Abstract: A power amplifier circuit comprises an amplifying transistor and a dc bias circuit. The dc bias circuit comprises a first transistor in a current mirror with the amplifying transistor, and a second transistor to provide the base currents to both the amplifying transistor and the first transistor. A dc bias power source is coupled to the base of the second transistor through a resistor and an inductor connected in series. A bypass capacitor is coupled between a ground and a node between the resistor and the inductor. Thus, the reduced voltage drop across the base-emitter junction of the amplifying transistor due to an increased input power is compensated. Furthermore, by properly scaling the emitter area ratio between the amplifying transistor and the first transistor, and/or the ratio between a bias resistor and a corresponding resistor coupled with the mirroring first transistor, the quiescent current in the amplifying transistor can be made to be in direct proportion to that of the first transistor.

Abstract: A power amplifier circuit includes an amplifying transistor and a dc bias circuit for biasing the amplifier transistor to obtain a conduction angle of at least about 180°. The dc bias circuit includes a self-bias boosting circuit which has a cascode current-mirror circuit having an output coupled to a control terminal of the amplifying transistor by a resistor, and a capacitor coupled from the cascode current-mirror circuit to a common terminal. The value of the capacitor can be selected to obtain the desired amount of self-bias boosting.

Abstract: A power amplifier circuit includes an amplifying transistor and a dc bias circuit for biasing the amplifier transistor to obtain a conduction angle of at least about 180°. The dc bias circuit includes a self-bias boosting circuit for initially decreasing and then increasing the dc bias voltage provided to a control terminal of the amplifying transistor by the dc bias circuit as the input signal provided to the power amplifier increases. The self-bias boosting circuit is extremely simple and compact in design, and permits the power amplifier circuits to operate in Class B or Class AB with improved power output characteristics.

Abstract: A high-frequency amplifier circuit includes an amplifying transistor and a bias circuit coupled to the amplifying transistor. The bias circuit includes a first bias subcircuit for controlling a quiescent current in the amplifying transistor and a second bias subcircuit for independently controlling a bias impedance of the amplifying transistor. Using this configuration, it is possible to set the gain and class of operation of the amplifying transistor, while independently controlling the bias impedance of the amplifying transistor to obtain improved linearity and tuning capability as well as increased efficiency.

Abstract: A power amplifier circuit includes an amplifying transistor and a dc bias circuit for biasing the amplifier transistor to obtain a conduction angle of at least about 180°. The dc bias circuit includes a dynamic bias boosting circuit for increasing the dc bias current provided to the amplifying transistor by the dc bias circuit in direct proportion to an increase in the input signal provided to the power amplifier. The bias boosting circuit permits the power amplifier circuits to operate in Class B or Class AB with improved power output characteristics and reduced power dissipation at low power levels.

Abstract: A high-frequency power amplifier circuit offers the advantages of high input impedance, high power efficiency and accurate bias current control in a compact and economical circuit configuration. The amplifier includes a single-ended output stage driven by a symmetrical push-pull emitter follower stage with both active pull-down and active pull-up capability. The emitter follower stage is driven by an active phase-splitter stage, with bias current for the phase-splitter stage and subsequent stages being provided by a bias-current control stage which is isolated at high frequencies from the high-frequency input signal to the amplifier.