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

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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.