Rugged HBT Class-C Power Amplifiers with Base-Emitter Clamping

The ruggedness of HBT Class-C power amplifiers was improved by adding an anti-parallel diode to the amplifier input to limit the negative swing of the base-emitter voltage. The improved amplifier could withstand 3:1 instead of 2:1 mismatch in CW operation, and 2.5:1 instead of 1.5:1 mismatch in pulse operation. In contrast to other approaches with emitter ballast, active feedback, or electrostatic discharge protection circuits, the present approach is simple to implement and has negligible impact on overall amplifier output power, gain or efficiency.