JPH0918536A - Modulation amplification system - Google Patents

Abstract

PURPOSE: To amplify an amplitude-modulating signal without distortion by using a power amplifier which has amplitude distortion by converting an inputted digital signal into plural phase-modulating signals, and amplifying and adding the respective output signals together. CONSTITUTION: The 4-bit digital signal inputted from an input terminal 100 is converted by a modulating signal generator 110 into the four phase signals. Respective modulators 120-123 impose phase modulation on the basis of the signals outputted by the modulating signal generator 110. Even when input/ output characteristics of the amplifier 130 are nonlinear, the input signal to the amplifier 130 shifts only in phase and is constant in amplitude, so distortion originating from the nonlinear characteristics never appears. Further, the phase modulation is imposed by the modulators 120-123, so the frequency spectrum of a modulated signal is wider than the frequency spectrum of an input signal, but the phase shift by the modulation is <=±45 deg., so the spread of the spectrum can nearly be ignored and then nearly the same frequency characteristics with linear modulation can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation amplification system for amplifying an amplitude modulation signal without distortion by using a power amplifier having amplitude distortion.

[0002]

2. Description of the Related Art A digital signal transmission method using a wireless line is widely used because not only binary data transmission but also voice and image can be digitized and transmitted. However, since the frequency for wireless transmission is finite, with the increase in demand, development of a high-efficiency transmission method capable of transmitting a larger amount of data within a limited frequency band is underway.

As one of high-efficiency transmissions, a quadrature amplitude modulation system is used which modulates not only the phase component but also the amplitude component of the transmission signal. In order to put information on the amplitude component as well, the power amplifier of the transmitter needs to have little amplitude distortion.

FIG. 2 shows an outline of a conventional modulation amplification technique.

The 4-bit signal series digital signal input from the terminal 200 is converted into two-dimensional 16-point signals by the mapper 210 as shown in FIG. This 2
The dimensional signal is quadrature amplitude modulated by the modulator 220 and output as a one-dimensional signal. The output signal of the modulator 220 is amplified by the amplifier 230 and output.

[0006]

However, in the power amplifier, as shown in FIG. 4, the amplitude relationship between the input signal and the output signal is not linear at all levels, and is non-linear when the input signal is small and when the input signal is large. The ingredient of appears.
When this non-linear component is included in the output signal, a harmonic component is also added to the output signal, so that the phenomenon that the frequency bandwidth of the transmission signal is increased appears.

In order to prevent harmonic components from being included in the output signal, it is necessary to amplify only the linear portion of the input output characteristic as shown in FIG. However, since the use of such a power amplifier causes a decrease in power efficiency, a high efficiency modulation method cannot be used in a region where power consumption is a problem, such as a mobile terminal, and a low efficiency such as FSK or PSK cannot be used. We have no choice but to rely on efficient modulation methods.

[0008]

According to the present invention, even in a power amplifier having large amplitude distortion, a plurality of power amplifiers are equivalently used to realize a power amplifier having small amplitude distortion.

According to the present invention, as a method of modulating and amplifying a digital signal, a modulation signal generator for converting an input digital signal into N (N is an integer of 3 or more) phase modulation signals, and the modulation signal generation. From N modulators each of which inputs N output signals of the modulator to perform phase modulation, N amplifiers of each output signal of the modulator that performs amplification, and N amplifiers It is characterized in that it is composed of an adder which inputs N output signals which are output, adds each of them, and outputs the added signals.

[0010]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of the present invention. Here, a method in which each of the modulator and the amplifier is composed of four will be described. A signal equivalent to 16-value QAM is used as an example of the modulation signal.

The 4-bit digital signal input from the input terminal 100 is converted into four phase signals by the modulation signal generator 110.

FIG. 8 shows the correspondence between the phase angles of the 4-bit input signal and the output signal of the modulation signal generator 110. 6 and 7 show the loci of the output signals of the modulation signal generator 110 that are input to the modulators 120, 121, 122 and 123, respectively.
The four output signals are 0 °, 90 °, 180 °,
The phase can be moved within a range of ± 45 ° with reference to −90 °.

Each modulator 120, 121, 122, 123
Then, phase modulation is performed based on the signal output from the modulation signal generator 110. Each modulator 120, 121, 122,
The output signal of 123 is output to each amplifier 130, 131, 132,
It is input to 133 and amplified.

Even if the input / output characteristic of the amplifier 130 has a non-linear characteristic as shown in FIG. 4, since the input signal of the amplifier 130 has a constant amplitude only with a change in phase, distortion due to the non-linear characteristic appears in the output. There is no. Also, since the modulators 120, 121, 122, 123 perform phase modulation, the frequency spectrum of the modulated signal is wider than the frequency spectrum of the input signal, but the phase change due to modulation is ± 45 ° or less. Since the spread of the spectrum can be almost ignored, it is possible to have a frequency characteristic almost equal to that when linear modulation is performed.

Each amplifier 130, 131, 132, 133
The signals amplified by are combined by the adder 140. Figure 6
When the four two-dimensional signals shown in FIG. 7 are combined, a signal equivalent to the 16-value QAM signal shown in FIG. 3 can be generated. 6 and 7, each signal has a constant amplitude, but the combined signal can express both the amplitude and the phase.

[0017]

As described above, according to the present invention, even if the signal transmitted from the antenna is equivalently in the high efficiency modulation system such as the quadrature amplitude modulation, it is input to each power amplification section. Since the signal amplitude is almost constant, class C amplification with large distortion but high power efficiency can be used, and a highly efficient modulation method should be adopted even in fields such as mobile terminals that want to minimize power consumption. You can

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional modulation amplification method.

FIG. 3 is a diagram showing signal points of a 16-value QAM signal.

FIG. 4 is a diagram showing amplitude characteristics of an input and an output of a power amplifier.

FIG. 5 is a diagram showing input and output amplitude waveforms when amplification is performed using the linear region of the power amplifier.

FIG. 6 is a diagram showing phase signals input to modulators 120 and 121.

FIG. 7 is a diagram showing phase signals input to modulators 122 and 123.

FIG. 8 is a table showing a correspondence between an input 4-bit digital signal and an output phase signal of the modulation signal generator.

[Explanation of symbols]

 100 input terminal 110 modulation signal generator 120 modulator 121 modulator 122 modulator 123 modulator 130 amplifier 131 amplifier 132 amplifier 133 amplifier 140 adder 200 input terminal 210 mapper 220 modulator 230 amplifier

Claims (1)

[Claims] 1. A modulation signal generator for modulating and amplifying a digital signal, the modulation signal generator converting an input digital signal into N (N is an integer of 3 or more) phase modulation signals, and the modulation signal generator. N modulators each of which inputs N output signals and performs phase modulation, and an N modulator that inputs each output signal of the modulator and performs amplification.
2. A modulation amplification system comprising: an amplifier composed of a plurality of amplifiers; and an adder that inputs N output signals output from the N amplifiers, adds the output signals, and outputs the added signals.