In this paper, we will discuss an integer-N frequency synthesizer operated at 10 GHz around the MB-OFDM UWB system 5th band group with only 1.5 V supply voltage which owns a varying frequency ranging from 9.29 GHz to 10.9 GHz and delivers −5.9 dBm output power. A single NMOS cross-coupled-pairs forms the core circuit of the voltage-controlled oscillator and delivers a −97 dBc/Hz phase noise at 1 MHz from the carrier signal. The frequency settling time is about 25 µs and the whole circuit power consumption is 23.55 mW.