Dual-Band CMOS RF Front-End Employing an Electrical-Balance Duplexer and N -Path LNA for IBFD and FDD Radios

This article proposes a dual-band complementary metal–oxide–semiconductor (CMOS) radio frequency (RF) front end employing a hybrid transformer-based electrical-balance duplexer (EBD) and $N$ -path filter embedded low-noise amplifier (LNA) for both in-band full duplexing (IBFD) and frequency-division duplexing (FDD) radios. To securely obtain sufficient self-interference cancellation (SIC) or transmitter (TX) leakage rejection in IBFD and FDD modes of the EBD at both low-band (LB) (0.7–1 GHz) and mid-band (MB) (1.8–2.2 GHz) frequency ranges, a band-switchable hybrid transformer is designed with a finely adjustable balance network to control the antenna impedance variations. In addition, the four-phase $N$ -path LNA is utilized to further offer TX leakage rejection in the FDD operation. This RF front-end is fabricated using a 65-nm CMOS technology and is mainly characterized by long-term evolution frequency bands. The demonstrated design achieves SIC and TX leakage rejection greater than 55 dB for IBFD and FDD modes of all measured frequency bands, which has a maximum power handling capability of +25 dBm. Furthermore, the design attains voltage gains greater than 8.7 dB for LB and 3.7 dB for MB, noise figures of 10.4 dB for LB and 12.1 dB for MB, out-of-band (OB) P1dBs greater than +21.4 dBm for LB and +21.5 dBm for MB, and OB IIP3s greater than +39.7 dBm for LB and +43.1 dBm for MB. It draws a bias current of 23.8 mA from the LNA and output buffer with a nominal supply of 1.2 V and has an active area of approximately 2 mm2.