JPH04286209A - Feedforward amplifier - Google Patents

Abstract

PURPOSE:To automatically suppress the deterioration of a characteristic based on the deterioration of the balance of a distortion detection circuit and a distortion removal circuit due to the change of temperature or the variation of power supply, etc. CONSTITUTION:A main amplifier 7 is constituted into two-stage configuration of amplifier units 20 and 21, and a coupler 23 is inserted between these stages, and a pilot signal is injected from an oscillator 22. The coupler 28 is inserted into the path 6 of an auxiliary amplifier 12, and the level of an input signal component is detected by a level detector 29, and a control circuit 32 controls an electric variable attenuator 24 and an electric variable phase shifter 25 inserted into the path 3 of the main amplifier 7 so that said detected level becomes minimum. The coupler 30 is inserted into the output path of this amplifier, and the level of the pilot signal component is detected by the level detector 31, and the control circuit 32 controls the electric variable attenuator 26 and the electric variable phase 27 so that this detected level becomes minimum.

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. 10, the circulator 18
This is realized by inserting a phase inversion circuit with a short-circuit termination 19 at one terminal of the 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, variable attenuator 10 and variable delay line 11
is the input terminal 14 of the power combiner 14 for path 3.
The transfer functions of the two paths 5 and 6 from a to the output terminal 17 of the power combiner 15 are adjusted so that they are equal in amplitude and delay amount and opposite in 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. 11 shows the results 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 each 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 reinjects it into the output of the main amplifier. In a feedforward amplifier having a distortion removal circuit that cancels distortion components by
An electrically variable attenuator and a first electrically variable phase shifter are inserted, and a second electrically variable attenuator and a second electrically variable phase shifter are inserted into the distortion removal circuit to adjust the signal level in the path of the auxiliary amplifier. A first level detection means is provided for detecting a pilot signal level in an output path of the feedforward amplifier, and a second level detection means is provided for detecting a pilot signal level in an output path of the feedforward amplifier.
The first electrical variable attenuation means and the first electrical variable phase means are controlled so that the detection level of the first level detection means is minimized, and the detection level of the second level detection means is minimized. Control means are provided for controlling the second electrically variable attenuation means and the second electrically variable phase shifting means.

[0008]

[Operation] The residual signal component and the residual pilot signal generated due to the imperfection of the signal cancellation conditions of the two circuits of the feedforward amplifier are detected by the first and second level detection means, and these detection levels are determined. While monitoring, the transmission characteristics of the circuit are automatically adjusted so that they take the minimum value.

[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. Main amplifier 7
In this example, it is composed of two stages of amplifier units 20 and 21 connected in cascade. Each of the amplifier units 20 and 21 may be composed of a single transistor element, or may be composed of a plurality of transistor elements connected in series or in parallel. An oscillator 22 such as a frequency synthesizer for generating a pilot signal is coupled between the output side of the amplifier unit 20 and the input side of the amplifier unit 21 via a directional coupler 23 . Furthermore, 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 transfer device 27 are inserted into the strain injection path 6 of the distortion removal circuit 2. These variable attenuators and variable phase shifters can be easily constructed using PIN diodes and varactor diodes, and commercially available products are also available. A level detector 29 is coupled to the input side of the variable attenuator 26 in the strain injection path 6 via a directional coupler 28 . A level detector 31 is coupled to the output path of the feedforward amplifier via a directional coupler 30. Each output of the level detectors 29 and 31 is input to a control circuit 32, which controls variable attenuators 24 and 26 and variable phase shifters 25 and 27. The level detector 29 is
Selective level meters with frequency converters and narrowband filters and detectors, which may be configured to detect the total power level of the input signal, or may be configured to detect the level of only specific frequency components in the input signal. There are cases where it is configured as follows. Further, the level detector 31 is composed of a selection level meter, and the selection frequency is set to the frequency of the pilot signal input from the oscillator 22. The control circuit 32 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 level detectors 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 32 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 pilot signal from the oscillator 22 is set to a frequency among the distortion components generated by the main amplifier 7 that is between the frequencies occupied by the original signal or outside the band. At this time, the level detector 29 detects the distortion component of the main amplifier 7 including the input signal that could not be suppressed by the distortion detection circuit 1. Here,
When the level detector 29 is configured with a selected level meter,
By setting the selection frequency to the continuous signal, only the level of the input signal that cannot be suppressed by the distortion detection circuit 1 can be detected. The control circuit 32 controls the variable attenuator 24 and the variable phase shifter 2 so that the output of the level detector 29 takes the minimum value.
Adjust the set point with 5. 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 level detector 29 is the minimum, the variable attenuator 24 and the variable phase shifter 25 are A method of holding each control voltage can be applied. This makes it possible to realize a condition in which the output of 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 32 includes a level detector 31
electrically variable attenuator 2 so that the output level of
6 and the set points of the electrically variable phase shifter 27 are adjusted. This control method is effective because it can be considered that the main amplifier 7 generates distortion of the same component as the pilot signal generated by the oscillator 22, and the condition that the distortion output included in the output signal is minimized is the condition that the distortion removal circuit A state in which the amount of signal suppression of No. 2 is maximized can be realized.

