Modulator and modulation method

Abstract

This modulator comprises: a carrier signal generation unit that outputs a carrier signal; and a plurality of modulation units which are cascade-connected downstream from the carrier signal generation unit and into which transmission signals of mutually different frequencies are input. Each of the modulation units comprises a distribution unit, a multiplication unit, a multiplexing unit, and a phase adjustment unit. The distribution unit outputs a first signal and a second signal obtained by bifurcating one carrier signal output by the carrier signal generation unit located upstream or one signal output by another modulation unit located upstream. The multiplication unit multiplies the first signal by the transmission signal inputted into the corresponding modulation unit. The multiplexing unit multiplexes the first signal which the multiplication unit multiplied by the transmission signal with the second signal which was output by the distribution unit, and outputs the resulting multiplexed signal. The phase adjustment unit rotates the phase of the first signal output from the distribution unit to the multiplication unit or the phase of the second signal output from the distribution unit to the multiplexing unit.

Description

Modulator and modulation method

[0001] The present invention relates to a modulator and a modulation method.

[0002] Armstrong modulators have been proposed and put into practical use (see, for example, Non-Patent Document 1). These modulators use a simple configuration to displace the phase or frequency of a carrier wave. That is, Armstrong modulators perform phase modulation or frequency modulation. FIG. 9 is a diagram showing an example of the configuration of a conventional modulator 99. The modulator 99 is an example of an Armstrong modulator configured as a frequency modulator, and an integrator is provided at the input of the transmission signal.

[0003] The divider divides the carrier signal output by the carrier signal generator into two. One of the divided carrier signals is input to the phase adjuster. The phase adjuster rotates the phase of the input carrier signal by 90 degrees and then outputs the result to the multiplier. Here, the phase adjuster may be configured to be disposed between the divider and multiplier, as shown in FIG. 9 , or may be disposed between the divider and multiplexer at the other divider output. When the phase adjuster is disposed between the divider and multiplexer, the phase rotation in the phase adjuster is minus 90 degrees. The integrator integrates the transmission signal and outputs the integrated transmission signal to the multiplier. The multiplier multiplies the phase-rotated carrier signal by the integrated transmission signal and outputs the multiplied signal to the multiplexer. The multiplexer outputs a signal obtained by multiplexing the signal output from the multiplier with the other carrier signal divided by the divider.

[0004] Ryozo Nagahama, "On the Phase Modulation Method for VHF-FM," Hitachi Review, Special Issue on Electron Tubes and Electron Tube Applications, Special Issue No. 3, 1953, pp. 71-81

[0005] In conventional modulators, the output signal from the carrier signal generator is split into two, one of which is phase-shifted by 90 degrees using a phase shifter (phase adjustment unit), and then this signal is multiplied by the transmission signal in a multiplier (multiplication unit).The signal multiplied by the multiplier is then added to the other split output signal to obtain a pseudo carrier signal and a first sideband signal.With this configuration, it is not possible to obtain second or subsequent sideband components.

[0006] Ideal frequency modulation and phase modulation signals have second and subsequent sideband components. In other words, the absence of a sideband indicates a deterioration in the signal's distortion characteristics. Furthermore, when multiple transmission signals are used, interference between the multiple signals increases the number of distortion components. This distortion further degrades signal quality, which presents a problem.

[0007] In view of the above circumstances, an object of the present invention is to provide a modulator and a modulation method that can realize modulation with low distortion.

[0008] A modulator according to one embodiment of the present invention comprises a carrier signal generating unit that outputs a carrier signal, and a plurality of modulation units that are connected in cascade downstream of the carrier signal generating unit and that each receive a transmission signal of a different frequency, and each of the modulation units comprises a distribution unit that outputs a first signal and a second signal obtained by branching the carrier signal output by the carrier signal generating unit in the immediately preceding stage or a signal output by another modulation unit in the immediately preceding stage into two, a multiplication unit that multiplies the first signal by the transmission signal input to the modulation unit, a combining unit that combines the first signal obtained by multiplying the transmission signal by the multiplication unit with the second signal output by the distribution unit, and outputs the combined signal, and a phase adjustment unit that rotates the phase of the first signal output from the distribution unit to the multiplication unit or the second signal output from the distribution unit to the combining unit.

