A U-Band PLL Using Implicit Distributed Resonators for Sub-THz Wireless Transceivers in 40 nm CMOS

A U-band phase-locked loop (PLL) with implicit distributed resonators in the voltage-controlled oscillator (VCO) and injection-locked frequency divider (ILFD) using 40 nm CMOS is investigated in this brief. While LC-based, transformer-based, and distributed resonators are typically adopted for mm-wave and sub-terahertz applications, implicit distributed resonators are proposed to enhance the oscillation frequency of the VCO and expand the locking range of the ILFD. The operating principles and the characteristics of the proposed implicit distributed resonators are discussed for intuitive insight. The presented PLL occupies 0.53 mm(2) core area and has 81.8 mW power consumption. The PLL achieves a measured frequency range of 8.15 GHz (16%) from 46.75 GHz to 54.9 GHz. The measured phase noise is -91.8 dBc/Hz at 1 MHz offset frequency from a carrier of 46.75 GHz. The proposed U-band PLL can provide a clear and stable local oscillation signal for the transceivers operating at mm-wave and sub-terahertz (sub-THz) frequency band.