JPH0483406A - Feedforward amplifier - Google Patents

Abstract

PURPOSE:To save the characteristic deterioration of an amplifier generated due to the variation of a peripheral temperature, a power supply, etc., by providing this feedforward amplifier with a means for controlling respective electric variable attenuation means and respective electric variable phase shifting means so that the detection levels of the 1st to 3rd level detecting means are minimized. CONSTITUTION:Respective outputs from selection level meters 29, 31, 37 are inputted to a control circuit 38, which controls variable attenuators 24, 26, 32 and variable phase shifters 25, 27, 33. The meters 29, 31, 37 for detecting the level of only a specific frequency component are respectively provided with frequency converters, narrow band filters and detectors to constitute them. Residual signal components generated due to the incompleteness of a signal offset conditions for two circuits in the feedforward amplifier are detected by a pilot signal detecting means and the transmission characteristic of the circuits are automatically adjusted so that the detection levels are minimized while monitoring the levels. Consequently, the characteristic deterioration of the feedforward amplifier generated due to a temperature change, power supply variation, or the like can be saved.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a linear amplifier mainly used in a high frequency band, and includes a distortion detection circuit that detects nonlinear distortion components of the main amplifier, and a distortion detection circuit that detects the detected distortion components. The present invention relates to a feedforward amplifier having a distortion removal circuit that cancels a distortion component by injecting it again into the output of a main amplifier after amplification using an auxiliary amplifier.

"Prior Art" The basic configuration of a feedforward amplifier is shown in FIG. A feedforward amplifier basically consists of two signal canceling circuits. One is the distortion detection circuit 1,
The other one is the distortion removal circuit 2. The distortion detection circuit 1 is composed of a main amplifier signal path 3 and a linear signal path 4, and also includes:
The distortion removal circuit 2 includes a main amplifier output signal path 5 and a total injection path 6.
It consists of Further, the King amplifier signal path 3 is comprised of a main amplifier 7, a variable attenuator 8, and a variable delay line 9 connected in series, and the linear signal path 4 is comprised of a transmission line. The main amplifier output signal path 5 consists of a transmission line, and the entire injection path 6 consists of a cascade connection of a variable attenuator 10, a variable delay line 11, and an auxiliary amplifier 12. Here, since there is no large difference in characteristics, both or only one of the variable attenuator 8 and the variable delay line 9 may be provided in the linear signal path 4. Similarly, both or only one of the variable attenuator IO and the variable delay line 11 may be provided in the main amplifier output signal path 5. In addition, the power divider 13 and the power combiner 1
4 and 15 are simple lossless power dividers/power combiners composed of transformer circuits, hybrid circuits, etc. First, this operation will be explained.

The input signal applied to the input terminal 16 is first distributed to the path j13 and the path 4 by the power divider 13, and then the power is combined by the power combiner 14. Here, variable attenuator 8
The variable delay line 'llll9 has the same amplitude and delay amount, and the opposite phases, for both signal components of the two paths 3 and 4 outputted from the power combiner 4 to the total injection path 6 side. It is adjusted so that However, the opposite phase condition can be achieved by appropriately setting the amount of phase shift between the input and output terminals in the power divider 13 or the power combiner 14, or by using phase inversion in the main amplifier 7.
Alternatively, as shown in FIG. 12, this can be realized by inserting a phase inversion circuit having a short-circuit termination @19 at one terminal of the circulator into either path 3 or 4.

Since the distortion detection circuit 1 is configured in this way, the difference component between the two signals on the two paths 3 and 4 will be detected as the output from the power combiner 14 to the path 6 side. . This difference component is exactly the distortion component generated by the main amplifier 7, and for this reason, the circuit 1 is called a distortion detection circuit.

