A Compact Digitally-Assisted Merged LNA Vector Modulator Using Coupled Resonators for Integrated Beamforming Transceivers

This paper presents a compact differential quadrature generation scheme using transformer coupled resonators for use in scalable fifth-generation (5G) phased-array architectures. A merged low-noise amplifier vector modulator (LNA-VM) architecture is introduced where quadrature generation, conventionally implemented using an explicit quadrature hybrid, is now seamlessly integrated with the load of an LNA gain stage facilitating a compact design. The outputs of a lowQ coupled-resonator load in the LNA is used for quadrature generation, and Cartesian combining is implemented by phase-invariant programmable gain amplifiers (PGAs) with constant input capacitance and output conductance across phase settings-this ensures low rms gain and phase errors. A 25.1-27.6-GHz phased array channel employing the proposed scheme is implemented in 65-nm CMOS. The merged LNA-VM is digitally tunable across 2.5 GHz (25.1-27.6 GHz) and achieves rms gain and phase errors (measured at band edges) better than 0.42 dB (0.64 dB) and 4.5° (6.9°), respectively, for a bandwidth of 500 MHz (700 MHz). It occupies a composite area of only 0.123 mm2while consuming 30.5 mW from a 1-V supply. To achieve quadrature locking at the desired frequency within the LNA-VM's tuning range, an on-chip mixer-based quadrature error detection and calibration scheme is presented. The proposed scheme is demonstrated to be robust in the face of gain and layout-induced mismatches which can be significant at millimeter-wave (mm-wave) frequencies.