A CMOS Code-Modulated Path-Sharing Multi-Antenna Receiver Front-End

This paper presents the design and implementation of a novel multi-antenna receiver front-end, which is capable of accommodating various multi-antenna schemes including spatial multiplexing (SM), spatial diversity (SD), and beamforming (BF). The use of orthogonal code-modulation at the RF stage of multi-antenna signal paths enables linear combination of all mutually orthogonal code-modulated RF received signals. The combined signal is then fed to a single RF/baseband/ADC chain. In the digital domain, all antenna signals are fully recovered using matched filters. Primary advantages of this architecture include a significant reduction in area and power consumption. Moreover, the path-sharing of multiple RF signals mitigates the issues of LO routing/distribution and cross-talk between receive chains. System-level analyses of variable gain/dynamic range, bandwidth/area/power trade-off, and interferers are presented. Designed for the 5-GHz frequency and fabricated in 0.18 mum CMOS, the 76 mW 2.3 mm² two-antenna receiver front-end prototype achieves a 10^-2 symbol error rate (SER) at 64, 77, and 78 dBm of input power for SM, SD, and BF, respectively, while providing 21-85 dB gain, 6.2 dB NF, and 10.6 dBm IIP3.