JP2711413B2 - Feedforward amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear amplifier mainly used in a high frequency band, and a distortion detecting circuit for detecting a non-linear distortion component of the main amplifier, and amplifying the detected distortion component using an auxiliary amplifier. Thereafter, the present invention relates to a feedforward amplifier having a distortion removing circuit for canceling distortion components by injecting the distortion component again into the output of the main amplifier.

[0002]

2. Description of the Related Art FIG. 5 shows a basic configuration of a feedforward amplifier. The feedforward amplifier is basically composed of two signal canceling circuits. One is a distortion detection circuit 1, and the other is a distortion removal circuit 2. The distortion detection circuit 1 includes a main amplifier signal path 3 and a linear signal path 4, and the distortion removal circuit 2 includes a main amplifier output signal path 5 and a distortion injection path 6. Further, the main amplifier signal path 3 is composed of a cascade connection of a main amplifier 7, a variable attenuator 8, and a variable delay line 9, and the linear signal path 4 is composed of a transmission line. The main amplifier output signal path 5 is composed of a transmission line, and the distortion injection path 6 is composed of a variable attenuator 10 and a variable delay line 11.
And the auxiliary amplifier 12 in cascade. Here, since there is no large difference in characteristics, both the variable attenuator 8 and the variable delay line 9 or only one of them may be provided in the linear signal path 4. Similarly, the variable attenuator 10 and the variable delay line 11
Both, or only one, may be provided in main amplifier output signal path 5. In addition, the power distributor 13
The power combiners 14 and 15 are simple lossless power dividers / power combiners composed of transformer circuits, hybrid circuits, and the like. First, this operation will be described.

The input signal applied to the input terminal 16 is first distributed to the paths 3 and 4 by the power distributor 13 and then power-combined by the power combiner 14. Here, the variable attenuator 8 and the variable delay line 9 have the same amplitude and delay amount with respect to both signal components of the two paths 3 and 4 output from the power combiner 14 to the distortion injection path 6, and , Are adjusted so that the phases are opposite. However, the reverse phase condition is realized by appropriately setting the amount of phase shift between the input and output terminals of the power divider 13 or the power combiner 14, or by using the phase inversion in the main amplifier 7, Alternatively, as shown in FIG.
This is realized by inserting a phase inversion circuit having a short-circuit termination 19 at one terminal into either of the paths 3 and 4. Since the distortion detection circuit 1 is configured as described above, a difference component between two signals of the two paths 3 and 4 is eventually detected as an output from the power combiner 14 to the path 6 side. . This difference component is just the distortion component itself generated by the main amplifier 7, and hence the circuit 1 is called a distortion detection circuit.

[0004] Next, the variable attenuator 10 and the variable delay line 11 transmit the signal from the input terminal 14a of the power combiner 14 on the path 3 to the output terminal 17 of the power combiner 15 via the two paths 5 and 6. The functions are adjusted so as to be equal to each other with respect to the amplitude and the delay amount, and to be opposite in phase with respect to the phase. Here, since the input signal on the path 6 is the distortion component of the main amplifier 7 detected by the distortion detection circuit 1, the path 6 is connected to the output terminal 17 of the power combiner 15 by the distortion component of the output signal of the main amplifier 7. Are injected with opposite phase equal amplitude, and as a result, the cancellation of the distortion component in the output of the entire circuit is realized.

[0005]

Although the operation of the ideal feedforward amplifier has been described above, it is actually easy to completely balance the two circuits of the distortion detection circuit 1 and the distortion removal circuit 2. However, even if the initial settings are perfect, it is usually extremely difficult to maintain a good balance over time because the amplifier characteristics change due to changes in ambient temperature, power supply, etc. It is. FIG. 7 shows the result of calculating the relationship between the amount of deviation and the amount of signal suppression in which the amplitude and phase of the two paths constituting the circuit deviate from the equal-amplitude anti-phase condition. From this figure, for example, in order to achieve a suppression amount of 30 dB or more, deviations of the phase and the amplitude are each ± 1.8.
Must be within ± and within ± 0.3 dB,
It can be clearly seen that strict conditions are required for the balance of the transmission characteristics of the two paths and the completeness of the adjustment. If the balance of the distortion detection circuit 1 deteriorates, an unnecessary distortion occurs because the main signal is added to the input of the auxiliary amplifier 12 at a level larger than the distortion component, and the balance of the distortion removal circuit 2 deteriorates. Then, the amount of distortion improvement as the feedforward amplifier is deteriorated by the amount of deterioration of the suppression amount. As described above, the conventional feedforward amplifier has a fundamental problem that a satisfactory linear amplifier cannot be realized because the stability of the circuit is not sufficient.

