A 1-GHz 16-Element Four-Beam True-Time-Delay Digital Beamformer

• Published in: IEEE journal of solid-state circuits Vol. 54; no. 5; pp. 1304 - 1314
• Main Authors: Jang, Sunmin, Lu, Rundao, Jeong, Jaehun, Flynn, Michael P.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-05-2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplitude modulation; Analog to digital conversion; Analog to digital converters; Array signal processing; Arrays; Bandpass; Bandwidth; Baseband; Beamforming; Delay; Delay effects; Delay line; digital beamforming; Digital to analog conversion; Digital to analog converters; Error analysis; linear array; linearity; multiple-input multiple-output (MIMO); Narrowband; phased array; Phased arrays; Power consumption; Radio frequency; receiver; Steering; Tapering; true-time-delay
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2019.2894357

Phased arrays are widely used due to their low power and small area usage. However, phased arrays depend on the narrowband assumption and, therefore, are not suitable for high-bandwidth applications. Emerging communication standards require increasingly higher bandwidths for improved data rates, which results in a need for timed arrays. However, high power consumption and large area requirements are drawbacks of radio frequency (RF) timed arrays. To resolve these issues, we introduce the first true-time-delay digital beamforming IC, which eliminates beam squinting error by adopting a baseband true-time-delay technique. Furthermore, we present a constant output impedance current-steering digital-to-analog converter (DAC), which improves the spurious-free dynamic range (SFDR) of a bandpass delta-sigma modulator by 7 dB. Due to the new DAC architecture, the 16-element beamformer improves SFDR by 13.7 dB from the array. Measured error vector magnitudes (EVMs) are better than 37 dB for 5-MBd quadratic-amplitude modulation (QAM)-64, QAM-256, and QAM-512. The prototype beamformer achieves nearly ideal beam patterns for both conventional and adaptive beamforming (i.e., adaptive nulling and tapering). The difference between normalized measured beam patterns and normalized simulated beam patterns is less than 1 dB within the 3-dB beamwidth. The beamformer, including 16 bandpass analog-to-digital converters (ADCs) occupies 0.29 mm 2 and consumes 453 mW in total power.