GaAs power HBTs with 84% power-added efficiency operating in C-X band

This paper describes the results of an experimental study of operating GaAs Power Heterojunction Bipolar Transistors (HBTs) in Class C bias mode over C-X frequency Bands. We find that the 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 12% percentage points (from 72% in Class AB to 84.5% in Class C) with concurrent loss of 4.3 dB in power gain. At 9 GHz, the PAE increased by only 8.1% in Class C mode compared to Class AB bias condition with an associated 4.5 dB reduction in power gain. The efficiency improves monotonically with lower operating frequency. In a single tone environment, the second harmonic of the RF signal increases by ~7 dB in Class C over Class AB.