Phase Noise Measurement Based On Phase Coincidence Detection Envelope Characteristics

The phase noise measurement method based on phase coincidence detection envelop characteristics is proposed in this article, and it is a new kind of measuring method. Its theoretical bases include:the phase relationship between periodic signals, the characteristics of phase coincidence detection circuit and the Wiener-Khintchine theorem. When the phase coincidence detection circuit is used to detect the phase coincident points of the reference and the measured signals, the coincidence pulses are output when the phase differences between the two signals are smaller than a certain value due to the limited resolution of the circuit. Because the reference and measured signals have the same or multiple nominal frequencies with a small offset, the phase differences between them change monotonously. Therefore, these coincidence pulses output by the phase coincidence detection circuit are intensive and present an envelope shape. According to the frequency measurement experiment based on the phase coincidence detection, the phase coincidence detection envelope is verified to be 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, and then the phase noise can be measured. Knowing from the phase relation of the reference and the measured signals, the ideal envelope presents the shape of a triangle. According to the practical envelope information gathered, the ideal envelope condition can be obtained. Comparing the envelope information gathered with the ideal envelope, the voltage fluctuates which are corresponding with the phase jitters are obtained. According to the relation of the envelope voltage stepping value and the quantization phase shift resolution, the phase jitters can be extracted from the voltage fluctuates. At last, the phase jitter is converted to the phase noise based on the Wiener-Khintchine theorem, and the phase noise curve is drawn.Compared with the traditional phase noise measuring methods, the one based on the phase coincidence detection envelope has three innovation points. Firstly, the reference and measured signals need not have the same frequency. However, the traditional methods can’t lock the phase and measure the phase the noise when the frequency difference between the two signals is big. Even the measurement can be done, the phase-locked process is complicated and much time is taken. Secondly, the phase jitter is extracted from the coincidence detection envelope without any complex and high-precision mixing and phase-locked circuits, so the circuit is simpler and the cost is lower. At last, the phase jitter is converted to the phase noise using the Wiener-Khintchine theorem, so the theory basis is sufficient.This article 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. The phase noise measurement system based on phase coincidence detection envelope now can reflect the overall trend of the phase noise of the frequency source, but some tiny characteristics cannot be reflected. In addition, the reasons of some late adjustments are not clear, so the subsequent research is needed.