Abstract: The microwave probing signal of the rubidium atomic frequency standard (RAFS) is used to excite the transitions between the ground-state energy levels of rubidium atoms, and realize resonance detection. At present, the microwave generation schemes commonly used all have the disadvantages of complicated circuit structure, high power consumption and inconvenient integration. This work introduces a design scheme for generating discontinuous microwave inquiry signal using the phase-locked loop (PLL) technology. The scheme takes the 10 MHz signal as a reference frequency, and is capable of obtain the (6 834.687 5 MHz ±f_M) signal directly under a reasonable configuration of single chip microcomputer. The scheme has the advantages of simple circuit structure, low power consumption and high digitization. The stability of the whole machine was found to be better than 1.5E-11/√τ(1 s ≤ τ ≤ 100 s). The performance indexes can meet the requirements of small commercial rubidium atomic clock.

Key words: phase-locked loop (PLL), microwave inquiry signal, rubidium atomic frequency standard (RAFS), additional instability, microwave-power frequency shift