JP2018093399A - Highly efficient digital modulation transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient digital modulation transmitter capable of achieving high power utilization efficiency and disuse of a distortion compensation circuit.SOLUTION: The digital modulation transmitter includes: a polar coordinate conversion part 3 which divides an input digital modulation base band signal into a phase information signal and an amplitude information signal; a mixer 42 which converts a phase information signal into a high frequency; a PTAM modulator 43 which produces a two-system high-frequency rectangular wave of a duty ratio of 50% with a relative phase difference added on the basis of the high frequency and the amplitude information signal; and an amplitude processing part which makes the two-system rectangular wave subjected to switching power amplification for synthesis and produces a high-frequency signal subjected to phase modulation and amplification modulation by removing a harmonic wave.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a transmitter based on a multicarrier or single carrier digital modulation scheme such as an OFDM (Orthogonal Frequency Division Multiplexing) scheme or a QPSK (Quadrature Phase Shift Keying) scheme, and in particular, a high linearity required for a power amplifier. It relates to an efficient digital modulation transmitter.

  For example, the current GMDSS (Global Maritime Distress and Safety System, a global maritime distress and safety system) is built on the premise of technology several decades ago, and considering the development of satellite communication technology, The entire system has been reviewed. As one of them, it is considered to shift (or operate in parallel) NAVTEX broadcasting capable of only text distribution to NAVDAT broadcasting capable of digital data distribution.

  In NAVDAT broadcasting, an OFDM modulation scheme is under study, but a transmitter such as a general OFDM scheme or a QPSK scheme requires high linearity and linearity in a power amplifier. For this reason, as shown in FIG. 6, it is necessary to use a linear amplifier as a power amplifier and to provide a distortion compensation circuit in order to further ensure linearity (for example, Patent Document 1). That is, after generating a baseband signal, distortion compensation is performed and power amplification is performed by a linear amplifier, thereby ensuring high linearity.

Japanese Patent Laid-Open No. 10-098421

  As described above, since the conventional transmitter uses a linear amplifier, the power use efficiency is low (for example, 50% or less), and there is a problem that the power transmitter is increased in size. Further, since high linearity cannot be ensured with only a linear amplifier, there is a problem that a distortion compensation circuit needs to be provided and the configuration becomes complicated.

  Therefore, an object of the present invention is to provide a high-efficiency digital modulation transmitter that can obtain high power utilization efficiency and does not require a distortion compensation circuit.

  In order to achieve the above object, the invention described in claim 1 includes a conversion unit that divides an input digital modulation baseband signal into a phase information signal and an amplitude information signal, and a mixer that converts the phase information signal into a high frequency. A PTAM modulator that generates two high-frequency rectangular waves with a duty ratio of 50%, which is obtained by adding a relative phase difference based on the high-frequency and the amplitude information signal, and amplifying the switching power of the two rectangular waves A high-efficiency digital modulation transmitter comprising: an amplification processing unit that synthesizes and generates a high-frequency signal that is subjected to phase modulation and amplitude modulation by removing harmonics.

  According to the present invention, the phase information signal and the amplitude information signal are generated and extracted from the input baseband signal by the conversion unit, and the phase information signal and the amplitude processing unit are generated by the PTAM (Phase To Amplitude Modulation) modulator and the amplification processing unit. A high-frequency signal that is phase-modulated and amplitude-modulated based on the amplitude information signal is generated.

  According to a second aspect of the present invention, in the high-efficiency digital modulation transmitter according to the first aspect, the amplification processing unit includes a plurality of amplification processing units, and the two high-frequency rectangular waves are input to the multiple amplification processing unit in pairs. And a power combiner that combines the high-frequency signals generated by the respective amplification processors.

  According to a third aspect of the present invention, in the high-efficiency digital modulation transmitter according to the first or second aspect, the digital modulation baseband signal includes a multicarrier signal based on an OFDM system, a QPSK system, a QAM system, or the like. It includes a single carrier signal. According to a fourth aspect of the present invention, in the high-efficiency digital modulation transmitter according to the first to third aspects, the two high-frequency frequencies generated by the PTAM modulator are sine waves.

