JP2003152458A - Adaptive predistortion type distortion compensation power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion compensation power amplifier that can accurately compensate distortion and is extremely practical even if a system frequency is in a wide band, in an adaptive predistortion system distortion compensation power amplifier used for a linear transmitter or the like of a radio communication apparatus. SOLUTION: The distortion compensation power amplifier includes a detector 206 for detecting the envelope level of an inputted transmission IF signal, a control signal generation section 207 for selecting preset distortion compensation data corresponding to the detected level for transmitting to an amplitude/phase modulator (predistortion compensation section) 204, and an IF/RF frequency converter 203 for converting the frequency of the transmission IF signal to that of an RF signal. The IF/RF frequency converter 203 is arranged at the prestage of the amplitude/phase modulator (predistortion compensation section) 204.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distortion compensating power amplifier used for a linear transmitter of a wireless communication device, and more particularly to an adaptive predistortion type distortion compensating amplifier.

[0002]

2. Description of the Related Art Conventionally, as a distortion compensation method for compensating the non-linear distortion of a power amplifier used in a linear transmitter or the like, an input signal is distorted in advance so as to cancel the distortion generated in the power amplifier, and the distortion from the power amplifier is distorted. A predistortion method is known in which an output signal without noise is obtained. An example of the prior art of the distortion compensation amplification circuit of the predistortion system is, for example, Japanese Patent No. 2746130. FIG. 6 is a block diagram showing a configuration example of Japanese Patent No. 2746130. The conventional technique will be described below with reference to FIG.

A high frequency signal for transmission (hereinafter referred to as an RF signal) is branched by a directional coupler 101, and a detector 106 is provided.
When the instantaneous value of the envelope level is detected by, the instantaneous value is converted into a digital signal by the A / D converter 5 and supplied to the amplitude / phase control signal generation unit 107. The amplitude / phase control signal generation unit 107 stores amplitude / phase control data for generating a required non-linear characteristic in advance, and converts the amplitude / phase control data corresponding to the input digital value into a D / A converter. Output to 7.

Further, the amplitude / phase modulator 104 is a D / A
The amplitude / phase control signal converted into an analog signal by the converter 7 is input as a modulation signal, and the input RF signal delayed by the delay device 102 for a predetermined time is subjected to amplitude and / or phase modulation. The distortion component added by the amplitude / phase modulator 104 is the amplitude / phase modulator 10
4 is connected to the latter stage. The compensation is controlled so as to cancel the distortion component caused by the non-linearity of the power amplifier.

FIG. 10 is a diagram for explaining the compensation control for the non-linear distortion of the power amplifier, taking the amplitude as an example. Figure 1
As shown in the amplifier characteristic of 0, the gain of the output power is suppressed with respect to the increase of the input power in the amplifier, and the nonlinearity occurs as shown in the figure. On the other hand, centering on the ideal characteristic of FIG. 10 assuming an ideal linear amplifier, a distortion compensation signal such as the amplitude control characteristic of FIG. By superimposing it on the input signal, the distortion component of the amplifier is canceled and the non-linear distortion is compensated. The same control is performed for the phase distortion compensation control.

Next, another example in which the envelope level is detected by a transmission intermediate frequency signal (hereinafter referred to as an IF signal) will be described with reference to FIG. The input transmission IF signal is branched by the directional coupler 101, and when the detector 106 detects the instantaneous value of the envelope level, the instantaneous value is converted into a digital value by the amplitude / phase control signal generator 107. To be done. The amplitude / phase control signal generation unit 107 stores amplitude / phase control data for generating a required nonlinear characteristic in advance, and outputs the amplitude / phase control data corresponding to the input digital value as an analog signal. Further, the amplitude / phase modulator 104 inputs the amplitude / phase control signal as a modulation signal and performs amplitude and / or phase modulation on the input IF signal delayed by the delay device 102 for a predetermined time.

