JP2007013946A - Band selection type feed forward amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide, in an environment where plural radio systems coexist, a feed forward amplifier capable of adaptively selecting a frequency band. <P>SOLUTION: The feed forward amplifier comprises: a distortion detection circuit and a distortion elimination circuit and has n first vector adjusters 4 which have different operating frequency bands and are inserted in a first vector adjustment path 14 of the distortion detection circuit; and n second vector adjusters 11 which have frequency bands corresponding to those of the first vector adjusters 4 and are inserted in a second vector adjustment path 8 of the distortion elimination circuit. By means of a first switching means 3 selecting one of the first vector adjusters 4 and a second switching means 10 selecting one of the second vector adjusters 11, the frequency band for which distortion component is compensated in the feed forward amplifier is controlled by switching. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio communication transmission amplifier that adaptively changes a frequency band. In particular, the present invention relates to a band selective feedforward amplifier that selects and amplifies an arbitrary frequency band from a plurality of frequency bands.

  The basic configuration of the feedforward amplifier is shown in FIG. The feedforward amplifier includes two signal processing circuits. One is a distortion detection circuit 100 and the other is a distortion removal circuit 101. The distortion detection circuit 100 includes a main amplifier signal path 103 and a linear signal path 104. The distortion elimination circuit 101 is composed of a main amplifier output signal path 108 and a distortion injection path 109. The main amplifier signal path 103 (also referred to as a vector adjustment path) includes a vector adjuster 105 and a main amplifier 106. The vector adjuster 105 includes a variable phase shifter 105a and a variable attenuator 105b. The linear signal path 104 is composed of a delay line. The main amplifier output signal path 108 is constituted by a delay line. The strain injection path 109 includes a vector adjuster 110 and an auxiliary amplifier 111. The vector adjuster 110 includes a variable phase shifter 110a and a variable attenuator 110b. The power distributor 102, the power combiner / distributor 107, and the power combiner 112 are simple lossless power distributors and power combiners configured by a transformer circuit, a hybrid circuit, and the like.

First, the basic operation of the feedforward amplifier will be described. The signal input to the feedforward amplifier is distributed to the main amplifier signal path 103 and the linear signal path 104 by the power distributor 102. At this time, the variable attenuator 105b and the variable phase shifter 105a of the main amplifier signal path 103 are adjusted so that the signals of the main amplifier signal path 103 and the linear signal path 104 have equal amplitude and opposite phase. As a method of making the phase opposite, there are a method in which the power distributor 102 or the power combiner / distributor 107 appropriately sets a phase shift amount between the input and output terminals, a method in which the main amplifier 106 inverts the phase, and the like.
Since the distortion detection circuit 100 is configured in this way, the power combiner / distributor 107 can output a difference component between the signal that has passed through the main amplifier signal path 103 and the signal that has passed through the linear signal path 104. This difference component is exactly the distortion component generated by the main amplifier 106. Therefore, the block from the power distributor 102 to the power combiner / distributor 107 shown in FIG. 1 is called a distortion detection circuit.

  Next, the distortion removal circuit 101 will be described. The output of the distortion detection circuit 100 is distributed to the main amplifier output signal path 108 and the distortion injection path 109 via the power combiner / distributor 107. The main amplifier output signal path 108 receives the output of the main amplifier 106 in the main amplifier signal path 103 (the signal that has passed through the main amplifier signal path 103). Further, the distortion component of the main amplifier 106 detected by the distortion detection circuit 100 (the difference component between the signal passing through the main amplifier signal path 103 and the signal passing through the linear signal path 104) is input to the distortion injection path 109. . The variable attenuator 110b and the variable phase shifter 110a in the distortion injection path 109 are the distortion elimination circuit output end, and the distortion component of the signal that has passed through the main amplifier output signal path 108 and the signal that has passed through the distortion injection path 109 have equal amplitude, And it adjusts so that it may become an antiphase. By adjusting in this way, the power combiner 112 can synthesize the distortion component of the main amplifier 106 having the same amplitude and the opposite phase with the signal that has passed through the main amplifier signal path 103. Then, the power combiner 112 outputs a signal that cancels out the distortion components of the entire amplifier circuit. As is well known, a linear amplifier is used as the auxiliary amplifier in order to remove distortion components generated in the main amplifier used in the feedforward amplifier. The above is the operation of an ideal feedforward amplifier. Actually, it is not easy to completely maintain the balance of the distortion detection circuit and the distortion removal circuit. Even if the initial setting is complete, the characteristics of the amplifier change due to fluctuations in the ambient temperature, power supply, etc., and it is extremely difficult to maintain good balance with time stability.