[0009] A modulation method according to one aspect of the present invention includes a signal output step in which a carrier signal generating unit outputs a carrier signal; and a modulation step in which a plurality of modulation units connected in cascade downstream of the carrier signal generating unit receive transmission signals of different frequencies as input, and use the input transmission signals to modulate the carrier signal output by the carrier signal generating unit in the immediately preceding stage or the signal output by another modulation unit in the immediately preceding stage, wherein the modulation step performed by each of the modulation units includes a distribution step in which the carrier signal output by the carrier signal generating unit in the immediately preceding stage or the signal output by another modulator in the immediately preceding stage is branched into two to obtain a first signal and a second signal; a multiplication step in which the first signal is multiplied by the transmission signal; a combining step in which the first signal and the second signal multiplied by the transmission signal are combined, and the combined signal is output; and a process of rotating the phase of the first signal before the multiplication step, or a phase adjustment step in which the phase of the second signal is rotated before the combining step.

[0010] The present invention makes it possible to perform modulation with low distortion.

[0011] FIG. 1 is a configuration diagram of a modulator according to a first embodiment. FIG. 2 is a configuration diagram of a modulator according to a second embodiment. FIG. 3 is a configuration diagram of a modulator according to a third embodiment. FIG. 4 is a configuration diagram of a modulator according to a fourth embodiment. FIG. 5 is a diagram showing the FM spectrum of a signal FM modulated with two waves. FIG. 6 is a diagram showing the frequency spectrum of an output signal from a modulator according to the prior art. FIG. 7 is a frequency spectrum of an output signal from the modulator according to the first embodiment. FIG. 8 is a diagram showing simulation results of a modulator according to the prior art and the modulator according to the first embodiment. FIG. 9 is a configuration diagram of a modulator according to the prior art.

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. This embodiment provides a modulator and modulation method for performing phase modulation or frequency modulation with lower distortion than conventional modulators. The modulator of this embodiment has a configuration in which multiple Armstrong modulators are connected in cascade. A transmission signal is branched off for each Armstrong modulator and input to a multiplier in each Armstrong modulator, or to a multiplier via an integrator. Each of the multiple Armstrong modulators performs multiplex modulation using the branched transmission signal, thereby making it possible to obtain an output frequency spectrum that is closer to an ideal frequency spectrum than conventional methods. Therefore, the output from the modulator of this embodiment has lower distortion. Using the modulator of this embodiment makes it possible to improve the quality of the transmission signal. Each embodiment will be described below.

[0013] [First Embodiment] A modulator according to the first embodiment has cascaded Armstrong modulators, each of which receives a transmission signal of a different frequency. Each Armstrong modulator has an integrator that integrates the transmission signal. This allows the modulator to function as a frequency modulator.

[0014] FIG. 1 is a configuration diagram of a modulator 1 according to a first embodiment of the present invention. The modulator 1 has a carrier signal generating unit 2 and n (n is an integer of 2 or greater) Armstrong modulation units 3. A conventional Armstrong modulation unit 3 can be used as the Armstrong modulation units 3. The n Armstrong modulation units 3 are cascaded after the carrier signal generating unit 2. The i-th (i is an integer of 1 to n) Armstrong modulation unit 3 will be referred to as Armstrong modulation unit 3-i. A transmission signal Pi is input to the Armstrong modulation unit 3-i. The transmission signals P1 to Pn have different wavelengths.

[0015] The Armstrong modulation unit 3 has a distribution unit 31, a phase adjustment unit 32, an integration unit 33, a multiplication unit 34, and a multiplexing unit 35. The distribution unit 31, phase adjustment unit 32, integration unit 33, multiplication unit 34, and multiplexing unit 35 of the Armstrong modulation unit 3-i will be referred to as distribution unit 31-i, phase adjustment unit 32-i, integration unit 33-i, multiplication unit 34-i, and multiplexing unit 35-i, respectively.

[0016] The carrier signal generating unit 2 outputs a carrier signal. The dividing unit 31-i inputs the carrier signal output by the carrier signal generating unit 2 in the immediately preceding stage, or the signal output by the multiplexing unit 35-(i-1) of the Armstrong modulation unit 3-(i-1) in the immediately preceding stage. The dividing unit 31-i divides the input signal into two. The dividing unit 31-i outputs one of the divided signals (first signal) to the phase adjusting unit 32-i, and outputs the other divided signal (second signal) to the multiplexing unit 35-i.