[0012] By constantly or intermittently executing the above two controls, it is possible to realize optimal operating conditions for a feedforward amplifier with good linearity. In either case where the amplifier units 20 and 21 are composed of a single transistor element or a plurality of transistor elements, the pilot signal is transmitted to the emitter, collector, or base of any one transistor element that constitutes the amplifier units 20 and 21. It may also be injected into the terminals of the device via a directional coupler. FIG. 2 shows an embodiment in which both amplifier units 20 and 21 are composed of a single transistor element with a common emitter, and a pilot signal from an oscillator 22 is injected into the collector terminal of the amplifier unit 21 via a directional coupler 23.
Shown below. However, Vcc represents the power supply voltage.

In the present invention, the main amplifier 7 may be constructed of three or more stages connected in cascade as represented by amplifier units 33, 34 and 35 as shown in FIG. In this case, the pilot signal is injected at one location other than the input end and output end of the main amplifier 7. Alternatively, a pilot signal may be injected via a directional coupler to any one of the emitter, collector, or base terminals of any one transistor element constituting the amplifier units 33, 34, and 35; Included in invention. FIG. 4 shows an embodiment in which the amplifier unit 33 is composed of a single transistor element whose emitter is grounded, and a pilot signal from the oscillator 22 is injected into the collector terminal of the amplifier unit 33 via the directional coupler 23. However, Vc
c represents the power supply voltage.

Furthermore, as shown in FIG. 5, the main amplifier 7 is configured by using a power divider 36 and a power combiner 37, and two or more amplifier units 38 and 39 are connected in parallel. Good too. In this case, the pilot signal is injected at the input end or output end of any one amplifier unit between the power divider 36 and the power combiner 37. Alternatively, amplifier units 38 and 39
the emitter of any one transistor element constituting the
A pilot signal may be injected into either the collector or the base terminal via a directional coupler, and this is also included in the present invention. FIG. 6 shows an embodiment in which the amplifier unit 39 is composed of a single transistor element whose emitter is grounded, and a pilot signal from the oscillator 22 is injected into the base terminal of the amplifier unit 39 via the directional coupler 23. However, Vcc represents the power supply voltage.

Furthermore, as an example of this is shown in FIG. 7, the main amplifier 7 may be configured as a combination of the embodiment shown in FIG. 3 and the embodiment shown in FIG. Alternatively, the amplifier units 40, 41,
A pilot signal may be injected into the emitter, collector, or base of any one of the transistor elements constituting 42, 43, 44, and 45 via a directional coupler, and this also applies to the present invention. included. FIG. 8 shows an embodiment in which the amplifier unit 42 is composed of a single transistor element with a common emitter, and a pilot signal from the oscillator 22 is injected into the base terminal of the amplifier unit 42 via a directional coupler 23. However, Vcc represents the power supply voltage.

[0016]

[Effect of the invention] As explained above, with this invention,
Since it can relieve characteristic deterioration due to a drop in the balance of feedforward amplifiers caused by temperature changes, power supply fluctuations, etc., it is useful not only for high-output amplifiers for transmission in communications and broadcasting, but also for practical applications such as wired communication repeaters and audio equipment. Feedforward amplifiers can be widely applied as linear amplifiers. Furthermore, in the present invention, since the pilot signal injection means is provided inside the main amplifier 7, the main amplifier 7 including the pilot signal injection means, for example,
can be modularized, and design and manufacture are easier than in the case where the pilot signal injection means is provided outside the main amplifier 7.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing a specific example of the main amplifier 7 and an example in which the pilot signal injection location is changed.

FIG. 3 is a diagram showing another example in which the main amplifier 7 is configured by direct connection.

FIG. 4 is a diagram illustrating a part of the main amplifier 7 of FIG. 3;

FIG. 5 is a diagram showing an example in which main amplifiers 7 are connected in parallel.

FIG. 6 is a diagram illustrating a part of the main amplifier 7 of FIG. 5;

FIG. 7 is a diagram showing an example in which the main amplifier 7 is configured in series-parallel connection.

FIG. 8 is a diagram illustrating a part of the main amplifier 7 in FIG. 7;

FIG. 9 is a block diagram showing a conventional feedforward amplifier.

FIG. 10 is a diagram showing a phase inversion circuit using a circulator.

FIG. 11 is a diagram showing an example of calculation of circuit amplitude, phase imbalance, and signal cancellation amount.

Claims (1)

[Claims] Claim 1: A distortion detection circuit that detects a nonlinear distortion component of a main amplifier, and cancels out the distortion component by amplifying the detected distortion component using an auxiliary amplifier and then reinjecting it into the output of the main amplifier. a feedforward amplifier having a distortion removal circuit, a means for injecting a pilot signal provided inside the main amplifier of the feedforward amplifier; a first electrical variable attenuation means inserted in the distortion detection circuit; 1 electrically variable phase shifting means;
a second electrically variable attenuation means and a second electrically variable phase shifter inserted in the distortion removal circuit; a first level detection means for detecting a signal level in the path of the auxiliary amplifier; and an output of the feedforward amplifier. a second level detection means for detecting the level of the pilot signal on the path; and the first electrically variable attenuation means and the first electrically variable phase shift means so that the detection level of the first level detection means is minimized. and control means for controlling the second electrically variable attenuating means and the second electrically variable phase shifting means so that the detection level of the second level detecting means is minimized. A feedforward amplifier featuring: