JP2945451B2 - Feedforward amplifier - Google Patents

Description

The present invention relates to a linear amplifier mainly used in a high frequency band, and a distortion detection circuit for detecting a non-linear distortion component of a main amplifier, and a distortion detection circuit for detecting the non-linear distortion component. The present invention relates to a feedforward amplifier having a distortion canceling circuit for canceling a distortion component by injecting again into an output of a main amplifier after amplification using an auxiliary amplifier.

"Prior Art" The basic configuration of a feedforward amplifier is shown in FIG. The feedforward amplifier is basically composed of two signal canceling circuits. One is a distortion detection circuit 1, and the other is a distortion removal circuit 2. The distortion detection circuit 1 includes a main amplifier signal path 3 and a linear signal path 4, and the distortion removal circuit 2 includes a main amplifier output signal path 5 and a distortion injection path 6. Further, the main amplifier signal path 3 is composed of a cascade connection of a main amplifier 7, a variable attenuator 8, and a variable delay line 9, and the linear signal path 4 is composed of a transmission line. The main amplifier output signal path 5 includes a transmission line, and the distortion injection path 6 includes 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 the variable attenuator 8 and the variable delay line 9 or only one of them may be provided in the linear signal path 4. Similarly, the variable attenuator 10 and / or the variable delay line 11 may be provided in the main amplifier output signal path 5 only in one or both. Further, the power distributor 13 and the power combiners 14 and 15
Is a simple lossless power divider / power combiner composed of a transformer circuit, a hybrid circuit and the like. First, this operation will be described.

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

Next, the variable attenuator 10 and the variable delay line 11 have a transfer function of 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 for the path 3, Adjustments are made 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 path 6 is connected to the output terminal 17 of the power combiner 15 by the Are injected with opposite phase equal amplitude, and as a result, the cancellation of the distortion component in the output of the entire circuit is realized.

[Problems to be Solved by the Invention] The above is the operation of the ideal feedforward amplifier. However, in practice, it is easy to completely balance the two circuits of the distortion detection circuit 1 and the distortion removal circuit 2. But also
Even if the initial settings are complete, it is usually very difficult to maintain a stable balance over time and good balance because the characteristics of the amplifier change due to changes in ambient temperature, power supply, and the like. FIG. 8 shows the result of calculation of the relationship between the amount of deviation and the amount of signal suppression in which the amplitude and phase of the two paths constituting the circuit deviate from the equal-amplitude anti-phase condition. From this figure, for example, 30
In order to achieve a suppression level of more than dB, the deviation of the phase and amplitude must be within ± 1.8 お よ び and ± 0.3dB, respectively, and the balance of the transmission characteristics of the two paths and the completeness of the adjustment It can be clearly understood that strict conditions are required for. If the balance of the distortion detection circuit 1 deteriorates, an unnecessary distortion occurs because the main signal is added to the input of the auxiliary amplifier 12 at a level larger than the distortion component, and the balance of the distortion removal circuit 2 deteriorates. Then, the amount of distortion improvement as the feedforward amplifier is deteriorated by the amount of deterioration of the suppression amount. As described above, the conventional feedforward amplifier has a fundamental problem that a satisfactory linear amplifier cannot be realized because the stability of the circuit is not sufficient.

