A circuit and method for protecting a radio frequency power amplifier
against peak drain voltage. A detector circuit has an input connected to
a drain of a power transistor of an amplification stage of the power
amplifier to detect a peak drain voltage therefrom. The detector circuit
outputs a protection signal when the detected peak drain voltage exceeds
a predetermined reference level. A shutdown circuit is coupled to the
detector circuit and inputs the protection signal therefrom. The
protection signal is used to remove a gate bias of at least one
amplification stage of the power amplifier. High frequency components are
used in the detector and protection circuits to immediately reduce the
drain voltage from one or more of the amplification stages.