Phase-Noise and Amplitude-Noise Measurement of DACs and DDSs

This article proposes a method for the measurement of Phase Noise (PN, or PM noise) and Amplitude Noise (AN, or AM noise) of Digital-to-Analog Converters (DAC) and Direct Digital Synthesizers (DDS) based on modulation-index amplification. The carrier is first reduced by a controlled amount (30-40 dB) by adding a reference signal of nearly equal amplitude and opposite in phase. Then, residual carrier and noise sidebands are amplified and sent to a conventional PN analyzer. The main virtues of our method are: (i) the noise specs of the PN analyzer are relaxed by a factor equal to the carrier suppression ratio; and, (ii) the capability to measure the AN using a PN analyzer, with no need for th…