JP2014023025A - Distortion compensation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion compensation circuit that can suppress a distortion component even when amplifying a wideband transmission signal.SOLUTION: The distortion compensation circuit includes a distributor, first and second amplifiers, a bandpass filter, first to third directional couplers, first and second delay sections and first and second converters. The first amplifier amplifies a first distribution signal from the distributor. The bandpass filter suppresses distortion components included in the amplified signal which are outside of a preset passband. The first directional coupler extracts a third distribution signal from the amplified signal passed through the bandpass filter. The second directional coupler combines a second distribution signal with the third distribution signal to extract a distortion component included in the third distribution signal. The second amplifier amplifies the extracted distortion component. The third directional coupler combines the amplified distortion signal with the band-passed amplified signal to remove the distortion component included in the amplified signal.

Description

  Embodiments described herein relate generally to a distortion compensation circuit that suppresses distortion components generated in an amplifier.

  In 3GPP (Third Generation Partnership Project), Release 10 (LTE-Advanced) has been formulated, and the CA (Carrier Aggregation) function is stipulated therein. The CA function is a function of multiplexing a plurality of frequency blocks (Component Carrier) in units of 20 MHz, and is intended to improve the transmission speed.

  The frequency band corresponding to the CA function is being promoted in each country, and when the frequency band corresponding to the CA function is secured, the mobile phone system using the 100 MHz band depends on the frequency administration in each country. Will be realized. On the other hand, a base station AMP and a distortion compensation method for outputting a signal in a 100 MHz band with high output and low distortion are under investigation.

  Examples of the distortion compensation method include a feed forward method and a DPD (Digital Pre-Distortion) method. In order to realize the above-described CA function, it is necessary to amplify a wide band transmission signal of 100 MHz band. For example, in a distortion compensation circuit using a feedforward method and a distortion compensation circuit using a DPD method, There is a problem. That is, in a distortion compensation circuit using the feedforward method, a delay error occurs when a wideband distortion signal is amplified, so that a sufficient distortion compensation effect cannot be obtained. In addition, since the distortion compensation circuit using the DPD method has a limit in the capture range of the analog-digital converter in the feedback loop, the DPD process is effective when the distortion component in the band exceeding the limit of the capture range is included. Can not be executed.

JP 2000-312116 A

  As described above, in the conventional distortion compensation circuit, when a broadband transmission signal is amplified, it is difficult to suppress the distortion component included in the amplified transmission signal.

  Accordingly, an object is to provide a distortion compensation circuit capable of suppressing distortion components even when a wideband transmission signal is amplified.

  According to the embodiment, the distortion compensation circuit includes a distributor, first and second amplifiers, bandpass filters, first to third directional couplers, first and second delay units, and first And a second converter. The distributor distributes the input signal into a first distribution signal and a second distribution signal. The first amplifier amplifies the first distribution signal to obtain an amplified signal. The band pass filter suppresses a distortion component out of a preset pass band from among distortion components included in the amplified signal. The first directional coupler extracts a third distribution signal from the amplified signal that has passed through the bandpass filter. The first delay unit gives a delay equivalent to the delay generated by the processing in the first amplifier and the processing in the bandpass filter to the second distributed signal. The first converter makes the level of the third distribution signal substantially equal to that of the second distribution signal, and converts the phase of the third distribution signal into a phase opposite to that of the second distribution signal. . The second directional coupler is included in the third distribution signal by synthesizing the delayed second distribution signal and the third distribution signal processed by the first converter. The distortion component to be extracted is extracted as a distortion signal. The second amplifier amplifies the distortion signal extracted by the second directional coupler to obtain an amplified distortion signal. The second delay unit gives the amplified signal supplied from the first directional distributor a delay equivalent to the delay generated by the processing in the second amplifier. The second converter adjusts the level of the amplified distortion signal to a distortion component included in the delayed amplified signal, and converts the phase of the amplified distortion signal to a phase opposite to that of the delayed amplified signal. The third directional coupler removes the distortion component included in the delayed amplified signal by synthesizing the delayed amplified signal and the amplified distortion signal processed by the second converter. To do.

