U.S. patent application number 09/840181 was filed with the patent office on 2002-02-21 for feedforward amplifier.
Invention is credited to Horiguchi, Kenichi, Ikeda, Yukio, Nagano, Junichi, Nakayama, Masatoshi, Sakai, Yuji, Senda, Haruyasu.
Application Number | 20020021170 09/840181 |
Document ID | / |
Family ID | 17163756 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020021170 |
Kind Code |
A1 |
Nakayama, Masatoshi ; et
al. |
February 21, 2002 |
Feedforward amplifier
Abstract
A feedforward amplifier combines an input signal delayed by a
delay circuit with an output signal by a combiner; down-converts
the output of the combiner to a low frequency by a frequency
converter; extracts a distortion component from the output of-the
frequency converter; measures the distortion component by a power
detector; and controls a second vector regulator of a distortion
canceling loop by a controller such that the distortion component
measured becomes minimum.
Inventors: |
Nakayama, Masatoshi; (Tokyo,
JP) ; Horiguchi, Kenichi; (Tokyo, JP) ; Sakai,
Yuji; (Tokyo, JP) ; Ikeda, Yukio; (Tokyo,
JP) ; Nagano, Junichi; (Tokyo, JP) ; Senda,
Haruyasu; (Tokyo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
17163756 |
Appl. No.: |
09/840181 |
Filed: |
April 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09840181 |
Apr 24, 2001 |
|
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|
PCT/JP00/02202 |
Apr 5, 2000 |
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Current U.S.
Class: |
330/52 ;
330/151 |
Current CPC
Class: |
H03F 1/3229
20130101 |
Class at
Publication: |
330/52 ;
330/151 |
International
Class: |
H03F 003/66 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 1999 |
JP |
11-247458 |
Claims
What is claimed is:
1. A feedforward amplifier that includes a distortion detecting
loop having a first vector regulator, and a distortion canceling
loop having a second vector regulator, and that carries out
feedforward distortion compensation, said feedforward amplifier
comprising: a directional coupler for extracting a part of an
output signal; a first splitter for extracting a part of an input
signal; a delay circuit for delaying the input signal extracted by
said first splitter; a combiner for combining the input signal
delayed by said delay circuit with the output signal extracted by
said directional coupler; a local oscillator for generating a
signal of a prescribed frequency; a frequency converter for
down-converting an output of said combiner to a low frequency using
the signal generated by said local oscillator; a first filter for
passing a distortion component and for rejecting a signal component
of an output of said frequency converter; a distortion component
detector for measuring the distortion component output from said
first filter; and a second vector regulator controller for
controlling said second vector regulator of said distortion
canceling loop such that the distortion component measured by said
distortion component detector becomes minimum.
2. The feedforward amplifier according to claim 1, further
comprising: a third vector regulator interposed between said delay
circuit and said combiner for changing pass amplitude and pass
phase of an output of said delay circuit; a second splitter
interposed between said combiner and said first filter for dividing
a signal supplied to it; a second filter for passing a signal
component and for rejecting a distortion component of a signal
delivered by said second splitter; a signal component detector for
measuring the signal component output from said second filter; and
a third vector regulator controller for controlling said third
vector regulator such that the signal component measured by said
signal component detector becomes minimum.
3. The feedforward amplifier according to claim 1, further
comprising: a third vector regulator interposed between said delay
circuit and said combiner for changing pass amplitude and pass
phase of an output of said delay circuit; a second splitter
interposed between said combiner and said first filter for dividing
a signal supplied to it; a signal component detector for measuring
a signal component delivered by said second splitter; and a third
vector regulator controller for controlling said third vector
regulator such that the signal component measured by said signal
component detector becomes minimum.
4. The feedforward amplifier according to claim 3, wherein second
splitter is interposed between said combiner and said frequency
converter.
5. The feedforward amplifier according to claim 1, wherein said
distortion detecting loop comprises an input side splitter for
dividing the input signal, and a main amplifier for amplifying a
first part of the input signal divided by said input side splitter,
and wherein said first splitter further divides a second part of
the input signal divided by said input side splitter.
6. The feedforward amplifier according to claim 1, wherein said
distortion detecting loop comprises an input side splitter for
dividing the input signal, a main amplifier for amplifying a first
part of the input signal divided by said input side splitter, and
an intra-distortion-detecting-lo- op delay circuit for delaying a
second part of the input signal divided by said input side
splitter, and wherein said first splitter is interposed into a path
on an output side of said intra-distortion-detecting-loop delay
circuit.
7. A feedforward amplifier that includes a distortion detecting
loop having a first vector regulator, and a distortion canceling
loop having a second vector regulator, and that carries out
feedforward distortion compensation, said feedforward amplifier
comprising: a first splitter for extracting a part of an input
signal; a delay circuit for delaying the input signal extracted by
said first splitter; a third vector regulator for changing pass
amplitude and pass phase of an output of said delay circuit; a
local oscillator for generating a signal of a prescribed frequency;
a first frequency converter for down-converting an output of said
third vector regulator to a low frequency using the signal
generated by said local oscillator; a directional coupler for
extracting a part of an output signal; a second frequency converter
for down-converting an output of said directional coupler to a low
frequency using the signal generated by said local oscillator; a
combiner for combining an output of said first frequency converter
and an output of said second frequency converter; a second splitter
for dividing an output of said combiner; a first filter for passing
a distortion component and for rejecting a signal component of a
first output of said second splitter; a distortion component
detector for measuring the distortion component output from said
first filter; a second vector regulator controller for controlling
said second vector regulator of said distortion canceling loop such
that the distortion component measured by said distortion component
detector becomes minimum; a second filter for passing a signal
component and for rejecting a distortion component of a second
output of said second splitter; a signal component detector for
measuring the signal component output from said second filter; and
a third vector regulator controller for controlling said third
vector regulator such that the signal component measured by said
signal component detector becomes minimum.