Next, the variable attenuator 10 and the variable delay line 11 have a transfer function between the two paths 5 and 6 from the input terminal 14a of the power combiner 14 to the output terminal 17 of the power combiner 15 regarding the path 3. They are adjusted so that they are equal in amplitude and delay amount, and opposite in phase. Here, the input signal of path 6 is the distortion detection circuit 1i! 31, the path 6 injects the distortion component into the output signal of the main amplifier 7 at the output terminal 17 of the power combiner 15 with opposite phase and equal amplitude. Cancellation of distortion components in the output of the entire circuit is achieved.

“Problem to be Solved by the Invention J The above is the operation of an ideal feedforward amplifier, but in reality it is easy to perfect the balance between the two circuits, the distortion detection circuit 1 and the distortion removal circuit 2. Moreover, even if the initial settings are perfect, it is usually extremely difficult to maintain good balance over time because the characteristics of the amplifier change due to fluctuations in ambient temperature, power supply, etc. Figure 13 shows the result of calculating the relationship between the amount of deviation of the amplitude and phase of the two paths constituting the circuit from the equal-amplitude and anti-phase condition and the amount of signal suppression.From this figure, for example, 3
In order to achieve a suppression amount of 0 dB or more, it is necessary for the phase and amplitude deviations to be within ±, 8@ and ±0.3 dB, respectively, and the balance of the transmission characteristics of the two paths and the adjustment. I understand that strict conditions are required regarding integrity.

If the balance of the distortion detection circuit 1 deteriorates, the main signal is added to the input of the auxiliary amplifier 120 at a level higher than the distortion component, resulting in unnecessary distortion, and if the balance of the distortion removal circuit 2 deteriorates. As the amount of suppression deteriorates, the amount of distortion improvement as a feedforward amplifier deteriorates. As described above, the conventional feedforward amplifier has a basic problem in that it cannot realize a good linear amplifier because the circuit stability is not sufficient.

An object of the present invention is to provide a feedforward amplifier that solves the instability of such characteristics.

"Means for Solving the Problem" According to the present invention, there is provided a distortion detection circuit that detects a nonlinear distortion component of a main amplifier, and an auxiliary amplifier that amplifies the detected distortion component and then reinjects it into the output of the main amplifier. In the feedforward amplifier, the feedforward amplifier has a distortion removal circuit that cancels out distortion components by A first electrically variable attenuation means and a first electrically variable phase shift means are inserted into the main amplifier, and a second injection means for injecting a second pilot signal of a specific frequency into the path of the main amplifier is further provided, and the distortion removal circuit A second electrically variable attenuation means and a second electrically variable phase shift means are inserted into the auxiliary amplifier, and a first level detection means for detecting the first pilot signal level is provided in the path of the auxiliary amplifier. A third injection means for injecting the first pilot signal into the path is provided, and a third injection means is provided in the passage for supplying the first pilot signal to the third injection means.
Electrical variable attenuation means and third electrical variable phase shifting means and an amplifier are provided, and second level detection means is provided for detecting the level of a second pilot signal in the output path of the feedforward amplifier; third level detection means for detecting the level of the first pilot signal on the output path of the eleventh electrical variable attenuation means and the first electrical The second electrical variable attenuation means and the 211th electrically variable phase shift means are controlled by the control means, and the second electrical variable attenuation means and the 211th electrically variable phase shift means are controlled by the control means so that the detection level of the second level detection means is minimized. and the third electrically variable attenuation means and the third electrically variable phase shift means are controlled by the control means so that the detection level of the third level detection means is minimized.

"Operation" The residual signal bone caused by the imperfection of the signal cancellation conditions of the two circuits of the feedforward amplifier is detected by the pilot signal detection means, and while monitoring these detection levels, it is determined whether The transmission characteristics of the circuit are automatically adjusted so that

