JP4925400B2 - Distortion compensation amplifier - Google Patents

Description

The present invention relates to a distortion compensation amplifying apparatus, and in particular, when a distortion compensation mode is adaptively controlled by feeding back a detection result of distortion included in the output signal of the apparatus, even if an external interference wave is mixed in the output signal. The present invention relates to a distortion compensation amplifying apparatus that operates normally.

Conventionally, when amplifying radio frequency signals such as CDMA signals and multicarrier signals for transmission, low power consumption is achieved by adding distortion compensation means to the common amplifier and extending the operating range of the common amplifier to near the saturation region. I am trying.

FIG. 5 is a block diagram of a conventional distortion compensation amplifying apparatus provided with distortion compensation means. In FIG. 5, 1 is an amplifier with distortion compensation for amplifying a signal in a predetermined band (amplification band) for transmission, 2 is a directional coupler for extracting a part of the traveling wave component of the output signal of the amplifier 1, 3 Is a filter unit that cuts off a return signal such as a reflected wave or a received signal from the antenna, 4 is an antenna (output unit) that radiates an output signal of the amplifier 1, and 5 is included in the level and output signal of the output signal of the amplifier A feedback unit that detects a distortion level, and 6 is an adaptive control unit that adaptively controls a distortion compensation mode with respect to a temperature change or the like based on a feedback signal from the feedback unit.

The output of the amplifier 1 is input to the feedback unit 5 by the directional coupler 2. In the feedback unit 5, the coupler 51 distributes the input signal, and outputs one to the mixer 52 and the other to the output detection circuit 53. The mixer 52 mixes the signal from the coupler 51 and the signal from the local oscillator 54 and outputs the mixed signal to a band pass filter (BPF) 55. The BPF 55 outputs to the distortion detection circuit 56 the frequency converted from the output of the amplifier 1 through the frequency corresponding to the band that the output of the amplifier 1 should originally have, that is, the band just outside the band (transmission band) of the input of the amplifier 1. To do. The output detection circuit 53 and the distortion detection circuit 56 are, for example, circuits having the same configuration, detect the power of each input signal on a logarithmic scale, and smooth and output with a time constant sufficiently slower than the modulation speed of the output of the amplifier 1. As a result, the total power of the output of the amplifier 1 is detected as the output level, and so-called adjacent channel leakage power is detected as the distortion level.

When the signal is distorted in the amplifier 1, a frequency component outside the transmission band that is not included in the input signal is generated in the output signal due to intermodulation within the transmission band. The adaptive control unit 6 appropriately controls the oscillation frequency of the local oscillator 54, so that the distortion level on one side or both sides of the third-order (intermodulation) distortion included in the output of the amplifier 1 or the fifth-order, The feedback unit 5 can detect a plurality of distortion levels as follows. Thereby, the distortion level can be accurately evaluated, and the distortion compensation mode in the amplifier 1 can be updated so that the distortion becomes smaller. In a state where distortion compensation is appropriately performed, an adjacent channel leakage power ratio (ACP) to carrier power is, for example, -60 dBc or less.

However, the frequency components outside the transmission band are not all due to distortion of the amplifier 1. For example, when a radio base station using another carrier adjacent to the transmission band exists nearby, a sneak wave from the radio base station reaches the directional coupler 2 via the antenna. When such an interference wave is strong, isolation is insufficient with the directional coupler 2 alone, and it is detected as a distortion level superimposed on the original distortion and no longer appropriately reflects the distortion amount by the amplifier 1. Therefore, the update of the distortion compensation mode cannot be sufficiently converged. That is, it malfunctions. In order to prevent this, a filter unit 3 having an isolator or a steep filter is provided to attenuate the interference wave.

As another prior art related to the present invention, even if a pilot wave is given to any one of pilot signals by using a plurality of pilot signals having different frequencies in a feedforward amplifier, other pilots are used. One that accurately controls the amount of suppression of the distortion removal loop by a signal is known (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2002-76783

  However, since the conventional distortion compensation amplifying device requires the filter unit 3 having a steep filter and a plurality of isolators, the output of the amplifier 1 must be increased by the amount of attenuation in the filter unit 3, and power consumption There was a problem that increased. Further, the filter used for the filter unit 3 is required to have characteristics that are much steeper than those for normal transmission / reception separation, and both the filter and the isolator must be expensive for power that satisfies the desired performance. There was a problem.

