A 2-30 GHz ring mixer with built-in active baluns for vital sign detection application is presented in this paper. This mixer was fabricated in 0.18-μm CMOS process. Two topologies of active baluns are utilized to increase the isolation between the LO and the RF ports to mitigate the dc-offset problem. With bandwidth-enhancement circuit  and the active load, the phase errors of both RF and LO baluns are less than 7 degree. The input return loss is better than 10 dB over 20-GHz bandwidth. The measured conversion gain is-18.5 ±2 dB from 2 to 30 GHz at 3-dBm LO power. The input third-order intercept point (IIP3) is 4 dBm at 16GHz. The proposed mixer with built-in active baluns consumes 20 mW dc power within a compact chip size of 0.81 × 0.63 mm2.