"Embodiments" Hereinafter, embodiments of the present invention will be described in detail based on the drawings. FIG. 1 shows an embodiment of the invention, and parts corresponding to those in FIG. 11 are given the same reference numerals. An oscillator 20 such as a frequency synthesizer for generating a first pilot signal with a specified frequency is coupled to the input terminal 13a side of the power divider 13 via a directional coupler 21. Further, an oscillator 22 such as a frequency synthesizer for generating a second pilot signal with a specified frequency is coupled to the output side of the main amplifier 7 via a directional coupler 23. variable attenuator 8,
In place of the variable delay line 9, an electrically adjustable variable attenuator 24 and an electrically adjustable variable phase shifter 25 are inserted into the main amplifier signal path 3 of the distortion detection circuit 1. Distortion removal circuit 2
The distortion injection path 6 includes a variable attenuator 10 and a variable delay line 11.
An electrically adjustable variable attenuator 26 and an electrically adjustable variable phase shifter 27 are inserted instead. These variable attenuators 24, 26 and variable phase shifter 2527 are
It can be easily configured using an N diode and a varactor diode, and commercially available products can also be used. A selection level meter 29 serving as first pilot signal level detection means is coupled to the input side of the electrically adjustable variable attenuator 26 via a directional coupler 28 . The first pilot signal is
The output of the feedforward amplifier is passed sequentially through an electrically adjustable variable attenuator 32, an electrically adjustable variable phase shifter 33, and a signal amplifier 34, and then via a power combiner 35 than the directional coupler 28. Joined to the side.

A selection level meter 31 serving as a second pilot signal level detection means is coupled to the output path of the feedforward amplifier via a directional coupler 30.

Furthermore, a selection level meter 37 serving as first pilot signal level detection means is coupled to the output path of the feedforward amplifier via a directional coupler 36. The directional couplers 30 and 36 may be interchanged. The respective outputs of the selection level meters 29, 31 and 37 are input to a control circuit 38, which controls variable attenuators 24, 26 and 32 and variable phase shifters 25, 27 and 33. The selection level meters 29, 31 and 37 detect the level of only a specific frequency component of the input signal, and are comprised of a frequency converter, a narrowband filter, and a detector.

The control circuit 38 is comprised of an A/D converter, a microprocessor, and a D/A converter as basic circuits, and monitors the input signals from the selection level meters 29.31 and 37, while monitoring the input signals from the variable attenuators 24.26. .32 and variable phase shifter 25.
It has the ability to adjust the 2733 set points. The control operation of this control circuit will be explained below. The first pilot signal generated by the oscillator 20 is set to a frequency slightly apart from the frequency band of the input signal of this feedforward amplifier, and the second pilot signal generated by the oscillator 22 is set to a frequency slightly apart from the frequency band of the input signal of the feedforward amplifier. Set the frequency to a gap between occupied frequencies or a frequency outside the original signal band.

The control circuit 38 adjusts the set points of the variable attenuator 24 and the variable phase shifter 25 so that the output of the selection level meter 29 takes the minimum value. As this control method, for example, the set point is changed little by little step by step, and after detecting the point where the output of the selection level meter 29 is the minimum, the variable attenuator 24 at that time is
A method of maintaining the control voltage of the variable phase shifter 25 can be applied. In this way, by using a signal with 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 adjusted to have equal amplitudes, independently of the input signal. , it is possible to reverse the phase. This makes it possible to realize a condition in which the original signal output from the auxiliary amplifier 12 is minimized, that is, a condition in which the amount of signal suppression of the distortion detection circuit 1 is maximized.

Next, the control circuit 38 adjusts the set points of the electrically variable attenuator 26 and the electrically variable phase shifter 27 so that the output level of the selected level meter 31 takes the minimum value.

This control method is effective because it can be considered that the main amplifier 7 generates distortion of the same component as the second pilot signal generated by the oscillator 22, and the condition that the distortion output included in the output signal is minimized is satisfied. A state in which the amount of signal suppression of the distortion removal circuit 2 is maximized can be realized.

