A Cascode VCO based on Enhanced Colpitts Structure in InGaP/GaAs HBT Technology

In this paper, an integrated InGaP/GaAs MMIC VCO for an adaptive feedback interference cancellation system (AF- ICS) application is proposed. The new enhanced Colpitts architecture designed with low current consumption and low phase noise performance is implemented. The feedback capacitors are added between two transistors to increase the negative resistance and reduce the external noise interference. The phase noise of this VCO is -128.08 dBc/Hz at 100 KHz and - 138.46 dBc/Hz at 10 MHz offset frequency from the carrier frequency of 1.52 GHz when applying the control voltage of 1 volt. Three BC diodes are integrated in the same chip as a varactor to increase the VCO tuning range. The VCO is designed within the size of 0.76 x 0.86 mm².