It is a block diagram which shows the function structure of the distortion compensation circuit which concerns on 1st Embodiment. It is a figure which shows the example of the signal which passes the band pass filter shown in FIG. It is a figure which shows the example of the distortion signal supplied to the auxiliary amplifier shown in FIG. It is a block diagram which shows the function structure of the distortion compensation circuit which concerns on 2nd Embodiment. It is a figure which shows the example of the signal supplied to the analog-digital converter shown in FIG. FIG. 5 is a diagram showing an example of a distortion signal supplied to the auxiliary amplifier shown in FIG. 4. It is a block diagram which shows the function structure of the distortion compensation circuit which concerns on 3rd Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a functional configuration of a distortion compensation circuit 10 according to the first embodiment. A distortion compensation circuit 10 shown in FIG. 1 includes a carrier cancellation loop 11 and a distortion cancellation loop 12.

  The carrier cancel loop 11 cancels a carrier from a signal obtained by amplifying an input signal so as to have a predetermined power, and extracts only a distortion component. The carrier cancellation loop 11 includes a distributor 111, a main amplifier 112, a band pass filter 113, a first directional coupler 114, a first converter 115, a first delay circuit 116, and a second directional coupler 117. Is provided.

  The distributor 111 distributes the input signal that is input into a first distribution signal and a second distribution signal. The distributor 111 outputs the first distribution signal to the main amplifier 112 and outputs the second distribution signal to the delay circuit 116.

  The main amplifier 112 amplifies the first distribution signal supplied from the distributor 111 to a desired level to obtain an amplified signal. The main amplifier 112 outputs the amplified signal to the band pass filter 113.

  The band pass filter 113 has a filter characteristic set to pass a predetermined band in the amplified signal. Here, the predetermined band represents a band in which the distortion component amplified by the auxiliary amplifier 121 in the distortion cancellation loop 12 does not cause a delay error with the signal that has passed through the second delay circuit 123. FIG. 2 is a diagram illustrating an example of a signal passing through the band pass filter 113. According to the bandpass filter 113 shown in FIG. 2, for example, from an amplified signal including a main signal component having a band of 100 MHz, a third-order intermodulation distortion (IMD3), and a fifth-order intermodulation distortion (IMD5). And a filter characteristic that allows only a part of the main signal component and the IMD 3 to pass therethrough. The band pass filter 113 outputs the passed amplified signal to the first directional coupler 114.

  The first directional coupler 114 extracts a part of the amplified signal supplied from the band pass filter 113 as a third distribution signal. The first directional coupler 114 outputs the extracted third distribution signal to the first converter 115, and outputs the amplified signal to the second delay circuit 123 in the distortion cancellation loop 12.

  The first converter 115 includes a resistor 1151 and a phase shifter 1152. The resistor 1151 is set so that the amplitude of the third distribution signal taken out by the first directional coupler substantially matches the amplitude of the second distribution signal supplied from the distributor 111.

  The phase shifter 1152 adjusts the phase of the third distribution signal whose amplitude is adjusted to be opposite to the phase of the second distribution signal. The phase shifter 1152 outputs the third distribution signal whose phase is adjusted to the second directional coupler.

  The first delay circuit 116 delays the second distribution signal supplied from the distributor 111 and outputs the delayed second distribution signal to the second directional coupler 117. The delay time in the first delay circuit 116 is set to substantially match the sum of delay times generated by the processing in the main amplifier 112 and the processing in the band pass filter 113.

  The second directional coupler 117 combines the third distribution signal supplied from the first converter 115 and the second distribution signal supplied from the first delay circuit 116, thereby 3 is extracted and output to the auxiliary amplifier 121 of the distortion cancellation loop 12 as a distortion signal. FIG. 3 is a diagram illustrating an example of a distortion signal output to the auxiliary amplifier 121. In addition, the broken line in FIG. 3 shows the main signal component removed by the second directional coupler 117.

  The distortion cancellation loop 12 amplifies the distortion signal supplied from the carrier cancellation loop 11 and synthesizes the amplified distortion signal and the amplification signal supplied from the carrier cancellation loop 11 to thereby include a distortion component included in the amplified signal. It has a function to cancel.

