This paper presents a current-mode 6~9GHz RF transmitter for OFDM-UWB system applications. By a current-mode low pass filter with variable gain between the digital-to-analog converter and the up-conversion mixer, this transmitter exceeds the traditional voltage-mode counterpart in terms of high linearity (+3.5-dBm output 1-dB compression point, +12.5-dBm output third intercept point) and low spurious emission (50-dB sideband rejection) with low power consumption (40-mA current under 1.2-V supply voltage). By an output power flattening technique, the output power ripple is restricted within ±0.5dB. By an inductor-less divider and active-inductor LO buffer, a small die area of 0.72 mm2is obtained with TSMC's 0.13-μm 1P8M RF CMOS technology. The design is verified through post-layout simulations.