JP2008219377A - Transmitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire a transmitting device, whose feedback system can be simplified, which compensates distortion of an EER system power amplifier and whose space-saving design can be obtained. <P>SOLUTION: The transmitting device includes a down converter which mixes part of an output high-frequency signal of the power amplifier with a local oscillation frequency signal whose phase has been set up and then produces a signal with the same frequency as that of an output-phase-component signal of quadrature modulation, a quadrature modulator which produces an in-phase-component signal IFB and a quadrature-component QFB, a first adder which adds the in-phase-component signal IFB to an in-phase-component analogue signal IFW, a second adder which adds the quadrature-component signal QFB to a quadrature-component analogue signal QFW, and a phase shifter which sets a phase of the local oscillation frequency signal so that the in-phase-component signals IFB, IFW added together by the first adder and the quadrature-component signals QFB, QFW added together by the second adder become in opposite phase to each other, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmission apparatus using an EER (Envelope Elimination and Restoration) type power amplifier.

  For example, as is well known, the performance and portability of wireless terminals typified by cellular phones have dramatically improved with the introduction of digital technology. Since such a wireless terminal uses a battery as a power source, battery life is one of the important performances. In order to extend the battery life, it is necessary to reduce the current drain, but most of the battery capacity is consumed in the power amplification stage in the portable wireless terminal. As a method for improving the efficiency of the power amplification stage to reduce power consumption, the transmission signal is separated into an amplitude component and a phase component, and the phase component is amplified. At that time, the bias of the amplifier is modulated by the amplitude component. There is a method called EER that re-inserts the amplitude component.

  FIG. 4 shows a functional configuration of a transmission apparatus to which this EER system power amplifier is applied. In the figure, a signal conversion unit 1 converts a baseband I signal (in-phase component signal) and a Q signal (quadrature component signal), which are transmission signals, into an amplitude component signal A and a phase component signal (in-phase component signal θi, quadrature component signal). θq). The converted phase component signals θi and θq are converted into analog signals IFW and QFW by D / A converters 2 and 3, respectively. The quadrature modulation unit 5 performs quadrature modulation on the analog signals IFW and QFW. The up-converter 8 mixes the phase signal generated by the quadrature modulation with the local oscillation frequency (carrier) from the local oscillator 9 to generate a high-frequency signal, which is given to the power amplifier 6 for amplification. On the other hand, the signal A of the amplitude component converted by the signal converter 1 is converted to an analog signal A ′ by the D / A converter 4. The analog signal A ′ is amplified by the bias amplifier 18 and applied to the power amplifier 6 as a bias voltage. Since the power amplifier 6 amplifies the high frequency signal with a bias voltage modulated with an analog amplitude component, the power amplifier 6 outputs a high frequency signal obtained by recombining the amplitude component signal and the phase signal component to the antenna 11. By this control, the power efficiency of the power amplifier 6 is kept high.

  By the way, in the case of the current portable radio terminal, a complex modulation, that is, a digital modulation scheme such as QPSK, HPSK, DQPSK, etc. is adopted, so as not to cause degradation of signal quality and interference with adjacent channels. The power amplifier is required to have extremely high linearity. However, in the case of the EER amplifier as described above, the power amplification efficiency is good, but distortion depending on the input amplitude during amplification, that is, AM / AM characteristics (amplitude distortion) and AM / PM characteristics (phase distortion) are generated. There is a problem of making the amplifier output non-linear. Therefore, it is necessary for the power amplification stage to improve linearity while maintaining high efficiency. For this purpose, a distortion compensation means having reverse distortion characteristics with respect to the distortion characteristics of the EER power amplifier is provided, and the inverse distortion characteristics are used to distort the amplitude component signal and the phase component signal converted from the transmission signal. A method for performing compensation processing has been proposed (see, for example, Patent Document 1).

JP 2006-135612 A

  In the distortion compensation method used in the transmission device described in Patent Document 1, the signal that feeds back the high-frequency signal output from the power amplifier is converted into a digital signal, and the amplitude component signal A and the phase component signal θi converted by the signal conversion unit. , Θq, distortion compensation is performed by digital signal processing. In this case, the actual feedback system requires an A / D converter after the quadrature demodulator, and also requires a signal converter, an error calculator, a compensation coefficient calculator, a memory, etc., and the circuit scale increases. However, there is a problem that it is not suitable for a wireless terminal such as a mobile phone that is becoming smaller.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a transmission apparatus that enables simplification and space saving of a feedback system that performs distortion compensation of an EER type power amplifier.

