Spurious components introduced by nonlinearity in Direct Digital Synthesis

In this paper, the mechanism of introducing spurious components by nonlinearity in Direct Digital Synthesisers (DDS) is analysed. An S-band frequency synthesiser for a stepped-frequency radar is presented. This frequency synthesiser is based on a DDS-driven wideband PLL architecture, which can achieve low spurious noise and rapid frequency hopping simultaneously. A novel DDS frequency planning method is utilised to ensure low colored noise within the entire output bandwidth. Measured results demonstrate that the overall SFDR is better than 58 dBc in a 320 MHz bandwidth.