JP2008028746A - Distortion compensating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify constitution of a distortion compensating device compensating distortion generated in an amplifier 5 for control over distortion compensation. <P>SOLUTION: A generating means 21 generates predistortion, and a phase shifting means 22 shifts the phase of the predistortion; and an amplitude varying means 23 varies the amplitude of the predistortion, and a composing means 4 puts together the predistortion processed by the phase shifting and amplitude variation and an input signal to be amplified by the amplifier 5, and then outputs a signal as the composition result to the amplifier 5. Component detecting means 6, 8, and 9 detect the level of a difference frequency component of the input signal based upon the signal having been amplified, output detecting means 7, 10, and 11 detect the output level based upon the signal having been amplified, and a control means 12 controls the phase shifting based upon the detection result of the component detecting means and also controls the amplitude variation based upon the detection result of the output detecting means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a distortion compensation apparatus that compensates for distortion generated in an amplifier, and more particularly to a distortion compensation apparatus that simplifies a configuration related to distortion compensation control.

  For example, as represented by a mobile phone system, in recent years, a system using radio is very popular. Many of the recent wireless systems employ a linear modulation system, and linearity is required for the amplification circuits of these signals. Further, as represented by multicarrier amplification, cost reduction and efficiency improvement are required by performing common amplification. In order to meet these demands, amplification methods employing a distortion compensation method have become common, and amplification devices employing various distortion compensation methods are known.

Nonlinear distortion generated in the amplifier includes odd-order distortion and even-order distortion.
Odd-order distortion is generally called intermodulation distortion, which is caused by odd-order terms when the nonlinear characteristics of an amplifier are approximated by a power series, and affects adjacent lines because it appears in the vicinity of the signal frequency. .
Distortion compensation by the distortion compensator is realized by canceling distortion generated in the amplifier. For example, it is different from a method of canceling distortion using distortion itself generated by an amplifier compensated using a feedforward method or a feedback method, or an amplifier compensated using a predistortion method (predistortion method). There is a method of generating distortion using an element and canceling the distortion.

FIG. 8 shows an example of a circuit configuration of a distortion compensation apparatus using a predistortion system. In addition, the same code | symbol is attached | subjected about the component similar to having shown in FIG. 1 which concerns on the Example mentioned later.
In the distortion compensator of this example, an input signal is input to the synthesizer 4 via the distributor 1 and the delay line 2, and the input signal includes a distortion generator 21, a variable phase shifter 22, and a variable attenuator 23. The distortion generated by the distortion generation circuit 3 is input to the synthesizer 4. In the synthesizer 4, the input signal and the distortion are combined, and the combined result is amplified by the amplifier 5.
The output signal from the amplifier 5 is input to the multiplier 34 through the distributor 31, and the multiplier 34 receives the signal input from the oscillator (for example, VCO) 32 and the synchronization circuit (SYN) 33 and the signal from the amplifier 5. Is multiplied. The multiplication result is detected by the detection circuit 35, and the detection result is A / D converted by the A / D converter (ADC) 36 and input to the control circuit 37. The control circuit 37 controls the variable phase shifter 22 and the variable attenuator 23 based on the input from the A / D converter 36.
Normally, when control is performed in a distortion compensation apparatus, a distortion generation circuit in the distortion compensation apparatus is detected so that the distortion component appearing in the output of the apparatus is detected and the level of the distortion component is reduced as in this example. 3 is used to adjust the phase and amplitude.

Japanese Patent No. 03696121 JP 2001-197002 A JP 2003-347854 A Japanese Patent Laid-Open No. 3-179824 US Pat. No. 6,687,466 European Patent No. 0849897

However, in the circuit of the distortion compensation apparatus as shown in FIG. 8, the output signal is once moved to the intermediate frequency band (IF band) in order to detect a distortion component having a high frequency due to the frequency limitation of the control circuit 12 to be used. Since conversion must be performed, an oscillator 32 and a multiplier 34 are required for this purpose. This causes a problem that the circuit scale is increased and a burden is increased in terms of cost. It was.
The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a distortion compensation apparatus capable of simplifying the configuration related to distortion compensation control.

