Amplifiers – With amplifier bypass means
Reexamination Certificate
2000-02-15
2001-12-04
Pascal, Robert (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06326845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feedforward amplifier which is mainly used in a device of a base station of a mobile communication system.
2. Related Art of the Invention
In order to collectively amplify a large number of signal channels, recently, a device of a base station of a mobile communication system is requested to be provided with a power amplifier which is excellent both in efficiency and linearity. The linearity is realized by performing distortion compensation according to the feedforward system.
A feedforward amplifier is described by, for example, John L. B. Walker, “High-Power GaAs FET Amplifiers,” Artech House, 1993, p.p. 332 to 333.
FIG. 7
is a diagram showing an example of the configuration of a feedforward amplifier of the conventional art. As shown in the figure, in a feedforward amplifier
600
, an input terminal
1
allows an external signal to be input to the feedforward amplifier
600
. An output terminal
2
allows a signal to be output from the feedforward amplifier
600
to the external. A power divider
3
divides the input from the input terminal
1
into two signals, and supplies the signals to a vector adjuster
5
, and a delay circuit
7
of a coaxial cable, respectively.
A main amplifier
6
amplifies an input from the vector adjuster
5
. Directional coupler
51
receives the output of the main amplifier
6
outputs almost signals to delay circuit
9
from main port and outputs few signals to after-mentioned power combiner
8
from couple port. The power combiner
8
receives the output from the couple port of the directional coupler
51
and the output of the delay circuit
7
and outputs signals to a vector adjuster
33
. An error amplifier
71
amplifies an input from the vector adjuster
33
.
A power combiner
4
combines inputs from the delay circuit
9
and the error amplifier
33
with each other and supplies the resulting signal to the output terminal
2
. The characters a to j, e′ and f′ attached to the power divider
3
, the power combiner
4
, directional coupler
51
and the power combiner
8
indicate signal input/output ports of the devices, respectively.
The operation of the thus configured feedforward amplifier of the conventional art will be described.
First, an input signal which is input via the input terminal
1
and contains multi-channel components is divided into two signals by the power divider
3
. One of the two divided signals is amplified by the main amplifier
6
via the vector adjuster
5
. At this time, because of the nonlinearity of the main amplifier
6
, the signal which contains distortion components is generated.
The signal which is amplified by the main amplifer
6
, is supplied to input port d of the directional coupler
51
, and almost signal are output from the output port f and a few signal is output from the output port f′ to be supplied to the input port e′ of the power combiner
8
.
The other of the two divided signals is input to the input port e of the power combiner
8
, via the delay circuit
7
.
When the vector adjuster
5
and the delay circuit
7
are adjusted so that the input signal components of the input signals at the input ports e and e′ have the equal amplitude and opposite phases, a signal in which the input signal components are canceled each other and which contains only distortion components is output from the output port g.
The signal which is output from the output port f and contains the input signal components and the distortion components is input to the input port h of the power combiner
4
via the delay circuit
9
.
The distortion component signal output from the output port g is amplified by the error amplifier
71
via the vector adjuster
33
, and the amplified signal is input to the input port i of the power combiner
4
. When the vector adjuster
33
and the delay circuit
9
are adjusted so that the distortion components of the input signals at the input ports h and i have the equal amplitude and opposite phases, a signal in which the distortion components are canceled each other and which contains only the input signal components can be obtained from the output terminal
2
.
FIG. 8
shows frequency spectra of the signals at the ports a, d, g and j of FIG.
7
.
The feedforward amplifier of the conventional art has the following problems.
A first problem is as follows. In the configuration of
FIG. 7
, in order to suppress the distortion component produced in the main amplifier
6
in a broader frequency band, the band of the error amplifier
71
must be broadened. Actually, it is difficult to configure the error amplifier
71
so as to have flat characteristics both in amplitude and phase over a broad frequency band. Although distortion components produced in a region very close to the channel band can be sufficiently suppressed, therefore, there arises a problem in that those produced in a region of the band edge are more hardly suppressed.
The configuration of the conventional art has a second problem in that the power consumption of the main amplifier
6
is large. In order to reduce distortion, a class A amplifier is usually used as the main amplifier
6
. This means that the main amplifier produces lower distortion, but is lower in power efficiency and consumes a large power.
When a class AB amplifier is used so as to enhance the efficiency, distortion is increased and higher order intermodulation is caused, so that distortion is produced over a very wide frequency band. As a result, there arises a problem in that the above-mentioned feedforward system is not sufficient for canceling distortion components.
Specifically, distortion in a frequency band very close to the signal is canceled by the feedforward system, but that in frequency bands outside the band cannot be canceled because deviations in amplitude and phase are produced among paths.
A third problem is as follows. Each of delay elements used in the delay circuits
7
and
9
is configured by, for example, winding a coaxial cable in a spiral form. The cable is required to have a length of about 3 m. Therefore, there is a problem in that the delay elements occupy a large space and, in the case of a large power output, a large loss is caused by the power passing therethrough.
SUMMARY OF THE INVENTION
In order to solve the first problem, according to the first and second aspects of the invention, the feedforward amplifier is configured in the following manner.
A feedforward amplifier of the first present invention (corresponding to claim
1
) comprises:
a first power divider which divides an input signal into two signals;
a first vector adjuster which adjusts an amplitude and a phase of one of output signals which are divided by said first power divider;
a main amplifier which amplifies an output signal of said first vector adjuster;
a first delay circuit which delays another output signals which are divided by said first power divider;
a directional coupler which receives an output signal of said main amplifier and an output signal of said first delay circuit, and has a main port for outputting almost signals from the main amplifier and a couple port for outputting a few signals from the main amplifier;
a power combiner which receives an output signal of said couple port and an output signal of said first delay circuit,to output a combined signals thereof;
a second delay circuit which delays an output signal from said main port of said directional coupler;
an auxiliary amplifier block which amplifies an output signal from said power combiner; and
a power combiner which outputs a combined signal of an output signal of said second delay circuit, and an output signal of said auxiliary amplifier block,
said auxiliary amplifier block being
a broadband auxiliary amplifier block having at least two error amplifiers which amplify the output signal from said power combiner while splitting the output signal into respective frequency bands that do not overlap with each other.
A feedforward amplifier of the second present invention
Ishida Kaoru
Kosugi Hiroaki
Kugou Shin'ichi
Miyaji Masayuki
Choe Henry
Matsushita Electric - Industrial Co., Ltd.
Pascal Robert
Ratner & Prestia, PC
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