Modulators – Phase shift keying modulator or quadrature amplitude modulator
Patent
1998-09-28
2000-08-01
Grimm, Siegfried H.
Modulators
Phase shift keying modulator or quadrature amplitude modulator
375271, 375298, 375302, H04L 2736
Patent
active
060972599
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a modulation apparatus and a modulation method for orthogonally modulating a digital baseband signal, such as is utilized in a digital mobile communication and other communication system.
2. Discussion of Background Information
In a digital mobile communication system such as portable telephone, as disclosed in Japanese Unexamined Patent Publication No. 6-21991, a modulator is utilized. The modulator divides a transmitted signal into an in-phase component and a quadrature phase component, .DELTA..SIGMA. modulates each component then orthogonal modulates each component.
In the following description, a conventional modulator is explained with respect to the drawings. FIG. 1 is a block diagram illustrating a configuration of a conventional modulator.
In FIG. 1, .DELTA..SIGMA. modulator 2 converts a modulated signal input from input terminal 1 into a binary signal and outputs it to a multiplying circuit 3. Multiplying circuit 3 generates an amplitude modulated signal by multiplying the binary signal output from .DELTA..SIGMA. modulator 2 by a carrier signal and outputs the multiplied signal to output terminal 4.
Next, the operations of a conventional modulator having the above configuration are explained.
First a modulated signal input from input terminal 1 is .DELTA..SIGMA. modulated at .DELTA..SIGMA. modulator 2, then a binary .DELTA..SIGMA. modulated signal is output. Then an amplitude modulated signal is generated by multiplying the .DELTA..SIGMA. modulated signal by a carrier signal, which is output to another apparatus, via output terminal 4. As described above, a conventional modulator modulates a transmission signal into a digital orthogonal signal.
However in the conventional modulator as described above, a multiplication process is necessary for an orthogonal modulation under a high sampling frequency that is not avoidable to process the .DELTA..SIGMA. modulation. Because this requires a high-rate multiplier, the conventional modulator has a problem in that the consumed electric power becomes high.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide a modulator without requiring a high-rate multiplier to make electric power consumption low.
According to the present invention, this object is achieved by utilizing a modulator for setting a center frequency of a digital baseband signal at four times the frequency of an intermediate frequency to .DELTA..SIGMA. modulate, and switching, at a switching circuit, an output signal of a .DELTA..SIGMA. modulation circuit and its code inverted signal at a sampling frequency of four times the frequency of an intermediate frequency to select.
This object is achieved by a modulator that arbitrarily sets a center frequency of a digital baseband signal to .DELTA..SIGMA. modulate the signal and selecting a carrier signal according to an output signal from a .DELTA..SIGMA. modulation circuit.
BRIEF DESCRIPTION OF DRAWINGS
The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:
FIG. 1 is a block diagram illustrating a configuration of a conventional modulator;
FIG. 2 is a block diagram illustrating a configuration of a modulator according to a first embodiment of the present invention;
FIG. 3 is a block diagram illustrating a configuration of a modulator according to a second embodiment of the present invention;
FIGS. 4(a)-4(d) are wave diagrams illustrating the relation of signal and noise at a modulator in the second embodiment of the present invention;
FIG. 5 is a block diagram illustrating a configuration of a modulator according to a third embodiment of the present invention;
FIG. 6 is a block diagram illustrating a configuration of a modulator according to a fourth embodi
REFERENCES:
patent: 5530722 (1996-06-01), Dent
patent: 5534827 (1996-07-01), Yamaji
patent: 5714916 (1998-02-01), Yamaji
Saito Yoshiko
Uesugi Mitsuru
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