No abstract

This paper presents a wideband 12 Bit 8 GS/s timeinterleaved successive approximation register (SAR) analog-todigital converter (ADC), featuring a sub-2 radix architecture with an overrange of 10% and randomized sampling with mismatch correction in a 28 nm CMOS technology. For this purpose, 18 500 MHz SAR-ADCs plus an additional reference ADC are interleaved. This topology enables a randomization approach, reducing mismatch related interleaving spurs. Furthermore, the additional reference ADC operating in parallel to the main ADC enables adaptive digital calibration to correct for static and time-interleaved mismatch effects. A wideband front-end features two subsequent push-pull buffer stages to achieve a high trackand-hold (T/H) bandwidth and high sampling linearity, while improving kickback related settling limitations. After calibration, the ADC achieves a signal to noise and distortion ratio (SNDR) of 56.8 dB and a spurious free dynamic range (SFDR) of 80 dBc applying a single full scale sine wave tone close to the Nyquist frequency of 4 GHz.

Single-Carrier Frequency Division Multiple Access (SC-FDMA) is a promising technique for high data rate indoor Terahertz (THz) communications in future beyond 5G systems. In an indoor propagation scenario, the Line-Of-Sight (LOS) component may be blocked by the obstacles. Thus, efficient THz SC-FDMA communications require a fast and reliable Beam Alignment (BA) method for both LOS and Non-Line-Of-Sight (NLOS) scenarios. In this paper, we first adopt the hierarchical discrete Fourier transform codebook for LOS BA, and introduce the hierarchical k-means codebook for NLOS BA to improve the beamforming gain. Simulation results illustrate that the hierarchical DFT codebook and the hierarchical k-means codebook can achieve the beamforming gain close to that of the maximum ratio transmission in LOS and NLOS cases, respectively. Based on these two codebooks, we propose a Multi-Armed Bandit (MAB) algorithm named Hierarchical Beam Alignment (HBA) for single-user SC-FDMA THz systems to reduce the BA latency. HBA utilizes a hierarchical structure in the adopted codebook and prior knowledge regarding the noise power to speed up the BA process. Both theoretical analysis and simulation results indicate that the proposed BA method converges to the optimal beam with high probability for both the hierarchical DFT codebook and the hierarchical k-means codebook in the LOS and NLOS scenarios, respectively. The latency introduced by HBA is significantly lower when compared to an exhaustive search method and other MAB-based methods.