8. A feedforward amplifier that includes a distortion detecting
loop having a first vector regulator, and a distortion canceling
loop having a second vector regulator, and that carries out
feedforward distortion compensation, said feedforward amplifier
comprising: a first splitter for extracting a part of an input
signal; a local oscillator for generating a signal of a prescribed
frequency; a first frequency converter for down-converting the
input signal extracted by said first splitter to a low frequency
using the signal generated by said local oscillator; a delay
circuit for delaying an output signal of said first frequency
converter; a third vector regulator for changing pass amplitude and
pass phase of an output of said delay circuit; a directional
coupler for extracting a part of an output signal; a second
frequency converter for down-converting an output of said
directional coupler to a low frequency using the signal generated
by said local oscillator; a combiner for combining an output of
said second frequency converter and a signal passing through said
third vector regulator; a second splitter for dividing an output of
said combiner; a first filter for passing a distortion component
and for rejecting a signal component of a first output of said
second splitter; a distortion component detector for measuring the
distortion component output from said first filter; a second vector
regulator controller for controlling said second vector regulator
of said distortion canceling loop such that the distortion
component measured by said distortion component detector becomes
minimum; a second filter for passing a signal component and for
rejecting a distortion component of a second output of said second
splitter; a signal component detector for measuring the signal
component output from said second filter; and a third vector
regulator controller for controlling said third vector regulator
such that the signal component measured by said signal component
detector becomes minimum.
Description
CROSS-REFERENCE TO THE RELATED APPLICATION
[0001] This application is a continuation of International
Application No. PCT/JP00/02202, whose international filing date is
Apr. 5, 2000, the disclosures of which Application are incorporated
by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a feedforward amplifier for
carrying out low distortion amplification in a radio frequency
band.
[0004] 2. Description of Related Art
[0005] A feedforward amplifier that achieves a low distortion
characteristic by feedforward distortion compensation is often used
as an amplifier for carrying out low distortion amplification in a
radio frequency band such as VHF, UHF and microwave frequency
bands. The feedforward distortion compensation can implement
favorable distortion compensation in principle, and has an
advantage of being able to configure a very low distortion, small
amplifier. However, it has a problem in that when the
characteristic of the amplifier varies because of ambient
temperature or deterioration with age, its distortion compensation
range is reduced and the distortion characteristic is impaired
significantly.
[0006] To solve the problem, a method is proposed that injects a
pilot signal into a loop constituting the feedforward distortion
compensation system, and controls the amplifier or the loop
constituting the feedforward system by detecting the pilot
signal.
[0007] FIG. 1 is a block diagram showing a configuration of a
feedforward amplifier disclosed in Japanese patent application
publication No. 7-77330. The technique is an example that injects
the pilot signal into the feedforward distortion compensation
system to control the feedforward system.
[0008] In FIG. 1, the reference numeral 1 designates an input
terminal of the amplifier; 2 designates a splitter for distributing
an input signal to two paths; 3 designates a first vector regulator
for electrically regulating the amplitude and phase of a signal
passing through the first path; 4 designates a main amplifier for
amplifying the input signal; 5 designates a delay circuit for
delaying the input signal distributed to the second path by the
splitter 2; 6 designates a splitter/combiner for distributing a
part of the output signal of the main amplifier 4 and for combining
the distributed output signal with a part of the input signal
passing through the delay circuit 5; 7 designates a directional
coupler; and 8 designates a pilot signal generator.
[0009] The reference numeral 101 designates a distortion detecting
loop that includes the splitter 2, first vector regulator 3, main
amplifier 4, delay circuit 5 and splitter/combiner 6 , and cancels
the input signal component by combining the input signal with the
output of the main amplifier 4, thereby extracting a distortion
component generated by the main amplifier 4. Here, the pilot signal
supplied from the pilot signal generator 8 is injected into the
output of the main amplifier 4 via the directional coupler 7. The
pilot signal is used for controlling a distortion canceling loop
102 as described later.
[0010] The reference numeral 9 designates a delay circuit; 10
designates a combiner; 11 designates a second vector regulator; 12
designates an auxiliary amplifier; 13 designates a directional
coupler; 102 designates the distortion canceling loop including the
delay circuit 9, combiner 10, second vector regulator 11, auxiliary
amplifier 12 and directional coupler 13. The reference numeral 14
designates a directional coupler; 15 designates an output terminal
of the amplifier; 16 designates a level detector; 17 designates a
pilot signal detector; and 18 designates a controller for
controlling the first vector regulator 3 and the second vector
regulator 11.
[0011] Next, the operation of the conventional feedforward
amplifier will be described.
[0012] The output signal of the main amplifier 4 passes through the
splitter/combiner 6, and its major part passing through the delay
circuit 9 is supplied to a first input terminal of the combiner 10
installed on the output side. The distortion component extracted by
the distortion detecting loop 101 appears at a terminal of the
splitter/combiner 6, passes through the second vector regulator 11,
is amplified by the auxiliary amplifier 12, and is input to the
second input terminal of the combiner 10. The combiner 10 combines
the output signal passing through the delay circuit 9 with the
distortion component amplified by the auxiliary amplifier 12 in the
same amplitude but in the opposite phase, thereby canceling the
distortion component and producing the output of small distortion
from the output terminal 15.
[0013] The optimizing control of the distortion detecting loop 101
in the feedforward amplifier is carried out as follows by
controlling the vector regulator 3.
[0014] The directional coupler 13 connected to the output of the
auxiliary amplifier 12 extracts a part of the signal, the level of
which is detected by the level detector 16. The minimum power level
of the signal indicates the best canceled state of the signal
component, in which the distortion detecting loop 101 is controlled
at the optimum state. Therefore, the controller 18 automatically
controls the first vector regulator 3 such that the power level
detected by the level detector 16 becomes minimum.
[0015] Besides, the optimizing control of the distortion canceling
loop 102 is carried out as follows by controlling the second vector
regulator 11.
[0016] The directional coupler 14 installed on the output side of
the feedforward amplifier extracts a part of the output signal, and
the pilot signal detector 17 detects the pilot signal included in
the output signal. The minimum level of the pilot signal indicates
the best regulated state of the distortion canceling loop 102.
Therefore, the controller 18 automatically controls the second
vector regulator 11 such that the pilot signal detected by the
pilot signal detector 17 becomes minimum.
[0017] Thus, the conventional feedforward amplifier implements the
optimum distortion compensation against the ambient temperature
variations and deterioration with age by optimally controlling the
two loops constituting the feedforward distortion compensation
system, that is, the distortion detecting loop 101 and the
distortion canceling loop 102.
[0018] As conventional feedforward amplifiers, many schemes other
than the foregoing method are proposed which carry out the control
of the feedforward system by injecting the pilot signal into the
loop. All these feedforward amplifiers exploiting the pilot signal
have a common problem in that they cannot help outputting the pilot
signal from the output terminal. Although the second vector
regulator 11 is controlled such that the pilot signal used for
controlling the distortion canceling loop 102 is canceled out in
principle, the pilot signal is not completely canceled in practice
because of the limited control accuracy or nonnegligible control
time of the feedforward system. Thus, it is unavoidable that the
pilot signal is output from the output terminal 15.
