Precision Measurement For Phase Noise With New Technology

Phase noise is an important technical indicator to measure the frequency standard sources and modern electronic devices, and the importance of which in researches of fundamental frequency source and tests of characteristics is increasing.Based on the periodic law of the phase change of the periodic signals, this article was using the phase coincidence detection technique to realize the phase noise measurement with high resolution. Through deep researching on the phase relationship between periodic signals, the theory of phase coincidence detection fuzzy area is provided. In the design of coincidence detection circuit, since existing a certain resolution in the phase coincidence detecting line, when the phase difference of the two input signals is smaller than a certain value, the coincidence of pulse can be achieved.This technique can complete phase noise measurement of any frequency signal in wide range with fast response time and high resolution by using only one reference source, and it differs from conventional phase noise measurement system based on complex circuit design, not only saves the cost, but also improve the measurement accuracy. Phase noise measurement is divided into proximal and distal points, specific design as follows:1、In the proximal phase noise measurement system, the principle is that through observing the ups and downs of count in gate, using the signal of phase coincidence points to carry out the counting without gaps and the envelope status of coincidence pulse cluster to extract phase jitter。After indirect conversion,and ultimately will convert phase jitter to a single-sideband phase noise.2、To the distal end of the phase noise measurement, the phase noise measurement method based on phase coincidence detection envelop characteristics is proposed in this paper, and it is a new kind of measuring method. Because the phase differences between them change monotonously when the reference and measured signals have the same or multiple nominal frequencies with a small offset, these coincidence pulses are output intensively and present an envelope shape. The resolution of the coincidence detectioncircuit is stable, so the coincidence detection envelop is relatively stable. At the same time, the envelope has imperceptible changes which are caused by the phase noise. Therefore, the phase jitters caused by the noise can be extracted from the phase coincidence detection envelop. The Wiener-Khintchine theorem is the arithmetic basis of realizing the phase noise measurement. This theorem describes the process of converting the phase jitter to the phase noise, including self-correlation and fast Fourier transform.This paper also particularly introduces the processes of extracting the phase jitter and converting it to the phase noise, and the hardware and software implementation of the phase noise measurement system. The hardware includes the shaping, amplifying, level switching and phase coincidence detection circuits. The software is mainly about the extracting of the phase jitter and its conversion to phase noise based on the Lab VIEW. At the same time, this system is used to measure the phase noise of the frequency sources, and the measuring results are compared with that of PN8010. The comparison results are analyzed to find the shortcomings of the system and improve it.