The Phase Stabilities of the Servo Circuit in a Rubidium Vapor Cell Frequency Standard

This paper mainly discusses the phase stabilities of a T-type frequency selector and RC phase-shift circuit which are used in the servo circuit of a rubidium vapor cell frequency standard, and analyses the mechanism how the additional phase variations which come from the two circuits influence the frequency stability of the rubidium standard. We present a new method of realizing a digital phase shifter based on CPLD (complex programmable logic device) for the synchronous detection reference signal. In comparison with traditional RC phase shifter, this method has many advantages such as good phase stability, high precision of phase shift and convenience for phase adjustment. It has been applied in a miniature rubidium frequency standard of our laboratory.