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

[Means for Solving the Problems] According to the present invention, a distortion detection circuit that detects a nonlinear distortion component of a main amplifier, amplifies the detected distortion component using an auxiliary amplifier, and then outputs the amplified signal to the output of the main amplifier again A feed-forward amplifier having a distortion removing circuit for canceling a distortion component by injecting, wherein a first injection means for injecting a first pilot signal of a specific frequency is provided in an input path of the feed-forward amplifier; A first electric variable attenuating means and a first electric variable phase shifting means inserted in the circuit are provided, and a second injection means for injecting a second pilot signal of another specific frequency is provided in a path of the main amplifier. A second electric variable attenuating means and a second electric variable phase shifting means are provided in the distortion removing circuit, and a first pilot signal of the first pilot signal is provided in a path of the auxiliary amplifier. First level detecting means for detecting a level; second level detecting means for detecting the level of a second pilot signal on an output path of the feedforward amplifier; and a first pilot signal on an output path of the feedforward amplifier. A third injection means for injecting a signal is provided, and an amplifier is inserted into the supply path of the first pilot signal supplied to the third injection means, as the third electric variable attenuation means and the third electric variable phase shift means. And a third level detecting means for detecting a level of a first pilot signal on an output side of the third injecting means in an output path of the feedforward amplifier, so that a detection level of the first level detecting means is minimized. The first electric variable attenuation means and the first electric variable phase shift means are controlled by a control means, and The second electric variable attenuation means and the second electric variable phase shift means are controlled by the control means so that the output level is minimized, and the detection level of the third level detection means is minimized. The third electric variable attenuation means and the third electric variable phase shift means are controlled by the control means.

[Operation] The residual signal component caused by the imperfect signal canceling condition of the two circuits of the feedforward amplifier is detected by the pilot signal detecting means. , The transmission characteristic of the circuit is automatically adjusted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and portions corresponding to FIG. 6 are denoted by the same reference numerals. An oscillator 20 such as a frequency synthesizer for generating a first pilot signal having a specified frequency is provided through a directional coupler 21 to a power divider.
13 are coupled to the input terminal 13a side. Further, an oscillator 22 such as a frequency synthesizer for generating a second pilot signal having a specified frequency is coupled to the output side of the main amplifier 7 via a directional coupler 23. Instead of the variable attenuator 8 and the variable delay line 9, an electrically adjustable variable attenuator 24 and an electrically adjustable variable phase shifter 25 are inserted in the main amplifier signal path 3 of the distortion detection circuit 1. . Distortion injection path 6 of distortion removal circuit 2
In addition, instead of the variable attenuator 10 and the variable delay line 11, an electrically adjustable variable attenuator 26 and an electrically adjustable variable phase shifter
27 is inserted. These variable attenuators 24 and 26 and variable phase shifters 25 and 27 can be easily configured using a PIN diode and a varactor diode, and commercially available products can also be used. Via the directional coupler 28 to the output path of the auxiliary amplifier 12,
A selection level meter 29 as means for detecting the level of the first pilot signal is connected. A selection level meter 31 as a level detection means of the second pilot signal is connected to an output path of the feedforward amplifier via a directional coupler 30. The first pilot signal passes through an electrically adjustable variable attenuator 32, an electrically adjustable variable phase shifter 33, and a signal amplifier 34, and passes through an output path of a feedforward amplifier via a power combiner 35. Is combined with 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 selection level meters 29, 31 and 37 are connected to the control circuit 38.
The control circuit 38 controls the variable attenuators 24, 26 and 32,
The variable phase shifters 25, 27 and 33 are controlled. Selection level total 29,
Reference numerals 31 and 37 each include a frequency converter for detecting a specific frequency component of an input signal, a narrow band filter, and a detector for detecting an output level of the narrow band filter. The control circuit 38 includes an A / D converter as a basic circuit, a microprocessor, a ROM, a RAM, and a D / A converter,
It has the function of adjusting the set points of the variable attenuators 24, 26, 32 and the variable phase shifters 25, 27, 33 while monitoring the input signals from the selection level meters 29, 31 and 37. Hereinafter, the control operation of the control circuit 33 will be described. The first pilot signal from the oscillator 20 is set to a frequency slightly apart from the frequency band of the input signal of the feedforward amplifier, and the second pilot signal from the oscillator 22 is used to generate the original signal of the distortion component generated by the main amplifier 7. Occupied frequency gap, or
The frequency is set outside the band of the original signal.

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 gradually changed step by step, and after the point at which the output of the selection level meter 29 is minimized is detected, the control of the variable attenuator 24 and the variable phase shifter 25 at that time is performed. A method for holding a voltage can be applied. Thus, by using a signal having a specific frequency, that is, the first pilot signal, independently of the input signal, and
The transmission characteristics of the two paths constituting the distortion detection circuit 1 can be easily made equal in amplitude and opposite in phase.
As a result, a condition in which the level of the first pilot signal in the output of the auxiliary amplifier 12 is minimum, that is, a state in which the signal suppression amount of the distortion detection circuit 1 is maximum can be realized.

