A 5 GHz transformer-coupled shifting CMOS VCO using bias-level technique

We report a low phase noise transformer-coupled CMOS VCO using a bias-level shifting technique. Two fully integrated voltage-controlled oscillators (VCOs) are presented as a proof of concept. A conventional LC VCO with a current source achieves a phase noise of -116.67 dBc/Hz at 1 MHz offset from the 5.6 GHz center frequency, taking 3.9 mA from a 1.5 V power supply. The proposed transformer-coupled VCO achieves a phase noise of -124.17 dBc/Hz at 1 MHz offset from a 5.8 GHz carrier frequency with 5.1 mA bias current from 1.5 V power supply. The VCO performances are compared with previously reported CMOS VCOs in the range of 4-6 GHz oscillation frequencies.