JPH0483407A - feedforward amplifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 J The basic configuration of a feedforward amplifier is shown in Figure 6.
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 total injection path 6. Furthermore, the main amplifier signal path 3 is the main amplification! 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 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, the variable attenuator 8
The linear signal path 4 may include both or only one of the variable delay line 9 and the variable delay line 9. Similarly, the variable attenuator 10 and the variable delay line 11 are both
Alternatively, only one of them 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 distributed to paths 3 and 4 by the power divider 13, and then the power is combined by the power combiner 14. Here, variable attenuator 8 and variable delay line? a9 is adjusted so that the signal components of the two paths 3 and 4 output from the power combiner 14 to the total injection path 6 have the same amplitude and delay amount, and have opposite phases. Ru. However, the condition for reverse phase 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.
This is achieved by inserting it into either of the following. Since the distortion detection circuit 1 is configured in this way, the power combiner 14
From the output to the side of route 6, there are two routes 3 and 4.
The difference component between the two signals will be detected. 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, 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.

"Problems to be Solved by the Invention" The above is the operation of an ideal feedforward amplifier, but in reality, the two circuits, the distortion detection circuit 1 and the distortion removal circuit 2, are perfectly balanced. 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. 8 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, 30
In order to achieve a suppression amount of dB or more, it is necessary that the phase and amplitude deviations are within ±1.8° and ±0.3dB, respectively, and the balance and adjustment of the transmission characteristics of the two paths is required. It is clear that strict conditions are required regarding the integrity of

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 instability of such characteristics.

"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. and a second electrically variable attenuation means and a second electrically variable phase shift means are provided in the distortion removal circuit, and a first level detection means for detecting the level of the first pilot signal is provided in the path of the auxiliary amplifier. a second level detection means for detecting the level of the second viroft signal in the output path of the feedforward amplifier, and a third injection means for injecting the first pilot signal into the output path of the feedforward amplifier. , a 31st electrically variable attenuator and a 3rd electrically variable phase shifter are inserted into the supply path for the first pilot signal to be supplied to the third injection means, and a 31st electrically variable attenuation means and an amplifier are inserted in the output path of the feedforward amplifier. Third level detection means for detecting the level of the first pilot signal on the output side of the injection means is provided, the third level detection means detecting the level of the first pilot signal on the output side of the injection means;
The first electrically variable attenuation means and the first electrically variable phase shift means are controlled by the control means so that the detection level of the level detection means is minimized, and the detection level of the second level detection means is minimized. The second electrically variable attenuation means and the second electrically variable phase shift means are controlled by the control means so that The electrically variable damping means and the third electrically variable phase shifting means are controlled by a control means.

"Operation" The residual signal bone produced 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, the remaining signal bone is detected by the pilot signal detection means. The transmission characteristics of the circuit are automatically adjusted to take the minimum value.

"Embodiments" Hereinafter, embodiments of the present invention will be described in detail based on concave surfaces. FIG. 1 shows an embodiment of the invention, and parts corresponding to those in FIG. 6 are given the same reference numerals.

An oscillator 20 such as a frequency synthesizer for generating a first viroft signal with a specified frequency is connected to a directional coupler 21
It is coupled to the input terminal 13a side of the power divider 13 via. 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.

An electrically adjustable variable attenuator 2 is installed in the main amplifier signal path 3 of the distortion detection circuit 1 instead of the variable attenuator 8 and the variable delay line 9.
4 and an electrically adjustable variable phase shifter 25 are inserted. 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 shifter 2
5 and 27 can be easily constructed using a PIN diode and a varactor diode, and commercially available products can also be used.

via a directional coupler 28 in the output path of the auxiliary amplifier 12,
A selection level meter 29 is coupled as a level detection means for the first pilot signal. A selection level meter 31 serving as a level detection means for the second pyroft signal is coupled to the output path of the feedforward amplifier via a directional coupler 30. Further, the first pilot signal is transmitted to the electrically adjustable variable attenuator 32 and the electrically adjustable variable phase shifter 3.
3 and a signal amplifier 34, and is coupled to the output path of the feedforward amplifier via a power combiner 35. Further, a selection level meter 37 is coupled to the output side of the power combiner 35 in the output path of the feedforward amplifier via a directional coupler 36 as means for detecting the level of the first pilot signal. The outputs of the level meters 29.3'l and 37 are input to a control circuit 38, which controls the variable attenuators 24, 26 and 32 and the variable phase shifters 2527 and 33.゜3
1 and 37 are constructed with 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 38 is comprised 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 2931 and 37, while controlling the variable attenuators 24, 26, and 32. and variable phase shifter 2
5.27.33 has the ability to adjust the 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 holding the control voltage of the variable phase shifter 25 can be used. 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. , and the phase can be reversed. 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 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 control circuit 38 adjusts the set points of the electrically variable attenuator 32 and the electrically variable phase shifter 33 so that the output level of the selection level meter 37 takes the minimum value. This is to inject 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. Therefore, the first pilot signal is injected into the output terminal 17. No signal appears.

