JP4939281B2 - Amplifier - Google Patents

Description

  The present invention relates to an amplifying apparatus that compensates for distortion of an amplifier, and more particularly to an amplifying apparatus that can realize a good distortion compensation amount even when the detuning frequency of signals of a plurality of carriers is large.

For example, in a base station device provided in a mobile communication system that employs a W-CDMA (Wide-Band Code Division Multiple Access) method as a mobile communication method, Since it is necessary to make the wireless signal reach the place, it is necessary to amplify the signal with an amplifier.
However, since the amplifier is an analog device, its input / output characteristics are nonlinear functions. In particular, after the amplification limit called the saturation point, the output power is almost constant even if the power input to the amplifier is increased. Then, nonlinear distortion is generated by this nonlinear output.

  The signal component outside the desired signal band of the transmitted signal before amplification is suppressed to a low level by the band limiting filter, but the signal component leaks outside the desired signal band (adjacent channel) due to nonlinear distortion in the signal after passing through the amplifier. To do. For example, since the transmission power is high as described above in the base station apparatus, the magnitude of the leakage power to such an adjacent channel is strictly defined, and how to reduce such adjacent channel leakage power is large. It is a problem.

One distortion compensation method is a predistortion method.
The predistortion method is a method of compensating for distortion of an output signal of an amplifier by giving in advance an amplifier input signal with inverse characteristics of AM-AM (amplitude) conversion and AM-PM (phase) conversion which are nonlinear characteristics of the amplifier. It is.

Here, since the amplifier is an analog device, the input / output characteristics of the amplifier change due to environmental changes and secular changes. For this reason, the predistortion to be applied to the input signal by the predistorter also changes. In order to cope with such environmental changes and aging changes, it is necessary to update the distortion compensation table and adapt the predistortion applied to the transmission data by the predistorter to the input / output characteristics of the amplifier after the change.
As one of the means for updating the predistortion, there is a method in which the transmission signal is fed back and the predistortion applied to the transmission data by the predistorter is updated using the feedback signal.

FIG. 5 shows a configuration example of a predistortion type amplification device (distortion compensation amplifier) using a feedback signal.
The amplification device of this example is provided, for example, in a transmitter of a base station device, and inputs a signal to be transmitted.
The amplification device of this example includes a predistorter 101, an amplification unit 102, a power detection unit 103, a distortion compensation table 104, a data conversion unit 105, a distortion power calculation unit 106, a control unit 107, and a directionality. A coupler 108 is provided.

An example of the operation performed in the amplifying apparatus of this example is shown.
An input signal is input to the predistorter 101 and the power detection unit 103.
The power detection unit 103 detects the power (or amplitude) of the input signal and outputs the detected value to the distortion compensation table 104.
The distortion compensation table 104 is configured using a memory or the like, and the distortion compensation table 104 stores a table for performing distortion compensation by a predistortion method. This table defines the inverse characteristic of the nonlinear characteristic of the amplifying unit (amplifier) 102 to be compensated. In general, the AM-AM characteristic and the AM-PM characteristic using the power (or amplitude) of the input signal as an index. Is used.
Based on the contents of the table, the distortion compensation table 104 uses the power value (or amplitude value) input from the power detection unit 103 as a reference argument, and sends a control value associated with the value to the predistorter 101. Output.

The predistorter 101 predistorts the input signal by controlling the amplitude and phase of the input signal according to the control value (reference result in the distortion compensation table 104) input from the distortion compensation table 104. The resulting signal is output to the amplification unit 102.
The amplifying unit 102 amplifies the signal input from the predistorter 101 and outputs the amplified signal.
Here, since the signal input to the amplification unit 102 is a signal that has been previously distorted by the predistortion method, the output signal amplified by the amplification unit 102 is (ideally) a signal without distortion.

