IF-Sampling Digital Beamforming with Bit-Stream Processing.

Abstract

Beamforming in receivers improves signal-to-noise ratio (SNR), and enables spatial filtering of incoming signals, which helps reject interferers. However, power consump-tion, area, and routing complexity needed with an increasing number of elements have been a bottleneck to implementing efficient beamforming systems. Especially, digital beamforming (DBF), despite its versatility, has not been attractive for low-cost on-chip implementation due to its high power consumption and large die area for multiple high-performance analog-to-digital converters (ADCs) and an intensive digital signal process-ing (DSP) unit. This thesis presents a new DBF receiver architecture with direct intermediate frequency (IF) sampling. By adopting IF sampling in DBF, a digital-intensive beamforming receiver, which provides highly flexible and accurate beamforming, is achieved. The IF-sampling DBF receiver architecture is efficiently implemented with continuous-time band-pass delta-sigma modulators (CTBPDSMs) and bit-stream processing (BSP). They have been separately investigated, and have not been considered for DBF until now. The unique combination of CTBPDSMs and BSP enables low-power and area-efficient DBF by removing the need for digital multipliers and multiple decimators. Two prototype digital beamformers (prototype I and prototype II) are fabricated in 65 nm complementary metal-oxide-semiconductor (CMOS) technology. The prototype I forms a single beam from four 265 MHz IF inputs, and an array signal-to-noise-plus-distortion ratio (SNDR) of 56.6 dB is achieved over a 10 MHz bandwidth. The prototype I consumes 67.2 mW, and occupies 0.16 mm2. The prototype II forms two simultaneous beams from eight 260 MHz IF inputs, and an array SNDR of 63.3 dB is achieved over a 10 MHz bandwidth. The prototype II consumes 123.7 mW, and occupies 0.28 mm2. The two prototypes are the first on-chip implementation of IF-sampling DBF.