Zhiqi Li

A time and frequency measurement method based on delay-chain technique

The short time-interval and frequency measurement are main research projects in the measurement of time and frequency. Traditional measurement methods include direct counting, analog interpolating, time-to-voltage conversion, time vernier and time-to-digital conversion. However these methods are all complicated and the instruments based on these methods are expensive. A novel method for short time-interval and frequency measurement based on delay-chain technique is presented in this paper. This method utilizes measured short time-interval or measured frequency signal to generate count gate. A delay-chain is used to delay reference frequency signal orderly. So a group of signals with phase-shifting evenly in a period of reference frequency signal are generated, and are counted respectively under the same count gate. With the average of the counts as the count of reference frequency, the decimal counting error is reduced and measurement accuracy is improved. The measurement resolution of this method for short time-interval and measurement accuracy for frequency are equal to the measurement results under condition of increasing frequency of reference frequency signal by the times of the number of delay unit in a delay-chain. An experiment demonstrates the resolution of short time-interval measurement and the accuracy of frequency measurement could be 100 ps and respectively and the theoretical measurement resolution and accuracy could be higher. Although it needs more delay units and counters in order to achieve high-accuracy measurement, this is not a problem because new device has been used, such as FPGA. This method is suitable for high-accuracy and low-cost measurement..

A Super High Resolution Phase Difference Measurement Method

Phase difference measurement techniques can be used widely in positioning and length measurement, and high resolution is necessary especially for some science research purposes. In this situation the request to the measuring device is different from that to the frequency standard comparison. It is difficult to improve the resolution of conventional counting measurement method with some high-resolution approaches and the phase noise and frequency instability of frequency sources will influence the measurement precision obviously. In this paper we present a super high-resolution phase difference measurement method that can show near 0.1ps resolution. With a high-linearity phase difference to voltage conversion approach and high-resolution voltage meter, it is possible to get very high phase measurement resolution, and the phase noise of frequency source used in the measurement can be filtered partly. When this method is used to measure the frequency stability of frequency standard, the integration time of voltmeter should be very short. However, when the measurement purpose is for length the integration time of volt measurement can be longer and it is favorable for high resolution. The method is suitable for a certain range distance measurement in a certain period.

The optimization of super-high resolution frequency measurement techniques based on phase quantization regularities between any frequencies.

Step phase quantization regularity between different nominal frequency signals is introduced in this paper. Based on this regularity, an optimized high resolution frequency measurement technique is presented. The key features and issues of phase quantization characteristics and measurements are described. Based on the relationship between the same or multiple nominal signals with a certain differences, the resolution of frequency measurements is developed and the range is widened. Several measurement results are provided to support the concepts with experimental evidence. The resolution of frequency measurement can reach 10(-12) (s(-1)) over a wide range or higher for specific frequency signals.

High-precise frequency measurement and link based on phase group synchronization

Frequency and phase measurement resolution close to Femtosecond level has great significance for the progress of frequency standard technology and the precise time and phase synchronization processing. The precise link between frequency signals is mainly used for quantum frequency standard and complex, precise frequency control situations. It makes signals which have great frequency difference establish strict correlation between frequency and phase, and achieves the transmission between frequency accuracy and stability. Traditional widely used frequency measurement and link technology which is based on frequency processing have disadvantages of complex equipment and limited resolution. Phase processing has the highest resolution in all time-frequency processing but it has been ignored in processing between complex signals, because the limit that only the same frequency signals can be phase processed. The characteristics of greatest common factor frequency, least common multiple period, phase quantization step phenomenon, equivalent phase comparison frequency make us achieve the phase group processing method based on phase group synchronization phenomenon. The phase quantization step value between different frequency signals which are often encountered in radio frequency will be small to picosecond, Femtosecond, and even sub-femtosecond, and that is to say the equivalent phase comparison frequency between the corresponding two radio frequency signals can enter into microwave band and light band. And it also provides basis for the precise frequency measurement and link which are based on phase group processing between frequency signals in different frequency bands. Based on phase group synchronization, this paper obtains a super high measurement resolution up to magnitude of fs. By the control of phase group synchronization the accuracy and stability in signals of different nominal frequencies can be transferred. It will be with significant application value in frequency measurement, quantum frequency standard and phase-locked loop field.

