JP2003060447A - Transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission system, capable of stably compensating nonlinear distortions of a unit amplifier which is not troubled, even if a plurality of unit amplifiers connected in parallel are troubled in the transmission system, in which adaptive predistortions are executed in a power amplifier in which the plurality of the unit amplifiers are connected in parallel, for improving the linearity of a transmission output. SOLUTION: The transmission system comprises the power amplifier, in which the plurality of the unit amplifiers are connected in parallel and the adaptive predistortion is executed in the power amplifier for improving the linearity of the transmission output. The system further comprises a constitution for detecting a level change of an input terminal or an output terminal of each of the plurality of the unit amplifiers, and other constitution for generating a reference signal of the adaptive predistortion by variably setting the gain of a base band signal to be output from a base band signal unit, corresponding to the detected level change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission system for improving linearity of transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel, and more particularly to units connected in parallel. The present invention relates to a transmission system capable of stably compensating for non-linear distortion of a unit amplifier that has not failed even if the amplifier fails.

In both the wireless communication system and the wired communication system, a power amplifier capable of outputting a large amount of power is provided at the final stage of the transmission system in consideration of attenuation in the communication path. In particular, in a wireless communication system, although the space in which radio waves propagate is restricted by the directivity of the antenna, refraction caused by unevenness of the propagation constant of the space, scattering by dust present in the space, and construction Electric power loss increases due to reflection from objects, hills, or forests. Furthermore, since the signal-to-noise ratio is lowered by the noise in the natural world existing in the propagation space and the noise generated by human social activities, it is necessary to transmit with sufficiently large output power.

However, the active element that constitutes the power amplifier has a high linearity when the power is relatively small,
At high power, the linearity is lost and the nonlinear distortion becomes large. This non-linear distortion becomes noise for signals of other channels in the same communication band and signals of different communication bands. Therefore,
It is essential to reduce non-linear distortion while obtaining a large output power, and a transmission system that improves the linearity of the transmission output by applying adaptive pre-distortion to a power amplifier consisting of multiple unit amplifiers connected in parallel has been put to practical use. Has been done.

[0004]

2. Description of the Related Art FIG. 5 shows the configuration of a conventional transmission system. In FIG. 5, reference numeral 1 is a baseband signal unit that processes an original signal and outputs a baseband signal. Reference numeral 2 is a compensation signal generation circuit that generates a compensation signal for performing adaptive pre-distortion. The baseband signal output from the baseband signal unit is supplied to the compensation signal generation circuit 2.

Further, 3 is an adder circuit for adding the baseband signal and the compensation signal, 4 is a quadrature modulation circuit for modulating the output of the adder circuit 3, and 5 is an analog conversion of the output of the quadrature modulation circuit 4. A digital-to-analog converter (in the figure, an abbreviation "DAC" which is an acronym for Digital Analog Convertor is described. It is also described in the following in the figure), 6 generates a carrier wave in a radio frequency band The radio frequency oscillator 7 is an up converter that frequency-converts the output of the digital-analog converter 5 into the radio frequency band by the radio frequency carrier wave output from the radio frequency oscillator 6.

Reference numerals 8 and 9 are unit amplifiers for power-amplifying the output of the up converter 7. In the example of FIG. 5, two unit amplifiers are connected in parallel to form a power amplifier.
Further, 12 is a directional coupler that branches a part of the output of the power amplifier, and 13 is an antenna that radiates the output power to the space. Further, 14 is an attenuator that adjusts the level of the radio frequency band signal branched by the directional coupler 12, and 15 is a down converter that frequency-converts the output of the attenuator 14 by the output of the radio frequency oscillator 6. .

Reference numeral 16 denotes a first analog-to-digital converter (abbreviated as "ADC" in the figure) for converting the output of the down converter 15 into a digital signal. This is an abbreviation for "Analog Digital Convertor". In addition, the same applies to the following figures.).
The first analog-to-digital converter is assumed to have a built-in amplifier.

Reference numeral 17 is a quadrature demodulation circuit for converting the output of the first analog-digital converter 16 into a baseband signal. Reference numeral 18 is a subtraction circuit that takes the difference between the feedback signal output from the quadrature demodulation circuit 17 and the baseband signal output from the baseband signal unit 1. Here, the baseband signal supplied to the subtraction circuit 18 will be referred to as a reference signal.

