A power amplifier protection circuit that includes protection circuitry to variably shunt an input radio frequency (RF) signal to AC ground, turn off bias to an output transistor of a power amplifier, and turn off the output transistor. The power amplifier protection circuit features an asymmetrical control that can quickly shut off a power amplifier, and turn on the power amplifier at a steady, controlled rate when an output transistor exceeds a predetermined threshold voltage.
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to commonly assigned U.S. Provisional Patent Application No. 60/470,629, filed on May 15, 2003, which is incorporated herein by reference in its entirety.
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.
