Amplification device

Details Amplification device Amplification device

2003-03-19

2004-11-16

Choe, Henry (Department: 2817)

Amplifiers

With amplifier bypass means

C330S149000

Reexamination Certificate

active

06819174

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an amplification device that has a distortion detection loop and distortion removal loop, and that compensates for the distortion that arises in an amplifier due to a feedforward scheme, and particularly to an amplification device intended to reduce costs.
2. Description of the Prior Art
For example, in base stations provided for mobile communications systems, when the signal subject to transmission is amplified with an amplifier, compensation for the distortion that arises in such an amplifier is performed in order to achieve wireless communication with minimal distortion while satisfying the radio regulations for leak power in adjacent channels and the like. In addition, one example of an amplification device used to perform the compensation of distortion is an amplification device that performs distortion compensation by means of the feedforward (FF) scheme.
FIG. 6
shows an example of the constitution of an amplification device that performs distortion compensation by means of the feedforward scheme.
With the amplification device shown in the figure, in the distortion detection loop, a directional coupler
71
divides the analog signal in the radio frequency (RF) band input from the input terminal P and subject to amplification, and a main amplifier
72
amplifies one branch of the divided signal while a delay line
73
delays the other branch of the divided signal, and a directional coupler
74
takes the amplified signal from the main amplifier
72
and subtracts the delayed other branch of the divided signal to detect the distortion arising in the main amplifier
72
. Here, the delay line
73
adjusts the timing of the processing of one branch of the divided signal and the other branch of the divided signal so that the distortion arising in the main amplifier
72
is detected by the directional coupler
74
.
In addition, with the amplification device shown in the figure, in the distortion removal loop, the signal amplified by the main amplifier
72
is delayed by a delay line
75
and the distortion detected by the distortion detection loop is amplified by an auxiliary amplifier
76
. A directional coupler
77
takes this delayed amplified signal from the main amplifier
72
and subtracts the amplified signal from the auxiliary amplifier
76
to obtain an amplified signal after compensation for the distortion in the amplified signal by the main amplifier
72
where the distortion components are reduced. This distortion-compensated amplified signal is then output from an output terminal Q. Here, the delay line
75
adjusts the timing of the processing of the signal amplified by the main amplifier
72
and the distortion detected by the distortion detection loop so that the distortion components in the signal amplified by the main amplifier
72
are removed.
Here, an example of the prior art is indicated by the circuit consisting of a modulator and the like as a distortion compensation circuit that uses a combination of a feedforward scheme and a pre-distortion scheme in the “distortion compensation circuit” recited in the publication of unexamined Japanese patent application (Kokai) No. JP-A-2000-212116 and in the circuit consisting of a delay circuit and the like as a pre-distortion scheme-based distortion compensation circuit that uses an image rejection-type frequency modulator in an up-converter and down-converter in the “base station used for wireless communication” recited in the publication of unexamined Japanese patent application (Kokai) No. JP-A-9-64780. Note that each of the techniques recited in the literature differ from the constitution and object of the present invention as recited hereinafter.
However, with a conventional amplification device based on the feedforward scheme as illustrated in
FIG. 6
above, the distortion detection loop is constituted by using a coaxial cable or filter or other delay means to delay harmonically the signal in the wireless frequency band, so there are problems in that a relatively large device footprint is required and achieving low costs is difficult.
The present invention is intended to solve these problems in the prior art and has as its object to provide an amplification device that has a distortion detection loop and distortion removal loop, and that can achieve low costs when compensating for the distortion that arises in an amplifier due to a feedforward scheme.
SUMMARY OF THE INVENTION
In order to achieve the aforementioned object, the amplification device according to the present invention has a distortion detection loop that amplifies the signal subject to amplification with an amplifier and detects the distortion arising in said amplifier, and a distortion removal loop that removes the distortion detected by the distortion detection loop from the signal amplified by said amplifier, and the distortion detection loop and distortion removal loop compensate for the distortion that arises in said amplifier by means of a feedforward scheme, based on a distortion detection loop constituted as follows.
To wit, in the distortion detection loop, among the two branches of the digital baseband signal subject to amplification that is divided into two, a first digital modulation means uses one branch of the digital baseband signal to modulate a carrier signal, an amplifier amplifies the modulated signal obtained from the first digital modulation means, delay means delays the other branch of the digital baseband signal, a second digital modulation means that uses the other branch of the digital baseband signal delayed by the delay means to modulate a carrier signal, phase-change means changes the phase of the modulated signal obtained from the second digital modulation means, and distortion detection means detects the distortion arising in said amplifier from the signal amplified by the amplifier and the modulated signal whose phase is changed by the phase-change means.
Accordingly, for example, if a constitution is adopted such that a baseband signal in a frequency band lower than the wireless frequency band (the other digital baseband signal) is subject to delay by the delay means of the distortion detection loop and this baseband signal is converted to a signal in the wireless frequency band by means of modulation of the carrier frequency of the wireless frequency band after this delay, it is possible to achieve a smaller device footprint and lower cost than in the prior art, for example. In addition, because the constitution is such that a digital baseband signal is delayed, it is possible to achieve lower costs by the conversion to digital and the adjustment of the delay time can be automated to simplify the work of adjusting this delay time.
Here, various signals may be used as the signal subject to amplification, as signals subject to wireless transmission may be used, for example.
In addition, amplifiers of various constitutions may be used.
In addition, amplifiers typically suffer from intermodulation distortion and other types of distortion when amplifying signals.
In addition, various levels of precision may be used as the precision of detection of distortion by the distortion detection loop as long as they are of a degree that is effective in practical use, for example.
In addition, various levels of precision may be used as the precision of removal of distortion by the distortion removal loop (to wit, the precision of compensation for distortion) as long as they are of a degree that is effective in practical use, for example.
In addition, the digital baseband signal used may be, for example, a baseband frequency band which is a digital signal consisting of an I component and a Q component.
In addition, various signals may be used as the carrier signal used by the first digital modulation means and the carrier signal used by the second digital modulation means.
In addition, various modulation schemes may be used as the modulation scheme used by the first digital modulation means and the modulation scheme used by the second digital modul

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