Then, the conventional transmission system is constituted by the components of the compensation signal generation circuit 2 to the subtraction circuit 18. In the configuration of FIG. 5, the baseband signal and the compensation signal output from the baseband signal unit 1 are added in the addition circuit 3, quadrature-modulated by the quadrature modulation circuit 4, and then analog-converted by the digital-analog converter 5 to be up-converted. -Upconverted to a radio frequency band signal by the converter 7.

The radio frequency band signal is amplified to a predetermined level by a power amplifier in which unit amplifiers 8 and 9 are connected in parallel, is radiated into space from an antenna 13 through a directional coupler 12. Here, the reason why a plurality of unit amplifiers are connected in parallel to form a power amplifier is that it is difficult to obtain the required output power with a single unit amplifier. On the other hand, the radio frequency band signal partially branched in the directional coupler 12 is adjusted in level in the attenuator 14 and supplied to the down converter 15, and is down converted by the carrier wave in the radio frequency band. Is converted into a digital signal by the analog-digital converter 16 and demodulated by the quadrature demodulation circuit 17 to become a feedback signal. The feedback signal is the baseband signal plus a distortion component generated in the power amplifier.

In the subtracting circuit 18, the baseband signal forming the feedback signal and the baseband signal forming the reference signal are subtracted at the same level and output as an error signal. The compensation signal generation circuit 2 calculates a coefficient for the baseband signal so that the level of the error signal generated in this way is minimized, and outputs a signal including an inverse component of distortion so that the feedback signal becomes the same as the reference signal. To do. This is the outline of the adaptive pre-distortion operation by the compensation signal generation circuit 2, and the distortion component generated in the power amplifier can be compensated by the adaptive pre-distortion. That is, the linearity of the output of the transmission system can be maintained.

[0012]

As described above, when the subtraction circuit subtracts the feedback signal from the reference signal, the baseband signal component and the reference signal included in the feedback signal are formed. It is necessary to match the levels of the baseband signals to be used. However, when some of the unit amplifiers connected in parallel fail, the level of the baseband signal component included in the feedback signal becomes lower than the level of the baseband signal output by the baseband signal unit 1.

As a result, contrary to the original adaptive pre-distortion operation, the compensation signal generation circuit 2 controls the amplitude and phase of the compensation signal so as to raise the level of the feedback signal, and the addition circuit 3 The output level can be raised higher. As a result, the input level to the power amplifier becomes high, exceeds the limit of the input level of the power amplifier, and causes a problem of increasing non-linear distortion of the output of the power amplifier. This is called adaptive pre-distortion divergence.

In view of the above problems, the present invention relates to a transmission system for improving the linearity of transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel, and particularly to parallel connection. It is an object of the present invention to provide a transmission system capable of stably compensating for the non-linear distortion of a unit amplifier which has not failed even if a part of the unit amplifier fails.

[0015]

A first aspect of the present invention is a transmission system for improving linearity of transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel. Reference for adaptive pre-distortion, with a configuration that detects a level change at either the input terminal or the output terminal of the amplifier and a variable gain for the baseband signal output by the baseband signal section in response to the detected level change And a structure for generating a signal.

According to the first aspect of the invention, there is provided a configuration for detecting a level change of any one of the input terminals or output terminals of a plurality of unit amplifiers, and a base band signal unit outputs a base band signal corresponding to the detected level change. Since a configuration is provided in which a gain for a band signal is made variable and an adaptive pre-distortion reference signal is generated, even if some unit amplifiers fail, an error signal for adaptive pre-distortion is generated. It is possible to match the levels of the baseband signal component forming the reference signal and the baseband signal component included in the feedback signal. Therefore, the divergence of adaptive pre-distortion can be prevented, and a stable transmission system can be obtained.

A second aspect of the present invention is a transmission system for improving linearity of transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel. A transmission system comprising: a configuration for detecting a level change of any of the terminals; and a configuration for varying a gain for a feedback signal of adaptive pre-distortion in accordance with the detected level change.

According to the second aspect of the present invention, a structure for detecting a level change at any one of the input terminals or output terminals of the plurality of unit amplifiers, and an adaptive pre-corresponding circuit corresponding to the detected level change.
Since it has a configuration that makes the gain of the distortion feedback signal variable, even if some unit amplifiers fail, the baseband signal component that forms the reference signal when generating the error signal for adaptive pre-distortion And the level of the baseband signal component included in the feedback signal can be matched. Therefore, the divergence of adaptive pre-distortion can be prevented, and a stable transmission system can be obtained.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The technique of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a first embodiment of the present invention. In FIG. 1, reference numeral 1 is a baseband signal unit that processes an original signal and outputs a baseband signal.

Reference numeral 2 denotes a compensation signal generation circuit for generating a compensation signal for performing adaptive pre-distortion. The compensation signal generation circuit 2 is supplied with the baseband signal output from the baseband signal section. Further, 3 is an adder circuit for adding the baseband signal and the compensation signal, 4 is a quadrature modulation circuit for modulating the output of the adder circuit 3, and 5 is a digital / analog for converting the output of the quadrature modulation circuit 4 into an analog signal. A converter, 6 is a radio frequency oscillator that generates a radio frequency band carrier, and 7 is a frequency converter that converts the output of the digital-analog converter 5 into a radio frequency band by the radio frequency band carrier output from the radio frequency oscillator 6. -It is a converter.

Reference numerals 8 and 9 denote unit amplifiers for power-amplifying the output of the up converter 7. In the example of FIG. 1, two unit amplifiers are connected in parallel to form a power amplifier.
Further, 10 and 11 are isolators inserted on the input side of the unit amplifiers 8 and 9. Further, 12 is a directional coupler that branches a part of the output of the power amplifier, and 13 is an antenna that radiates the output power to the space.

Further, 14 is an attenuator for adjusting the level of the signal in the radio frequency band branched by the directional coupler 12, and 15 is
A down converter that frequency-converts the output of the attenuator 14 by the output of the radio frequency oscillator 6, 16 is a first analog-digital converter that converts the output of the down converter 15 into a digital signal, and 17 is a first analog-digital converter. It is a quadrature demodulation circuit that converts the output of the analog-digital converter 16 into a baseband signal. The first analog-digital converter 16 has a built-in amplifier.

Further, 19 is a power combining circuit for combining the power output from the two isolators 10 and 11 from the isolation terminals. Further, 20 is a power combining circuit 19
Power detection circuit that monitors the output of the
Reference numeral 21 is a second analog-digital converter that digitally converts the output of the power detection circuit 20.

Further, 22 is a second analog digital
A variable gain circuit that controls the gain for the baseband signal corresponding to the output of the converter 21, and the output of the variable gain circuit is the reference signal. Reference numeral 18 is a subtraction circuit that takes the difference between the feedback signal output from the quadrature demodulation circuit 17 and the reference signal output from the variable gain circuit 22.

The compensation signal generating circuit 2 and the variable gain circuit 22 constitute the first embodiment of the present invention. In the configuration of FIG. 1, the operation when the two unit amplifiers are operating normally is exactly the same as the operation in the conventional transmission system. That is, the baseband signal and the compensation signal are added in the adder circuit 3, subjected to quadrature modulation by the quadrature modulation circuit 4, and then converted into analog signals by the digital-analog converter 5 and up-converted into radio frequency band signals by the up converter 7. To be done.

The radio frequency band signal is amplified to a predetermined level by a power amplifier in which unit amplifiers 8 and 9 are connected in parallel, and is radiated from an antenna 13 to space through a directional coupler 12. On the other hand, the radio frequency band signal partially branched in the directional coupler 12 is adjusted in level in the attenuator 14 and supplied to the down converter 15, and is down converted by the carrier wave in the radio frequency band. Is converted into a digital signal by the analog-digital converter 16 and demodulated by the quadrature demodulation circuit 17 to become a feedback signal. The feedback signal is the baseband signal plus a distortion component generated in the power amplifier.

In the subtraction circuit 18, the baseband signal forming the feedback signal and the baseband signal forming the reference signal output from the special variable circuit 22 are compared at the same level to generate an error signal. And supplies it to the compensation signal generation circuit 2. The compensation signal generation circuit 2 distorts the baseband signal in advance and outputs a distortion component so that the level of the error signal generated in this way is minimized. This makes it possible to maintain the linearity of the output of the transmission system by compensating for the distortion component generated in the power amplifier.

Now, in the isolators 10 and 11, when the unit amplifier 8 or 9 is operating normally and there is no reflection from the input terminal of the unit amplifier 8 or 9, no output appears at the isolation terminal, but the unit When the amplifier 8 or 9 fails and reflection occurs at the input terminal of the failed unit amplifier, an output appears at the isolation terminal of the isolator connected to the input terminal of the failed unit amplifier.

As a result, the power due to the above-mentioned failure is output to the power detection circuit 20, the information of the detected power is supplied to the variable gain circuit 22, and the level of the reference signal for generating the error signal is controlled. It Here, the outline of the gain control in the variable gain circuit 22 is as follows. That is, in the example of FIG. 1, since two unit amplifiers are connected in parallel, if one unit amplifier fails, the output power is 3
It decreases by dB. Therefore, the level of the feedback signal output from the quadrature demodulation circuit 17 is also reduced by 3 dB, and at the same time, the power detection circuit 2
0 detects the power from the isolator 10 or 11.
The second analog-digital converter 21 can output a digital signal according to the output change of the power detection circuit 20.

On the other hand, in the variable gain circuit 22, for example, one of the circuits of loss 0 dB and loss 3 dB can be selected by the output signal of the second analog-digital converter 21, and one unit amplifier fails. By selecting a circuit with a loss of 3 dB when the level of the feedback signal drops by 3 dB, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 can be matched. Loss 0 dB
Since it is easy for a person skilled in the art to select one of the circuit having a loss of 3 dB and the circuit having a loss of 3 dB, the gain variable circuit 22
The illustration of the configuration is omitted.

As a result, the levels at the two input terminals of the subtraction circuit 18 match, so that the divergence of the adaptive pre-distortion can be prevented. Here, FIG.
In consideration of the fact that two unit amplifiers are connected in parallel to form a power amplifier in the above configuration, the level of the reference signal is reduced by 3 dB when one unit amplifier fails. When three unit amplifiers are connected in parallel and one or two of them fail, the following configuration may be adopted. That is, when one unit amplifier fails, the output level of the directional coupler 12 decreases by about 1.8 dB, and when two unit amplifiers fail, the directional coupler 1
The output level of 2 decreases by about 4.8 dB, and the output of the power detection circuit 20 changes accordingly. Since the output of the second analog-digital converter 21 changes according to the number of failed amplifiers, the gain variable circuit 22 has losses of 0 dB, 1.8 dB and 4.8 dB according to the number of failed amplifiers. If the circuit is selected, the levels of the reference signal and the feedback signal can be matched.

In this case, the case where the unit amplifier is completely down is the main case, so the description has been made assuming the case where the unit amplifier is completely down. However, the unit amplifier is not completely down and the output is performed at a lowered level. To do so, increase the number of bits of the second analog-digital converter 21,
In the variable gain circuit 22, the second analog / digital
If the circuits of various types of loss are combined and selected according to the output of the converter 21, the levels of the reference signal and the feedback signal can be matched in this case as well.

That is, the feature of the first embodiment of the present invention is that in a transmission system for improving the linearity of transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel, A configuration that detects level changes at the input terminals of multiple unit amplifiers, and the adaptive pre-distortion reference signal is generated by varying the gain for the baseband signal output by the baseband signal section in response to the detected level changes. And a configuration to do so.

FIG. 2 shows a second embodiment of the present invention. In FIG. 2, reference numeral 1 is a baseband signal unit that processes an original signal and outputs a baseband signal. Reference numeral 2 denotes a compensation signal generation circuit that generates a compensation signal for performing adaptive pre-distortion, and the compensation signal generation circuit 2 is supplied with the baseband signal output from the baseband signal unit.

Further, 3 is an adder circuit for adding the baseband signal and the compensation signal, 4 is a quadrature modulator circuit for modulating the output of the adder circuit 3, and 5 is an analog converter for the output of the quadrature modulator circuit 4. A digital-analog converter, 6 is a radio frequency oscillator that generates a radio frequency carrier wave, and 7 is a radio frequency carrier wave that is output from the radio frequency oscillator 6, and outputs the frequency of the digital analog converter 5 to the radio frequency band. It is an up converter that converts.