[0019] To solve this problem, a filter is often connected to the
output terminal of the feedforward amplifier to pass the desired
signal and reject the frequency of the pilot signal. However, to
achieve the control using the pilot signal at high accuracy, the
frequency of the desired signal must be close to that of the pilot
signal. Accordingly, it is unavoidable that the filter to separate
them becomes large in size and loss, bringing about an increase in
size and reduction in efficiency of the amplifier.
[0020] In view of this, some schemes are proposed that control the
feedforward distortion compensation system without utilizing the
pilot signal.
[0021] FIG. 2 is a block diagram showing another configuration of
the feedforward amplifier disclosed in Japanese patent application
publication No. 7-77330. In FIG. 2, the same or like portions to
those of FIG. 1 are designated by the same reference numerals, and
the description thereof is omitted here.
[0022] This feedforward amplifier lacks the pilot signal generator
8 of FIG. 1. It supplies part of the output signal extracted by the
directional coupler 14 to the distortion detector 19 for detecting
the distortion of the output signal to control the feedforward
system in such a manner that the distortion becomes minimum.
[0023] This configuration has the following problem.
[0024] Specifically, it is very difficult for the feedforward
amplifier to carry out the control by detecting the distortion
component of its output signal because the distortion component is
usually much smaller than the signal component by a factor from 50
dB to 60 dB. Therefore, the distortion detector 19 cannot be
realized in practice, or even if it is realized, its circuit
configuration will be complicated, resulting in an increase in its
size and cost.
[0025] Another conventional feedforward amplifier without using the
pilot signal is disclosed in Japanese patent application laid-open
No. 7-336153. FIG. 3 is a block diagram showing a configuration of
the feedforward amplifier. In FIG. 3, the same or like portions to
those of FIG. 2 are designated by the same reference numerals, and
the description thereof is omitted here. In FIG. 3, the reference
numeral 20 designates a controller for controlling the first vector
regulator 3; 21 designates a level detector; 22 designates a signal
suppressor; 23 designates a controller for controlling the second
vector regulator 11; 24 designates a delay circuit; and 25
designates a splitter. The reference numeral 103 designates a
distortion detecting loop that comprises the splitters 2 and 25,
the first vector regulator 3, the main amplifier 4, the delay
circuit 5 and the splitter/combiner 6. FIG. 4 is a block diagram
showing a configuration of the signal suppressor 22 as shown in
FIG. 3. In FIG. 4, the reference numeral 201 designates a vector
regulator, 202 designates a splitter/combiner, 203 designates a
delay circuit, 204 designates an amplifier, and 205 designates a
level detector.
[0026] The feedforward amplifier detects the distortion component
signal extracted by the directional coupler 13 by the level
detector 21, and controls the first vector regulator 3 by the
controller 20 such that the power level of the distortion component
signal becomes minimum, thereby carrying out the optimum control of
the distortion detecting loop 103. Although the directional coupler
13 is installed before the second vector regulator 11 in FIG. 3, it
can be provided after the auxiliary amplifier 12 as in FIG. 1
because the scheme of the optimizing control of the distortion
detecting loop 103 is the same as that of FIG. 1.
[0027] In FIG. 3, the pilot signal generator 8 as shown in FIG. 1
is not installed. Instead, the splitter 25 provided on the input
side of the feedforward amplifier extracts a part of the input
signal, and supplies it to the signal suppressor 22 via the delay
circuit 24. In addition, the directional coupler 14 on the output
side of the feedforward amplifier extracts a part of the output
signal, and supplies it to the signal suppressor 22.
[0028] The signal suppressor 22 has an internal configuration as
shown in FIG. 4. The input signal and output signal of the
feedforward amplifier supplied to the signal suppressor 22 are
combined by the signal suppressor 22 with the internal
configuration including the multi-staged vector regulators 201,
splitter/combiners 202 and delay circuits 203. Using the
multi-stage internal configuration of the signal suppressor can
cancel out the signal component by a factor of 50 dB to 60 dB,
leaving the distortion component included in the feedforward
amplifier. The distortion component is amplified by the amplifier
204, and detected by the level detector 205. The controller 23
controls the second vector regulator 11 such that the power level
of the distortion component is reduced, thereby carrying out the
optimizing control of the distortion canceling loop 102.
[0029] The conventional feedforward amplifier has a problem of
increasing size and complexity because it employs the signal
suppressor 22 including the multi-staged splitter/combiners 202,
vector regulators 201 and delay circuit 203. In addition, it has a
problem in that the adjustment is tedious of the many vector
regulators 201 and delay circuits 203 included in the signal
suppressor 22.
[0030] For example, even the slightest variations in the
amplification frequency involved in the change of the channels to
be amplified by the feedforward amplifier presents a problem of
requiring readjustment of all the vector regulators or all the
delay circuits of the signal suppressor 22.
[0031] In summary, the conventional feedforward amplifiers with the
foregoing configurations have the following problems. First, the
feedforward amplifiers that control their feedforward system by
injecting the pilot signal have a problem of outputting the
residual pilot signal resulting from the control process from the
output terminal.
[0032] Installing the output filter to eliminate the pilot signal
presents another problem of increasing the size and reducing the
efficiency of the amplifier because of the large size and loss of
the output filter.
[0033] As for the configuration as shown in FIG. 2 without the
pilot signal generator 8, which controls the feedforward system in
such a manner that the distortion becomes minimum by detecting the
distortion of the output signal, it is difficult to detect the
distortion signal smaller than the signal component by a factor of
50 dB to 60 dB to carry out the control. Thus, it presents a
problem in that the distortion detector cannot be implemented in
practice, or that even if it can be implemented, its configuration
will become complicated, large and expensive.
[0034] As for the feedforward amplifier as shown in FIGS. 3 and 4,
it presents a problem of increasing its size and complexity because
of the signal suppressor 22 with the multi-stage configuration.
[0035] In addition, since the slightest variations in the
amplification frequency requires the readjustment of all the vector
regulators and delay circuits of the signal suppressor 22, it has a
problem of requiring complicated adjustment in actual
operation.
SUMMARY OF THE INVENTION
[0036] The present invention is implemented to solve the foregoing
problems. Therefore, it is an object of the present invention to
provide a feedforward amplifier that can implement favorable
distortion characteristic unaffected by the variations in the
ambient temperature or deterioration with age, and that has a small
size and high efficiency, and can cope with the frequency changes
with ease.