  The present invention has been made from the above-described background, and provides a distortion compensation amplification device that does not increase power consumption, does not use expensive components, and does not malfunction even when receiving external interference waves. Objective.

An amplifier (1) with distortion compensation for amplifying a signal in a predetermined band, a coupler (2) for extracting a part of the output signal of the amplifier, and the level and output signal of the output signal of the amplifier A distortion compensation amplifying apparatus comprising: a feedback unit (5) that detects a distortion level; and an adaptive control unit (6 ′) that controls a distortion compensation mode in the amplifier based on a feedback signal from the feedback unit.
The feedback unit detects a distortion level at a frequency designated by the adaptive control unit among frequencies corresponding to both sides of a band of an input signal to the amplifier, and the adaptive control unit detects the distortion When the value based on the level does not fall below the threshold value, the distortion compensation amplifying apparatus is characterized in that the frequency opposite to the currently designated frequency is designated in the feedback unit.

The threshold value includes a first threshold value set to 60 dBc or less in carrier level and a second threshold value set in absolute level, and the adaptive control unit has the output signal level lower than a third threshold value. A distortion compensation amplifying apparatus characterized in that at least the comparison with the first threshold value is stopped.

  According to the distortion compensation amplifying apparatus of the present invention, it is possible to operate normally against an interference wave from the outside without increasing power consumption and without using expensive components.

Embodiments of the present invention will be described below with reference to the drawings.
The function realizing means described in each embodiment may be any circuit or device as long as it realizes the function, and part or all of the function may be realized by software. Is possible. Furthermore, the function realizing means may be realized by a plurality of circuits, and the plurality of function realizing means may be realized by a common circuit.
In addition, any combination of characteristic portions of each embodiment and a combination with the prior art such as Patent Document 1 cited above can be included in the present invention.

FIG. 1 is a configuration diagram of a distortion compensation amplifying apparatus according to the first embodiment. The distortion compensation amplifying apparatus of the present embodiment is for a transmission amplifier of a mobile phone base station apparatus, and differs from the prior art only in that it has an improved control unit 6 'instead of having a filter unit 3. Other components that are the same as those of the conventional art are denoted by the same reference numerals as those of the conventional art, and description thereof is omitted.

FIG. 2 is a spectrum diagram of a signal extracted from the directional coupler 2 when receiving an interference wave. In the figure, an amplification band means a band that is assigned in advance to the base station for transmission, and includes a plurality of carriers that can be used by a specific communication carrier. The distortion compensation amplifier of this embodiment has the ability to uniformly amplify a plurality of carriers in this amplification band. In an actual base station, not all carriers in the amplification band are used. FIG. 2 shows a case where the amplification band is composed of four carriers, and two of the high frequency side carriers are used. A band occupied by a carrier to be actually used is called a transmission band and is distinguished from the above-described amplification band. A spectrum due to distortion (third-order intermodulation) occurs on both sides of the transmission band, and the distortion spectrum on the low frequency side is within the amplification band, but the distortion spectrum on the high frequency side is a frequency outside the amplification band. Yes. Conventionally, there is a case where a distortion level is detected using a frequency only outside the amplification band.

In FIG. 2, an interference wave is further added to substantially the same frequency as the higher one of the two distortion spectra generated outside the transmission band. As an example of such an interference wave, a transmission wave (carrier) from a base station outside the jurisdiction by another communication carrier provided in the vicinity of the base station is assumed. The higher distortion spectrum is outside the amplification band, and it is no wonder that it is used for the carrier frequency of other communications. Note that the amount of coupling between antennas and the carrier used can be appropriately designed so that the sneak wave does not become a problem between the base stations (antennas) in the jurisdiction, so both of the two distortion spectra are rarely exposed to the interference wave. It is.

