Power amplifier

Abstract

A power amplifier includes a front-stage amplifier including first and second transistors connected in parallel, and a rear-stage amplifier including a third transistor. The first transistor is biased into near-Class A without a distortion compensation circuit. The second and third transistors are biased into near-Class B with a distortion compensation circuit. The gain characteristics of the first to third transistors are adjusted so that the concave portion of the gain characteristics of the front-stage amplifier and the convex portion of the gain characteristics of the rear-stage amplifier match each other, to thereby flatten the gain characteristic of the entire power amplifier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram showing a configuration of a power amplifier according to one embodiment of the present invention.

FIGS. 2A-2C show gain characteristics of a front-stage amplifier shown in FIG. 1.

FIG. 3 is a block diagram showing a modification of the embodiment.

FIG. 4 is a circuit block diagram showing a configuration of a conventional power amplifier.

FIG. 5 is a circuit diagram exemplifying a configuration of a distortion compensation circuit shown in FIG. 4.

FIG. 6 is another circuit diagram exemplifying a configuration of the distortion compensation circuit shown in FIG. 4.

FIG. 7 is still another circuit diagram exemplifying a configuration of the distortion compensation circuit shown in FIG. 4.

FIG. 8 is still another circuit diagram exemplifying a configuration of the distortion compensation circuit shown in FIG. 4.

FIGS. 9A-9C show gain characteristics of the power amplifier shown in FIG. 4.

Claims

1. A power amplifier, comprising a plurality of amplification stages, whereina first amplification stage in said plurality of amplification stages includes a first amplification element, a second amplification element connected in parallel to said first amplification element, and a first distortion compensation circuit adjusting distortion of a gain characteristic of said second amplification element,a second amplification stage in said plurality of amplification stages includes a third amplification element and a second distortion compensation circuit adjusting distortion of a gain characteristic of said third amplification element,a dependency characteristic of gain relative to output power is opposite between said first amplification element and said second amplification element having the gain characteristic adjusted by said first distortion compensation circuit, anda dependency characteristic of gain relative to output power is opposite between said first amplification stage and said third amplification element having the gain characteristic adjusted by said second distortion compensation circuit.

2. The power amplifier according to claim 1, wherein said first to third amplification elements are first to third bipolar transistors, respectively, andsaid first and second distortion compensation circuits also serve as bias circuits of said second and third bipolar transistors, respectively.

3. The power amplifier according to claim 2, wherein said first bipolar transistor is biased into Class A to Class AB,said second bipolar transistor is biased into Class B to Class AB, andsaid third bipolar transistor is biased into Class B to Class AB.