[0037] According to a first aspect of the present invention, there
is provided a feedforward amplifier that includes a distortion
detecting loop having a first vector regulator, and a distortion
canceling loop having a second vector regulator, and that carries
out feedforward distortion compensation, the feedforward amplifier
comprising: a directional coupler for extracting a part of an
output signal; a first splitter for extracting a part of an input
signal; a delay circuit for delaying the input signal extracted by
the first splitter; a combiner for combining the input signal
delayed by the delay circuit with the output signal extracted by
the directional coupler; a local oscillator for generating a signal
of a prescribed frequency; a frequency converter for
down-converting an output of the combiner to a low frequency using
the signal generated by the local oscillator; a first filter for
passing a distortion component and for rejecting a signal component
of an output of the frequency converter; a distortion component
detector for measuring the distortion component output from the
first filter; and a second vector regulator controller for
controlling the second vector regulator of the distortion canceling
loop such that the distortion component measured by the distortion
component detector becomes minimum.
[0038] According to this, the feedforward amplifier can obviate the
need for employing a circuit configuration operating at a high
frequency in the control for minimizing the distortion component of
the second vector regulator in the distortion canceling loop. This
offers an advantage of being able to facilitate implementing the
favorable distortion characteristic resistant to variations in the
ambient temperature or deterioration with age, to facilitate
reduction in size and increase in efficiency, and to cope with the
frequency change of the input signal by varying the local
oscillation frequency used for the frequency conversion that
converts the output of the combiner to the low frequency by the
frequency converter.
[0039] Here, the feedforward amplifier can further comprise: a
third vector regulator interposed between the delay circuit and the
combiner for changing pass amplitude and pass phase of an output of
the delay circuit; a second splitter interposed between the
combiner and the first filter for dividing a signal supplied to it;
a second filter for passing a signal component and for rejecting a
distortion component of a signal delivered by the second splitter;
a signal component detector for measuring the signal component
output from the second filter; and a third vector regulator
controller for controlling the third vector regulator such that the
signal component measured by the signal component detector becomes
minimum.
[0040] According to this, the feedforward amplifier can obviate the
need for the distortion component detector and signal component
detector to measure the distortion component and signal component
at the radio frequency. This offers an advantage of being able to
improve the detection accuracy, and to cancel out the signal
component without failure at high accuracy using the input signal
and output signal in spite of the variations in the circuit
characteristic due to the deterioration with age or ambient
temperature variations, thereby implementing good feedforward
distortion compensation.
[0041] The feedforward amplifier can further comprise: a third
vector regulator interposed between the delay circuit and the
combiner for changing pass amplitude and pass phase of an output of
the delay circuit; a second splitter interposed between the
combiner and the first filter for dividing a signal supplied to it;
a signal component detector for measuring a signal component
delivered by the second splitter; and a third vector regulator
controller for controlling the third vector regulator such that the
signal component measured by the signal component detector becomes
minimum.
[0042] According to this, the feedforward amplifier can obviate the
second filter for passing the signal component and for rejecting
the distortion component of the first low frequency signal
distributed by the second splitter, which offers an advantage of
being able to implement the feedforward amplifier with the reduced
size and cost by an amount of removing the second filter.
[0043] The second splitter can be interposed between the combiner
and the frequency converter.
[0044] According to this, the feedforward amplifier can detect in
the radio frequency band the output power obtained by combining the
output of the third vector regulator and the part of the output
signal extracted by the directional coupler. It offers an advantage
of being able to implement the cancellation of the signal component
by the combining at practical accuracy, and to carry out the
control of the feedforward distortion compensation system at high
accuracy.
[0045] The distortion detecting loop can comprise an input side
splitter for dividing the input signal, and a main amplifier for
amplifying a first part of the input signal divided by the input
side splitter, wherein the first splitter can further divide a
second part of the input signal divided by the input side
splitter.
[0046] According to this, the feedforward amplifier can obviate the
need for installing a splitter on the main path of the input signal
from the input terminal of the feedforward amplifier to the
splitter/combiner via the main amplifier, that is, on the path of
the signal constituting the major part of the output signal of the
feedforward amplifier. Thus, it offers an advantage of being able
to prevent the reduction in the total gain of the amplifier due to
the loss of the splitter, and to implement a favorable distortion
characteristic resistant to the variations in the ambient
temperature or deterioration with age.
[0047] The distortion detecting loop can comprise an input side
splitter for dividing the input signal, a main amplifier for
amplifying a first part of the input signal divided by the input
side splitter, and an intra-distortion-detecting-loop delay circuit
for delaying a second part of the input signal divided by the input
side splitter, wherein the first splitter can be interposed into a
path on an output side of the intra-distortion-detecting-loop delay
circuit.
[0048] According to this, the feedforward amplifier can utilize the
delay circuit in the distortion detecting loop as a part of the
delay circuit for delaying the input signal, which is installed on
the path of the input signal to be combined with the output signal.
Thus, it offers an advantage of being able to miniaturize the delay
circuit by an amount corresponding to the delay the input signal
undergoes through the delay circuit in the distortion detecting
loop, thereby reducing the total size of the amplifier.
[0049] According to a second aspect of the present invention, there
is provided a feedforward amplifier that includes a distortion
detecting loop having a first vector regulator, and a distortion
canceling loop having a second vector regulator, and that carries
out feedforward distortion compensation, the feedforward amplifier
comprising: a first splitter for extracting a part of an input
signal; a delay circuit for delaying the input signal extracted by
the first splitter; a third vector regulator for changing pass
amplitude and pass phase of an output of the delay circuit; a local
oscillator for generating a signal of a prescribed frequency; a
first frequency converter for down-converting an output of the
third vector regulator to a low frequency using the signal
generated by the local oscillator; a directional coupler for
extracting a part of an output signal; a second frequency converter
for down-converting an output of the directional coupler to a low
frequency using the signal generated by the local oscillator; a
combiner for combining an output of the first frequency converter
and an output of the second frequency converter; a second splitter
for dividing an output of the combiner; a first filter for passing
a distortion component and for rejecting a signal component of a
first output of the second splitter; a distortion component
detector for measuring the distortion component output from the
first filter; a second vector regulator controller for controlling
the second vector regulator of the distortion canceling loop such
that the distortion component measured by the distortion component
detector becomes minimum; a second filter for passing a signal
component and for rejecting a distortion component of a second
output of the second splitter; a signal component detector for
measuring the signal component output from the second filter; and a
third vector regulator controller for controlling the third vector
regulator such that the signal component measured by the signal
component detector becomes minimum.
