Low noise coupling techniques for multi-phase oscillators

This paper presents a capacitive-coupling technique for low phase noise multi-phase oscillators. The proposed coupling techniques can improve the phase noise performance while maintain good phase accuracy over wide frequency range. A 4.3-5.3 GHz two-phase VCO prototype is implemented to demonstrate the effectiveness of the proposed technique. It achieves a measured phase noise of -120 to -124.04dBc /Hz @ 1MHz offset and a measured phase error of 0.23-0.91° across a 1GHz tuning range.