Amplifiers – With amplifier bypass means
Reexamination Certificate
2000-02-07
2001-08-14
Lee, Benny (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06275105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to feedforward power amplifiers, and more specifically to a method and circuit for conducting adaptive linearization of power amplifiers.
2. Brief Description of the Prior Art
RF power amplifiers are used in a wide variety of communications and other electronic applications. These amplifiers are made of one or more cascaded amplifier stages, each of which increases the level of the signal applied to the input of that stage by an amount known as the stage gain. Ideally, the input-to-output transfer of each stage is linear; that is, a perfect replica of the input signal increased in amplitude appears at the amplifier output. In reality, however, all RF amplifiers have a degree of non-linearity in their transfer characteristics. This non-linearity results in a distortion of the output signal so that it is no longer a perfect replica of the input. This distortion produces spurious signal components known as intermodulation products. Intermodulation products are undesirable because they cause interference, cross-talk and other deleterious effects on the performance of a system employing RF power amplifiers. Accordingly, the prior art reflects various methods and devices designed to reduce the distortion produced by RF power amplification.
Three methods have commonly been used in the prior art to reduce distortion: predistortion, feedback and feedforward. The main advantages of the feedforward approach over the two others methods are an unconditional stability over large frequency bandwidths without inherent frequency limitations, and a high degree of distortion cancellation irrespective of the order of the intermodulation products.
With the rapid development of satellites, mobiles, cellular radios and PCS communication systems, a common broadband power amplifier for a multi-channel usage is eagerly desired. This demand is stimulating continuous investigation of the feedforward linearization technique.
OBJECTS OF THE INVENTION
An object of the present invention is therefore to further improve performance of an adaptive feedforward amplifier through the use of the feedforward linearization technique.
SUMMARY OF THE INVENTION
More specifically, in accordance with the present invention, there is provided a method for adaptively linearizing a feedforward amplifier which, in operation, supplies an amplified output signal on a feedforward amplifier output and produces an error signal representative of distortion in the amplified output signal. This adaptive linearization method comprises controllably adjusting at least one feature of the error signal, and controlling the error signal feature adjusting in relation to the error signal and the feature-adjusted error signal. In this manner, the feature-adjusted error signal, when combined with the amplified output signal, substantially cancels distortion in the amplified output signal.
In accordance with preferred embodiments of the method of the invention:
the method further comprises combining the feature-adjusted error signal and the amplified output signal;
the error signal feature adjusting comprises: attenuating an amplitude of the error signal; shifting a phase of the error signal; and amplifying the amplitude-attenuated and phase-shifted error signal and producing a corresponding amplified error signal constituting the feature-adjusted error signal;
controlling of the error signal feature adjusting comprises: comparing the error signal and the feature-adjusted error signal and producing a corresponding output comparison signal; and controlling the error signal feature adjusting in response to the output comparison signal;
controlling of the error signal feature adjusting comprises: combining the error signal and the amplified error signal 180° out of phase with respect to each other and producing a corresponding output combination signal; detecting the power level of the output combination signal and producing a corresponding output power level signal; and controlling the error signal amplitude attenuating and the error signal phase shifting and thereby adjusting the amplitude and phase of the error signal in view of minimizing the output power level signal; and
controlling of the error signal feature adjusting comprises: comparing waveforms of the error signal and the amplified error signal and producing an output waveform comparison signal; and controlling the error signal amplitude attenuating and the error signal phase shifting and thereby adjusting the amplitude and phase of the error signal in view of keeping a complex ratio between the error signal and the amplified error signal substantially constant.
The present invention also relates to an adaptive linearization circuit for a feedforward power amplifier which, in operation, supplies an amplified output signal on a feedforward amplifier output and produces an error signal representative of distortion in the amplified output signal. This adaptive linearization circuit comprises:
a controllable signal feature-adjusting circuit responsive to the error signal for producing a feature-adjusted error signal; and
a comparator/controller circuit for comparing the error signal and the feature-adjusted error signal, and for controlling the signal feature-adjusting circuit in relation to the comparison between the error signal and the feature-adjusted error signal.
In operation, the controllable signal feature-adjusting circuit supplies a feature-adjusted error signal which, when combined with the amplified output signal, substantially cancels distortion in the amplified output signal.
The present invention further relates to an adaptive linearization circuit for a feedforward power amplifier which, in operation, supplies an amplified output signal on a feedforward amplifier output and produces an error signal representative of distortion in the amplified output signal. This adaptive linearization circuit comprises:
a controllable signal feature-adjusting circuit having an input responsive to the error signal and a feature-adjusted error signal delivering output; and
a comparator/controller circuit having a first input responsive to the error signal, a second input responsive to the feature-adjusted error signal, and a control output connected to the controllable signal feature adjusting circuit so that, in operation, the signal feature-adjusting circuit is controlled in relation to a comparison between the error signal and the feature-adjusted error signal.
In operation, the controllable signal feature-adjusting circuit supplies a feature-adjusted error signal which, when combined with the amplified output signal, substantially cancels distortion in the amplified output signal.
Further in accordance with the present invention, there is provided a feedforward amplifier for amplifying an input signal in order to produce an amplified output signal, comprising:
a main amplifier circuit responsive to the input signal for producing the amplified output signal supplied on a feedforward amplifier output;
a signal comparator circuit responsive to the input signal and the amplified output signal for comparing the input signal and the amplified output signal and, as a result of this comparison, supplying an error signal representative of distortion in the amplified output signal;
an adaptive linearization circuit comprising: a controllable signal feature-adjusting circuit responsive to the error signal for producing a feature-adjusted error signal; and a comparator/controller circuit for comparing the error signal and the feature-adjusted error signal, and for controlling the signal feature-adjusting circuit in relation to the comparison between the error signal and the feature-adjusted error signal; and
a coupling member for transmitting the feature-adjusted error signal to the feedforward amplifier output in order to combine the feature-adjusted error signal and the amplified output signal in order to substantially cancel distortion in the amplified output signal.
Still further in accordance with the present inv
Beauregard Francois
Bouchard Marco
Ghannouchi Fadhel M.
Kouki Ammar B.
Altera Law Group LLC
Amplix
Choe Henry
Lee Benny
LandOfFree
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