Next, referring to FIG. 11, distortion suppression (distortion compensation)
Will be described. In FIG. 11A, the frequency is on the horizontal axis,
For example, a signal in which a distortion component indicated by diagonal lines is superimposed by an amplifier on an OFDM modulated signal having no compensation component is shown. In order to suppress this distortion component, an amplitude / phase modulator is used to create a component that cancels out the distortion component of the vertical line portion shown in b of FIG. 11 and superimposes it on the main signal. The output is obtained by canceling out the distortion components in the shaded area. Figure 11
C indicates a signal in which a component for suppressing distortion is superimposed by the amplitude / phase modulator input to the amplifier. With such a configuration, after generating an output IF signal having a nonlinear characteristic with respect to the input IF signal, the IF / RF frequency converter 103 frequency-converts the RF signal into the RF signal, and the signal is input to the amplifier 105 to generate the nonlinear distortion. To generate an output RF signal.

[0008]

However, in the above-mentioned conventional technique, in the configuration in which the envelope level of the input RF signal is detected by the wave detector as shown in FIG. 6, the wave detector also has a frequency characteristic. For example, when applied to a communication system in which the system frequency (RF frequency) is extremely wide band such as a terrestrial digital broadcasting system (for example,
470 MHz to 770 MHz: 6 MHz / channel), depending on the RF frequency of the channel used,
There was the annoyance that the detector had to be adjusted.

Further, as shown in FIG. 9, even in a configuration in which the envelope level of the input IF signal is detected, this signal is used in the band limiting filter in the IF / RF frequency converter for frequency converting the IF signal into the RF signal. Since it is necessary to pass the signal on which the distortion compensation signal is superimposed, it is necessary to use a band-limited filter having an extremely wide pass band, which cannot be put to practical use.

In view of the above situation, the present invention has been made to solve the above problems, and is capable of highly accurate distortion compensation even when the system frequency is wide band, and is a practical distortion compensation power. The purpose is to provide an amplifier.

[0011]

In order to achieve the above-mentioned object, the present invention has a predistortion compensator for superimposing a distortion compensation signal for compensating the non-linear distortion of the power amplifier on the input signal of the power amplifier. In a predistortion type distortion compensating power amplifier, an IF that performs detection of an input level of a transmission signal with an intermediate frequency signal (IF signal) and frequency conversion from the transmission intermediate frequency signal (IF signal) to a high frequency signal (RF signal) The / RF frequency converter is arranged before the predistortion compensator.

As a result, even if the system frequency (RF) of the applied communication system is extremely wide band, the transmission intermediate frequency (IF) of the transmitter can be composed of a single frequency or a narrow band, so that the transmission input signal The troublesomeness of adjusting the detector for detecting the level can be eliminated, and the distortion compensation accuracy of the power amplifier can be significantly improved. Further, by arranging the IF / RF frequency converter for the transmission signal in the preceding stage of the predistortion compensating unit and superimposing the distortion compensating signal on the RF unit instead of the IF unit, the IF / RF
In the band limiting filter in the signal frequency conversion unit, since it is not necessary to pass the signal including the distortion compensation signal component, it is possible to narrow the pass band of the band limiting filter, and a frequency converter that can be put to practical use A very practical distortion compensation power amplifier can be provided.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. In the following embodiments, for example, as in a terrestrial digital broadcasting system, the system frequency (RF frequency) is extremely wide band (470 MHz).
.About.770 MHz: 6 MHz band is used per channel), while the frequency of the IF signal for transmission in the transmitter uses a single frequency (or multiple frequencies in a narrow band) such as 37.15 MHz. An embodiment will be described. However, these frequencies are examples, and the present invention is not limited to the above frequencies.

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention. In FIG. 1, 201 is a directional coupler, and 202
Is a delay device, 203 is an IF / RF frequency converter, 204 is an amplitude / phase modulator (predistortion compensator), 205 is an amplifier,
Reference numeral 206 is a wave detector, and 207 is an amplitude / phase control signal generator.