  In the transmission apparatus according to the present invention, the signal conversion unit converts the in-phase component signal I and the quadrature component signal Q of the transmission signal into the amplitude component signal A and the phase component signals θi and θq, and the converted phase component signals θi and θq. Is converted into analog signals IFW and QFW by a corresponding D / A converter, respectively, and then quadrature modulated by a quadrature modulation unit, and a phase signal generated by this quadrature modulation is mixed with a local oscillation frequency by an up converter to generate a high frequency signal. On the other hand, after the amplitude component signal A converted by the signal converter is converted to the analog signal A ′ by the D / A converter, it is amplified by the bias amplifier and generated as the bias voltage of the power amplifier. Amplifying the output high-frequency signal of the up-converter based on the bias voltage modulated by the analog signal A ′ of the amplitude component, and outputting to the antenna In this configuration, a part of the output high-frequency signal of the power amplifier is mixed with a phase-set local oscillation frequency signal to generate a signal having the same frequency as the output phase signal of the quadrature modulation unit, and generated by the down-converter. A quadrature demodulator that performs quadrature demodulation on the received signal and generates an in-phase component signal IFB and a quadrature component signal QFB; and an in-phase component signal IFB that is generated by the quadrature demodulator from the analog signal IFW of the in-phase component that is input to the quadrature modulator A first adder that adds the quadrature component signal QFB generated by the quadrature demodulation unit to the quadrature component analog signal QFW input to the quadrature modulation unit, and a first adder The in-phase component signals to be added and the quadrature component signals to be added by the second adder are input to the down converter so that they have an opposite phase relationship. And a phase shifter for setting the phase of a signal having a local oscillation frequency.

  According to the present invention, in a feedback system that performs distortion compensation of an EER type power amplifier, the signal having an antiphase characteristic of the power amplifier is added to the transmission signal as it is without converting it to a digital signal, and distortion compensation is performed. As a result, the apparatus configuration can be simplified and the space can be saved.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a functional configuration of a transmitting apparatus according to Embodiment 1 of the present invention.
In the figure, the transmitting apparatus according to the first embodiment has a low-pass filter (LPF) 7, 16, a band-pass filter (BPF) 10, a directional coupler 12, and a down converter with respect to the basic functional configuration shown in FIG. 14, a phase shifter 15, a quadrature demodulator 17, and adders 19 and 20.
The down converter 14 is a unit that generates a signal having the same frequency as the output phase signal of the quadrature modulation unit 5 by mixing a part of the output high frequency signal of the power amplifier 6 with the signal of the local oscillation frequency whose phase has been adjusted. The quadrature demodulation unit 17 is means for performing quadrature demodulation on the signal generated by the down converter 14 and generating an in-phase component signal IFB and a quadrature component signal QFB. The adder (first adder) 19 is means for adding the in-phase component signal IFB generated by the quadrature demodulator 17 to the in-phase component analog signal IFW input to the quadrature modulator 5. The adder (second adder) 20 is means for adding the quadrature component signal QFB generated by the quadrature demodulation unit 17 to the quadrature component analog signal QFW input to the quadrature modulation unit 5. The phase shifter 15 is a local oscillation that is input to the down converter 14 so that the signals of the in-phase components added by the adder 19 and the signals of the quadrature components added by the adder 20 have an opposite phase relationship. It is means for adjusting the phase of the frequency signal.

Next, the operation will be described.
The signal conversion unit 1 converts the baseband in-phase component signal I and the quadrature component signal Q of the transmission signal into an amplitude component signal A and phase component signals θi and θq, and the converted amplitude component signal A to the D / A converter 4. The phase component signals (in-phase component signal θi and quadrature component signal θq) are output to the corresponding D / A converters 2 and 3, respectively. The D / A converter 2 converts the in-phase component signal θi into an analog signal IFW. The D / A converter 3 converts the quadrature component signal θq into an analog signal QFW. The D / A converter 4 converts the amplitude component signal A into an analog signal A ′. The quadrature modulation unit 5 performs quadrature modulation on the analog signals IFW and QFW of the phase component to generate a phase signal. In the low-pass filter 7, unnecessary harmonic components of the phase signal generated by the quadrature modulation unit 5 are limited and output to the up-converter 8. In the up-converter 8, the output of the low-pass filter 7 is mixed with the local oscillation frequency (carrier) from the local oscillator 9 to perform frequency conversion and output a high-frequency signal. The band pass filter 10 limits the band of the high frequency signal output from the up-converter 8 and outputs it to the power amplifier 6. On the other hand, the analog signal A ′ having an amplitude component converted by the D / A converter 4 is amplified by the bias amplifier 18, and the amplified output is given to the power amplifier 6 as a bias voltage. The power amplifier 6 amplifies the high-frequency signal input through the band-pass filter 10 in accordance with the level of the bias voltage modulated by the analog signal A ′ having the amplitude component from the bias amplifier 18. The output of the power amplifier 6 is a high-frequency signal obtained by recombining the amplitude component signal and the phase signal component, and is output to the antenna 11 via the directional coupler 12. Further, the directional coupler 12 separates a part of the output high-frequency signal from the power amplifier 6 and applies it to the feedback down converter 14.

In the down converter 14, the high frequency signal fed back from the directional coupler 12 and the local oscillation frequency of the local oscillator 9 given through the phase shifter 15 are mixed, and a signal having the same frequency as the output phase signal of the quadrature modulation unit 5 is mixed. Is output to the low-pass filter 16. In the low-pass filter 16, unnecessary harmonic components of the output signal of the down converter 14 are limited and supplied to the orthogonal demodulation unit 17. The quadrature demodulator 17 performs quadrature demodulation on the output signal of the down converter 14, generates an in-phase component signal QFW and a quadrature component signal QFB, and outputs them to the corresponding adders 19 and 20. The adder 19 adds the in-phase component signal IFB generated by the quadrature demodulator 17 to the in-phase component analog signal IFW input to the quadrature modulator 5, and the adder 20 adds the quadrature signal input to the quadrature modulator 5. The quadrature component signal QFB generated by the quadrature demodulator 17 is added to the component analog signal QFW. Here, in the phase shifter 15, the in-phase component analog signal IFW and the in-phase component signal IFB generated by the quadrature demodulator 17 have an anti-phase relationship, and the quadrature component analog signal QFW and the quadrature demodulator 17 generate them. The phase of the local oscillation frequency signal applied to the down converter 14 is adjusted so that the quadrature component signal QFB has an antiphase relationship.
Therefore, in the above operation, if IFW, QFWIFB, and QFB include distortion components of the power amplifier 6, by generating IFB and QFB in an inverse correlation system with these and adding them to the corresponding signals, The high frequency signal input to the amplifier 6 has the reverse distortion characteristic of the power amplifier 6. Therefore, the distortion of the power amplifier 6 can be compensated and its linearity can be improved.

  As described above, according to the first embodiment, in a feedback system that performs distortion compensation of an EER type power amplifier, an analog signal remains as it is without converting a signal having an antiphase characteristic of the power amplifier into a digital signal. Since the distortion is compensated by adding to the transmission signal, the apparatus configuration can be simplified and the space can be saved.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing a functional configuration of a transmission apparatus according to Embodiment 2 of the present invention. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted in principle. The second embodiment is a configuration in which a phase comparator 21 is provided with respect to the configuration of the first embodiment.
Here, the phase comparator 21 compares the phase of the in-phase component analog signal IFW converted by the D / A converter 2 with the phase of the in-phase component signal IFB generated by the quadrature demodulator 17, and a phase based on the phase difference Setting signals sin θ and cos θ are generated and supplied to the phase shifter 15. In the phase shifter 15, based on the phase setting signals sin θ and cos θ given from the phase comparator 21, the phase of the signal of the local oscillation frequency is set so that IFW and IFB and QFW have an opposite phase to QFB.
As a result, even when the phase characteristics of the circuit change, signals having an opposite phase are always added to the analog signals IFW and QFW of the phase component, thereby enabling accurate distortion compensation. It should be noted that the same phase can be set even if the signals to be compared by the phase comparator 21 are the quadrature component analog signal QFW and the quadrature component signal QFB.