[0017] The phase adjustment unit 32-i rotates the phase of the signal input from the distribution unit 31-i by 90 degrees and then outputs the signal to the multiplication unit 34-i. The integrator 33-i integrates the transmission signal Pi and outputs the signal Si obtained by the integration to the multiplication unit 34-i. The multiplier 34-i multiplies the signal received from the phase adjustment unit 32-i by the signal Si received from the integrator 33-i and outputs the signal obtained by the multiplication to the multiplexer 35-i. The multiplexer 35-i multiplexes the signal input from the multiplier 34-i and the signal input from the distribution unit 31-i and outputs the signal obtained by the multiplication to the next stage. When i is n-1 or less, the next stage is the Armstrong modulation unit 3-(i+1). When i=n, ​​the next stage is the device subsequent to the modulator 1.

[0018] With the above configuration, the modulator 1 operates as follows. The carrier signal generating unit 2 of the modulator 1 outputs a carrier signal. The Armstrong modulation unit 3-i, where i=1, operates as follows. That is, the distribution unit 31-1 of the Armstrong modulation unit 3-1 receives the carrier signal output by the carrier signal generating unit 2 and branches the received signal into two. The distribution unit 31-1 outputs one signal to the phase adjustment unit 32-1 and outputs the other signal to the multiplexer 35-1. The phase adjustment unit 32-1 performs a 90-degree phase rotation on the signal received from the distribution unit 31-1. The integrator 33-1 outputs a signal S1 obtained by integrating the transmission signal P1. The multiplier 34-1 multiplies the signal received from the phase adjustment unit 32-1 by the signal S1 received from the integrator 33-1. The multiplexer 35-1 multiplexes the signal multiplied by the multiplier 34-1 and the signal distributed by the distributor 31-1, and outputs the resulting signal.

[0019] Next, the Armstrong modulation unit 3-i, where i=2, performs the same processing as above. That is, the distribution unit 31-2 branches the signal output by the multiplexing unit 35-1 of the Armstrong modulation unit 3-1 into two, and outputs one signal to the phase adjustment unit 32-2 and the other signal to the multiplexing unit 35-2. The phase adjustment unit 32-2 performs a 90-degree phase rotation on the signal input from the distribution unit 31-2. The integrator 33-2 outputs a signal S2 obtained by integrating the transmission signal P2. The multiplier 34-2 multiplies the signal received from the phase adjustment unit 32-2 by the signal S2 received from the integrator 33-2. The multiplexer 35-2 outputs a signal obtained by combining the signal multiplied by the multiplier 34-2 and the signal distributed by the distribution unit 31-2.

[0020] The modulator 1 performs the same processing as described above for the Armstrong modulation unit 3-i while increasing n by 1 until the value of i reaches n. Then, the modulator 1 outputs the signal output by the multiplexer 35-n of the Armstrong modulation unit 3-n to a device downstream of the modulator 1 via a transmission line or the like.

[0021] [Second Embodiment] The modulator of the second embodiment is configured such that the modulator of the first embodiment further includes a demultiplexing section for separating signals input to the integrating section of each Armstrong type modulator according to frequency. The second embodiment will be described focusing on the differences from the first embodiment described above.

[0022] FIG. 2 is a configuration diagram of a modulator 11 according to a second embodiment of the present invention. In the figure, the same components as those of the modulator 1 according to the first embodiment shown in FIG. 1 are assigned the same reference numerals, and their description will be omitted. The modulator 11 shown in FIG. 2 differs from the modulator 1 shown in FIG. 1 in that the modulator 11 further includes a demultiplexing unit 4. The demultiplexing unit 4 receives a transmission signal P and demultiplexes the received transmission signal P into transmission signals P1 to Pn based on wavelength. The demultiplexing unit 4 outputs the transmission signal Pi to the integrating unit 33-i of the Armstrong modulation unit 3-i. The carrier signal generating unit 2 and the Armstrong modulation units 3-1 to 3-n operate in the same manner as in the first embodiment.

[0023] [Third Embodiment] The modulator of the third embodiment has a configuration in which the integrating section is removed from the modulator of the first embodiment. As a result, the modulator of the third embodiment functions as a phase modulator. The third embodiment will be described, focusing on the differences from the above-mentioned embodiments.

