JP2011035640A - Transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission apparatus for efficiently removing an out-of-band unnecessary wave (spurious wave) caused by a ΔΣ modulation method. <P>SOLUTION: The apparatus includes: a ΔΣ modulator 111 for performing a delta sigma modulation of a transmitted bit line into a modulation signal with a signal component and a quantization noise component; a first amplifier 15 for amplifying an electric power of the modulation signal; a signal generator 113 for generating a signal obtained by a phase inversion of the quantization noise component of the modulation signal; a second amplifier 20 for amplifying the electric power of the signal generated by the signal generator 113; and a combining means for combining an output of the first amplifier 15 with the output of the second amplifier 20 to generate a transmission signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a transmission apparatus using a ΔΣ modulation method.

  In recent years, an OFDM (Orthogonal Frequency Division Multiplexing) modulation method has been used in various systems as a communication method means that enables communication even in a broadband service such as a cellular phone or in a high-speed mobile environment. On the other hand, there is a drawback that the PAPR (Peak to Average Power Ratio) of the modulated wave is large, which causes non-linear distortion of the transmission power amplifier, and degradation of the transmission signal is a problem.

  In order to reduce such non-linear distortion, it is necessary to operate the transmission power amplifier in a back-off region equal to or higher than PAPR, but this causes a new problem that the efficiency of the amplifier is lowered. In other words, there is a trade-off between low-distortion operation and high-efficiency operation, and various proposals and methods have been made to achieve both of them, and a ΔΣ amplifier that has been handled in the AUDIO frequency band in the past has been adopted at the radio frequency. In recent years, proposals for realizing high efficiency have been increasing.

  In the ΔΣ amplifier, a method for compensating (removing) both a distortion signal generated by the amplifier at the amplifier output and an out-of-band unnecessary wave generated by handling the ΔΣ signal is required. The former is compensated by using a DPD (Digital Pre-Distortion) method, and the latter has many literatures and examples of a method of removing an out-of-band signal component by using a band pass filter (BPF) for an amplifier output. . Here, the out-of-band signal removed by the BPF is actually totally reflected by the BPF and consumed by an amplifier or a terminator for consuming unnecessary power, resulting in a decrease in efficiency.

  The following is disclosed as a publicly known document related to the present application (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2004-72735

  As described above, the ΔΣ amplifier requires a method for compensating (removing) both the distortion signal generated by the amplifier at the amplifier output and the out-of-band unwanted wave generated by handling the ΔΣ signal. In the conventional method, the former is compensated by using the DPD method, and the latter is often a method of removing the out-of-band signal component by using BPF as an amplifier output. However, the out-of-band signal removed by the BPF is actually totally reflected by the BPF and consumed by an amplifier or a terminator for consuming unnecessary power, resulting in a decrease in efficiency.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a transmission apparatus that can efficiently remove out-of-band unnecessary waves generated by the ΔΣ modulation method.

  In order to achieve the above object, a transmission apparatus according to the present invention includes a modulation unit that delta-sigma-modulates a transmission bit string into a modulation signal having a signal component and a quantization noise component, and a first amplifier that amplifies the modulation signal. A generation unit that generates a signal obtained by inverting the quantization noise component of the modulation signal, a second amplifier that amplifies the power of the signal generated by the generation unit, an output of the first amplifier, and a second amplifier Combining means for combining the output and generating a transmission signal is provided.

  Therefore, according to the present invention, it is possible to provide a transmission device that efficiently removes unnecessary out-of-band waves generated by the ΔΣ modulation method.

The circuit block diagram which shows 1st Embodiment of the transmitter which concerns on this invention. The circuit block diagram which shows 2nd Embodiment of the transmitter which concerns on this invention. The basic circuit block diagram of the conventional transmitter.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
The first embodiment according to the present invention is a method of canceling out-of-band noise by using the second route and performing the same-amplitude anti-phase synthesis (coupling) at the output section of the amplifier.

  FIG. 1 is a diagram illustrating a circuit configuration of the transmission apparatus according to the first embodiment. The signal processing unit 11 includes, for example, an FPGA (Field-Programmable Gate Array), and includes a ΔΣ modulation unit 111, a DPD (Digital Pre-Distortion) distortion compensation unit 112, and a signal generation unit 113.

