JP2000092008A - Signal transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To multiplex and transmit plural base band digital signals by inexpensive constitution without being restricted by the band characteristics of a transmission line. SOLUTION: The base band digital signals 11a-11c of mutually different transmission rates are respectively converted to differential codes in differentiation devices 21a-21c. At the time, the respective differentiation devices 21a-21c are operated as a kind of high-pass filters on a frequency axis. The respective differential codes outputted from the differentiation devices 21a-21c are, after a high frequency band is limited by filters 22a-22c, multiplexed by a multiplex part 23 and sent out from a transmission circuit 24 onto the transmission line 30. Multiplex signals 32 transmitted on the transmission line are received in a reception circuit 42, then branched in a branching part 43 and respectively demultiplexed to the differential codes corresponding to the base band digital signals 11a-11c in demultiplex parts 45a-45c. The demultiplexed signals are amplified in amplifiers 46a-46c and then, DC reproduced by signal reproducing devices 47a-47c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a signal transmission system, and more particularly to a system for frequency-multiplexing and transmitting a plurality of baseband digital signals.

[0002]

2. Description of the Related Art Conventionally, as a method of simultaneously transmitting a plurality of baseband digital signals (digital signals including DC components), a parallel transmission method, a time division multiplexing method in which multiplexing is performed on a time axis, and a method on a frequency axis. For example, a frequency multiplexing method for performing multiplexing has been used.

Here, the parallel transmission system is a system for simultaneously and independently transmitting a plurality of baseband digital signals using a plurality of transmission lines provided in parallel. Also,
The time division multiplexing method is a method in which a plurality of baseband digital signals are switched in time sequence, converted into one high-speed multiplexed signal on the time axis, and transmitted using one transmission path. The frequency multiplexing method converts a plurality of baseband digital signals into one multiplexed signal on the frequency axis by performing frequency conversion using carrier signals of different frequencies, and transmits the multiplexed signal using one transmission path. It is a method to do.

[0004]

However, the above-mentioned parallel transmission system has a problem that the cost of the system becomes high because a plurality of transmission lines are required. When a spatial light transmission line is used as the transmission line, the cost of laying the transmission line is unnecessary, but it is necessary to prepare the light emitting elements and the light receiving elements by the number of baseband digital signals to be transmitted. The cost of the system increases.

In the above-described time division multiplexing system and frequency multiplexing system, only one transmission line is used. However, since circuit elements that operate at high speed are required on both the transmission side and the reception side, the system is required. Cost increases. In the time division multiplexing method and the frequency multiplexing method, as the number of baseband digital signals to be transmitted increases, the frequency of the multiplexed signal increases (or the band increases).
Therefore, there is a problem that the number of baseband digital signals that can be simultaneously transmitted is limited by the band characteristics of the transmission path.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal transmission system capable of multiplex-transmitting a plurality of baseband digital signals with an inexpensive configuration without being restricted by band characteristics of a transmission line. It is.

[0007]

Means for Solving the Problems and Effects of the Invention The present invention has the following features in order to achieve the above object.

A first aspect of the present invention is a system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, provided for each of the plurality of baseband digital signals. By differentiating the digital signal, a plurality of differentiators for outputting a differential code corresponding to each baseband digital signal, and provided corresponding to each of the plurality of differentiators,
A plurality of filters for band-limiting the high frequency region of each differentiator output signal with different cutoff frequencies, a multiplexing unit for multiplexing the output signals from each filter and outputting the multiplexed signal as a frequency multiplexed signal, A transmission unit for transmitting a frequency multiplexed signal output from the transmission line on a transmission line, a reception unit for receiving the frequency multiplexed signal transmitted on the transmission line, and a frequency multiplexed signal received by the reception unit into a plurality of frequency multiplexed signals. A branching unit for branching, and a plurality of branching units provided corresponding to each of the plurality of frequency multiplexed signals branched by the branching unit and branching a signal corresponding to a plurality of baseband digital signals from each frequency multiplexed signal And a plurality of signal regenerators provided corresponding to each of the plurality of demultiplexing units and reproducing a baseband digital signal from each output signal.

As described above, according to the first aspect, a plurality of baseband digital signals can be multiplex-transmitted with a simple circuit configuration using a differentiator and a filter. Further, since multiplexing processing is performed within the signal band of the baseband signal, a circuit element that operates at high speed is not required. Furthermore, since a plurality of baseband digital signals are handled as one frequency multiplexed signal, there is no need to provide a plurality of transmission lines unlike the conventional spatial multiplexing method, and signal transmission can be realized at low cost.

A second invention is an invention according to the first invention, wherein the multiplexing section includes, in addition to the output signals from the respective filters, an empty area which does not interfere with the output signals of these filters on the frequency axis. At least one or more passband signals arranged in frequency are multiplexed and output as a frequency multiplexed signal. Of the plurality of demultiplexers, some of the demultiplexers are frequency multiplexed by the splitter. A signal corresponding to a plurality of baseband digital signals is demultiplexed from the signal, and the remaining demultiplexing unit demultiplexes the passband signal.

