JPH09270642A - Broad band distortion compensation amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a broad frequency band by inserting a constant impedance isolator to at least one of input and output sides of a 1st delay line in the distortion compensation amplifier provided with a distortion elimination circuit that cancels a distortion component generated in a main amplifier to provide a multi-frequency amplifier signal to suppress multiple reflection. SOLUTION: Isolators 40a, 40b, 50, 60 are added to a conventional circuit. The isolator 40a or 40b with a constant impedance having a broad frequency band characteristic is inserted to an input side or an output side of a delay line 6 of a distortion detection circuit 20 to suppress multiple reflection in a path of components 1-6-7-8 and to make a broad frequency band stable. Furthermore, the isolator 50 is inserted to an output side of a main amplifier 5 to make an output impedance of a power combiner 7 stable over a broad frequency band. The similar effect is obtained by inserting the isolator 60 to a pre-stage of a power distributer 2 to make an input impedance of the distortion detection circuit 20 stable over a broad frequency band. Thus, the amplitude frequency characteristic over a broad frequency band is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a kind of high linear amplifier used for a base station or a repeater of a mobile communication system such as a car phone, a mobile phone, a personal handyphone system, etc. and for simultaneously amplifying multi-frequency signals. The present invention relates to a certain distortion compensation amplifier (feedforward amplifier), and particularly to widening its bandwidth.

[0002]

2. Description of the Related Art A base station and a radio relay device in an 800 MHz band or 1500 MHz band mobile phone, a mobile phone system, etc. are provided with a multi-frequency common amplifier for simultaneously amplifying multi-frequency signals. This multi-frequency common amplifier is required to have sufficiently good linearity in order to minimize the occurrence of intermodulation distortion, and a small and highly linear amplifier is used. One of them is a distortion compensation amplifier (self-adjusting 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 detection circuit and a distortion removal circuit, detects a distortion component other than an input signal by a distortion detection circuit including a main amplifier which is an amplifier to be compensated, and detects the detected distortion component (error). Component) is input to a distortion removal circuit including an auxiliary amplifier (error amplifier) to amplify the distortion component, and then is anti-phase combined with the multi-frequency amplified signal 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 distributor 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, 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 is a distortion detection circuit, and 30 is a distortion removal circuit.

The multi-frequency input signal Pin is input to the power distributor 2 via the drive amplifier 1, is distributed to the delay line 6 and the variable attenuator 3 through the main line that is branched into two, and is supplied to the variable attenuator 3. The output is amplified by the main amplifier 5 via the variable phase shifter 4. The multi-frequency amplified signal including the distortion component generated during the amplification is input to the power combiner 7, and the input signal that has passed through the main line and the delay line 6 distributed by the power distributor 2 and the power combiner 7 And the distortion component is detected.

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

[0007]

In such a feedforward amplifier, the path of the variable attenuator 8-variable phase shifter 9-auxiliary amplifier 10 in which the level and phase of the distortion component in the distortion elimination circuit 30 are adjusted and amplified. It is necessary that the frequency characteristics are as close as possible to the wide band characteristics of the frequency characteristics of the delay line 11.

2 is a route of 8-9-10, and FIG. 3 is 7-1.
The frequency characteristic at the time of 50Ω termination of the path 1-12 is shown. The measurement confirms that it has wide-band characteristics at a 50Ω (load that does not depend on frequency) termination.

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.
The frequency characteristics of -6-7-8-8-9-10-14 are as shown in FIG. 6 due to the multiple reflections, in which an amplitude deviation appears in the portion outside the band due to the relationship of the reflection coefficient.

In reality, the reflection coefficient Γ _A of the variable attenuator 8 is not 0.1 but about 0.1, so that the path 1-6-7-
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 its output impedance. If the reflection coefficient is not brought close to 0 in the wide band here, multiple reflection occurs between the drive amplifier 1 and the variable attenuator 8 on the path 1-6-7-8 to generate a standing wave, and finally the path 1 The transmission characteristics of -6-7-8-9-9-10-14 slightly change as shown in FIG.

Similarly, the transmission characteristic of the path 7-11-12-13 requires a wide band of the output impedance of the main amplifier 5. If there is such a factor of a slight change in the frequency characteristics, the amount of distortion cancellation by the distortion detection circuit 20 and the distortion removal circuit 30 becomes smaller than the expected value, and the problem of distortion improvement deteriorates.

The object of the present invention is, in particular, in the system which becomes a problem of the above-mentioned prior art, in a wide band distortion compensation due to the multiple reflection occurring in the path of the first delay line 6 due to the reflection by the second variable attenuator 8. An object of the present invention is to provide a wide band distortion compensation amplifier which can solve the decrease in the amount and can maintain a stable wide band characteristic especially in the distortion removing circuit in the system.

