A high isolation CMFB downconversion micromixer using 0.18-μm deep n-well CMOS technology

CMOS deep n-well technology can eliminate body effects of NMOS transistors and improve LO-IF and LO-RF isolation in a Gilbert micromixer. A 37 dB LO-IF and 38 dB LO-RF isolation downconversion micromixer with 19 dB conversion gain, IP_1dB=-19.5 dBm and IIP₃=-12.5 dBm when RF=2.4 GHz and LO=2.25 GHz is demonstrated in this paper by using 0.18 μm deep n-well CMOS technology. The input return loss and output return loss are better than 15 dB for frequencies up to 6 GHz. On the other hand, a downconversion micromixer without deep n-well has almost identical power performance but achieves only 20 dB LO-IF isolation and 21 dB LO-RF isolation even if two kinds of mixers are fabricated in adjacent areas of the same wafer. The downconversion micromixer used here has an intrinsically single-to-differential input stage and active differential PMOS loads to increase IF differential gain while CMFB is used to stabilize bias points. An IF differential amplifier converts differential output into a single-ended output. Finally, an off-chip rat-race coupler provides balanced LO signals to facilitate isolation measurement.