[0050] According to this, the feedforward amplifier can obviate the
need for employing radio frequency connecting wire as the
connecting wire on the input side of the combiner that combines the
output of the third vector regulator and the output signal
extracted by the directional coupler, thereby miniaturizing the
amplifier. In addition, the feedforward amplifier can utilize a low
frequency circuit configuration after combining the output of the
third vector regulator and the output signal extracted by the
directional coupler. Thus, it offers an advantage of being able
facilitate reducing the size and cost of the amplifier.
[0051] According to a third aspect of the present invention, there
is provided a feedforward amplifier that includes a distortion
detecting loop having a first vector regulator, and a distortion
canceling loop having a second vector regulator, and that carries
out feedforward distortion compensation, the feedforward amplifier
comprising: a first splitter for extracting a part of an input
signal; a local oscillator for generating a signal of a prescribed
frequency; a first frequency converter for down-converting the
input signal extracted by the first splitter to a low frequency
using the signal generated by the local oscillator; a delay circuit
for delaying an output signal of the first frequency converter; a
third vector regulator for changing pass amplitude and pass phase
of an output of the delay circuit; a directional coupler for
extracting a part of an output signal; a second frequency converter
for down-converting an output of the directional coupler to a low
frequency using the signal generated by the local oscillator; a
combiner for combining an output of the second frequency converter
and a signal passing through the third vector regulator; a second
splitter for dividing an output of the combiner; a first filter for
passing a distortion component and for rejecting a signal component
of a first output of the second splitter; a distortion component
detector for measuring the distortion component output from the
first filter; a second vector regulator controller for controlling
the second vector regulator of the distortion canceling loop such
that the distortion component measured by the distortion component
detector becomes minimum; a second filter for passing a signal
component and for rejecting a distortion component of a second
output of the second splitter; a signal component detector for
measuring the signal component output from the second filter; and a
third vector regulator controller for controlling the third vector
regulator such that the signal component measured by the signal
component detector becomes minimum.
[0052] According to this, the feedforward amplifier can configure
all the circuit components after the frequency conversion by using
the low frequency components. Thus, it offers an advantage of being
able to facilitate reducing the size and cost of the amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] FIG. 1 is a block diagram showing a configuration of a
feedforward amplifier disclosed in Japanese patent application
publication No. 7-77330;
[0054] FIG. 2 is a block diagram showing another configuration of
the feedforward amplifier disclosed in Japanese patent application
publication No. 7-77330;
[0055] FIG. 3 is a block diagram showing a configuration of a
feedforward amplifier disclosed in Japanese patent application
laid-open No. 7-336153;
[0056] FIG. 4 is a block diagram showing a configuration of the
signal suppressor of the feedforward amplifier disclosed in
Japanese patent application laid-open No. 7-336153;
[0057] FIG. 5 is a block diagram showing a configuration of an
embodiment 1 of the feedforward amplifier in accordance with the
present invention;
[0058] FIG. 6 is a block diagram showing a configuration of an
embodiment 2 of the feedforward amplifier in accordance with the
present invention;
[0059] FIG. 7 is a block diagram showing a configuration of an
embodiment 3 of the feedforward amplifier in accordance with the
present invention;
[0060] FIG. 8 is a block diagram showing a configuration of an
embodiment 4 of the feedforward amplifier in accordance with the
present invention;
[0061] FIG. 9 is a block diagram showing a configuration of an
embodiment 5 of the feedforward amplifier in accordance with the
present invention;
[0062] FIG. 10 is a block diagram showing a configuration of an
embodiment 6 of the feedforward amplifier in accordance with the
present invention;
[0063] FIG. 11 is a block diagram showing a configuration of an
embodiment 7 of the feedforward amplifier in accordance with the
present invention; and
[0064] FIG. 12 is a block diagram showing a configuration of an
embodiment 8 of the feedforward amplifier in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0065] The embodiments of the present invention will now be
described with reference to the accompanying drawings.
[0066] Embodiment 1
[0067] FIG. 5 is a block diagram showing a configuration of an
embodiment 1 of the feedforward amplifier in accordance with the
present invention. In FIG. 5, the reference numeral 1 designates an
input terminal of the amplifier; 2 designates a splitter (input
side splitter) for delivering the input signal supplied from the
input terminal 1 to two paths; 3 designates a first vector
regulator for electrically adjusting the amplitude and phase of the
signal passing through the first path; 4 designates a main
amplifier for amplifying the input signal; 5 designates a delay
circuit (a delay circuit in the distortion detecting loop) for
delaying the input signal that is delivered by the splitter 2 and
passes through the second path; and 6 designates a
splitter/combiner for dividing a part of the output signal of the
main amplifier 4, for supplying a first part of that signal to the
delay circuit 9, and for combining a second part of the signal and
the part of the input signal passing through the delay circuit 5 to
be supplied to a directional coupler 13.
[0068] The reference numeral 103 designates a distortion detecting
loop comprising the splitters 2 and 25, the first vector regulator
3, the main amplifier 4, the delay circuit 5 and the
splitter/combiner 6. It cancels out the input signal component by
combining the input signal with the output of the main amplifier 4,
thereby extracting the distortion component of the main amplifier
4.
[0069] The reference numeral 9 designates the delay circuit; 10
designates a combiner; 11 designates a second vector regulator; 12
designates an auxiliary amplifier; 13 designates the directional
coupler for extracting part of the output signal; 102 designates a
distortion canceling loop comprising the delay circuit 9, the
combiner 10, the second vector regulator 11, the auxiliary
amplifier 12 and the directional coupler 13. The reference numeral
14 designates a directional coupler; and 15 designates an output
terminal of the amplifier. The reference numeral 20 designates a
controller for controlling the first vector regulator 3; 21
designates a level detector; 24 designates a delay circuit for
delaying the input signal extracted by a splitter 25; and 25
designates the splitter (first splitter) for extracting a part of
the input signal.
[0070] The reference numeral 51 designates a combiner for combining
the input signal delayed by the delay circuit 24 with the output
signal extracted by the directional coupler 14; 52 designates a
local oscillator for generating a signal of a prescribed frequency;
53 designates a frequency converter for down-converting the output
of the combiner 51 to a low frequency signal using the signal
output from the local oscillator 52; 54 designates a filter (first
filter), a bandpass filter for rejecting the signal component and
for passing the distortion component of the signal output from the
frequency converter 53; 55 designates a power detector (distortion
component detector) for measuring the distortion component output
from the filter 54; and 56 designates a controller (second vector
regulator controller) for controlling the second vector regulator
11 of the distortion canceling loop 102 such that the distortion
component detected by the power detector 55 becomes minimum.
