This paper presents a 8-bit RFDAC for quadrature transmitter by 130nm CMOS process, targeted for medical body area network application as per recently released IEEE 802.15.6 standard. Circuit architecture and design considerations are briefly introduced. To achieve output power range over 20dB, gain control by two voltage biases is adopted. Compared with the gain control by single voltage bias, this control method offers wider output power range and better power efficiency.