X-band HBT VCO with high-efficiency CB buffer amplifier

A monolithic AlGaAs-GaAs HBT VCO with common-base (CB) buffer amplifier was demonstrated at X-band. Overall efficiency of 30% was achieved with 93-mW output power at 9.8 GHz. The MMIC chip is only 1 mm*2 mm, including the monolithic varactor diode. The circuit design offers several unique advantages: (1) the CB buffer amplifier reduces the frequency-pull effect from the external load; (2) the design for the oscillation condition and the output impedance match for power are separated; and (3) the overall efficiency can be high. A step-by-step design procedure is discussed.<
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