An object of the present invention is to provide a feed-forward amplifier which solves such instability of characteristics.

[0007]

According to the present invention, a distortion detection circuit for detecting a non-linear distortion component of a main amplifier, an amplifier for amplifying the detected distortion component using an auxiliary amplifier, and then outputting the amplified signal to the output of the main amplifier again. A feed-forward amplifier having a distortion removing circuit for canceling a distortion component by injecting, wherein a first injection means for injecting a first pilot signal of a specific frequency is provided in an input path of the feed-forward amplifier; A first electric variable attenuating means and a first electric variable phase shifting means inserted in the circuit are provided, and a second injection means for injecting a second pilot signal of another specific frequency is provided in a path of the main amplifier. A second electric variable attenuating means and a second electric variable phase shifting means are provided in the distortion removing circuit, and a first pilot signal of the first pilot signal is provided in a path of the auxiliary amplifier. First level detection means for detecting a bell; second level detection means for detecting the level of a second pilot signal on the output path of the feedforward amplifier; and first level detection means for the output path of the feedforward amplifier. A third injection means for injecting a signal is provided, and a semi-fixed variable attenuating means, a semi-fixed variable phase shift means and an amplifier are inserted into a supply path of a first pilot signal supplied to the third injection means, The first electric variable attenuating means and the first electric variable phase shifting means are controlled by the control means so that the detection level of the detecting means is minimized, and the detection level of the second level detecting means is minimized. The second electric variable attenuating means and the second electric variable phase shifting means are controlled by the control means.

[0008]

[Operation] The residual signal generated due to the imperfect signal cancellation condition of the two circuits of the feedforward amplifier is:
The transmission characteristics of the circuit are automatically adjusted such that the detected level is detected by the pilot signal detecting means and monitored, and the detected level is minimized.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and FIG.
The parts corresponding to are denoted by the same reference numerals. An oscillator 20 such as a frequency synthesizer for generating a first pilot signal whose frequency is specified is coupled to the input terminal 13a side of the power distributor 13 via a directional coupler 21. Also,
An oscillator 22 such as a frequency synthesizer for generating a second pilot signal having a specified frequency is provided with a directional coupler 23.
To the output of the main amplifier 7. Instead of the variable attenuator 8 and the variable delay line 9, an electrically adjustable variable attenuator 24 and an electrically adjustable variable phase shifter 25 are inserted in the main amplifier signal path 3 of the distortion detection circuit 1. . Instead of the variable attenuator 10 and the variable delay line 11, an electrically adjustable variable attenuator 26 and an electrically adjustable variable phase shifter 27 are inserted into the distortion injection path 6 of the distortion removing circuit 2. . These variable attenuators 24 and 26 and variable phase shifters 25 and 2
7 can be easily configured using a PIN diode and a varactor diode, and commercially available products can also be used. A selection level meter 2 as a level detection means of the first pilot signal is provided to the input side of the variable attenuator 26 via a directional coupler 28.
9 are combined. A selection level meter 31 as a level detecting means of the second pilot signal is connected to an output path of the feedforward amplifier via a directional coupler 30.
Further, the first pilot signal passes through a semi-fixed variable attenuator 32, a semi-fixed variable phase shifter 33, and a signal amplifier 34, and is coupled to an output path of a feedforward amplifier via a directional coupler 35. Each output of the selection level meters 29 and 31 is input to a control circuit 36, which controls the variable attenuators 24 and 26 and the variable phase shifters 25 and 27. Each of the selection level meters 29 and 31 includes a frequency converter for detecting a specific frequency component of an input signal, a narrow band filter, and a detector for detecting an output level of the narrow band filter. The control circuit 36 includes an A / D converter, a microprocessor, and a D / A converter as basic circuits, and monitors input signals from the selection level meters 29 and 31 while controlling the variable attenuators 24 and 26 and the variable attenuators 24 and 26. It has a function of adjusting the set points of the phase shifters 25 and 27. Hereinafter, the control operation of the control circuit will be described.