Next, the control circuit 38 adjusts the set points of the electric variable attenuator 26 and the electric variable phase shifter 27 so that the output level of the selection level meter 31 takes the minimum value. This is because the control method is effective because the main amplifier 7 can be regarded as having generated the same component distortion as the second pilot signal by the oscillator 22, and the condition that the distortion output level included in the output signal becomes minimum, that is, A state in which the signal suppression amount of the distortion removal circuit 2 is maximized can be realized.

Further, in order to remove the first pilot signal by the oscillator 20 from the output signal of the feedforward amplifier,
The control circuit 38 adjusts the set points of the electric variable attenuator 32 and the electric variable phase shifter 33 so that the output level of the selection level meter 37 takes the minimum value. This means that the first pilot signal is injected into the output signal of the feedforward amplifier under the same amplitude and opposite phase conditions as the first pilot signal included in the output signal. No signal appears.

By executing the above three controls constantly or intermittently, it is possible to realize the optimum operating condition of the feedforward amplifier having good linearity.

As shown in FIG. 2, the directional coupler 28 is connected to the variable attenuator 26.
May be inserted on the input side. Further, as shown in FIG. 2, a directional coupler 23 may be inserted on the input side of the main amplifier 7.

FIG. 3 shows another embodiment of the present invention. Instead of the selection level meters 29, 31 and 37 for detecting the level of the pilot signal, homodyne detection circuits 39, 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. The homodyne detection is performed by a local signal from the oscillator 20, and the The level of one pilot signal can be detected with high sensitivity. The homodyne detection circuit 40 includes a mixer 45, an LPF 46, and a DC amplifier 47. The homodyne detection is performed by a local signal from the oscillator 22, and the second pilot signal level by the oscillator 22 in the output signal of the feedforward amplifier is highly sensitive. Can be detected. Further, the homodyne detection circuit 41 includes a mixer 48, an LPF 49, and a DC amplifier 50. It can be detected with high sensitivity.

The operation of this circuit is as follows. When a signal is input as in the case of FIG. 1, the control circuit 38 controls the electric variable attenuator 24 and the electric variable transfer so that the output level of the homodyne detection circuit 39 takes the minimum value. By adjusting the set point with the phase shifter 25, the operation of the distortion detection circuit 1 is adjusted so that the transmission characteristics of the two paths constituting the distortion detection circuit 1 are equal in amplitude and opposite to each other in a desired balanced state. Next, the control circuit 38 includes a homodyne detection circuit.
Similarly, the set points of the electric variable attenuator 26 and the electric variable phase shifter 27 are adjusted so that the output level of 40 takes the minimum value.
In this way, regarding the operation of the distortion removing circuit 2, the transmission characteristics of the two paths constituting the distortion removing circuit 2 have the same amplitude, and
A desired equilibrium state where the phases are opposite to each other is set. Further, the control circuit 38 similarly adjusts the set points of the electric variable attenuator 32 and the electric variable phase shifter 33 so that the output level of the homodyne detection circuit 41 takes the minimum value. by this,
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 optimum adjustment points of the two circuits are automatically set, a feedforward amplification operation with good linearity is realized, and the first pilot signal can be removed from the output signal of the feedforward amplifier. Here, all of the selection level meters 29, 31, and 37 in FIG.
Although the configuration includes 9, 40, and 41, one or two of the selection level meters 29, 31, and 37 may be configured with a homodyne detection circuit. Similarly, one, two, or all of the selection level meters 29, 31, and 37 in FIG. 2 may be configured by a homodyne detection circuit.

