Study On Precision Digital Measurement Method Of High Frequency Signal Based On Low Sampling Rate

As the rapid development of the digital technology and various technologies based on frequency, the signal source frequency accuracy and stability are of higher and higher demands. The most direct way of evaluating the signal source is high precision measurement for it.Digital measurement has the advantage of fast measurement speed, high precision, easy operation and so on, but at present, high-precision measurement of high frequency signal still rarely use this technology. This is because the two key steps of digital measurement are the process of signal sampling and signal processing. The signal sampling process is restricted by the Nyquist sampling theorem, which requires that the sampling rate must be 2 times greater than the input signal frequency. The high frequency characteristics of atomic clock signal defines that the signal acquisition requires cost highly to be matched with high sampling rate. This makes the digital measurement technology in the field of precision measurement of high frequency signal to be greatly restricted.In this paper, a frequency measurement algorithm named Sub-Nyquist sampling is presented,which breaks the limit of sampling frequency. The core of the algorithm is setting proper sample sate, so the high frequency signal sampling is translated into low frequency signal sampling. And that the frequency and phase information is unchanged after the translation. Using this Sub-Nyquist sampling algorithm, we can sample the high-frequency signal just via low suitable sampling rate and lay the foundation for data analysis and processing.Be based on LabWindows/CVI Virtual Instrument technology, a hardware platform is successfully set up .and besides that we design a frequency measurement software. We set up command and data exchange interface through ActiveX control and carry out the acquisition and signal processing by the multi-software program ideas.In this paper, Sub-Nyquist sampling method is studied on the frequency measurement system. The results show that: when this method is used for 1MHz atomic clock signal measurement, the accuracy can come up to 10-12 . This shows that the precision digital measurement method for high frequency signal based on low sampling rate is feasible. The study in this paper will be helpful to promote the development of data acquisition and precision frequency measurement technology.