The study of BeiDou timing receiver delay calibration

This paper gives a test method of BeiDou timing receiver delay. A BeiDou System simulator and a time interval counter were used in the experiments. During the process, the most important step is to calibrate the delay of the simulator. The uncertainty of this method is analyzed to be less than 1.5ns. Using this method, some typical Chinese commercial timing receivers were tested, and the results are shown in figures. The receiver delay variations with temperature have been studied.

An Ultra-high Resolution Phase Difference Measurement meter

Conventional linear phase comparison meters are used widely in the measurement of the frequency and stability. It can also be used in the measurement of length or distance in the navigation and orientation. Phase comparison methods not only reduce the cost of system, but also enhance precision, which can reach the measurement resolution of 10-13/tau in time domain. By the research on the major factors of precision effect of in the measurement of the length with phase comparison method, such as the linearity and trigger error, a solution to the improvement of the high precision is proposed in this paper. The avoidance of the dead region and the improvement of the linearity can be realized in small scope by sampling and phasing the geminated signals, controlling the region of the discriminator and phase displacing of the fixed region. In order to improve precision, this measuring technique must reduce trigger error as much as possible. The trigger error can be decreased by small signal reshaping, frequency transformation and wave filtering. In addition, the temperature shift of the whole circuit can be improved by the supply power of the low noise, the low shift & the high stability, the simple self-adjustment technique for the shift and the filtering treatment. Besides, by the choices of circuit components and the improvement of circuit design, output saturation voltage shift can be conquered and higher precision can be obtained. In this paper, the measurement precision of length or distance can be reached 0.1 ps-C. The change on the delay in the method of the linear can reflect the subtle change on the object distance. By collecting the data of the stimulated time of the phase change, the data can be transferred into the measurement of the distance or the length so as to realize the measurement of the subtle change on the distance.

The border effect in frequency signal processing and the phase measurement with arbitrary frequency relationship

Based on the achievement of phase coincidence detection, the processing and elimination of quantization error is possible in digital frequency measurement. Because of the limited resolution of phase detection, a fuzzy area is to be formed. The higher precision can be obtained using the border stability of fuzzy areas. The decisive factor of the actual precision is the resolution stability of the border of fuzzy area, called the border effect. Therefore, utilizing the circuit with ns resolution one can obtain ps level or higher precision. On the basis of improving measuring resolution significantly and the phase variation regularity of periodic signals, through the frequency measurement with phase continuous, the measured frequency signal is compared with its theoretical nominal frequency by multiple periods and with measuring gate time one by one. Eventually, the measurement of phase variation of any measured signal in a wide frequency range can be realized. Compared with other measurement techniques and instruments it is a great advancement. Because of the phase information is obtained for the different even very complicated frequency signals, higher frequency measurement precision can be realized without any frequency transformation. It is possible to realize higher measurement and control precision.

Generalized phase measurement and processing with application in the time-frequency measurement control and link

Traditional phase measurement is limited by the identical nominal frequencies of two compared signals. In a lot of applications, there are higher requirements not only on measurement accuracy, but also on the frequency range of compared signals. After years of exploration and efforts, we have discovered some concepts and characteristics which can reflect mutual phase relationship among different frequency signals, such as Least Common Multiple Period, Phase Difference Quantization Step, Equivalent Phase Comparison Frequency, and the continuous phase group characteristics with the least common multiple period (as the time interval and the quantization step phenomenon that the phase difference of the two different frequency signals will change according to a specific value in one least common multiple period). In the process of experiments, we have discovered ambiguity zone edge effects and measurement method of periodic signal parameter quantization error elimination. We achieved precise frequency source synchronization and link, phase processing and measurement between completely different frequency signals with complex relationship. Through updating concepts, we move phase comparison and processing beyond identical frequency signals and extend to arbitrary frequency signals. Major applications include measurement of transient stability, phase noise measurement, edge effects for accurate frequency measurement method of Serial and Parallel. These breakthroughs promote rapid development in the area of measurement and instrument, and some difficult research problems have been solved.