Abstract: A Film Bulk Acoustic Resonator(FBAR) oscillator with tail-current source feedback is designed to improve the phase noise performance of the oscillator. Research shows that the flicker noise of the transistor of tail current source and the resonant loop are main sources of phase noise of the oscillator. In order to reduce the impact of flicker noise in the transistor of tail current source on phase noise of the oscillator, the tail current feedback technique is adopted, which employs two sets of symmetrical split Positive channel Metal Oxide Semiconductor(PMOS) biased current source operating in the subthreshold region. Compared with the traditional single tail current source, it shows better phase noise performance. Based on the analysis of Hajimiri noise model, the tail current source feedback technology is used to control the current magnitude of the oscillator when the amplitude reaches peak and zero-ride-through point to improve the phase noise performance. A high Q resonator can significantly improve the phase noise performance of the oscillator. The design is based on the TSMC 180 nm RF CMOS process. With a high Q value Micro-Electro-Mechanical Systems(MEMS) device FBAR as the resonator, the oscillator has a output frequency of 1.93 GHz. The post simulation results show that power consumption is 580 μW, the oscillator can achieve phase noise at 1 kHz offset frequency of −89.7 dBc/Hz and Factor Of Merit, FOM(FOM) of 217 dB.