In order to achieve the above object, the distortion compensator according to the present invention compensates for distortion generated in an amplifier with the following configuration.
That is, the generating means generates predistortion. The phase changing means changes the phase of the predistortion generated by the generating means. Amplitude changing means changes the amplitude of the predistortion generated by the generating means. A synthesizing unit synthesizes the predistortion processed by the phase changing unit and the amplitude changing unit and an input signal to be amplified by the amplifier, and outputs a signal of the synthesis result to the amplifier.
Component detection means detects the level of the difference frequency component of the input signal based on the amplified signal output from the amplifier. The output detection means detects the output level (for example, the output level of the linear component) based on the amplified signal output from the amplifier. The control means controls the phase change by the phase change means based on the detection result by the component detection means, and controls the amplitude change by the amplitude change means based on the detection result by the output detection means.
Therefore, it is possible to simplify the configuration related to the distortion compensation control by the configuration that controls the distortion compensation based on the level of the difference frequency component.

The distortion compensation apparatus according to the present invention has the following configuration as one configuration example.
That is, the control means controls the phase change by the phase change means so that the level of the difference frequency component detected by the component detection means becomes large (for example, maximizes), and the output detection means The amplitude change by the amplitude changing means is controlled so that the gain (for example, the gain of the linear component) based on the detection result of is a specified value.
Therefore, accurate distortion compensation can be realized corresponding to the case where the phase between the linear component and the distortion component generated by the amplifier is 180 ° (= π).

The distortion compensation apparatus according to the present invention has the following configuration as one configuration example.
That is, the component detection means detects a level of the difference frequency component from the amplified signal output from the amplifier, and converts the detection result by the level detection circuit from an analog signal to a digital signal A It was configured using a / D converter. The output detection means includes an output level detection circuit for detecting the output level from the amplified signal output from the amplifier, and an A / A for converting the detection result by the output level detection circuit from an analog signal to a digital signal. It was configured using a D converter.
Therefore, for example, the configuration relating to distortion compensation control can be simplified as compared with the configuration of the distortion compensating apparatus as shown in FIG. 8, and specifically, an oscillator 32 or a multiplier for performing frequency conversion. 34 can be dispensed with.

  As described above, according to the distortion compensation device according to the present invention, it is possible to simplify the configuration related to the distortion compensation control by the configuration that controls the distortion compensation based on the level of the difference frequency component of the input signal. Thus, distortion generated in the amplifier can be compensated with a simple configuration.

Embodiments according to the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of a circuit of a predistortion type distortion compensation apparatus according to an embodiment of the present invention.
The distortion compensation apparatus of this example is provided in an amplifying apparatus in a base station of a wireless communication system or an amplifying apparatus in a repeater. Non-linear distortion generated when amplified by an amplifier is reduced.
The distortion compensator of this example includes a distributor 1, a delay line 2, a third-order distortion generator 21, a variable phase shifter 22 and a variable attenuator 23, a synthesizer 4, and an amplifier 5. A distributor 6, a distributor 7, a level detection circuit 8, an A / D converter 9 that performs analog / digital conversion, an output level detection circuit 10, an A / D converter 11, and a control circuit. 12.

An example of the operation performed by the distortion compensation apparatus of this example is shown.
The signal input to the distortion compensator is distributed by the distributor 1, and one distributed signal is delayed by the delay line 2 provided on one output side from the distributor 1 and input to the synthesizer 4. The distributed signal is input to the distortion generating circuit 3 provided on the other output side from the distributor 1.
In the distortion generation circuit 3, the other distributed signal is input to the third-order distortion generator 21 to generate third-order distortion based on the signal, and the phase of the third-order distortion signal is variable by the variable phase shifter 22. The amplitude of the third-order distortion signal is variably adjusted by the variable attenuator 23. The same effect can be obtained even if the variable phase shifter 22 and the variable attenuator 23 are on the input side of the third-order distortion generator 21. The third-order distortion signal subjected to these adjustments is input to the synthesizer 4.

