Feed forward amplifier - Patent Review 5477187

We claim:

1. A feed forward amplifier comprising:

RF amplification means,.supplied with an input RF signal at an input terminal, for amplifying the input RF signal and thereby producing an output RF signal;

a distortion extraction loop, supplied with said input RF signal from said input terminal and further with said output RF signal from said RF amplification means, for extracting, from said output RF signal, non-linear distortion components formed in said output RF signal as a result of amplification in said RF amplification means;

variable phase shifter meanst in said distortion extraction loop, for varying a phase of said input RF signal that has been supplied to said distortion extraction loop;

variable attenuation means, in said distortion extraction loop, for attenuating an amplitude of said input RF signal that has been supplied to said distortion extraction loop;

distortion extraction means, in said distortion extraction loop and supplied with said input RF signal after processing in said variable phase shifter means and said variable attenuation means and with said output RF signal from said RF amplification means, for producing a distortion output signal that includes non-linear distortion components;

distortion elimination means, supplied with said distortion output signal from said distortion extraction means and said output RF signal from said RF amplification means, for canceling out said non-linear distortion components contained in said output RF signal by said non-linear distortion components contained in said distortion output signal;

first control means, supplied with said input RF signal that has been supplied to said input terminal and further with said distortion output signal, for extracting a main signal component contained in said distortion output signal said first control means controlling said variable phase shifter means and said variable attenuation means independently of each other so as to decrease a ratio of a level of said main signal component to a level of said input RF signal;

said first control means further comprising branching means for branching said input RF signal supplied to said input terminal, first level detection means for detecting a level of said input RR signal that has been branched by said branching means, second level detection means for detecting a level of said main signal component contained in said distortion output signal of said distortion elimination means, and a control circuit supplied with output signals from said first and second level detection means for controlling said variable attenuation means and said variable phase shifter means in said distortion extraction means; and

automatic gain control means, supplied with said output signal from said first level detection means, for controlling a level of said input RF signal supplied to said distortion extraction loop from said input terminal.

2. A feed forward amplifier comprising:

RF amplification means, supplied with an input RF signal at an input terminal, for amplifying the same and thereby producing an output RF signal;

a distortion extraction loop, supplied with said input RF signal from said input terminal and further with said output RF signal from said RF amplification means, for extracting, from said output RF signal, non-linear distortion components formed in said output RF signal as a result of amplification in said RF amplification means;

distortion elimination means, supplied with a distortion output signal from said distortion extraction loop and further with said output RF signal from said amplification means, for canceling out said non-linear distortion components contained in said output RF signal by said non-linear distortion components contained in said distortion output signal and producing a distortion-eliminated output signal;

pilot signal generation means for producing a pilot signal;

pilot signal injection means for injecting said pilot signal into said output RF signal produced by said RF amplification means;

pilot signal detection means, supplied with said pilot signal from said pilot signal generation means, for detecting a pilot signal component contained in the distortion-eliminated output signal produced by said distortion elimination means and for conducting d.c. detection by mixing said pilot signal into said distortion-eliminated output signal and producing a d.c. detection signal as an output; and

control means supplied with the d.c. detection signal produced by said pilot signal detection means, said d.c. detection signal being produced by said pilot signal detection means as a result of said d.c. detection, said control means controlling said distortion elimination means so as to minimize the level of said d.c. detection signal;

said pilot signal detection means further comprising phase control means for coinciding the respective phases of said pilot signal component contained in said distortion-eliminated output signal and said pilot signal injected for said d.c. detection.

3. A feed forward amplifier as claimed in claim 2, wherein said phase control means further comprises second pilot signal detection means for mixing said pilot signal contained in said distortion-eliminated output signal and said pilot signal injected for said d.c. detection, said second pilot signal detection means thereby producing a d.c. output signal, and a control circuit, supplied with said d.c. output signal from said second pilot signal detection means, for coinciding the respective phases of said pilot signal contained in said distortion-eliminated output signal and said pilot signal injected for said d.c. detection, such that said d.c. output signal of said second pilot signal detection means is maximized.

