JPS61287304A - Single side band modulator - Google Patents

Abstract

PURPOSE:To operate the title modulator even when a carrier frequency is lower than a half of the maximum frequency of a modulation signal by applying digital signal processing to a modulation wave and a carrier wave so as to produce directly a single side band wave signal without producing both side band signals. CONSTITUTION:A modulation signal is fed to a modulation signal input terminal 1 and a carrier is fed to a carrier input terminal 2. They are divided into two respectively, the one is fed respectively to the 1st and 2nd 90 deg. phase shifters 3, 4. Four kinds of analog signals in total; the modulation signal, the carrier, output signals of the phase shifters 3, 4, are converted into digital signals by the 1st-4th A/D converters 5-8. Output signals of the 1st and 3rd A/D converters 5, 7 are multiplied by the 1st multiplier 9, and digital output signals of the 2nd and 4th A/D converters 6, 8 are multiplied by the 2nd multiplier 10 respectively. Digital output signals of the multipliers 9, 10 are added by an adder 11, its output signal is converted into an analog signl by a A/D converter 12 and a single side band signal is outputted directly at an output terminal 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Minute Hand] The present invention relates to a single sideband modulator that can operate even when the carrier frequency is low.

[Conventional technology]

FIG. 2 is a block diagram showing an example of a conventional single sideband modulator using analog signal processing. In the figure, %1 is a modulation signal input terminal, 2 is a carrier wave input terminal, 14 is a balanced modulator, and 15 is a sideband P-wave device, and 13 is an output terminal.

Next, the operation will be explained. The highest frequency of the modulation signal input to the modulation signal input terminal 1 is fmax[:HzI.

The carrier wave frequency input to carrier wave input terminal 2 is fcCH
z]. At this time, the frequency spectrum of the modulated signal is
It is expressed as shown in Figure 3a. When the modulated signal shown in FIG. 3a and a carrier wave with a carrier frequency of fc[:Hz:l are applied to the balanced modulator 14, the output is a double-sided band wave having the frequency spectrum already shown in FIG. I get a signal. This both-sideband signal is processed by the sideband p-wave device 15.
A single sideband signal as shown in FIG. 3C is obtained, and a modulated wave is output from the output terminal 13.

Next, the above will be clarified mathematically. For ease of explanation, the modulation signal is assumed to be a sine wave of frequency P. The modulation signal m (t) is (2)2πP t (o<P<fmax
) The carrier wave signal c (t) is assumed to be 2πfat. At this time, the Fourier transform pair B (f) of the outputs b (t) and b (t) of the balanced modulator 14 is expressed as follows. However, δ is a Dirac delta function.

b(t)=A−c(t)・m(t) (A: constant) The double sideband signal represented by b(t) or B(f) is converted into a single sideband signal by the sideband P-wave unit 15. It becomes a wave signal. This corresponds to making the first term of b (t) and B (f) in the above equation a P wave and blocking the second term.

[Problem that the invention seeks to solve]

Conventional single sideband modulator, as above, once.

Since a double sideband signal is generated and then a single sideband signal is generated, there is a problem in that it does not function as a modulator when the carrier frequency is lower than half of the highest frequency of the modulation signal. This is clear from the fact that one frequency spectrum overlaps with each other in the %g4 diagram. However, a and b in Figure 4
, c correspond to a, b, and c in FIG.

This invention was made with the aim of solving the above-mentioned problems, and its purpose is to obtain a single sideband modulator that can operate even when the carrier frequency is lower than half of the highest frequency of the modulation signal. do.

[Means for solving problems]

The single sideband modulator according to the present invention performs signal processing of a modulated wave and a carrier wave in the first . a second 90 phase shifter, first to fourth transducers; a second multiplier, an adder, and V
By performing digital signal processing using an h-converter, a single sideband signal is directly generated without generating a single double sideband signal.

