JPH0470203A - Feed forward amplifier - Google Patents

Abstract

PURPOSE:To obtain a feed forward amplifier without instability in a characteristic by munitoring a detected remaining signal and automatically adjusting the transmission characteristic of a circuit so that the signal takes a minimum value. CONSTITUTION:A control circuit 33 adjusts the setting point of a variable attenuator 24 and a variable phase shifter 25 so that the output of a selection level meter 29 takes the minimum value. The setting point is slightly changed stepwise and the point where the output of the selection level meter 29 becomes the minimum is detected. Then, respective control voltages of the variable attenuator 24 and the variable phase shifter 25 at that time are held, for example. Then, a control circuit 3 adjusts the setting point of an electrically variable attenuator 26 and an electrically variable phase shifter 27 so that the output level of a selection level meter takes the minimum value. It can be considered that a main amplifier 7 generates the distortion of the same component of 2 second pilot signal by an oscillator 22. Thus, the control method is effective and a condition that distortion output included in an output signal becomes the minimum, namely, the suppression quantity of the signal of a distortion removal circuit 2 becomes the maximum. Thus, two said control can always or intermittently executed and the optimum operation condition of the feed forward amplifier whose linearity is satisfactory can be realized.

Description

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

[Prior Art] The basic configuration of a feedforward amplifier is shown in FIG.
A feedforward amplifier basically consists of two signal canceling circuits. One is the distortion detection circuit 1, and the other is the 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 consists of a variable attenuator 10, a variable delay line 11, and an auxiliary amplifier 12 connected in series. 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. In addition, a power divider 13 and a power combiner 14
and 15 are simple lossless power dividers/power combiners composed of transformer circuits, hybrid circuits, etc.

First, this operation will be explained.

The input signal applied to the input terminal 16 is first distributed to paths 3 and 4 by the power divider 13, and then the power is combined by the 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 IO 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, and in the end, the distortion components in the output of the entire circuit are cancelled. [Problem to be solved by the invention] The above is the operation of an ideal feedforward amplifier, but in reality It is not easy to achieve perfect balance between the two circuits, distortion detection circuit 1 and distortion removal circuit 2, and even if the initial settings are perfect, the amplifier may be affected by fluctuations in ambient temperature, power supply, etc. Due to the changing properties, it is usually very difficult to maintain good equilibrium over time. FIG. 7 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, 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 deteriorates by the amount of suppression. 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 reinjects it into the output of the main amplifier. In the feedforward amplifier, the feedforward amplifier has a distortion removal circuit that cancels distortion components by electrically variable attenuation means, first electrically variable phase shift means, and means for injecting a second pilot signal of another specific frequency into the path of the main amplifier;
Electrically variable attenuation means, second electrically variable phase shift means are provided, and a first level detection means for detecting the first pilot signal level is provided in the path of the auxiliary amplifier, and second level detection means is provided in the output path of the feedforward amplifier. Second level detection means for detecting a pilot signal level is provided, and means for removing a first pilot signal component in the output path of the feedforward amplifier is provided so that the detection level of the second level detection means is minimized. The first electrically variable attenuating means and the first electrically variable phase shifting means are controlled, and the second electrically variable attenuating means and the 21i
Control means are provided for controlling the mechanically variable phase shifting means.

[Function] The residual signal bone 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

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings. FIG. 1 shows an embodiment of the invention, and parts corresponding to those in FIG. 5 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 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 pyroft 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. A variable attenuator lO5 is connected to the distortion removal injection path 6 of the distortion removal circuit 2.
An electrically adjustable variable attenuator 26 and an electrically adjustable variable phase shifter 27 are inserted in place of the variable delay line 11. These variable attenuators 24, 26 and variable phase shifters 25, 27 can be easily constructed using PIN diodes and varactor diodes, and commercially available products can also be used. A selection level meter 29 is coupled to the output path of the auxiliary amplifier 12 via a directional coupler 28 as means for detecting the first pilot signal level. A selection level meter 31 is provided in the output path of the feedforward amplifier as a means for detecting the second pilot signal level via the directional coupler 30.
A bandpass filter (BPF) 32 is inserted to remove the first pilot signal component. The respective outputs of the selection level shapes 29 and 31 are input to a control circuit 33, which controls variable attenuators 24 and 26 and variable phase shifters 25 and 27.

The selection level meters 29 and 31 include a frequency converter, a narrowband filter, and a detector. The control circuit 33 is composed of an A/D converter, a microprocessor, and a D/A converter as a basic circuit, and includes a selection level meter 29.31.
It has the ability to adjust the set points of the variable attenuator 24.26 and the variable phase shifter 25.27 while monitoring the input signal from the variable attenuator 24.26 and the variable phase shifter 25.27. 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 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 this amplifier. The gap between
Or set it to a frequency outside the band. The bandpass filter 32 passes the input signal and its neighboring bands, but
The first pilot signal is set to have a blocking passband.