A part of the output signal from the amplification unit 102 is acquired by, for example, the directional coupler 108 and input to the data conversion unit 105 as a feedback signal.
The data conversion unit 105 converts the data of the feedback signal from the amplification unit 102 from time axis data to frequency axis data, and outputs the resulting frequency axis data to the distortion power calculation unit 106.
The distortion power calculation unit 106 calculates the power of the frequency band in which the intermodulation distortion occurs based on the frequency axis data input from the data conversion unit 105, and outputs the result information to the control unit 107.
The control unit 107 calculates predistortion, updates the contents of the distortion compensation table 104, and the like based on the power (distorted power) calculated by the distortion power calculation unit 106. As an example, the control unit 107 can adaptively control the contents of the distortion compensation table 104 using a perturbation method.

JP 2003-078451 A

However, as described above, in an amplifying apparatus that updates the distortion compensation table 104 using the perturbation method using power in a frequency band in which intermodulation distortion occurs as an evaluation value, detuning when transmitting signals of a plurality of carriers is performed. When the frequency is large, there is a problem that the amount of distortion compensation decreases.
The present invention has been made to solve such a conventional problem, and an amplification device capable of realizing a good distortion compensation amount even when the detuning frequency of signals of a plurality of carriers is large. The purpose is to provide.

In order to achieve the above object, according to the present invention, an amplifier that compensates for distortion of an amplifier has the following configuration.
That is, the predistorter means applies distortion for distortion compensation to the signal to be amplified by the amplifier. Based on the signal output from the amplifier, the distortion power detection means includes a signal to be amplified by the amplifier including signals of a plurality of carriers, and the detuning frequency is equal to or higher than a predetermined threshold (or a predetermined value) In the case of exceeding the threshold), the combination of the power of the frequency band where the intermodulation distortion occurs and the power of the frequency band near the carrier frequency is detected as the distortion power, while in other cases (that is, by the amplifier) Intermodulation distortion when the signal to be amplified does not include signals of a plurality of carriers, or when included, but the detuning frequency is lower than a predetermined threshold (or lower than the predetermined threshold). Is detected as distortion power. The control means controls the distortion compensation mode by the predistorter means based on the distortion power detected by the distortion power detection means.

  Therefore, when controlling the distortion compensation mode using the power of the frequency band where the intermodulation distortion occurs after amplification by the amplifier as distortion power, the signal to be amplified by the amplifier includes signals of a plurality of carriers and the detuning thereof. When the frequency is equal to or higher than a predetermined threshold (or exceeds the predetermined threshold), the distortion power is obtained by combining the power of the frequency band where the intermodulation distortion occurs and the power of the frequency band near the carrier frequency. By controlling the distortion compensation mode, for example, even when the detuning frequency of the signals of a plurality of carriers is large, referring to the distortion power effective for controlling the distortion compensation mode, a good distortion compensation amount can be obtained. Can be realized.

Here, various signals may be used as the signals of the plurality of carriers. For example, signals of two carriers or signals of three or more carriers arranged at equal frequency intervals can be used. .
In addition, various values may be used as the predetermined threshold regarding the detuning frequency of the signals of a plurality of carriers. For example, mutual power is used rather than using power in a frequency band in which intermodulation distortion occurs as distortion power. It is better to use distortion power as a combination of power in the frequency band where modulation distortion occurs and power in the frequency band near the carrier frequency (or that is preferable in practice) ) Can be set.

  Various powers may be used in the frequency band where the intermodulation distortion occurs. For example, the power in the frequency band having a predetermined width centered on the frequency where the intermodulation distortion occurs is used. Can do. In addition, various modes can be used as the order of the intermodulation distortion and the number thereof. As an example, m (m is 3 of the odd-order distortions such as third order, fifth order, seventh order,...). It is possible to use the sum of powers for all the intermodulation distortions below the above (arbitrary odd) order. In general, intermodulation distortion occurs on the upper side (high frequency side) and the lower side (low frequency side), and the sum of the powers on both sides is used, or the power on only one side is used.

  Various powers may be used as the power of the frequency band in the vicinity of the carrier frequency. For example, for each carrier, the power of a predetermined band on the upper side (high frequency side) of the carrier, For the power in a predetermined band on the lower side (lower frequency side) of the carrier, the sum of the powers on both sides is used, or the power on only one side is used. In addition, as the power in the frequency band near the carrier frequency, for example, the sum of the power obtained for each carrier for the signals of a plurality of carriers is used. Here, as a frequency band in the vicinity of each carrier (band for detecting power), for example, a frequency band having a preset fixed width may be used, or for each carrier, the same frequency band may be used. Also in this carrier, frequency bands having different widths may be used on the upper side and the lower side.