Furthermore, in order to remove the first viroft signal generated by the oscillator 2o from the output signal of the feedforward amplifier, the control circuit 38 connects the electrically variable attenuator 32 and the electrically variable attenuator 32 so that the output level of the selection level meter 37 takes the minimum value. The set point of the variable phase shifter 33 is adjusted accordingly. At this time, since the distortion removal circuit 2 has been controlled to be in a parallel state, the transmission characteristics of the paths 5 and 6 are equal in amplitude and out of phase with each other. Therefore, the first viroft signal is
Inputting the first Byront signal to the power combiner 35 while being adjusted by the electrically adjustable variable attenuator 32, the electrically adjustable variable phase shifter 33, and the signal amplifier 34 allows the first Byront signal to be input to the power combiner 35 by the feedforward amplifier. Since the output signal is injected with the same amplitude and opposite phase conditions as the first pilot signal included in it, the first pilot signal is injected into the output terminal 17.
Pyroft signal does not appear.

By constantly or intermittently performing the above three controls, it is possible to achieve optimal operating conditions for a feedforward amplifier with good linearity.

As shown in FIG. 2, the power combiner 35 is connected to the auxiliary amplifier 12.
Alternatively, the directional coupler 23 may be inserted at the input side of the main amplifier 7.

FIG. 3 shows another embodiment of the invention. Homodyne detection circuit 3 instead of selection level meter 29.31 and 37
9.40 and 41 are used.

The homodyne detection circuit 39 includes a mixer 42, a low-pass filter (LPF) 43, and a DC amplifier 44, and performs homodyne detection using the local signal from the oscillator 20 to detect the oscillator in the output signal of the directional coupler 2. 2
The level of the first pilot signal due to zero can be detected with high sensitivity.

The homodyne detection circuit 40 is composed of a mixer 45, an LPF 46, and a DC amplifier 47, and performs homodyne detection using a local signal from the oscillator 22 to make the level of the second pilot signal from the oscillator 22 in the output signal of the feedforward amplifier highly sensitive. can be detected.

Further, the homodyne detection circuit 41 includes a mixer 48, an LP
Composed of F49 and DC amplifier 50, oscillator 20
By performing homodyne detection using a local signal from the oscillator 20, the level of the first pilot signal generated by the oscillator 20 in the output signal of the feedforward amplifier can be detected with high sensitivity.

The operation of this circuit is similar to the case of FIG. 1, when a signal is input, the control circuit 38 uses the electrically variable attenuator 24 and the electrically variable shifter so that the output level of the homodyne detection circuit 39 takes the minimum value. Adjust the set point with the phase shifter 25, and the distortion detection circuit 1
With regard to the operation, the transmission characteristics of the two paths constituting this are made to be in a desired balanced state in which they have equal amplitude and opposite phases. Next, the control circuit 38 similarly adjusts the set points of the electrically variable attenuator 26 and the electrically variable phase shifter 27 so that the output level of the homodyne detection circuit 40 takes the minimum value. In this way, the operation of the distortion removal circuit 2 is brought to a desired balanced state in which the transmission characteristics of the two paths constituting the distortion removal circuit 2 have equal amplitudes and opposite phases. Furthermore, the control circuit 38 similarly adjusts the set points of the electrically variable attenuator 32 and the electrically variable phase shifter 33 so that the output level of the homodyne detection circuit 41 takes the minimum value. As a result, the first pilot signal is injected into the feedforward amplifier output signal with equal amplitude and opposite phase, as in the case of FIG. As a result, the optimal 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 feedforward amplifier output signal. Here, all of the selection level meters 29.3 and 37 in FIG. 1 are constructed with homodyne detection circuits 39 and 40.41, respectively. One may be constructed from a homodyne detection circuit. Similarly, one or two of the selection level meters 293137 in FIG.
Alternatively, all of them may be configured with homodyne detection circuits.

FIG. 4 shows yet another embodiment of the invention.

In this embodiment, a signal switcher 5 is added to the third configuration example.
1 is newly provided, and the detection circuit has a configuration of homodyne detection circuits 39 and 40.

