A Multi-Phase Coupled Oscillator Using Inductive Resonant Coupling and Modified Dual-Tank Techniques

This paper presents a novel coupled oscillator RFIC for multi-phase clock generation. The design achieves low phase noise while maintaining strong coupling among oscillator cores. The proposed transformer-based dual-tank topology forms a loop of coupling path for enhanced multi-phase coupling. To facilitate strong magnetic coupling among oscillator cores, the proposed transformers utilize resonant inductive coupling to enhance the voltage swing at the coupled wing. The phase noise optimization is accomplished by leveraging the adaptive biasing feedback and the enhanced dual-tank technique. The behavioral model based on Alder's equation as well as the analysis of the tank response is given. Full electromagnetic (EM) modeling involving all transformers and the passive interconnecting routes has been performed using the EMX software in order to ensure that simulated performance reflects measurement environment. The prototype RFIC of the proposed circuit with eight phases is implemented in a 65-nm CMOS radio frequency (RF) silicon on insulator technology. The measured phase noise is -124.3 dBc/Hz at 1-MHz offset from 2.41 GHz with 7-mW power consumption per core, and the operating frequency can be digitally tuned from 1.81 to 2.41 GHz. The phase noise can be further improved to -128.2 dBc/Hz at 1-MHz offset from 2.41 GHz by increasing the power consumption to 15 mW per core.