High power and high efficiency monolithic HBT VCO circuit

A description is given of the design, fabrication, and performance of the first reported monolithic voltage-controlled oscillator (VCO) using a heterojunction bipolar transistor (HBT) as the active device and an integrated p-n junction diode as the varactor. The monolithic VCO employs a self-aligned AlGaAs-GaAs HBT with ten emitter fingers (2.5 mu m*20 mu m each) whose maximum frequency of oscillation (f/sub max/) is 60 GHz. A continuous tuning bandwidth of 10.78-13.04 GHz (19%) was achieved with an output power of 219 mW and a DC-to-RF conversion efficiency of 31%. Maximum output power of 277 mW and 30% efficiency was also demonstrated at somewhat lower tuning bandwidths (11.00-11.88 GHz). The effects of bias voltage and current variations on the performance of the VCO have been studied. The single sideband FM noise of the free-running VCO was measured to be -55 dBc/Hz at 10 kHz offset and -75 dBc/Hz at 100 kHz offset from the carrier (11.26 GHz). These results indicate that HBT can be a viable broadband microwave source for high-power, low-phase-noise system applications.<
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