[0071] Next, the operation of the present embodiment 1 will be
described.
[0072] In the present embodiment 1 of the feedforward amplifier,
the output signal of the main amplifier 4 passes through the
splitter/combiner 6, and the major part thereof passes through the
delay circuit 9 to be supplied to the first input terminal of the
combiner 10 installed on the output side. The distortion component
extracted by the distortion detecting loop 103 appears at a
terminal of the splitter/combiner 6, passes through the directional
coupler 13 and second vector regulator 11, and is amplified by the
auxiliary amplifier 12 to be input to the second input terminal of
the combiner 10. The combiner 10 combines the output signal passing
through the delay circuit 9 with the distortion component amplified
by the auxiliary amplifier 12 in the same amplitude but in the
opposite phase to cancel the distortion component, thereby
producing the output with little distortion from the output
terminal 15.
[0073] The feedforward amplifier carries out the optimizing control
of the distortion detecting loop 103 as follows by controlling the
vector regulator 3.
[0074] Specifically, the level detector 21 detects the distortion
component signal extracted by the directional coupler 13, and the
controller 20 controls the first vector regulator 3 such that the
power level of the distortion component becomes minimum. Thus, the
optimum control of the distortion detecting loop 103 is carried
out. In this case, the directional coupler 13 can be installed
after the auxiliary amplifier 12 without any problem.
[0075] On the other hand, the combiner 51 is supplied with the part
of the signal extracted by the splitter 25 installed at the input
side of the feedforward amplifier via the delay circuit 24. The
combiner 51 is also supplied with the part of the output signal of
the feedforward amplifier from the directional coupler 14 on the
output side. Thus, the combiner 51 combines the output signal of
the feedforward amplifier supplied from the directional coupler 14
with the input signal extracted by the splitter 25 installed at the
input side. By combining the input signal with the output signal in
the opposite phase but with the same amplitude, the signal
component of the output signal of the feedforward amplifier is
canceled out, leaving only the distortion component.
[0076] The delay circuit 24 is installed to place the input signal
and the output signal in the opposite phase but in the same
amplitude at the combiner 51.
[0077] To bring the input signal and output signal in the opposite
phase but in the same amplitude perfectly at the combiner 51 is
difficult because of the accuracy of the circuit components. It is
practical to assume that the signal component is canceled out by a
factor of about 30 dB. The ratio of the signal component to the
distortion component of the feedforward amplifier is from 50 dB to
60 dB. Accordingly, the signal component is greater than the
distortion component by 20 dB to 30 dB even at the output of the
combiner 51. Taking account of this, the frequency converter 53
down-converts the output of the combiner 51 to a sufficiently lower
frequency using the output of the local oscillator 52, and the
filter 54, rejecting the signal component and passing the
distortion component, extracts only the distortion component. The
power of the distortion component is detected by the power detector
55. When the power of the distortion component is minimum, the
distortion canceling loop 102 is adjusted to the optimum state of
the feedforward distortion compensation system. Therefore, the
controller 56 controls the second vector regulator 11 such that the
power detected by the power detector 55 becomes minimum.
[0078] Incidentally, it is very difficult to fabricate a filter
capable of extracting only the distortion component directly from
the radio frequency output of the combiner 51 without
down-converting it.
[0079] As described above, since the present embodiment 1 does not
use the pilot signal, the pilot signal is not produced from the
output terminal 15. Thus, the present embodiment 1 can obviate the
filter for eliminating the pilot signal, and offers an advantage of
being able to miniaturize the feedforward amplifier with ease.
[0080] In addition, since the present embodiment 1 can prevent the
efficiency of the amplifier from being decreased by the loss of the
filter, it can configure a high efficiency amplifier, thereby
offering an advantage of being able to promote the miniaturization
and improve the efficiency of devices utilizing the feedforward
amplifier.
[0081] Furthermore, since the present embodiment 1 cancels out the
signal component by the combiner 51 that combines the input signal
extracted by the splitter 25 with the output signal extracted by
the directional coupler 14, the power difference between the
frequency components of the signal and of the distortion passing
through the filter 54 can be a feasible value from 30 dB to 40 dB,
for example. Thus, it offers an advantage of being able to
implement the feedforward amplifier enabling the reduction in its
size and cost.
[0082] Moreover, since the present embodiment 1 detects the power
of the distortion component using the low frequency filter 54 after
down-converting the radio-frequency signal to the low frequency by
the frequency converter 53, it is unnecessary to achieve signal
suppression of about 60 dB in the radio frequency as the
feedforward amplifier of FIGS. 3 and 4, but the suppression of
about 30 dB is sufficient. Therefore, the multi-stage signal
suppressor 22 as shown in FIG. 4 is not required, offering an
advantage of being able to implement a small size, practical
feedforward amplifier.
[0083] In addition, the present embodiment 1 can easily cope with
the frequency change in amplification by varying the oscillation
frequency of the local oscillator 52. In this case, employing a
voltage controlled oscillator (VCO) as the local oscillator 52
enables the oscillation frequency to be electrically controlled
easily, offering an advantage of being able to implement a
feedforward amplifier that can flexibly deal with the change in the
amplification frequency.
[0084] Embodiment 2
[0085] FIG. 6 is a block diagram showing a configuration of an
embodiment 2 of the feedforward amplifier. In FIG. 6, the same or
like portions to those of FIG. 5 are designated by the same
reference numerals, and the description thereof is omitted here. In
FIG. 6 , the reference numeral 57 designates a splitter (second
splitter) interposed between the combiner 51 and the filter 54 for
dividing the signal; 58 designates a filter (second filter), a
bandpass filter for rejecting the distortion component and passing
the signal component of the signal delivered by the splitter 57; 59
designates a power detector (signal component detector) for
measuring the power of the signal component output from the filter
58; 60 designates a controller (third vector regulator controller)
for controlling a third vector regulator 61 such that the signal
component measured by the power detector 59 becomes minimum; and 61
designates the third vector regulator.
[0086] Next, the operation of the present embodiment 2 will be
described.
