An LC-VCO with low and constant KVCO in TSMC 55nm CMOS is designed for NB-IoT application. Capacitors used in LC resonator are solely comprised of varactors. The VCO covers 3GHz-4GHz frequency range and shows a constant KVCO around 35 MHz/V with only 2.6% variation. The phase noise at the center oscillation frequency of 3.5GHz is -122.1dBc/Hz @ 1MHz with 1.78mA current under 1.2V supply, leading to a superior FoM of -190dBc/Hz.