The Research On Timing Application Of Miniature Rubidium Frequency Standards

The atomic frequency standard most widely used at present is the miniature rubidium frequency standard (MRAFS), which is characterized as small size, high performance and suitability to the environment and more inexpensive than other atomic frequency standard. With the rapid development of the communication, navigation and positioning, and smart grid technology, higher performance of time synchronization and time hold are demanded. MRAFS composed with GNSS receiver can provide high-quality low-cost precision time synchronization in large spatial scales. When GNSS receiver does not work properly, it can provide better time hold capacity.This paper is mainly focused on improving the timing performance of the MRAFS.As a secondary frequency standard, the time and frequency accuracy of the MRAFS must be calibrated continually, so it can be used as a high-precision time reference. There are three ways to improve the performance of the MRAFS. First, through theoretical analysis and experimental verification, the physical parameters of the MRAFS are optimized, and the MRAFS’s medium and long term frequency stability is improved, and the frequency drift rate is reduced. Second, with the GNSS receiver, after the MRAFS is disciplined, the accuracy of the satellite clock frequency and time is transferred to the MRAFS. Inside the MRAFS, FPGA (Field Programmable Gate Array) and TDC (Time Digital Converter) are laid to achieve high-precision digital phase shifter and phase measurement, and an algorithm to discipline the MRAFS is designed for timing application. After disciplined by the GNSS receiver, the time difference is less than20ns between two MRAFSs. Third, the MRAFS is used to improve the GNSS receiver’s performance because the MRAFS has better short term frequency stability and accuracy than the GNSS receiver. The GNSS’s performance is improved, in turn, can further enhance the MRAFS’s performance.A practical application is also presented in this paper about the MRAFS in a NTP (network time protocol) server.