Reference numerals 8 and 9 denote unit amplifiers for power-amplifying the output of the up-converter 7. In the example of FIG. 1, two unit amplifiers are connected in parallel to form a power amplifier.
Further, 12 is a directional coupler that branches a part of the output of the power amplifier, and 13 is an antenna that radiates the output power to the space. Further, 14 is an attenuator that adjusts the level of the signal in the radio frequency band branched by the directional coupler 12, 15 is a down converter that frequency-converts the output of the attenuator 14 by the output of the radio frequency oscillator 6, 16 Is a first analog-digital converter for converting the output of the down converter 15 into a digital signal, and 17 is a first analog-digital converter.
It is a quadrature demodulation circuit that converts the output of the digital converter 16 into a baseband signal. The first analog-digital converter 16 has a built-in amplifier.

Further, 23 is a directional coupler that further branches the branched output of the directional coupler 12, and 20 is a directional coupler 2.
A power detection circuit that monitors the output of the power supply 3 to detect a change in power, and a second analog-digital converter 21 that digitally converts the output of the power detection circuit 20. or,
Reference numeral 22 is a gain variable circuit that controls the gain with respect to the baseband signal corresponding to the output of the second analog-digital converter 21, and the output of the gain variable circuit is the reference signal.

Reference numeral 18 is a subtraction circuit for taking the difference between the feedback signal output by the quadrature demodulation circuit 17 and the reference signal output by the variable gain circuit 22. The components of the variable gain circuit 22 from the compensation signal generation circuit 2 constitute a second embodiment of the present invention. Comparing the configuration of FIG. 1 and the configuration of FIG. 2, it can be seen that the configuration of FIG. 2 is different only in that the level change due to the failure of the power amplifier is performed at the output side of the directional coupler 12. Therefore, regarding the configuration of FIG. 2, only the differences from the configuration of FIG. 1 will be described.

In the configuration of FIG. 2, when one of the two unit amplifiers fails, the output of the power amplifier formed by the two unit amplifiers drops by 3 dB. Therefore, the power of the signal branched by the directional coupler 23 is also reduced by 3 dB. Then, the power detection circuit 20 detects this decrease in level and outputs a signal of a level different from that when the power amplifier is operating normally, so that the second analog-digital converter 21 outputs the signal. Output a digital signal different from that normally operating to supply the variable gain circuit 22.

Here, the variable gain circuit 22 is arranged so that, for example, one of the circuits of loss 0 dB and loss 3 dB can be selected by the output signal of the second analog-digital converter 21, and one unit amplifier is If a circuit having a loss of 3 dB is selected when the level of the feedback signal drops by 3 dB due to a failure, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 can be matched.

Even when the number of unit amplifiers constituting the power amplifier is different from 2, or when the unit amplifiers do not completely go down, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 are made equal to each other. What can be done is the same as the configuration of FIG. The feature of the second embodiment of the present invention is that a plurality of unit amplifiers are used in a transmission system for performing adaptive pre-distortion to improve linearity of a transmission output. A configuration for detecting a level change on the output terminal side of the amplifier,
It can be said that a configuration is provided in which the gain for the baseband signal output from the baseband signal unit is made variable in response to the detected level change to generate the adaptive pre-distortion reference signal.

FIG. 3 shows a third embodiment of the present invention. In FIG. 3, reference numeral 1 is a baseband signal unit that processes an original signal and outputs a baseband signal. Reference numeral 2 denotes a compensation signal generation circuit that generates a compensation signal for performing adaptive pre-distortion, and the compensation signal generation circuit 2 is supplied with the baseband signal output from the baseband signal unit.

Further, 3 is an adder circuit for adding the baseband signal and the compensation signal, 4 is a quadrature modulation circuit for modulating the output of the addition circuit 3, and 5 is an analog conversion of the output of the quadrature modulation circuit 4. A digital-analog converter, 6 is a radio frequency oscillator that generates a radio frequency carrier wave, and 7 is a radio frequency carrier wave that is output from the radio frequency oscillator 6, and outputs the frequency of the digital analog converter 5 to the radio frequency band. It is an up converter that converts.

