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 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 dBc/Hz at 10 MHz offset. Both designs operate in a reliable voltage and swing regime.