A ΔΣ fractional-N synthesizer design for multi-standard WiMAX/WLAN applications is presented. By having a VCO frequency of up to four times the channel frequency, the tuning range requirement of the VCO is significantly relaxed. Two low-noise LC VCOs with small inductor area are designed to cover three frequency bands for WiMAX/WLAN applications, where only one polyphase filter is used to generate multi-band quadrature outputs. Based on noise analysis, a low power 12 GHz frequency divider having an optimum partition among asynchronous, CML, and single-ended operations is designed. The prototype synthesizer implemented in 90 nm CMOS consumes about 58 mW from a 1.2 V supply.