JPH04233811A - Feedforward amplifier - Google Patents

Abstract

PURPOSE:To keep timely stable excellent balance regardless of variance of ambient temperature and a power supply. CONSTITUTION:A selective levelmeter 29 detects a 1st pilot signal of an oscillator 20 from a signal extracted via a directional coupler 28 at a pre-stage of an auxiliary amplifier 12 in a distortion elimination circuit 2 and a control circuit 36 controls a variable attenuator 24 and a variable phase shifter 25 so as to minimize the level of the 1st pilot signal. A selection level meter 31 detects a 2nd pilot signal of an oscillator 22 from a signal extracted via a directional coupler 30 from the output of the distortion elimination circuit 2 and the control circuit 36 controls a variable attenuator 26 and a variable phase shifter 27 so as to minimize the level of the 2nd pilot signal. The output of the oscillator 20 is fed to the output of the distortion eliminating circuit 2 via a semi-fixed variable attenuator 32, a semi-fixed variable attenuator 33, an amplifier 34 and a directional coupler 35 to cancel out the 1st pilot signal at an output terminal 17.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a linear amplifier mainly used in a high frequency band, which includes a distortion detection circuit for detecting nonlinear distortion components of the main amplifier, and an auxiliary amplifier to amplify the detected distortion components. The present invention also relates to a feedforward amplifier having a distortion removal circuit that cancels distortion components by reinjecting them into the output of the main amplifier.

0002

2. Description of the Related Art The basic configuration of a feedforward amplifier is shown in FIG. A feedforward amplifier basically consists 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 is comprised of a main amplifier signal path 3 and a linear signal path 4, and the distortion removal circuit 2 is comprised of 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 consists of a transmission line, and the distortion injection path 6 includes a variable attenuator 10 and a variable delay line 11.
and an auxiliary amplifier 12 in cascade. 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 10 and the variable delay line 11 may be provided in the main amplifier output signal path 5. Further, the power divider 13 and the power combiners 14 and 15 are simple lossless power dividers/power combiners configured with transformer circuits, hybrid circuits, and the like. First, this operation will be explained.

The input signal applied to the input terminal 16 is first divided into paths 3 and 4 by a power divider 13, and then power-combined by a 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 outputted from the power combiner 14 to the distortion injection path 6 side, and , the phases are adjusted so that they are out of phase. 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. 6, this can be realized by inserting a phase inversion circuit having a short-circuit termination 19 at one terminal of the circulator 18 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 are used to communicate 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. The functions are adjusted so that they are equal to each other in terms of amplitude and amount of delay, and are opposite to each other in terms of phase. Here, since the input signal of the path 6 is the distortion component of the main amplifier 7 detected by the distortion detection circuit 1, the input signal of the path 6 is the distortion component of the output signal of the main amplifier 7 at the output terminal 17 of the power combiner 15. are injected with opposite phases and equal amplitudes, eventually canceling out the distortion components in the output of the entire circuit.

[0005]

[Problem to be solved by the invention] 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. It is. FIG. 7 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, in order to achieve a suppression amount of 30 dB or more, the phase and amplitude deviations must be ±1.
It is clear that strict conditions are required regarding the balance of the transmission characteristics of the two paths and the completeness of adjustment. When the balance of the distortion detection circuit 1 deteriorates, the main signal is added to the input of the auxiliary amplifier 12 at a level higher than the distortion component, causing unnecessary distortion, and the balance of the distortion removal circuit 2 also deteriorates. Then, the amount of distortion improvement as a feedforward amplifier is degraded by the amount of suppression degraded. 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 problem of instability in characteristics.

[0007]

[Means for Solving the Problems] According to the present invention, there is provided a distortion detection circuit that detects a nonlinear distortion component of a main amplifier, and a distortion detection circuit that amplifies the detected distortion component using an auxiliary amplifier, and then returns the detected distortion component to the output of the main amplifier. In the feedforward amplifier, the feedforward amplifier has a distortion removal circuit that cancels distortion components by injecting the distortion component into the input path of the feedforward amplifier. A first electrically variable attenuation means and a first electrically variable phase shift means are inserted into the circuit, and a second injection means is provided for injecting a second pilot signal of another specific frequency into the path of the main amplifier. The distortion removal circuit is provided with a second electrically variable attenuation means and a second electrically variable phase shifter, and a first electrically variable attenuator is provided in the path of the auxiliary amplifier.
A first level detection means for detecting a level of a pilot signal is provided, a second level detection means for detecting a level of a second pilot signal in an output path of the feedforward amplifier is provided, and a second level detection means is provided in an output path of the feedforward amplifier. A third injection means for injecting the first pilot signal is provided, and a semi-fixed variable attenuation means, a semi-fixed variable phase shift means and an amplifier are inserted in the supply path of the first pilot signal supplied to the third injection means, and the above-mentioned The first electrically variable attenuation means and the first electrically variable phase shift means are controlled by a control means so that the detection level of the first level detection means is minimized, and the detection level of the second level detection means is controlled by a control means. The second electrically variable attenuation means and the second electrically variable phase shift means are controlled by the control means so that the second electrically variable phase shift means is minimized.

