UC Berkeley

Directional communication, a pivotal feature in 5G technology and beyond, expands channel capacity by leveraging spatial information from a multiple-antenna front-end. Fully digital beamforming facilitates advanced signal processing techniques like spatial blocker suppression and beam search. However, in the presence of spatial blockers, the digital backend requires high dynamic range data converters and other front-end components to maintain information integrity. Since the system is typically designed based on worst-case scenarios, the high dynamic range modules can consume substantial energy. This has sparked increased interest in beamforming or spatial filtering research in the analog/RF front-end. While inserting a spatial filter in the signal path can attenuate spatial blockers early and benefit the following signal path, it generally increases the power budget and additional noise.

In this work, we present the design of an integrated phase shifter based on switched capacitors. Subsequently, the proposed phase shifter is utilized in the beamformer. The baseband beamforming operation is executed in the charge domain, immediately preceding the analog-to-digital conversion. This approach diverges from existing research, which typically incorporates additional active beamforming blocks in the signal path, necessitating supplementary gain stages. Instead, our proposed beamformer is fully passive and integrated into successive approximation register (SAR) ADCs with the existing circuitry. The modification is limited to the sampling phase of the SAR ADC to ensure compatibility with the beamforming functions, without impacting the ADC's throughput.

The proposed data converter assisted beamforming method leads to low area and power overheads while maintaining compatibility with various other spatial filtering methods. Two test chips were fabricated using 16nm node technology. The measured data converter beamformer demonstrated a null depth exceeding 32dB with arbitrary programmability, consuming 52.1mW for each digital output beam.