A fast frequency/mode switching SSB mixer/amplifier topology is proposed for the implementation of low power multi-tone generator (MTG) in MB-OFDM UWB system. The proposed SSB mixer/amplifier topology is fabricated for the generation of mode-1 band center carrier with 0.18mum CMOS technology. The measurement result shows the 8.5ns mixer/amplifier mode switching time. The center carrier output power levels are -13.0dBm, -12.88dBm, and -14.33dBm in 3432MHz, 3960MHz, and 4488MHz, respectively. The harmonic suppressions are -40dBc and -30dBc in 3432MHz and 4488MHz, where the SSB mixer mode is selected. In the amplifier mode, the 3960MHz tone does not have any harmonics tone. For measurement, 1.8V supply voltage is used while drawing 26mA total current