[0008]

[Operation] The residual signal generated due to 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 The transmission characteristics of the circuit are automatically adjusted so that

[0009]

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 FIG.
Corresponding parts 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. Also,
An oscillator 22 such as a frequency synthesizer for generating a second pilot signal with a specified frequency is connected to a directional coupler 23
is coupled to the output side of the main amplifier 7 via. In place 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 into the main amplifier signal path 3 of the distortion detection circuit 1. . 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 removal circuit 2 in place of the variable attenuator 10 and the variable delay line 11. . These variable attenuators 24, 26 and variable phase shifters 25, 2
7 can be easily constructed using a PIN diode and a varactor diode, and commercially available products are also available. A selective level meter 2 is connected to the input side of the variable attenuator 26 via a directional coupler 28 as a level detection means for the first pilot signal.
9 are combined. 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. Further, the first pilot signal passes through the semi-fixed variable attenuator 32, the semi-fixed variable phase shifter 33, and the signal amplifier 34, and is coupled to the output path of the feedforward amplifier via the directional coupler 35. Each output of the selection level meters 29 and 31 is input to a control circuit 36, which controls variable attenuators 24 and 26 and variable phase shifters 25 and 27. The selection level meters 29 and 31 are comprised of a frequency converter and a narrowband filter that detect a specific frequency component of an input signal, and a detector that detects the output level of the narrowband filter. The control circuit 36 is composed of an A/D converter, a microprocessor, and a D/A converter as a basic circuit, and monitors the input signals from the selection level meters 29 and 31 while controlling the input signals from the variable attenuators 24 and 26 and the variable It has a function of adjusting the set points of the phase shifters 25 and 27. The control operation of this control circuit will be explained below.

First, a signal is input to the feedforward amplifier. As the input signal, for example, a combination of a plurality of continuous signals with specified frequencies is used. Also, the oscillator 20
The first pilot signal generated by the oscillator 22 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 the gap between the two or to a frequency outside the original signal band. Furthermore, the selection frequencies of selection level meters 29 and 31 are set to the oscillation frequencies of 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 the variable phase shifter 9 takes the minimum value. This control method includes, for example, changing the set point step by step, detecting the point where the output of the selection level meter 29 is minimum, and then controlling the variable attenuator 24 and the variable phase shifter 25 at that point. A method of maintaining voltage can be applied. By using a signal with a specific frequency, that is, the first pilot signal, the distortion detection circuit 1 can be easily controlled independently of the input signal.
The transmission characteristics of the two paths constituting the can be made to have equal amplitudes and opposite phases. 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 36 controls the selection level meter 31.
electrically variable attenuator 2 so that the output level of
6 and the electrically variable phase shifter 27 are adjusted. This control method is effective because it can be considered that the main amplifier 7 has generated distortion of the same component as the second pilot signal from the oscillator 22. A state in which the signal suppression amount of the removal circuit 2 is maximized can be realized.

Furthermore, in order to remove the first pilot signal from the oscillator 20 from the output signal of the feedforward amplifier, the semi-fixed variable attenuator 3 is installed so that the output level of the first pilot signal at the output terminal 17 takes a minimum value.
2 and the semi-fixed variable phase shifter 33 are adjusted. At this time, since the distortion detection circuit 1 and the distortion removal circuit 2 have been controlled to be in a balanced state, the level of the first pilot signal leaking from the output terminal 17 is maintained at a certain constant value. Therefore, instead of setting the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 all the time, it is only necessary to set them once when starting the operation of the feedforward amplifier. In addition, if the setting 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 can be used instead of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33. A container may also be used. In this way, the first pilot signal is transmitted to the directional coupler 35 by the semi-fixed variable attenuator 32, the semi-fixed variable phase shifter 33, and the signal amplifier 34.
Inputting the first pilot signal into the feedforward amplifier means injecting the first pilot signal into the output signal of the feedforward amplifier with the same amplitude and opposite phase condition as the first pilot signal contained therein. The first pilot signal does not appear.

[0014] By constantly or intermittently executing the two controls for achieving a balanced state between the distortion detection circuit 1 and the distortion removal circuit 2, the optimum operating conditions of the feedforward amplifier with good linearity are realized. 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 invention. Homodyne detection circuits 39 and 40 are used in place of selective level meters 29 and 31 that detect the level of the pilot signal. The homodyne detection circuit 39 includes a mixer 42,
Low pass filter (LPF) 43 and DC amplifier 44
By performing homodyne detection using the local signal from the oscillator 20, the level of the first pilot signal from 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 second pilot signal level of the oscillator 22 in the output signal of the feedforward amplifier with high sensitivity by performing homodyne detection using the local signal from the oscillator 22. can.