In the present embodiment, since the filter unit 3 for blocking the interference wave is not provided, when an interference wave having a level equal to or exceeding the original distortion is mixed as shown in FIG. 2, the original distortion is buried in the interference wave. The original distortion level cannot be detected. In this state, even if the adaptive control unit 6 updates the distortion compensation mode, the result is not reflected on the distortion level, so that the feedback is not effective, that is, the control becomes impossible. In such a case, it is only necessary to detect the distortion level on the opposite side while ignoring the distortion buried in the interference wave among the distortions occurring on both sides of the transmission band.

As an example, the adaptive control unit 6 ′ of this embodiment sets a threshold value for the distortion level. If the distortion level does not fall below the threshold value even when the distortion compensation mode is updated for a predetermined time or number of times, the adaptive control unit 6 ′ Stop using the level and try to use the opposite distortion level.

As another example, the operation of the adaptive control unit 6 ′ that performs adaptive control by detecting distortion levels at a plurality of frequencies will be described with reference to FIG.
FIG. 3 is a spectrum diagram when the signal extracted from the directional coupler 2 has a plurality of distortions.
First, as Step 1, information on the carrier used is acquired from a higher-level device or the like, or a change in the level of the distortion detection circuit when the frequency of the local oscillator 54 is swept is acquired, and the current transmission band is specified and specified. A plurality of distortion detection frequencies suitable for the determined transmission band are determined.
In step 2, the current distortion compensation mode is updated with a minute change. When there are a plurality of locations that give a change, the location is cyclically changed each time Step 2 is executed.
As step 3, distortion levels are detected and stored at a plurality of distortion detection frequencies. At this time, the distortion level is not detected at a distortion detection frequency with a use prohibition flag described later. In addition, the distortion level up to the past n times is stored as necessary.
In step 4, the distortion level detected n times (n is an arbitrary integer equal to or greater than 2) times for each distortion detection frequency is compared with the distortion level detected immediately before, and the level ratio (level change rate) is equal to or less than a predetermined threshold. If the previous distortion level exceeds the threshold value determined in advance for each distortion detection frequency, corresponds to at least one, or both, the use prohibition flag is set for the distortion detection frequency. . FIG. 3 shows a case where a threshold value is set for the distortion level. This threshold value is equal to or lower than an allowable distortion level, for example, for each distortion detection frequency such as 60 dBc for the third order distortion and 75 dBc for the fifth order distortion. Can also be given to. Note that the use prohibition flag is set when the number of executions of step 2 is less than n (when there is no distortion level before n times) or when there is already one distortion detection frequency for which the use prohibition flag is not set. Don't do it when only it remains. In this way, when the use prohibition condition is satisfied even for the only remaining distortion detection frequency, all the use prohibition flags may be once released.
As step 5, distortion levels at a plurality of distortion detection frequencies detected immediately before are integrated by a weighted average to obtain a distortion evaluation value. When the distortion evaluation value is decreased from the previous distortion evaluation value, the change in the immediately preceding step 2 is changed. If it is maintained and increases, the distortion compensation mode is renewed by applying a change opposite to that in the previous step 2 again.
Thereafter, the processing from step 2 to step 5 is repeated.

  When the threshold value for the distortion level is determined by the carrier level such as 60 dBc, the adaptive control unit 6 outputs the output value of the output detection circuit 53 (log level output level) and the output value of the distortion detection circuit 56 (logarithm). A value based on the difference in scale distortion level is compared with a threshold value. Note that the threshold value determined for the distortion level may be determined by an absolute level, and the first threshold value determined by the carrier level and the second threshold value determined by the absolute level may be used in combination. Further, when the carrier level falls below the third threshold (when the carrier level is extremely low and the distortion level cannot be measured accurately), at least the comparison with the first threshold is stopped so that the use prohibition flag is not set. As a result, it is possible to reliably speed up the convergence until it falls below and below the second threshold value.

