JP4637331B2 - Nonlinear distortion compensation circuit and nonlinear distortion compensation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an orthogonal modulation circuit used in a radio transmitter or the like, and more particularly to a nonlinear distortion compensation circuit and a nonlinear distortion compensation method for compensating for nonlinear distortion that occurs when a baseband signal is subjected to orthogonal modulation and then subjected to high power amplification.
[0002]
[Prior art]
Conventionally, in quadrature modulation circuits, the baseband signal is quadrature modulated, and then the modulated signal is amplified with high power. At this time, nonlinear amplification is performed to improve power efficiency, and nonlinear distortion is generated in the amplified modulated signal. Therefore, the input / output characteristics are linearized by compensating for the generated distortion. As a conventional method for compensating for such nonlinear distortion, there is a predistortion type nonlinear distortion compensation system as shown in FIG.
[0003]
In FIG. 7, the baseband signals I and Q pass through the distortion compensation calculation unit 1 and are input to the D / A converter 2 and the D / A converter 3, where they are converted into analog signals and input to the orthogonal transformer 4. . The baseband signals I and Q input to the quadrature converter 4 are quadrature-modulated, further amplified by a high power amplifier (HPA) 5 and output.
[0004]
Here, the compensation data table 7 stores compensation data created using a result obtained by measuring in advance the nonlinear characteristics during amplification of the high power amplifier 5 in a table. The power calculator 6 calculates the power of the baseband signals I and Q and outputs the obtained power to the compensation data table 7. The compensation data table 7 refers to the table according to the power of the baseband signals I and Q, reads the corresponding compensation data, and outputs it to the distortion compensation calculation unit 1.
[0005]
As a result, the distortion compensation calculation unit 1 adds in advance a distortion having an inverse characteristic that cancels the nonlinear distortion generated in the high-power amplifier 4 to the input baseband signals I and Q before the orthogonal modulation, and the D / A converter Output to 2 and 3. For this reason, the modulation signal amplified with high power by the high power amplifier 5 does not include nonlinear distortion.
[0006]
[Problems to be solved by the invention]
In the above-described conventional predistortion type non-linear distortion compensation method, the compensation data table is referred to according to the power of the baseband signal, so that the entire circuit is affected by variations in characteristics of the high power amplifier 5 and temperature changes. There was a drawback that the performance was likely to deteriorate.
[0007]
Therefore, as shown in FIG. 8, the output of the high power amplifier 5 is branched by the directional coupler 8, and the branched output signal is quadrature demodulated by the quadrature demodulator 9, and then fed back to the compensation data calculation unit 10. There is a circuit. The compensation data calculation unit 10 of this circuit multiplies the data of the built-in compensation data table (the same as 7 in FIG. 1) by a coefficient corresponding to the feedback table information to correct the characteristics, and thereby the characteristics of the high power amplifier 5 Regardless of the variation and the temperature change, highly accurate compensation data is output to the distortion compensation calculation unit 1 to reduce the influence of the above-mentioned defects.
[0008]
However, since any of the above circuits generates and uses pseudo-nonlinear distortion, the above disadvantages are not sufficiently solved, and neither of the above circuits performs complicated digital operations. As a result, the circuit scale becomes large, resulting in an increase in power consumption, and there is a problem that the operation time is shortened particularly in a transmitter using a battery as a power source.
[0009]
The present invention has been made to solve the above-described conventional problems, and its purpose is to accurately compensate for nonlinear distortion caused by high power amplification even if the characteristics of the high power amplifier fluctuate. A nonlinear distortion compensation method and a nonlinear distortion compensation circuit capable of compensating for nonlinear distortion generated by high power amplification without using a complicated and large-scale digital arithmetic circuit or pseudo distortion generation circuit, and reducing power consumption Is to provide.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a feature of the invention of claim 1 is that a non-linear high-power amplifier that compensates for non-linear distortion generated when performing non-linear high-power amplification in a transmitter that performs non-linear high-power amplification after orthogonally modulating a baseband signal. In the distortion compensation circuit, a distortion extraction unit that extracts a nonlinear distortion component from the nonlinear high-power amplified modulated signal, and a carrier that is used to orthogonally demodulate the distortion component extracted from the distortion extraction unit and convert it into a baseband region A phase adjuster that adjusts a phase; a quadrature demodulator that orthogonally demodulates a distortion component extracted from the distortion extractor to a baseband region using the phase-adjusted carrier; and a baseband region that is output from the quadrature demodulator of a distortion superimposing section opposite phase distortion components of the distortion component superimposed on the baseband signal, comprising a, the distortion extracting unit, leaving the nonlinear high An attenuator that attenuates the amplified modulation signal by the amount of non-linear high-power amplification, a phase shifter that shifts the phase of the modulation signal before non-linear high-power amplification, and the phase shifter from the output signal of the attenuator And a subtractor for subtracting the modulation signal whose phase is shifted by the above.
[0012]
According to a second aspect of the present invention, the distortion superimposing unit includes an amplitude adjuster for adjusting an amplitude level of a distortion component in the baseband region output from the quadrature demodulating unit, and a baseband region whose amplitude is adjusted by the amplitude adjuster. And a subtractor for subtracting the distortion component of the baseband signal from the baseband signal.
[0013]
A feature of the invention of claim 3 resides in that the carrier used for orthogonal demodulation of the distortion component extracted from the distortion extraction unit is generated separately from the carrier used for orthogonal modulation of the baseband signal.
[0014]
According to a fourth aspect of the present invention, there is provided a nonlinear distortion compensation method for compensating for nonlinear distortion generated when the nonlinear high-power amplification is performed by a transmitter that performs nonlinear high-power amplification after orthogonally modulating a baseband signal. Extracting a nonlinear distortion component from the output amplified modulation signal; adjusting a phase of a carrier used to orthogonally demodulate the extracted distortion component to convert it into a baseband region; and extracting the extracted distortion component comprising the steps of orthogonal demodulation to the baseband region using the phase adjusted carrier, and a step of superimposing the antiphase distortion components of the distortion component in the baseband region are generated is the orthogonal demodulation to the baseband signal The step of extracting the non-linear distortion component is the non-linear high-power amplification of the non-linear high-power amplified modulation signal. Attenuating step for attenuating only, a phase shifting step for shifting the phase of the modulation signal before nonlinear high-power amplification, and a subtraction for subtracting the modulation signal whose phase is shifted by the phase shifting step from the output signal of the attenuation step And a step.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a nonlinear distortion compensation circuit according to the first embodiment of the present invention. This circuit includes a quadrature modulator 11, a directional coupler or distributor 12, a high power amplifier (HPA) 13, a directional coupler or distributor 14, an attenuator 15, a subtractor 16, a delay circuit or phase shifter 17. , A quadrature demodulator 18, a phase adjuster 19, a carrier generator 20, amplitude adjusters 21 and 22, and subtractors 23 and 24.
[0016]
The quadrature modulation unit 11 includes a π / 2 phase shifter 111, multipliers 112 and 113, and an adder 114, and the quadrature demodulation unit 18 includes a π / 2 phase shifter 181 and multipliers 182 and 183. . The attenuator 15, delay circuit or phase shifter 17, subtractor 16, quadrature demodulator 18, phase adjuster 19, amplitude adjusters 21 and 22, and subtractors 23 and 24 are the nonlinear distortion compensation circuit of the present invention. It is composed.
[0017]
Next, the operation of this embodiment will be described. The baseband signals I and Q are input to the quadrature modulation unit 11 after distortion components described later are subtracted by subtracters 23 and 24, respectively. In the quadrature modulation unit 11, the carrier generated by the carrier generator 20 and phase-shifted by π / 2 by the π / 2 phase shifter 111 and the baseband signal Q are multiplied by the multiplier 112 and then input to the adder 114. The The baseband signal I is multiplied by the carrier generated by the carrier generator 20 and the multiplier 113, and then input to the adder 114. The baseband signal I is added to the output signal of the multiplier 112 and is orthogonally modulated. The signal is input to the high power amplifier 13 through the directional coupler or distributor 12.
[0018]
The high power amplifier 13 performs nonlinear high power amplification (gain K) on the quadrature modulation signal and outputs the amplified signal through a directional coupler or distributor 14. The output signal branched by the directional coupler or distributor 14 is input to the attenuator 15, attenuated (1 / K) by the amplification gain of the high power amplifier 13, and input to the subtractor 16. The subtractor 16 subtracts the distortion-free quadrature modulation signal branched by the directional coupler or distributor 12 from the signal including the nonlinear distortion output from the high power amplifier 13 and extracts only the nonlinear amplification distortion component. Is done.
[0019]
The nonlinear amplification distortion component is generated by the carrier generator 20 and further multiplied by the carrier j whose phase is adjusted by the phase adjuster 19 and the multiplier 182. The phase-shifted carrier k is multiplied by the multiplier 183 and demodulated, and the distortion components h and i in the baseband region are input to the amplitude adjusters 21 and 22. The distortion components in the baseband region whose amplitude has been adjusted by the amplitude adjusters 21 and 22 are input to the subtracters 23 and 24.
[0020]
Therefore, in the subtractor 23, the baseband signal I on which the inverse distortion component is superimposed is input to the quadrature modulation unit 11 by subtracting in advance the distortion component that will be generated in the high power amplifier 13 from the baseband signal I. The In the subtractor 24, the baseband signal Q on which the inverse distortion component is superimposed is input to the quadrature modulation unit 11 by subtracting in advance the distortion component that will be generated in the high power amplifier 13 from the baseband signal Q.
[0021]
That is, the subtracters 23 and 24 have reverse distortion characteristics (characteristics for canceling nonlinear distortion components generated during high power amplification) in the baseband region generated by orthogonal demodulation of the distortion components extracted by the subtractor 16. It can be said that a distortion component is superimposed on the baseband signal. Accordingly, after the baseband signal on which the reverse distortion component is superimposed is orthogonally modulated by the orthogonal modulation unit 11, the nonlinear distortion that occurs when nonlinear high power amplification is performed by the high power amplifier 13 is canceled.
[0022]
Here, the principle of the above-described nonlinear distortion compensation will be described. First, the distortion component g extracted by the subtractor 16 is normally phase-adjusted before quadrature demodulation and then quadrature demodulated and converted into a baseband band (there is no phase adjuster 19). First, this configuration will be described. The nonlinear distortion component extracted by the subtracter 16 is A · e ^{j ( φ + α )} (A is the amplitude, φ is the phase when distortion is completely compensated, and α is the phase shift to be adjusted). , If the operation performed by the phase adjuster is multiplication of e ^{−j α} (that is, the phase is shifted by α [rad]), the distortion component after the phase adjustment is
A · e ^{j ( φ + α )} · e ^{−j α} = A · e ^{j φ} (1)
It becomes. If the output of the carrier generator 20 is cos θ, in this case, since there is no phase adjuster 19, the carriers input to the multipliers 182 and 183 are
cos θ and sin θ (for simplicity, the amplitude is 1) (2)
Therefore, when (1) is orthogonally demodulated using these, the output signals of the multipliers 182 and 183 are as follows.
[0024]
A ・ e ^{j φ}・ cos θ (3)
A ・ e ^{j φ}・ sinθ (4)
It becomes.
[0025]
Next, nonlinear distortion compensation in the configuration of the present embodiment shown in FIG. 1 will be described. In FIG. 1, similarly, the distortion component at the point g is A · e ^{j ( φ + α )} . The carrier signal (j point, k point) when this is orthogonally demodulated is because the signal at point e is cos θ and the operation of phase adjuster 19 is “multiplication of e ^{−j α} ”.
The j point is e ^{−j α} · cos θ, the k point is e ^{−j α} · sin θ (5)
It becomes. Therefore, the signals (h point, i point) after quadrature demodulation are as follows.