  The distortion cancellation loop 12 includes an auxiliary amplifier 121, a second converter 122, a second delay circuit 123, and a third directional coupler 124.

  The auxiliary amplifier 121 amplifies the distortion signal supplied from the second directional coupler 117 to obtain an amplified distortion signal. The auxiliary amplifier 121 outputs the amplified distortion signal to the second converter 122.

  The second delay circuit 123 delays the amplified signal supplied from the second directional coupler 114 and outputs the delayed amplified signal to the third directional coupler 124. The delay time in the second delay circuit 123 is set to substantially match the delay time generated by the processing in the auxiliary amplifier 121.

  The second converter 122 includes a phase shifter 1221 and a resistor 1222. The phase shifter 1221 adjusts the phase of the amplified distortion signal supplied from the auxiliary amplifier 121 so as to be opposite in phase to the amplified signal supplied from the second delay circuit 123.

  The resistor 1222 is set so that the amplitude of the amplified distortion signal whose phase is adjusted matches the amplitude of the distortion component included in the amplified signal supplied from the second delay circuit 123. The resistor 1222 outputs the amplified distortion signal whose amplitude is adjusted to the third directional coupler 124.

  The third directional coupler 124 synthesizes the amplified signal supplied from the second delay circuit 123 and the amplified distortion signal supplied from the second converter 122, thereby distorting the amplified signal. Suppresses the component. The third directional coupler 124 outputs a signal in which the distortion component is suppressed to the subsequent stage.

  As described above, in the first embodiment, the band-pass filter 113 is arranged after the main amplifier 112 and before the first directional coupler 114. Here, the pass band in the band pass filter 113 is supplied from the second delay circuit 123 and the signal amplified by the auxiliary amplifier 121 even if the distortion component included in the signal after passing the band is amplified by the auxiliary amplifier 121. This is a band that does not cause a delay error with the amplified signal. As a result, even when the main amplifier 112 amplifies a wide band transmission signal, the band of the distortion component is limited by the band pass filter 113, so the band of the distortion signal supplied to the auxiliary amplifier 121. Will be suppressed. Even when the main amplifier 112 amplifies a broadband transmission signal, the band of the signal supplied to the second delay circuit 123 is suppressed.

  Therefore, according to the distortion compensation circuit 10 according to the first embodiment, distortion components can be suppressed even when a wideband transmission signal is amplified.

  On the other hand, in a conventional distortion compensation circuit using a feedforward method, when a wideband transmission signal is amplified, a bandpass filter 113 is disposed after the main amplifier 112 and before the first directional coupler 114. Therefore, a wideband amplified signal including intermodulation distortion is supplied to the delay circuit, and a wideband distortion signal including intermodulation distortion is supplied to the auxiliary amplifier. Due to the wideband distortion, an error occurs between the delay amount in the delay circuit and the processing time in the auxiliary amplifier, and the distortion compensation circuit cannot effectively suppress distortion caused by amplification in the main amplifier. .

(Second Embodiment)
FIG. 4 is a block diagram illustrating a functional configuration of the distortion compensation circuit 20 according to the second embodiment. In FIG. 4, parts that are the same as those in FIG.

  The distortion compensation circuit 20 illustrated in FIG. 4 includes a carrier cancellation loop 13 and a distortion cancellation loop 12.

  The carrier cancellation loop 13 processes in advance so as to reduce the distortion component, cancels the carrier from the amplified signal so that the processed signal becomes a predetermined power, and extracts only the distortion component. The carrier cancellation loop 13 includes a DPD (Digital Pre-Distortion) processing unit 131, a first frequency converter 132, a distributor 111, a main amplifier 112, a band-pass filter 133, a first directional coupler 114, a first A converter 115, a first delay circuit 116, a second directional coupler 117, a fourth directional coupler 134, a second frequency converter 135, and an analog-digital converter 136 are provided.

  The DPD processing unit 131 receives a baseband signal in the baseband and a digital signal supplied from the analog-digital converter 136. The DPD processing unit 131 refers to the digital signal and corrects the baseband signal so that distortion generated by amplification by the main amplifier 112 is reduced.

