we have successfully developed an innovative, low-noise, and straightforward 6.834 GHz microwave frequency synthesizer designed for rubidium atomic clocks. This synthesizer's core components include an ultra-low-phase-noise 10 MHz OCXO, an active frequency multiplier, a step recovery diode multiplier, and a digital signal generator using FPGA technology. Utilizing frequency multiplication and mixing techniques, frequency precision is achieved in generating the output atomic resonance frequency. The phase noise performance of the 6.834 MHz signal was thoroughly evaluated, resulting in -50 dBc/Hz @1 Hz and -97 dBc/Hz @ 1 kHz. These measurements resulted in an instability contribution of 3.2E-12 for a 1-second averaging time, a performance level that closely matches the clock shot noise limit due to the Dick effect. This dedicated microwave frequency synthesizer not only enhances the compactness but also reduces power consumption in engineering rubidium atomic clocks. Moreover, this synthesizer scheme holds potential for application in other high-performance rubidium atomic clocks.