CMOS I/Q demodulator using a high-isolation and linear mixer for 2 GHz operation

An I/Q direct demodulator employing passive mixers and a phase shifter for 2 GHz operation is designed and implemented with 0.35 /spl mu/m CMOS technology. CMOS switching elements are used to improve the linearity and isolation property of the mixer. A DC bias to the switching elements is devised to reduce LO power for the passive mixer. This bias effect on linearity and isolation is analyzed. A low-loss simple RC/CR pair with a feedback network is used to reduce the LO power and maintain I/Q channel balance instead of using a poly-phase network. Measurements showed 15 dBm IIP3 (third order input intercept point) for 4 dBm LO power, 62 dBc isolation, and 2.8/spl deg/ phase imbalance.