Bias circuit, high-power amplifier, and portable information terminal

Abstract

To provide a bias circuit for gain control that can reduce gain variation at low-power output, facilitate setting of output power, and is unlikely to be affected by variation in element values and variations among products. Use in an HPA having three bias circuits serially-connected is assumed. Current of the third bias circuit is varied with a square-law characteristic. The square-law characteristic is amplified by a buffer amplifier including a linear amplifier and a peripheral circuit thereof. Output current of the third bias circuit varies depending on a current drivability coefficient of the diode-connected FET branched from the connection point between a constant current source and the linear amplifier. The output current of the third bias circuit is controlled by providing a circuit that draws a certain amount of current from the current flowing in the FET.