A thin film bulk acoustic wave resonator (FBAR)-based differential Colpitts oscillator was presented. Compared to the traditional architectures, the proposed Colpitts oscillator removed the tail current source to reduce the phase noise. The combination of the cross-coupled pair and transformer in the oscillator increased the effective gm, reduced the star-up current requirement, increased output swing under a lower supply voltage, and reduced the phase noise. The oscillator operated in a Class-C state by adjusting the bias voltage. The current utilization was effectively improved to reduce the phase and the power consumption. The 1865 GHz-FBAR with high Q value was used as resonant network of the oscillator, and the CMOS circuit was completed in the SMIC 55 nm RFCMOS process. Simulation results showed that the output carrier frequency was 1876 GHz under 06 V voltage supply. This oscillator achieved a phase noise of -84 dBc/Hz, -146 dBc/Hz at 1 kHz, 1 MHz offset frequency respectively. The power dissipation was only 83 μW, and the FOM value was -225 dB.