An Active Marchand Balun and Its Application to a 24-GHz CMOS Mixer

A fully integrated 24-GHz Gilbert-cell mixer incorporating two on-chip Marchand baluns to convert singleended signals into differential signals is presented in this paper. One is a passive balun at local oscillator (LO) port to improve isolation between the LO and radio-frequency (RF) ports, and the other is an active balun at RF port to enhance the conversion gain (CG) of the down-conversion mixer. The active balun utilizes complementary cross-coupled pairs (CCPs) to compensate for its resistive losses. Moreover, the gate-to-source capacitances (C
_gs
) of the CCPs are also absorbed into coupled lines and then reduce the chip size. The chip area of the active balun is about one quarter of the passive one. The mixer is designed and implemented in a 0.18-μm CMOS technology, and its chip size is 0.38 mm2 including all testing pads. With a power consumption of 18.9 mW and an LO power of 0 dBm, the mixer exhibits a measured CG of 12.8 dB, an input P
_in,1
dB of -14.5 dBm, and LO-RF isolations better than 43 dB.