  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.
