A Wideband Beamforming Lowpass Filter for 60 GHz Phased-Array Receivers

This paper presents an analog baseband beamforming topology, which combines phase shifting, signal combination, and biquadratic lowpass filtering in one block. This reduces the number of stages cascaded in a receiver chain, leading to a shorter signal path, thus improving the dynamic range. Flexibility of the proposed solution is illustrated with different possible implementations depending on the top-level chip floorplan. It is shown that the proposed structure does not introduce extra power consumption compared to the conventional approach, while obtaining a higher SNR. A four-antenna-path version of the proposed topology is implemented in 40 nm low-power CMOS as a prototype together with a variable gain block forming a complete analog baseband section for a phased-array receiver. The functionality includes beamforming with a resolution better than 6.8 degrees, fourth-order lowpass filtering with a 1 GHz cutoff frequency, variable gain between 10.6 and 30 dB and automatic DC offset compensation. Output IP3 above 10 dBm and output noise below 4.2 mVrms over the whole gain range yield an SFDR larger than 31.2 dB, which is sufficient for 16-QAM modulation according to IEEE 802.11ad. The circuit consumes between 30 and 42 mW.