A 40-nm CMOS Phase-Tunable Four-Phase Injection-Locked Ring VCO Utilizing Unbalanced Feedforward Topology Achieving −211.1- to −207.3-dBc/Hz FoM A Over Differential/Orthogonal Phase Range of −90.0° to 80.9°/−69.6° to 76.5°

This article proposes a phase-tunable four-phase injection-locked ring voltage-controlled oscillator (RVCO) voltage-controlled oscillator (VCO), where the functions of muti-phase generation and clock phase tuning are merged in the VCO, and no additional phase-tuning block is needed in the clock system. The ring oscillator (RO) utilizes a novel unbalanced feedforward topology with high power and area efficiency. By tuning the ratio of the feedforward current to the input current at each stage of the oscillator, the phase of the four-phase output clock can be precisely and flexibly controlled. The proposed VCO achieves an inherent phase-tunable/calibration feature for desired phase outputs, without the need for additional back-end calibration circuits, avoiding the deterioration of noise performance and the increase in power consumption in the clock path. The injection locking technique is applied in the proposed VCO to maintain good noise performance over a wide frequency and phase-tuning range. The VCO prototype in a 40-nm CMOS can cover the frequency range of 3.27.5 GHz and achieves a wide differential/orthogonal phase-tuning range of 90.0° to 80.9°/69.6° to 76.5° and a small phase-tuning step of 0.14°/mV on average. Over the full phase range, the VCO achieves an FoM_A of 211.1 to 207.3 dBc/Hz, which is the best FoM_A among the state of the arts.