Biasing circuit and power amplifier circuit thereof

The invention discloses a biasing circuit. The biasing circuit comprises an input end, an output end, a second transistor, a first resistor, a second resistor and a digital adjustable resistor, wherein the digital adjustable resistor and the second resistor are orderly connected between the input end and the collector of the second transistor in series; the first resistor is connected between the output end and the base of the transistor in series; the second resistor and the intermediate node of the digital adjustable resistor are connected with the base of the second transistor; the emitter of the second transistor is connected with the ground; and the biasing circuit is connected with a bias voltage through the input end and provides bias for the power amplifier through the output end.