Amplifiers – With pilot frequency control means
Utility Patent
1998-11-13
2001-01-02
Mottola, Steven J. (Department: 2817)
Amplifiers
With pilot frequency control means
C330S151000
Utility Patent
active
06169450
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to power amplifiers, and in particular to linearizing the input/output transfer function for amplifiers, particularly high power Class AB power amplifiers.
High power, broad band power amplifiers are well known. These amplifiers may operate in a feed forward configuration, or may have other forms of linearization which are required when the main power amplifier operates, for example, as a Class AB amplifier. Although class A amplifiers usually produce less distortion than Class AB amplifiers, class A amplifiers are also less efficient than Class AB amplifiers. Thus, in order to retain the advantages of efficiency while minimizing distortion, Class AB amplifier configurations have been developed which implement various forms of error or distortion correction.
One form of error correction uses an injected quadrature modulated pilot signal to correct distortions in the input signal caused by the Class AB amplifier. In another error correction approach, a predistortion circuit in a first loop, using, for example, a gain-phase circuit, can be provided with various adjustments to produce a gain-phase signal from the original signal, so that when the gain-phase signal is input to the power amplifier, operating as a Class AB amplifier, the output is a corrected amplification of the original input signal to the amplifier arrangement.
Even in a properly adjusted amplifier arrangement using predistortion, a certain amount of instability can be observed. As a result, a second loop, using an error amplifier is employed and is tuned using, for example, the pilot signal noted above. While these remaining distortions can be attended to in the feed forward cancellation loop circuitry, for example, the quadrature pilot signal detection and cancellation circuitry, such as that described in U.S. Pat. No. 5,796,304, is again somewhat expensive.
The invention provides an advantageous approach toward maintaining an adequately linear input/output relationship in a high power Class AB power amplifier arrangement using a low cost approach employing a pilot signal, but requiring fewer components and able to adjust, within limits, drift and other parameter changes in the circuit.
SUMMARY OF THE INVENTION
The invention relates to an amplifier arrangement which includes a main amplifier in which feed-forward cancellation is applied. The invention features a comparison loop including a comparator which compares a signal input to the main amplifier with a signal output from the main amplifier to provide an error signal, a cancellation loop including correction circuitry which adjusts the error signal, a pilot signal generation circuit including an oscillation signal source, a coupler for coupling the pilot signal to the amplifier input, and a detector circuit connected to the output of the amplifier arrangement which provides control signals to the correction circuitry, the detector circuit extracting information from a chopped, quadrature modulated derivative of the pilot signal in the amplifier arrangement output to provide the control signals.
In another aspect, the invention relates to an amplifier configuration having a main amplifier having an input and an output, a pilot signal generator which generates a pilot signal, the pilot signal being coupled to the input of the main amplifier, a phase and a gain circuit in communication with the main amplifier to correct phase and gain distortion in an output signal at the output of the main amplifier, and a detection circuit which derives control signals from a chopped and quadrature modulated derivative of the pilot signal present in the output signal which controls a phase and a gain adjustment of the phase and gain correction circuit.
In yet another aspect, the invention relates to a method of correcting gain and phase distortion in an amplified signal output from an amplifier having an input and an output. The method features inputting a signal to be amplified at the input of the amplifier, injecting a pilot signal at the input of the amplifier, detecting a chopped, quadrature modulated pilot signal component in the output of the amplifier, and, using the detected pilot signal, generating phase and gain correction signals to provide phase and gain correction of the amplified output signal.
In another aspect, the invention relates to a method of reducing distortion in an amplified signal comprising encoding a constant-frequency, known, pilot signal with intelligence having at least two distinguishable modulation codes, chopping the encoded pilot signal, adding the encoded and chopped pilot signal to a signal to be amplified, amplifying the signal, detecting the amplified signal, including the injected, encoded, and chopped pilot signal, decoding the intelligence encoded on the pilot signal to obtain information indicative of the distortion in the amplified signal, and independently adjusting phase and amplitude circuit parameters based upon the information to reduce the distortion.
In yet another aspect, the invention relates to a method of reducing distortion in a signal amplified within an amplifier circuit including a plurality of feed-forward signal correction loops to produce an amplified signal. The method features introducing a pilot signal into only one of the correction loops, detecting the amplified signal including a chopped and quadrature modulated derivative of the introduced pilot signal to provide amplitude and phase correction signals, and adjusting phase and amplitude parameters within at least one of the plurality of feed-forward correction loops, based upon the amplitude and phase correction signals.
REFERENCES:
patent: 5455537 (1995-10-01), Larkin et al.
patent: 5796304 (1998-08-01), Gentzler
patent: 5815036 (1998-09-01), Yoshikawa et al.
Fish & Richardson P.C.
Mottola Steven J.
Powerwave Technologies Inc.
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