Reference numerals 8 and 9 denote unit amplifiers for power-amplifying the output of the up converter 7. In the example of FIG. 1, two unit amplifiers are connected in parallel to form a power amplifier.
Further, 12 is a directional coupler that branches a part of the output of the power amplifier, and 13 is an antenna that radiates the output power to the space. Further, 14 is an attenuator that adjusts the level of the signal in the radio frequency band branched by the directional coupler 12, 15 is a down converter that frequency-converts the output of the attenuator 14 by the output of the radio frequency oscillator 6, 16 Is a first analog-digital converter for converting the output of the down converter 15 into a digital signal, and 17 is a first analog-digital converter.
It is a quadrature demodulation circuit that converts the output of the digital converter 16 into a baseband signal. The first analog-digital converter 16 has a built-in amplifier.

Reference numerals 24 and 25 respectively denote a directional coupler for branching the output signal of the unit amplifier 8 and a directional coupler for branching the output signal of the unit amplifier 9, and 19 denotes a directional coupler 24 and a direction, respectively. A power combiner circuit for combining the signals branched by the sex coupler 25; a power detector circuit 20 for monitoring the output of the power combiner circuit 19 to detect a level change;
Is a second analog-to-digital converter that digitally converts the output of the power detection circuit 20.

Further, 22 is a second analog digital
A variable gain circuit that controls the gain for the baseband signal corresponding to the output of the converter 21, and the output of the variable gain circuit is the reference signal. Reference numeral 18 is a subtraction circuit that takes the difference between the feedback signal output from the quadrature demodulation circuit 17 and the reference signal output from the variable gain circuit 22.

The components from the compensation signal generating circuit 2 to the directional coupler 25 constitute the third embodiment of the present invention. Comparing the configuration of FIG. 1 with the configuration of FIG. 3, it can be seen that the configuration of FIG. 3 is different only in that the level change due to the failure of the power amplifier is detected at the output terminal side of the unit amplifier. Therefore, only the differences between the configuration of FIG. 3 and the configuration of FIG. 1 will be described.

In the configuration of FIG. 3, when one of the two unit amplifiers fails, the level of the signal output from the power combiner circuit 19 drops by 3 dB. Then, the power detection circuit 2
0 detects this drop in level and outputs a signal at a level different from that when the power amplifier is operating normally, so the second analog-digital converter 21 operates normally. A digital signal different from that during the output is supplied to the variable gain circuit 22.

Here, the variable gain circuit 22 is arranged so that, for example, one of the circuits of loss 0 dB and loss 3 dB can be selected by the output signal of the second analog-digital converter 21, and one unit amplifier is If a circuit having a loss of 3 dB is selected when the level of the feedback signal drops by 3 dB due to a failure, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 can be matched.

Even when the number of unit amplifiers constituting the power amplifier is different from 2, or when the unit amplifiers do not completely go down, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 are matched. What can be done is the same as the configuration of FIG. The characteristic of the third embodiment of the present invention is that a plurality of unit amplifiers are provided in a transmission system in which adaptive pre-distortion is applied to a power amplifier formed by connecting a plurality of unit amplifiers in parallel to improve linearity of a transmission output. A configuration for detecting a level change on the output terminal side of the amplifier,
It can be said that a configuration is provided in which the gain for the baseband signal output from the baseband signal unit is made variable in response to the detected level change to generate the adaptive pre-distortion reference signal.

FIG. 4 shows a fourth embodiment of the present invention. In FIG. 4, reference numeral 1 is a baseband signal unit that processes an original signal and outputs a baseband signal. Reference numeral 2 denotes a compensation signal generation circuit that generates a compensation signal for performing adaptive pre-distortion, and the compensation signal generation circuit 2 is supplied with the baseband signal output from the baseband signal unit.

Further, 3 is an adder circuit for adding the baseband signal and the compensation signal, 4 is a quadrature modulation circuit for modulating the output of the adder circuit 3, and 5 is an analog conversion of the output of the quadrature modulation circuit 4. A digital-analog converter, 6 is a radio frequency oscillator that generates a radio frequency carrier wave, and 7 is a radio frequency carrier wave that is output from the radio frequency oscillator 6, and outputs the frequency of the digital analog converter 5 to the radio frequency band. It is an up converter that converts.