[Effect]

By using digital signal processing for signal processing, the single sideband modulator of the present invention can operate even when the carrier frequency is lower than half of the highest frequency of the modulation signal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1.2.13 indicates the same or equivalent parts as those in FIG. 2 mentioned above. 3 and 4 are the 1st and second 90 phase shifters; 5, 6 and 7.8 are the first to fourth 90 degree converters; 9, 1
0 is the first. 2 multipliers, 11 adders, 12 IIM
It is an A converter.

Next, the operation will be explained. The modulated signal is applied to a modulated signal input terminal 1, and the carrier wave is applied to a carrier wave input terminal 2. These modulated wave signals and carrier waves are each divided into two parts, and one of them is divided into two parts, and one of them is divided into two parts.
, 4 respectively. The modulating signal and the carrier wave and the first
．． A total of four types of analog signals including the output signals of the second 9♂ phase shifters 3 and 4 are transmitted to the first to fourth N0 converters 5, 6, 7.
8, it is converted into a digital signal. The first . The digital output signals of the third A/D converters 5 and 7 are converted into the first
．． The output signal of the second 90' phase shifter 3.4 is converted into A/D
The digital output signals of the fourth N0 converter 8.8 are multiplied by a second multiplier 10, respectively. 1st
．． The digital output signals of the second multipliers 9 and 10 are added by an adder 11, and the digital output signals of the adder 11 are:

The signal is converted into an analog signal by the IMA converter 12, and a single sideband signal is directly output to the output terminal 13.

Next, the above operation will be explained using mathematical formulas.

The signal input to modulation signal input terminal 1 is m (t) =
coi2πpt (o≦p≦fmax) carrier wave input terminal 2
The carrier wave input to e (t) = ax 2πfa
When t, the first to fourth A/D converters 5, 6, 7.8
The input for is as follows. (However, the first and second 90 phase shifters 3 and 4 change the phase of the input signal by 90 degrees.
It delays the phase. ) First N0 converter 5: cm 2πpt Second N0 converter 6: 2πpt Third N0 converter 7: (2) 2πfat Fourth N0 converter a: m2πfat Signal processing are digital signal processing converters 5, 6,
7.8, the single sideband signal S (t) is obtained as follows. That is, S (t)=am 2πfat-eag2πpt-gt
o2πfctIIlrh+2πpt= ax 2π(f
c+p)t (However, the adder 11 calculates the difference between the two digital signals.) [Effects of the Invention] As described above, according to the present invention, the modulated wave and the carrier wave can be subjected to digital signal processing. By.

Since the configuration is configured to directly generate a single sideband signal without generating a double sideband signal, a single sideband modulator that can operate even when the carrier frequency is lower than half of the highest frequency of the modulation signal can be obtained. There is.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a single sideband modulator according to an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional single sideband modulator, and FIGS. 3a and bfc are conventional single sideband modulators. Frequency spectrum diagram explaining the operation of the device, Figure 4' l b
j (! is a frequency spectrum diagram explaining the problems of a conventional single sideband modulator. In the figure, 1 is a modulation signal input terminal, 2 is a carrier wave input terminal, 3 and 4 are first and second 90 Phase shifter, 5, 6,
7.8 is the first to fourth transducer, 9.10 is the first to fourth transducer. Second
, 11 is an adder, 12 is a converter, and 13 is an output terminal. In Figure 1, the same reference numerals indicate the same or corresponding parts. Patent applicant Mitsubishi Electric Corporation Agent Patent attorney 1) Hiroshi Sawa (2 others) Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] The first 90° delaying the phase of the A/D modulated wave signal by 90°
a phase shifter, a second 90° phase shifter that delays the phase of the carrier wave by 90°, a first A/D converter that A/D converts the modulated wave signal, and the first 90° phase shifter. a second A/D converter that A/D converts the output signal of the device;
a third A/D converter that A/D converts the carrier wave; a fourth A/D converter that A/D converts the output signal of the second 90° phase shifter; , a first multiplier that multiplies the digital output signals of the third A/D converter;
a second multiplier that multiplies the digital output signals of the second and fourth A/D converters; an adder that adds the digital output signals of the first and second multipliers; A single sideband modulator comprising: an A/D converter that A/D converts a digital output signal to obtain an analog single sideband modulated wave.