[0024] Figure 3 is a configuration diagram of a modulator 12 according to a third embodiment of the present invention. In this figure, the same parts as those of the modulator 1 according to the first embodiment shown in Figure 1 are given the same reference numerals, and their description will be omitted. The modulator 12 shown in Figure 3 differs from the modulator 1 shown in Figure 1 in that it includes an Armstrong-type modulation section 3a instead of the Armstrong-type modulation section 3. The Armstrong-type modulation section 3a differs from the Armstrong-type modulation section 3 shown in Figure 1 in that it does not include an integrating section 33.

[0025] The n Armstrong modulation units 3a are cascaded in the subsequent stage of the carrier signal generating unit 2. The i-th (i is an integer between 1 and n) Armstrong modulation unit 3a is referred to as Armstrong modulation unit 3a-i. The distribution unit 31, phase adjustment unit 32, multiplication unit 34, and multiplexing unit 35 included in the Armstrong modulation unit 3a-i are referred to as distribution unit 31-i, phase adjustment unit 32-i, multiplication unit 34-i, and multiplexing unit 35-i, respectively.

[0026] The carrier signal generating unit 2, and the dividing unit 31-i, phase adjusting unit 32-i, and multiplexing unit 35-i of each Armstrong type modulator 3a-i operate in the same manner as in the first embodiment. The multiplying unit 34-i multiplies the signal received from the phase adjusting unit 32-i by the transmission signal Pi, and outputs the signal obtained by the multiplication to the multiplexing unit 35-i.

[0027] [Fourth embodiment] The modulator of the fourth embodiment is configured such that the modulator of the third embodiment further includes a demultiplexing section for separating signals input to the multiplier sections of each Armstrong type modulation section according to frequency. The fourth embodiment will be described focusing on the differences from the above-mentioned embodiments.

[0028] FIG. 4 is a configuration diagram of a modulator 13 according to a fourth embodiment of the present invention. In the figure, the same components as those in the modulator 11 according to the second embodiment shown in FIG. 2 and the modulator 12 according to the third embodiment shown in FIG. 3 are designated by the same reference numerals, and their description will be omitted. The modulator 13 shown in FIG. 4 differs from the modulator 12 according to the third embodiment shown in FIG. 3 in that the modulator 13 further includes a demultiplexing unit 4. The demultiplexing unit 4 receives a transmission signal P and demultiplexes the received transmission signal P into transmission signals P1 to Pn based on wavelength. The demultiplexing unit 4 outputs the transmission signal Pi to the multiplier 34-i of the Armstrong modulation unit 3a-i. The carrier signal generating unit 2 and the Armstrong modulation units 3a-1 to 3a-n operate in the same manner as in the third embodiment.

[0029] Next, the reason why the modulators 1, 11, 12, and 13 of the embodiments have lower distortion than conventional modulators will be explained.

[0030] The reason why the modulator of this embodiment has lower distortion than the conventional method is that when the frequency spectrum of the output signal from the modulator is compared, the frequency spectrum of this embodiment is closer to the ideal frequency spectrum than the conventional method. This will be further explained below.

[0031] For simplicity, let us consider the case where the number of transmission signals is two, the number of cascaded Armstrong modulators is two, and frequency modulation is assumed. １ , f ２ and the frequency of the carrier signal output from the carrier signal generating unit 2 is f ｃ Here, the frequency f ｃ A carrier signal of frequency f １ , f ２ The FM wave SFM(t) obtained by FM modulation with the above two signals is expressed by the following equation (1).

[0032]

[0033] Here, m １ , m ２ is the FM modulation index. For simplicity, the initial phase of each signal is normalized to zero and the signal amplitude is normalized to 1, but this does not affect the essence.

[0034] Furthermore, equation (1) can be expanded in Bessel functions as described on page 18 of Reference 1. This can be expressed as equation (2) below.