As described above, according to the second aspect, it is possible to multiplex a passband signal in addition to a baseband digital signal.

A third invention is an invention according to the first invention, provided between each demultiplexing unit and each signal regenerator,
Before the output signal of each demultiplexer is given to each signal regenerator,
It further includes a plurality of amplifiers for amplifying the output signal of each demultiplexing unit.

A fourth invention is an invention according to the third invention, and is provided corresponding to each of the plurality of amplifiers, detects an amplitude of an output signal of each amplifier, and, based on the detection result, It further comprises a plurality of AGC circuits for generating a control signal and feeding the control signal back to a corresponding amplifier, wherein each amplifier has its gain controlled based on a control signal from the corresponding AGC circuit. I do.

As described above, according to the fourth aspect of the present invention, the amplitude of the signal input to each signal regenerator is always constant even when the aging occurs in the transmission path or the like. Accurate signal reproduction becomes possible.

A fifth invention is an invention according to the third invention, wherein the amplitude of any one output signal of the plurality of amplifiers is detected, and a control signal is generated based on the detection result. There is further provided one AGC circuit for feeding back a control signal to each amplifier, and each amplifier includes one AGC circuit.
The gain is controlled based on a control signal from a circuit.

As described above, according to the fifth aspect, the signal amplitude is detected by one AGC circuit, and the output amplitudes of all the amplifiers are controlled based on the detection result. Accurate signal reproduction becomes possible.

A sixth invention is an invention according to the first invention, wherein the multiplexing section includes, in addition to the output signals from the respective filters, an empty area which does not interfere with the output signals of these filters on the frequency axis. Are multiplexed and output as a frequency multiplexed signal, and one of a plurality of demultiplexing units demultiplexes the pilot carrier signal and outputs the remaining pilot carrier signal. The demultiplexing section is provided between each demultiplexing section and each signal regenerator to demultiplex a signal corresponding to a plurality of baseband digital signals, and an output signal of each demultiplexing section is provided to each signal regenerator. Before being performed, a plurality of amplifiers that amplify the output signal of each demultiplexing unit, and among the plurality of amplifiers, detect the amplitude of the output signal of the amplifier that amplifies the pilot signal,
A single AGC circuit that generates a control signal based on the detection result and feeds back the control signal to each amplifier, wherein each amplifier has a gain controlled based on a control signal from one AGC circuit. It is characterized by being performed.

As described above, according to the sixth aspect, the amplitude of the signal corresponding to the pilot carrier signal is detected by the AGC circuit, and the output amplitudes of all the amplifiers are controlled based on the detection result. It is possible to always detect the signal amplitude stably without being affected by the disturbance of the signal pattern of the differential code, and it is possible to reproduce the signal more accurately.

A seventh aspect of the present invention is a system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates, wherein the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. A differentiating means for outputting a differential code corresponding to a baseband digital signal other than the above, and a band limiting of a high frequency region of the baseband digital signal having the lowest transmission rate and a high frequency region of the differential signal outputted from the differentiating means. A filter unit for limiting, a multiplexing unit that multiplexes an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal, a transmitting unit that sends out the frequency multiplexed signal output from the multiplexing unit onto a transmission path, A receiver for receiving a frequency multiplexed signal transmitted on a road, and a frequency multiplex received by the receiver Branching unit into a plurality of frequency multiplexed signals, and from the plurality of frequency multiplexed signals branched by the branching unit, a baseband digital signal having the lowest transmission rate is demultiplexed and converted to other baseband digital signals. Demultiplexing means for demultiplexing a corresponding signal, and signal reproducing means for reproducing another baseband digital signal from a signal corresponding to another baseband digital signal demultiplexed by the demultiplexing means. .

An eighth aspect of the present invention is a system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other. Differentiating means for outputting a corresponding differential code, and filter means for band-limiting a high frequency region of a differential code corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among a plurality of differential codes. A multiplexing unit that multiplexes a differential code corresponding to a baseband digital signal having the highest transmission rate and an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal, and a frequency output from the multiplexing unit. A transmission unit for transmitting a multiplexed signal on a transmission line, and a frequency multiplexed signal transmitted on the transmission line. A receiving unit for receiving, a branching unit for branching the frequency multiplexed signal received by the receiving unit into a plurality of frequency multiplexed signals, and a signal corresponding to a plurality of baseband digital signals from the plurality of frequency multiplexed signals branched by the branching unit And a signal reproducing means for reproducing a plurality of baseband digital signals from an output signal of the demultiplexing means.

