Wide-band direct synthesizer driven by DDS employing phase accumulator over flow

摘要

A wide-band method of a narrow step, fast frequency switching, low phase noise direct synthesizer was proposed in this report. The proposed synthesizer consists of a quadrature mixer and DDS for a base-band signal generator of the mixer. The proposed synthesizer forces to overflow a DDS phase accumulator to accomplish twice wider bandwidth compared with a typical direct synthesizer driven by a DDS. Also DDS is capable to switch frequency phase continuously. A developed 2GHz-band frequency synthesizer with 120MHz output DDS achieved phase continuous frequency switching of 240MHz band employing the proposed method. Spurious level below -29dBc and dissipated current of 69mA were also obtained.