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 directional coupler 28 is connected to the variable attenuator 2.
Alternatively, as shown in FIG. 2, the directional coupler 23 may be inserted at the input end of the main amplifier 7.

FIG. 3 shows another embodiment of the invention. Selection level meter 29° 31 and 3 for detecting the level of the pilot signal
Homodyne detection circuit 39, 40 and 41 instead of 7
is used. The homodyne detection circuit 39 includes a mixer 42
, low pass filter (LPF) 43 and DC amplifier 4
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 auxiliary amplifier 12 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 pyloft 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. Further, the homodyne detection circuit 41 includes a mixer 48, an LPF 49, and a DC amplifier 50, and performs homodyne detection using a local signal from the oscillator 20 to determine the level of the first pilot signal from the oscillator 20 in the output signal of the power combiner 35. 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. Further, the control circuit 3 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 output signal of the feedforward amplifier with the same amplitude and opposite phase as the first pilot signal included therein. As a result, the optimal adjustment points of the two circuits are automatically set, and feedforward amplification operation with good linearity is realized.
The pilot signal can be removed. In addition, all of the selection levels 29, 31, and 37 in Figure 1 are shown here.
Although each of the selected level meters 29, 31, and 37 is configured with a homodyne detection circuit 39, 4041, one or two of the selected level meters 29, 31, and 37 may be configured with a homodyne detection circuit. One, two, or all of the level meters 29, 31, and 37 may be configured with a homodyne detection circuit.

FIG. 4 shows a further 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 homodyne detection circuits 39 and 40 are the only level detection means. This is because the switch 51 shares the homodyne detection circuit 39.

When the switch 51 is connected to the directional coupler 28 as shown by the solid line, the operation is the same as when automatically adjusting the strain detection port B1 in FIG. 3. Furthermore, when the switch 51 is connected to the directional coupler 36 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. The operation of the distortion removal circuit 2 is similar to that in FIG. Note that the homodyne detection circuit 40 may be replaced with a selection level needle. As described above, the control circuit 3 switches the switch 51 so that the output of the homodyne detection circuit 39 takes the minimum value.
By operating 8, the optimum operating state of the distortion detection circuit 1 is realized, and the first pilot signal is removed from the output signal of the feedforward amplifier. Further, by operating the control circuit 38 so that the output of the homodyne detection circuit 40 takes the 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. 5 shows an example in which a switch 5253 is further provided in the embodiment shown in FIG. This is because one homodyne detection circuit 39 is shared for three operations. When the switches 52 and 53 are connected as shown by the solid line, and the switch 51 is connected to the directional coupler 28 as shown by the solid line, the operation automatically adjusts the distortion detection circuit 1 in FIG. 3. Same as in case. 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 the same as when the distortion removal circuit 2 of FIG. 3 is automatically adjusted. By switching the switches 51, 52 and 53 as described above 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 are brought into an optimal operating state. At the same time, the first pilot signal is removed from the output signal of the feedforward amplifier. 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 the characteristic deterioration of feedforward amplifiers caused by temperature changes, power supply fluctuations, etc. Of course, feedforward amplifiers can be widely applied as practical linear amplifiers for wired communication repeaters, audio equipment, and the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
5 through 5 are block diagrams showing other embodiments of the present invention, FIG. 6 is a block diagram showing a conventional feedforward amplifier, FIG. 7 is a diagram showing a phase inversion circuit using a circulator, and FIG. The figure is a diagram showing an example of calculation of the amplitude of the circuit, the degree of phase imbalance, and the amount of signal cancellation.

Claims (1)

[Claims] (1) A distortion detection circuit that detects the 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 reinjecting it into the output of the main amplifier. a first injection means for injecting a first pilot signal of a specific frequency into the input path of the feedforward amplifier; a first electrically variable attenuation means inserted in the distortion detection circuit;
a second injection means inserted into the path of the first electrically variable phase shifting means 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 the path of the auxiliary amplifier of the distortion removal circuit and detecting the level of the first pilot signal; Second
a second level detection means for detecting the level of the pilot signal; and a second level detection means for detecting the level of the pilot signal;
a third injection means for injecting a pilot signal; a third electrically variable attenuation means, a third electrically variable phase shift means, and an amplifier inserted into a supply path of the first pilot signal injected by the third injection means; , third level detection means for detecting the level of the first pilot signal on the output side of the third injection means in the output path of the feedforward amplifier; and a detection level of the first level detection means is minimized. The first electrically variable attenuation means and the first electrically variable phase shift means are controlled so that the detection level of the second level detection means is minimized. 2 electrically variable phase shifting means, and further controlling the third electrically variable attenuation means and the third electrically variable phase shifting means so that the detection level of the third level detecting means is minimized. A feedforward amplifier comprising: means;