Research On CPT Atomic Clock,Space Atomic Clock And New Technologies In The Time-Frequency Measurement And Control Field

The atomic clock based on the CPT phenomenon has been a focus of the domestic and international research in recent years. Two types of atomic clocks CPT-Maser and passive CPT atomic clock can be developed according to the CPT phenomenon. The former has the characteristic of high precision and stability, but with a very complicate structure. Howerver, one outstanding feature of the latter is the simple structure, which is one kind of atomic clocks can be miniaturized.After a brief discription of the working principle of the Rb CPT -Maser atomic clock, functions of the three subsystems, and their design and measurement methods,the study of the paper places emphasis on the sub-circuit system and its realiazation,The action of the Frequency synthesize circuit of the CPT maser clock is to make a linkage of the user frequency (normally 5MHz and 10 MHz) to the laser modulation frequency. The low noise frequency synthesize technology is used in the high performance atomic clock. The user frequency to the 100MHz and 100MHz to the 3.417GHz frequency synthesis circuits have been designed and realized in the CPT-Maser clock and the performance of these frequency synthesis circuits have achieved an advanced level.The locking of the CPT-Maser atomic clock is realized by detecting the change of the power of the CPT-Maser signal. As the CPT-Maser signal has a power usually below-90 dBm and a frequency approximately 6.834GHz, the heterodyne receiver and power detection circuit are designed and used to detect the power. There is a high request to the detection resolution of the power detection circuit and to the temperature stability of the whole circuits.The above problems are mainly solved by using high quality components in the circuit.Theory analysis explains the relationship between the outputs frequency's precision and stability to the performance of these circuits.The servo circuit processes the output error signal of the power detecting circuits to the control voltage of the local oscillation. A digital servo circuit, mainly coinsist of an A/D , a chip of monolithic integrated circuit and a D/A is designed,which has quality that the debug is easier and some functions that traditional analog servo's atomic clock does not have such as the frequency temperature coefficient can be improved and the locking belt can be expanded by procedures. Atomic clock's frequency temperature coefficient is one of the key parameters. The overseas'rubidium space atomic clock's temperature frequency coefficient has reached 10-14 level at present, but CPT-Maser is only at 10-12 level. A method of using the software procedure to compensate frequency temperature coefficient is proposed. The experimental result indicated that frequency temperature coefficient can hopefully reach 10-14 level in the CPT-Maser clock by using the method mentioned above.The circuit for expanding the locking belt of the CPT-Maser atomic clock is designed and realized,which can solve the unlocking problem caused by the deviation of the local oscillation's frequency from the looking belt of the atomic clock.Theoretically, the digital atomic clock has the advantages in producing, measuring and software compensation. The experiments of the compensation of the frequency temperature coefficient by procedures, unreal time control of the atomic clock and locking frequency circle based on the phase coincident point detection are carried out to validate the design. Meanwhile the digitalization and intelligentization of the atomic clock are studied in this paper.The design features of the space atomic clocks, the main characters of them and the main research departments, the current characters of our space atomic clocks, the gap of technologies between our country and the foreign countries, the detailed techniques of the space atomic clock developed by the foreign countries are described. Some proposal that may hopefully improve our space atomic clock technologies are also described in the paper.The development of the time-frequency measurement instruments and the novel time-frequency signal processing techniques are another research branch in the time-frequency field.Time-to-digital is a foundation of many kinds of measurement equipments and the demand of its resolution is to picosecond level at present. Present CMOS time-to-digital converter with picosecond level resolution is difficulty to realize and the difficulty will be much greater when in higher resolution case. Signal will be delayed when transmission and this paper study whether a high precision time-to-digital converter can be worked out based on this phenomena .First the resolution and precision are pointed out then some experiments are done to test the analysis and the results are exciting. Analysis and experiments results show that this technology is a new and can be used in the making of a high resolution time-to-digital converter. Characteristics and applications are also pointed out in this paper.A novel clock interpolation technology is proposed by utilizing the characteristics such as stabilization and regularity of the transmission delay to improve the measurement precision of a Time Interval Measurement Module (TIMM). A length of transmission line is used to delay the clock signal of the TIMM. Many of detection points are set along the transmission line. The D triggers are used to detect the phase coincidence between the delayed clock signal and the beginning or ending signal of the time interval. Finally, the time difference between them can be deduced based on the position of the phase coincidence. A high precision Time Interval Measurement Instrument is designed by using the FPGA chip EP2C5Q204 and the clock interpolation technology proposed above and the corresponding TIMM has the advantages of simple realization, good in stability and so on.There is a big demand to the stability measurement instruments at present. In this article ,an instrument for measuring Allen division is designed based on the DDS technology as well as a high precious frequency measurement method that measure the difference frequency's period of the under test frequency and the reference. The instrument's background stability surpasses 4.5×10^-13/1s,1.5×10^-13/10s and its measurement range is form 1MHz to 30MHz at present. It mainly has low cost high accuracy merit compared with the overseas main products.At present a time interval counter is always used when doing time comparison and the time interval counter's precision restrict the time comparison's precision. This paper analyzes the affiliation between the phase comparison and the time comparison and get a conclusion that the time comparison result can be get from the frequency comparison result under some conditions. An experiment is done to prove that. The advantages of this indirect measurement are also shown.The change law of the phase difference between two frequency signals is analyzed and a new method to get standard time signal which is used in promulgating time is put forward. Theory of the new method is founded and some basic experiments have been done. The experiments results meet the theory and a second signal whose stability is better than 200ps is gotten by this method .Advantages of the new method are also put forward in this paper.When use the PLL(phase locked loop) technology lock one frequency to another, as the two frequencies are usually un-correlated, frequency transformation circuits are usually needed to process the two frequencies to make them have an equal or an integral multiple relations. There is a periodic phase coincidence phenomenon between two arbitrary frequency signals and the period of the phase coincidence is relation with the frequency relation of those two signals. Based on this principle a new FLL (frequency locked loop) is realized. Compared with the tradition PLL, this FLL has the advantages that it's advanced in principle, the circuit is simple when realizing and is easy to adjust the output frequency of the loop. Theory analyses and experimental studies are done in the paper, the experiment results are confirmed with the theory analysis. The related circuits'working principles and realization methods are also proposed in this paper.