The control circuit 33 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 each control voltage of the variable phase shifter 25 can be applied. In this way, a signal with a specific frequency, i.e.
By using the first pilot signal, the transmission characteristics of the two paths constituting the distortion detection circuit 1 can be easily made to have equal amplitude and opposite phase to each other, independently of the input signal. 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 33 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. Further, the first pilot signal from the oscillator 20 is blocked by the bandpass filter 32 and does not appear at the output terminal 17. Instead of this bandpass filter, a low pass filter (LPF) or a high pass filter (I( It is likewise possible to use PF).

By constantly or intermittently performing the above two 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.
The directional coupler 23 may be inserted at the input end of the main amplifier 7, or the directional coupler 23 may be inserted at the input side of the main amplifier 7.

FIG. 3 shows another embodiment of the invention. Selection level meter 29.3 for detecting the levels of the first and second pyroft signals
1, homodyne detection circuits 34 and 35 are used. The homodyne detection circuit 34 includes a mixer 36, a low-pass filter (LPF) 37, and a DC amplifier 38, and performs homodyne detection using the local signal from the oscillator 20 to detect the oscillator 2 in the output signal of the auxiliary amplifier 12.
The first pilot signal level due to zero can be detected with high sensitivity. Similarly, the homodyne detection circuit 35 is composed of a mixer 39, an LPF 40, and a DC amplifier 41, and performs homodyne detection using the local signal from the oscillator 22 to generate a second pilot signal from the oscillator 22 in the output signal of the feedforward amplifier. The level can be detected with high sensitivity. Now, the operation of this circuit is similar to the case of FIG. 1, when a signal is input, the control surface Nl3
3 is an electrically variable attenuator 24 and an electrically variable phase shifter 2 so that the output level of the homodyne detection circuit 34 takes a minimum value.
5 and the operation of the distortion detection circuit 1.
The transmission characteristics of the two paths that make up this are equal amplitude,
In addition, a desired equilibrium state with opposite phases is achieved.

Next, the control circuit 33 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 35 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. As a result, the optimal adjustment points of the two circuits are automatically set, and feedforward amplification operation with good linearity is realized. Here, both of the selection level meters 29 and 31 in FIG. 1 are constructed with homodyne detection circuits 34 and 35, respectively, but either one may be constructed with a homodyne detection circuit. Both or one of the selection level meters 29 and 31 may be configured with a homodyne detection circuit.

FIG. 4 shows yet another embodiment of the invention.

In this embodiment, a signal switch 4 is added to the configuration example shown in FIG.
2.43 is newly provided, each output of the directional coupler 28.30 is switched and connected to the input side of the homodyne detection circuit 34 by the signal switch 42, and the output of the oscillator 20.22 is connected to the homodyne detection circuit 34 by the signal switch 43. The signal is switched and supplied to the detection circuit 34 as a local signal. When the switchers 42 and 43 are connected as shown by the solid line, the operation is the same as the automatic adjustment of the distortion detection circuit 1 in FIG. 3. In addition, the switch 4
If 2 and 43 are connected as shown in the dashed line, the operation will be the same as the third one.
This is similar to the case where the distortion removal circuit 2 shown in the figure is automatically adjusted.

As described above, the control circuit 3 switches the switches 42 and 43 so that the output of the homodyne detection circuit 34 takes the minimum value.
By operating the distortion detection circuit 1 and the distortion removal circuit 2, the optimum operating state of the two circuits can be realized.

[Effects of the Invention] As explained above, the present invention can relieve characteristic deterioration of feedforward amplifiers caused by temperature changes, power 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 drawings]

FIG. 1 is a block diagram showing a first embodiment of this invention, and FIG.
3 and 4 are block diagrams showing other embodiments of the present invention, FIG. 5 is a block diagram showing a conventional feedforward amplifier, and 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 the circuit. Patent applicant Nippon Telegraph and Telephone Corporation

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 electrical variable attenuation means inserted into the distortion detection circuit; means for injecting a second pilot signal of a specific frequency different from the specific frequency, inserted into the path of the main amplifier of the distortion detection circuit and the variable phase shifting means of the distortion detection circuit; variable damping means,
a first level detection means inserted in a path of a second electrically variable phase shifter and the auxiliary amplifier of the distortion removal circuit and detecting the level of the first pilot signal; a second level detection means for detecting the level of the second pilot signal; a means for removing the first pilot signal component from the output of the feedforward amplifier; 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.
A feedforward amplifier comprising: control means for controlling an electrically variable phase shift means.