This is because the switch 51 is used to share the homodyne detection circuit 39. When the switch 51 is connected to the directional coupler 28 side as shown by the solid line, the operation is the same as when automatically adjusting the distortion detection circuit 1 in FIG. 3. Further, when the switch 51 is connected to the directional coupler 36 side as shown by the broken line, the operation is similar to the case where the first pilot signal is removed from the output signal of the feedforward amplifier in FIG. 3. Note that the operation of the distortion removal circuit 2 is similar to that in FIG. 3.

Note that the homodyne detection circuit 40 may be replaced with a selection level meter. As described above, by switching the switch 51 and operating the control circuit 38 so that the output of the homodyne detection circuit 39 takes the minimum value, the optimal operating state of the distortion detection circuit 1 is realized, and the feedforward amplifier The first pilot signal is removed from the output signal of the distortion removal circuit 2, and the control circuit 38 is operated so that the output of the homodyne detection circuit 40 takes the minimum value.
Optimum operating conditions can be achieved. In this way, optimal operating conditions of the feedforward amplifier can be achieved.

FIG. 5 shows an example in which a switch 5253 is further provided in the embodiment shown in FIG. This is because the homodyne detection circuit 39 is shared. If the switches 51 and 52 are connected to the directional coupler 28 as shown by the solid line, and the switch 53 is connected to the oscillator 20 as shown by the solid line, the operation will be the automatic one of the distortion detection circuit 1 in FIG. This is the same as when making adjustments.

Also, if the switch 53 is connected as shown in the solid line and the switch 52 is connected as shown in the broken line, the operation will be the same as the third one.
This is similar to the case where the first pilot signal is removed from the output signal of the feedforward amplifier in the figure. On the other hand, when the switches 51 and 53 are connected as shown by the broken line and the switch 52 is connected as shown by the solid line, the operation is the same as the automatic adjustment of the distortion removal circuit 2 shown in FIG. The same is true. As described above, by switching the switchers 5, 52, and 53 and operating the control circuit 38 so that the output of the homodyne detection circuit 39 takes the minimum value, the distortion detection circuit 1 and the distortion removal circuit 2 can be operated optimally. state, and also removes the first pilot signal from the feedforward amplifier output signal. In this way, optimal operating conditions of the feedforward amplifier can be achieved.

FIG. 6 shows a second embodiment of the invention. The configuration is the same as that in FIG. 1 except that a directional coupler 28 is inserted on the output side of the auxiliary amplifier 12. The control operation of this control circuit will be explained below.

First, a signal is input to the feedforward amplifier. As the input signal, as in the case of FIG. 1, for example, a combination of a plurality of continuous signals with specified frequencies is used. Also, the selected frequencies of the selected level meters 29, 31 and 37 are changed to the oscillators 20, 22, respectively, as in the case of FIG.
and 20 frequencies. Furthermore, as in the case of FIG. , the gap between the occupied frequencies of the original signal,
Or set it to a frequency outside the band.

First, the control circuit 38 adjusts the set points of only the variable attenuator 24 and the variable phase shifter 25 so that the output of the selected level meter 29 takes the minimum value. This is similar to other variable attenuators 26.32
This is because if the variable phase shifters 27 and 33 are adjusted simultaneously, the level detected by the level detector 29 will fluctuate, making it impossible to accurately achieve a balanced state of the distortion detection circuit 1 using the first pilot signal. Alternatively, the attenuation amount of the variable attenuator 32 is set to infinite, and the first pilot signal is transmitted to the power combiner 35.
or subtract from the output of the selection level meter 29 an amount corresponding to the amount supplied to the power combiner 35 through the variable attenuator 32. The transmission characteristics of the routes are
Equal amplitude and opposite phase conditions can be achieved.

Next, the control circuit 38 adjusts the set points of only the electrically variable attenuator 26 and the electrically variable phase shifter 27 so that the output level of the selected level meter 31 takes the minimum value. This is also in order to accurately achieve the balanced state of the distortion removal circuit 2 using the second pilot signal, as in the case of the distortion detection circuit 1.