  As a method for maintaining the balance of the distortion detection circuit and distortion removal circuit of the feedforward amplifier with high accuracy, an automatic adjustment method using a pilot signal is known. For example, there is Patent Document 1. Non-Patent Document 1 is known as a device that puts these to practical use. These feedforward amplifiers are put into practical use in the 800 MHz band and 1.5 GHz band of the PDC (Personal Digital Cellular) system. Such a feedforward amplifier is generally designed and adjusted for each frequency band to be amplified.

  Conventional wireless systems have used a single system that complies with any standard such as PDC, GSM (Global System for Mobile Communications), or IMT-2000 (International Mobile Telecommunication 2000). On the other hand, there is a technique for softwareizing a radio so that a single hardware can support a plurality of radio systems. If a single hardware can support a plurality of wireless systems, the user can use the mobile communication environment without being aware of the wireless system and the core network behind it. However, in reality, a single hardware corresponding to a plurality of wireless systems has not been realized.

  In addition, the services provided by the wireless system will be different for each region or operator, and the wireless system will be diversified. For this reason, in the future, it will be necessary to mix optimal radio systems for each purpose at the same time and in the same place.

  There is a multiband radio system as a method using these plural radio systems. This wireless system adaptively changes the frequency band or the number of frequency bands used according to the propagation environment and traffic conditions. In order to ensure a predetermined transmission quality or transmission amount, multiband transmission using an unused frequency band is effective. Therefore, in a multiband wireless system, the number of frequency bands is changed in order to ensure transmission quality and transmission amount that the wireless system should guarantee. The same change is made within the same band. Furthermore, when the frequency bands used by multiple operators are mixed, the multiband wireless system uses interference recognition technology, frequency sharing technology, interference cancellation technology, interference reduction avoidance technology, multiband control technology, etc. By performing adaptive control using a vacant frequency band, frequency utilization efficiency can be increased.

  The feedforward amplifier is used as a linear amplifier for a base station corresponding to such a multiband radio system. However, when multiple frequency bands to be amplified are far apart compared to the bandwidth of each frequency band, the electrical length of the delay line for each frequency band is different. The amount of adjustment of the variable phase shifter and variable attenuator for setting the balance to a predetermined range differs depending on the frequency band to be amplified.

  Specifically, when a delay line common to all frequency bands is used, the set value of the vector adjuster must always follow a signal that rotates at the angular speed of the frequency difference due to the frequency difference of the input signals. . However, conventional vector adjusters have not been able to follow such high-speed rotating signals. In addition, conventional vector adjusters have been unable to set optimum amplitude and phase for a plurality of input signals simultaneously due to structural reasons.

  For example, when signals in the 800 MHz band and the 1.5 GHz band are input to the same vector adjuster, optimal vector adjustment can be performed for any frequency band. However, optimal vector adjustment that follows a frequency difference of 700 MHz cannot be performed. Therefore, the conventional feedforward amplifier cannot simultaneously amplify the 800 MHz band signal and the 1.5 GHz band signal below a predetermined distortion compensation amount.

As a method for solving this problem, a non-patent document 2 proposes a dual-band feedforward amplifier. In this configuration, a vector adjuster having a band extracting unit is provided for each frequency band. In other words, this dual-band feedforward amplifier extracts a frequency band signal to be vector-adjusted from two input frequency band signals by means of a filter provided in front of the vector adjuster. Then, vector adjustment is performed for each frequency band. This dual-band feedforward amplifier configuration can compensate for distortion in a plurality of frequency bands. The band to be compensated is fixed by a filter.
JP-A-1-198809 Toshio Nojima, Shoichi Takahashi, "Ultra Low Distortion Multi-frequency Common Amplifier for Mobile Communications ---- Self-Adjusting Feedforward Amplifier (SAFF-A) ----", IEICE, Radio Communication Systems Study Group, RCS90 -4, 1990. Suzuki Yuri, Takahashi Shoichi, “Dual-Band Feedforward Amplifier”, 2005 IEICE General Conference, C-2-2, March 2005.