4. A feed forward amplifier as claimed in claim 3, wherein said phase control means further comprises automatic gain control means for maintaining a level of said pilot signal, contained in said distortion-eliminated output signal, at a constant level.

5. A feed forward amplifier as claimed in claim 3, wherein said phase control means further comprises automatic gain control means for setting a level of said pilot signal, contained in said distortion output signal to be coincident with a level of the pilot signal mixed for said d.c. detection.

6. A feed forward amplifier comprising:

RF amplification means, supplied with an input RF signal, for amplifying the same and thereby producing an output RF signal;

a distortion extraction loop, supplied with said input RF signal and further with said output RF signal from said RF amplification means, for extracting, from said output RF signal, non-linear distortion components formed in said output RF signal as a result of amplification in said RF amplification means, said distortion extraction loop thereby producing a distortion output signal containing therein non-linear distortion components;

a distortion elimination loop, supplied with said distortion output signal from said distortion extraction loop and further with said output RF signal from said amplification means, for canceling out said non-linear distortion components contained in said output RF signal by non-linear distortion components contained in said distortion output signal, said distortion elimination loop further comprising:

variable attenuation means, supplied with said distortion output signal produced by said distortion extraction loop, for modifying an amplitude of said distortion output signal,

variable phase shifter means, supplied with said distortion output signal produced by said distortion extraction loop, for varying a phase of said distortion output signal, and

distortion elimination means, supplied with said distortion output signal after processing thereof in said variable attenuation means and said variable phase shifter means and with said output RF signal from said amplification means, for synthesizing said distortion output signal and said output RF signal and thereby canceling out the non-linear distortion components contained in said output RF signal by the non-linear distortion components contained in said distortion output signal; and

control means, supplied with said distortion output signal and said output RF signal, for controlling said variable attenuation means and said variable phase shifter means such that said non-linear distortion components in said output RF signal have an amplitude and a phase that are identical, respectively, to an amplitude and a phase of said non-linear distortion components contained in said distortion output signal.

7. A feed forward amplifier as claimed in claim 6, wherein said control means further comprises:

phase inversion means for inverting a phase of said output RF signal supplied to said distortion elimination loop from said distortion extraction loop;

a synthesizer for synthesizing an output signal of said phase inversion means and said distortion output signal supplied to said distortion elimination loop for producing a synthetic output signal;

a first detector for detecting an output of said synthesizer to produce a first detection signal, a second detector for detecting said distortion output signal for producing a second detection signal, and a third detector for detecting said output signal of said phase inversion means for producing a third detection signal; and

a control circuit supplied with said first through third detection signals for controlling said variable attenuation means and said variable phase shifter means such that said second and third detection signals have a common magnitude and such that a sum of said second and third detection signals has a magnitude which is identical to a magnitude of said first detection signal.

8. A feed forward amplifier as claimed in claim 6, wherein said control means further comprises:

phase inversion means for inverting a phase of said distortion output signal after processing in said variable attenuation means and said variable phase shifter means;

a synthesizer for synthesizing an output signal of said phase inversion means and said output RF signal for producing a synthetic output signal;

a first detector for detecting said synthetic signal of said synthesizer to produce a first detection signal, a second detector for detecting said output RF signal to produce a second detection signal, and a third detector for detecting said output signal of said phase inversion means to produce a third detection signal; and

a control circuit, supplied with said first through third detection signals, for controlling said variable attenuation means and said variable phase shifter means such that said second and third detection signals have a common magnitude and such that a sum of said second and third detection signals has a magnitude which is identical to a magnitude of said first detection signal.

