Dual-band quad-core transformer coupled VCO with phase noise optimization

This work presents a dual-band transformer-based voltage controlled oscillator (VCO) with phase noise optimization. Transformers consisting of four inductors are employed to reduce area. Four cross-coupled VCO cores are connected to the four wings of two pairs of transformers to allow individual control of the cores, whose mutual inductance is utilized to enhance the frequency tuning. Also, the capability of transformer coupling for phase noise reduction is demonstrated. The proposed transformer-based VCO can oscillate at two frequency bands centered at 1.9GHz and 3.6GHz with around 30% tuning range for each band. Experimental implementation in a 0.18 um SiGe BiCMOS technology demonstrates a measured phase noise of -114/119dBc/Hz and -115/120dBc/Hz at 1MHz offset for high and low bands, respectively.