[0035]

[0036] (Reference 1) Sugawara Teizan, "FM Radio Engineering (New Edition)", Nikkan Kogyo Shimbun, July 1964

[0037] In equation (2), J Ｎ is the Nth-order Bessel function. ｃ A carrier signal of frequency f １ Each side wave obtained by FM modulation with the transmission signal of frequency f ２This means that the signal is FM modulated by a transmission signal of m. The frequency spectrum of the signal of equation (2) is shown in Figure 5. Figure 5 shows the FM spectrum of a signal FM modulated by two waves. For simplicity, in Figure 5, １ , m ２ is sufficiently smaller than 1, and J ２ The figure shows the case where subsequent components can be ignored. In other words, since the FM modulation index from the second sideband onwards is <<1, Fig. 5 shows only up to the first sideband. ２ If the following components are also included in the spectrum, it will become an ideal frequency spectrum.

[0038] Next, the signal S at the output of the prior art modulator 99 shown in FIG. ａｒｍｓｔｒｇ Consider the frequency spectrum of (t). ｃ The carrier signal is split into two, and the phase of one of the carrier signals is shifted by π / 2, and then a multiplier (multiplication unit) is used to multiply it by the frequency f １ Transmission signal and frequency f ２ The modulator 99 combines the multiplied signal with the other branched carrier signal. Therefore, this combined signal can be written as in the following equation (3).

[0039]

[0040] Here, the carrier signal amplitude is normalized to 1. Also, k １ , k ２ is a parameter related to the modulation depth of the two transmission signals, and is determined by the carrier signal amplitude and transmission signal amplitude input to the multiplier. Figure 6 is a diagram showing the frequency spectrum of the output signal from modulator 99 shown in equation (3). That is, Figure 6 shows the frequency spectrum of the output signal from a conventional Armstrong modulator when the number of transmission signals is two.

[0041] Next, the signal S output from the modulator 1 in the first embodiment shown in FIG. ａｒｍｓｔｒｇ２ In this embodiment, two Armstrong FM modulation circuits are connected in cascade, and each modulation circuit operates at a frequency f１ , f ２ The transmission signal is Armstrong modulated, and the output spectrum is given by the following equation (4).

[0042]

[0043] 7 is a diagram showing the frequency spectrum of equation (4). That is, FIG. 7 shows the frequency spectrum of the output signal from the modulator 1 when the number of transmission signals is 2. Comparing the output frequency spectrum of the modulator 99 of the prior art shown in FIG. 6 with the output frequency spectrum of the modulator 1 of this embodiment shown in FIG. 7, the output from the modulator 1 of this embodiment has a frequency f ｃ ±f １ f for the sidewaves of ２ The four side waves caused by the modulation of ｃ ±f １ ±f ２ Since the spectrum has components similar to the ideal FM signal spectrum shown in Figure 5, deviation from the ideal spectrum appears as distortion after FM demodulation, so it can be said that the modulator 1 of this embodiment is a system with lower distortion. This also holds true when the Armstrong modulation system is phase modulation.

[0044] 8 shows the results of a MATLAB® simulation of a conventional modulator 99 and the modulator 1 of the first embodiment shown in FIG. 1. The simulation conditions are as follows: the FM carrier signal frequency is 3 GHz, the transmission signal P1 is 106 MHz, the transmission signal P2 is 497 MHz, and the FM demodulation method is a differential detection method.

[0045] Using a conventional modulator 99 shown in Fig. 9, a 3 GHz FM carrier signal was Armstrong-modulated (FM modulated) using transmission signals P1 and P2, and then FM demodulated using differential detection. Fig. 8(a) shows an example of the frequency spectrum of the signal after this FM demodulation.

[0046] On the other hand, using the modulator 1 of Figure 1, a 3 GHz FM carrier signal was Armstrong-modulated (FM modulated) using transmission signals P1 and P2, and then FM demodulated using differential detection. Figure 8(b) shows an example of the frequency spectrum of the signal after this FM demodulation. Figures 8(a) and 8(b) show that the output signal of the modulator 1 of this embodiment has less distortion than the output signal of a conventional modulator.

[0047] In the above embodiment, the phase adjustment unit 32 of the Armstrong modulation unit 3, 3a is provided between the distribution unit 31 and the multiplication unit 34, but it may also be provided between the distribution unit 31 and the multiplexing unit 35. When the phase adjustment unit 32 is provided between the distribution unit 31 and the multiplexing unit 35, the phase adjustment unit 32 rotates the phase of the signal input from the distribution unit 31 by minus 90 degrees and outputs the signal to the multiplexing unit 35, and the multiplexing unit 35 outputs the signal obtained by multiplexing the signal input from the multiplication unit 34 and the signal input from the phase adjustment unit 32 to the next stage.

