Amplifiers – With pilot frequency control means
Reexamination Certificate
1999-12-14
2001-03-27
Pascal, Robert (Department: 2817)
Amplifiers
With pilot frequency control means
C330S149000, C330S151000
Reexamination Certificate
active
06208204
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a feed-forward amplifier for use mainly in the high-frequency band and, more particularly, to a feed-forward amplifier which has a distortion detector for detecting a nonlinear distortion component generated by a main amplifier and a distortion canceller which amplifies the detected distortion component by an auxiliary amplifier and injects it again to the output of the main amplifier, thereby canceling the distortion component.
In
FIG. 1
there is depicted the basic configuration of a feed-forward amplifier. The feed-forward amplifier comprises two signal cancellers for compensating for distortions that the main amplifier produces. One of the signal cancellers is a distortion detector
11
and the other a distortion canceller
12
. The distortion detector
11
is made up of an input path
8
, a main amplifier signal path
13
, and a linear signal path
14
. The distortion canceller
12
is made of up a main signal path
15
, a distortion injection path
16
, and an output path
9
. The main amplifier signal path
13
is formed by a cascade connection of a variable attenuator
17
, a variable phase shifter
18
and a main
20
amplifier
19
, whereas the linear signal path
14
is formed by a delay line
28
and a phase inverter
29
. In the main signal path
15
there is connected a delay line
21
, whereas in the distortion injection path
16
there are connected in cascade a variable attenuator
22
, a variable phase shifter
23
and an auxiliary amplifier
24
. Reference numerals
25
,
26
and
27
denote a power
25
divider, a power combiner/divider and a power combiner, which are simple no-loss power divider and simple power combiners each formed by a transformer circuit, a hybrid circuit or the like.
A description will be given first of the basic operation of the feed-forward amplifier. An input signal to the feed-forward amplifier is divided by the power divider
25
to two signals for input the main amplifier signal path
13
and the linear signal path
14
. In this case, the variable attenuator
17
and the variable phase shifter
18
in the main amplifier signal path
13
are adjusted so that the signals on the main amplifier signal path
13
and the linear signal path
14
are equal in amplitude but opposite in phase to each other. The “opposite phase” condition is met by setting an appropriate amount of phase shift between the input and output terminals of the power divider
25
or power combiner/divider
26
, or through utilization of a phase inversion in the main amplifier
19
. The distortion detector
11
of such a construction detects a difference component between the main amplifier signal path
13
and the linear signal path
14
. It is this difference component that is the distortion component the main amplifier
19
generates. On account of this, the above circuit arrangement is commonly referred to as a distortion detector.
The output from the distortion detector
11
is divided by a power/combiner divider
26
to two outputs that are provided to the main signal path
15
and the distortion injection path
16
. The input to the main signal path
15
is the sum of the output from the main amplifier signal path
13
and the output from the linear signal path
14
. The input to the distortion injection path
16
is the difference between the output from the main amplifier signal path
13
and the output from the linear signal path
14
. The variable attenuator
22
and the variable phase shifter
23
in the distortion injection path
16
are adjusted so that the signals on the main signal path
15
and the distortion injection path
15
are equal in amplitude but opposite in phase at the output end of the distortion canceller
12
. As the result of this, the distortion components by the main amplifier
19
are injected into the distortion canceller
12
in the opposite-phase but equal-amplitude relation, and hence they can be cancelled.
The above is an ideal distortion compensating operation of the feed-forward amplifier. In practice, however, it is not easy to maintain perfect balance in the respective circuits of the distortion detector
11
and the distortion canceller
12
. And even if their initialization is perfect, amplifier characteristics vary with ambient temperature, the power supply and so forth; hence, it is extremely difficult to provide stable and excellent balance over a long period of time.
To maintain the balance of the distortion detector
11
and the distortion canceller
12
of the feed-forward amplifier, there has been proposed an automatic adjustment method using a pilot signal, for example, in Japanese Patent Application Laid-Open Gazette No. 1-198809 entitled “Automatic Adjuster for Feed-forward Amplifier.” A device based on such a scheme is described in “Extremely Low-Distortion Multi-Carrier Amplifier for Mobile Communication System—Self-Adjusting Feed-forward Amplifier (SAFF-A)” The Institute of Electronics, Information and Communication Engineers of Japan, Technical Report, RCS90-4, 1990.
In
FIG. 2
there is shown in block form an example of the configuration of the feed-forward amplifier using the pilot signals. As depicted, the feed-forward amplifier is provided with: a first pilot injector
32
connected to the input path
8
of the distortion detector
11
to multiplex a first pilot signal PL
1
from a first pilot signal generator
31
onto a transmission signal; a first pilot signal extractor
33
connected between the power combiner/divider
26
and the variable attenuator
22
to extract the pilot signal PL
1
; a second pilot injector
35
connected between stages of the main amplifier
19
to inject a second pilot signal PL
2
from a second pilot signal generator
34
into the transmission signal; and a second pilot signal extractor
36
connected to the output path
9
of the distortion canceller
12
to detect the second pilot signal PL
2
. The levels of the first and second pilot signals PL
1
and PL
2
extracted by the first and second pilot signal extractors
33
and
36
are detected by first and second pilot level detectors
37
and
38
, respectively, and the level detected outputs are provided to a controller
39
. The controller
39
controls the variable attenuators
17
and
22
and the variable phase shifters
18
and
23
. That is, the first and second pilot signals PL
1
and PL
2
are used to detect the balance of the distortion detector
11
and the distortion canceller
12
; and the detected balance is appropriately adjusted using the first variable attenuator
17
and the first phase shifter
18
inserted in the main amplifier signal path
13
and the second variable attenuator
22
and the second variable phase shifter
23
inserted in the distortion injection path
16
of the distortion canceller
12
. By this, the distortions produced by the main amplifier
19
are compensated for. To achieve the balance of the circuits
11
and
12
, the variable attenuators
17
and
22
and the variable phase shifters
18
and
23
are electrically controlled on a stepwise basis to minimize the levels of the pilot signals, for example, by such a simple control algorithm as the perturbation method or steepest descent method or by an adaptive control algorithm based on the least square estimation method. Such automatic control can easily be implemented by a microcomputer.
To process pilot signals in such an automatic adjustment circuit, there has been proposed a simple method using single-frequency pilot signals (for instance, Japanese Pat. Appln. No. 3-49688 entitled “Feed-forward Amplifier”). This method permits simplification of the circuit configuration but involves the necessity for raising the level of the pilot signal to enhance the sensitivity of its detection because the optimum operating point in this method is set at a point of the lowest level of the pilot signal detection. In this instance, if an interference signal such as leakage power of other devices or noise gets mixed into the pilot signal detection band in the feed-forward amplifie
Narahashi Shoichi
Nojima Toshio
Suzuki Yasunori
Connolly Bove Lodge & Hutz
Nguyen Patricia T.
NTT Mobile Communications Network Inc.
Pascal Robert
LandOfFree
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