In the synthesizer 4, the one distributed signal and the adjusted third-order distortion signal are synthesized. Here, the delay line 2 has a delay amount that adapts the timing of the third-order distortion signal based on the one distribution signal and the other distribution signal at the synthesizer 4.
The signal resulting from the synthesis by the synthesizer 4 is amplified by the amplifier 5, and the amplified signal is output from the distortion compensation device via the two distributors 6 and 7. Here, if the third-order distortion (predistortion) generated in the distortion generation circuit 3 and the third-order distortion generated in the amplifier 5 have the same amplitude and opposite phases, the third-order distortion generated in the amplifier 5 is canceled out. In addition, even if the same amplitude and opposite phase are not completely achieved, the third-order distortion generated in the amplifier 5 can be canceled and reduced depending on the degree.

In the distributor 6, the amplified signal output from the amplifier 5 is input and distributed, one is output to the distributor 7, and the other is output to the level detection circuit 8.
In the distributor 7, the signal output from the distributor 6 is input and distributed, one is output from the distortion compensation device, and the other is output to the output level detection circuit 10.
In the level detection circuit 8, the level of the difference frequency component is detected based on the signal input from the distributor 6, and an analog detection signal as the detection result is output to the A / D converter 9. In the A / D converter 9, the analog detection signal is converted into a digital signal, and the digital signal is input to the control circuit 12. In this example, A / D conversion is performed after the power of the difference frequency component is detected by the detection circuit.
The output level detection circuit 10 detects the level of a signal component (for example, a linear component corresponding to the input to the distortion compensation device) based on the input from the distributor 7, and an analog detection signal as the detection result is detected. It is output to the A / D converter 11. In the A / D converter 11, the analog detection signal is converted into a digital signal, and the digital signal is input to the control circuit 12.

  The control circuit 12 calculates amplitude data and phase data for reducing distortion components based on the detection signal input from the A / D converter 9 and the detection signal input from the A / D converter 11. The phase shift amount (phase change amount) of the variable phase shifter 22 is controlled with the calculated phase data, and the attenuation amount of the variable attenuator 23 is controlled with the calculated amplitude data. In the control circuit 12 of this example, when the level of the signal input to the distributor 1 is constant, the level of the signal output from the distributor 7 is constant, that is, the gain is constant. The phase and amplitude of the distortion generating circuit 3 related to predistortion are controlled.

In this example, it is assumed that the level of the signal input to the distributor 1 is constant, and the level of the signal output from the distributor 7 is detected. However, as another configuration example, the distributor 1 includes A configuration in which the level of the input signal and the level of the signal output from the distributor 7 are detected to control the gain to be constant can be used, particularly when the input level fluctuates. It is valid.
Further, in this example, the difference frequency component is extracted from the distributor 6, but as another configuration example, the difference frequency component is passed from the output of the amplification element of the amplifier 5 via a light low frequency filter that does not affect the high frequency signal. It is also possible to use a configuration that detects.

Here, the difference frequency component output from the amplifier 5 is, for example, a frequency component generated by even-order distortion when an input signal having a plurality of frequencies is input. When signals having two different frequencies are input, , The components that appear at the frequency of the difference between these two different frequencies.
FIG. 2 shows an example of the output spectrum of the amplifier 5. The horizontal axis indicates the frequency, and the vertical axis indicates the output level.
In this example, the signal components of the frequency f1 and the frequency f2 are input signals to the distortion compensator, and a third-order distortion component is generated at the frequency (2f2-f1) and the frequency (2f1-f2). The component of -f1) is the difference frequency component.

Next, the control performed by the control circuit 12 of this example will be described in more detail.
FIG. 3A shows an example of changes in output due to distortion, using vectors V0, V1, and V3 (in the figure, a vector display having an arrow). V1 indicates a linear component (for example, a component of an input signal to the distortion compensation device), V3 indicates a third-order distortion component generated by the amplifier 5, and V0 indicates a combined output thereof. Further, an angle φ3 between V1 and V3 is shown.
When distortion as shown in FIG. 3 (a) occurs in the amplifier 5, in order to cancel this distortion using the predistortion compensation circuit, as shown in FIG. It is necessary to add an equiamplitude antiphase component to the input of the amplifier 5.
FIG. 3B shows an example of the output when distortion compensation is performed using the vector A3 (shown as a vector display having an arrow in the figure). A3 indicates an output (third-order distortion component) from the distortion generation circuit 3, and this third-order distortion component A3 has the same amplitude and opposite phase to the third-order distortion component V3 (the angle θ3 with respect to the linear component V1 is π−). If it is φ3), the combined output V0 coincides with the linear component V1.

4A shows the phase θ3 [deg.] Of the third-order distortion component output from the distortion generation circuit 3. FIG. ] With respect to (horizontal axis), the level of the input signal to the amplifier 5 | with some showing the relationship between P1 (left vertical axis), the output level of difference frequency component | | V1 + A3 V1 + A3 | relationship between ² P2 (Right vertical axis) is shown.
As shown in FIG. 4B, the level of the input signal to the amplifier 5 when the output vector A3 of the distortion generating circuit 3 is added to the linear signal vector V1 by the predistortion circuit is the vector V1 and the vector A3. And the sum | V1 + V3 |. Further, since the difference frequency component to the amplifier 5 is generated from the square term, this input level | V1 + V3 | is squared.

FIG. 4C shows a synthesis result of the linear component V1 and the third-order distortion component A3 from the distortion generation circuit 3 when θ3 = 0 °, and FIG. 4D shows θ3 = 180 °. The combined result of the linear component V1 and the third-order distortion component A3 from the distortion generation circuit 3 when (= π) is shown.
As shown in the figure, under any condition of the output amplitude | A3 | of the distortion generating circuit 3, when the phase of the output of the distortion generating circuit 3 is θ3 = 0 °, the combined result takes the maximum value, and θ3 = Cosine wave characteristic in which the synthesis result takes a minimum value when 180 °. Similarly, since the output difference frequency component is expressed by the square of the input signal, the output difference frequency component also has a cosine wave characteristic.
When θ3 = π−φ3, which is a condition for canceling distortion, is satisfied, the level of the output difference frequency component is expressed as (Equation 1).

Here, in this example, description will be made assuming that the phase φ3 of the third-order distortion component V3 generated in the amplifier 5 is 180 °.
First, the reason will be described. That is, the phase φ3 of the third-order distortion component V3 is determined by the element (basically, although it may be changed by some factor), it is different from the phase that varies with the AM / PM characteristics. Conceivable. The phase φ3 of the third-order distortion component V3 has a direction opposite to that of the linear component V1, that is, a direction that reduces the linear component V1. Note that the phase φ3 of the third-order distortion component V3 generated in all elements is not 180 ° just because it faces in the opposite direction, but it can be applied when it has an angle close to 180 °. Become. Thus, when φ3 = 180 ° is the ideal operating state of the distortion compensation apparatus according to the present example, description will be made on the assumption of this.

In the operation region of the amplifier 5 where the value of the phase φ3 of the third-order distortion component V3 is 180 °, the optimum phase condition of the third-order distortion generation circuit 3 is θ3 = 0 °. Since the level of the output difference frequency component becomes maximum when θ3 = 0 °, the level of the output difference frequency component becomes maximum at the point where the third-order distortion is most compensated.
FIG. 5 shows the phase θ3 [deg.] Of the third-order distortion component output from the distortion generation circuit 3. ] (Horizontal axis) and the relationship P11 (left vertical axis) with the level | A3 + V3 | of the third-order distortion component (IM3) output from the amplifier 5, and the output level of the difference frequency component | A relationship P12 (right vertical axis) with V1 + A3 | ² is shown.
As shown in FIG. 5, the third-order distortion component and the output difference frequency component have a correlation. When φ3 = 180 ° and θ3 = 0 °, the third-order distortion component | A3 + V3 | is minimum, and the difference frequency component | V1 + A3 | ² is maximum.

In the control circuit 12, the phase of the distortion generation circuit 3 (the phase shift by the variable phase shifter 22 is made so that the level of the output difference frequency component notified through the level detection circuit 8 and the A / D converter 9 becomes maximum. The phase condition can be optimized with respect to distortion compensation.
FIG. 6 shows that the phase φ3 of the third-order distortion component V3 generated in the amplifier 5 is shifted from 180 ° (phase deviation) Δφ3 [deg. ] (Horizontal axis) and the amount of distortion cancellation [dB] (vertical axis).
As shown in FIG. 6, for example, even when the phase φ3 of the third-order distortion component V3 generated in the amplifier 5 is shifted from 180 °, the distortion cancellation amount (reduction amount) has changed by 20 °. Even in this case, about 10 dB is ensured, and the effect of distortion compensation is sufficiently obtained in practical use. Further, when the direction in which the phase φ3 deviates from 180 ° is grasped, the direction of the phase θ3 of the third-order distortion component A3 generated by the distortion generation circuit 3 is also grasped. It is possible to improve the performance by shifting to a slightly lower direction in a suitable direction.

