Harmonically-Coupled, Current‑Sharing 4-Phase and 6-Phase Oscillators in 65 nm CMOS

A technique is introduced for generating four or more multiphase signals by coupling class-B cores through a shared tail current source. This approach eliminates additional coupling devices while enabling 2nd-harmonic coupling and current shaping to operate between class-B and class-C to improve phase noise. Prototypes of two-core and three-core oscillators, generating 4 and 6 phases respectively, are implemented in 65 nm CMOS. The 4-phase 5 GHz design consumes 1.2–1.33 mW, and achieves a tuning range of 22% with a phase noise of –142 to –141 dBc/Hz at 10 MHz offset. The 6-phase 9.5 GHz oscillator with 17.5% tuning range achieves a phase noise of –141.6 to –138.3 dBc/Hz at 10 MHz offset. Both designs operate in a reliable voltage and swing regime.