A 0.7-5.7 GHz Reconfigurable MIMO Receiver Architecture for Analog Spatial Notch Filtering Using Orthogonal Beamforming

A highly reconfigurable direct-conversion softwaredefined MIMO receiver with 4 RF inputs and 4 I/Q baseband outputs is proposed. It allows for digital MIMO but also analog interference rejection by spatial notch filtering through 4 flexible and simultaneous orthogonal beams. A segmented constant-Gm vector modulator with improved interference tolerance and wide RF frequency range targeting the sub-6 GHz bands is proposed. It exploits current-domain beamforming before I-V conversion by transimpedance amplifiers. A 0.7-5.7 GHz 22 nm FD-SOI prototype chip achieves >29 dB spatial filtering for a single notch and an ultra-wideband 20 dB notch suppression bandwidth of 2.3 GHz at broadside excitation at an LO frequency of 2.5 GHz. In the notches, an IIP3 of +16 dBm and B1dB of -11.5 dBm at 41 dB gain is achieved, improving IIP3 and B1dB by 35dB and 27dB, respectively, by spatial filtering. A single-element noise figure of 5.5-7 dB is achieved on the vector modulator constellation corners, degrading about 2 dB on the points nearby the biggest circle fitting into square constellation. However, sub-3dB system noise figure is potentially achievable taking into account up to 6 dB improvement by the 4-element beamforming. Given both gain and phase control provided by the vector modulator, spatial patterns with up to 3 independent nulls can be synthesized with the 4-element antenna array. The chip of 0.52 mm2 active area consumes 77-139mW at an LO-frequency of 0.7-5.7 GHz from a 0.8V supply.