JP2007028564A - Power amplification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power amplification apparatus in which a power amplification capability required for an amplifier in the power amplification of an OFDM signal can be reduced. <P>SOLUTION: The amplitude of an OFDM digital signal quadrature-modulated by digital signal processing is bisected (2) by an amplitude limiter circuit (3) and a subtraction circuit (4). Divided two signals are individually subjected to D-A conversion (6, 9) and frequency conversion (7, 10) and composed of a composer (13) after power amplification (8, 11). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an OFDM (Orthogonal Frequency Division Multiplex) signal power amplifier.

Since an OFDM signal is a signal in which a large number of carrier waves having different frequencies are modulated with amplitude and phase shift, an unnecessary component is generated in its own frequency band due to nonlinear distortion of the amplifier, and equivalently becomes noise. For this reason, since the power amplifier is required to have excellent linear characteristics (amplification characteristics), a power amplifier having high power amplification capability is required. For example, when the effective power of the OFDM signal and the video power of the NTSC system are the same, the OFDM signal requires a higher power amplification capability than the NTSC system. A power amplifier with a large signal power uses a semiconductor element that can amplify the power up to a large power, so that the power consumption increases. In addition, the cooling system for cooling the power amplifier is increased in size to cope with an increase in the amount of heat generated due to power loss. In order to suppress the power amplification capability of the amplifier as much as possible, a power amplifier of a type in which the power amplification capability is reduced and the nonlinear characteristic is compensated with a compensator is employed.
Mamoru Nagatsuka, Aiichiro Miyatake “Construction of OFDM Transmitting Station Using Current System Broadcaster” The Institute of Image Information and Television Engineers, Technical Report Vol. 21. No. 44. PP. 1-6

  An object of the present invention is to provide a power amplifying apparatus capable of reducing the power amplifying capability required for an amplifier in power amplification of an OFDM signal.

In order to achieve this object, an OFDM power amplifying device of the present invention includes a signal dividing unit that divides the amplitude of an OFDM digital signal that is orthogonally modulated by digital signal processing, and converts each divided signal from a digital signal to an analog signal. A power amplifying unit that combines after frequency conversion and power amplification,
The signal dividing unit includes a first step of limiting an amplitude of the orthogonally modulated OFDM digital signal, and a second step of subtracting the output signal of the first step from the orthogonally modulated OFDM digital signal; ,
The power amplification unit includes a third step of converting the output signal of the first step from a digital signal to an analog signal, and a fourth step of converting the output signal of the second step from a digital signal to an analog signal; The fifth step of converting the output signal of the third step into a transmission frequency, the sixth step of converting the output signal of the fourth step into a transmission frequency, and the output signal of the fifth step A seventh step for amplifying; an eighth step for amplifying the output signal of the sixth step; a ninth step for converting to a transmission frequency; an output signal of the seventh step; And a tenth step of synthesizing the output signals of the steps.

The signal dividing unit includes an amplitude limiting circuit for limiting an amplitude of the OFDM digital signal orthogonally modulated by digital signal processing, and a subtraction for subtracting an output signal of the amplitude limiting circuit from the orthogonally modulated OFDM digital signal. Circuit,
The power amplification unit includes a first D / A converter that converts an output signal of the amplitude limiting circuit from a digital signal to an analog signal, and a second D / A converter that converts the output signal of the subtraction circuit from a digital signal to an analog signal. D / A converter, a first up converter that converts the output signal of the first D / A converter into a transmission frequency, and an output signal of the second D / A converter into a transmission frequency A second up-converter, a first power amplifier that amplifies the output signal of the first up-converter, a second power amplifier that amplifies the output signal of the second up-converter, and a transmission frequency And a combiner for combining the output signal of the first power amplifier and the output signal of the second power amplifier.

  In addition, the signal division unit of the present apparatus, the first step of limiting the amplitude of the orthogonally modulated OFDM digital signal, the eleventh step of band limiting the output signal of the first step, A twelfth step of delaying the orthogonally modulated OFDM digital signal by the same delay time as the eleventh step; and the output signal of the eleventh step is subtracted from the output signal of the twelfth step. And a second step.