  The ΔΣ modulator 111 performs ΔΣ modulation on a modulated signal having a signal component and a quantized noise component by quantizing the transmission bit string by oversampling and performing noise shaping. The modulated signal is converted into an analog signal by the D / A converter 12 through the first route, the oscillation signal from the oscillator 13 is mixed by the mixer 14, and is up-converted to the radio frequency band by the amplifier 15.

  The signal generator 113 generates an antiphase signal obtained by inverting the phase of the noise-shaped quantized noise component with the same amplitude. This antiphase signal is converted into an analog signal by the D / A converter 18 through the second route, and the oscillation signal from the oscillator 13 is mixed by the mixer 19 and up-converted to the radio frequency band by the amplifier 20. Then, the output from the amplifier 20 is combined with the output from the amplifier 15, so that out-of-band noise can be canceled before the band pass filter (BPF) 21.

  The DPD distortion compensation unit 112 compensates for distortion generated by power amplification in the amplifier 15. The output from the amplifier 15 is combined with the output from the amplifier 20 and fed back via the mixer 16 and the A / D converter 17. That is, after the out-of-band noise is canceled, the DPD distortion compensation unit 112 compensates for the distortion component generated in the amplifier 15.

  The signal whose out-of-band noise is reduced as described above is subjected to band limitation and waveform shaping by the BPF 21, and is transmitted from the antenna 23 to the radio line via the frequency divider 22.

  Here, FIG. 3 shows a general circuit configuration of a conventional transmission apparatus. By using the ΔΣ modulation method, a binary (or multilevel) input signal including noise having a frequency component higher than the main signal frequency is input to the amplifier 15. Conventional input signals include OFDM (Orthogonal Frequency Division Multiplexing) modulation system, etc., and multi-value signal increases PAPR (Peak to Average Power Ratio), and the back-off required for the amplifier also increases and the amplifier's It was hindering efficiency. However, in binary, the amplifier can be operated in the switch mode, and backoff is unnecessary (or reduced), and the amplifier can be operated with high efficiency.

  The switch operation speed of the amplifier requires a switch at a speed higher than that of the main signal. With the recent increase in the speed of devices, not only the AUDIO amplifier but also the RF amplifier in the radio communication field, the ΔΣ method Research is underway.

  One of the problems with increasing amplifier efficiency is out-of-band noise processing. The out-of-band noise that is noise-shaped by the ΔΣ modulator is reflected by using a BPF and is consumed by a terminator (PAD 41 in FIG. 3). Therefore, the size, cost, and heat treatment of PAD41 became one of the concerns.

  On the other hand, in the first embodiment, the out-of-band unnecessary wave generated by handling the ΔΣ modulation signal is canceled by synthesizing the same amplitude and opposite phase at the output of the amplifier 15. In this way, by removing distortion and out-of-band unnecessary waves in the previous stage of the BPF 21, a system can be constructed without using an expensive BPF. That is, the out-of-band noise is canceled and the attenuation characteristic of the BPF can be relaxed, so that the cost of the BPF can be reduced and the terminator (PAD 41 in FIG. 3) can be made unnecessary.

  Further, by removing the out-of-band noise in advance by the signal of the second route for the DPD distortion compensator 112 used for compensating the distortion generated in the amplifier 15, the amount of improvement in DPD distortion compensation can be increased. effective. In other words, there is a considerable amount of noise-shaped quantization noise in the main signal band. It is difficult to distinguish this quantization noise from the distortion generated by passing through the amplifier, which affects the amount of improvement in DPD distortion.

  In order to reduce the noise component in the main signal band, for example, there is a method of increasing the oversample ratio at the time of ΔΣ modulation. However, according to this method, higher-order frequency components are generated, and it is necessary to increase the switching speed of the amplifier. This complicates the amplifier and affects the manufacturing cost. On the other hand, in the first embodiment, since the quantization noise component can be canceled in advance, it can be used without deteriorating the distortion improvement amount of the DPD.

