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A 0.8-5.2 GHz broad-band quadrature mixer for SDR (software designed radio) direct conversion receivers has been developed using 0.35 μm SiGe BiCMOS process. The quadrature mixer employs a high speed static frequency divider for a 90 deg LO power divider and broad-band SiGe HBT unit mixers. High speed operation of the static frequency divider is realized by adding 2-stage emitter follower to its output section. The fabricated quadrature mixer achieves an EVM of 3.1%rms for W-CDMA signals at 0.8 GHz and an EVM of 2.1%rms for W-LAN (IEEE 802.11a) signals at 5.2 GHz, respectively. It also has constant conversion gain over the wide base-band frequency range up to 500 MHz at RF frequency of 0.8 GHz.