6-GHz all-pass-filter-based delay-and-sum beamformer in 130nm CMOS

A broadband RF delay-and-sum (DAS) beamformer, which employs wide-band CMOS all-pass filters for achieving the desired time delays, is discussed in this work. The use of all-pass filters eliminates the need of I/Q mixers and transmission line-based delay stages used in the previously reported DAS beamformers. The proposed all-pass filter can achieve approximately linear-phase delay across GHz-range of frequencies, which is amendable for wide-band beamforming. The delay-and-sum section of the beamformer was designed and simulated for an array of 4 antennas, with the desired signal direction of arrival of 11° from broadside direction. The performance of the wide-band DAS beamformer is obtained with simulations in IBM 130-nm CMOS technology. Moreover, experimental results for the main building block of the circuit, the voltage-mode all-pass filter with the nominal 33 ps delay, are given to strengthen the feasibility of physical implementation of such a beamformer.