  Note that the FPGA constituting the signal processing unit 11 may be configured to have the functions of the D / A converters 12 and 18, the mixers 14, 16 and 19, and the A / D converter 17.

(Second Embodiment)
In the first embodiment, the configuration is such that the quantization noise component is synthesized with the same amplitude and opposite phase using the second route and canceled out. However, the second embodiment according to the present invention further includes the second route. In addition, an object of the present invention is to achieve a high-efficiency system by obtaining a higher output by synthesizing the main signals in phase.

  FIG. 2 is a diagram illustrating a circuit configuration of the transmission apparatus according to the second embodiment. The configuration of FIG. 2 is obtained by providing a synthesis circuit 24 in the configuration of FIG. Further, the operation of the signal generation unit 113 in the signal processing unit 11 is different. Since other configurations are the same as those in FIG. 1, the same components as those in FIG. 1 are denoted by the same reference numerals and detailed description thereof is omitted.

  The signal generation unit 113 inverts the noise-shaped quantized noise component with the same amplitude and generates a signal obtained by adding the signal component in the same phase. This signal is converted into an analog signal by the D / A converter 18 through the second route, and the oscillation signal from the oscillator 13 is mixed by the mixer 14 and up-converted to the radio frequency band by the amplifier 20. The combining circuit 24 combines the output from the amplifier 20 and the output from the amplifier 15. Thereby, it is possible to cancel out-of-band noise and double the output of the signal component.

  As described above, the second embodiment cancels out-of-band noise by canceling out-of-band noise with the same amplitude and opposite phase using the second route, as in the first embodiment. The output level from the amplifier can be doubled by outputting the signal to the root and performing in-phase synthesis with the main signal of the first route. Furthermore, by multiplexing the routes, it is possible to multiply the outputs by multiplying them with the amplifier output. As a result, the output level remains the same, and the output of the amplifier can be halved (or reduced to 1 / multiple) to make the system cheaper.

  Furthermore, in the first and second embodiments, it is possible to perform noise calibration by outputting only noise-shaped signals. Specifically, noise calibration can be performed by the following procedure. That is, in the first route, the main signal is attenuated by the filter, and only the quantization noise component outside the band is output. Similarly, in the second route, the main signal is attenuated by the filter, and the out-of-band quantization noise component is output in the opposite phase. The noise component is canceled by synthesizing the signal of the first route and the signal of the second route, but the canceled noise signal is returned to the FB loop of the DPD, and noise is measured by the signal processing unit 11. The amount that is canceled (the amount that has not been canceled) is quantitatively confirmed, and the amplitude and phase of the out-of-band noise component of the second route are adjusted so that this amount becomes the minimum value. Since this calibration can minimize out-of-band noise components, the attenuation characteristics of the BPF 21 can be relaxed, and the size and cost of the BPF 21 can be reduced.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 11 ... Signal processing part, 111 ... (DELTA) Σ modulation part, 112 ... DPD distortion compensation part, 113 ... Signal generation part, 12 ... D / A converter, 13 ... Oscillator, 14 ... Mixer, 15 ... Amplifier, 16 ... Mixer, 17 DESCRIPTION OF SYMBOLS ... A / D converter, 18 ... D / A converter, 19 ... Mixer, 20 ... Amplifier, 21 ... Band pass filter, 22 ... Frequency divider, 23 ... Antenna, 24 ... Synthesis circuit.

Claims (4)

A modulation unit that delta-sigma modulates a transmission bit string into a modulation signal having a signal component and a quantization noise component;
A first amplifier for amplifying power of the modulated signal;
A generating unit that generates a signal obtained by inverting the quantization noise component of the modulated signal;
A second amplifier that amplifies the power of the signal generated by the generation unit;
A transmission apparatus comprising: combining means for combining the output of the first amplifier and the output of the second amplifier to generate a transmission signal. A compensation unit for compensating for a distortion component generated in the first amplifier;
The transmission apparatus according to claim 1, wherein an output of the combining unit is fed back to the compensation unit.   The transmission device according to claim 1, wherein the generation unit further generates a signal obtained by adding signal components of the modulation signal in phase.   4. The transmission apparatus according to claim 3, wherein outputs of the first amplifier and the second amplifier are halved.

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