Thus, in this example, the level of the difference frequency component indicates whether or not the predistortion A3 generated by the distortion generation circuit 3 is in phase with the linear signal V1. When the phase φ3 of the third-order distortion component V3 generated in the amplifier 3 is 180 °, the optimum phase θ3 of the predistortion A3 is 0 °, and the distortion is most canceled when it is in phase with the linear signal V1. You can take a lot.
Therefore, if it is known from the difference frequency component whether or not the predistortion A3 and the linear signal V1 are in phase, it can be determined whether or not the phase condition is such that the maximum amount of distortion cancellation can be obtained.

The control circuit 12 of this example optimizes the amplitude condition after optimizing the phase condition regarding distortion compensation as described above.
In this example, when the magnitude | V3 | of the third-order distortion component V3 generated by the amplifier 5 and the magnitude | A3 | of the third-order distortion component A3 generated by the distortion generation circuit 3 match, the distortion compensation effect is obtained. This is the maximum, and this is the appropriate (optimal) case.
FIG. 7A shows the case where the amplitude of the output (third-order distortion component) of the distortion generation circuit 3 is smaller than the appropriate value, the linear component V1 and the third-order distortion component V3 in the amplifier 5 and the distortion generation circuit 3. A state in which the synthesized output V0 is obtained by synthesizing the third-order distortion component A3 is shown. The horizontal axis indicates the output amplitude.
7B shows a case where the amplitude of the output (third-order distortion component) of the distortion generation circuit 3 is larger than an appropriate value, the linear component V1, the third-order distortion component V3 in the amplifier 5, and the distortion generation circuit 3. A state in which the synthesized output V0 is obtained by synthesizing the third-order distortion component A3 is shown. The horizontal axis indicates the output amplitude.
FIG. 7 (c) shows a case where the amplitude of the output (third-order distortion component) of the distortion generation circuit 3 matches an appropriate value with the linear component V 1, the third-order distortion component V 3 in the amplifier 5, and the distortion generation circuit 3. The third order distortion component A3 is synthesized to obtain a synthesized output V0. The horizontal axis indicates the output amplitude.

As shown in FIG. 7A, when the amplitude of the output A3 of the distortion generation circuit 3 is smaller than the optimum condition, the amplitude of the synthesized output V0 is smaller than the amplitude of the synthesized output under the optimum condition. End up. As shown in FIG. 7B, when the amplitude of the output A3 of the distortion generation circuit 3 is larger than the optimum condition, the amplitude of the synthesized output V0 is compared with the amplitude of the synthesized output under the optimum condition. It gets too big.
On the other hand, as shown in FIG. 7C, when the amplitude of the output A3 of the distortion generating circuit 3 is an appropriate value, the output of the amplifier 5 is distorted or influenced by the output of the distortion generating circuit 3. Without being received, it is output with the original gain of the amplifier 5.

The control circuit 12 detects the output gain based on the output level notified through the output level detection circuit 10 and the A / D converter 11, and distorts the detected gain to an appropriate value. By adjusting the amplitude of the generating circuit 3 (attenuation amount by the variable attenuator 23), the amplitude condition can be optimized with respect to distortion compensation. The appropriate gain value may be set in advance in the distortion compensator, or may be automatically detected by the distortion compensator.
Here, in this example, the phase data and the amplitude data are calculated by the control circuit 12, but as another configuration example, optimal control is performed for the data of the difference frequency component or the gain data in the control circuit 12 or the like. In this configuration, phase data or amplitude data is stored in a memory table, and the control circuit 12 reads a value corresponding to the detected value from the table to control the variable phase shifter 22 or the variable attenuator 23. It can also be used.

