A study of Class C operation of GaAs power HBTs

GaAs power HBTs are traditionally biased in Class A or Class AB mode for power amplifiers. This paper describes the tradeoffs of operating these devices in Class C bias. We find that power-added efficiency (PAE) improves and power gain decreases in Class C when compared to Class AB bias. At 6 GHz, the PAE increased by greater than 10 percentage points (from 68.9% in Class AB to 80.6% in Class C) with concurrent loss of 4.3 dB in power gain. The efficiency improves monotonically with lower operating frequency. In a single-tone environment, the second harmonic increases by /spl sim/7 dB in Class C over Class AB. To our knowledge, this is the first report on the experimental study of Class C operation of GaAs HBTs.< >