【作者】 屈八一；

【导师】 周渭；

【作者基本信息】 西安电子科技大学 ， 测试计量技术及仪器， 2010， 博士

【摘要】 基于CPT（Coherent Population Trapping,相干布居囚禁）现象的原子钟是近年来国际国内的一个研究热点。基于CPT现象可以开发出两种不同的原子钟即CPT-Maser型原子钟和被动型CPT钟,前者的特点是结构复杂但是准确度和稳定度却很高,后者的特点是结构非常简单,是可以实现微型化的原子钟之一。在描述了Rb CPT maser原子钟的工作原理,三个子系统的功能,设计及测试等内容后,对电路子系统中的有关内容进行重点研究和实现。CPT-Maser钟中频率链电路的作用是联系用户频率（通常是5MHz和10MHz）和调制激光器的频率（通常是原子基态超精细能级跃迁频率的一半）。在高性能原子钟中都采用低噪声频率合成技术。在CPT-Maser钟中设计和实现了用户频率到100MHz锁相式倍频电路和100MHz到3.417GHz频综电路,该频综电路的性能达到了国内先进水平。CPT-Maser原子钟是通过检测CPT-Maser信号的功率变化来实现锁定的,而CPT-Maser信号通常在-90dBm以下,频率约为6.834GHz,因此设计了外差式接收机和检波电路实现功率检测。该电路中对检波分辨率,温度稳定性有很高的要求,通过选择高性能的器件来解决上述问题。分析说明了这部分电路与整机闭环后输出的频率准确度和稳定度之间存在的关系。伺服电路将检波电路输出的误差信号处理成本振的控制电压。设计和实现了主要由A/D,单片机,D/A构成的数字伺服,它的主要优点是利用软件便能完成调试和具有一些传统模拟伺服原子钟不具有的功能例如软件补偿和扩捕功能。针对10-13的频率准确度和稳定度,理论分析了数字伺服的设计方法。原子钟的频率温度系数是一个重要参数,目前国外星载铷钟的该参数已达10-14量级,而CPT-Maser的为10-12量级。设计和实现了基于软件补偿频率温度系数的方法。扩捕电路能解决传统的原子钟中出现的当本振频率偏出原子钟的捕获带时环路不能锁定的问题。设计和实现了CPT-Maser原子钟扩捕电路。围绕被动型CPT钟的微型化设计了适宜于微型化要求的整机设计方案,它在细节上它具有以下四个特点:一是采用了VCSEL激光器;二是采用了小型化的频率链电路;三是采用了数字式的锁激光器和锁本振电路;四是利用一个铷泡的输出同时实现锁激光器和锁本振。基于DDS,单片机,锁相环芯片等研制了一个适应于小型化CPT钟或其它小型化原子钟的频综电路。它借助了高速数字化器件,简化了频综设计,具有数字化,输出频率可高精度软件调节,软件产生FSK调制和同时可输出同步解调信号等优点。研究了被动型CPT钟的智能化和数字化,理论上数字化原子钟具有便于生产,测试,软件补偿等优势,对频率温度系数的补偿,原子钟的非实时控制,基于相位重合点检测实现的锁频环等内容作了实验研究。阐述了星载钟设计的特点,国外星载钟的主要性能和主要研究单位,我国星载钟的研制水平和国外的差距,国外星载钟研制的技术细节等内容,同时提出了一些有望提高我们星载钟研制水平的建议。时频测试设备的研制和新型时频信号处理技术是时频领域的另一个研究方向。时间量化技术是很多测试设备的一个基础,目前对其分辨率的要求已达ps量级。基于CMOS门延迟的时间量化技术实现起来比较复杂,继续采用该技术提高分辨率将会很困难。研究了利用信号在介质中传输时会出现延迟这种现象来进行时间量化的可行性及其特点。首先分析采用该技术的进行时间量化时理论上的分辨率和误差,及各种影响稳定度的因素,然后对导线延迟的分辨力,准确度,线性度做了实验验证,并对温度,信号衰减和色散等量对延迟稳定度的影响做了实验研究。分析和实验表明,基于传输延迟的时间量化技术是一种新的可以获得高分辨的时间量化技术,同时指出了该方法的一些特点及其应用。设计了一种新的时钟插入技术以实现高分辨率的时间间隔测量仪。该时钟插入技术利用信号在传输时会有稳定的、规律的延迟特性,用一段传输线对时钟信号延迟,在传输线上根据设计分辨率的大小设置一些离散的检测点,用D触发器完成对延迟后的时钟信号与被测时间间隔开始或者结束信号的重合检测,根据重合点出现的位置推算出时钟信号与被测时间间隔开始或者结束信号的时差大小。采用FPGA芯片EP2C5Q204和上述时钟插入技术实现了一个高精度时间间隔测量仪.实现的时间间隔测量仪具有分辨力高,稳定性好等优点。目前对稳定度测试设备有较大的需求量。主要基于DDS技术和测差频周期法研制了一个稳定度测量仪器。它的本底稳定度优于4.5×10^-13/1s,1.5×10^-13/10s,它的测量范围是1MHz到30MHz。与国外的主要产品比较,它主要具有低成本高分辨率的优点。目前的时间比对中通常采用时间间隔测量仪作为测量仪器,在这种条件下时间间隔测量仪的分辨力制约时间比对的分辨力。分析了时间比对过程中的时间比对和频率源比相之间的关系,提出了利用频率源比相测量间接完成时间比对的思路并完成了验证上述思路的实验,同时指出了这种间接测量的优势。分析了双频信号的相对相位变化特点,提出了一种新的秒信号的产生方式即利用两个频率信号的周期性的相位重合点作为标准时间信号。完成了利用双频信号的相位重合点获得标准时间信号的说明及初步实验,结果是该方法能用来产生秒信号且产生的秒信号稳定性优于200ps。阐述了新方法在授时过程中的优势并指出了进一步研究内容。采用目前广泛应用的锁相环技术来实现两频率间的锁定时,由于它们的频率关系往往不相关以至于实现时必须借助于频率变换电路,将两不相关频率信号处理成具有同频或者是有整倍数的关系的信号。两任意频率信号间会出现周期性的相位重合现象且相位重合周期和两频率信号的频率关系密切联系,基于此原理实现了一种新型的锁频环。它较一般的锁相环的优点是原理先进,输出频率调整容易。对该方法做了理论说明和实验研究,实验结果与理论预期相符。文中同时叙述了有关电路的工作原理和设计。更多还原

【Abstract】 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.更多还原