Amplifiers – With pilot frequency control means
Reexamination Certificate
2003-06-04
2004-10-05
Choe, Henry (Department: 2817)
Amplifiers
With pilot frequency control means
C330S151000
Reexamination Certificate
active
06801083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a feedforward amplifier that, in a distortion detection loop, uses a main amplifier to amplify a plurality of signal groups wherein each has a different frequency band, and in a distortion compensation loop, also compensates for the distortion that arises in said main amplifier and particularly to a feedforward amplifier that is able to perform precise distortion compensation on a plurality of wideband signal groups as a whole without adopting broadband frequency-band characteristics for the auxiliary amplifier used to amplify the distortion detected by the distortion detection loop.
2. Description of the Prior Art
For example, in base station units and relay station units used for mobile communications, a multi-carrier signal that contains a plurality of carriers at stipulated frequency intervals that are each modulated appropriately is transmitted wirelessly after high-frequency amplification. Unless the amplifier used for high-frequency amplification has sufficient linearity, various kinds of distortion including intermodulation distortion and the like may occur. This distortion becomes an impediment to achieving normal and high-quality communication. For this reason, the amplifiers used for the amplification of multi-carrier signals are required to have good linearity over the entire frequency band to which the multi-carrier signal belongs.
One example of a method of achieving an ultra-low-distortion amplifier suited to the amplification of a multi-carrier signal is the feedforward (FF) amplification scheme.
Here in this Specification, within the FF amplification scheme, the signal path from the signal input terminal via the main amplifier to the signal output terminal, namely the signal path for conveying the signal to be amplified and the amplified signal is referred to as the “main line.”
In addition, in the FF amplification scheme, a distortion detection path that couples a signal branching from a point after the main amplifier in the main line to a signal branching from a point before the main amplifier in the main line. In this Specification, the loop consisting of the main line and the distortion detection path is called the distortion detection loop.
Moreover, in the distortion detection loop, the electrical lengths of the signal paths over which both the signal conveyed along the main line and the signal conveyed along the distortion detection path are equal to each other, and, if both signals have mutually opposite phases at the same amplitude, then with the aforementioned signal coupling action, it is possible to cancel the carrier-wave components and extract a signal equivalent to the distortion arising in the main amplifier and its peripheral circuits.
Moreover, in the FF amplification scheme, a distortion compensation path is provided to recouple the signal extracted by the distortion detection loop, namely a signal equivalent to the distortion, to the signal on the main line. In this Specification, the loop consisting of the main line and the distortion compensation loop is called the distortion compensation loop.
Moreover, signal delay in the distortion compensation loop is compensated for in the main line and as long as adjustment of the amplitude and phase is performed appropriately in the distortion compensation loop so that the distortion components contained in the signal on the main line have the same amplitude and the opposite phase from the distortion signal obtained from the distortion compensation loop, it is possible to compensate for the distortion occurring in the main amplifier.
FIG. 3
shows an example of the constitution of a conventional FF amplifier.
In the FF amplifier shown in the figure, three directional couplers (hybrid)
41
,
46
and
51
are utilized to form a distortion detection loop L
11
consisting of the main line and the distortion detection path and a distortion compensation loop L
12
consisting of the main line and the distortion compensation path.
Specifically, the signal path from the signal input terminal P
2
via the first directional coupler
41
, first variable attenuator
42
, first variable phase shifter
43
, first coupler
61
, main amplifier (first amplifier)
44
, second directional coupler
46
, second coaxial delay line
47
, third directional coupler
51
and third coupler
63
to the signal output terminal Q
2
is equivalent to the main line.
In addition, the signal path from the signal input terminal P
2
via the first directional coupler
41
and first coaxial delay line
45
to the output terminal of the second directional coupler
46
is equivalent to the distortion detection path.
In addition, the signal path from the output terminal of the second directional coupler
46
via the second coupler
62
, second variable attenuator
48
, second variable phase shifter
49
and auxiliary amplifier (second amplifier)
50
to the output terminal of the third directional coupler
51
is equivalent to the distortion compensation path.
Note that the terminating resistors R
11
and R
12
are connected to one input terminal of the first directional coupler
41
and one output terminal of the third directional coupler
51
as terminating dummy loads. These terminating resistors R
11
and R
12
have an impedance of Z
0
equal to the characteristic impedance of the path.
In addition, with the FF amplifier shown in the figure, the three couplers
61
,
62
and
63
and a control circuit
71
which has a control signal generation circuit
72
constitute the feedback control system which performs control using pilot signals and the like.
Here follows one example of the operation performed by the FF amplifier shown in the figure.
For example, when a multi-carrier signal is applied to the signal input terminal P
2
, this signal is input via the first directional coupler
41
to the first variable attenuator
42
and first variable phase shifter
43
, where its amplitude and phase are adjusted, and then further input to the main amplifier
44
where it is amplified. The signal amplified by the main amplifier
44
is input via the second directional coupler
46
and second coaxial delay line
47
to the third directional coupler
51
, and further output from the third directional coupler
51
via the signal output terminal Q
2
to the circuits after this FF amplifier. Note that the second coaxial delay line
47
is a delay line that compensates for the signal delay arising in the circuit constituting the distortion compensation loop L
12
, e.g., the auxiliary amplifier
50
.
In addition, the signal input from the signal input terminal P
2
is divided into two branches by the first directional coupler
41
. The two branches of the signal are the same signal from the standpoint of the constitution of component frequencies, and the signal branch supplied to the main line side is amplified by the main amplifier
44
, while the signal branch supplied to the distortion detection path side is supplied at roughly its original amplitude from the first directional coupler
41
via the first coaxial delay line
45
to the second directional coupler
46
. Note that the first coaxial delay line
45
is a delay line for compensating for the signal delay arising in the main amplifier
44
in particular.
The signal supplied via the first coaxial delay line
45
to the second directional coupler
46
is coupled by this second directional coupler
46
to the amplified signal that contains distortion components.
Specifically, the second directional coupler
46
divides the signal containing distortion components output from the main amplifier
44
into two branches. The two branches of the signal are the same signal from the standpoint of the constitution of component frequencies; one signal branch is supplied to the main line side while the other signal branch is supplied to the distortion compensation path side When this other signal branch is supplied to the distortion compensation path side, the second directional coupler
46
couples this other signal branch t
Ishigami Takeshi
Nanao Yoshinari
Choe Henry
Hitachi Kokusai Electric Inc.
Wenderoth , Lind & Ponack, L.L.P.
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