First, a signal is input to a feedforward amplifier. As the input signal, for example, a combination of a plurality of continuous signals whose frequency is specified is used. The oscillator 20
Is set to a frequency slightly apart from the frequency band of the input signal of the feedforward amplifier, and the second pilot signal by the oscillator 22 is the frequency occupied by the original signal among the distortion components generated by the main amplifier 7. Or a frequency outside the band of the original signal. Further, the selection frequencies of the selection level meters 29 and 31 are set to the oscillation frequencies of the oscillators 20 and 22, respectively.

At this time, the control circuit 36 controls the selection level meter 2
The set points of the variable attenuator 24 and the variable phase shifter 25 are adjusted so that the output of No. 9 takes the minimum value. As a control method, for example, the set point is gradually changed step by step, and a point at which the output of the selection level meter 29 becomes minimum is detected, and then the control of the variable attenuator 24 and the variable phase shifter 25 at that time is performed. A method for holding voltage can be applied. By using a signal having a specific frequency, that is, the first pilot signal, the transmission characteristics of the two paths constituting the distortion detection circuit 1 can be easily and independently of each other, independent of the input signal. ,
In addition, the phases can be reversed. This realizes a condition in which the original signal in the output of the auxiliary amplifier 12 is minimized, that is, a state in which the signal suppression amount of the distortion detection circuit 1 is maximized.

Next, the control circuit 36 controls the selection level meter 31.
Electric variable attenuator 2 so that the output level of
6 and the electric variable phase shifter 27 are adjusted. This is because the control method is effective because the main amplifier 7 can be regarded as having generated the same component distortion as the second pilot signal by the oscillator 22, and the condition that the distortion output included in the output signal is minimized, that is, the distortion A state where the signal suppression amount of the removal circuit 2 is maximized can be realized.

Further, in order to remove the first pilot signal by the oscillator 20 from the output signal of the feedforward amplifier, the semi-fixed variable attenuator 3 is controlled so that the output level of the first pilot signal at the output terminal 17 takes a minimum value.
2 and the set point of the semi-fixed variable phase shifter 33 are adjusted. At this time, the level of the first pilot signal leaking from the output terminal 17 is maintained at a certain value because the distortion detection circuit 1 and the distortion removal circuit 2 have been controlled to be in a balanced state. Therefore, the setting of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 need not be performed all the time, but only needs to be performed once when the operation of the feedforward amplifier is started. If the set values of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 are known, the fixed attenuator and the fixed phase shifter are used instead of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33. A vessel may be used. In this manner, the first pilot signal is divided into a directional coupler 35 by the semi-fixed variable attenuator 32, the semi-fixed variable phase shifter 33, and the signal amplifier 34.
Is to inject the first pilot signal into the output signal of the feedforward amplifier under the same amplitude and opposite phase conditions as the first pilot signal included in the output signal. The first pilot signal does not appear.

The optimum operation conditions of the feedforward amplifier having good linearity are realized by always or intermittently executing the two controls for achieving the balanced state of the distortion detection circuit 1 and the distortion removal circuit 2. it can. As shown in FIG. 2, a directional coupler 28 may be inserted at the output side of the auxiliary amplifier 12. Further, as shown in FIG. 2, a directional coupler 23 may be inserted on the input side of the main amplifier 7.