9. A feed forward amplifier comprising:

RF amplification means supplied with an input RF signal for amplifying the same and thereby to produce an output RF signal;

a distortion extraction loop, supplied with said input RF signal and further with said output RF signal of said RF amplification means, for extracting non-linear distortion components formed in said output RF signal as a result of amplification by said RF amplification means, said distortion extraction loop thereby producing a distortion output signal containing said non-linear distortion components; and

a distortion elimination loop, supplied with said distortion output signal from said distortion extraction loop and further with said output RF signal from said RF amplification means, for canceling out said non-linear distortion components contained in said output RF signal by said non-linear distortion components contained in said distortion output signal, 1 said distortion extraction loop further comprising:

variable phase shifter means, supplied with said input RF signal, for changing a phase thereof;

phase shifter means, supplied with said output RF signal from said RF amplification means, for causing a 90.degree. degree phase shift therein,

synchronous detection means, supplied with said input RF signal after processing in said variable phase shifter means and further with said output RF signal as processed by said phase shifter means, for synchronously detecting same and thereby detecting main signal components contained in said output RF signal;

control means, supplied with said main signal components detected by said synchronous detection means, for controlling said variable phase shifter means such that said main signal components are minimized; and

distortion extraction means, supplied with said input RF signal after processing by said variable phase shifter means and further with said output RF signal as produced by said RF amplification means, for canceling said main signal contained in said input RF signal and main signal components contained in said output RF signal, said distortion extraction means producing an output signal essentially consisting of said non-linear distortion components.

10. A feed forward amplifier as claimed in claim 9, wherein said synchronous detection means comprises a mixer for mixing said input RF signal, as supplied thereto, and said output RF signal and thereby for detecting said main signal components, said control means controlling said variable phase shifter means such that main signal components contained in an output signal of said mixer become zero, said control means thereby controlling said main signal in said input RF signals and said main signal components in said output RF signal to have respective, opposite phases in said distortion extraction means.

11. A feed forward amplifier comprising:

RF amplification means, supplied with an input RF signal from an input terminal, for amplifying the same and thereby producing an output RF signal;

a plurality of distortion extraction loops, each supplied with said input RF signal from said input terminal and further with said output RF signal of said RF amplification means, for extracting, from said output RF signal, non-linear distortion components formed in said output RF signal as a result of amplification means, each of said distortion extraction loops producing a corresponding distortion output signal containing therein said non-linear distortion components;

a plurality of distortion elimination loops, provided in correspondence to said plurality of distortion extraction loops, said distortion elimination loops being cascaded with each other and supplied with said output RF signal from said RF amplification means, each of said distortion elimination loops being further supplied with a corresponding distortion output signal from a corresponding distortion extraction loop for removing said non-linear distortion components from said output RF signal supplied thereto; and

a plurality of distortion elimination loop control means, respectively provided in said plurality of distortion elimination loops and each thereof supplied with said output RF signal from which said non-linear distortion components are eliminated, for controlling said respective distortion elimination loop such that a level of said non-linear distortion components remaining in said output RF signal is minimized.

12. A feed forward amplifier as claimed in claim 11, wherein an output RF signal is supplied to said distortion elimination loop in correspondence to each of said plurality of distortion elimination loops.

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TECHNICAL FIELD

The present invention generally relates to radio telecommunication systems and more particularly to a feed forward amplifier suitable for a broadband RF amplifier used in base stations of mobile telephone systems as well as to a control of such a feed forward amplifier.

BACKGROUND ART

With the deployment of digital mobile telephone systems, there is a demand for compact, low-power consumption base stations that can be constructed at a reduced cost. In order to achieve this object, a common amplification construction is employed for the RF amplifiers of the base stations, wherein a plurality of carriers of different frequencies are amplified by a common, single amplifier. In order to amplify a plurality of signals of different frequencies simultaneously, such amplifiers generally employ the feed forward construction which is suitable for eliminating cross modulation distortion.

In the conventional feed forward amplifiers, however, there has been a problem that the equilibrium of the feed forward loop tend to be lost due to a change in the operational environment such as ambient temperature. Such a deviation of the feed forward loop results in a degradation in the compensation of distortions. In order to avoid such a deviation of the feed forward loop, therefore, the conventional feed forward amplifier generally has a control function for detecting the operational state of the loop and for controlling the loop automatically in response to the detected state of the loop.