  In a multiband wireless system having a plurality of transmission bands, it is conceivable to change the frequency band depending on the service status of the wireless system, interference with other wireless systems, and the like. However, as described above, the distortion compensation bandwidth of the feedforward amplifier is determined by the adjustment accuracy of each loop of the distortion detection circuit and the distortion removal circuit. Therefore, in the conventional feedforward amplifier, the distortion compensation adjustment cannot be made to correspond to the change of the frequency band. Further, the conventional dual band feedforward amplifier in which the frequency band for distortion compensation is fixed cannot adaptively change the operating frequency. For a feedforward amplifier that is used for a long period of time, a change in the frequency band involves a modification or change of the feedforward amplifier at the base station. Therefore, a great deal of labor and time is required to readjust many feedforward amplifiers. There is a need for a feedforward amplifier configuration that can eliminate this effort and time.

  For example, a dual-band feedforward amplifier that simultaneously compensates for distortion of a signal in the frequency band f1 and a signal in the frequency band f2 is changed from the signal in the frequency band f1 and the signal in the frequency band f3 when the frequency band f2 is changed to f3. Cannot be compensated for at the same time. This is because the operating band of the conventional dual-band feedforward amplifier is fixed, and as described above, loop adjustment cannot be performed due to the frequency difference between f1 and f3.

  Another possible method is to provide a dual-band feedforward amplifier with fixed filters and vector adjusters corresponding to all frequency bands expected to be serviced in the future. However, having a fixed filter and a vector adjuster that can handle all frequency bands also has a fixed filter and a vector adjuster that are not used, which is contrary to the construction of an economical feedforward amplifier. Thus, with the change of the frequency band or the increase / decrease of the carrier wave, there has been a demand for a feedforward amplifier that does not require the replacement of the components and the configuration is not redundant.

  The present invention relates to a feedforward amplifier including a distortion detection circuit and a distortion removal circuit. In the first vector adjustment path of the distortion detection circuit, n first vector adjusters having different operating frequency bands are provided in parallel. In addition, n second vector adjusters whose operating frequency bands correspond to the first vector adjusters are provided in parallel on the second vector adjustment path of the distortion removal circuit. Further, a first switching means for selecting one of the n first vector adjusters, and a second switch for selecting a second vector adjuster having the same operating frequency band as the selected first vector adjuster. Means. A frequency control unit that adaptively switches and controls the first and second switching means is provided.

  Furthermore, a feedforward amplifier according to the present invention includes a local oscillator, a local oscillator frequency control unit that controls the frequency of the local oscillator, a mixer that multiplies an input signal from the first distribution unit and a signal from the local oscillator, and a mixer The low-pass filter that passes only the low-frequency component of the output of the output, the local oscillator frequency controller detects the frequency band of the input signal from the signal that controls the local oscillator and the output signal of the low-pass filter, frequency control A band detector having an analysis unit for outputting a control signal to the detector.

  According to the present invention, a vector adjuster suitable for each frequency band of the feedforward amplifier input signal can be used. Therefore, optimal distortion compensation can be performed for each frequency band. Further, even in a communication environment in which a plurality of wireless systems are mixed, the operating frequency band of the feedforward amplifier can be adaptively changed.

  Thus, the feedforward amplifier of the present invention can linearly amplify the frequency band corresponding to the service status of the wireless system. Therefore, the present invention can eliminate the need for additional equipment associated with a change in frequency band or an increase in carrier waves. Further, in the prior art, a plurality of feedforward amplifiers having different operating frequency bands had to be installed in the base station. However, according to the present invention, a single feedforward amplifier may be installed. And is advantageous in terms of power consumption.

