This paper presents a low power direct frequency modulation IC in LF Band for the indoor voice broadcast application. The IC is mainly composed of a current starved voltage controlled ring oscillator modulated by the voice signal directly. A digital background frequency calibration loop is proposed to calibrate the frequency error/drift. Fabricated in 180nm CMOS, the chip occupies an area of 2.52mm 2 . Under 1.8V supply voltage, the frequency modulation IC consume less than 41μA with a 5pF load capacitor. The measured conversion gain in the voice band is not less than 4.0kHz/mV.