This work presents a design and analysis of a bulk-driven mixer using variant Volterra series approach. Topologies of the bulk-driven mixer (BDM) with and without a current source have been investigated. The analysis shows that the LO voltage swing has a limit in the BDM with a current source due to turn-on of the bulk-to-source diode. The operational principle of the BDM without a current source is discussed and indicates that it shall be characterized in terms of weakly nonlinear operation. With the insight gained from the nonlinear analysis, the proposed BDM is designed and implemented in 0.18-um CMOS technology. The measurement result shows that the voltage conversion gain, SSB noise figure, and IIP3 are 16 dB, 19.65 dB, and 0.5 dBm, respectively. The power consumption is only 0.25 mW from a supply voltage of 1 V.