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Practical implementation of monolithic hybrid transformer duplexers have been limited by the poor common-mode isolation. In this paper, a differential hybrid transformer duplexer that covers 3GPP bands I, II, III, and IX between 1.7 and 2.2 GHz is introduced. It achieves a differential to differential isolation of 60 dB in the transmit (TX) band and 40 dB in the receive (RX) band, and a differential to common-mode isolation of 60 dB in both bands. The duplexer with a cascaded low-noise amplifier (LNA) achieves a noise figure of 5.6 dB in the RX path and an insertion loss of 3.7 dB in the TX path. The duplexer and LNA are implemented in a 90-nm CMOS process, consume 20 mA, and occupy an active area of 0.6 mm2.