[0087] A part of the input signal divided by the splitter 25 passes
through the delay circuit 24 and the third vector regulator 61 to
be supplied to the combiner 51. The combiner 51 combines the input
signal with the output signal extracted by the directional coupler
14, and the frequency converter 53 down-converts the output of the
combiner 51. The splitter 57 delivers a first part of the output of
the frequency converter 53 to the filter 54 that passes only the
distortion component to be detected by the power detector 55.
[0088] The splitter 57 supplies a second part of the output to the
filter 58 so that the power detector 59 detects the power level of
the signal component.
[0089] To improve the accuracy of the cancellation of the signal
component by the combiner 51 that combines the input signal with
the output signal for the cancellation, the controller 60 controls
the third vector regulator 61 such that the power level detected by
the power detector 59 becomes minimum.
[0090] As for the distortion component, on the other hand, the
power detector 55 detects its power level and supplies it to the
controller 56 that controls the second vector regulator 11 such
that the power level becomes minimum. The control of the second
vector regulator 11 by the controller 56 is carried out
independently of the control of the third vector regulator 61 by
the controller 60.
[0091] Although the third vector regulator 61 is installed on the
path on the input signal side, it can be interposed into the path
on the output signal side from the directional coupler 14.
[0092] As described above, the present embodiment 2 can achieve
similar advantages of the embodiment 1. In addition, it can always
carry out the cancellation of the signal component at high accuracy
by the combiner 51 using the input signal and output signal, in
spite of the changes in the characteristics of the splitter 25,
delay circuit 24, directional coupler 14 and combiner 51 due to the
deterioration with age or ambient temperature variations. Thus, the
present embodiment 2 can reduce the residual signal component due
to insufficient cancellation to a favorable level, and reduce the
(adverse) effect of the residual signal component on the power
detection of the distortion component by the power detector 55.
Therefore, the power detector 55 can detect the power of the
distortion component at high detection accuracy, and the controller
56 can control the second vector regulator 11 satisfactorily,
thereby always maintaining the feedforward distortion compensation
at a good condition.
[0093] Furthermore, even when the frequency of the amplification
changes, since the frequency characteristics of the splitter 25,
delay circuit 24, directional coupler 14 and combiner 51 can be
compensated for by adjusting the third vector regulator 61, the
combiner 51 can always cancel the signal component at high
accuracy, thereby implementing satisfactory feedforward distortion
compensation.
[0094] Embodiment 3
[0095] FIG. 7 is a block diagram showing a configuration of the
present embodiment 3 of the feedforward amplifier. In FIG. 7, the
same or like portions to those of FIG. 6 are designated by the same
reference numerals, and the description thereof is omitted
here.
[0096] The present embodiment 3 of the feedforward amplifier is
configured by eliminating the filter 58 for passing the signal
frequency component from the configuration as shown in FIG. 6.
[0097] Next, the operation of the present embodiment 3 will be
described.
[0098] The accuracy of the cancellation of the signal component by
the combiner 51 is determined by the accuracy of the components of
the system, and is about 30 dB at best. Accordingly, the signal
component occupies the major portion of the output of the frequency
converter 53. As a result, it usually presents little problem to
eliminate the filter for passing only the signal component from
before the power detector 59 for detecting the power level of the
signal component.
[0099] Thus, the configuration as shown in FIG. 7 that removes the
filter 58 for passing the signal frequency component from the
configuration as shown in FIG. 6 can not only achieve the
advantages of the foregoing embodiment 2, but also offer an
advantage of being able to implement the reduction in size and cost
of the feedforward amplifier.
[0100] Embodiment 4
[0101] FIG. 8 is a block diagram showing a configuration of the
present embodiment 4 of the feedforward amplifier. In FIG. 8, the
same or like portions to those of FIG. 7 are designated by the same
reference numerals, and the description thereof is omitted here. In
FIG. 8, the reference numeral 62 designates a splitter (second
splitter) for dividing the output of the combiner 51; and 63
designates a radio-frequency power detector (signal component
detector) for detecting the power of the signal delivered by the
splitter 62.
[0102] Next, the operation of the present embodiment 4 will be
described.
[0103] The output of the combiner 51 is divided by the splitter 62,
and the first part thereof is supplied to the frequency converter
53 that down-converts it to the low frequency. The low frequency
signal passes through the filter 54 for passing the distortion
component frequency and is supplied to the power detector 55 so
that the controller 56 controls the second vector regulator 11 such
that the power level of the distortion component detected by the
power detector 55 becomes minimum.
[0104] The second part delivered by the splitter 62 is directly
supplied to the radio-frequency power detector 63 that detects its
power level. The controller 60 controls the third vector regulator
61 such that the power level becomes minimum to reduce the signal
component in the output of the combiner 51, thereby improving the
detection accuracy of the distortion component by the level
detector 21.
[0105] As described in the foregoing embodiment 3, although the
signal component in the output of the combiner 51 is canceled to
some extent, it still occupies the major portion of the output.
Accordingly, the present embodiment 4 directly detects the output
power of the combiner 51 in the radio frequency band, and controls
the third vector regulator 61 such that the power becomes minimum.
Thus, the present embodiment 4 can implement the cancellation of
the signal component by the combiner 51 at practical accuracy,
offering an advantage of being able to provide the feedforward
amplifier capable of controlling the feedforward distortion
compensation system at high accuracy.
[0106] Embodiment 5
[0107] FIG. 9 is a block diagram showing a configuration of the
present embodiment 5 of the feedforward amplifier. In FIG. 9, the
same or like portions to those of FIG. 6 are designated by the same
reference numerals, and the description thereof is omitted here. In
FIG. 9, the reference numeral 64 designates a frequency converter
(second frequency converter) for down-converting the output signal
split by the directional coupler 14 to a low frequency using the
signal output from the local oscillator 52; 65 designates a
frequency converter (first frequency converter) for down-converting
the output of the third vector regulator 61 to a low frequency
using the signal output from the local oscillator 52; and 66
designates a combiner for combining the outputs of the frequency
converters 64 and 65.
[0108] Next, the operation of the present embodiment 5 will be
described.
[0109] A part of the input signal divided by the splitter 25 passes
through the delay circuit 24 and the third vector regulator 61, and
is down-converted to the low frequency signal by the frequency
converter 65.
[0110] On the other hand, a part of the output signal extracted by
the directional coupler 14 is down-converted to the low frequency
signal by the frequency converter 64. The combiner 66 combines the
outputs of the frequency converters 64 and 65 in the same amplitude
but in the opposite phase to cancel out the signal component. The
output signal of the combiner 66 is divided into two portions by
the splitter 57. The first portion passes through the filter 54
that passes only the distortion component frequency, and is
supplied to the power detector 55. The second portion passes
through the filter 58 that passes only the signal component
frequency, and is supplied to the power detector 59.