  The signal dividing unit of the apparatus includes an amplitude limiting circuit that limits an amplitude of the orthogonally modulated OFDM digital signal, a band-pass filter that band-limits an output signal of the amplitude limiting circuit, and the orthogonally modulated signal. A delay circuit having the same delay time as that of the band-pass filter for the OFDM digital signal, and a subtraction circuit for subtracting the output signal of the band-pass filter from the output signal of the delay circuit.

  According to the present invention, by dividing the amplitude of the OFDM digital signal to reduce the individual signal, the power amplifier can use a semiconductor element having a power amplification capability smaller than that in the case where the amplitude of the OFDM digital signal is not divided. . This enables simplification of the cooling system by reducing power consumption and heat generation due to power loss.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 shows a block diagram of a first embodiment of the present invention. FIG. 1 includes two blocks, a signal divider 2 and a power amplifier 5. A signal dividing unit 2 includes an amplitude limiting circuit 3 that limits the amplitude of an input signal (an OFDM digital signal that has been orthogonally modulated by digital signal processing) at the input terminal 1, and the amplitude limiting circuit 3 based on the input signal. The subtracting circuit 4 subtracts the output signal.

  FIG. 2 illustrates the characteristics of the amplitude limiting circuit 3 of FIG. Fig. 2 Amplitude limiting characteristic (characteristic A) 21 has a characteristic that the output signal is limited to a constant value when the absolute value of the input signal exceeds a certain value, and the amplitude limiting characteristic (characteristic B) 22 has a large input signal. This is an example of the characteristic of greatly compressing the output signal.

  3A illustrates a sampling signal of an OFDM digital signal that is orthogonally modulated by digital signal processing, and is an input signal of the input terminal 1 of FIG. Further, FIG. 3B illustrates the signal 32 whose amplitude is limited by the amplitude limiting circuit 3 shown in FIG. The difference signals 33 and 34 in FIG. 3C are signals obtained by subtracting FIG. 3B from FIG. 3A, and are executed by the subtraction circuit 4 in FIG.

  1 includes a first D / A converter 6 that converts an output signal of the amplitude limiting circuit 3 from a digital signal to an analog signal, and an output signal of the subtraction circuit 4 from the digital signal. A second D / A converter 9 for converting to an analog signal; a first U / C 7 (upconverter 7) for converting an output signal of the D / A converter 6 into a transmission frequency; and a D / A converter 9 The second U / C 10 that converts the output signal of the U / C 7 into a transmission frequency, the first power amplifier 8 that amplifies the output signal of the U / C 7, and the second power amplifier that amplifies the output signal of the U / C 10 11, a local oscillator 12 that supplies a local oscillation signal to U / C 7 and U / C 10, and a combiner 13 that combines the output signal of the power amplifier 8 and the output signal of the power amplifier 11.

  FIG. 4 shows a configuration diagram of the second embodiment of the present invention. The OFDM signal is a signal in which a large number of carrier waves having different frequencies are modulated with amplitude and phase shift, and the occupied frequency band is expanded by the amplitude nonlinearity characteristic of the amplitude limiting circuit 3 in FIG. When the occupied frequency band is expanded, the power amplifier is required to have a wide band characteristic, so the band is limited by the band pass filter 41 in FIG. FIG. 5 illustrates frequency characteristics of the band-pass filter 41 in FIG. FIG. 5 shows a band-pass filter characteristic (characteristic A) 51 when the output signal of the amplitude limiting circuit 3 shown in FIG. 4 is limited to the same frequency band as that of the OFDM signal. A case where the output signal of the limiting circuit 3 is band-limited gently is illustrated. 4 performs a discrete convolution operation in the time domain between the impulse response of the band pass filter 41 and the output signal of the amplitude limiting circuit 3 in FIG. 4 to output the output signal of the amplitude limiting circuit 3. Limit bandwidth. Since the output signal of the bandpass filter 41 in FIG. 4 is delayed by the convolution operation time (denoted by τ), the delay circuit 42 delays the input signal at the input terminal 1 in FIG. 4 subtracts the output signal of the bandpass filter 41 from the output signal of the delay circuit 42 of the same figure.

