JP2001237652A - Wide band distortion compensating amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide band distortion compensating amplifier capable of stably maintaining the wide band characteristics of a distortion removing circuit 30 by solving a problem of drop in distortion compensation quantity over a wide band caused by multiple reflections generated on the route of first and second delay lines 6 and 11 in the conventional technology for a self- controlled feedforward distortion compensating amplifier. SOLUTION: By providing isolators 40a and 40b or isolators 50 and 60 on the route of the first delay line 6 or signal route of a main amplifier 5 and on an input signal route in a distortion detecting circuit 20, the band of fixed impedance is widened to a distortion generating band spread outside bands on both the sides of an amplified signal frequency band, and the band of distortion compensation is widened by suppressing the multiple reflections on the route of delay lines caused by an amplifier or variable attenuator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a type of high linear amplifier which is used for a base station or a relay device of a mobile communication system such as an automobile telephone, a portable telephone, a personal handy phone system, etc. and amplifies multi-frequency signals simultaneously. The present invention relates to a certain distortion compensating amplifier (feedforward amplifier), and more particularly, to widening the band thereof.

[0002]

2. Description of the Related Art A base station and a radio relay device in an 800 MHz band, 1500 MHz band mobile telephone, a portable telephone system and the like are provided with a multi-frequency common amplifier for simultaneously amplifying multi-frequency signals. In this multi-frequency common amplifier, it is necessary to sufficiently improve the linearity in order to minimize the occurrence of intermodulation distortion, and a small high linearity amplifier is used. One of them is a distortion compensation amplifier (self-adjustment type feedforward amplifier), which is configured to compensate for intermodulation distortion and noise generated in the amplifier by self-adjustment.

This feedforward amplifier is composed of a distortion detecting circuit and a distortion removing circuit. A distortion detecting circuit including a main amplifier, which is a compensation target amplifier, detects a distortion component other than an input signal, and detects the detected distortion component (error). The component is input to a distortion removal circuit including an auxiliary amplifier (error amplifier) to amplify the distortion component, and then, is combined with the multi-frequency amplified signal in reverse phase to cancel the distortion component.

FIG. 1 is a block diagram of a conventional self-adjusting feedforward amplifier. In the figure, 1 is a drive amplifier for amplifying an input signal Pin, 2 is a power divider for distributing its output, 3 is a variable attenuator, 4 is a variable phase shifter, 5 is a main amplifier, 6 is a delay line, and 7 is power A combiner, 8 is a variable attenuator, 9 is a variable phase shifter, 10 is an auxiliary amplifier, 11 is a delay line, 12 is a power combiner, 13 is an isolator, and 14 is a terminating resistor. Reference numeral 20 denotes a distortion detection circuit, and reference numeral 30 denotes a distortion removal circuit.

[0005] The multi-frequency input signal Pin is input to the power divider 2 via the drive amplifier 1 and is branched into two to be delayed by the delay line 6.
To the variable attenuator 3. The output of the variable attenuator 3 is
The signal is amplified by the main amplifier 5 via the variable phase shifter 4. The multi-frequency amplified signal including the distortion component generated at the time of the amplification is input to the power combiner 7, distributed by the power distributor 2, and combined with the input signal passed through the delay line 6 by the power combiner 7. , A distortion component is detected.

[0006] The multi-frequency amplified signal output from the power combiner 7 is input to a power combiner 12 via a delay line 11.
On the other hand, the distortion component output from the power combiner 7 is amplified by the auxiliary amplifier 10 through the variable attenuator 8 and the variable phase shifter 9, and
The power is input to the power combiner 12, the polarity is inverted, and the delay line 1
The distortion component is canceled by being combined with the multi-frequency amplification signal including the distortion component input through the step 1, and a multi-frequency common amplification signal with little distortion is output. This output is isolator 1
Then, the output signal Pout is obtained through the step S3. In this feedforward amplifier, the variable attenuators 3, 8 and the variable phase shifters 4, 9 are adjusted by pilot signal control, and a desired operation is performed. However, illustration of these control systems is omitted.

[0007]

In such a feedforward amplifier, in the distortion removing circuit 30, the path of the variable attenuator 8, the variable phase shifter 9, and the auxiliary amplifier 10 in which the level and the phase of the distortion component are adjusted and amplified. Needs to be as similar as possible to the frequency characteristics of the delay line 11 in a wide band.