FIG. 4 shows still another embodiment of the present invention. In this embodiment, a signal switch 51 is additionally provided in the configuration example of FIG. 3, and the level detection means is a homodyne detection circuit 39.
And only 40. 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 that in the case of performing the automatic adjustment of the distortion detection circuit 1 in FIG. Further, the switch 51 is connected to the directional coupler 36 as indicated by a broken line.
, The operation is the same as that of removing the first pilot signal from the output signal of the feedforward amplifier in FIG. The operation of the distortion removing circuit 2 is the same as in the case of FIG. The homodyne detection circuit 40
May be replaced with a selection level meter. By switching the switch 51 as described above and operating the control circuit 38 so that the output of the homodyne detection circuit 39 takes the minimum value, the optimum operation state of the distortion detection circuit 1 is realized, and the feedforward amplifier of the feedforward amplifier is realized. The first pilot signal is removed from the output signal. Further, by operating the control circuit 38 so that the output of the homodyne detection circuit 40 takes the minimum value, the optimum operation state of the distortion removal circuit 2 can be realized. Thus, the optimum operation state of the feedforward amplifier can be realized.

FIG. 5 shows an example in which switches 52 and 53 are further provided in the embodiment of FIG. This is one homodyne detection circuit
This is because 39 is shared for the three operations. Switch 52 and
When the switch 53 is connected as shown by a solid line and the switch 51 is connected to the directional coupler 28 as shown by a solid line, the operation is the same as that in the case of performing the automatic adjustment of the distortion detection circuit 1 in FIG. is there. Further, the switches 52 and 53 are connected as shown by a solid line,
When the switch 51 is connected as indicated by a broken line, the operation is the same as that in the case where the first pilot signal is removed from the output signal of the feedforward amplifier in FIG. On the other hand, when the switches 52 and 53 are connected as indicated by broken lines, the operation is the same as that in the case where the automatic adjustment of the distortion removal circuit 2 in FIG. 3 is performed. As described above, the switches 51 and 5
By switching 2 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 realize the optimum operation state, and remove the first pilot signal from the output signal of the feedforward amplifier. In this way,
The optimum operation state of the feedforward amplifier can be realized.

[Effects of the Invention] As described above, according to the present invention, the characteristic deterioration of the feedforward amplifier caused by temperature change, power supply fluctuation, etc. can be relieved. Wired communication repeater,
A feedforward amplifier can be widely applied as a practical linear amplifier for audio equipment and the like.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
5 to 5 are block diagrams showing another embodiment 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 a calculation example of the amplitude, the degree of phase imbalance, and the signal cancellation amount of the circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 1/32

Claims (1)

(57) [Claims] 1. A distortion detection circuit for detecting a nonlinear distortion component of a main amplifier, and amplifying the detected distortion component using an auxiliary amplifier, and then injecting the amplified distortion component into an output of the main amplifier to cancel the distortion component. A first injection means for injecting a first pilot signal of a specific frequency into an input path of the feedforward amplifier, and a first electric variable attenuation inserted in the distortion detection circuit. means,
First electric variable phase shift means and second injection means inserted into a path of the main amplifier of the distortion detection circuit for injecting a second pilot signal of a specific frequency different from the specific frequency, and inserted into the distortion removal circuit Second electrically variable damping means,
First level detection means inserted into the path of the auxiliary amplifier of the distortion removing circuit and the second electrically variable phase shift means and detecting the level of the first pilot signal; and the first level detection means of the output path of the feedforward amplifier. Second
Second level detection means for detecting the level of a pilot signal; and the first level detection means in the path of the output of the feedforward amplifier.
A third injection means for injecting a pilot signal, a third electrically variable attenuating means, a third electrically variable phase shifting means and an amplifier inserted in a supply path of the first pilot signal to be injected by the third injection means; Third level detecting means for detecting the level of the first pilot signal on the output side of the third injecting means in the output path of the feedforward amplifier; and detecting the level of the first level detecting means to be minimum. The second electric variable attenuating means and the first electric variable attenuating means are controlled to control the first electric variable attenuating means and the first electric variable phase shifting means, and to minimize the detection level of the second level detecting means. (2) controlling the electrically variable phase shifting means, and further controlling the third electrically variable attenuating means and the third electrically variable attenuating means so that the detection level of the third level detecting means is minimized; Feedforward amplifier, characterized by comprising control means for controlling the phase shifting means.