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Recently, digitizing RF circuits has attracted extensive attention by exploiting high speed transistors offered in nano-scale CMOS processes. The digitally-assisted or digital-intensive RF transceivers not only benefit from technology scaling in terms of power efficiency and die area, but also improve functional flexibility. The polar architecture is well recognized for digital RF transmitters [1,2,4,5], while the bandwidth expansion resulting from Cartesian-to-polar transformation makes it difficult to comply with high-speed wireless standards. Open-loop phase interpolation topology was employed in an outphasing transmitter [3], where 12dBm output power was demonstrated with 40MHz 802.11n signal. In this work, an all-digital RF transmitter with direct quadrature architecture is presented to address the need for broadband wireless connectivity.