FIG. 3 shows another embodiment of the present invention. Instead of the selection level meters 29 and 31 for detecting the level of the pilot signal, homodyne detection circuits 39 and 40 are used. The homodyne detection circuit 39 includes a mixer 42,
Low-pass filter (LPF) 43 and DC amplifier 44
By performing homodyne detection with the local signal from the oscillator 20, the level of the first pilot signal by the oscillator 20 in the output signal of the directional coupler 28 can be detected with high sensitivity. Homodyne detection circuit 40
Is composed of a mixer 45, an LPF 46, and a DC amplifier 47, and can detect the level of the second pilot signal by the oscillator 22 in the output signal of the feedforward amplifier with high sensitivity by performing homodyne detection with the local signal from the oscillator 22. it can.

The operation of this circuit is as follows. When a signal is input as in the case of FIG. 1, the control circuit 36 controls the electric variable attenuator 24 so that the output level of the homodyne detection circuit 39 takes the minimum value. The set point with the variable phase shifter 25 is adjusted so that the operation of the distortion detection circuit 1 is in a desired equilibrium state in which the transmission characteristics of the two paths constituting the distortion detection circuit 1 are equal in amplitude and opposite in phase. I do. Next, the control circuit 36
Similarly, the electric variable attenuator 26 and the electric variable phase shifter 2 are arranged so that the output level of the homodyne detection circuit 40 takes the minimum value.
Adjust the set point with 7. In this way, the operation of the distortion removal circuit 2 is set to a desired equilibrium state in which the transmission characteristics of the two paths constituting the circuit have equal amplitudes and opposite phases. Further, in order to remove the first pilot signal by the oscillator 20 from the output signal of the feedforward amplifier, the semi-fixed variable attenuator 32 and the semi-fixed variable attenuator 32 are set so that the output level of the first pilot signal at the output terminal 17 takes a minimum value. The set point with the fixed variable phase shifter 33 is adjusted. At this time, since the distortion detection circuit 1 and the distortion removal circuit 2 have been controlled so as to be in a balanced state, the output terminal 1
The level of the first pilot signal leaking from 7 is kept at a certain value. Therefore, the setting of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 need not be performed at all times, but only once when the operation of the feedforward amplifier is started. If the set values of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 are known,
Instead of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33, a fixed attenuator and a fixed phase shifter may be used. In this way, inputting the first pilot signal to the directional coupler 35 by the semi-fixed variable attenuator 32, the semi-fixed variable phase shifter 33, and the signal amplifier 34 converts the first pilot signal into an output signal of the feedforward amplifier. The first pilot signal is injected with the same amplitude and opposite phase as the included first pilot signal, and the first pilot signal does not appear at the output terminal 17.
As a result, the optimum adjustment points of the two circuits are automatically set, a feedforward amplification operation with good linearity is realized, and the first pilot signal can be removed from the output signal of the feedforward amplifier. Here, all of the selection level meters 29 and 31 in FIG. 1 are configured by the homodyne detection circuits 39 and 40, respectively. However, one of the selection level meters 29 and 31 may be configured by the homodyne detection circuit. . Similarly, one or all of the selection level meters 29 and 31 in FIG. 2 may be constituted by a homodyne detection circuit.

FIG. 4 shows still another embodiment of the present invention. In this embodiment, signal switches 51 and 52 are additionally provided in the configuration example of FIG. 3, and the level detection means is only the homodyne detection circuit 39. This is the switch 5
1 and 52 share the homodyne detection circuit 39. When the switches 51 and 52 are connected to the directional coupler 28 and the oscillator 20, respectively, as shown by the solid lines, the operation is as shown in FIG.
This is the same as the case where the automatic adjustment of the distortion detection circuit 1 is performed. When the switches 51 and 52 are connected to the directional coupler 30 and the oscillator 22, respectively, as indicated by broken lines, the operation is the same as that in the case of performing the automatic adjustment of the distortion removing circuit 2 in FIG. Further, in order to remove the first pilot signal by the oscillator 20 from the output signal of the feedforward amplifier, the semi-fixed variable attenuator 32 and the semi-fixed variable attenuator 32 are set so that the output level of the first pilot signal at the output terminal 17 is minimized. Adjust the set point of the phase shifter 33. At this time,
Since the distortion detection circuit 1 and the distortion removal circuit 2 have been controlled so as to be in a balanced state, the level of the first pilot signal leaking from the output terminal 17 is kept at a certain value. Therefore, these semi-fixed variable attenuators 32
And the setting of the semi-fixed variable phase shifter 33 are not always performed.
It only needs to be performed once when the operation of the feedforward amplifier is started. When the set values of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 are known, a fixed attenuator, a fixed phase shifter are used instead of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33. A vessel may be used. In this way,
Inputting the first pilot signal to the directional coupler 35 by the signal amplifier 34 including the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 converts the first pilot signal into an output signal of the feedforward amplifier. Since the injection is performed under the same phase and the opposite phase condition as the first pilot signal component included therein, the first pilot signal does not appear at the output terminal 17. As described above, the switches 45 and 4
6 to operate the control circuit 36 so that the output of the homodyne detection circuit 37 takes the minimum value, thereby realizing the optimum operation state of the distortion detection circuit 1 and the distortion removal circuit 2 and the output signal of the feedforward amplifier. , The first pilot signal can be removed. Thus, the optimum operation state of the feedforward amplifier can be realized.

