Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2001-03-29
2002-07-09
Shingleton, Michael B (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S151000
Reexamination Certificate
active
06417731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distortion-compensated amplifier device that, when amplifying the signal by a main amplifier, compensates a distortion that is generated in the main amplifier with use of a circuit comprised of a distortion-detecting loop and a distortion-compensating loop and a pre-distortor, or a method of performing such distortion-compensated amplification. More particularly, the invention concerns a technique for realizing excellent compensation of the distortion.
2. Description of the Related Art
In a mobile wireless communication system such as, for example, a portable telephone system, a base station apparatus and a mobile station apparatus have been performing wireless communication of a signal. Also, there is a case where between the base station apparatus and the mobile station apparatus there is provided a relay station apparatus for relaying wireless communication. In this case, the relay station apparatus receives and amplifies the signal that is wireless-transmitted from the base station apparatus, and wirelessly transmits this amplification signal to the mobile station apparatus.
In the above-described base station apparatus or the relay station apparatus, it has been performed to amplify, for example, a signal becoming an object to be transmitted with use of an amplifier (a main amplifier). However, in such a main amplifier, due to its non-linearity characteristic, in case the level of the input signal is high, it inconveniently happens that a distortion occurs. Accordingly, it becomes necessary to eliminate the distortion (i.e. compensate the distortion) from the amplification signal.
As an amplifier device having a circuit for eliminating the above-described distortion from the amplification signal there is known, for example, a feed forward type distortion-compensated amplifier device. This distortion-compensated amplifier device has a distortion-detecting loop and a distortion-compensating loop. The distortion-detecting loop amplifies the signal by the main amplifier and simultaneously detects a distorted component from this amplification signal. The distortion-compensating loop eliminates the distortion component that has been detected from the amplification signal that is output from the main amplifier. It is to be noted that, as one example, such a distortion-compensated amplifier device has a construction wherein a circuit construction portion regarding a pre-distortor
63
has been omitted from the circuit construction illustrated in
FIG. 9
, as later described.
However, even in case compensating the distortion by the above-described distortion-compensated amplifier device, when inconveniently the following signal is input to the distortion-compensated amplifier device, at the following time the following inconvenience occurs. The signal is the one that inconveniently contains peak powers that instantaneously occur as in the case of, for example, a multi-carrier signal or a CDMA (Code Division Multiple Access) signal. Said time is when such peak powers inconveniently reach the non-linearity region of the main amplifier. Said inconvenience is that, in the instant of such reach, the amount of signal canceled (the amount of cancel of the input signal other than the distortion component) at the distortion-detecting loop placed under the control of feed forward control gets degraded. For this reason, the level of the signal (originally, the signal corresponding to the distortion component) that is output from the distortion-detecting loop inconveniently increases.
Here, in
FIG. 8
there is illustrated an example of the model that has been prepared by simplifying the distortion-detecting loop. In this model, a signal that is input is distributed by a distributor K
1
. With respect to one distribution signal, vector adjustment (the adjustment of the amplitude and phase) is performed using a vector adjuster K
2
. Also, the (one) distribution signal after the adjustment of the vector and the other distribution signal are composed by a composer K
3
, whereby a composite signal is output. In this case, in the vector adjuster K
2
, vector adjustment is performed so that the two signals, which are to be composed by the composer K
3
, may have the same amplitude (a state where the amplitudes are the same) and opposite phases (a state where the phases are displaced 180° from each other). As a result of this, in the composer K
3
, the two signals that are to be composed together cancel each other by this composing.
In this model, it is known that the amount of signals canceled in the distortion-detecting loop, W, is expressed in the form of the following equation. It is to be noted that the d in the equation represents the amplitude deviation (dB) and the p represents the phase deviation (deg).
(First Equation)
W=10 log(1+10
d/10
−2×10
d/20
×cos p) (1)
Specifically, in the distortion-detecting loop, the vector adjuster K
2
(e.g. a vector adjuster
62
in
FIG. 9
as later described) equipped in this loop is controlled so that the level of the signal (e.g. the level of the distorted component detected by a level detector
72
in
FIG. 9
as later described) may become minimum (i.e. so that the amount of cancel of the input signal in the loop may become maximum).
However, assume that, for example, in case the instantaneous peak powers such as those described above are inconveniently input, for some reason or other, the operational balance of the distortion-detecting loop has collapsed 1 dB. Then, the amount of signal canceled in the loop degrades to approximately 18 dB. In this case, assume that the loop was so far at all times operating with an amount of signal cancel of, for example, 30 dB or more. Then, a signal (distorted component) the level of that is even approximately 12 dB higher than in an ordinary case is inconveniently input to an error amplifier equipped to the loop. (The amplifier is the one for amplifying the distortion component detected by the distortion-detecting loop, and is e.g. an error amplifier
70
in
FIG. 9
as later described.)
And, once an excessively high level of signal has been input to the error amplifier, the amount of distortion that occurs in this error amplifier increases. Thereby, the amount of distortion occurring from the distortion-compensated amplifier device as a whole (the amount of the distortion remaining, and contained, in the amplification signal that is output from the distortion-compensated amplifier device) also increases. Assume that, further, the excessively high level of input signal to the error signal has reached a gain-saturation region (the region where the gain is saturated) or a phase non-linearity region (the region where the phase of the output signal is deviated from a flat straight line). Then, the operational balance of the distortion-compensating loop collapses with the result that the amount of signal canceled in the loop (the amount of distortion-compensated) is degraded. Therefore, the signal is inconveniently output from the distortion-compensated amplifier device without having sufficiently suppressed its distortion occurring in the main amplifier.
As a construction for solving the above-described problem of input in excess, for example, a construction of adding a pre-distortor to the main amplifier is known. In this construction, it is intended to cancel the distortion that occurs in the main amplifier, by the distortion that is generated in the pre-distortor. By this cancellation, it is possible to approach the gain linearity (that the gain is linear) of the main amplifier or the phase flatness (that the phase of the output signal goes along a flat straight line) to an ideal state. It is thereby possible to improve the distortion compensation characteristic of the distortion-compensated amplifier device.
Here, in
FIG. 9
there is illustrated an example of the circuit construction of the feed forward type distortion-compensated amplifier device that is equipped with the above-describ
Dosaka Junya
Funada Kiyoshi
Sera Yasuo
Yamakawa Junichiro
Hitachi Kokusai Electric Inc.
Shingleton Michael B
Wenderoth , Lind & Ponack, L.L.P.
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