Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
1999-06-30
2001-06-05
Mottola, Steven J. (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
active
06242978
ABSTRACT:
BACKGROUND OF THE INVENTION
Spectral re-growth due to an amplifier's non-linear distortion characteristics has become an important issue in modern amplifier design. With the increased demand for channel allocations, closer channel spacing and new modulation techniques with their higher peak to average power ratios comes an increased demand for amplifiers exhibiting extremely high linearity. Class A amplifiers exhibit good linearity but they suffer from poor efficiency and high cost when high power levels are required. Class A/B amplifiers are more cost effective but suffer from poor linearity. Methods of correction exist which can improve an amplifier's linearity. Pre-correction with linearizers will improve an amplifier's linearity, but since such linearizers are open-loop they exhibit stability problems with time and temperature. Feedforward correction of an amplifier will improve the amplifier's linearity, but this type of correction requires a higher power amplifier due to losses inherent with the feedforward correction. Feedback correction will improve an amplifier's linearity, but these are usually band width limited.
A feedforward system in the prior art of interest takes the form of the U.S. Pat. No. to D. Danielsons 5,850,162. In that system, an output amplifier having a non-linear signal response characteristic is linearized by selecting a preceding amplifier in a multi-stage amplifier network and providing feedforward overcorrection to the preceding amplifier to compensate for the non-linear signal response characteristics of the output amplifier.
It is contemplated that an amplifier having non-linear response characteristic can be linearized with a corrected input signal obtained from another amplifier which has been selected as exhibiting similar non-linear characteristics as the amplifier to be corrected. Also, it is contemplated that practicing the invention will result in efficiencies rivaling that of a Class A/B amplifier while yielding linearity that exceeds that of a Class A amplifier with wide bandwidth operation.
It is further contemplated that the invention herein may reduce the memory-full and/or non-memory-full distortions of an amplifier having a non-linear signal characteristic. Memory-full distortions refer to time dependent or historic distortions whereas non-memory-full distortions refer to non-time dependent distortions.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, apparatus and method are provided for linearizing a first amplifier having a non-linear signal response characteristic to an input signal wherein the amplifier is located between a signal source and a load. This is accomplished by selecting a second amplifier that exhibits a non-linear signal response characteristic similar to that of the first amplifier. A first portion of the input signal obtained from the signal source is applied to the second amplifier to generate an output signal. A determination is made as to whether there is any difference between a second portion of the input signal and the output signal and a difference signal is provided in accordance therewith. The difference signal is then phase inverted to obtain an inverted difference signal. This inverted difference signal is combined with the second portion of the input signal to provide a corrected input signal. The corrected input signal is applied to the first amplifier to obtain a corrected output signal therefrom.
In accordance with another aspect of the present invention, the memory-full and/or non-memory-full distortions of an output amplifier having a non-linear signal response characteristic to an applied input signal is reduced by providing a corrected input signal which is a memory-full and/or non-memory-full in an inverse or negative manner. This aspect of the invention is accomplished by selecting an amplifier having similar memory-full and/or non-memory-full distortions as the output amplifier. A portion of the input signal is applied to the selected amplifier, which is a scaled version of the output amplifier, to produce memory-full and/or non-memory-full distortions. These distortions mimic the distortions of the output amplifier. The output of the selected amplifier contains both the amplified version of the input signal and the memory-full and/or non-memory-full distortions of the input signal. A portion of the input signal is subtracted from a portion of the output of the selected amplifier. This difference represents the negative of the memory-full and/or non-memory-full distortions of the selected amplifier. At least a portion of the negative distortions of the selected amplifier are combined with at least a portion of the original input signal. The combined input signal, with the negative distortions of the selected amplifier, is applied to the output amplifier. The resulting output of the output amplifier is essentially distortion free and contains essentially no memory-full and/or non-memory-full distortions.
REFERENCES:
patent: 4453133 (1984-06-01), Travis
patent: 5258722 (1993-11-01), Jeffers
patent: 5621354 (1997-04-01), Mitzlaff
patent: 5781069 (1998-07-01), Baskin
patent: 5850162 (1998-12-01), Danielsons
patent: 0367458 A2 (1990-05-01), None
PCT International Search Report Dated Oct. 30, 2000 (3 pgs.) for PCT/US00/18101.
Harris Corporation
Mottola Steven J.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
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