The input IF signal for transmission is the directional coupler 2
When it is supplied to 01, it is branched into two by the directional coupler 201. For one of the branched outputs, the instantaneous value of the envelope level is detected by the detector 206, and the instantaneous value is converted into a digital signal by the amplitude / phase control signal generation unit 207. The amplitude / phase control signal generation unit 207 stores amplitude / phase control data for generating required distortion compensation data (data having a nonlinear characteristic of an inverse tendency of the nonlinear distortion of the power amplifier) in advance, and inputs it. A value corresponding to the obtained digital value is converted into an analog signal and output to the amplitude / phase modulator (predistortion compensator) 204. The amplitude / phase modulator (predistortion compensator) 204 includes an amplitude / phase control signal generator 207.
The control signal converted into the analog signal is input.

Further, the transmission IF signal branched to the other by the directional coupler 201 passes through the delay unit 202 and IF /
The RF frequency converter 203 converts the frequency into an RF signal,
An amplitude / phase modulator (predistortion compensator) 204 performs amplitude and phase modulation on the frequency-converted RF signal, and a predetermined distortion compensation signal is generated and superimposed. Thus, the amplitude / phase modulator (predistortion compensator) 204 generates and superimposes a distortion compensation signal for compensating the nonlinear distortion of the amplifier 205 on the input transmission IF signal, and the amplifier 20
The signal is amplified to a predetermined power at 5 and then transmitted and output as an output RF signal.

Here, the envelope connecting level of the input transmission IF signal (single frequency or a plurality of frequencies within a narrow band) is detected by the detector 206, and nonlinear distortion compensation is performed according to the detected level. Since it is configured so as to perform, the detector 2 can be used according to the wide band RF frequency to be used as in the conventional case.
It is possible to eliminate the inconvenience of having to frequently adjust 06, and it is possible to significantly improve the accuracy of distortion compensation of the power amplifier. In addition, the transmission signal IF /
Since the RF frequency converter 204 is arranged in front of the amplitude / phase modulator (predistortion compensator) 204, and the distortion compensation signal is superposed on the RF unit instead of the IF unit, In the band limiting filter in the / RF signal frequency converter, it is not necessary to pass the signal including the distortion compensation signal component. Therefore, the pass band of the band limiting filter can be narrowed and the frequency converter can be put to practical use. As a result, a very practical distortion compensation power amplifier can be provided.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, 203 is an IF / RF frequency converter, 201 is a directional coupler, 202 is a delay device, and 204.
Is an amplitude / phase modulator (predistortion compensator), 205 is an amplifier, 214 is an RF / IF frequency converter, 206 is a detector, and 207 is an amplitude / phase control signal generator.

The input IF signal is an IF / RF frequency converter 2
When the signal is supplied to 03, the IF signal is frequency-converted into an RF signal and is branched by the directional coupler 201. One of the branch signals is converted into an IF signal again by the RF / IF frequency converter 214 provided in the preceding stage of the wave detector 206, and when the wave detector 206 detects the instantaneous value of the envelope level, the instantaneous value is obtained. Is converted into a digital signal by the amplitude / phase control signal generation unit 207. The amplitude / phase control signal generation unit 207 stores amplitude / phase control data for compensating the nonlinear distortion of the amplifier 205 in advance, converts a value corresponding to the input digital value into an analog signal, and / Outputs to the phase modulator (predistortion compensator) 204. In the amplitude / phase modulator 204, the control signal converted into an analog signal by the amplitude / phase control signal generation unit 207 is input. Further, the transmission RF signal branched to the other by the directional coupler 201 passes through the delay device 202, is subjected to amplitude and phase modulation by the amplitude / phase modulator 204, and a predetermined distortion compensation signal is generated, It is superimposed. That is, the amplitude / phase modulator (predistortion compensator) 204 generates and superimposes a distortion compensation signal for compensating the nonlinear distortion of the amplifier 205 on the input transmission IF signal, and superimposes the signal on the amplifier 205 to a predetermined power. After amplification, it is transmitted and output as an output RF signal.