  The first frequency converter 132 converts the frequency of the baseband signal corrected by the DPD processing unit 131 to, for example, 2 GHz or 800 MHz. The first frequency converter 132 outputs the frequency converted signal to the distributor 111.

  The band pass filter 133 has a filter characteristic set to pass a predetermined band in the amplified signal output from the main amplifier 112. Here, the predetermined band is a band in which the distortion component amplified by the auxiliary amplifier 121 in the distortion cancellation loop 12 does not cause a delay error with the signal that has passed through the second delay circuit 123, and This represents a band in which the frequency bandwidth of the fourth distribution signal distributed by the fourth directional coupler 134 falls within ½ or less of the sampling frequency in the analog-digital converter 136. The band pass filter 133 outputs the amplified signal that has been passed to the fourth directional coupler 134.

  The fourth directional coupler 134 distributes the fourth distribution signal from the amplified signal supplied from the band pass filter 133 and outputs the distributed fourth distribution signal to the second frequency converter 135. The fourth directional coupler 134 outputs the amplified signal to which the fourth distribution signal is distributed to the first directional coupler 114.

  The second frequency converter 135 converts the frequency of the fourth distribution signal supplied from the fourth directional coupler 134 into a baseband. The second frequency converter 135 outputs a baseband signal to the analog-to-digital converter 136.

  The analog-digital converter 136 converts the baseband signal supplied from the second frequency converter 135 into a digital signal. FIG. 5 is a diagram illustrating an example of a signal supplied to the analog-digital converter 136. Since the IMD 3 falls within the capture range by the band pass filter 133, the analog-to-digital converter 136 can convert the supplied signal into a digital signal. The analog-digital converter 136 outputs a digital signal to the DPD processing unit 131.

  As described above, in the second embodiment, the band-pass filter 133 is arranged after the main amplifier 112 and before the fourth directional coupler 134. Here, the pass band in the band pass filter 133 is supplied from the second delay circuit 123 and the signal amplified by the auxiliary amplifier 121 even if the distortion component included in the signal after passing the band is amplified by the auxiliary amplifier 121. The analog-to-digital converter 136 has a bandwidth that does not cause a delay error with respect to the amplified signal and the frequency bandwidth of the signal supplied from the second frequency converter 135 to the analog-to-digital converter 136. The bandwidth is within the capture range. As a result, even when the main amplifier 112 amplifies a wide band transmission signal, the band of the distortion component is limited by the band pass filter 133, so the band of the distortion signal supplied to the auxiliary amplifier 121. Will be suppressed. Even when the main amplifier 112 amplifies a broadband transmission signal, the band of the signal supplied to the second delay circuit 123 is suppressed. Even when the main amplifier 112 amplifies a wideband transmission signal, the frequency bandwidth of the signal supplied to the analog-to-digital converter 136 falls within the capture range of the analog-to-digital converter 136, so that the DPD processing Will be done effectively. By this DPD processing, the distortion signal supplied to the auxiliary amplifier 121 is as shown in FIG. 6, for example, and has a smaller amplitude than the distortion signal shown in FIG. In addition, the broken line in FIG. 6 shows the distortion signal in FIG.

  Therefore, according to the distortion compensation circuit 20 according to the second embodiment, distortion components can be suppressed even when a wideband transmission signal is amplified.

  On the other hand, in a conventional distortion compensation circuit using the DPD method, when a wideband transmission signal is amplified, a band pass filter 133 is disposed after the main amplifier 112 and before the fourth directional coupler 134. Therefore, a wideband signal including intermodulation distortion is supplied to the analog-to-digital converter. Since the capture range of the analog-to-digital converter is limited, the distortion compensation circuit cannot sufficiently obtain the effect of DPD processing when the bandwidth of the supplied signal does not fall within this capture range.

(Third embodiment)
FIG. 7 is a block diagram illustrating a functional configuration of the distortion compensation circuit 30 according to the third embodiment. In FIG. 7, parts common to those in FIGS.

  The distortion compensation circuit 30 illustrated in FIG. 7 includes a carrier cancellation loop 14 and a distortion cancellation loop 15.