[First Embodiment]
FIG. 2 shows a basic configuration of the feedforward amplifier of the present invention. The feedforward amplifier according to the present invention includes a distortion detection circuit 100, a distortion removal circuit 101, and a frequency control unit 9. The distortion detection circuit 100 includes a first linear signal path 2 and a first vector adjustment path 14. The distortion removal circuit 101 includes a second linear signal path 7 and a second vector adjustment path 8. The first vector adjustment path 14 is configured by connecting the first switching unit 3 and the first multiband amplifier 5 in series. The first switching means 3 includes a first input switch 3a, n first vector adjusters 4, and a first output switch 3b. The n first vector adjusters 4 have different operating frequency bands and are arranged in parallel.

  The second vector adjustment path 8 is constituted by a series connection of the second switching means 10 and the second multiband amplifier 12. The second switching means 10 includes a second input switch 10a, n second vector adjusters 11, and a second output switch 10b. The n second vector adjusters 11 each have an operating frequency band corresponding to the first vector adjuster, and are arranged in parallel. In FIG. 2, the first switching means 3 is a single pole double throw switch (SPDT) for the sake of simplicity. The first vector adjuster 4 is composed of two vector adjusters 4a and 4b that can adjust the amplitude and phase of signals in two different frequency bands. However, it is not necessary to limit to two, and n is an integer of 2 or more.

  The first distributor 1 distributes an input signal to the feedforward amplifier to a first linear signal path 2 and a first vector adjustment path 14 configured by delay lines. The frequency controller 9 switches the first input switch 3a, the first output switch 3b, the second input switch 10a, and the second output switch 10b in accordance with a control signal from the operation center. For example, when the first vector adjuster 4a and the second vector adjuster 11a are connected, in the first vector adjustment path 14, the signal distributed by the first distributor 1 is input to the first vector adjuster 4a. Is done. The first vector adjuster 4a adjusts the phase of the input signal and outputs it. The first multiband amplifier 5 amplifies the output of the first vector adjuster 4a. In this way, the first vector adjuster 4a and the first multi-band amplifier 5 receive the signal input to the first vector adjustment path 14 on the input side of the synthesizer / distributor 6 in the first linear signal path 2. Is adjusted to a signal having the same phase and the same phase as that of the signal that has passed through. By adjusting in this way, the distortion component generated in the first multiband amplifier 5 can be obtained by taking the difference between the first linear signal path 2 and the first vector adjustment path 14. The synthesizer / distributor 6 outputs the distortion component generated in the first multiband amplifier 5 to the second linear signal path 7 of the distortion removal circuit 101 while being added to the transmission signal. Further, the synthesizer / distributor 6 outputs a distortion component that is a difference between the first linear signal path 2 and the first vector adjustment path 14 to the second vector adjustment path 8 of the distortion removal circuit. In the second vector adjustment path 8, the second vector adjuster 11a adjusts and outputs the phase of the distortion component. The second multiband amplifier 12 amplifies the output of the second vector adjuster 11a. In this way, the second vector adjuster 11a and the second multiband amplifier 12 convert the distortion component input to the second vector adjustment path 8 into the second linear signal path on the input side of the second synthesizer 13. 7 is adjusted to a signal having the same phase and the same phase as the distortion component included in the signal having passed through 7. Since the phase and amplitude of the distortion component are adjusted in this way, if the second synthesizer 13 synthesizes the signal that has passed through the second linear signal path 7 and the signal that has passed through the second vector adjustment path 8, distortion will occur. The components are offset.

  As described above, the first input switching unit 3a, the first output switching unit 3b, the second input switching unit 10a, and the second output switching unit 10b are controlled by the frequency control unit 9. For example, when the first vector adjuster 4a is for the 800 MHz band and the first vector adjuster 4b is for the 1.5 GHz band, the second vector adjuster 11a is for the 800 MHz band, and the second vector adjuster 11b is 1. What is necessary is just to use for 5 GHz band. When the first switching unit 3 selects the 800 MHz band vector adjuster 4a by the frequency controller 9, the second switching unit 10 also selects the 800 MHz band vector adjuster 11a.

  A feature of the present invention is that when a frequency band to be used is changed, a distortion compensation suitable for the frequency band to be used is obtained by connecting a vector adjuster for the corresponding frequency band to a distortion detection circuit and a distortion removal circuit. The point is to do.

  FIG. 3 shows the concept of distortion compensation. In FIG. 3, the horizontal axis represents frequency, and the vertical axis represents distortion compensation amount. When the operation center frequency of the first vector adjustment path 14 and the second vector adjustment path 8 is f1, the distortion of the signal centered on the frequency f1 is compensated. If the first vector adjuster 4a and the second vector adjuster 11a are for the frequency band f1, the first input switch 3a, the first output switch 3b, the second input switch 10a, and the second output switch 10b are What is necessary is just to set to the 1st vector adjuster 4a and the 2nd vector adjuster 11a side. By compensating the distortion, for example, the distortion amount with respect to the signal amplitude in the signal band is set to about −30 dB.

  When the operation center frequency of the first vector adjustment path 14 and the second vector adjustment path 8 is changed to f2, distortion compensation in a frequency band centered on the frequency f2 is performed. If the first vector adjuster 4b and the second vector adjuster 11b are for the frequency band f2, the first input switch 3a, the first output switch 3b, the second input switch 10a, and the second output switch 10b are What is necessary is just to set to the 1st vector adjuster 4b and the 2nd vector adjuster 11b side. By setting in such a manner, the range of the frequency subjected to distortion compensation is the frequency band f2. In FIG. 3, the bandwidth of the frequency f2 is narrower than the frequency f1. Thus, the first vector adjuster 4 and the second vector adjuster 11 can set the center frequency and the bandwidth of the frequency band for performing distortion compensation.

  As described above, the feedforward amplifier according to the present invention can switch and connect vector adjusters having different operating frequency bands to the vector adjustment path. Therefore, the feedforward amplifier of the present invention can compensate for distortion components of transmission signals in a plurality of frequency bands. In the above description, an example in which SPDT switches are used for the first switching unit 3 and the second switching unit 10 has been described. However, by using a single-pole n-throw switch having n contacts and providing n vector adjusters with different operating frequency bands, distortion compensation can be performed with high accuracy for the n frequency bands. . For example, a vector adjuster for each frequency band may be provided in order to support wireless systems such as 800 MHz, 1.5 GHz, 2.0 GHz, 2.4 GHz, and 5.2 GHz. Even in such a radio system that adaptively selects a large number of frequency bands, the feedforward amplifier of the present invention performs sufficient distortion compensation and can be realized with a relatively small hardware scale and software scale.

[Modification]
FIG. 4 shows a modification of the first embodiment in which the first and second switching means are composed of one input switch and an output combiner that combines the output signals of a plurality of vector adjusters. The output ends of the first vector adjusters 4 a and 4 b are connected to the first output combiner 30. The output terminal of the first output synthesizer 30 is connected to the input terminal of the first multiband amplifier 5.

  The output ends of the second vector adjusters 11a and 11b are connected to the second output combiner 31. The output terminal of the second output synthesizer 31 is connected to the input terminal of the second multiband amplifier 12. The first output synthesizer 30 and the second output synthesizer 31 can be realized by, for example, a well-known Wilkinson power synthesizer or a 3 dB hybrid circuit. In this way, the first and second output switching units of the first and second switching units can be replaced with a synthesizer.

[Second Embodiment]
FIG. 5 shows an example in which the input switching device is configured by a switching distributor and a frequency band extractor. The signal distributed by the first distributor 1 is input to the first switching distributor 40. The first switching distributor 40 distributes the input signal to the first frequency band extractors 41a and 41b. The first frequency band extractors 41a and 41b can be composed of a band pass filter, a band rejection filter, or the like. In these filters, frequencies in different frequency bands, for example, 800 MHz band and 1.5 GHz band, are extracted and output to the first vector adjusters 4a and 4b.

Similarly, in the second switching means 10, the distortion component from the synthesizer / distributor 6 is input to the second switching distributor 42. The second switching distributor 42 distributes the input signal to the second frequency band extractors 43a and 43b. The second frequency band extractors 43a and 43b extract frequencies in different frequency bands, for example, 800 MHz band and 1.5 GHz band, and output them to the second vector adjusters 11a and 11b.
The frequency control unit 9 selects which of the first frequency band extractors 41a and 41b and the second frequency band extractors 43a and 43b is operated. For example, when the distortion component of the transmission signal in the 800 MHz band is compensated, the first frequency band extractor 41a and the second frequency band extractor 43a are selected.

