Power amplifier having a cascode current-mirror self-bias boosting circuit

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 DEG . 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.

Description

Background of the invention [0001] The present invention relates to the field of transistor amplifier circuits, and more particularly, to a power amplifier circuit with a cascode current mirror self-bias boost circuit. [0002] This general-purpose type of amplifier is mostly used in high-frequency RF amplifiers, as well as in audio amplifiers and other applications. In order to obtain a linear input-output relationship and high operating efficiency, such amplifiers are usually operated with a conduction angle of about 180° (Class B), or a slightly larger conduction angle (Class AB) to avoid crossover distortion . [0003] Typically, such amplifiers require a dc bias circuit to establish a quiescent bias current in the amplifier circuit to ensure operation in Class B or Class AB mode. In the prior art, the bias is usually provided by a fixed current source, as shown in U.S. Patent No. 5,844,443, or by an external power supply, which can be set to a desired constant value to ...

AI Technical Summary

Problems solved by technology

Although this scheme is able to achieve high power-increased efficiency while maintaining linearity, it employs rather complex circuitry and contributes a significant noise level to the output stage

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