19.4 A 0.07 mm²20-to-23.8GHz 8-phase Oscillator Incorporating Magnetic + Dual-Injection Coupling Achieving 189.2dBc/Hz FoM_{@10 MHz}and 200.7dBc/Hz FoM_Ain 65nm CMOS

Multiphase local oscillators (LOs) with low phase noise (PN) and low phase errors are the cornerstone of high-data-rate wireless transceivers, especially with the increasingly more complex modulation schemes. Frequency division, polyphase filters, and ring oscillators are the widespread topologies for multiphase LO generation at RF. Yet, these topologies suffer from considerable trade-offs between the key performance metrics and power budget, limiting their achievable Figure-of-Merit (FoM) at the millimeter-wave (mm-wave) frequencies. Combining the multiphase characteristic of a ring oscillator with the high-quality LC resonator could be a direction to achieve low PN and low phase error in mm-wave LO generation with multiple output phases. A typical multicore oscillator merging the beneficial properties of LC and ring oscillators is depicted in Fig. 19.4.1 (upper). In [1], a capacitor-coupling network links up the quad-core oscillators for 8-phase generation. This undertaking, however, loads the resonators heavily, limiting the frequency tuning range (FTR). [2] is based on an active-coupling network to make the quad-core oscillators uniform, but it comes at the cost of PN degradation due to the extra noise injected by the coupling transistor. In fact, both such coupling networks suffer from a weak coupling strength between the multiple cores, leading to unbalanced phase intervals between the multiphase outputs. Finally, the use of standalone inductors incurs a large area footprint.