[0013]

According to the broadband distortion compensation amplifier of the present invention, a multi-frequency input signal is amplified by a drive amplifier and then branched and output by a power distributor, and one of the signals is divided into a first variable attenuator and a first variable attenuator. The signal amplified by the main amplifier via the variable phase shifter 1 and the signal of which the other signal is timed by the first delay line are generated by the main amplifier by combining them in the first power combiner. A distortion detection circuit for detecting a distortion component, a signal obtained by amplifying the distortion component output from the first power combiner with an auxiliary amplifier via a second variable attenuator and a second variable phase shifter, and The distortion generated in the main amplifier is generated by subjecting the signal amplified by the main amplifier output from the power combiner No. 1 and the signal whose timing is adjusted by the second delay line to the opposite phase by the second power combiner. Multi-frequency amplified signal by canceling components In a distortion compensating amplifier including a distortion removing circuit for outputting, a wideband constant impedance isolator is inserted into at least one of the input and output sides of the first delay line to suppress multiple reflections and achieve a wider band. It is characterized by.

[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 in the conventional circuit of FIG. 40a, 40b, 5
Reference numerals 0 and 60 are isolators added according to the present invention.
In order to suppress the multiple reflection in the path 1-6-7-8 and stabilize the wide band, the constant impedance isolator 40a or 40b having the 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 in a wide band,
An isolator 50 was inserted on the output side of the main amplifier 5.

FIG. 9 shows the return loss frequency characteristic 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 termination of 50Ω (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 the isolator 60 in the preceding stage of the power distributor 2 as shown in FIG. Therefore, a wide band amplitude frequency characteristic as shown in FIG. 10 can be obtained.

The load of the distortion eliminating circuit 30 is normally stabilized by inserting the wideband isolator 13 into the load, but the amount of cancellation of the distortion eliminating circuit 30 ensures an improved amount.
It is necessary to make the amplitude deviation in the loop (distortion removing circuit) stricter than that in the distortion detecting circuit. Therefore, the isolator 13
Even if the reflection amount due to the influence of 1 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, which shows two 90 ° hybrid transformers (HY).
B) Two isolators 41, 4 between (directional couplers composed of strip lines having a length difference of λ / 4)
It is a circuit in which 2 is connected. By using such a hybrid isolator instead of the above-mentioned isolator, it is possible to improve the band to the octave band.

As an application of FIG. 11, the amplifier configuration of the main amplifier 5 and the drive amplifier 1 is shown in FIG. 12, in which two amplifiers A1 and A2 are provided between two 90 ° hybrid transformers (HYB). 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 is 50Ω, which has the same effect as when the isolator is inserted. However, if the amplifiers A1 and A2 are non-linear class AB or class C, A1 and A2
Since it is difficult to balance the two, it is preferable to insert an isolator. With the configuration 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. Since it can be used, a significant economic effect can be obtained.

[0020]

According to the present invention, by inserting an isolator having a wide return loss, it is possible to reduce a decrease in distortion compensation amount due to multiple reflection. 80
Taking the 0 MHz band as an example, it is possible to improve the band by a factor of 2 to 3 compared with the conventional case.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing an example of frequency characteristics of a delay line system at the time of termination of 50Ω.

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

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

FIG. 6 is a frequency characteristic example diagram of a delay line 6 side system in the case of a conventional actual load.

FIG. 7 is a frequency characteristic example diagram of a conventional auxiliary amplifier 10 side system when an actual load is applied.

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

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

FIG. 10 is an auxiliary amplifier when the isolator of the present invention is used,
It is a frequency characteristic example figure of a delay line system.

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

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

[Explanation of symbols]

 1 Drive Amplifier 2 Power Divider 3,8 Variable Attenuator 4,9 Variable Phaser 5 Main Amplifier 6,11 Delay Line 7,12 Power Combiner 10 Auxiliary Amplifier 13 Isolator 14 Termination Resistor 20 Distortion Detection Circuit 30 Distortion Removal Circuit 40 , 50,60 Isolator 41,42 Isolator

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Yoichi Okubo, 3-14-20 Higashi-Nakano, Nakano-ku, Tokyo Kokusai Electric Co., Ltd. (72) Takashi Yokote, 3-14-20 Higashi-Nakano, Nakano-ku, Tokyo Kokusai Electric Within the corporation

Claims (1)

[Claims] 1. A multi-frequency input signal is amplified by a drive amplifier, then branched and output by a power divider, and one of the signals is amplified by a main amplifier via a first variable attenuator and a first variable phase shifter. A distortion detection circuit that detects a distortion component generated in the main amplifier by combining a signal and a signal whose other signal is timed by a first delay line by a first power combiner; Signal amplified by the auxiliary amplifier via the second variable attenuator and the second variable phase shifter, and amplified by the main amplifier output from the first power combiner. Distortion for canceling the distortion component generated in the main amplifier and outputting a multi-frequency amplified signal by performing anti-phase combination of the generated signal and the signal whose timing is adjusted by the second delay line in the second power combiner. In a distortion compensation amplifier equipped with a removal circuit A wideband distortion compensating amplifier that suppresses multiple reflections by inserting a wideband constant impedance isolator into at least one of the input and output sides of the first delay line to achieve a wideband.