Low noise 5 GHz differential VCO using InGaP/GaAs HBT technology

The authors present the first InGaP/GaAs HBT differential VCOs with low phase noise performance. One is a cross coupled differential VCO, and the other is a Colpitts differential VCO. To achieve a fully integrated VCO, collector-base junction capacitance of HBT transistor is used for the frequency tuning varactor. The measured output frequency ranges of VCOs are 290 MHz and 190 MHz, and the phase noises at an offset frequency of 1 MHz are -118 dBc/Hz and -117 dBc/Hz respectively. The each VCO core dissipates 13.2 mW from a 3.5 V supply, and the output power is about -0.2 dBm. Concerned with cross coupled VCO, it shows the figure of merit of -179 dBc/Hz, which is the best result among the reported compound semiconductor FET and HBT VCOs.