Method for close-to-the-carrier phase noise measurement

A new digital signal-processing method for close-to-the carrier phase noise measurement is proposed. By suitably undersampling the input sinusoidal carrier and exploiting an optimised quadrature demodulation scheme, the method provides accurate phase noise estimates at very low frequency offsets (<1 Hz), thus overcoming a notable limit of other measurement techniques. Moreover, its input frequency range can be very wide, extending from fractions of a hertz up to the analogue bandwidth of the adopted data acquisition system. In addition, no large memory size is needed to assure good frequency resolution (<1 Hz) over the whole input frequency range. A detailed description of the proposed method, in terms of both fundamental relations and measurement algorithm, is presented. Its performance is assessed through laboratory tests, and compared to that obtained using currently commercially available measurement equipment. Numerous experiments on actual sinusoidal carriers confirm the reliability and efficacy of the method.