US Patent 6961554 Power amplifier including a desensitized bias circuit

A desensitized bias circuit for a power amplifier includes, in one embodiment, a notch filter incorporated into the bias circuit. The notch filter behaves as a resonant circuit at the operating frequency of the power amplifier, thus coupling to ground any RF energy that migrates from the power amplifier input to the bias circuitry. The notch filter acts as a virtual ground to couple any RF energy present in the bias circuit to ground. Various implementations of the bias circuitry including the notch filter can be used. In other embodiments, the invention includes phase cancellation circuitry in the bias circuit to suppress any RF energy in the bias circuit.