FIG. 2 shows a route 8-9-10, and FIG. 3 shows a route 7-1.
The frequency characteristics at the time of 50Ω termination of the path 1-12 are shown. The measurement confirms that it has a broadband characteristic at a termination of 50Ω (load independent of frequency).

However, if the output return loss frequency characteristic of the drive amplifier 1 shown in FIG. 4 and the input impedance frequency characteristic of the variable attenuator 8 shown in FIG.
In the frequency characteristic of -6-7-8-9-10-14, an amplitude deviation appears outside the band due to the reflection coefficient due to multiple reflection, as shown in FIG.

[0010] In practice, the reflection coefficient gamma _A variable attenuator 8 not zero, because of the order of 0.1, the route 1-6-7-
The reflection occurs in the variable attenuator 8 of 8-9-10-14, returns to the drive amplifier 1, and is reflected again by the reflection coefficient of the output impedance. Here, unless the reflection coefficient is brought close to 0 in a wide band, multiple reflections occur between the drive amplifier 1 and the variable attenuator 8 in the path 1-6-7-8, and a standing wave is generated. The transmission characteristic of -6-7-8-9-10-14 slightly changes as shown in FIG.

Similarly, the transmission characteristics along the path 7-11-12-13 require the output amplifier of the main amplifier 5 to have a wide band. If there is such a factor that the frequency characteristics slightly change, the amount of distortion cancellation by the distortion detecting circuit 20 and the distortion removing circuit 30 becomes smaller than an expected value, causing a problem that the distortion improving effect is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problem of the prior art described above and to solve the problem of a reduction in the amount of wideband distortion compensation due to multiple reflections occurring in the paths of the first and second delay lines and to stabilize the wideband characteristics of the distortion removing circuit. It is an object of the present invention to provide a wideband distortion compensating amplifier that can be maintained at a low level.

[0013]

SUMMARY OF THE INVENTION A wide band distortion compensating amplifier according to the present invention comprises a main amplifier which splits an input signal into two by a power splitter and passes one of the two signals through a first variable attenuator and a first variable phase shifter. The amplified signal amplified in the step (a) is input to a first power combiner, and the amplified signal and the other of the two divided signals are converted to a first power combiner.
And a distortion detection circuit for detecting a distortion component generated in the main amplifier by synthesizing the signal whose timing is adjusted by the delay means in the first power combiner, and outputting the distortion component from the first power combiner. Converting the distortion component into a second variable attenuator,
A signal amplified by an auxiliary amplifier via a second variable phase shifter and a signal output from the first power combiner and amplified by the main amplifier and adjusted in timing by a second delay unit are converted into a second signal. A distortion removing circuit that outputs an amplified signal in which a distortion component included in the amplified signal of the main amplifier is canceled by performing reverse-phase synthesis by the power combiner of the second power combiner. Is provided with at least one isolator. With this configuration, the band of constant impedance is widened to the distortion generation band extending outside the band on both sides of the band, and the multiple reflection of the delay line path due to the amplifier and the variable attenuator is suppressed to widen the band of distortion compensation. Can be achieved.

[0014]

FIG. 8 is a circuit diagram showing an embodiment of the present invention. In the figure, reference numerals 1 to 14 and 20, 30 denote the same parts as the conventional circuit of FIG. 40a, 40b, 5
Numerals 0 and 60 are isolators added according to the present invention.
In order to suppress the multiple reflection on the path 1-6-7-8 and stabilize a wide band, a constant impedance isolator 40a or 40b having a wide band characteristic is provided on the input side or the output side of the delay line 6 of the distortion detection circuit 20. Inserted. Furthermore, in order to stabilize the output impedance of the power combiner 7 over a wide band,
An isolator 50 was inserted on the output side of the main amplifier 5.

FIG. 9 shows the return loss frequency characteristics of the isolator inserted in the present invention. By setting the output impedance of the isolator as shown in FIG. 9, the frequency characteristics of the system can be made as close as possible to the characteristics at the time of 50Ω termination (when the measuring instrument is connected) shown in FIGS.

Similarly, in order to widen the input impedance of the distortion detection circuit 20, a similar effect can be obtained by inserting an isolator 60 before the power divider 2 as shown in FIG. Therefore, a wide-band amplitude frequency characteristic as shown in FIG. 10 is obtained.

Although a wideband isolator 13 is normally inserted into the load of the distortion removing circuit 30 to stabilize the load, the amount of improvement is ensured by the offset amount of the distortion removing circuit 30.
It is necessary to make the amplitude deviation in the loop (distortion removing circuit) stricter than that of the distortion detecting circuit. Therefore, the isolator 13
Even if the amount of reflection due to the influence of is small, if the isolator 50 is inserted on the output side of the main amplifier 5, the amplitude deviation can be further suppressed.

