A 12-GHz GaInP/GaAs HBT VCO based on push-push output extraction from capacitive common-node

A new push-push VCO architecture takes the second harmonic output signal from a capacitive common-node in a negative-g/sub m/ oscillator topology. The generation of the 2nd harmonics is accounted for by the nonlinear current-voltage characteristic of the emitter-base junction diode causing; 1) significant voltage clipping and 2) different rising and falling time during the switching operation of core transistors. A prototype 12-GHz MMIC VCO realized in GaInP/GaAs HBT achieves an output power of -5 dBm, a phase noise of -108 dBc/Hz at 1 MHz offset while drawing 10.7 mA from a 2.4-V supply, which is equivalent to -175.8 dBc/Hz of VCO figure-of-merit.