Application of Direct Digital Synthesis and Cross Correlation Solution in Phase Noise Measurement System

Abstract

To provide a high accuracy of measuring system it is essential to minimize errors of that very system that is used in measurements. The accuracy of phase noise measurement system greatly depends on its own internal noise. Furthermore while investigating the phase noise in narrow band it is necessary to use the heterodyne scheme to apply deep low pass filtering and much decimation. As a heterodyne signal it had been applied direct digital synthesizer (DDS) signal which has many advantages in comparison with other kinds of synthesizers but quantization processes and finite digit capacity in digital signal processing systems cause quantization noise appearance. The investigation purpose is to analyze signal stability dependence on the DDS system resolution. Such exploration brings much interest for quantum frequency standard development and highly precision measurement systems which are based on exactly digital signal processing. It is preferably to use the Allan variance as a factor of signal stability as long as this very signal property is usually applied to describe quantum standard signal stability. In many cases the heterodyne scheme is not able to shift the central signal frequency exactly to zero. The offset area is always take place after multiplying by the heterodyne signal and its magnitude depends on the signal center frequency estimation accuracy and DDS resolution. The investigation of how such distortion affects the signal stability is very actual for precision instrument development. To minimize the influence of measurement system noise on the result precision it is preferably to use cross correlation signal processing. Such method is based on application of two channel signal processing with further averaging of cross spectrum sequence. Applying the cross spectrum solution brings a satisfaction level of the residual phase noise as a result.