Furthermore, in order to remove the first pyroft signal generated by the oscillator 20 from the output signal of the feedforward amplifier, the control circuit 38 connects the electrically variable attenuator 32 and the electrically variable attenuator 32 so that the output level of the selection level meter 37 takes the minimum value. Only the variable phase shifter 33 adjusts the set point. At this time, since the distortion removal circuit 2 has been controlled to be in an equilibrium state,
The transmission characteristics of path 5 and path 6 are equal in amplitude and out of phase with each other. Therefore, inputting the first pilot signal to the power combiner 35 while adjusting it by the electrically adjustable variable attenuator 32, the electrically adjustable variable phase shifter 33, and the signal amplifier 34 means that the first pilot signal Since the signal is injected into the output signal of the feedforward amplifier with equal amplitude and with opposite phase conditions, the output terminal 17
The first pilot signal does not appear in .

By constantly or intermittently performing the above three controls in sequence, it is possible to achieve optimal operating conditions for the feedforward amplifier with good linearity.

As shown in FIG. 7, the directional coupler 28 is connected to the power combiner 3.
It may be inserted immediately after 5.

FIG. 8 shows another embodiment of the invention. Similar to FIG. 3, homodyne detection circuits 39, 40 and 41 are used in place of selection level meters 29, 31 and 37. The operation of this circuit is similar to the case of FIG. 5, when a signal is input, the control circuit 38 uses the electrically variable attenuator 24 and the electrically variable shifter so that the output level of the homodyne detection circuit 39 takes the minimum value. The set point of only the phase shifter 25 is adjusted so that the operation of the distortion detection circuit 1 is brought into a desired balanced state in which the transmission characteristics of the two paths constituting the circuit have equal amplitudes and opposite phases. Next, the control circuit 38 similarly adjusts the set points of only the electrically variable attenuator 26 and the electrically variable phase shifter 27 so that the output level of the homodyne detection circuit 40 takes the minimum value. In this way, the operation of the distortion removal circuit 2 is brought to a desired balanced state in which the transmission characteristics of the two paths constituting the distortion removal circuit 2 have equal amplitudes and opposite phases. Further, the control circuit 38 includes a homodyne detection circuit 41
Similarly, the set points of only the electrically variable attenuator 32 and the electrically variable phase shifter 33 are adjusted so that the output level of is at the minimum value. As a result, the first pilot signal is injected into the feedforward amplifier output signal with equal amplitude and opposite phase, as in the case of FIG. As a result of performing the above three controls in order, the optimal adjustment points of the two circuits are automatically set, feedforward amplification operation with good linearity is realized, and the first pilot is output from the output signal of the feedforward amplifier. The signal can be removed. In addition, here, the selection level totals of 29.3 and 37 in Figure 6 are used.
are all connected to homodyne detection circuits 39, 40, respectively.
41, one or two of the selection level meters 29.3 and 37 may be constructed with a homodyne detection circuit.Similarly, the selection level meters 29.3 and 37 in FIG.
One, two, or all of 7 may be configured with a homodyne detection circuit.

FIG. 9 shows yet another embodiment of the invention.

In this embodiment, a signal switch 5 is added to the configuration example of FIG.
1 is newly provided, and the detection circuit is a homodie detection circuit 39.
and 40 configurations. This is because the switch 51 is used to share the homodyne detection circuit 39. Also, the directional couplers 30 and 36 are exchanged. When the switch 51 is connected as shown by the solid line, the operation is the same as when the distortion detection circuit 1 is automatically adjusted in FIG. Furthermore, when the switch 51 is connected as shown by the broken line, the operation is similar to that in which the first pilot signal is removed from the output signal of the feedforward amplifier in FIG. The operation of the distortion removal circuit 2 is the same as that shown in FIG. Note that the homodyne detection circuit 40 may be replaced with a selection level meter. The distortion can be reduced by switching the switch 51 and operating the control circuit so that the output of the homodyne detection circuit 39 takes the minimum value. The optimum operating state of the detection circuit 1 is realized, and the first pilot signal is removed from the output signal of the feedforward amplifier. In addition, the homodyne detection circuit 40
By operating the control circuit 38 so that the output of the distortion removal circuit 2 takes a minimum value, the optimum operating state of the distortion removal circuit 2 can be realized. In this way, optimal operating conditions of the feedforward amplifier can be achieved.