FIG. 11 is a circuit diagram of a hybrid isolator, showing two 90 ° hybrid transformers (HY
B) Two isolators 41, 4 between (a directional coupler composed of striplines having a difference in length of λ / 4)
2 is connected to the circuit. By using such a hybrid isolator instead of the above-described isolator, it is possible to improve the bandwidth up to the octave band.

As an application of FIG. 11, the two amplifiers A1 and A2 are provided between two 90 ° hybrid transformers (HYB) as shown in FIG. It may be configured to be connected. If the output impedances of the amplifiers A1 and A2 are equal, the output impedance of the HYB becomes 50Ω, which has the same effect as when an isolator is inserted. However, when the amplifiers A1 and A2 are of a class AB or class C nonlinear type, A1 and A2
Since it is difficult to balance the two, it is preferable to further insert an isolator. With the configuration as shown in FIG. 12, the effect of improving the distortion compensation amount of the feedforward amplifier is further increased, and the configuration of the main amplifier is simplified with respect to the amplifier having the same distortion. Because of this, a great economic effect can be obtained.

[0020]

According to the present invention, it is possible to reduce a reduction in distortion compensation amount due to multiple reflections by inserting an isolator having a wide return loss. 80
Taking the 0 MHz band as an example, it is possible to improve the band by two to three times as compared with the conventional case.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a conventional distortion compensation amplifier.

FIG. 2 is a diagram illustrating an example of a frequency characteristic of an auxiliary amplifier system at the time of termination of 50Ω.

FIG. 3 is a diagram illustrating a frequency characteristic example of a delay line system at the time of termination of 50Ω.

FIG. 4 is a diagram illustrating an example of return loss frequency characteristics of the drive amplifier 1;

FIG. 5 is an example of an input impedance characteristic of the variable attenuator 8;

FIG. 6 is a diagram illustrating an example of a frequency characteristic of a delay line 6 side system when a conventional actual load is applied.

FIG. 7 is a diagram illustrating an example of a frequency characteristic of a conventional auxiliary amplifier 10 side system at the time of an actual load.

FIG. 8 is a circuit diagram showing an embodiment of the present invention.

FIG. 9 is an example of return loss frequency characteristics of an isolator inserted according to the present invention.

FIG. 10 shows an auxiliary amplifier when the isolator of the present invention is used,
FIG. 4 is a diagram illustrating an example of frequency characteristics of a delay line system.

FIG. 11 is a configuration example diagram of a hybrid isolator.

FIG. 12 is a configuration example diagram of a hybrid amplifier.

[Description of Signs] 1 Drive amplifier 2 Power divider 3,8 Variable attenuator 4,9 Variable phase shifter 5 Main amplifier 6,11 Delay line 7,12 Power combiner 10 Auxiliary amplifier 13 Isolator 14 Termination resistor 20 Strain detection circuit Reference Signs List 30 Distortion removal circuit 40, 50, 60 Isolator 41, 42 Isolator

Continued on the front page (72) Inventor Kotaro Takenaga 3-14-20 Higashinakano, Nakano-ku, Tokyo Inside Hitachi Kokusai Electric Inc. (72) Inventor Yoichi Okubo 3-14-20 Higashinakano, Nakano-ku, Tokyo Hitachi Kokusai Inc. (72) Inventor Takashi Yokote 3-14-20 Higashinakano, Nakano-ku, Tokyo Hitachi Kokusai Electric Inc.

Claims (1)

[Claims] 1. An amplified signal obtained by amplifying a signal obtained by dividing an input signal into two by a power divider through a first variable attenuator and a first variable phase shifter by a main amplifier to a first power combiner. The first power combiner combines the amplified signal with the signal obtained by adjusting the timing of the other signal divided into two by the first delay means, thereby distorting a distortion component generated in the main amplifier. A distortion detection circuit for detecting, and a second distortion component output from the first power combiner.
The timing of the signal amplified by the auxiliary amplifier via the variable attenuator and the second variable phase shifter and the signal amplified by the main amplifier output from the first power combiner are matched by the second delay means. A distortion removal circuit that outputs an amplified signal in which a distortion component included in the amplified signal of the main amplifier is canceled out by performing a reverse-phase synthesis of the amplified signal with a second power combiner. A wideband distortion compensation amplifier, wherein at least one isolator is provided in a signal path of a detection circuit.