LAUSR

Signal oscillators based on DDS (Direct Digital Synthesis) are widely used in recent years. However, order metrological characteristics of signals generated by these oscillators have not been studied in many cases, and uses of such oscillators are not always justified. First of all, signals of the most popular sine waveform are unsatisfactory in terms of metrology, including errors of amplitude, period and their instability, total harmonic distortion. Certainly, with the development of integrated circuit fabrication technology, errors of basic units decrease. Therefore, it can be expected that instrumental errors will be decreasing in the nearest future. However, not only instrumental but also method errors are intrinsic to direct digital synthesis of signals. These method errors will determine limiting metrological characteristics as a hardware component of digital oscillators continue to be improved. When considering metrological characteristics of DDS-based digital oscillators, it is necessary to take into account that their output signals are quasiperiodic. This produces a complex spectrum of signals. Three methods for estimating a spectrum are proposed. Summation of amplitudes of spectral components in modulus is found to determine the level of signal amplitude and its instability, while vector summation determines period and its instability. Finally, root mean square summation determines total harmonic distortion. This paper analyzes limiting distortions of an output sine-wave signal with the aim of identifying the most appropriate application of these oscillators. It should be noted that the method error in this case is a theoretical error, which is very difficult to determine experimentally against other errors. Therefore, only results of mathematical modeling are given in the article. We present the graphics that allow right sampling frequency to be chosen depending on a specified error of amplitude, error of period, and total harmonic distortion of output voltage.