A Frequency-and-Spatial Blocker Tolerant Butler Matrix based 4x4 MIMO Receiver using a Switched-Capacitor Quadrature Coupler

Recent advances in passive mixer-first receivers enhanced the frequency-blocker tolerance of radio-frequency (RF) receivers. These mixer-first receiver architectures are also extended to Multi-Input Single-Output (MISO) receivers. The current state-of-art Multi-Input Multi-Output (MIMO) receivers still use a low-noise amplifier (LNA) as the first block, thus have low frequency-blocker tolerance. This paper presents a Butler-matrix based 4x4 beamforming MIMO receiver with high frequency-and-spatial blocker tolerance using a novel switched-capacitor quadrature coupler. Other advantages of this RF LNA-less MIMO architecture include reduced power consumption, reduced active area, and improved in-band linearity. Measurement results of a CMOS prototype 4x4 MIMO receiver are presented. The prototype MIMO has a single-element P1dB of -9.6 dBm and an in-band/in-notch B1dB of -4 dBm at 0.8 GHz.