Reasearch On Phase Locked Loop Based Time And Frequency Transfer

The technology of time and frequency transmission plays an important role in many areas,such as satellite navigation,communication,atomic clock alignment,remote distributed radio telescopes,physical fundamentals testing.Time and frequency transmission based on optical fiber have an advantage over traditional satellite transmission in stability,loss,bandwidth and so on,which has received wide attention from researchers.Transmission link,which transmission medium is optical fiber,has a problem of phase jitter caused by the interference of external factors.To improve quality of received signal,we have to compensate the phase jitter.Caused by interference of external factors,phase jitter will worsen the quality of Transmitted signal.In order to resolve this problem,this paper mainly studies the phase compensation technique.Specific include the following work:(1)Studying the theory knowledge of time-frequency transmission and phase compensation technique of time and frequency transmission.Round-trip phase compensation is a basic phase compensation technique,which can be divided into active compensation and passive compensation.This paper mainly studies the active compensation based on phase-locked loop(PLL),introduces the design method of PLL,choice of phase discriminator,design of loop filter and other key issues.This paper also studies the influence of the noise from reference source,optical fiber transmission and PLL circuit.(2)Proposing a frequency reduction scheme based on down converter circuit.Long distance transmission scheme in high frequency have great difficulty.The higher the frequency,the higher the detection sensitivity of transmission delay,but it can also lead to greater phase jitter,the ability of phase adjustm ent and system bandwidth limit the quality of the signal transmitted over a long distance.This paper proposes a frequency reduction scheme based on down converter circuit which can solve the problem.In this scheme,2.4GHz signal will be moved to 10MHz before its phase being detected.Detection sensitivity will be completely preserved,while The difficulty of phase discrimination will not be raised.(3)Build a time and frequency transmission system based on PLL.By the proving of experimentation,2.4GHz signal which transmitted 1000 kilometers in optical fiber achieved being locked,and the stability of this system in 9 hours is 2 × 10-15,and the Peak-to-peak of jitter is within 8ps.The system has high stability of PLL,few cycle slips and high long-term stability,which make it a good choice to become a system of time and frequency transmission over a long distance.