BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are diagrams showing a structure according to an exemplary embodiment of a phase modulating device in accordance with the present invention. FIG. 1A is a block diagram showing the structure according to the exemplary embodiment of the phase modulating device. FIG. 1B is a block diagram showing an example of a structure of an orthogonal modulator.
FIG. 2 is a vector diagram showing a phase-modulated signal over an I-Q plane.
FIGS. 3A and 3B are graphs showing a waveform distortion. FIG. 3A shows a calculation result of a waveform difference in a modulated phase angle θ with respect to a modulation signal P=m·sin(pt) in the phase modulating device according to the exemplary embodiment. FIG. 3B shows the same calculation result in a related-art device.
FIGS. 4A and 4B are diagrams showing another exemplary embodiment. FIG. 4A is a block diagram showing a structure in which a variable attenuator for varying a modulation index of the phase-modulated signal is provided. FIG. 4B is a block diagram showing a structure in which a change-over switch is provided between a modulation signal generator 2 and a Q terminal of an orthogonal modulator 3.
FIGS. 5A and 5B are diagrams showing another exemplary embodiment. FIG. 5A is a block diagram showing a structure in which a frequency multiplier is provided on an output side of the orthogonal modulator 3. FIG. 5B is a block diagram showing a structure in which a phase modulation waveform distortion is suppressed by a correction signal.
FIG. 6 is a vector diagram showing a phase-modulated signal over the I-Q plane according to the structure of FIG. 5B.
FIGS. 7A and 7B are diagrams showing a related-art device. FIG. 7A is a block diagram showing a structure of the related-an device. FIG. 7B is a vector diagram showing a relationship between a carrier signal and a modulation signal.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
An exemplary embodiment of a phase modulating device according to the invention will be described below with reference to FIGS. 1 to 6.
FIG. 1A is a block diagram showing a structure according to an exemplary embodiment of the phase modulating device in accordance with the present invention.
As shown in FIG. 1A, a phase modulating device according to the exemplary embodiment includes: a carrier signal generator 1 for outputting a carrier signal having a frequency ω; a modulating signal generator 2 for outputting a modulation signal P=m·sin(pt); an orthogonal modulator 3; a DC power supply 4 for applying a DC voltage to the orthogonal modulator 3; and a limiter amplifier 5 (amplitude adjustment means) for amplifying a signal output from the orthogonal modulator 3 and adjusting an amplitude thereof to be constant.
As shown in FIG. 1A, the carrier signal transmitted from the carrier signal generator 1 is input to an LO input terminal of the orthogonal modulator 3. The modulation signal transmitted from the modulation signal generator 2 is input to a Q terminal of the orthogonal modulator 3. The DC voltage applied from the DC power supply 4 is input to an I terminal of the orthogonal modulator 3. The inputs to the Q and I terminals of the orthogonal modulator 3 may be replaced with each other.
FIGS. 1B is a block diagram showing an example of a structure of the orthogonal modulator 3. As shown in FIG. 1B, the orthogonal modulator 3 is constituted by a 90-degree distributor 31 for receiving the carrier signal, a double balanced mixer 32 for receiving one of output signals of the 90-degree distributor 31 and the modulation signal, a double balanced mixer 33 for receiving the other output signal of the 90-degree distributor 31 and the DC voltage, and an adder 34 for adding signals output from the double balanced mixer 32 and the double balanced mixer 33. The orthogonal modulator 3 can be obtained inexpensively in combination of components of the respective elements or as an IC put on the market.
FIG. 2 is a vector diagram showing a signal output from the orthogonal modulator 3 (a phase-modulated signal) over an I-Q plane. For simplicity, an I vector length is set to be one in FIG. 2.
As shown in the vector diagram of FIG. 2, a phase-modulated angle θ and a phase-modulated signal f(t) are expressed in the following equation:
θ=tan−1{m·sin(pt)}
f(t)=cos{ωt+tan−1(m·sin(pt))}
FIG. 3A shows a calculation result of a waveform difference in the phase-modulated angle θ with respect to a modulation signal P=m·sin(pt). FIG. 3A displays the modulation signal P=m·sin(pt), the phase-modulated angle θ, and furthermore, the waveform difference (a phase modulation waveform distortion). The case of a modulation index m=0.1π[rad] is shown.
On the other hand, FIG. 3B shows the same calculation result in a related-art device illustrated in FIG. 7A. In the same manner as FIG. 3AFIG. 313 displays a modulation signal P=m·sin(pt), a phase-modulated angle θ, and the waveform difference in the case of a modulation index m=0.1π[rad].
As is apparent from a comparison between FIGS. 3A and 3B, the phase modulation waveform distortion is considerably reduced in the phase modulating device according to the exemplary embodiment as compared with the related-art device.
As described above, in the phase modulating device according to the exemplary embodiment, only the carrier signal generator 1 is used as a high frequency signal generator for generating a signal having a high frequency. Compared with the related-art device using two high frequency signal generators, therefore, a cost and a size of the device can be reduced considerably. Moreover, it is possible to control the phase modulation waveform distortion.
FIG. 4A is a block diagram showing a structure in which a variable attenuator for varying a modulation index of a phase-modulated signal is provided,
In an example shown in FIG. 4A, a variable attenuator 11 is inserted between the modulation signal generator 2 and the Q terminal of the orthogonal modulator 3. By controlling an amplitude of the modulation signal through the variable attenuator 11, it is possible to vary a modulation index. Therefore, it is possible to easily control the modulation index without adjusting a gain of the high frequency signal as in the related-art device (FIGS. 7A and 7B).
FIG. 4B is a block diagram showing a structure in which a change-over switch is provided between the modulation signal generator 2 and the Q terminal of the orthogonal modulator 3.
In an example of FIG. 4B, the modulation signal and an external signal can be optionally selected as a signal to be input to the Q terminal of the orthogonal modulator 3 by means of a change-over switch 12. Therefore, it is possible to utilize the device as a general-purpose phase modulator.
FIG. 5A is a block diagram showing a structure in which a frequency multiplier is provided on an output side of the orthogonal modulator 3.
In an example of FIG. 5A, a frequency multiplier 13 is connected to the output side of the orthogonal modulator 3, and furthermore, a signal transmitted from the frequency multiplier 13 is output through a band pass filer 14 so that a phase-modulated signal having a frequency corresponding to a multiple and a certain amplitude can be obtained.
FIG. 5B is a block diagram showing a structure in which a phase modulation waveform distortion is suppressed by a correction signal.
In an example of FIG. 5B, a correction signal based on a modulation signal is generated in a correction signal generator 15 and is added to a DC voltage applied from the DC power supply 4 in an adder 16, and a result obtained by the addition is given to the I terminal of the orthogonal modulator 3.
The correction signal may be set to a sine wave (b·cos(2pt)) having a frequency which is a double of a frequency of the modulation signal. FIG. 6 is a vector diagram showing a phase-modulated signal in this case over an I-Q plane. As shown in FIG. 6, a resultant vector obtained by I and Q signals approaches a circumference by the correction signal. Therefore, it is possible to further suppress the phase modulation waveform distortion to be a difference between θ and m·sin(pt).
The coverage of the present invention is not limited to the above-described exemplary embodiments. A phase modulating device according to the invention can be applied to wide uses without a limitation to an application to the jitter generating device. Moreover, it is also possible to optionally combine a plurality of components in the serial exemplary embodiment.
Patent Application
20080088386