[0026]
The point h is A · e ^{j ( φ + α )} · e ^{−j α} · cos θ = A · e ^{j φ} · cos ^φ (6)
The point i is A · e ^{j ( φ + α )} · e ^{−j α} · sin θ = A · e ^{j φ} · sin φ (7)
[0027]
Therefore, as can be seen by comparing (3) and (6) and (4) and (7), the signal after quadrature demodulation is the same as the configuration for phase adjustment before quadrature demodulation, and equivalent phase adjustment Can do.
[0028]
FIG. 2 is a flowchart showing a processing procedure according to an embodiment of the distortion compensation method of the present invention. First, in step 201, a nonlinear distortion component is extracted from the nonlinear high-power amplified modulated signal. In step 202, the phase of the carrier used for quadrature demodulation of the extracted distortion component is extracted. In step 203, extraction is performed. The obtained distortion component is orthogonally demodulated and converted into a distortion component in the baseband region. Next, in step 204, the distortion component of the inverse distortion characteristic in the baseband region (characteristic for canceling the nonlinear distortion generated when nonlinear high-power amplification is performed) is superimposed on the baseband signal.
[0029]
FIG. 3 is a characteristic diagram showing an operation confirmation result by computer simulation of the circuit shown in FIG. FIG. 3A shows the waveform of the output signal of the high power amplifier 13 when the nonlinear distortion compensation circuit of the present invention is turned off. FIG. 3B shows the waveform of the output signal of the high power amplifier 13 when the nonlinear distortion compensation circuit of the present invention is turned on. When the distortion is compensated by the nonlinear distortion compensation circuit, an effect of 14 to 16 dB is seen as an improvement rate of the adjacent channel power ratio (ACPR).
[0030]
Furthermore, as can be seen by referring to the ACPR vs. input level characteristic shown in FIG. 4, when the nonlinear distortion compensation circuit is turned on, if the phase and amplitude are adjusted to optimum values in the maximum output state, the output below that Since ACPR does not deteriorate further at the level, dynamic control such as an adaptive circuit is not necessary, and thereafter there is an effect that it can be used without adjustment.
[0031]
According to the present embodiment, the distortion generated in the high power amplifier 13 is converted into the distortion in the baseband region and then fed back to the baseband signal, so that a complicated and large-scale digital arithmetic circuit, pseudo distortion generation circuit, or the like can be obtained. Non-linear distortion caused by high power amplification without using it can be compensated. In addition, since the circuit scale is reduced, power consumption can be reduced. For this reason, when the quadrature modulation circuit of this example is used for a transmitter such as a mobile phone using a battery as a power source, there is an effect that the operation time is prolonged.
[0032]
Further, this example employs a configuration in which the phase of the carrier of the quadrature demodulator 18 is adjusted by the phase adjuster 19, and the phase adjuster 19 only needs to adjust the phase of the carrier signal having a single frequency. As shown in FIGS. 5A to 5F, the phase adjuster can be easily configured using a variable capacitor and an inductor (or a variable inductor) as well as the phase shifter, and the circuit scale can be further reduced. Can be configured at low cost.
[0033]
FIG. 6 is a circuit diagram showing a configuration of a nonlinear distortion compensation circuit according to the second embodiment of the present invention. In the present embodiment, a carrier generator 25 for a quadrature demodulation carrier is provided separately from the carrier generator 20, and the phase of the output signal of the carrier generator 25 is adjusted by the phase adjuster 19. The same operation and effect as the embodiment shown in FIG.
[0034]
The present invention is not limited to the above-described embodiment, and can be implemented in various other forms in specific configurations, functions, operations, and effects without departing from the scope of the invention. A phase adjuster that adjusts the phase of the carrier for orthogonally demodulating the distortion can be made simple and inexpensive.
[0035]
【The invention's effect】
As described above in detail, according to the present invention, since distortion that has actually occurred is fed back, nonlinear distortion due to high power amplification can be compensated more accurately, and complex and large-scale digital Non-linear distortion due to high power amplification can be compensated without using an arithmetic circuit, a pseudo-distortion generation circuit, etc., and power consumption can be reduced, and the phase of the carrier for orthogonal demodulation of distortion can be reduced. The phase adjuster to be adjusted can be made simple and inexpensive.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a nonlinear distortion compensation circuit according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing a processing procedure according to an embodiment of the distortion compensation method of the present invention.