The operation of this circuit is similar to the case of FIG. 1, when a signal is input, the control circuit 36 connects the electrically variable attenuator 24 and the electrically 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 balanced state in which the transmission characteristics of the two paths constituting it are equal in amplitude and in opposite phases. do. Next, the control circuit 36
Similarly, the electrically variable attenuator 26 and the electrically variable phase shifter 2 are connected 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 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, in order to remove the first pilot signal generated by the oscillator 20 from the output signal of the feedforward amplifier, a semi-fixed variable attenuator 32 and a semi-fixed variable attenuator 32 are connected so that the output level of the first pilot signal at the output terminal 17 takes a minimum value. Adjust the set point with the fixed variable phase shifter 33. At this time, since the distortion detection circuit 1 and the distortion removal circuit 2 have been controlled 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 constant value. Therefore, the setting of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 need not be done all the time, but only once when starting the operation of the feedforward amplifier. Also, if the setting values of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 are known,
A fixed attenuator or a fixed phase shifter may be used instead of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33. 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 causes the output signal of the feedforward amplifier to be input to the directional coupler 35. 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 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 output signal of the feedforward amplifier. In addition,
Here, all of the selection level meters 29 and 31 in FIG. 1 are constructed from homodyne detection circuits 39 and 40, respectively, but one of the selection level meters 29 and 31 may be constructed from a homodyne detection circuit. Similarly, the selection level meter 2 in FIG.
One or all of 9 and 31 may be configured with a homodyne detection circuit.

FIG. 4 shows yet another embodiment of the invention. In this embodiment, signal switchers 51 and 52 are newly added to the configuration example of FIG. 3, and the homodyne detection circuit 39 is the only level detection means. This is switch 5
1 and 52 share the homodyne detection circuit 39. When the switchers 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 similar to the case of automatically adjusting the distortion detection circuit 1 in . Further, when the switchers 51 and 52 are connected to the directional coupler 30 and the oscillator 22, respectively, as shown by the broken lines, the operation is the same as when automatically adjusting the distortion removal circuit 2 in FIG. 3. Furthermore, in order to remove the first pilot signal generated by the oscillator 20 from the feedforward amplifier output signal, a semi-fixed variable attenuator 32 and a semi-fixed variable Adjust the set point of phase shifter 33. At this time,
Since the distortion detection circuit 1 and the distortion removal circuit 2 have been controlled to be in a balanced state, the level of the first pilot signal leaking from the output terminal 17 is maintained at a certain constant value. Therefore, these semi-fixed variable attenuators 32
Rather than setting the semi-fixed variable phase shifter 33 all the time,
It only needs to be done once when starting the operation of the feedforward amplifier. In addition, if the setting values of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 are known, the fixed attenuator and fixed phase shifter can be used instead of the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33. A container may also be used. In this way,
Inputting the first pilot signal to the directional coupler 35 through the semi-fixed variable attenuator 32 and the semi-fixed variable phase shifter 33 through the signal amplifier 34 converts the first pilot signal into the output signal of the feedforward amplifier. The first pilot signal does not appear at the output terminal 17 because it is injected with the same amplitude and opposite phase conditions as the first pilot signal component included therein. As described above, the switching devices 45 and 4
6 to operate the control circuit 36 so that the output of the homodyne detection circuit 37 takes the minimum value, the optimum operating state of the distortion detection circuit 1 and the distortion removal circuit 2 is realized, and the feedforward amplifier output signal The first pilot signal can be removed from . In this way, optimal operating conditions of the feedforward amplifier can be achieved.

[0018]

[Effect of the invention] As explained above, with this invention,
Since it can relieve characteristic deterioration of feedforward amplifiers 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, audio equipment, etc. Feedforward amplifiers can be widely applied.

[Brief explanation of the drawing]

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

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

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

FIG. 4 is a block diagram showing still another embodiment of the 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 an example of calculating the amplitude, phase unbalance, and signal cancellation amount of a feedforward amplifier.

[Explanation of symbols]

1 Distortion detection circuit 2 Distortion removal circuit 7 Main amplifier 12 Auxiliary amplifier 20 Oscillators 21 and 2 that output the first pilot signal
3, 28, 30, 35 Directional coupler 22 Oscillator 24, 26 that outputs the second pilot signal Electrical variable attenuator 25, 27 Electrical 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

Claims (1)

[Claims] 1. A distortion detection circuit that detects a nonlinear distortion component of a main amplifier, and a distortion component that is amplified using an auxiliary amplifier and then injected into the 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 the input path of the feedforward amplifier; and a first electrically variable attenuation inserted into the distortion detection circuit. means, inserted in a path of the first electrically variable phase shifting means and the main amplifier of the distortion detection circuit,
a second injection means for injecting a second pilot signal of a specific frequency different from the specific frequency; a second electrically variable attenuator inserted in the distortion removal circuit; a second electrically variable phase shift device; and the distortion removal circuit. a first pilot signal for detecting the level of the first pilot signal;
level detection means; 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 injecting the first pilot signal into the output path of the feedforward amplifier.
an injection means, and the first injection means injected by the third injection means.
a semi-fixed variable attenuation means, a semi-fixed variable phase shift means, and an amplifier inserted in a pilot signal supply path;
The first electrically variable attenuation means and the first electrically variable phase shift 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. control means for controlling the second electrically variable attenuation means and the second electrically variable phase shifting means;
A feedforward amplifier comprising: