E-Band Multi-Phase LC Oscillators With Rotated-Phase-Tuning Using Implicit Phase Shifters

A rotated-phase-tuning (RPT) technique is proposed for millimeter-wave (mmW) LC-based oscillators. Without using varactors, the oscillation frequency is tuned by phase interpolation to vary the phase of the current flowing into the LC tank. Interestingly, the intrinsic delay of transistors is leveraged to rotate the phases for interpolation and thus to optimize the oscillator's performance in terms of frequency tuning range and phase noise. Two E-band RPT oscillator prototypes are designed and implemented in a 65-nm CMOS process. The first one with four-phase output measures oscillation frequency from 67.8 to 81.4 GHz and phase noise of -108 to -113 dBc/Hz at 10-MHz offset, while consuming 13 to 25 mW from a 1-V supply. With similar power consumption, the second prototype featuring eight-phase output operates from 74.8 to 79 GHz and achieves phase noise of -116 to -118 dBc/Hz at 10-MHz offset. The four-phase and eight-phase oscillators occupy small core areas of 0.02 and 0.06 mm², respectively.