FIG. 3 is a characteristic diagram showing an operation confirmation result by computer simulation of the circuit shown in FIG. 1;
4 is a characteristic diagram showing a relationship between ACPR and input level of the circuit shown in FIG. 1; FIG.
5 is a circuit diagram showing a specific configuration example of the phase adjuster shown in FIG. 1. FIG.
FIG. 6 is a circuit diagram showing a configuration of a nonlinear distortion compensation circuit according to a second embodiment of the present invention.
FIG. 7 is a circuit diagram showing a configuration example of a transmitter equipped with a conventional nonlinear distortion compensation circuit.
FIG. 8 is a circuit diagram showing another configuration example of a transmitter equipped with a conventional nonlinear distortion compensation circuit.
[Explanation of symbols]
11 Quadrature Modulation Units 12, 14 Directional Coupler or Divider 13 HPA (High Power Amplifier)
15 Attenuator 16, 23, 24 Subtractor 17 Delay circuit or phase shifter 18 Quadrature demodulator 19 Phase adjuster 20, 25 Carrier generator 21, 22 Amplitude adjuster 111, 181 π / 2 phase shifter 114 Adder 112 113, 182, 183 Multiplier

Claims (4)

In a non-linear distortion compensation circuit that compensates for non-linear distortion that occurs when performing non-linear high-power amplification in a transmitter that performs non-linear high-power amplification after orthogonally modulating a baseband signal,
A distortion extractor that extracts a nonlinear distortion component from the nonlinear high-power amplified modulated signal;
A phase adjuster that adjusts the phase of the carrier used to orthogonally demodulate the distortion component extracted from the distortion extraction unit and convert it into a baseband region;
An orthogonal demodulation unit that orthogonally demodulates a distortion component extracted from the distortion extraction unit to a baseband region using the phase-adjusted carrier;
A distortion superimposing unit that superimposes a distortion component having an opposite phase to the distortion component of the baseband region output from the quadrature demodulation unit on the baseband signal ,
The distortion extraction unit includes an attenuator that attenuates the nonlinear high-power amplified modulation signal by the amount of nonlinear high-power amplification, a phase shifter that shifts the phase of the modulation signal before nonlinear high-power amplification, A non-linear distortion compensation circuit comprising: a subtractor that subtracts a modulation signal whose phase is shifted by the phase shifter from an output signal of an attenuator . The distortion superimposing unit adjusts the amplitude level of the distortion component of the baseband region output from the quadrature demodulation unit, and the baseband region distortion component adjusted by the amplitude adjuster. nonlinear distortion compensating circuit according to claim 1 Symbol mounting and having a subtractor for subtracting from the baseband signal. 3. The non-linearity according to claim 1, wherein the carrier used for quadrature demodulation of the distortion component extracted from the distortion extraction unit is generated separately from the carrier used for quadrature modulation of the baseband signal. Distortion compensation circuit. In a non-linear distortion compensation method for compensating for non-linear distortion that occurs when performing non-linear high-power amplification in a transmitter that performs non-linear high-power amplification after orthogonally modulating a baseband signal,
Extracting a nonlinear distortion component from the nonlinear high-power amplified modulated signal; adjusting a phase of a carrier used for orthogonally demodulating the extracted distortion component and converting it to a baseband region;
Orthogonally demodulating the extracted distortion component into a baseband region using the phase adjusted carrier;
Superimposing an antiphase distortion component of the baseband domain distortion component generated by the orthogonal demodulation to the baseband signal;
Equipped with,
The step of extracting the non-linear distortion component includes an attenuation step of attenuating the modulated signal amplified by the nonlinear high output by an amount corresponding to the nonlinear high output amplification, and a phase shift for shifting the phase of the modulated signal before the nonlinear high output amplification. And a subtracting step of subtracting the modulation signal whose phase is shifted by the phase shifting step from the output signal of the attenuation step .

Images