A 2.5-GHz CMOS Full-Duplex Front-End for Asymmetric Data Networks

Abstract

Electrical balance-based full-duplex front-end allows high power operation but has strong tradeoff between Tx and Rx insertion loss. In this paper, we present a capacitive bridge-based duplexer for full-duplex operation with tunable Tx/Rx insertion loss to improve link budget in an asymmetric data network. Theoretical analysis is done to show that capacitive bridge-based duplexer can be better than hybrid transformer in CMOS process. Capacitive bridge architecture is suitable for insertion loss tunability and this tunability gives an additional advantage of increasing the range of allowed antenna impedance for the given balance network. The fully integrated duplexer with receiver is implemented in a 130-nm CMOS process, and is capable of handling Tx power of upto +16dBm at antenna. The prototype chip demonstrates tunable Tx/Rx insertion loss achieving an overall receiver noise figure of 5.7-7.5dB and a Tx insertion loss of 3.9-5.6dB. Self-interference cancellation of >50dB is measured for 20-MHz RF bandwidth in 2.4-2.6-GHz frequency range.