FIG. 5 shows an example in which two frequency band extractors are provided. However, n frequency bands may be provided in parallel so that n frequency bands can be handled.
When each frequency band extractor is constituted by a band pass filter, there is an advantage that it is easy to extract the periphery of the band of the center frequency, and the isolation from the center frequency is relatively easy. However, since the center frequency is the resonance frequency of the bandpass filter, the signal delay increases. Therefore, it is necessary to lengthen the line length of the delay line constituting the linear signal path in accordance with the delay amount.

  On the other hand, if each frequency band extractor is configured by a band rejection filter, the frequency band to be extracted is not the center frequency of the band rejection filter, and therefore the delay amount of the passing frequency band is small. Therefore, there is an advantage that the line length of the linear signal path can be shortened and the loss can be reduced. Further, the band rejection filter can be easily designed.

[Third Embodiment]
FIG. 6 shows an example in which individual amplifiers are provided for each frequency band to be amplified as the first multi-frequency band amplifier and the second multi-frequency band amplifier. The input terminal of the main amplifier 50a that amplifies the frequency band of the first vector adjuster 4a is connected to the output terminal of the first vector adjuster 4a. The input terminal of the main amplifier 50b that amplifies the operating frequency band of the first vector adjuster 4b is connected to the output terminal of the first vector adjuster 4b. The input terminal of the auxiliary amplifier 51a that amplifies the operating frequency band of the second vector adjuster 11a is connected to the output terminal of the second vector adjuster 11a. The input terminal of the auxiliary amplifier 51b that amplifies the operating frequency band of the second vector adjuster 11b is connected to the output terminal of the second vector adjuster 11b.

  Thus, by providing the main amplifier and the auxiliary amplifier having frequency characteristics matched to the operating frequency band of each vector adjuster, an amplifier having a narrow bandwidth that can be amplified can be used in the present invention. The first multiband amplifier 5 and the second multiband amplifier 12 shown in FIGS. 2, 4, and 5 can be replaced with a plurality of amplifiers having operating frequency bands corresponding to the respective frequency bands. is there.

[Fourth Embodiment]
FIG. 7 shows another configuration example of the first multiband amplifier 5 and the second multiband amplifier 12. In FIG. 7, the amplifier has a two-stage configuration of a preamplifier 60 and final stage amplifiers 62a and 62b. The final stage amplifiers 62a and 62b are amplifiers that can obtain a high gain in a corresponding frequency band. The preamplifier 60 of the first multiband amplifier or the second multiband amplifier amplifies the input signal. The distributor 61 distributes to each frequency band. The final stage amplifiers 62a and 62b amplify signals in the corresponding frequency bands. The combiner 63 combines the amplified signals.

  It is also possible to configure the main amplifier or the auxiliary amplifier with a single amplifier. In this case, rather than preparing amplifiers for each frequency band, the number of amplifiers can be reduced and power consumption can be reduced. Even when the main amplifier and the auxiliary amplifier are configured by a single amplifier, it is possible to provide a feedforward amplifier that adaptively selects a frequency band.

[Fifth Embodiment]
In the description so far, the frequency control unit 9 has been controlled by a control signal from an operator. In this embodiment, an example of using the band detector 33 shown by the dotted line in FIG. 2 to automatically detect the frequency band of the input signal from the signal input to the feedforward amplifier and compensate for the distortion component of the transmission signal. Indicates. In the case of this configuration, the first distributor 1 also distributes a part of the input signal to the band detector 33. The band detector 33 detects the frequency band of the input signal by the following method and outputs a control signal to the frequency control unit 9. Other operations are the same as those in the first embodiment.

