Amplifiers – With amplifier bypass means
Reexamination Certificate
2002-09-19
2004-04-27
Choe, Henry (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06727751
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a distortion compensation amplifier that compensates for distortion arising in an amplifier when the amplifier amplifies a signal. This invention particularly relates to a distortion compensation amplifier that, by reducing the distortion suppression required in a distortion removal loop, enables amplification with distortion compensation of signals over a broader band of frequencies than heretofore.
DESCRIPTION OF THE PRIOR ART
The transmitter unit of a base station used in a mobile phone system, Personal Handy phone System (PHS) or other such mobile telecommunications system uses an amplifier to amplify signals to be wirelessly transmitted. Since distortion occurs during the amplification of the signals by the amplifier, the transmitter unit is equipped with a circuit for compensating for the distortion.
FIG. 5
shows an example of a conventional distortion compensation amplifier unit. Specifically, it shows the configuration of a common amplifier capable of performing distortion compensation by the feedforward method. (A common amplifier uses an amplifier to amplify signals that include multiple frequency components.)
The illustrated common amplifier unit is equipped with three directional combiners
1
,
5
and
9
, two vector adjusters
2
and
7
, a main amplifier
3
, two delay lines
4
and
6
, an auxiliary amplifier
8
, a pilot signal generator
10
, a receiver
11
and a control circuit
12
. Also shown are an input terminal C and an output terminal D of the common amplifier unit.
The directional combiner
1
, directional combiner
5
and the group of components between them (the vector adjuster
2
, main amplifier
3
and delay line
4
) constitute a circuit that functions as a distortion detection loop.
A multifrequency signal input to the distortion detection loop through the input terminal C is divided by the directional combiner
1
. One divided signal is adjusted in amplitude and phase by the vector adjuster
2
, amplified to a desired power by the main amplifier
3
, and input to the directional combiner
5
. Another divided signal is delayed by the delay line
4
and input to the directional combiner
5
. The directional combiner
5
outputs (part of) the amplified signal received from the main amplifier
3
to the delay line
6
, adds the (remaining part of) the amplified signal and the delayed input multifrequency signal received from the delay line
4
to detect the distortion component generated in the (remaining part) of the amplified signal in the main amplifier
3
, and outputs the result to the vector adjuster
7
.
The distortion occurring in the main amplifier
3
when the input multifrequency signal is amplified is, for example, intermodulation distortion.
Preferably, the distortion detection loop detects and outputs to the vector adjuster
7
only the distortion component produced in the main amplifier
3
. Insofar as effective distortion compensation can be practically realized, however, the distortion component detected by the distortion detection loop can include other components such as the input multifrequency signal.
The amplified signal sent from the main amplifier to the directional combiner
5
contains the multifrequency signal component amplified by the main amplifier
3
and the distortion component generated in the main amplifier
3
. On the other hand, the multifrequency signal sent from the delay line
4
to the directional combiner
5
does not contain the distortion component. By appropriately setting the amount of signal amplitude and phase adjustment by the vector adjuster
2
and the amount of signal delay by the delay line
4
, therefore, the distortion component can be detected in the directional combiner
5
by subjecting the two input signals to reverse-phase addition with respect to the input multifrequency signals. In the reverse-phase addition, the two signals are, for example, added (synthesized) at the same delay, same amplitude and opposite phase (phase difference of 180 degrees).
The delay line
6
, vector adjuster
7
, auxiliary amplifier
8
and directional combiner
9
constitute a distortion removal loop downstream of the directional combiner
5
.
In the distortion removal loop, the amplified signal output from the directional combiner
5
is delayed by the delay line
6
and input to the directional combiner
9
. The distortion component detected by the directional combiner
5
is adjusted in amplitude and phase by the vector adjuster
7
, amplified to a desired power by the auxiliary amplifier
8
, and input to the directional combiner
9
. The directional combiner
9
removes the distortion component from the amplified signal by adding the delayed amplified signal received from the delay line
6
and the distortion component received from the auxiliary amplifier
8
and outputs the result from the output terminal D.
The amplified signal sent from the delay line
6
to the directional combiner
9
contains the multifrequency signal component amplified by the main amplifier
3
and the distortion component generated in the main amplifier
3
. On the other hand, the singal sent from the auxiliary amplifier
8
to the directional combiner
9
contains the distortion component. By appropriately setting the amount of amplitude and phase adjustment of the distortion component by the vector adjuster
7
and the signal delay by the delay line
6
, therefore, the distortion component can be removed from the amplified signal in the directional combiner
9
by subjecting the two input signals to reverse-phase addition with respect to the distortion component.
The pilot signal generator
10
generates and outputs a prescribed signal as a pilot signal. The pilot signal is synthesized with the input multifrequency signal transmitted from the vector adjuster
2
to the main amplifier
3
. The receiver
11
receives part of the signal output by the directional combiner
9
and detects the pilot signal contained in the received part of the signal. The vector adjuster
7
is controlled to diminish the pilot signal detected by the receiver
11
. The distortion removal loop is thus optimized by using the pilot signal. The control circuit
12
controls the vector adjuster
2
based on the result of pilot signal detection by the receiver
11
. The two vector adjusters
2
and
7
are provided to set optimum adjustment values in the respective loops.
The common amplifier unit shown in
FIG. 5
deals not only with the input multifrequency signal and the distortion component it causes to be generated in the main amplifier
3
but also with the pilot signal and the distortion component it causes to be generated in the main amplifier
3
. In the interest of simplicity, however, the ensuing explanation and the associated drawings will touch on only the input multifrequency signal and the distortion component generated as a result thereof and no explanation or elements in the drawings will be presented regarding the pilot signal and the distortion component generated as a result thereof.
FIG. 6
is a graph showing an example of the amplified signal output by the main amplifier
3
when a two-component signal composed of signal component of a frequency of f
0
[MHz] and a signal component of a frequency f
1
[MHz] is input to the input terminal C of the common amplifier unit. The horizontal axis of the graph represents frequency [MHz] and the vertical axis represents signal level. It can be seen from this graph that when the main amplifier
3
amplifies the input multifrequency signal composed of the signal components of frequencies f
0
and f
1
, intermodulation distortion occurs that consists of low-frequency side distortion at a frequency of {f
0
−(f
1
−f
0
)} [MHz] and high-frequency distortion at a frequency of {f
1
+(f
1
−f
0
)} [MHz]. The interval between two frequencies at which these distortions occur increases in proportion as the bandwidth of the signal input through the input terminal C
Funada Kiyoshi
Takenaga Kotaro
Yonenaga Hiroichi
Choe Henry
Hitachi Kokusai Electric Inc.
Wenderoth , Lind & Ponack, L.L.P.
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