A low-power fully-integrated type-2 4th-order 1.7GHz CMOS frequency synthesizer for DCS- 1800 application is designed and simulated in a 0.25pm process technology. The frequency switching is achieved using a novel architecture exploiting a direct digital synthesis (DDS) device as the frequency reference. The new topology significantly lowers the undesired sideband power due to divider ratio switching by directly shifting the frequency of the DDS reference. The frequency synthesizer (excluding the DDS device) dissipates only 9mW of power from a 2V power supply. It employs a fast-switching novel charge pump circuit and a low-noise fully-integrated differential LC voltage controlled oscillator using on-chip spiral inductors and accumulation-mode capacitors to meet the requirements of a DCS- 1800 system. A detailed analysis of the phase noise in the 4th-order loop is presented.