FIG. 10 shows a switch 52, 53 in addition to the embodiment of FIG.
This is an example where . This is the homodyne detection circuit 3
This is because 9 is shared. When the switches 52 and 53 are connected as shown in the solid line and the switch 51 is connected as shown in the solid line, the operation is similar to the automatic adjustment of the distortion detection circuit l in FIG. In addition, when the switches 52 and 53 are connected as shown in the solid line and the switch 51 is connected as shown in the broken line, the operation changes from the output signal of the feedforward amplifier to the first pilot signal in FIG. This is the same as when performing removal. On the other hand, when the switchers 52 and 53 are connected as shown by the broken lines, the operation is similar to the case where the distortion removal circuit 2 of FIG. 8 is automatically adjusted.

As mentioned above, by switching the switchers 5, 52 and 53,
By operating the control circuit 38 so that the output of the homodyne detection circuit 39 takes the minimum value, the optimum operating state of the distortion detection circuit 1 and the distortion removal circuit 2 is realized, and the first pilot signal is extracted from the output signal of the feedforward amplifier. Perform signal removal. In this way, optimal operating conditions of the feedforward amplifier can be achieved.

"Effects of the Invention" As explained above, the present invention can relieve characteristic deterioration of feedforward amplifiers caused by temperature changes, power supply fluctuations, etc. Feedforward amplifiers can be widely applied as practical linear amplifiers for wired communication repeaters, audio equipment, etc.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of this invention, and FIG.
5 to 5 are block diagrams showing modifications of the first embodiment, FIG. 6 is a block diagram showing a second embodiment of the invention, and FIGS. 7 to 10 are modifications of the second embodiment, respectively. A block diagram showing an example, Fig. 11 is a block diagram showing a conventional feedforward amplifier, Fig. 12 is a diagram showing a phase inversion circuit using a circulator, Fig. 13 is a diagram showing the amplitude, phase imbalance, and signal cancellation of the circuit. It is a figure which shows the calculation example of quantity. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] (1) A distortion detection circuit that detects a nonlinear distortion component of the main amplifier, and a distortion component that cancels out the distortion component by amplifying the detected distortion component using an auxiliary amplifier and then injecting it into the output of the main amplifier again. 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 electrically variable attenuation means inserted in the distortion detection circuit;
a second injection means inserted into a path of a first electrically variable phase shifter and the main amplifier of the distortion detection circuit, and for injecting a second pilot signal having a specific frequency different from the specific frequency; and inserted into the distortion removal circuit. a second electrically variable damping means;
a second electrically variable phase shift means, and a first level detection means inserted in a path of the auxiliary amplifier of the distortion removal circuit to detect the first pilot signal level; and a path of the auxiliary amplifier of the distortion removal circuit. a third injection means for injecting the first pilot signal into the first pilot signal; a third electrically variable attenuation means inserted into a supply path of the first pilot signal injected by the third injection means; and a third electrically variable phase shifter. means and an amplifier; second level detection means for detecting the level of the second pilot signal in the output path of the feedforward amplifier; and third level detection means for detecting the level of the first pilot signal in the output path of the feedforward amplifier. level detection means; controlling the first electrically variable attenuation means and the first electrically variable phase shifting means so that the detection level of the first level detection means is minimized; and the second level detection means The second electrically variable attenuating means and the second electrically variable phase shifting means are controlled so that the detection level of the third level detecting means is minimized, and the second electrically variable phase shifting means is controlled so that the detection level of the third level detecting means is minimized. 3. A feedforward amplifier comprising: control means for controlling the third electrically variable attenuation means and the third electrically variable phase shift means.