  The carrier cancel loop 14 processes the input signal in advance so that the distortion component becomes small, cancels the carrier from the signal obtained by amplifying the processed signal to have a predetermined power, and extracts only the distortion component. The carrier cancellation loop 14 includes a DPD processing unit 141, a first frequency converter 132, a distributor 111, a main amplifier 112, a band pass filter 142, a first directional coupler 114, a first converter 115, a first Delay circuit 116 and second directional coupler 117.

  The DPD processing unit 141 receives a baseband signal in the baseband and a digital signal supplied from the analog-digital converter 153. The DPD processing unit 141 refers to the digital signal and corrects the baseband signal so that distortion generated by amplification by the main amplifier 112 is reduced.

  The band pass filter 143 has a filter characteristic set to pass a predetermined band in the amplified signal output from the main amplifier 112. Here, the predetermined band is a band in which the distortion component amplified by the auxiliary amplifier 121 in the distortion cancellation loop 15 does not cause a delay error with the signal that has passed through the second delay circuit 123, and This represents a band in which the frequency bandwidth of the fifth distribution signal distributed by the fifth directional coupler 151 falls within ½ of the sampling frequency in the analog-digital converter 153. The band pass filter 142 outputs the amplified signal that has passed therethrough to the first directional coupler 114.

  The distortion cancellation loop 15 amplifies the distortion signal supplied from the carrier cancellation loop 14 and synthesizes the amplified distortion signal and the amplification signal supplied from the carrier cancellation loop 14 to thereby include a distortion component included in the amplified signal. It has a function to cancel.

  The distortion cancellation loop 15 includes an auxiliary amplifier 121, a second converter 122, a second delay circuit 123, a third directional coupler 124, a fifth directional coupler 151, a second frequency converter 152, and An analog-digital converter 153 is provided.

  The fifth directional coupler 151 distributes a part of the signal with the distortion component suppressed, supplied from the third directional coupler 124, as the fifth distribution signal, and the fifth distribution signal. 2 to the frequency converter 152.

  The second frequency converter 152 converts the frequency of the fifth distribution signal supplied from the fifth directional coupler 151 into a baseband. The second frequency converter 152 outputs a baseband signal to the analog-digital converter 153.

  The analog-digital converter 153 converts the baseband signal supplied from the second frequency converter 152 into a digital signal. The analog-digital converter 153 outputs a digital signal to the DPD processing unit 141.

  As described above, in the third embodiment, the band pass filter 142 is arranged at the subsequent stage of the main amplifier 112 and at the previous stage of the first directional coupler 114. Here, the passband in the bandpass filter 142 is supplied from the second delay circuit 123 and the signal amplified by the auxiliary amplifier 121 even if the distortion component included in the signal after bandpass is amplified by the auxiliary amplifier 121. The frequency band of the signal to be supplied from the second frequency converter 152 to the analog-to-digital converter 153 is such that a delay error does not occur between the amplified signal and the amplified signal, and the analog-to-digital converter 153 has a frequency bandwidth. The bandwidth is within the capture range. As a result, even when the main amplifier 112 amplifies a wide band transmission signal, the band of the distortion component is limited by the band pass filter 142, so that the band of the distortion signal supplied to the auxiliary amplifier 121 is reduced. It will be suppressed. Even when the main amplifier 112 amplifies a broadband transmission signal, the band of the signal supplied to the second delay circuit 123 is suppressed. Further, even when the main amplifier 112 amplifies a wideband transmission signal, the frequency bandwidth of the signal supplied to the analog-digital converter 153 is within the capture range of the analog-digital converter 153, so that the DPD processing Will be done effectively.

