SYSTEM UND VERFAHREN ZUR AUTOMATISCHEN EINSTELLUNG DER VORSPANNUNG EINES VERSTÄRKERS

The present invention provides a method and apparatus for auto-biasing an amplifier. The invention is particularly useful in biasing non-linear amplifiers and amplifiers whose input signal may be amplitude modulated (AM). The auto-bias system of the present invention has an active bias feedback loop that continuously adjusts the bias condition of an amplifier to a wanted state during amplifier operation by monitoring a physical quantity indicative of the operating state of the amplifier and controlling the amplifier bias so as to control the amplifier operating point sufficiently to compensate for variations in amplifier electrical characteristics, amplifier load, amplifier temperature, and input signals. In the case of an AM input signal, the auto-bias system of the present invention may provide sample and hold function so that the amplifier bias is the same during high power periods and low power periods, even though during high power periods the amplifier may be operating in a non-linear region. In one variation of the invention the amplifier may be an RF transistor, for example, a bipolar transistor, and may be used in a mobile cellular communications system. Further, the present amplifier auto-bias system eliminates the need for manually setting the amplifier bias during production and enables use of any transistor type in the amplifier.