Design of microwave signal source for CS chip-scale atomic clock

Abstract

Nowadays, some countries have already invented chip-scale atomic clock (CSAC) based on coherent population trapping (CPT), and it has been applied in every areas. According to its working principle, the microwave signal source is one of the decisive factors affecting its stability. Usually the microwave signal source is a phase-locked loop circuit, it mainly includes a frequency synthesizer, a voltage controlled oscillator (VCO) and a loop filter. This paper aims to develop a microwave signal source for Cs CSAC. First, a VCO should be designed, in order to validate the characteristic of the designed VCO, the VCO needs to be tested at high and low temperatures, and the results show that it has good stability of high and low temperatures. Second, for the purpose of verifying that the design and production consistency of the VCO are in good condition, 1000 VCOs are test, respectively. The statistical distribution of the phase noise at 1 kHz offset would be painted a curve. Finally, the designed VCO (PN: 61.01dBc/Hz@1kHz) will be applied in phase-locked loop, the test results show that the phase noise is −83.57dBc/Hz@300Hz, it is much better than −43dBc/Hz@300Hz which is the spec of CSAC. If the microwave signal source would be used in CSAC, its stability would be greatly improved.