As described above, in the second embodiment of the present invention, the RF signal demultiplexed by the directional coupler 201 is converted into RF /
The IF frequency converter 214 converts the frequency into an IF signal again, the envelope level of the IF signal is detected by the detector 206, and the amplifier 20 in the RF band corresponds to the detected signal level.
5 is configured to compensate for the non-linear distortion.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment shown in FIG. 3, in addition to the configuration of the first embodiment described above, a directional coupler 209 for branching the output of the amplifier 205 is provided in the output signal path, an RF / IF frequency converter 210, and a detector. It has a configuration in which 211 is added. The configuration and operation until the compensated RF signal is amplified by the amplifier 205 are the same as in the first embodiment. here,
The RF signal amplified by the amplifier 205 is branched into two by the directional coupler 209, and one is output as an output RF signal. The other RF signal is frequency-converted by the RF / IF frequency converter 210, and then the detector 211 detects the envelope level of the IF signal. The detected level signal is given to the amplitude / phase control signal generation unit 207. The amplitude / phase control signal generator 207 digitizes the detected level and
The update of the phase control data is configured to adaptively compensate the distortion in response to the temperature change and the secular change of the input / output characteristics of the amplifier 205 and the like.

Next, a specific example of the frequency converter in the third embodiment will be described with reference to FIGS. 7 and 8. Figure 7
FIG. 3 is a diagram showing an example of a frequency converter. FIG. 8 is a diagram showing an example of a frequency converter for externally inputting a local oscillation signal input to the mixer. In FIG. 7, the reference signal oscillator 7
The reference signal generated by 0 is input to the PLL 56,
56 controls the oscillation frequency of the VCO 55 with a voltage,
The CO 55 produces the required frequency. Also, VCO55
The VCO 55 generates a stable local oscillation signal by inputting a part of the signal generated in (1) to the PLL 56. The mixer 51 converts the signal input from the input terminal 50 into a desired frequency signal by the local signal. Further, the local oscillator output signal of the frequency converter is output from the local signal output end 54, and is input to the local signal input end 63 of the frequency converter that inputs the local oscillator signal from the outside shown in FIG.
The frequency of the signal input from the input terminal 60 is converted into a desired frequency signal. With the above configuration, the signals input to the mixer can be shared by the frequency converters.

The construction of the fourth embodiment of the present invention is shown in FIG.
The fourth embodiment of FIG. 4 is different from that of FIG. 3 in structure because the IF / RF frequency converter 20 transfers the local oscillator signal.
3 to the RF / IF frequency converter 210, and other configurations and operations are similar to those of the third embodiment.

A fifth embodiment of the present invention will be described with reference to FIG. The input IF signal is demultiplexed by the directional coupler 201 and input to the amplitude / phase control signal generation unit 207 by the A / D converter 215. The operation and configuration after the other demultiplexed signal are the same as those in the third and fourth embodiments. In the fifth embodiment, the A / D converter 215 obtains the envelope level from the digitized value and uses the value as the address, so that the element of the third and fourth embodiments can be obtained. It is possible to adaptively perform distortion compensation operation in response to temperature changes and aging changes.

[0025]

As described above, the distortion compensation value is obtained corresponding to the detection level of the transmission IF signal, frequency-converted into the transmission RF signal, and the amplitude / phase modulation operation is performed based on the obtained distortion compensation value. And the distortion compensation signal is superimposed on the transmission RF signal, the system frequency (RF
Even if the frequency) is wide band, distortion compensation of the power amplifier can be performed with extremely high accuracy.

Further, the distortion compensating signal for compensating the non-linear distortion of the power amplifier is constructed so as to be superposed on the RF signal instead of the IF signal, so that the distortion in the band limiting filter in the IF / RF frequency converting section is increased. Since it is not necessary to pass it including the compensation component, it is possible to narrow the pass band of the band limiting filter, and to realize a frequency converter that can be put to practical use, and thus an extremely practical distortion compensation power amplifier. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a second embodiment of the present invention.

FIG. 3 is a block diagram showing the configuration of a third embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing the configuration of a fifth embodiment of the present invention.

FIG. 6 is a block diagram showing an example of a conventional technique.

FIG. 7 is a block diagram showing a configuration example of a frequency converter having a local signal output terminal.

FIG. 8 is a block diagram showing a configuration example of a frequency converter that performs frequency conversion in response to an external local signal.

