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

Abstract

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 55nm CMOS process, the VCO covers the frequency tuning range from 22.3 to 27.1GHz and from 31.2 to 36.6GHz when the switched VCO is under ON or OFF state, respectively. The dual-mode VCO achieves a phase noise of -127.6dBc/Hz at 10MHz offset for 22.3GHz carrier frequency.