Low phase noise and wide tuning range VCO using switchable weakly coupled VCO-cores

A dual-mode wide tuning range voltage-controlled oscillator (VCO) based on switchable weakly coupled cores is presented in this paper. The dual-mode operation is achieved when the two switched VCO cores are under ON and OFF states. A weakly coupled transformer with small coupling coefficient of the two-coupled LC tanks of two VCO cores is used to ensure that the VCO works at desired frequency under both modes. The results show that large coupling coefficient between the LC tank of two VCOs and LC tank of buffer enhances the quality factor of the VCO’s LC tank at lower resonant frequency under both modes. Fabricated in a 55 nm CMOS process, the VCO covers the frequency tuning range from 22.3 to 27.1 GHz and from 31.2 to 36.6 GHz when the switched VCO is under ON or OFF state, respectively. The dual-mode VCO achieves a phase noise of -127.6 dBc/Hz at 10 MHz offset for 22.3 GHz carrier frequency.