Modulators – Phase shift keying modulator or quadrature amplitude modulator
Patent
1990-12-05
1992-02-25
Pascal, Robert J.
Modulators
Phase shift keying modulator or quadrature amplitude modulator
332124, 375 52, 375 67, H03C 300
Patent
active
050917056
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to FM modulators for use in recording video signals and for radio communication, and particularly, to FM modulators for FM-modulating integrated modulation signals by phase-modulating the same.
BACKGROUND ART
Video signals are ordinarily recorded on optical discs and magnetic tapes after being FM modulated once.
Such a multivibrator system modulator as shown in FIG. 1 and a frequency converting system modulator as shown in FIG. 2 are well known as FM modulators for use in such a case as described above.
The FM modulator shown in FIG. 1 has a pair of transistors 1 and 2. A video signal as a modulation signal is supplied in common to a base terminal 3 of transistors 1 and 2. Then, an FM modulated output is obtained from an output terminal 4.
The FM modulator shown in FIG. 2 includes an FM modulator 6 having a center frequency of f1 and an FM modulator 7 having a center frequency of f2. The frequencies of the FM modulated outputs of FM modulators 6 and 7 are mixed by a frequency converter 8. Extracted by a low pass filter 9 is a frequency of the difference (f1-f2) of the FM modulated outputs after the frequency mixing. FM modulators 6 and 7 are structured to have frequency deviation directions opposite to each other. That is, FM modulators 6 and 7 are structured such that when one FM modulation frequency is increased with respect to the positive input, the other FM modulation frequency is decreased. Consequently, the frequency of the difference (f1-f2) which is the ultimate FM modulated output has become in practice a frequency of the sum of the center frequencies f1 and f2.
Such FM modulators as shown in FIGS. 1 and 2 are structured to process modulation signals in a purely analog manner, thereby causing the following problems (1)-(4). non-linear. secondary distortion). temperature characteristic.
Various adjustments and condensors are required to improve the above-described problems, even by which it is difficult to obtain sufficient precision.
Therefore, the object of the present invention is to provide a highly reliable FM modulator of high precision causing none of such problems as described above.
SUMMARY OF THE PRESENT INVENTION
A first FM modulator according to the present invention includes integration means for converting an analog modulation signal to a digital integration output, carrier signal generating means for generating a carrier signal and phase modulating means for phase-modulating the output of the integration means in response to the carrier signal. The phase modulating means includes digital modulation signal outputting means, carrier signal converting means, first and second D/A converting means with a multiplication function, and operation means. The digital modulation signal outputting means outputs first and second digital modulation signals having phases orthogonal to each other based on the output of the integration means. The carrier signal converting means converts a carrier signal to first and second carrier signals having phases orthogonal to each other. The first D/A converting means with multiplication function receives the first digital modulation signal and the first carrier signal to output an analog signal corresponding to the multiplication result of the first digital modulation signal and the first carrier signal. The second D/A converting means with multiplication function receives the second digital modulation signal and the second carrier signal to output an analog signal corresponding to the multiplication result of the second modulation signal and the second carrier signal. The operation means adds or subtracts the outputs of the first and the second D/A converting means with multiplication function.
A second FM modulator according to the present invention includes integration means for converting an analog modulation signal to a digital integration output, a digital carrier signal group generating means for generating a digital carrier signal group having four digital carrier signals each out of phase
REFERENCES:
patent: 3320552 (1967-05-01), Glasser
patent: 3909721 (1975-09-01), Bussgang et al.
patent: 3973201 (1976-08-01), Andren
patent: 4613976 (1986-09-01), Sewerinson et al.
patent: 4726039 (1988-02-01), Piesinger
Hiramatsu Yonejirou
Satou Shun-ichi
Pascal Robert J.
Sharp Kabushiki Kaisha
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