Design And Research For Electronic System And Prototype Of Miniature Rubidium Atomic Frequency Standards

Miniaturization has been one of the main developing directions of rubidium atomic frequency standards (RAFS). For the purpose both the electronics system and the physics package should be reduced in size. In the thesis techniques concerning miniaturization and noise compression of the electronics system were investigated, and a small size RAFS was built. Main results are as follows.A small size oven temperature controlled crystal oscillator for rubidium atomic frequency standards was designed. In the design, a Pierce oscillator circuit, a two step π type LC filter and a COMS inversion isolator were used. Low thermal noise transistors were used in the circuit. The temperature of the crystal was set at the turning point of the frequency-temperature curve. A crystal oscillator with volume of4ml, phase noise of-115.5dBc/Hz@1Hz and-152.6dBc/Hz@10kHz, and short-term frequency stability of1.8×10-12/1s, has been realized.OCXO noise transfer in RAFS frequency-locked loop (FLL) was theoretically analyzed. Through the work, we come to the conclusion that the effect of the OCXO noise on RAFS frequency stability includes two parts, one is the OCXO’s intrinsic noise, and another is the phase noise at the twice modulation frequency2fM. The analysis showed also that, for the miniaturized OCXO developed by ourselves, the total noise contribution to RAFS stability is about3.1×10-13τ-1/2, meeting the requirement to build a RAFS with frequency stability of3.1×10-13τ-1/2.A frequency-locked loop (FLL) circuit was designed and realized for a miniaturized high performance RAFS. The10MHz signal from a VCXO was transformed into a microwave interrogation signal with frequency of6834.6875MHz by a x45.5645833multiplier and a follow-up×15one. The x45.5645833multiplier was designed by using the digital phase-locked technique. The frequency modulation of the interrogation signal was realized in the455.645833MHz signal. The phase noise of the signal was measured and analyzed. Results showed that the fractional stability of the microwave signal is at a level of3.5×10-12τ-1/2. The short-term frequency stability of a RAFS containing the FLL circuit was tested, and a result of5.7×10-12τ-1/2(1s≤τ≤100s) was obtained, obviously better than that of an average commercial RAFS.Based on the electronics system and the existing small size physics package in our laboratory, a miniaturized RAFS was designed. After needed mechanical and thermal structure designs, a prototype of miniaturized RAFS with volume of140cm3and power consumption of7.5W has been realized. According a preliminary test, the RAFS has a short-term frequency stability of1.3×10-11τ-1/2(1s≤τ≤100s), better than an average commercial one. Analysis showed that the performance of the RAFS can be improved further.