[0018]

As described above, according to the present invention,
Since it is possible to remedy the degradation of the characteristics of the feedforward amplifier caused by temperature changes, power supply fluctuations, etc., it can be used not only as a high-output amplifier for transmission in communications and broadcasting, but also as a practical linear amplifier for wired communication repeaters and audio equipment. Feedforward amplifiers can be widely applied.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing still another embodiment of the present invention.

FIG. 4 is a block diagram showing still another embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional feedforward amplifier.

FIG. 6 is a diagram showing a phase inversion circuit using a circulator.

FIG. 7 is a diagram showing a calculation example of the amplitude, the degree of phase imbalance, and the amount of signal cancellation of the feedforward amplifier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 distortion detection circuit 2 distortion removal circuit 7 main amplifier 12 auxiliary amplifier 20 oscillator for outputting first pilot signal 21, 23, 28, 30, 35 directional coupler 22 oscillator for outputting second pilot signal 24, 26 electrical Variable attenuator 25, 27 Electric variable phase shifter 29, 31 Selection level meter 32 Semi-fixed variable attenuator 33 Semi-fixed variable phase shifter 34 Amplifier 36 Control circuit 39, 40 Homodyne detection circuit

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Makoto Maeda 1-6-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-1-198809 (JP, A)

Claims (1)

(57) [Claims] 1. A distortion detecting circuit for detecting a nonlinear distortion component of a main amplifier, and amplifying the detected distortion component using an auxiliary amplifier, and then injecting the amplified distortion component into an output of the main amplifier to cancel the distortion component. A first injection means for injecting a first pilot signal of a specific frequency into an input path of the feedforward amplifier, and a first electric variable attenuation inserted in the distortion detection circuit. means,
First electric variable phase shift means and second injection means inserted into a path of the main amplifier of the distortion detection circuit for injecting a second pilot signal of a specific frequency different from the specific frequency, and inserted into the distortion removal circuit Second electrically variable damping means,
First level detection means inserted into the path of the auxiliary amplifier of the distortion removing circuit and the second electrically variable phase shift means and detecting the level of the first pilot signal; and the first level detection means of the output path of the feedforward amplifier. Second
Second level detection means for detecting the level of a pilot signal; and the first level detection means in the path of the output of the feedforward amplifier.
A third injection means for injecting a pilot signal, a semi-fixed variable attenuating means, a semi-fixed variable phase shift means and an amplifier inserted in a supply path of the first pilot signal to be injected by the third injection means; The first electrically variable attenuating means and the first electrically variable phase shifting means are controlled so that the detection level of the level detection means is minimized, and the detection level of the second level detection means is minimized. and control means for controlling said second electrically variable attenuator means and said second electrical variable phase shifting means, were provided in the attenuation of the semi-fixed variable attenuating means, the semi-fixed variable phase
The amount of phase shift of the means and the gain of the amplifier are equal to the third injection.
The first pilot signal injected by the means
The first pilot signal appearing in the output amplifier output path
Signal is set to have almost the same amplitude and almost the opposite phase.
Feedforward amplifier, characterized in that that.