FIG. 1 shows the fundamental construction of a well known feed forward amplifier. Referring to FIG. 1, it will be noted that the feed forward amplifier is generally formed of a distortion extraction loop 1 and a distortion elimination loop 2.

In the distortion extraction loop 1, an input RF signal including therein a main signal component is supplied to an input terminal 3, wherein the RF signal is branched by a hybrid circuit 4 into a first branch signal and a second branch signal. The first branch signal is amplified in a main amplifier 5 and branched further in a directional coupler 6. One of the signals thus branched in the directional coupler 6 is then supplied to a power synthesizer 8 via an attenuator 7. On the other hand, the signal of the second branch is supplied to a variable attenuator 10 and a variable phase shifter 11 via a delay line 9, and the signal thus passed through the attenuator 10 and the phase shifter 11 is supplied to the power synthesizer 8. Thereby, the variable attenuator 10 and the variable phase shifter 11 are set such that both main signal components, supplied to the power synthesizer 8 along the first and second paths, have an equal amplitude and delay time as well as a mutually opposite phase difference of 180.degree. (inverse phase relationship). As a result, the main signal components are suppressed in the output of the power synthesizer 8, and the output of the power synthesizer 8 contains only the non-linear distortion components that are formed in the main amplifier 5.

In the distortion elimination loop 2, on the other hand, the other output of the directional coupler 6 is supplied to the power synthesizer 13 via a delay line 12. Further, the non-linear distortion components extracted by the power synthesizer 8 are supplied to a secondary amplifier 16 for amplification via a variable attenuator 14 and a variable phase shifter 15. After amplification in the secondary amplifier 16, the signal is supplied to the power synthesizer 13. In this case, too, the variable attenuator 14 and the variable phase shifter 15 are set such that both of the distortion components supplied to the power synthesizer 13 via respective paths have the same amplitude and delay time as well as a mutually opposite phase difference of 180.degree. and thereby the distortion components are suppressed effectively from the output RF signal of the directional coupler 6 and, hence, in the output RF signal of the main amplifier 5. As a result, the distortion of the main signal is minimized.

As described above, the feed forward amplifier functions effectively only when the two suppression loops are set properly. When the characteristics of various elements forming the loop have changed as a result of the environmental change such as the change of ambient temperature, on the other hand, the desired effect of the loop for suppressing distortion reduces substantially.

In order to overcome this problem, a construction shown in FIG. 2 is proposed in the Japanese Laid-open Patent Publication 1-198809. In the conventional art disclosed therein, there is provided another directional coupler 18 on the output line of the main amplifier 5 in correspondence to the distortion extraction loop 1, in addition to the fundamental construction of FIG. 1. Thereby, a pilot signal produced by a pilot signal generator 19 is injected to the output RF signal a that is outputted from the main amplifier 5. Further, a directional coupler 23 is provided on the output line of the secondary amplifier 16 which is included in the distortion elimination loop 2, for branching the output of the amplifier 16. One of the output signals of the secondary amplifier 16 thus branched in the directional coupler 23 is supplied to a power detector 24. Further, there is provided another directional coupler 20 on the output line of the power synthesizer 13, wherein an output signal c of the feed forward amplifier, which has been branched in the directional coupler 20, is supplied to a pilot signal detector 21 together with the pilot signal produced by the pilot oscillator 19. Further, the output signal of the pilot detector 21 and the output of the power detector 24 are supplied to a control circuit 22. The control circuit 22, in turn, supplies control voltage signals to the variable attenuators 10 and 14 and the variable phase shifters 11 and 15 in the distortion extraction loop 1 and in the distortion elimination loop 2.

