A New Synchronized Miniature Rubidium Oscillator With an Auto-Adaptive Disciplining Filter

Pascal Rochat, Bernard Leuenberger

Abstract:	A new rubidium line (SRO) integrating timing functions and time interval measurements was developed using an auto-adaptive disciplining algorithm. This led to an ultra-stable time & frequency machine usable for many applications such as: synchronization of telecommunications systems (SOH, SONET, CDMA), military communications, navigation, and instrumentation. The frequency and phase-time correction is calculated from an internal phase-time error signal measured within I ns resolution issued from an internal PPS signal (PPSINT) aligned to the PPS reference signal (PPSREF). Furthermore, the SRO itself analyzes the stability of the PPSREF signal Thanks to the very good mid-term frequency stability offered by the rubidium technology. The PPS reference of a GPS engine can be directly applied to the SRO without specific analysis of the internal parameters of the engine (number of satellites in view, signal-to-noise ratio, etc.). When the “track” mode is selected, the PPSINT is aligned to the PPSREF. Then midterm frequency stability analysis of the PPSREF (learning phase) may start providing an internal crystal oscillator locked to the rubidium atomic resonance. Such analysis is performed continuously and the PPSINT will then be phase-locked to the PPSREF as long as the Allan variance of the PPSREF is lower than a pre-defined value stored in EEPROM memory. The phase-lock loop time constant t is automatically selected as a function of PPSREF short-term stability. When a standard GPS receiver is used, being affected by selective availability, the typical time constant will be 10,000 to 100,000 sec. Without SA, the typical selected time constant is 1,000 see. Details of the principles of the disciplining algorithm are presented as step response and holdover performance data.
Published in:	Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting November 27 - 27, 2001 Hyatt Regency Long Beach Long Beach, California
Pages:	535 - 542
Cite this article:	Rochat, Pascal, Leuenberger, Bernard, "A New Synchronized Miniature Rubidium Oscillator With an Auto-Adaptive Disciplining Filter," Proceedings of the 33th Annual Precise Time and Time Interval Systems and Applications Meeting, Long Beach, California, November 2001, pp. 535-542.
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