Improved linear power amplifier

Abstract

A bias circuit for a radio frequency linear power amplifier having an input for selecting one of a plurality of operating modes varying in quiescent current of an bipolar transistor, a thermally responsive element for sensing a temperature, a circuit for biasing the output bipolar transistor, receiving said selecting input and incorporating said thermally responsive element, for maintaining linearperformance in each of said modes over a range of temperatures, and a filter 6, 41, 42, 43 for attenuating noise generated within the linear power amplifier. The use of a tank circuit at the collector of a power radio frequency transistor, having an inductor capable of handling the collector current, resonating with a capacitor at the design frequency, permits a reduction in the required inductance and therefore higher levels of integration. The tank circuit, including the self-inductance of the capacitor, is preferably designed to also resonate at the second harmonic of the design frequency,to provide improved linearity. The bias circuit may be bandwidth limited, to reduce noise and improve phase margin. Improved bias circuits increase efficiency for operating a radio frequency power amplifier in a linear operation range, with respect to changes in temperature Hfe and voltage, while maintaining low quiescent current. The bias circuits also maintain low noise levels.

Description

Background technique [0001] Typically, a linear power amplifier (LPA) is biased with a bias circuit about the operating point such that there is a linear relationship between the input signal and the amplified output signal. In class "A" or "AB" linear operation, this bias typically establishes a quiescent current through the power transistor. While other amplifier modes are theoretically possible, they produce various distortions of the signal. Therefore, both cost and complexity considerations typically point to an "A" or "AB" amplifier topology. See US 6333677 and US 6043714, expressly incorporated herein by reference. [0002] "Bias Circuits for GaAs HBT Power Amplifiers" by E. Jarvinen, S. Kalajo, M. Matilainew, 2001 IEEE MTT-S describes a typical known power amplifier design. [0003] With known class "A" or "AB" RF power amplifier designs, the signal at the collector of the power output transistor must be isolated from the supply (Vcc), and an inductor large enough t...

AI Technical Summary

Problems solved by technology

While this technique avoids bulky inductors, the transmission line itself has a large physical size and poses a similar dilemma

[0005] Silicon semiconductor technologies typically do not have sufficient gain, efficiency, linearity, and high noise to meet competing requirements in many high-frequency operating LPAs

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