  For example, in OFDM terrestrial digital television broadcasting, transmission power reaches about 5 KW. By applying the present invention to these transmitters having large transmission power, the power consumption of the transmitter can be reduced and the cooling system can be simplified.

  It is a block diagram of the first embodiment of the present invention.   It is an example of a characteristic of an amplitude limiting circuit.   It is an example of a sampled OFDM digital signal, a signal obtained by limiting the amplitude of the signal, and a difference signal.   It is a block diagram of the second embodiment of the present invention.   It is an example of a characteristic of a band pass filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal 2 Signal division part 3 Amplitude limiting circuit 4 Subtraction circuit 5 Power amplification part 6, 9 D / A converter 7, 10 U / C (up converter)
8, 11 Power amplifier 12 Local transmitter 13 Synthesizer 14 Output terminal 21 Amplitude limiting characteristic of amplitude limiting circuit (characteristic A)
22 Amplitude limiting characteristics of amplitude limiting circuit (Characteristic B)
31 Sampled OFDM digital signal 32 Signal obtained by subtracting 32 from sampled OFDM digital signal 33, 34 31 41 Band pass filter 42 Delay circuit 51 Band pass filter characteristic (characteristic A)
52 Band pass filter characteristics (Characteristic B)

Claims (4)

A signal dividing unit that divides the amplitude of the orthogonally modulated OFDM digital signal, and a power amplifying unit that converts each divided signal from a digital signal to an analog signal, frequency-converts and amplifies the power,
The signal dividing unit includes a first step of limiting an amplitude of the orthogonally modulated OFDM digital signal, and a second step of subtracting the output signal of the first step from the orthogonally modulated OFDM digital signal; ,
The power amplification unit includes a third step of converting the output signal of the first step from a digital signal to an analog signal, and a fourth step of converting the output signal of the second step from a digital signal to an analog signal; The fifth step of converting the output signal of the third step into a transmission frequency, the sixth step of converting the output signal of the fourth step into a transmission frequency, and the output signal of the fifth step A seventh step for amplifying; an eighth step for amplifying the output signal of the sixth step; a ninth step for converting to a transmission frequency; an output signal of the seventh step; And a tenth step of synthesizing the output signals of the steps. The signal dividing unit includes an amplitude limiting circuit that limits an amplitude of the orthogonally modulated OFDM digital signal, a subtracting circuit that subtracts an output signal of the amplitude limiting circuit from the orthogonally modulated OFDM digital signal,
The power amplification unit includes a first D / A converter that converts an output signal of the amplitude limiting circuit from a digital signal to an analog signal, and a second D / A converter that converts the output signal of the subtraction circuit from a digital signal to an analog signal. D / A converter, a first up converter that converts the output signal of the first D / A converter into a transmission frequency, and an output signal of the second D / A converter into a transmission frequency A second up-converter, a first power amplifier that amplifies the output signal of the first up-converter, a second power amplifier that amplifies the output signal of the second up-converter, and a transmission frequency A power amplifying apparatus comprising: a local transmitter for performing the operation; and a combiner that combines the output signal of the first power amplifier and the output signal of the second power amplifier.   The signal dividing unit includes: a first step for limiting the amplitude of the orthogonally modulated OFDM digital signal; an eleventh step for band limiting the output signal of the first step; and the orthogonally modulated OFDM A twelfth step of delaying the digital signal by the same delay time as the eleventh step; and a second step of subtracting the output signal of the eleventh step from the output signal of the twelfth step. The power amplifying apparatus according to claim 1 or 2, further comprising:   The signal dividing unit includes: an amplitude limiting circuit that limits an amplitude of the orthogonally modulated OFDM digital signal; a band-pass filter that band-limits an output signal of the amplitude limiting circuit; and the orthogonally modulated OFDM digital signal The delay circuit which delays only the delay time same as a band pass filter, and the subtraction circuit which subtracts the output signal of the said band pass filter from the output signal of the said delay circuit, The 1 or 2 characterized by the above-mentioned. Alternatively, the power amplifying device according to 3.

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