Collaborative Research: Terahertz PLL-Based Phased Array for Wideband Radar/Sensing Systems in Silicon

众所周知，毫米波和太赫兹（300 GHz - 3太赫兹）系统在卫生、安全和工业中具有独特而重要的应用。遥感和主动/被动成像是这些应用中的一种，为了实现更高的分辨率，它们正在不断地向毫米波和太赫兹（THz）频率快速发展。这些系统用于高分辨率雷达、3D成像、安全筛查和隐蔽武器探测。然而，今天，太赫兹（THz）系统是使用昂贵而笨重的设备实现的。该项目介绍了一种新颖的方法来实现紧凑的片上太赫兹系统，并克服了这些高频系统面临的许多挑战。虽然所提出的电路和系统对集成和小型化下一代太赫兹系统具有重大影响，但该项目的影响超出了一些新颖电路拓扑的设计和实现。所提出的方法具有变革性，为设计师打开了新的大门。此外，凭借片上太赫兹系统，独特的太赫兹应用将迅速蓬勃发展，为高科技市场和研究机构带来新的机遇。在雷达应用中，横向距离分辨率和距离分辨率分别随着带宽和工作频率的增加而提高。然而，太赫兹频率下射频功率的宽带产生和辐射是具有挑战性的，特别是因为这些频率接近大多数先进硅技术平台的截止频率。稳定和准确的辐射频率是大多数传感/雷达应用（如调频雷达）的必要条件。在太赫兹频率下，锁相环（PLL）的宽带频率锁定变得非常具有挑战性，主要是因为压控振荡器（VCO）的输出功率低，硅分频器的锁定范围小。此外，需要相控阵来提高辐射功率和定位天线波束。在传统相控阵系统的本振（LO）或射频（RF）信号路径中存在有损移相器，以及将锁定信号与相控阵系统集成的复杂性，阻碍了设计人员在芯片上实现太赫兹相控阵系统。本文提出了一种新的基于锁相环的相控阵结构，该结构利用耦合锁相环阵列中的控制电压来校准和改变辐射信号的相位，并引导阵列波束。这可以在不使用显式移相器的情况下实现。该架构的核心是锁相机制，它采用了一种新的方法来设计压控振荡器（VCO）和随后的分频器，从本质上有助于提高输出功率和调谐范围，并降低相位噪声。

The mm-wave and terahertz (300 GHz - 3 THz) systems are known to have unique and significant applications in health, security and industry. Remote sensing and active/passive imaging are among these applications and are continually evolving at a rapid pace toward mm-wave and terahertz (THz) frequencies in order to achieve higher resolution. These systems are used for high-resolution radar, 3D imaging, security screening, and detection of concealed weapons. Today, however, terahertz (THz) systems are realized using expensive and bulky devices. This project introduces a novel methodology to implement a compact and on-chip THz system and to overcome many challenges facing these high frequency systems. While the proposed circuits and systems have significant effect on integrating and miniaturizing next generation THz systems, the impact of this project is beyond the design and implementation of few novel circuit topologies. The proposed methodologies are transformative and open new doors to designers. Furthermore, with on-chip THz systems the unique THz applications will rapidly flourish, resulting in new opportunities in the high-tech marketplace and research institutions.In radar applications the cross-range and range resolutions improve as the bandwidth and the operation frequency increase, respectively. However, wide-band generation and radiation of the RF power at THz frequencies is challenging, especially because, these frequencies are close to the cut-off frequencies of most advanced silicon technology platforms. Stable and accurate radiated frequency is a necessity for most sensing/radar applications such as frequency-modulated radars. Wide-band frequency locking in a phase-locked loop (PLL) at THz frequencies becomes extremely challenging mainly because of low output power of voltage controlled oscillators (VCO) and low locking range of frequency dividers in silicon. Moreover, phased arrays are needed to boost the radiated power and to localize the antenna beam. Having lossy phase shifters in the Local Oscillator(LO) or Radio-frequency(RF) signal paths in conventional phased array systems and the complications of integrating a locked signal with a phased array system have prevented designers to implement THz phased array systems on chip. Here,a novel PLL-based phased array architecture is proposed, which uses control voltages in the coupled PLL array to both calibrate and vary the phase of the radiated signal and steer the array beam. This can be achieved without the use of explicit phase shifters. At the heart of this architecture is a phase-locking mechanism, which adopts a new approach in designing the Voltage-Controlled Oscillator(VCO) and the following frequency divider that essentially helps increase the output power and tuning range and lower the phase noise.