  Therefore, according to the distortion compensation circuit 30 according to the third embodiment, distortion components can be suppressed even when a wideband transmission signal is amplified.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10, 20, 30 ... Distortion compensation circuit 11, 13, 14 ... Carrier cancellation loop, 111 ... Divider, 112 ... Main amplifier, 113, 133, 142 ... Band pass filter, 114 ... First directional coupler, DESCRIPTION OF SYMBOLS 115 ... 1st converter, 1151, 1222 ... Resistance, 1152, 1221 ... Phase shifter, 116 ... 1st delay circuit, 117 ... 2nd directional coupler, 12, 15 ... Distortion cancellation loop, 121 ... Auxiliary amplifier 122 ... second converter 123 ... second delay circuit 124 ... third directional coupler 131, 141 ... DPD processing unit 132 ... first frequency converter 134 ... fourth Directional coupler, 135, 152 ... second frequency converter, 136, 153 ... analog-to-digital converter, 151 ... fifth directional coupler

Claims (4)

A distributor that distributes an input signal into a first distribution signal and a second distribution signal;
A first amplifier for amplifying the first distribution signal to obtain an amplified signal;
A band-pass filter that suppresses a distortion component out of a preset pass band among distortion components included in the amplified signal;
A first directional coupler that extracts a third distribution signal from the amplified signal that has passed through the bandpass filter;
A first delay unit that gives a delay equivalent to the delay generated by the processing in the first amplifier and the processing in the band-pass filter to the second distribution signal;
A first converter that makes the level of the third distribution signal substantially equal to that of the second distribution signal and converts the phase of the third distribution signal into a phase opposite to that of the second distribution signal;
The distortion component included in the third distribution signal is extracted as a distortion signal by synthesizing the delayed second distribution signal and the third distribution signal processed by the first converter. A second directional coupler;
A second amplifier for amplifying the distortion signal extracted by the second directional coupler to obtain an amplified distortion signal;
A second delay unit that gives the amplified signal supplied from the first directional distributor a delay equivalent to the delay generated by the processing in the second amplifier;
A second converter that adjusts the level of the amplified distortion signal to a distortion component included in the delayed amplified signal and converts the phase of the amplified distortion signal to a phase opposite to that of the delayed amplified signal;
A third directional coupler that removes a distortion component included in the delayed amplified signal by combining the delayed amplified signal and the amplified distortion signal processed by the second converter; A distortion compensation circuit comprising:   Even if the distortion component included in the amplified signal after passing the band is amplified by the second amplifier, the pass band is obtained by multiplying the signal amplified by the second amplifier and the amplified signal after the delay. The distortion compensation circuit according to claim 1, which has a bandwidth that does not cause a delay error. A fourth directional coupler for extracting a part of the amplified signal after passing through the band as a fourth distribution signal;
A first frequency converter for converting the frequency of the fourth distribution signal to a baseband;
An analog-to-digital converter that converts the frequency converted signal into a digital signal;
A DPD (Digital Pre-Distortion) processing unit that refers to the digital signal and corrects the supplied baseband signal so as to reduce distortion caused by amplification in the first amplifier;
A second frequency converter that converts the frequency of the baseband signal corrected by the DPD processing unit to a radio frequency band and outputs the converted signal to the distributor;
Even if the bandpass filter amplifies the distortion component contained in the amplified signal after passing through the band by the second amplifier, the signal amplified by the second amplifier, the amplified signal after the delay, 2. The distortion according to claim 1, wherein the signal is supplied to the analog-to-digital converter so that a delay error does not occur between them, and the frequency bandwidth of the signal supplied to the analog-to-digital converter is within the capture range of the analog-to-digital converter. Compensation circuit. A fourth directional coupler for extracting a part of the signal synthesized by the third directional coupler as a fourth distribution signal;
A first frequency converter for converting the frequency of the fourth distribution signal to a baseband;
An analog-to-digital converter that converts the frequency converted signal into a digital signal;
A DPD (Digital Pre-Distortion) processing unit that refers to the digital signal and corrects the supplied baseband signal so as to reduce distortion caused by amplification in the first amplifier;
A second frequency converter that converts the frequency of the baseband signal corrected by the DPD processing unit to a radio frequency band and outputs the converted signal to the distributor;
Even if the bandpass filter amplifies the distortion component contained in the amplified signal after passing through the band by the second amplifier, the signal amplified by the second amplifier, the amplified signal after the delay, 2. The distortion according to claim 1, wherein the signal is supplied to the analog-to-digital converter so that a delay error does not occur between them, and the frequency bandwidth of the signal supplied to the analog-to-digital converter is within the capture range of the analog-to-digital converter. Compensation circuit.

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