Capacitor coupled dynamic bias boosting circuit for a power amplifier

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 dynamic bias boosting circuit for increasing the dc bias current provided to the amplifying transistor by the dc bias current in direct proportion to an increase in the input signal provided to the power amplifier. An input to the dc bias circuit is coupled to a stage of the power amplifier circuit by a capacitor. The bias boosting circuit permits the power amplifier circuits to operate in Class B or Class AB with improved linearity, improved efficiency and reduced idle current.

Description

technical field [0001] The invention relates to the field of transistor amplifier circuits, in particular to a power amplifier with a bias boost circuit, which is used to enhance the linearity of the amplifier and reduce reactive current. Background technique [0002] This general-purpose type of amplifier is often used in high-frequency RF amplifiers, audio amplifiers, and other applications. In order to obtain a linear input-output relationship and high operating efficiency, the amplifier is typically operated at a conduction angle of approximately 180° (Class B) or slightly larger (Class AB) to avoid crossover distortion. [0003] Typically, such amplifiers require a DC bias circuit in order to establish the 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 described in US Pat. mode, as described in US Patent No. 5,548,248. [0004] However, in am...

AI Technical Summary

Problems solved by technology

This would inevitably lead to higher power dissipation at low power output levels in prior art circuits, thus resulting in an undesirable compromise in operating characteristics

[0005] The inventors have developed various techniques in the past including improved biasing circuits and bias boosting techniques, but these did not have the signal input to the amplifier circuit, or did not have a DC coupled signal input, which would have a negative impact on the biasing circuit and The operation of the coupled stage is unfavorable, making it design-limited

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