Patent ID: 7274258

Claim:
A bias circuit for use with a radio-frequency (RF) amplifier having an amplifying transistor, said bias circuit dynamically adjusting its DC output voltage based on the power of an input signal received by said RF amplifier and changing the operation current of said RF amplifier, said RF amplifier having an input port and an output port, said input port being for receiving said input signal and said output port being for transmitting an amplified signal, an output terminal of said bias circuit being connected to said input port of said RF amplifier, said input port of said RF amplifier being a controlling electrode of said amplifying transistor, and said bias circuit comprising: an active device having the same I-V characteristics as a diode, wherein a cathode of said active device is said output terminal of said bias circuit and is connected to said controlling electrode of said amplifying transistor; a DC voltage source having one of its two terminals grounded; and a coupling device used to control the magnitude of a leaked signal that is coupled to said input signal, and said bias circuit being driven by said leaked signal and drawing no DC operating current; wherein a first side of said coupling device is connected to an anode of said active device, and a second side of said coupling device is connected to the ungrounded terminal of said DC voltage source.