Embodiment 3 FIG.
FIG. 3 is a block diagram showing a functional configuration of a transmission apparatus according to Embodiment 3 of the present invention. 3, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted in principle. In the third embodiment, a down converter (second down converter) 21, a low pass filter (LPF) 22, and an adder (third adder) 23 are provided in addition to the configuration of the second embodiment. is there.
Here, the down converter 21 mixes the output signal of the quadrature modulation unit 5 and the output signal of the down converter 14 to generate an amplitude component signal included in the output signal of the down converter 14. The output signal of the down converter 21 is output to the adder 23 after the harmonics are limited by the low-pass filter 22. The adder 23 adds the output signal of the low-pass filter 22 to the analog signal A ′ of the amplitude component converted by the D / A converter 4.
Therefore, by mixing the output signal of the quadrature modulation unit 5 and the output signal of the down converter 14 having the same high frequency component, the amplitude component of the output high frequency signal of the power amplifier 6 can be extracted. Since the extracted amplitude component is added to the analog signal A ′ and reflected in the bias voltage of the power amplifier 6, distortion of the amplitude component of the power amplifier 6 can be compensated.

It is a block diagram which shows the function structure of the transmitter by Embodiment 1 of this invention. It is a block diagram which shows the function structure of the transmitter by Embodiment 2 of this invention. It is a block diagram which shows the function structure of the transmitter by Embodiment 3 of this invention. It is a block diagram which shows the function structure of the transmitter which applied the power amplifier of an EER system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Signal conversion part, 2-4 D / A converter, 5 Quadrature modulation part, 6 Power amplifier, 7, 16, 22 Low pass filter (LPF), 8 Up converter, 9 Local oscillator, 10 Band pass filter (BPF), 11 Antenna, 12 directional coupler, 14, 21 down converter, 15 phase shifter, 17 quadrature demodulator, 18 bias amplifier, 19, 20, 23 adder.

Claims (3)

The signal conversion unit converts the in-phase component signal I and the quadrature component signal Q of the transmission signal into an amplitude component signal A and phase component signals θi and θq, and the converted phase component signals θi and θq by a corresponding D / A converter. After conversion to analog signals IFW and QFW, respectively, quadrature modulation is performed by a quadrature modulation unit, and a phase signal generated by this quadrature modulation is mixed with a local oscillation frequency by an up-converter to generate a high-frequency signal. After the amplitude component signal A converted in the unit is converted into an analog signal A ′ by a D / A converter, it is amplified by a bias amplifier and generated as a bias voltage of the power amplifier. In the transmitter for amplifying the signal based on the bias voltage modulated by the analog signal A ′ having the amplitude component and outputting the amplified signal to the antenna,
A down converter that generates a signal having the same frequency as the output phase signal of the quadrature modulation unit by mixing a part of the output high-frequency signal of the power amplifier with a signal of the local oscillation frequency that has been phase-set,
A quadrature demodulation unit that performs quadrature demodulation on the signal generated by the down converter and generates an in-phase component signal IFB and a quadrature component signal QFB;
A first adder that adds the in-phase component signal IFB generated by the quadrature demodulation unit to the analog signal IFW of the in-phase component input to the quadrature modulation unit;
A second adder that adds the quadrature component signal QFB generated by the quadrature demodulation unit to the quadrature component analog signal QFW input to the quadrature modulation unit;
The local oscillation frequency input to the down-converter is such that the in-phase component signals added by the first adder and the quadrature component signals added by the second adder have an antiphase relationship with each other. And a phase shifter for setting a phase of the signal. Phase difference between the in-phase component analog signal IFW input to the quadrature modulation unit and the in-phase component signal IFB generated by the quadrature demodulation unit or the quadrature component analog signal QFW input to the quadrature modulation unit and the quadrature demodulation unit A phase comparator that outputs a phase setting signal corresponding to the phase difference of the quadrature component signal QFB;
2. The transmission apparatus according to claim 1, wherein the phase shifter sets a phase of a signal having a local oscillation frequency based on the phase setting signal. A second down converter that mixes the output phase signal of the quadrature modulation unit and the output signal of the down converter to generate a signal of an amplitude component included in the output signal of the down converter;
3. A third adder for adding the amplitude component signal generated by the second down converter to the amplitude component analog signal A ′ input to the bias amplifier. Item 3. The transmission device according to Item 2.

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