A Transformer-Based Broadband Front-End Combo in Standard CMOS

This paper presents a broad band front-end combo scheme based on a three-way on-chip transformer. The combo scheme functions as the T/R switch, balun, and impedance matching network simultaneously. A design example implemented in a standard 90 nm CMOS process demonstrates a 2 GHz 1-dB bandwidth from 5 GHz to 7 GHz. During the transmitting (TX) mode, the reported design achieves 2.65 dB insertion loss, +45.7 dBm IIP3, and 42 dB antenna-to-receiver isolation; in the receiving (RX) mode, the design demonstrates 2.52 dB insertion loss, +44.2 dBm IIP3, and 42 dB antenna-to-transmitter isolation. The TX-to-RX isolation is kept below 50 dB. The front-end combo design occupies a compact core area of 0.5 mm² which includes the on-chip transformer.