  Various methods may be used as a method of controlling the distortion compensation mode based on the distortion power. For example, a method of controlling the distortion compensation mode so as to reduce the detected distortion power is used. As an example, when the distortion compensation mode (for example, control value) is shifted in a certain direction, if the detected distortion power is reduced, the distortion power is further increased while the detected distortion power is increased. For example, a perturbation method that repeatedly executes shifting in the opposite direction can be used.

As an example, the correspondence between the level of the signal to be amplified by the amplifier (for example, the power or amplitude level) and the control value specifying the distortion compensation mode is stored in the distortion compensation table, and the content of the distortion compensation table is stored. Based on this, when distortion compensation is controlled using a control value corresponding to the level (detection value) of the signal to be amplified by the amplifier, the contents of the distortion compensation table (distortion compensation mode) so that the distortion power is reduced. ) Can be used (for example, updating).
As another example, distortion (amplitude distortion and phase distortion) applied to a signal by a predistorter is calculated by a predetermined arithmetic expression (not a method of reading a control value from a distortion compensation table), and the distortion is realized. When a control value is given to the predistorter, a mode is used that controls (for example, rewrites) the arithmetic expression or the control value (distortion compensation mode) so that the distortion power is reduced. Can do.

  As described above, according to the amplifying apparatus of the present invention, the signal to be amplified by the amplifier includes a plurality of carrier signals, and the detuning frequency is equal to or higher than a predetermined threshold (or exceeds the predetermined threshold). ) In this case, the distortion compensation mode is controlled by using a combination of the power of the frequency band in which the intermodulation distortion occurs and the power of the frequency band near the carrier frequency as distortion power. Even when the detuning frequency of the carrier signal is large, a good distortion compensation amount can be realized.

Embodiments according to the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of a predistortion type amplification device (distortion compensation amplifier) using a feedback signal according to an embodiment of the present invention.
The amplification device of this example is provided, for example, in a transmitter of a base station device, and inputs a signal to be transmitted.
The amplifying apparatus of this example includes a predistorter (for example, DPD: digital predistorter) 1, an amplifying unit 2, a data converting unit 3, a distortion power calculating unit 4, a control unit 5, and a directional coupler. 6 is provided.

An example of the operation performed in the amplifying apparatus of this example is shown.
An input signal is input to the predistorter 1.
The predistorter 1 predistorts the input signal by controlling the amplitude and phase of the input signal in accordance with the control signal input from the control unit 5, and outputs the resulting signal to the amplification unit 2. .
The amplifying unit 2 amplifies the signal input from the predistorter 1 and outputs the amplified signal.
Here, since the signal input to the amplification unit 2 is a signal that has been previously distorted by the predistortion method, the output signal amplified by the amplification unit 2 is (ideally) a signal without distortion.

A part of the output signal from the amplification unit 2 is acquired by, for example, the directional coupler 6 and input to the data conversion unit 3 as a feedback signal.
The data conversion unit 3 converts the data of the feedback signal from the amplification unit 2 from time axis data to frequency axis data, and outputs the resulting frequency axis data to the distortion power calculation unit 4. Note that conversion from time-axis data to frequency-axis data can be performed using, for example, fast Fourier transform (FFT).
Based on the frequency axis data input from the data converter 3, the distortion power calculation unit 4 calculates the power in the frequency band in which the intermodulation distortion occurs and the power in the frequency band near the transmission carrier, and information on the result (Distortion power information) is output to the control unit 5.

The control unit 5 adaptively controls the predistorter 1 by outputting a control signal to the predistorter 1 based on the power (distorted power) calculated by the distortion power calculating unit 4. Specifically, the control unit 5 uses a perturbation method to control the distortion compensation mode (predistortion) by the predistorter 1 so that the distortion power is reduced.
The control unit 5 is configured by using, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor).

