Abstract: The output frequency of the magnetically selected cesium atomic clock is related to the weak current signal output by the cesium beam tube, which affects its frequency stability. In order to improve its frequency stability, on the basis of the comparison between the weak signal voltagefrequency conversion and A/D(analog-to-digital) direct sampling of the main servo circuit of the magnetically selected cesium atomic clock, an A/D direct sampling circuit was designed based on the DSP28335 chip, using CAN bus communication technology to communicate with main control CPU board, and the wholeclock closed-loop locking scheme was realied. The experiment was compared with the existing voltagefrequency conversion method of the measured magnetically selected cesium atomic clock. The result shows that, compared with the voltagefrequency conversion method, the designed A/D direct sampling method reduces the relative frequency deviation range of the magnetically selected cesium atomic clock and improves the short-term frequency stability, presenting certain practical value.

Key words: magnetically selected cesium atomic clock, sampling method；voltage-to-frequency conversion, relative frequency deviation, frequency stability