A 194-238GHz Fully On-Chip Self-Referenced Frequency Stabilized Radiator for High Range Resolution Imaging

The mmWave and THz frequency bands provide unique opportunities for wideband communication and sensing. In particular, the high frequency and large bandwidth available in these bands enable compact frequency-modulated continuous wave (FMCW) radars with integrated antennas that have stunning range resolution. Free-running harmonic voltage-controlled oscillators (VCO) can be used for the FMCW radar application to provide high frequency chirp with large bandwidth. However, the uncompensated frequency drift due to environmental variations, supply noise, etc. can introduce unpredicted errors in the imaging process, degrading the high range resolution capability. In general, a phase-locked loop (PLL) can be used to stabilize the frequency. However, mmWave and THz PLLs encounter several challenges. First, FMCW radars require a wide tuning range to provide high range resolution which can be hardly achieved due to the limited locking range of PLLs. In fact, such high frequency PLLs demand dividers with an extremely large division ratio (N). Usually, the fastest divider that is used in the first stage of the divider chain is an injection-locking frequency divider (ILFD) which cannot provide a sufficient turning range for such high range resolution applications. Of course, higher injection power can be utilized to increase the tuning range at the cost of significantly increased power consumption. Second, the high N requires employing several dividers in the divider chain, remarkably increasing the power consumption. Third, to alleviate the severe output phase noise degradation caused by phase noise multiplication due to the extremely high division ratio of the PLL, a high-quality off-chip reference source is usually required which is unfavorable. In [1], an entirely on-chip frequency stabilization technique is introduced to radiate a stabilized THz signal, however, the narrow bandwidth $(3 \mathrm{GHz} / 1 \%)$ makes it less attractive for high range resolution imaging. This paper introduces a 220 GHz radiator with 44 GHz/ 20.4 % bandwidth and a self-referenced frequency stabilization (SRFS) technique, which obviates the need for external reference, lowering the cost and power consumption. A prototype is implemented and fabricated in a $55 \mathrm{~nm}$ BiCMOS process.