[0111] As in the embodiment 2 described before, the controllers 56
and 60 control the second vector regulator 11 and third vector
regulator 61, respectively.
[0112] The present embodiment 5 of the feedforward amplifier
differs from the foregoing embodiment 2 in that the combiner 66
combines the two low frequency signals, that is, the input signal
divided by the splitter 25 and the output signal extracted by the
directional coupler 14, to extract the distortion component by
canceling out the signal component. Accordingly, the combiner 66
can be a combiner for the low frequency.
[0113] As described above, the present embodiment 5 offers the same
advantages of the foregoing embodiment 2. In addition, it can
obviate the radio-frequency connecting wire on the input side of
the combiner 66, thereby offering an advantage of being able to
provide greater flexibility of wiring, and by extension to
miniaturize the device.
[0114] Furthermore, the present embodiment 5 can implement the
circuit configuration using the low frequency combiner 66, splitter
57 and filters 54 and 58, making it easier to integrate them into
an IC. Thus, it offers an advantage of being able to implement the
feedforward amplifier that can reduce its size and cost with
ease.
[0115] Embodiment 6
[0116] FIG. 10 is a block diagram showing a configuration of the
present embodiment 6 of the feedforward amplifier. In FIG. 10, the
same or like portions to those of FIG. 9 are designated by the same
reference numerals, and the description thereof is omitted here. In
FIG. 10, the reference numeral 67 designates a frequency converter
(first frequency converter) for down-converting a part of the input
signal divided by the splitter 25 by using the output signal from
the local oscillator 52; 68 designates a low frequency delay
circuit for delaying the output of the frequency converter 67; and
69 designates a low frequency vector regulator for adjusting the
pass amplitude and pass phase of the output of the delay circuit
68.
[0117] The present embodiment 6 of the feedforward amplifier
differs from the foregoing embodiment 5 in that the part of the
input signal divided by the input side splitter 25 is immediately
down-converted to the low frequency by the frequency converter 67.
The output of the frequency converter 67 passes through the low
frequency delay circuit 68 and the low frequency vector regulator
69, and is supplied to the combiner 66. The subsequent operation is
the same as that of the foregoing embodiment 5.
[0118] As described above, the present embodiment 6 can achieve the
same advantages as the foregoing embodiment 5. In addition, the
present embodiment 6 can utilize low frequency components for the
delay circuit 68 and the vector regulator 69, which are fabricated
easier than those of the radio-frequency counterparts. In addition,
the vector regulator can be configured using a signal processing
circuit (DSP: Digital Signal Processor) which can provide greater
flexibility to the vector regulator, making it easier to
miniaturize and adjust the vector regulator, and by extension to
reduce the size of the feedforward amplifier and to improve the
distortion characteristic.
[0119] Furthermore, since all the circuit components following the
frequency converters 64 and 67 are low frequency components, it
possible to integrate them into an IC including the controller 56
for controlling the distortion canceling loop 102 (that is, the
second vector regulator 11) of the feedforward distortion
compensation circuit. Thus, the present embodiment 6 offers an
advantage of being able to implement the feedforward amplifier with
a reduced size and cost.
[0120] Embodiment 7
[0121] FIG. 11 is a block diagram showing a configuration of the
present embodiment 7 of the feedforward amplifier. In FIG. 11, the
same or like portions to those of FIG. 6 are designated by the same
reference numerals, and the description thereof is omitted here. In
FIG. 11, 25 the reference numeral 71 designates a splitter (first
splitter) interposed between the splitter 2 and the delay circuit 5
for further dividing the part of the input signal divided by the
splitter 2.
[0122] The present embodiment 7 of the feedforward amplifier
differs from the foregoing embodiment 2 in that it comprises the
splitter 71, which is interposed between the splitter 2 and the
delay circuit 5 for further dividing the part of the input signal
divided by the splitter 2, instead of the splitter 25 for dividing
the input signal supplied from the input terminal 1.
[0123] The foregoing configuration can remove the splitter 25 from
the main path of the input signal from the input terminal 1 to the
splitter/combiner 6 via the main amplifier 4, that is, the path of
the major part of the signal to become the output signal of the
feedforward amplifier, thereby preventing the reduction in the
total gain of the amplifier due to the loss of the splitter 25.
[0124] Although the configuration of FIG. 11 changes the position
of the splitter 25 for dividing the input signal in the foregoing
embodiment 2, the foregoing embodiments 1, and 3-6 can also offer
the same advantage as the present embodiment 7 by changing the
position of their splitter 25.
[0125] Embodiment 8
[0126] FIG. 12 is a block diagram showing a configuration of the
present embodiment 8 of the feedforward amplifier. In FIG. 12, the
same or like portions to those of FIG. 6 are designated by the same
reference numerals, and the description thereof is omitted here. In
FIG. 12, the reference numeral 72 designates a splitter interposed
into the path on the output side of the delay circuit 5 for further
dividing a part of the input signal divided by the splitter 2 and
passing through the delay circuit 5.
[0127] The present embodiment 8 of the feedforward amplifier
differs from the foregoing embodiment 2 in that it comprises the
splitter 72, which is interposed into the path on the-output side
of the delay circuit 5 for further dividing the part of the input
signal divided by the splitter 2 and passing through the delay
circuit 5, instead of the splitter 25 for dividing the input signal
supplied from the input terminal 1.
[0128] This configuration makes it possible for the delay circuit 5
to share the function of the delay circuit 24 in part, reducing the
delay time of the delay circuit 24. Thus, it is possible to reduce
the size of the delay circuit 24, and by extension to reduce the
size of the device.
[0129] Although the configuration of FIG. 12 utilizes the splitter
72 interposed into the path on the output side of the delay circuit
5 in place of the splitter 25 for dividing the input signal in the
foregoing embodiment 2, the foregoing embodiments 1, and 3-6 can
also offer the same advantage as the present embodiment 8 by
changing the position of their splitter 25 to the output side of
the delay circuit 5.
[0130] Industrial Applicability
[0131] As described above, the feedforward amplifier in accordance
with the present invention can be preferably applied to the low
distortion amplification in a radio frequency band such as VHF, UHF
and microwave frequency bands for implementing favorable distortion
compensation without being affected by the ambient temperature or
deterioration with age.
* * * * *