  FIG. 8 shows a functional configuration example of the band detector 33. The band detector 33 includes a local oscillator frequency control unit 331, a local oscillator 332, a mixer 333, a low-pass filter 334, and an analysis unit 335. The local oscillator frequency control unit 331 controls the local oscillator 332 so as to continuously sweep the frequency from the lower limit frequency to the upper limit frequency of the input signal. The local oscillator 332 oscillates according to an instruction from the local oscillator frequency control unit 331. The mixer 333 multiplies the input signal distributed from the first distributor 1 by the signal from the local oscillator 332. The output signal from the mixer 333 includes the frequency component of the difference between the frequency of the input signal and the frequency of the signal from the local oscillator 332. That is, when the frequency of the input signal and the frequency of the signal from the local oscillator 332 are very close, the output from the mixer 333 includes a component near DC (low frequency component). The low pass filter 334 passes only the low frequency component of the output from the mixer 333. Therefore, the band detector output signal is obtained from the low-pass filter 334 only when the frequency of the input signal and the frequency of the signal from the local oscillator 332 are very close. The analysis unit 335 compares the frequency sweep signal from the local oscillator frequency control unit 331 with the band detector output signal from the low-pass filter 334, detects the frequency band of the input signal, and outputs a control signal to the frequency control unit 9 Is output.

  FIG. 9 shows an example of the spectrum of the input signal of the feedforward amplifier. The center frequency of the first frequency band is f1, the lower limit frequency is f1L, and the upper limit frequency is f1H. The center frequency of the second frequency band is f2, the lower limit frequency is f2L, and the upper limit frequency is f2H. FIG. 10 shows the relationship between the sweep frequency and the frequency of the input signal. The horizontal axis is the sweep frequency, and the vertical axis is the frequency of the input signal. This figure shows that a signal in the vicinity of DC is output from the low-pass filter 334 when the sweep frequency is from the frequency f1L to the frequency f1H and from the frequency f2L to the frequency f2H. FIG. 11 shows temporal changes in the signal output from the local oscillator 332. The horizontal axis is time, and the vertical axis is the output from the local oscillator 332. FIG. 12 shows a temporal change in the output from the low-pass filter 334. The horizontal axis is time, and the vertical axis is the output from the low-pass filter 334. As shown in FIG. 12, when the frequency of the output from the local oscillator 332 corresponds to the frequency f1L to the frequency f1H and the frequency f2L to the frequency f2H, the output from the low-pass filter 334 is obtained.

Note that when a threshold is set for the output from the low-pass filter 334, the bandwidth of the frequency band is narrowed as shown in FIG. Therefore, the analysis unit 335 may correct each frequency by multiplying the obtained lower limit frequencies f1L and f2L and the upper limit frequencies f1H and f2H by a predetermined coefficient.
Further, the local oscillator frequency control unit 331 and the analysis unit 335 can be realized by an analog / digital converter and a microprocessor. As the local oscillator 332, a generally used signal transmitter or the like may be used. The mixer 333 and the low-pass filter 334 can be realized by an active filter using an LC filter or an operational amplifier.

Since the band detector 33 operates in this way, the feedforward amplifier can adaptively cope with the case where the input signal is dynamically changed. The time required to change the frequency band processed by the feedforward amplifier depends on the period of the signal swept by the local oscillator 332. When the frequency change at high speed is necessary, the period of the signal swept by the local oscillator 332 may be shortened.
Note that the band detector 33 can also be used in all of the above embodiments, as indicated by the dotted lines in FIGS. 4, 5, and 6. In any embodiment, if the band detector 33 is used, the frequency band of the input signal can be automatically detected. The configuration of the feedforward amplifier can be dynamically changed via the frequency control unit 9.

  As described above, since the feedforward amplifier according to the present invention can freely switch the frequency band for distortion compensation, the frequency band to be used can be adaptively changed in an environment where a plurality of radio systems are mixed. Therefore, no additional equipment is required for changing the frequency band or increasing the number of conveyances.

It is a figure which shows the basic composition of the conventional feedforward amplifier. It is a figure which shows the principle structure of the feedforward amplifier of this invention. It is a figure which shows the conceptual diagram of distortion compensation. It is a figure showing a 1st embodiment of this invention. It is a figure which shows 2nd Embodiment of this invention. It is a figure which shows 3rd Embodiment of this invention. It is a figure which shows the other structural example of a 1st, 2nd multiband amplifier. It is a figure which shows the function structural example of a band detector. It is a figure which shows the example of the spectrum of the input signal of a feedforward amplifier. It is a figure which shows the relationship between a sweep frequency and the frequency of an input signal. It is a figure which shows the time change of the signal output from a local oscillator. It is a figure which shows the time change of the signal output from a low-pass filter. It is the figure which showed that the bandwidth of the frequency band detected becomes narrow when a threshold value is set to the output from a low-pass filter.

