Frequency-Domain-Multiplexing Single-Wire Interface and Harmonic-Rejection-Based IF Data De-Multiplexing in Millimeter-Wave MIMO Arrays

Recently, mm-wave multi-in multi-out (MIMO) arrays are garnering significant attention because of their ability to form multiple spatial beams, achieving significantly higher data rates compared to traditional phased array-based approaches. Furthermore, scalable MIMO arrays can provide many other functionalities, such as full digital beamforming and per-power amplifier (PA) digital pre-distortion. In this work, an MIMO four-element TX array architecture is presented with a frequency-domain multiplexing-based single-wire interface (SWI), breaking the tradeoff between channel-to-channel isolation and single wire (SW) bandwidth (BW). The concept of harmonic-rejection mixing (HRM) is used to de-multiplex the four modulated signals simultaneously from the SW using a single passive mixer driven by a multi-phase local oscillator (LO). The two-stage harmonic recombination circuits are implemented in baseband and, hence, achieve high channel-to-channel isolation with a low power overhead. A 60-GHz four-element TX prototype demonstrates the proposed architecture in 45-nm RF silicon-on-insulator (RFSOI) CMOS. The frequency-division-multiplexed (FDM)-based SWI can support 8-GHz total intermediate frequency (IF) BW across the four channels with 30-40-dB channel-to-channel isolation. Each TX element in the array achieves 20-35-dB conversion gain and +8.8-10.9-dBm OP1dB while consuming 225 mW/element.