Full-Duplex CMOS Duplexer

Abstract

To accommodate the growing demand for wireless communications, new techniques are required to increase throughput of wireless networks. One technology aiming to increase the spectral efficiency of wireless devices is full duplex (FD) radios. These systems are capable of single carrier transmission and reception and could ideally double the spectral efficiency of future wireless systems. To make such systems a commercial reality, self-interference cancellation (SIC) techniques are required to suppress transmitter leakage into the receiver. This work investigates the level of SIC an integrated hybrid transformer can provide to make FD a reality. This work also includes an investigation in the SIC capabilities of an integrated hybrid transformer operating with a commercially available planar inverted-F antenna (PIFA) and presents the design and evaluation of a prototype in UMC 180nm RFCMOS. The prototype consists of a transformer, a tunable impedance and a LNA. Measurement results on this prototype showed isolation peaks of 80 dB, with an isolation band width of 1 MHz for 60 dB isolation and a Tx insertion loss, measured gain and NF of 3.5 dB, 5dB and 9dB, respectively, while providing a IIP3 of 0dBm at the LNA output and a common-mode Tx isolation at the input of the LNA of 20 dB. The measurements also showed that the duplexer can be made self-tunable by using search algorithms that converge within 150 measurements. The relation between isolation and impedance resolution is derived and proven to be 6dB every time the absolute difference between the impedances at both sides of the transformer is halved.