A CMOS down-conversion micromixer for IEEE 802.11b WLAN transceivers is presented. The micromixer is a class-AB single-ended input double balanced mixer with on-chip bias loop. The operating principle of the CMOS micromixer is quantitively discussed and some design insights are given out. The mixer has been implemented in 0.18mum CMOS process. The measured results show that the mixer achieves 1.5dB conversion gain, 12.2dB SSB NF, -1.5dBm input P1dB, 4dBm IIP3 with -16dB S11 (2.45GHz RF, 280MHz IF). The mixer draws 5.7mA current from a power supply of 1.8V