Further, in this example, the variable attenuator 23 is provided at the subsequent stage of the variable phase shifter 22, but these may be provided in the reverse order.
Further, control for maximizing the level of the difference frequency component input to the control circuit 12 via the level detection circuit 8 and the A / D converter 9, and via the output level detection circuit 10 and the A / D converter 11. In the control in which the gain based on the output level input to the control circuit 12 is a specified value, the control does not necessarily have to be performed with a strict value, and even if there is some error as long as it is practically effective. Good.

As described above, in this example, in the distortion compensation apparatus of the predistortion compensation system that reduces the nonlinear distortion generated when the amplifier 5 amplifies a signal composed of a plurality of frequency components and linear modulation components, Generated in the distortion generator 21 and the distortion generator 21 that generate distortion corresponding to each order (in this example, the third order, but can be implemented for one or a plurality of arbitrary orders). A non-linear circuit having a vector adjuster (in this example, variable phase shifter 22 and variable attenuator 23) that independently controls the phase and amplitude of the distortion is provided in parallel with the linear circuit. Then, the level of the difference frequency component output from the amplifier 5 is detected, and the level (for example, power) of the distortion component output from the amplifier 5 is estimated based on the detected value. The vector adjuster (in this example, the variable phase shifter 22 and the variable attenuator 23) is adjusted according to the detected value of the difference frequency component level.
Specifically, in the distortion compensator of this example, the predistortion (third-order distortion in this example) is calculated based on the detected value of the level of the difference frequency component (even-order distortion) included in the output from the amplifier 5. As a control mode, the distortion phase is controlled so that the level of the difference frequency component is maximized, the gain of the linear component is detected, and the amplitude of the distortion is adjusted so that the gain of the linear component becomes a specified value. To control.

  Therefore, in the circuit configuration and control method of the distortion compensation apparatus of this example, the level of the difference frequency component output from the compensated amplifier 5 is detected, and the level of the distortion component output from the amplifier 5 is determined according to the level. A circuit for controlling distortion compensation is simplified by a configuration that estimates and adjusts the vector adjuster (in this example, the variable phase shifter 22 and the variable attenuator 23) according to the level of the difference frequency component. Therefore, a high distortion compensation amount can be realized by a stable control with a simple configuration.

  In the distortion compensator of this example, the predistortion generating means is configured by the function of the third-order distortion generator 21, and the predistortion phase changing means is configured by the function of the variable phase shifter 22. The function of the variable attenuator 23 constitutes the amplitude change means of the predistortion, and the function of the synthesizer 4 constitutes the synthesizing means for synthesizing the predistortion and the input signal. Component detection means for detecting the level of the difference frequency component is configured by the functions of the level detection circuit 8 and the A / D converter 9, and the functions of the distributor 7, the output level detection circuit 10 and the A / D converter 11 are used. Output detecting means for detecting the output level is configured, and control means for controlling distortion compensation by the function of the control circuit 12 for controlling the variable phase shifter 22 and the variable attenuator 23 based on the detection results is configured. Has beenIn this example, the amplifier 5 constitutes an amplifier (compensated amplifier) that is a distortion compensation target.

Next, the third-order distortion generator will be described in detail.
(1) The basic principle of complex synthesis predistortion (cuber predistortion) will be described.
Non-linearity (AM / AM conversion, AM / PM conversion) of the microwave amplifier causes intermodulation distortion. Cuber predistortion (CPD) is a technique for compensating for these distortions using a third-order distortion generator having complex coefficients.
As a means for analyzing the nonlinear system, a power series, a Volterra series, or the like is used. In this example, a model that is a complex power series that is simplified and easy to handle is used. This model removes even-order terms and expresses input / output characteristics with only odd-order terms by considering that the amplifier has a band-pass characteristic that allows only signals near the fundamental frequency band to pass. Also, assuming a complex power series, it is necessary for the input and output to have uniform convergence (characteristic that the nonlinear distortion converges to zero as the input signal becomes smaller), so class A or AB close to class A Application is possible for a class of amplifiers.

The output voltage e _{O of the} amplifier using such a complex power series is expressed as (Equation 2).
Here, e _i represents the input voltage, Δt represents the delay of the amplifier, A _n (vector) represents the complex coefficient of each order term, and H [e _i ⁿ (t)] represents e _i ⁿ (t). Represents the Hilbert transform of. N is an odd number.