According to the first aspect of the present invention, the phase difference between the two rectangular waves having a duty ratio of 50% is changed, the two rectangular waves are switched and amplified to be synthesized, the harmonics are removed, and the high frequency signal is removed. Therefore, a switching amplifier can be used without using a linear amplifier. As a result, high power utilization efficiency is obtained, and it is easy to apply to large power.
In addition, since the amplitude modulation is realized by the relative phase difference between the two types of rectangular waves, high linearity is obtained, and a distortion compensation circuit is not required. As a result, the configuration is simplified, and high reliability and cost reduction can be achieved.

  According to the second aspect of the invention, since the high frequency signals generated by the plurality of amplification processing units are combined by the power combining unit, the power can be increased.

1 is a schematic block diagram showing a high-efficiency digital modulation transmitter according to Embodiment 1 of the present invention. It is a block diagram which shows the concept of the amplitude modulation transmitter of a PTAM system. It is a figure which shows the waveform of each part by the PTAM system transmitter of FIG. It is a figure which shows the pulse width modulation principle by the PTAM system transmitter of FIG. It is a schematic block diagram showing a high-efficiency digital modulation transmitter according to Embodiment 2 of the present invention. It is a schematic block diagram showing a conventional digital modulation transmitter.

  The present invention will be described below based on the illustrated embodiments.

(Embodiment 1)
1 is a schematic block diagram showing a high-efficiency digital modulation transmitter 1 according to Embodiment 1 of the present invention. The high-efficiency digital modulation transmitter 1 is a transmitter using a digital modulation scheme such as the OFDM scheme or the QPSK scheme. In this embodiment, the case of the OFDM scheme will be mainly described. The high-efficiency digital modulation transmitter 1 mainly includes a polar coordinate conversion unit (conversion unit) 3 and a PTAM modulation unit 4.

  The polar coordinate conversion unit 3 is a conversion unit that divides an input digital modulation signal into a phase information signal and an amplitude information signal V2. That is, a modulation digital signal is input to the OFDM modulator 2, and a baseband signal (digital signal) output after being OFDM-modulated by the OFDM modulator 2 is input to the polar coordinate conversion unit 3. Then, the polar coordinate conversion unit 3 performs signal processing, that is, polar coordinate conversion, on the baseband signal and divides it into a phase information signal (phase component) and an amplitude information signal (amplitude component) V2.

  The PTAM modulation unit 4 changes the phase difference between the two rectangular waves having a duty ratio of 50% based on the phase information signal and the amplitude information signal V2 by the polar coordinate conversion unit 3, and performs switching amplification on the two rectangular waves. Are synthesized, and the high-frequency signal which is subjected to phase modulation and amplitude modulation by removing the harmonics is generated. Specifically, a carrier signal generator 41, a correlator (mixer) 42, a PTAM modulator 43, switching amplifiers 44 and 45, an output transformer 46, and a low-pass filter 47 are provided. Here, the switching amplifiers 44 and 45, the output transformer 46, and the low-pass filter 47 constitute an amplification processing unit.

  The carrier signal generator 41 generates a high frequency RF carrier signal, and the correlator 42 correlates the input phase information signal from the polar coordinate converter 3 and the carrier signal from the carrier signal generator 41, An RF carrier wave V1 is output. Here, the RF carrier V1 has a waveform obtained by phase-modulating a multicarrier sine wave.

  Here, the PTAM system, which is the core of amplitude modulation, will be described. The basic block diagram is as shown in FIG. 2, and the basic operation waveform is shown in FIG.

