A method to lower VCO phase noise by using HBT darlington pair

The paper presents a novel method to enhance tank voltage swing in LC VCOs design using bipolar transistor. The method is successfully demonstrated in an InGaP/GaAs HBT MMIC process. A gm-boosted VCO and a modified version, using Darlington-pair transistors, are compared. The latter exhibits lower phase noise, increased tuning range, and less variation in output power. The gm-boosted VCO has tuning range of 22.8% centered at 5.7GHz and phase noise ranging from −103 to −95 dBc/Hz at offset frequency of 100kHz. The modified version using Darlington pair has tuning range of 26% centered at 5.9 GHz and phase noise ranging from −103.5 to −98.5 dBc/Hz at offset frequency of 100kHz.