Amplifiers – With pilot frequency control means
Reexamination Certificate
2001-04-24
2002-09-24
Mottola, Steven J. (Department: 2817)
Amplifiers
With pilot frequency control means
C330S151000
Reexamination Certificate
active
06456160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feedforward amplifier for carrying out low distortion amplification in a radio frequency band.
2. Description of Related Art
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.
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.
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.
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.
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.
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
.
Next, the operation of the conventional feedforward amplifier will be described.
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
.
The optimizing control of the distortion detecting loop
101
in the feedforward amplifier is carried out as follows by controlling the vector regulator
3
.
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.
Besides, the optimizing control of the distortion canceling loop
102
is carried out as follows by controlling the second vector regulator
11
.
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.
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
.
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
.
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.
In view of this, some schemes are proposed that control the feedforward distortion compensation system without utilizing the pilot signal.
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.
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 s
Horiguchi Kenichi
Ikeda Yukio
Nagano Junichi
Nakayama Masatoshi
Sakai Yuji
LandOfFree
Feedforward amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Feedforward amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Feedforward amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2864625