  The PTAM modulator 43 changes the phase difference between the two systems of RF rectangular waves having a duty ratio of 50% based on the input RF carrier wave V1 from the correlator 42 and the amplitude information signal V2 from the polar coordinate converter 3. , RF rectangular waves W1 and W2 are generated. That is, the phase difference between the two RF rectangular waves W1 and W2 having a duty ratio of 50% is changed according to the amplitude of the amplitude information signal V2. Specifically, as shown in FIG. 3, the RF carrier wave V1 and the amplitude information signal V2 are overlapped, and a rectangular wave is alternately raised at the intersection (falling W1 at the intersection when V1 is lowered, W2 is raised at the intersection when V1 rises), and two RF rectangular waves W1 and W2 having different phases are generated.

  In the above processing, a large number of delay circuits may be prepared, and the number of delay circuits used in the two systems may be changed.

From the generation of such RF rectangular waves W1 and W2 to the generation of W4 is based on the following principle. First, as shown in FIG. 4, the amplitude E ′ of the fundamental wave component of the rectangular wave having a period of 2π and a pulse width of 2θ is obtained by the following equation.

これを（数１）に代入すると、

であるから、基本波ｅは、ｘ＝ωｔとして

となり、振幅変調されていることがわかる。 From this equation, it can be seen that the amplitude E ′ of the fundamental wave is proportional to the sine of the pulse width θ. Therefore, if the pulse width θ is changed in proportion to the arc sine of the modulation signal, the amplitude of the fundamental wave also changes in proportion to the modulation signal and is amplitude-modulated. The relationship between the pulse width θ and the modulation angular frequency p is expressed as follows:

Substituting this into (Equation 1),

Therefore, the fundamental wave e is x = ωt

Thus, it can be seen that the amplitude is modulated.

となり、θは変調信号ｇのアークサインになる。 As shown in FIG. 3, the RF rectangular waves W1 and W2 thus obtained are phase-adjusted by θ with respect to the original RF carrier wave V1 by increasing or decreasing the modulation signal, as shown in FIG. The second RF rectangular wave W2 operates so that the phase is delayed by θ. The relationship between this modulation signal g (pt) and θ is

And θ becomes the arc sine of the modulation signal g.

  The switching amplifiers 44 and 45 are class D power amplifiers having high power efficiency, and the first switching amplifier 44 performs switching amplification of the first RF rectangular wave W1 from the PTAM modulator 43, and the second switching amplifier 45. Switches and amplifies the second RF rectangular wave W2 from the PTAM modulator 43. Here, the reason why the duty ratio of the RF rectangular waves W1 and W2 is set to 50% is that amplification is easy.

  The output transformer 46 synthesizes the RF rectangular waves W1 and W2 amplified by the switching amplifiers 44 and 45. That is, the difference between the first RF rectangular wave W1 and the second RF rectangular wave W2 is taken to generate a PWM (Pulse Width Modulation) pulse W3 as shown in FIG. Here, the pulse width H of the PWM wave W3 is increased according to the amplitude of the amplitude information signal V2.

  The low-pass filter 47 extracts only the fundamental wave component excluding the harmonic component of the PWM wave W3 input from the output transformer 46, and generates and outputs an amplitude-modulated high-frequency signal W4.

  According to the high-efficiency digital modulation transmitter 1 (FIG. 1) configured to incorporate the above PTAM modulation unit 4, the baseband signal OFDM-modulated by the OFDM modulator 2 is converted into a phase information signal and an amplitude by the polar coordinate conversion unit 3. It is divided into an information signal V2. Next, the phase information signal and the carrier signal are subjected to correlation processing by the correlator 42 to output the RF carrier wave V1, and the carrier wave input of the PTAM modulator 43 becomes a phase-modulated waveform. In the PTAM modulator 43, two RF rectangular waves V3 and V4 having a duty ratio of 50% and different phases are generated based on the RF carrier wave V1 and the amplitude information signal V2. Note that the phases of the RF rectangular waves V3 and V4 change simultaneously based on the phase information.

  Subsequently, the RF rectangular waves V3 and V4 are respectively switched and amplified by the switching amplifiers 44 and 45, and the two RF rectangular waves V3 and V4 are synthesized by the output transformer 46 to generate the PWM wave V5. Then, the harmonic component of the PWM wave V5 is removed by the low-pass filter 47, and a high-frequency signal V6 subjected to phase modulation and amplitude modulation is generated and output.

