Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
1999-09-03
2001-07-03
Mottola, Steven J. (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S145000
Reexamination Certificate
active
06255908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linearizer for use in conjunction with a power amplifier, and to a linearizer channel amplifier using this linearizer for predistorting an input signal in view of cancelling signal distortions subsequently produced by the power amplifier.
2. Brief Description of the Prior Art
Microwave power amplifiers (solid state or travelling wave amplifiers) used in ground station transmitters and communication satellites should ideally be highly efficient and provide linear amplification over a wide range of input power. Obviously, the performance of these microwave power amplifiers is limited by the non-linearities of the inner parts or constituents. A wide variety of correction methods for microwave power amplifier's non-linearities have been proposed and implemented (e.g., power back-off, negative feedback, feed forward, etc.). However, in most cases the efficiency of the linearized amplifier drops significantly relatively to the efficiency of the non-linearized amplifier specially when this amplifier input is a high crest factor modulated signal such as a CDMA (Code Division Multiple Access), NPR (Noise Power Ratio), or other types of signals.
Predistortion is one of the best cost-effective approaches to reduce the level of non-linear distortion generated by microwave power amplifiers. Predistortion consists of introducing in the input microwave signal amplitude and phase distortion opposite to the distortion produced by the microwave power amplifier to thereby cancel any distortion and obtain at the output of the power amplifier a signal that is an amplified replica of the input signal with almost no power efficiency decrease. Therefore, the function of a predistorter circuit is to generate both inverse amplitude and phase non-linearities. Since the characteristics of a microwave power amplifier significantly change with temperature, the predistortion circuit has to maintain the overall performance of linearity of the system and to follow the amplifier changes.
OBJECT OF THE INVENTION
An object of the present invention is therefore to provide a linearizer for use in conjunction with power amplifiers, and to provide a linearizer channel amplifier using this linearizer for predistorting an input signal in view of cancelling signal distortion subsequently produced by the power amplifier.
SUMMARY OF THE INVENTION
More specifically, in accordance with the present invention, there is provided a linearizer channel amplifier for use in conjunction with a power amplifier, comprising a linearizer which comprises:
a) a splitter for splitting an input signal into first and second signal portions;
b) a first controllable signal-distorting and amplitude-adjusting path for distorting and adjusting the amplitude of said first signal portion;
c) a second controllable phase-shifting and amplitude-adjusting path for phase-shifting and adjusting the amplitude of said second signal portion; and
d) a combiner for combining the distorted and amplitude-adjusted first signal portion and the phase-shifted and amplitude-adjusted second signal portion to form a predistorted output signal;
whereby the predistorted output signal cancels a distortion subsequently produced by the power amplifier.
In accordance with preferred embodiments of the linearizer channel amplifier, the first path comprises a predistorter connected in series with a variable attenuator, the first path is a non-linear path and the variable attenuator is a controllable variable attenuator, the second path comprises a phase shifter connected in series with a variable attenuator, and the second path is a linear path, the phase shifter is a controllable phase shifter and the variable attenuator is a controllable variable attenuator.
The present invention also relates to a linearizer channel amplifier for use in conjunction with a power amplifier, comprising:
a) a controllable input variable-attenuator, drive-amplifier and power-limiter circuit for attenuating an input signal, amplifying the input signal and limiting the power of said input signal;
b) a linearizer comprising:
i) splitter for splitting into first and second signal portions the attenuated, amplified and power-limited input signal from the input variable-attenuator, drive-amplifier and power-limiter circuit;
ii) a first controllable signal-distorting and amplitude-adjusting path for distorting and adjusting the amplitude of said first signal portion;
iii) a second controllable phase-shifting and amplitude-adjusting path for phase-shifting and adjusting the amplitude of said second signal portion; and
iv) a combiner for combining the distorted and amplitude-adjusted first signal portion and the phase-shifted and amplitude-adjusted second signal portion to form a predistorted output signal;
c) a controllable output variable-attenuator and drive-amplifier circuit for attenuating the predistorted output signal and amplifying said predistorted output signal before supplying said predistorted output signal to said power amplifier; and
d) a controller for controlling the first and second paths in view of distorting and amplitude-adjusting the first signal portion and phase-shifting and amplitude-adjusting the second signal portion so as to produce a predistorted output signal which cancels a distortion subsequently produced by the power amplifier.
In accordance with preferred embodiments of the linearizer channel amplifier:
the first path comprises a predistorter connected in series with a first variable attenuator, and the second path comprises a phase shifter connected in series with a second variable attenuator;
the first path is a non-linear path, and the first variable attenuator is a first controllable variable attenuator, and the second path is a linear path, the phase shifter is a controllable phase shifter, and the second variable attenuator is a second controllable variable attenuator;
the controllable input variable-attenuator, drive-amplifier and power-limiter circuit comprises a third controllable variable attenuator, an input drive amplifier and a power limiter connected in series, and the controllable output variable-attenuator and drive-amplifier circuit comprises a fourth controllable variable attenuator connected in series with an output drive amplifier;
the controller is a digital controller comprising:
means for measuring the level of a condition of operation of the power amplifier;
means for selecting predistortion control parameters in relation to the measured level of the condition of operation; and
means for applying the selected predistortion control parameters to the controllable input and output circuits and to the first and second controllable paths in view of producing a predistorted output signal which cancels a distortion subsequently produced by said power amplifier;
the predistortion control parameter selecting means comprises:
a look-up table for storing predistortion control parameters associated to different levels of said condition of operation; and
means connected to the look-up table for selecting predistortion control parameters in relation to the measured level of the condition of operation.
In accordance with a more specific preferred embodiment of the present invention, the digital controller comprises:
a processor for measuring the level of a temperature of operation of the power amplifier through an interface;
a look-up table for storing predistortion control parameters related to different levels of the temperature of operation; and
the processor being connected to the look-up table for selecting predistortion control parameters in relation to the measured temperature level, and for applying through a digital-to-analog converter and a signal conditioner the selected predistortion control parameters to the first, second, third and fourth controllable variable attenuators and to the controllable phase shifter in view of producing a predistorted output signal which cancels a distortion subsequently produced by the power amplifier.
A linearizer channel ampl
Beauregard Francois
Ghannouchi Fadhel
Kouki Ammar B.
Touimer Said
Amplix
Mottola Steven J.
Quarles & Brady LLP
LandOfFree
Temperature compensated and digitally controlled amplitude... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Temperature compensated and digitally controlled amplitude..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Temperature compensated and digitally controlled amplitude... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2438248