Experimental Verification of Mathematical Models of Noise Curves of Direct Digital Synthesizer AD9910

The results of simulation and experimental measurements of the noise curves of the direct digital synthesizer AD9910 are analyzed including studies at the images of the fundamental frequency. The use of images of direct digital synthesizers can significantly increase the frequency of the output signal. The studies are performed when the PLL reference clock multiplier is disabled. The mathematical model of the power spectral density of phase noise of direct digital synthesizer is based on the approximation of the noise characteristics of power functions. These exponential functions describe the effects of each of phase noise on the resulting view of the noise characteristics of direct digital synthesizer. The R&S®SMA100A low-noise signal generator, the R&S®FSUP signal source analyzer, and the AD9910 evaluation board are used for phase noise measurements. According to the experimental data, the modeling error is 2-3 dB, it is determined by the accuracy of the approximation coefficients. The conclusion is made that the mathematical models of the power spectral density (PSD) of the DDS phase noise match the results of experimental studies.