  Thus, according to the high-efficiency digital modulation transmitter 1, the phase difference between the two RF rectangular waves V3 and V4 having a duty ratio of 50% is changed, and the two RF rectangular waves V3 and V4 are switched and amplified. In order to generate the high-frequency signal V6, the switching amplifiers 44 and 45 can be used without using the linear amplifier. As a result, high power utilization efficiency (for example, about 80%) is obtained, and it is easy to apply to large power. In particular, since amplitude modulation is performed by the PTAM modulator 43 (phase modulation) in the low power stage before amplification, it is suitable for high power and a high power modulator becomes unnecessary.

  In addition, as can be seen from (Equation 1) to (Equation 4), the output amplitude is determined by the phase difference between V3 and V4 and hardly depends on the device characteristics of the switching power amplifier, so that high linearity is obtained. , No distortion compensation circuit is required. As a result, the configuration is simplified, and high reliability and cost reduction can be achieved.

(Embodiment 2)
FIG. 5 is a schematic block diagram showing a high-efficiency digital modulation transmitter according to Embodiment 2 of the present invention. This embodiment is different from the first embodiment in that it includes a plurality of amplification processing units and a power combining unit 5 that combines high-frequency signals generated by the respective amplification processing units, and is equivalent to the first embodiment. About the structure of this, the description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  That is, a plurality of sets of switching amplifiers 44 and 45, an output transformer 46, and a low-pass filter 47 constituting an amplification processing unit are provided, and RF rectangular waves V3 and V4 from the PTAM modulator 43 are respectively amplified and combined in each amplification processing unit. And harmonics are removed, and a phase modulated and amplitude modulated high frequency signal is generated. And since these high frequency signals are synthesize | combined in the electric power synthetic | combination part 5, more electric power can be increased.

  The embodiment of the present invention has been described above, but the specific configuration is not limited to the above embodiment, and even if there is a design change or the like without departing from the gist of the present invention, Included in the invention. For example, in the above embodiment, the case of the OFDM multicarrier has been described, but a single carrier digital modulation method such as a QPSK method or a QAM (Quadrature Amplitude Modulation) method may be used. Moreover, although the case where two systems of rectangular waves are amplified with switching power has been described, two systems of sine waves may be amplified with switching power.

1 High-efficiency digital modulation transmitter 2 OFDM modulator 3 Polar coordinate converter (converter)
4 PTAM modulator 41 Carrier signal generator 42 Correlator (mixer)
43 PTAM modulator 44, 45 Switching amplifier 46 Output transformer 47 Low pass filter 5 Power combiner V1 RF carrier wave (phase modulated wave)
V2 amplitude information signal

Claims (4)

A converter that divides the input digital modulation baseband signal into a phase information signal and an amplitude information signal;
A mixer for converting the phase information signal into a high frequency;
A PTAM modulator that generates two high-frequency rectangular waves with a duty ratio of 50%, to which a relative phase difference is added based on the high-frequency and the amplitude information signal;
An amplification processing unit that generates a high-frequency signal that is phase-modulated and amplitude-modulated by combining the two systems of rectangular waves by amplifying switching power and removing harmonics;
A high-efficiency digital modulation transmitter characterized by comprising:   A plurality of amplification processing units, and a power combining unit that combines the two high-frequency rectangular waves into the plurality of amplification processing units and combines the high-frequency signals generated by the amplification processing units. The high-efficiency digital modulation transmitter according to claim 1.   The digital modulation baseband signal includes a multi-carrier signal based on a scheme including an OFDM scheme and a single carrier signal based on a scheme including a QPSK scheme and a QAM scheme. The high-efficiency digital modulation transmitter described in the paragraph. The high-efficiency digital modulation transmitter according to any one of claims 1 to 3, wherein the two high-frequency waves generated by the PTAM modulator are sinusoidal waves.

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