Reference numerals 8 and 9 denote unit amplifiers for power-amplifying the output of the up converter 7. In the example of FIG. 1, two unit amplifiers are connected in parallel to form a power amplifier.
Further, 10 and 11 are isolators inserted on the input side of the unit amplifiers 8 and 9. Further, 12 is a directional coupler that branches a part of the output of the power amplifier, and 13 is an antenna that radiates the output power to the space.

Further, 14 is an attenuator for adjusting the level of the signal in the radio frequency band branched by the directional coupler 12, and 15 is
A down converter that frequency-converts the output of the attenuator 14 by the output of the radio frequency oscillator 6, 16 is a first analog-digital converter that converts the output of the down converter 15 into a digital signal, and 17 is a first analog-digital converter. It is a quadrature demodulation circuit that converts the output of the analog-digital converter 16 into a baseband signal. The first analog-digital converter 16 has a built-in amplifier.

Reference numeral 19 is a power combining circuit for combining the power of the signals output from the two isolators 10 and 11 from the isolation terminals. Reference numeral 20 is a power detection circuit that monitors the output of the power combination circuit 19 to detect a change in power, and reference numeral 21 is a second analog-digital converter that digitally converts the output of the power detection circuit 20.

22 is a second analog digital
A variable gain circuit that controls the gain for the baseband signal corresponding to the output of the converter 21, and the output of the variable gain circuit is a feedback signal. Reference numeral 18 is a subtraction circuit that outputs the error signal by taking the difference between the feedback signal output from the variable gain circuit 22 and the reference signal equal to the baseband signal output from the baseband signal section.

The components from the compensation signal generation circuit 2 to the variable gain circuit 22 constitute the fourth embodiment of the present invention. Comparing the configuration of FIG. 1 with the configuration of FIG. 4, it can be seen that the configuration of FIG. 4 is different only in that the variable gain circuit 22 is inserted between the quadrature demodulation circuit 17 and the subtraction circuit 18 in the feedback loop. Therefore, regarding the configuration of FIG. 4, only the differences from the configuration of FIG. 1 will be described.

In the configuration of FIG. 4, when one of the two unit amplifiers fails, a signal is output from the isolation terminal of the isolator connected to the failed unit amplifier, so the output level of the power combining circuit rises. To do. Then, the power detection circuit 20 detects this level change and outputs a signal at a level different from that when the power amplifier is operating normally, so that the second analog-digital converter 21 outputs the power amplifier. Output a digital signal different from that when the gain variable circuit 2 operates normally.
Supply to 2.

On the other hand, when one of the two unit amplifiers fails, the level of the signal on the feedback loop side branched by the directional coupler 12 decreases by 3 dB. Here, the variable gain circuit 2
2 is, for example, such that one of the circuits of loss 0 dB and loss 3 dB can be selected by the output signal of the second analog-digital converter 21, and one of the unit amplifiers fails and the signal on the feedback loop side is If a circuit with a loss of 0 dB is selected when the level drops by 3 dB, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 can be matched.

Even when the number of unit amplifiers forming the power amplifier is different from 2, or when the unit amplifiers do not completely go down, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 are matched. What can be done is the same as the configuration of FIG. The feature of the fourth embodiment of the present invention is that a plurality of unit amplifiers are provided in a transmission system in which adaptive pre-distortion is applied to a power amplifier in which a plurality of unit amplifiers are connected in parallel to improve linearity of a transmission output. A configuration for detecting a level change on the input terminal side of the amplifier,
It can be said that the transmission system is characterized by having a configuration for varying the gain for the feedback signal of the adaptive pre-distortion in accordance with the detected level change.

In the configuration of FIG. 4, the variable gain circuit 22 is inserted between the quadrature demodulation circuit 17 and the subtraction circuit 18 in the feedback loop in the configuration of FIG. Even if it is inserted between the analog-digital converter 16 and the quadrature demodulation circuit 17, the down converter 1
5 and the first analog-to-digital converter 16 or between the attenuator 14 and the down converter 15, the adaptive pre-distortion feedback corresponding to the detected level change. There is no difference in that the gain of the signal is variable.

