The factors that impact the intermodulation distortion performance of an active downconverting mixer are investigated. Through a Volterra-series analysis of the RF transconductor stage of the mixer, design principles are formulated to maximize the mixer's IIP3. To verify the theoretical analysis, a 0.3-1.2-GHz low-voltage mixer operating from a 0.9-V supply was designed, fabricated, and tested. The mixer employs a common-gate common-source RF transconductor stage with simultaneous distortion and noise cancellation. Experimental results reveal that the mixer can yield an IIP3 of - 0.8 dBm, a double-sideband noise figure below 4.8 dB, and a maximum conversion gain of 8.8 dB.