As for (Expression 2), when a single tone e _i = a · cos ω ₀ t is given, the output is expressed as (Expression 3). Here, a represents the amplitude of the signal.

  In (Expression 3), R (a) and Ψ (a) represent AM / AM conversion and AM / PM conversion, respectively, and are expressed as (Expression 4) and (Expression 5), respectively.

By transforming (Equation 4) and (Equation 5), (Equation 6) relating AM / AM conversion and AM / PM conversion is obtained.
Here, the terms of the fifth order or higher of a are expressed by an expression approximated to the third order (ignoring the fifth and subsequent orders) on the assumption that the influence on distortion is small.

In FIG. 9, (expression 6) relating AM / AM conversion and AM / PM conversion is expressed in a vector form. The linear component V1, the third-order distortion component V3, and the output signal V0 each represent a vector.
The third-order distortion component V3 is a third-order term in (Expression 4), and represents a third-order distortion component having a fixed phase φ3 with respect to the linear component V1.
Since the third-order distortion component V3 can be ignored while the input level is small, the output is not different from the linear component V1, but when the input level increases, the third-order distortion component V3 is the cube of the input amplitude. The output V0, which is a rapid increase and is a combination of the linear component V1 and the third-order distortion component V3, decreases from the output of only the linear component V1 (AM / AM conversion), and a phase change occurs with respect to the linear component V1 (AM / AM). PM conversion).

In order to bring the output V0 close to linear, the third-order distortion component V3 may be made as small as possible.
In CPD, based on these ideas, a distortion generator that generates a distortion component having the same amplitude and antiphase as the third-order distortion component V3 is inserted in the previous stage to cancel out the distortion component generated by the amplifier. To compensate.

(2) A circuit configuration of the CPD will be described.
FIG. 10 shows an example of a basic circuit configuration of the CPD.
An input signal is distributed by a distributor (DIV) 41 into a main signal path and a third-order distortion generation path.
In the main signal path, the distributed signal is delayed by the delay line 42 and input to the combiner (COM) 47. In the third-order distortion generation path, the distributed signal is converted into a third-order distortion signal by the third-order distortion generator 43, the third-order distortion signal is amplified by the amplifier 44, and the amplitude of the amplified signal is adjusted by the variable attenuator 45. The phase of the amplified signal is adjusted by the variable phase shifter 46, and these adjusted signals are input to the synthesizer 47.
The synthesizer 47 synthesizes the signal from the main signal path (main signal) and the signal from the third-order distortion generation path (distortion component), and outputs the resultant signal. The output signal from the synthesizer 47 becomes the input of the compensated amplifier.

(3) A circuit that generates third-order distortion will be described.
In the third-order distortion generator, for example, a distortion component is created by using a non-linear characteristic of the diode (characteristic that the VI characteristic is an exponential function).
Nonlinear characteristics in the case of a single diode are expressed as (Equation 7).

In the case of (Expression 7), even-order distortion occurs in addition to odd-order distortion.
Therefore, as a method for suppressing this, there is a configuration of an anti-parallel type diode in which the diodes are connected in antiparallel. In the configuration of the anti-parallel diode, the VI characteristic is an odd function, in which a single configuration characteristic and a point-symmetric curve are connected to the original single configuration characteristic.
The characteristic of the anti-parallel diode is expressed as (Equation 8), and the occurrence of even-order distortion can be suppressed.
When this is used as a third-order distortion generator, a third-order distortion is generated by biasing each anti-parallel diode and lowering the rising voltage to approximate the third power characteristic. .

FIG. 11 shows a configuration example of the circuit of the third-order distortion generator.
In this configuration, in order to realize the characteristics necessary for the third-order distortion generator, only the third-order distortion is output from the fundamental wave input by suppressing the fundamental wave component output simultaneously with the distortion.
Specifically, the third-order distortion generator of this example includes a branch-line coupler 51, a third-order distortion generation circuit composed of an anti-parallel type diode in which two diodes 52 and 53 are connected in antiparallel, a resistor 54, A fundamental wave canceling circuit using a capacitor 55 is used.
An input terminal (input) for inputting a signal is connected to the in port of the coupler 51, an output terminal (output) for outputting a signal is connected to the iso port of the coupler 51, and the third order is connected to the out port of the coupler 51. A distortion generation circuit is connected, and a fundamental wave cancellation circuit is connected to the cpl port of the coupler 51.