Further, even if the variable gain circuit 22 is inserted in the feedback loop in the configuration of FIG. 2 or 3, the levels of the feedback signal and the reference signal supplied to the subtraction circuit 18 are made to match as in FIG. be able to. The configuration in this case is such that in the transmission system in which the linearity of the transmission output is improved by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel, the level at the output terminal side of the plurality of unit amplifiers is improved. It can be said that the transmission system is provided with a configuration for detecting a change and a configuration for varying the gain for the feedback signal of the adaptive pre-distortion corresponding to the detected level change.

[0063]

As described in detail above, the present invention relates to a transmission system for improving the linearity of transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel. Even if the connected unit amplifier fails, it is possible to obtain a transmission system capable of stably compensating for the non-linear distortion of the unit amplifier that has not failed.

That is, according to the first aspect of the invention, the structure for detecting the level change of any of the input terminals or the output terminals of the plurality of unit amplifiers, and the baseband signal section outputs corresponding to the detected level change. And a configuration for generating a reference signal for adaptive pre-distortion by varying the gain with respect to the base band signal to be used, and a base band signal component forming a reference signal when generating an error signal for adaptive pre-distortion It is possible to match the levels of the baseband signal components included in the feedback signal. Therefore, the divergence of adaptive pre-distortion can be prevented, and a stable transmission system can be obtained.

According to the second aspect of the invention, the structure for detecting the level change at any of the input terminals or output terminals of the plurality of unit amplifiers and the adaptive pre-distortion feedback corresponding to the detected level change. Since the configuration for varying the gain for the signal is provided, the levels of the baseband signal component forming the reference signal and the baseband signal component included in the feedback signal when generating the error signal for adaptive pre-distortion are matched. be able to. Therefore, the divergence of adaptive pre-distortion can be prevented, and a stable transmission system can be obtained.

[Brief description of drawings]

FIG. 1 is a first embodiment of the present invention.

FIG. 2 is a second embodiment of the present invention.

FIG. 3 is a third embodiment of the present invention.

FIG. 4 is a fourth embodiment of the present invention.

FIG. 5 is a configuration of a conventional transmission system.

[Explanation of symbols]

1 Baseband signal section 2 Compensation signal generation circuit 3 adder circuit 4 Quadrature modulation circuit 5 Digital-to-analog converter 6 Radio frequency oscillator 7 up converter 8, 9 unit amplifier 10, 11 Isolator 12-way coupler 13 antennas 14 attenuator 15 Down Converter 16 First analog-to-digital converter 17 Quadrature demodulation circuit 18 Subtraction circuit 19 Power combiner circuit 20 Power detection circuit 21 Second analog-to-digital converter 22 Variable gain circuit 23, 24, 25 directional coupler

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenzo Nishikawa             4-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             No. 1 within Fujitsu Limited F term (reference) 5J069 AA01 AA21 AA41 CA21 FA17                       KA00 KA23 KA26 KA32 KA34                       KA53 KA55 KA68 KC04 KC06                       KC07 MA11 SA14 TA01                 5J090 AA01 AA21 AA41 CA21 FA17                       GN03 GN06 KA00 KA23 KA26                       KA32 KA34 KA53 KA55 KA68                       MA11 SA14 TA01                 5J091 AA01 AA21 AA41 CA21 FA17                       KA00 KA23 KA26 KA32 KA34                       KA53 KA55 KA68 MA11 SA14                       TA01                 5K060 BB07 CC04 CC16 HH06 KK03

Claims (2)

[Claims] 1. A transmission system for improving linearity of a transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel, wherein the input terminals or the output terminals of the plurality of unit amplifiers are connected. It is provided with a configuration for detecting a level change in any one of them and a configuration for generating a reference signal of adaptive pre-distortion by varying a gain with respect to a baseband signal output from a baseband signal unit in response to the detected level change. A transmission system characterized by the above. 2. A transmission system for improving linearity of a transmission output by applying adaptive pre-distortion to a power amplifier formed by connecting a plurality of unit amplifiers in parallel, in which the input terminals or the output terminals of the plurality of unit amplifiers are connected. A transmission system, comprising: a configuration for detecting a level change in any of the above, and a configuration for varying a gain for a feedback signal of adaptive pre-distortion in response to the detected level change.