In the control circuit 22, the variable attenuator 10 and the variable phase shifter 11 are controlled such that the output voltage signal of the power detector 24 is minimized. In response to this, the degree of suppression of the main signal component in the output signal (distortion signal b) of the distortion extraction loop 1 is maximized. In the foregoing control operation, the total power of the main signal a and the distortion signal b is detected, and the variable phase attenuator 10 and the variable phase shifter 11 are controlled such that the detected power is minimized. As a result, the suppression of the main signal component in the output distortion signal outputted from the distortion extraction loop is maximized.

FIGS. 3(A)-3(H) show the operation of the pilot detector 21. The pilot detector 21 is formed of a mixer 211 shown in FIG. 3(B) and a low pass filter 212 shown in FIG. 3(F), wherein the mixer 211 is supplied with main signal components f.sub.1 and f.sub.2 and distortion signal components f.sub.3 and f.sub.4 shown in FIG. 3(A) and further with a pilot signal f.sub.o ' shown in FIG. 3(C). Thereby, ten sets of frequency component signals shown in FIG. 3(D) are obtained in the output of the mixer 211. As the signal component f.sub.p ' and the signal component f.sub.p have the same frequency, the sum of the signal components f.sub.p and f.sub.p ' produced by the mixer 211 has a frequency of 2f.sub.p ' (2f.sub.p). Further, the mixer 211 produces a d.c. component of zero frequency as the difference signal.

Thus, by causing the output signal of the mixer 211 shown in FIG. 3(E) to pass through the low pass filter 212, the frequency components shown in FIG. 3(G) are eliminated, and the d.c. component shown in FIG. 3(H) is obtained as the difference signal having the frequency of f.sub.p '-f.sub.p.

Meanwhile, the control circuit 22 controls the variable attenuator 14 and the variable phase shifter 15 such that the d.c. output voltage of the pilot detector 21 shown in FIG. 3(H) becomes minimum. In other words, the control circuit 22 controls the variable attenuator 14 and the variable phase shifter 15 such that the pilot signal component in the output RF signal a and the pilot signal component in the distortion output signal b have a mutually identical level and mutually opposite phases. As a result of such a control, the elimination of distortion components in the distortion elimination loop 2 is maximized. As the pilot signal injected to the output of the main amplifier 5 passes through the same signal path as the distortion components formed in the main amplifier 5, the suppression of the pilot signal is equivalent to the suppression of the distortion components. FIGS.4(A)-4(C) show the waveform of the signals a-c in the distortion elimination loop 2.

In such a conventional feed forward amplifiers, on the other hand, there has been a problem in that a long time is needed for reaching a convergence of operation of the feed forward loop because of the fact that the variable attenuator 10 and the variable phase shifter 11 in the distortion elimination loop 1 are controlled in response to the output of the pilot detector 21 while the variable attenuator 14 and the variable phase shifter 15 are controlled simultaneously. In the worst case, the operation of the feed forward amplifier may not converge at all.

The above problem will be described in more detail with reference to FIGS. 5(A)-5(C), wherein FIG. 5(A) shows the case where both the magnitude and phase of the output signal c change in response to a change in the phase of the distortion signal b. In FIG. 5(A), it should be noted that there is no substantial change in the magnitude of the signal b. FIG. 5(B), on the other hand, shows the case wherein both the magnitude and phase of the output signal c change in response to a change in the magnitude of the distortion signal b alone. In the case of FIG. 5(B), the phase of the signal b does not change substantially.

Thus, in the conventional system, it is extremely difficult to obtain the desired convergence of the system as shown in FIG. 5(C) by merely changing the phase and the magnitude of the distortion signal b at the same time.

In order to overcome the problem, the conventional system has employed a complex time sequential process for controlling the foregoing loop 1 and the loop 2 separately. However, such a time sequential process is complex and takes a long time until the operation of the loop converges. Further, such a system has a drawback in that one cannot determine which one of the loop 1 and the loop 2 contains a defect when the system shows a failure.