Further description will be given below.
In this example, when signals of a plurality of carriers are transmitted and the detuning frequency of the transmission carriers is equal to or higher than a predetermined threshold, the power of the frequency band in which intermodulation distortion occurs and the frequency band near the transmission carrier The power obtained by adding the two powers is used as the distortion power, and is used as an evaluation value when the control unit 5 performs control using the perturbation method.
Here, as a method for recognizing the frequency of the input carrier, for example, since the frequency of the input carrier is designated from the base station apparatus side, the information on the frequency is used as the control unit 5 of the predistorter 1 or distortion power calculation. By setting in the unit 4, the frequency of the input carrier is recognized. The frequency information indicates, for example, the center frequency of the carrier, and the carrier detuning frequency is calculated by subtraction.

FIG. 2 shows an example of a processing procedure for calculating distortion power by the distortion power calculation unit 4 of this example.
The distortion power calculation unit 4 of this example calculates the distortion power a in the generation band of intermodulation distortion (step S1). Further, it is determined whether or not the carrier detuning frequency is equal to or higher than a predetermined threshold (step S2). If so, the distortion power b in the band near the carrier is calculated (step S3). Then, these two distortion powers a and b are added, and the addition result is acquired as the final distortion power value (a + b) (step S4). When the carrier detuning frequency is less than the predetermined threshold (step S2), the distortion power b in the band near the carrier is not calculated, and the value b is set to zero (0).

  In the configuration for calculating the distortion power as in this example, for example, even when the detuning frequency of the transmission carrier is large and the band where the intermodulation distortion occurs is far away from the carrier frequency, the distortion power in the vicinity of the carrier is always maintained. Is reflected in the update of the control mode of the predistorter 1 by the perturbation method, the distortion compensation amount can be improved as compared with the configuration in which the distortion power is calculated only in the band where the intermodulation distortion occurs. Various control modes of the predistorter 1 may be used. For example, in the configuration in which the predistorter 1 is controlled using a distortion compensation table, the distortion power near the carrier is determined by the perturbation method. This is reflected in the update of the table contents of the distortion compensation table.

  Here, various values may be used as the predetermined threshold related to the carrier detuning frequency. For example, the frequency band where the intermodulation distortion occurs and the frequency band near the transmission carrier do not overlap. It is preferable to set.

Hereinafter, (Specific Example 1) to (Specific Example 2) will be described.
In this example, the threshold of the detuning frequency of the transmission carrier is set to 9 MHz with the power obtained by adding the power of the frequency band in which the intermodulation distortion occurs and the power of the frequency band near the transmission carrier as the distortion power. The width is 5 MHz, and the power in the band up to the fifth order intermodulation distortion (third order and fifth order in this example) is the distortion power. In addition, a case where the signal to be processed is a W-CDMA wave and 2-carrier transmission (frequency C0 [MHz], C1 [MHz]: C0 <C1) is shown.

(Specific example 1)
FIG. 3 shows an example of a spectrum when the detuning frequency is less than the threshold value.
For example, when the detuning frequency is 5 MHz, it is less than the threshold (| C1-C0 | <9 MHz), and in the calculation of the distortion power, only the bands (1) and (2) where the intermodulation distortion occurs are included. Electric power is used as distortion power.
In this example, the band (frequency) in which the intermodulation distortion occurs is (C0−n × 5 MHz, C1 + n × 5 MHz) (n = 1, 2), and the power is detected with a bandwidth of 5 MHz for each.

(Specific example 2)
FIG. 4 shows an example of a spectrum when the detuning frequency is equal to or higher than a threshold value.
For example, when the detuning frequency is 15 MHz, it is equal to or higher than the threshold (| C1-C0 | ≧ 9 MHz), and in the calculation of distortion power, the power in the bands (1) and (2) where the intermodulation distortion occurs And a value obtained by adding the power of the frequency band (3) in the vicinity of the carrier is used as the distortion power.

In this example, the band (frequency) in which the intermodulation distortion occurs is (C0−n × 15 MHz, C1 + n × 15 MHz) (n = 1, 2), and the power is detected with a bandwidth of 5 MHz for each.
The frequencies near the carrier are, for example, (C0-5 MHz, C0 + 5 MHz, C1-5 MHz, C1 + 5 MHz), and the power is detected with a bandwidth of 5 MHz for each.