FIG. 9 is a block diagram showing another example of the conventional technique.

FIG. 10 is a diagram showing a distortion compensation principle of an amplifier.

FIG. 11 is a diagram showing the principle of predistortion compensation.

[Explanation of symbols]

101, 201: directional coupler, 102, 202: delay device, 103, 203: IF / RF frequency converter, 10
4, 204: amplitude / phase modulator, 105, 205: amplifier, 106, 206: detector, 107, 207: amplitude /
Phase control signal generator, 209: Directional coupler, 210,
214: RF / IF frequency converter, 211: detector,
5, 215: A / D converter, 7: D / A converter, 50:
Input end, 51: mixer, 52: band-limiting filter, 5
3: output end, 54: local signal output end, 55: VC
O, 56: PLL, 57: source device, 60: input terminal, 6
1: mixer, 62: band limiting filter, 63: local signal input terminal, 64: output terminal.

Continued front page    (72) Inventor Osamu Osamu             Hitachi, Ltd. 32 Miyuki-cho, Kodaira-shi, Tokyo             Kokusai Electric Koganei Factory (72) Inventor Shinro Hirose             Hitachi, Ltd. 32 Miyuki-cho, Kodaira-shi, Tokyo             Kokusai Electric Koganei Factory F term (reference) 5J090 AA01 AA41 CA21 FA20 GN03                       GN07 KA00 KA15 KA16 KA32                       KA41 KA53 KA55 KA68 MA14                       MA20 SA14 TA01 TA02                 5J091 AA01 AA41 CA21 FA20 KA00                       KA15 KA16 KA32 KA41 KA53                       KA55 KA68 MA14 MA20 SA14                       TA01 TA02                 5J500 AA01 AA41 AC21 AF20 AK00                       AK15 AK16 AK32 AK41 AK53                       AK55 AK68 AM14 AM20 AS14                       AT01 AT02

Claims (5)

[Claims] 1. A distortion compensating power amplifier having a predistortion compensating section for superimposing a distortion compensating signal for compensating the non-linear distortion of a power amplifier on an input signal of the power amplifier, wherein a transmission intermediate frequency signal is applied to the input signal. Distributing means for distributing, detecting means for detecting the level of the input signal supplied with one of the distributed signals, and distortion compensation data set in advance corresponding to the detected signal level to select the predistortion. And a frequency conversion means for frequency-converting the other signal distributed by the distribution means from an intermediate frequency signal to a high-frequency signal, the frequency conversion means being provided in the preceding stage of the predistortion compensation section. Distortion-compensating power amplifier characterized by being arranged. 2. A distortion compensating power amplifier having a predistortion compensating section for superimposing a distortion compensating signal for compensating the non-linear distortion of the power amplifier on an input signal of the power amplifier, wherein a transmission intermediate frequency signal is given to the input signal. First frequency conversion means for frequency-converting into a high-frequency signal, distribution means for distributing the frequency-converted high-frequency signal, and second frequency conversion means for frequency-converting one of the distributed signals into an intermediate-frequency signal again Detecting means for detecting the input signal level from the re-converted signal, control means for selecting distortion compensation data set in advance corresponding to the detected signal level and transmitting the selected distortion compensation data to the predistortion compensating section, and the distribution A distortion compensating power amplifier, comprising: delay means for giving a required delay time to the other signal thus generated and sending it to the predistortion compensating section. 3. The distortion compensating power amplifier according to claim 1 or 2, wherein a distribution means for distributing the output signal of the power amplifier and a distortion signal component contained in the output signal distributed by the distribution means are detected. An adaptive predistortion type distortion compensating power amplifier, characterized by comprising: 4. The power amplifier according to claim 3, wherein the local oscillation signal input to the frequency conversion means for frequency converting the intermediate frequency signal to the high frequency signal is used as means for detecting the distortion signal component. Predistortion type distortion compensation power amplifier. 5. The power amplifier according to claim 1, further comprising means for digitizing an input signal distributed by the directional coupler and detecting an envelope level by digital signal processing. Predistortion type distortion compensation power amplifier.