As described above, in the present embodiment, the erroneous detection of the distortion level due to the mixing of the interference wave is detected as the delay or stagnation of the convergence of the distortion compensation mode that always occurs as a result. Can be dealt with. The present embodiment can be applied to any distortion compensation amplification apparatus that adaptively controls the distortion compensation mode by feeding back the detection result of the distortion level included in the output signal of the apparatus. The distortion compensation system is a predistortion system, a feed. Regardless of the forward method.
By the way, Japanese Patent Application No. 2005-37211 by the same applicant as this application describes an embodiment that employs a method of detecting a larger distortion level of two ACP reception frequencies, and a large value that exceeds a threshold value is described. Although this seems to be contrary to the present embodiment in which the distortion level is ignored, these embodiments are not necessarily contradictory, and can be combined in a manner that gives priority to the determination of the present embodiment. That is, the larger distortion level may be detected within a range not exceeding the threshold value.
The prior application also describes an example in which the distortion level is more responsive to the fluctuation of the input level and the distortion level with the more remarkable response is adopted. The distortion level that is more sensitive to input level fluctuations reflects the distortion that is more likely to be compensated for distortion, and the response to updating the distortion compensation mode (vector adjustment amount) is better, so the convergence is faster. However, it is also effective for the interference wave assumed in the present invention. However, in order to prevent misjudgment when the input level of the device itself and the interference wave level happen to show the same fluctuation, it is necessary to determine the correlation between the input (output) level and the distortion level. The process is simpler and better.

In this embodiment, a feedforward amplifier is employed as the amplifier 1 in the first embodiment described above, and other configurations are the same as those in the first embodiment. In other words, the feedback unit 5 of the present embodiment also detects the distortion level at one or more frequencies designated by the adaptive control unit 6 ′ out of a plurality of frequencies corresponding to both sides of the band of the input signal to the amplifier 1. To do. If the value based on the detected distortion level does not fall below the threshold value, the adaptive control unit 6 ′ specifies a frequency excluding the currently specified frequency to the feedback unit 5. Thereby, the distortion level which received the interference wave is ignored.

  FIG. 4 is a configuration diagram of the amplifier 1 according to the present embodiment, which is a very general feedforward amplifier. The distortion compensation mode described in the first embodiment corresponds to the adjustment amount of the vector adjuster 106 provided in the distortion removal loop in this embodiment, and includes an attenuation amount and a phase amount. The attenuation amount and the phase amount are alternately updated by the adaptive control unit 6 ′ by the method described in the first embodiment, for example, and supplied to the vector adjuster 106. Note that the vector adjuster 102 of the distortion detection loop is controlled by a known method.

1 is a configuration diagram of a distortion compensation amplifying apparatus according to Embodiment 1 of the present invention. The spectrum figure of the signal taken out from the directional coupler 2 when it receives an interference wave. The spectrum figure which has a some distortion. FIG. 3 is a configuration diagram of an amplifier 1 according to a second embodiment. The block diagram of the conventional distortion compensation amplifier.

Explanation of symbols

1 amplifier,
2-directional coupler,
3 Filter section,
4 Antenna,
5 Feedback section,
51 coupler, 52 mixer, 53 output detector circuit, 54 local oscillator,
55 band pass filter (BPF), 56 distortion detection circuit,
6 Adaptive control unit.

Claims (1)

An amplifier with distortion compensation for amplifying a signal in a predetermined band;
A coupler for extracting a portion of the output signal of the amplifier;
A feedback unit for detecting a level of an output signal of the amplifier and a distortion level included in the output signal;
In a distortion compensation amplifying apparatus comprising: an adaptive control unit that controls a distortion compensation mode in the amplifier based on a feedback signal from the feedback unit;
The feedback unit cyclically detects a distortion level at a plurality of distortion detection frequencies designated by the adaptive control unit among frequencies corresponding to both sides of a band of an input signal to the amplifier,
If the distortion level at the detected distortion detection frequency does not fall below a threshold, the adaptive control unit prohibits the use of the distortion detection frequency and sets a frequency opposite to the currently designated frequency to the feedback unit. A distortion compensation amplifying apparatus characterized by specifying.

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