Digital Design of Servo Loop for Passive Hydrogen Maser

The passive hydrogen maser is an atomic frequency standard with outstanding performance, which utilizes a hyper-fine transition of hydrogen atoms as a frequency discriminator. It uses two servo loops to control and outputs a stable signal. Previously, the servo loop design was implemented using analog circuit, which has difficult in debugging and poor loop control ability. Compared with the analog circuits, the digital design of servo loop can process signals more accurately, enhance the loop control capabilities, and thereby improve the medium-and short-term frequency stability of the passive hydrogen maser. Therefore, the performance indicators are better than 5E-13/1s, 2E-13/10s, and 5E-14/100s, reaching the current international advanced level.