As described above, in the amplifying apparatus of this example, the predistorter 1 for performing distortion compensation, the amplifying unit 2 for amplifying the transmission signal, and the feedback signal from the amplifying unit 2 are converted from the time axis data to the frequency axis. A data converter 3 for converting to data, and a distortion power calculator 4 for calculating power in a frequency band where intermodulation distortion occurs and power in a band near the transmission frequency using the feedback signal converted by the data converter 3 The control unit 5 controls the predistorter 1 based on the distortion power calculated by the distortion power calculation unit 4.
In the amplification device of this example, the distortion power calculation unit 4 calculates the distortion power in the frequency band in which the intermodulation distortion occurs and the band in the vicinity of the transmission frequency only when the detuning frequency of the transmission carrier is greater than or equal to a certain threshold value. .

  Therefore, in the amplifying apparatus of this example, when performing distortion compensation of a predistortion system in which the inverse characteristic of the nonlinear characteristic of the amplifier (in this example, the amplifier of the amplifying unit 2) is given to the signal to compensate for distortion generated by the amplifier. When a plurality of carriers are transmitted and the detuning frequency of the transmission carrier is large, based on the distortion power that combines both the power in the frequency band where the intermodulation distortion occurs and the power in the band near the transmission frequency. Since the control value (for example, the table contents of the distortion compensation table) used for the control of the predistorter 1 is calculated or updated, for example, the perturbation method is performed using only the power in the frequency band where the intermodulation distortion occurs as the evaluation value. Compared to a configuration in which the distortion compensation table is updated by using the distortion compensation amount, the distortion compensation amount can be improved.

  In the amplification device (distortion compensation amplifier) of this example, the predistorter means is configured by the function of the predistorter 1, the amplification unit (amplifier) 2 is a distortion compensation target, and the directional coupler 6 The data converter 3 and the distortion power calculation unit 4 constitute a distortion power detection means by the function of detecting a predetermined distortion power according to the state of the signal to be amplified, and the control unit 5 performs preprocessing based on the distortion power. The control means is constituted by the function of controlling the mode of distortion compensation by the distorter 1.

Here, the configuration of the system and apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a recording medium for recording the program. It is also possible to provide various systems and devices.
The application field of the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields.
In addition, as various processes performed in the system and apparatus according to the present invention, for example, the processor executes a control program stored in a ROM (Read Only Memory) in hardware resources including a processor and a memory. A controlled configuration may be used, and for example, each functional unit for executing the processing may be configured as an independent hardware circuit.
The present invention can also be understood as a computer-readable recording medium such as a floppy (registered trademark) disk or a CD (Compact Disc) -ROM storing the control program, and the program (itself). The processing according to the present invention can be performed by inputting the program from the recording medium to the computer and causing the processor to execute the program.

It is a figure which shows the structural example of the amplifier (distortion compensation amplifier) which concerns on one Example of this invention. It is a figure which shows an example of the procedure of the process which calculates distortion electric power. It is a figure which shows an example of the spectrum which concerns on the specific example 1. FIG. It is a figure which shows an example of the spectrum which concerns on the specific example 2. FIG. It is a figure which shows the structural example of an amplifier (distortion compensation amplifier).

Explanation of symbols

  1, 101... Predistorter 2, 102... Amplifier section 3, 105 Data converter 4, 106 Distortion power calculation section 5 107 Control section 6 108 Direction Sex coupler, 103.. Power detector 104, distortion compensation table,

Claims (1)

In an amplifying apparatus that compensates for distortion of an amplifier,
Predistorter means for applying distortion for distortion compensation to a signal to be amplified by the amplifier;
Based on the signal output from the amplifier, when the signal to be amplified by the amplifier includes a plurality of carrier signals and the detuning frequency is equal to or higher than a predetermined threshold or exceeds a predetermined threshold, intermodulation is performed. The power of the frequency band where distortion occurs and the power of the frequency band adjacent to the carrier frequency are detected as distortion power, while in other cases, the power of the frequency band where intermodulation distortion occurs is distorted. Distortion power detection means for detecting as power;
Control means for controlling an aspect of distortion compensation by the predistorter means based on the distortion power detected by the distortion power detection means;
An amplifying apparatus comprising:

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