Further, in the RF amplifiers for use in the base stations of mobile telephone network, the input level tends to change with time in response to the movement of the mobile terminals. Thereby, there may be a case where one cannot ascertain the cause of the apparent variation of the output voltage signal of the power detector 24. It will be noted that one cannot ascertain whether such a variation has been caused as a result of the problems in the feed forward loop or as result of the variation in the level of the incoming RF signal. When the optimization of the feed forward loop is carried out in such a situation, there can even be a case where the cross distortion in the signal increases as a result of the control.

In the feed forward amplifier of FIG. 2 and with reference to FIG. 6, it should also be noted that the non-linear distortion components in the RF signal B, which signal B being outputted from the amplifier 5, are canceled out by the non-linear distortion components contained in the RF signal E that is produced by the variable phase shifter 15, as indicated schematically in FIG. 6. Thereby, the control of the variable attenuator 10 or 14, as well as the control of the variable phase shifter 1 or 15, are achieved based upon the residual non-linear distortion components remaining in the RF signal F by detecting the residual non-linear distortion components by the directional coupler 20. The non-linear distortion component remaining in the signal F is naturally very small, as a result of the distortion compensation operation conducted by the feed forward loop 1, and because of this, there is a tendency that the control of the distortion extraction loop 1 or the distortion elimination loop becomes unstable. This problem is not resolved completely even when a pilot signal is injected to the output of the amplifier 5 as in the circuit of FIG. 2. In FIG. 6, it should be noted that the signal A represents the spectrum of the RF signal as supplied to the feed forward amplifier, the signal B represents the spectrum of the RF signal outputted from the amplifier 5, the signal C represents the spectrum of the RF signal outputted from the variable phase shifter 11, the signal D represents the spectrum of the RF signal outputted from the power synthesizer 8, the signal E represents the spectrum of the RF signal outputted from the variable phase shifter 15, and the signal F represents the spectrum of the output RF signal detected by the directional coupler 20. While the spectrum A contains only the main signal components, it will be noted that the spectrum B contains the non-linear distortion components in addition to the main signal components. Further, the spectrum C contains the main signal components in the state that the phase thereof is inverted, while the spectrum D represents the non-linear distortion components that have been extracted by canceling out the main signal components in the spectrum C by the main signal components in the spectrum B. Further, the spectrum E represents the signal components wherein the phase of the non-linear distortion components is inverted.

DISCLOSURE OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a novel and useful feed forward amplifier.

Another and more specific object of the present invention is to provide a feed forward amplifier including a distortion extraction loop for extracting non-linear distortion components formed in a main amplifier and a distortion elimination loop for canceling out said distortion components by injecting said non-liner distortion components into an output signal of said main amplifier after modification, wherein said feed forward amplifier controls said two loops independently for reducing the time needed for achieving control, said feed forward amplifier thereby facilitating a detection of failures, and wherein said feed forward amplifier operates with reliability even under existence when of variations in the level of the incoming input signals exist.

Another object of the present invention is to provide a feed forward amplifier comprising:

RF amplification means supplied with an input RF signal at an input terminal for amplifying the same, said RF amplification means thereby producing an output RF signal;

a distortion extraction loop supplied with said input RF signal from said input terminal and further with said output RF signal from said RF amplification means, for extracting non-linear distortion components formed in said output RF signal as a result of amplification in said RF amplification means;

variable phase shifter means provided in said distortion extraction loop for varying a phase of said input RF signal that has been supplied to said distortion extraction loop;

variable attenuation means provided in said distortion extraction loop for attenuating an amplitude of said input RF signal that has been supplied to said distortion extraction loop; and

distortion extraction means provided in said distortion extraction loop, said distortion extraction means being supplied on the one hand with said input RF signal after processing in said variable phase shifter means and said variable attenuation means and on the other and with said output RF signal from said RF amplification means, for producing a distortion output signal that includes non-linear components;

wherein said feed forward amplifier further comprises control means supplied with said input signal that has been supplied to said input terminal and further with said distortion output signal for extracting a main signal component contained in said distortion output signal, said control means controlling said variable phase shifter means and said variable attenuation means such that a ratio in level of said main signal component is decreased with respect to said input RF signal.

