Scalable Inter-Core-Shaping Multi-Core Oscillator With Canceled Common-Mode Destructive Coupling and Robust Common-Mode Resonance

Abstract

In this article, a scalable inter-core-shaping multicore oscillator is proposed to achieve low phase noise and high figure of merit (FoM) at millimeter-wave (mm-wave) band. Adjacent NMOS and PMOS cores generate common-mode (CM) resonance simultaneously, but with opposite signs; thus, differential capacitors can be used to create resonance at twice the oscillation frequency. Such a CM resonance limits flicker noise upconversion and reduces phase noise. The capacitors in differential mode (DM) and CM are all differential, which avoids the degradation of quality factor caused by the single-end capacitor. Besides, the magnetic coupling among the cores only operates in DM. In CM, the negative and positive mutual couplings cancel each other, which increases the CM inductance and its quality factor. Moreover, the topology shows low sensitivity to the parasitics in the return path and the mismatch among the cores, which makes it suitable for the massive-core extension. The 28-GHz quad-core and 20-core circuits are prototyped in a conventional 40-nm CMOS process. Occupying a core area of 0.06 mm 2 , the quad-core oscillator achieves 1-MHz FoM of 193.3 dBc/Hz. The 20-core circuit exhibits 1-MHz phase noise of −120.8 dBc/Hz at 28 GHz and 1-MHz FoM of 192.7 dBc/Hz. Index Terms-Figure of merit (FoM), figure-of-merit area (FoM A ), inter-core shaping, low phase noise, millimeter wave (mm wave), multi-core, oscillator.