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Linear power amplifier with distortion detection
| Details |
Inventors: Buer, Kenneth Vern; Corman, David Warren; Agar, Jr., Bill Tabano;
Assignee: Motorola, Inc. (Schaumburg, IL)
Primary Examiner: Mottola; Steven
Assistant Examiner:
Attorney, Agent or Firm: Gorrie; Gregory J.
A power amplifier (10) suitable for satellite cellular communication systems provides highly efficient linear amplification of noise-like RF signals that have multiple carriers spread over a large instantaneous bandwidth. The amount of distortion present in the output is detected (14, 16, 18) and a feedback signal is provided to control the bias point of the active devices. As drive levels increase, the increased harmonic distortion power detected causes the power amplifier bias to increase thus reducing distortion. The control circuit (20) continually re-biases the power amplifier (12) for maximum efficiency for a predetermined level of distortion. The control circuit (20) may be adjusted to maximize efficiency while maintaining an allowable distortion level over the entire dynamic range of the devices. |
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DETAILED DESCRIPTION OF THE DRAWINGS The present invention provides, among other things, a power amplifier that linearly amplifies noise-like multi-carrier signals over a wide range of power levels.
The present invention also provides a high efficiency RF power amplifier suitable for use in satellite telecommunication systems.
The present invention also provides an RF power amplifier suitable for fabrication on a Gallium Arsenide (GaAs) substrate.
FIG.
1 shows a block diagram of power amplifier 10 in accordance with a preferred embodiment of the present invention.
Power amplifier 10 includes power amplifier portion 12, sampler 14 coupled to an output of power amplifier portion 12, loop filter 16 coupled to sampler 14, power detector 18 coupled to filter 16, and bias control portion 20 coupled to power detector 18 and power amplifier portion 12.
Power amplifier portion 12 receives RF input signals from an input port of power amplifier 10 and provides an amplified output signal.
Preferably, power amplifier portion 12 comprises amplifier circuits that provide substantially linear amplification of the RF input signal.
For example class "A" type amplifiers are suitable, and a class "AB" type multistage amplifier circuit is preferable.
In the preferred embodiment, power amplifier portion 12 comprises a plurality of custom monolithic microwave integrated circuit (MMIC) devices (preferably between one and fifteen devices) fabricated on Gallium Arsenide (GaAs) substrates.
The MMIC devices desirably include between six and twelve Pseudomorphic High Electron Mobility Transistors (PHEMT) with 0.
25 micron gate lengths along with the associated matching and interconnect structures.
The MMICs may be fabricated, for example, using a Raytheon 06A MMIC process.
In one embodiment, power amplifier portion 12 includes nine MMIC device.
In this embodiment, five of the MMIC devices are medium power amplifier chips (MPA's) that include two gain stages with total gate widths between 0.
8 and 1.
6 millimeters.
In this embodiment, the other four MMICs are High power amplifiers (HPA's) that include two gain stages and having total gate widths between 2
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Telecommunications 