According to the present invention, one can minimize the level of the main signal component in the distortion output signal relatively to the level of the input RF signal. Associated therewith, the suppression of the main signal component in the foregoing distortion output signal is maximized even when the power level of the incoming RF signal has been changed. Thus, the feed forward amplifier of the present invention is particularly suitable for the broad band RF amplifiers used in the base station of mobile telephone networks wherein the level of the input RF signal changes variously with time. In the feed forward amplifier of the present invention, as the suppression of the main signal component in the distortion output signal is achieved with respect to the level of the input RF signal, the operation of the amplifier converges easily by a simple control system. Further, because of the fact that the optimization of the distortion extraction loop and the optimization of the distortion elimination loop are carried out independently from each other, the optimization process of the distortion extraction loop does not cause interference with the optimization process of the distortion elimination loop, and the control system is quickly stabilized to a converged state. Further, according to the present invention, any abnormal operation of the distortion extraction loop is easily detected by examining whether or not the level of the main signal component in the distortion output signal exceeds a predetermined threshold.

Another object of the present invention is to provide a feed forward amplifier comprising:

RF amplification means supplied with an input RF signal at an input terminal for amplifying the same, said RF amplification means thereby producing an output RF signal;

a distortion extraction loop supplied with said input RF signal from said input terminal and further with said output RF signal from said RF amplification means, for extracting non-linear distortion components formed in said output RF signal as a result of amplification in said RF amplification means;

distortion elimination means supplied with a distortion output signal from said distortion extraction loop and further with said output RF signal from said amplification means, for canceling out said non-liner distortion components contained in said output RF signal by said non-linear distortion components contained in said distortion output signal;

pilot signal generation means for producing a pilot signal; and

pilot signal injection means for injecting said pilot signal to said output RF signal produced by said RF amplification means;

wherein said feed forward amplifier further comprises:

pilot signal detection means supplied with said pilot signal from said pilot signal generation means for detecting a pilot signal component contained in a distortion-eliminated output signal that has been produced by said distortion elimination means, said pilot signal detection means conducting a d.c. detection by mixing said pilot signal into said distortion output signal; and

control means supplied with a d.c. detection signal from said pilot signal detection means, said d.c. detection signal being obtained in said pilot signal detection means as a result of said d.c. detection, said control means controlling said distortion elimination means such that said d.c. detection signal is minimized.

According to the present invention, the pilot signal component contained in the distortion-eliminated output signal is subjected to the d.c. detection. Thereby, the main signal component contained in the distortion output signal is detected with reliability. Further, the main signal component contained in the foregoing distortion output signal is minimized with reliability. As the pilot signal is injected into the output signal of the foregoing RF amplification means, the signal path of the pilot signal is identical with the signal path of the non-linear distortion components. Thereby, the pilot signal behaves exactly like the non-linear distortion components.

Another object of the present invention is to provide a feed forward amplifier having a distortion extraction loop, wherein the pilot signal, which has been injected to an output RF signal produced by an amplifier in the distortion extraction loop for detection of non-linear distortion, can be detected with a high precision even after the process for eliminating said non-linear distortion has been conducted in a distortion elimination loop.

Another object of the present invention is to provide a feed forward amplifier comprising:

RF amplification means supplied with an input RF signal for producing the same to form an output RF signal;

a distortion extraction loop supplied with said input RF signal and further with said output RF signal from said RF amplifier for extracting non-linear distortion components formed in said output RF signal as a result of amplification in said RF amplifier, said distortion extraction loop thereby producing a distortion output signal that contains therein non-linear distortion components; and

a distortion elimination loop supplied with said distortion output signal from said distortion extraction loop and further with said output RF signal from said amplification means for canceling out said non-linear distortion components contained in said output RF signal by non-linear distortion components contained in said distortion output signal;

said distortion elimination loop comprising:

variable attenuation means supplied with said distortion output signal obtained by said distortion extraction means for modifying an amplitude of said distortion output signal;