[0048] According to the above-described embodiment, the modulator performs phase modulation or frequency modulation on a carrier signal using multiple transmission signals of different frequencies. The modulator includes a carrier signal generating unit and multiple modulation units. The multiple modulation units are cascaded downstream of the carrier signal generating unit, and each receives a transmission signal of a different frequency. Each modulation unit includes a divider, a multiplier, a combiner, and a phase adjuster. The divider outputs a first signal and a second signal obtained by branching a carrier signal output by a carrier signal generating unit in a previous stage or a signal output by another modulation unit in a previous stage. The multiplier multiplies the first signal by the transmission signal input to the modulator. The combiner combines the first signal, obtained by multiplying the transmission signal by the multiplier, with the second signal output by the divider, and outputs the combined signal to the next subsequent stage. The phase adjuster rotates the phase of the first signal output from the divider to the multiplier by 90 degrees, or rotates the phase of the second signal output from the divider to the combiner by minus 90 degrees. The modulation section corresponds to, for example, the Armstrong type modulation section 3a in the embodiment.

[0049] The modulation unit may further include an integrator that integrates the transmission signal input to the modulation unit. The multiplier multiplies the first signal by the transmission signal integrated by the integrator. In this case, the modulation unit corresponds to, for example, the Armstrong modulation unit 3 of the embodiment.

[0050] The modulator may further include a demultiplexing unit that receives a transmission signal, demultiplexes the received transmission signal according to frequency, and outputs the demultiplexed transmission signals to different modulation units.

[0051] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and include designs within the scope of the present invention that do not deviate from the gist of the present invention.

[0052] 1, 11, 12, 13, 99 Modulator 2 Carrier signal generating section 3-1 to 3-n, 3a-1 to 3a-n Armstrong type modulation section 31-1 to 31-n Distribution section 32-1 to 32-n Phase adjustment section 33-1 to 33-n Integration section 34-1 to 34-n Multiplication section 35-1 to 35-n Multiplexing section 4 Demultiplexing section

Claims

1. A modulator comprising: a carrier signal generating unit that outputs a carrier signal; and a plurality of modulation units that are connected in cascade downstream of the carrier signal generating unit and each receive as input a transmission signal of a different frequency, each of the plurality of modulation units comprising: a distribution unit that outputs a first signal and a second signal obtained by branching the carrier signal output by the carrier signal generating unit in the previous stage or a signal output by another modulation unit in the previous stage into two; a multiplication unit that multiplies the first signal by the transmission signal input to the modulation unit; a combining unit that combines the first signal obtained by multiplying the transmission signal by the multiplication unit with the second signal output by the distribution unit and outputs the combined signal; and a phase adjustment unit that rotates the phase of the first signal output from the distribution unit to the multiplication unit or the second signal output from the distribution unit to the combining unit.

2. The modulator according to claim 1, wherein the modulation section further has an integrating section that integrates the transmission signal input to the modulation section, and the multiplying section multiplies the first signal by the transmission signal integrated by the integrating section.

3. The modulator according to claim 1 or 2, further comprising a demultiplexing section that receives a transmission signal, demultiplexes the input transmission signal according to frequency, and outputs the demultiplexed transmission signals to different modulation sections.

4. A modulation method comprising: a signal output step in which a carrier signal generating unit outputs a carrier signal; and a modulation step in which a plurality of modulation units connected in cascade downstream of the carrier signal generating unit each input a transmission signal of a different frequency and modulate the carrier signal output by the carrier signal generating unit in the previous stage or the signal output by another modulation unit in the previous stage using the input transmission signal, the modulation steps performed by each of the modulation units including: a distribution step in which the carrier signal output by the carrier signal generating unit in the previous stage or the signal output by another modulator in the previous stage is branched into two to obtain a first signal and a second signal; a multiplication step in which the first signal is multiplied by the transmission signal; a combining step in which the first signal and the second signal multiplied by the transmission signal are combined and the combined signal is output; and a process of rotating the phase of the first signal before the multiplication step, or a phase adjustment step in which the phase of the second signal is rotated before the combining step.

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