  In the third-order distortion generator of this example, the fundamental wave component that has entered from the input terminal (input) is distributed by the coupler 51 to the out port and the cpl port. In the third-order distortion generation circuit, the fundamental wave component and the third-order distortion component are reflected to the in port and the iso port with a certain amplitude and phase according to the input fundamental wave component. In the fundamental wave canceling circuit, the inputted fundamental wave component is reflected to the in port and the iso port with a certain amplitude and phase. In this regard, when the fundamental wave component reflected from the third-order distortion generation circuit and the fundamental wave component reflected from the fundamental wave cancellation circuit are adjusted so as to have the same amplitude and opposite phase, the fundamental wave component is suppressed, and distortion is reduced. Only the components can be removed.

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 distortion compensation apparatus which concerns on one Example of this invention. It is a figure which shows an example of the output spectrum of an amplifier. It is a figure for demonstrating the principle of distortion compensation using a vector. It is a figure for demonstrating the relationship between the output phase of a distortion generation circuit, the input signal level to an amplifier, and the output level of a difference frequency component. It is a figure for demonstrating the relationship between the output level of a difference frequency component, and the output level of a tertiary distortion component. It is a figure which shows an example of the change of the distortion cancellation amount by the shift | offset | difference of the phase of a tertiary distortion. It is a figure for demonstrating the difference of the synthetic | combination output by the amplitude condition of the output of a distortion generation circuit. It is a figure which shows the structural example of a distortion compensation apparatus. It is a figure for demonstrating AM / AM conversion and AM / PM conversion using a vector. It is a figure which shows the structural example of a cue bar predistorter. It is a figure which shows the structural example of a tertiary distortion generator.

Explanation of symbols

  1, 6, 7, 31, 41,... Distributor, 2, 42 .. delay line, 3 .. distortion generation circuit 4 .. synthesizer 5, 44. , 11, 36... A / D converter, 10.. Output level detection circuit, 12, 37... Control circuit, 21, 43... Third order distortion generator, 22, 46. 45, Variable attenuator, 32, Oscillator, 33, Synchronous circuit, 34, Multiplier, 35, Detection circuit, 51, Coupler, 52, 53, Diode, 54, Resistor, 55・ Capacitor,

Claims (3)

In a distortion compensation device that compensates for distortion generated in an amplifier,
Generating means for generating predistortion;
Phase changing means for changing the phase of the predistortion generated by the generating means;
Amplitude changing means for changing the amplitude of the predistortion generated by the generating means;
Combining means for combining the predistorted signal processed by the phase changing means and the amplitude changing means and an input signal to be amplified by the amplifier, and outputting the resultant signal to the amplifier;
Component detection means for detecting the level of the difference frequency component of the input signal based on the amplified signal output from the amplifier;
Output detection means for detecting an output level based on the amplified signal output from the amplifier;
Control means for controlling the phase change by the phase change means based on the detection result by the component detection means and for controlling the amplitude change by the amplitude change means based on the detection result by the output detection means;
A distortion compensation apparatus comprising: The distortion compensation apparatus according to claim 1,
The control means controls the phase change by the phase change means so that the level of the difference frequency component detected by the component detection means becomes large, and the gain based on the detection result by the output detection means becomes a specified value. So as to control the amplitude change by the amplitude changing means,
A distortion compensation apparatus characterized by the above. The distortion compensation apparatus according to claim 1 or 2,
The component detection means detects a level of the difference frequency component from the amplified signal output from the amplifier, and an A / D for converting a detection result by the level detection circuit from an analog signal to a digital signal. Configured with a converter,
The output detection means includes an output level detection circuit for detecting the output level from the amplified signal output from the amplifier, and an A / D conversion for converting a detection result by the output level detection circuit from an analog signal to a digital signal. Configured with a container,
A distortion compensation apparatus characterized by the above.

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