variable phase shifter means supplied with said distortion output signal obtained by said distortion extraction means for varying a phase of said distortion output signal; and

distortion elimination means supplied with said distortion output signal after processing in said variable attenuation means and said variable phase shifter means, said distortion elimination means being further supplied with said output RF signal from said amplification means for synthesizing said distortion output signal and said output RF signal, said distortion elimination means thereby canceling out the non-linear distortion components contained in said output RF signal by the non-linear distortion components contained in said distortion output signal;

wherein said feed forward amplifier further comprises control means supplied with said distortion output signal and further with said output RF signal for controlling said variable attenuation means and said variable phase shifter means, such that said non-linear distortion components in said output RF signal have an amplitude and a phase that are identical to an amplitude and a phase of said non-linear distortion components contained in said distortion output signal.

According to the present invention, the control of the distortion elimination loop is achieved based upon the output RF signal produced by the RF amplification means and further upon the distortion output signal produced by the distortion extraction loop. Thereby, the problem pertinent to the conventional feed forward amplifiers, that the control of the distortion elimination loop is carried out based upon the minute, residual non-linear distortion components that remain after the cancellation of distortion, is effectively avoided, and a reliable optimization of the distortion elimination loop is achieved.

Another object of the present invention is to provide a feed forward amplifier wherein an effective compensation of non-linear distortion is achieved by a simple control process.

Another object of the present invention is to provide a feed forward amplifier comprising:

RF amplification means supplied with input RF signal for amplifying the same to produce an output RF signal;

a distortion extraction loop supplied with said input RF signal and further with said output RF signal of said RF amplification means for extracting non-linear distortion components formed in said output RF signal as a result of amplification by said RF amplifier, said distortion extraction loop thereby producing a distortion output signal that contains said non-liner distortion components; and

a distortion elimination loop supplied with said distortion output signal from said distortion extraction loop and further with said output RF signal from said RF amplification means, for canceling out said non-linear distortion components contained in said output RF signal by said non-linear distortion components contained in said distortion output signal;

wherein said distortion extraction loop comprises:

variable phase shifter means supplied with said input RF signal for changing a phase thereof;

phase shifter means supplied with said output RF signal from said RF amplification means for causing a 90.degree. degree phase shift therein;

synchronous detection means supplied with said input RF signal after processing in said variable phase shifter means and further with said output RF signal processed by said phase shifter means for carrying out a synchronous detection, said synchronous detection means thereby detecting main signal components contained in said output RF signal;

control means supplied with said main signal components detected by said synchronous detection means for controlling said variable phase shifter means such that said main signal components are minimized; and

distortion extraction means supplied with said input RF signal after processing by said variable phase shifter means and further with said output RF signal produced by said RF amplification means, for causing a cancellation of said main signal contained in said input RF signal and main signal components contained in said output RF signal, said distortion extraction means producing an output signal essentially consisting of said non-linear distortion components, as an output signal.

According to the present invention, the variable phase shifter means is controlled explicitly based upon the main signal components outputted from the synchronous detection means, such that the main signal components in the input RF signal that has been supplied to the foregoing distortion extraction means have a phase shifted by 180.degree. with respect to the phase of the main signal components in the output RF signal. As a result, the extraction of distortion components is achieved by a simple control process. Further, one can eliminate the injection of the pilot signal for extracting the distortions.

Another object of the present invention is to provide a feed forward amplifier wherein the elimination of distortion can be achieved more or less completely.

Another object of the present invention is to provide a feed forward amplifier comprising:

RF amplification means supplied with an input RF signal from an input terminal for amplifying the same to produce an output RF signal;

a plurality of distortion extraction loops each being supplied with said input RF signal from said input terminal and further with said RF signal from said RF amplification means for extracting non-linear distortion components formed in said output RF signal as a result of amplification by said RF amplification means, each of said distortion extraction loops producing a distortion output signal containing therein said non-linear distortion components;

a plurality of distortion extraction loops provided in correspondence to said plurality of distorti