Claims (5)

A feedforward amplifier having a distortion detection circuit and a distortion removal circuit,
n is an integer greater than or equal to 2,
The distortion detection circuit is
A first linear signal path constituted by first delay means;
A first vector adjustment path;
A first distributor for distributing an input signal to the first linear signal path and the first vector adjustment path;
N first vector adjusters provided in the first vector adjustment path, each for adjusting the phase and amplitude of signals in different frequency bands;
First switching means for selecting one of the n first vector adjusters and inserting it into the first vector adjustment path;
A first multiband amplifier for amplifying the output of the first vector adjuster;
A combiner / distributor that outputs a sum component and a difference component of the output of the first linear signal path and the output of the first multiband amplifier, respectively;
The distortion removal circuit is
A second linear signal path configured by second delay means and receiving the sum component;
A second vector adjustment path through which the difference component is input;
N second vector adjusters which are provided in the second vector adjustment path and adjust the phase and amplitude of signals in the same frequency band as the n first vector adjusters,
Second switching means for selecting one of the n second vector adjusters and inserting it into the second vector adjustment path;
A second multiband amplifier for amplifying the output of the second vector adjuster;
A second synthesis unit that synthesizes and outputs the output of the second linear signal path and the output of the second multiband amplifier;
A band-selective feedforward amplifier, comprising: a frequency control unit that performs switching control between the first switching unit and the second switching unit. The feed forward amplifier according to claim 1.
The first switching means includes a first input switch for inputting an output of the first distributor to one first vector adjuster among the n first vector adjusters, and the first vector adjustment. A first output switch for inputting the output of the amplifier to the first multi-band amplifier,
The second switching means includes a second input switch for inputting the output of the combiner / distributor to one second vector adjuster among the n second vector adjusters, and the second vector adjuster. And a second output switching device for inputting the output of the output to the second multiband amplifier. The feed forward amplifier according to claim 1.
The first switching means includes a first input switch for inputting an output of the first distributor to one first vector adjuster among the n first vector adjusters, and the n first switches. A first output synthesizer for synthesizing the output signal of one vector adjuster,
The second switching means includes a second input switch for inputting the output of the combiner / distributor to one second vector adjuster among the n second vector adjusters, and the n second switch. And a second output synthesizer for synthesizing the output signal of the vector adjuster. The feed forward amplifier according to claim 1.
The first switching means is
A first switching distributor for distributing the signal input from the first distributor to n;
From the n distributed signals, signals in a frequency band that can be adjusted by the n first vector adjusters can be extracted, and n first frequency bands for outputting the extracted signals to the first vector adjuster. An extractor;
A first output synthesizer for synthesizing the output signals of the n first vector adjusters,
The second switching means is
A second switching distributor for distributing the signal input from the combining distributor to n;
From the n distributed signals, signals in a frequency band that can be adjusted by the n second vector adjusters can be extracted, and n second frequency bands for outputting the extracted signals to the second vector adjuster. An extractor;
A second output synthesizer for synthesizing the output signals of the n second vector adjusters,
The frequency control unit selects and operates the n first frequency band extractors and the n second frequency band extractors. A band selective feedforward amplifier, wherein: The feedforward amplifier according to any one of claims 1 to 4,
Also equipped with a band detector
The first distribution unit distributes a part of the input signal to the band detector,
The band detector is
A local oscillator,
A local oscillator frequency control unit for controlling the frequency of the local oscillator;
A mixer for multiplying an input signal from the first distribution unit by a signal from the local oscillator;
A low-pass filter that passes only low-frequency components of the output of the mixer;
The local oscillator frequency control unit detects the frequency band of the input signal from the signal for controlling the local oscillator and the output signal of the low-pass filter, and outputs the control signal to the frequency band controller. A band-selective feedforward amplifier characterized by comprising:

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