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A digital signal-processing method for phase noise measurement is presented. By properly over-sampling the input signal and adopting an optimized quadrature demodulation scheme, the method grants acceptable performance in analyzing sinusoidal carriers, the frequencies of which range from fractions of hertz up to hundreds of megahertz. Moreover, the method shows itself a valid alternative both to analog measurement systems, especially for the evaluation of close-to-the-carrier phase noise and time interval analyzers, particularly for carrier frequencies greater than a few units of megahertz. At first, the fundamental stages of the proposed method are described in detail. Its theoretical performance is then derived and compared to that offered by other measurement solutions already available on the market. Finally, the results of experiments carried out on actual signal sources are presented.