Design and Analysis of Windmill-Shaping-Geometry Eight-Phase Oscillator Incorporating Magnetic and Dual-Injection Coupling Techniques

This article reports a compact millimeter-wave (mm-wave) quad-core eight-phase oscillator featuring magnetic coupling and dual-injection coupling. Specifically, the quad-core oscillator is integrated in an LC-ring configuration via a windmill-shaping transformer for phase noise (PN) and chip area reduction. The eight-phase oscillator could eliminate the oscillation mode ambiguity and save the power budget by exploiting a large transformer coupling factor. In addition, the inherent multiphase outputs are routed to the cascode tail-injection transistors to implement the dual-injection coupling. This act enables noise circulating and strengthens quad-core coupling that benefits the PN and phase accuracy simultaneously. Prototyped in a 65-nm CMOS process, the proposed eight-phase oscillator consumes 5.8mW from a 0.55-V supply, scoring a PN_{@10 MHz} of −129.3dBc/Hz with the corresponding FoM_{@10 MHz} of 189.2dBc/Hz across the frequency tuning range (FTR) of 17.4% (20–23.8GHz). Thanks to the windmill-shaping transformer, the quad-core eight-phase oscillator only occupies a core area of 0.07mm² with a superior FoM_A of 200.7dBc/Hz at a 10-MHz offset. The measured transient multiphase output waveforms exhibit a quadrature phase error < 1.5°.