A ninth aspect of the present invention is an apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, and provided for each of the plurality of baseband digital signals. A plurality of differentiators for outputting a differential code corresponding to each baseband digital signal by differentiating the digital signal, and a plurality of differentiators provided corresponding to each of the plurality of differentiators; , A plurality of filters for band-limiting each with a different cutoff frequency, a multiplexing unit that multiplexes output signals from each filter and outputs a frequency multiplexed signal, and a frequency multiplexed signal output from the multiplexing unit on a transmission line. And a transmission unit for transmitting the data to

A tenth invention is an invention according to the ninth invention, wherein the multiplexing section includes, in addition to the output signals from the respective filters, an empty area which does not interfere with the output signals of these filters on the frequency axis. And multiplexing at least one or more passband signals arranged in frequency and outputting as a frequency multiplexed signal.

An eleventh invention is according to the tenth invention, wherein the passband signal is a pilot carrier signal having a constant frequency.

A twelfth invention is an apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates, wherein the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. A differentiating means for outputting a differential code corresponding to a baseband digital signal other than the above, and a band limiting of a high frequency region of the baseband digital signal having the lowest transmission rate and a high frequency region of the differential signal outputted from the differentiating means. A filter unit for limiting, a multiplexing unit that multiplexes an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal, and a transmission unit that sends out the frequency multiplexed signal output from the multiplexing unit onto a transmission path. ing.

A thirteenth invention is an apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, and differentiating the plurality of baseband digital signals to each baseband digital signal. Differentiating means for outputting a corresponding differential code, and filter means for band-limiting a high frequency region of a differential code corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among a plurality of differential codes. A multiplexing unit that multiplexes a differential code corresponding to a baseband digital signal having the highest transmission rate and an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal, and a frequency output from the multiplexing unit. A transmission unit for transmitting a multiplexed signal onto a transmission path.

As described above, according to the seventh to thirteenth aspects, a simple circuit configuration using a differentiator and a filter is provided.
Multiple baseband digital signals can be multiplexed and transmitted. Further, since multiplexing processing is performed within the signal band of the baseband signal, a circuit element that operates at high speed is not required. Further, a plurality of baseband digital signals are
Since the signals are handled as one frequency multiplexed signal, there is no need to provide a plurality of transmission lines unlike the conventional spatial multiplexing method, and signal transmission can be realized at low cost.

A fourteenth aspect of the present invention is a system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other. The system is provided corresponding to each of the plurality of baseband digital signals. A plurality of encoders for converting a digital signal into a digital signal of a DC-balanced code rule and outputting the signals; and a plurality of encoders provided for each of the plurality of encoders. A plurality of filters that band-limit the area with different cutoff frequencies, a multiplexing unit that multiplexes output signals from each filter and outputs them as a frequency multiplexed signal, and transmits a frequency multiplexed signal output from the multiplexing unit A transmitting unit for transmitting the signal on the road, a receiving unit for receiving the frequency multiplexed signal transmitted on the transmission line, and a frequency multiplexing signal received by the receiving unit. A branching unit for branching into a plurality of frequency multiplexed signals, and a plurality of frequency multiplexed signals branched by the branching unit. A plurality of demultiplexing units and a plurality of decoding units provided corresponding to each of the plurality of demultiplexing units and decoding a baseband digital signal from each output signal are provided.

A fifteenth aspect of the present invention is a system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates, wherein the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. Encoding means for converting a baseband digital signal other than the above into a DC-balanced code-law digital signal and outputting the converted signal, and band-limiting a high-frequency region of the baseband digital signal having the lowest transmission rate. Filter means for band-limiting the high frequency region of the output digital signal, a multiplexing unit for multiplexing the output signal from the filter means and outputting the multiplexed signal as a frequency multiplexed signal, and a frequency multiplexed signal output from the multiplexing unit And a receiving unit for receiving the frequency multiplexed signal transmitted on the transmission path. Unit, a branching unit that branches the frequency multiplexed signal received by the receiving unit into a plurality of frequency multiplexed signals, and a baseband digital signal having the lowest transmission rate from the plurality of frequency multiplexed signals branched by the branching unit. And a demultiplexing means for demultiplexing a signal corresponding to the other baseband digital signal, and a signal corresponding to the other baseband digital signal demultiplexed by the demultiplexing means from the other baseband digital signal. And decoding means for decoding.

A sixteenth aspect of the present invention is a system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein the plurality of baseband digital signals are converted into DC balanced digital signals of a code rule. Encoding means for converting and outputting, and a high frequency region of a digital signal corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among a plurality of digital signals output from the encoding means. Filter means for band limiting, a digital signal output from the encoding means, a digital signal corresponding to a baseband digital signal having the highest transmission rate, and an output signal from the filter means,
A multiplexing unit for outputting a frequency multiplexed signal, a transmitting unit for transmitting the frequency multiplexed signal output from the multiplexing unit onto a transmission path, a receiving unit for receiving the frequency multiplexed signal transmitted on the transmission path, and a receiving unit A splitter for splitting the frequency multiplexed signal received by the splitter into a plurality of frequency multiplexed signals, and a splitter for splitting a signal corresponding to a plurality of baseband digital signals from the plurality of frequency multiplexed signals split by the splitter. Decoding means for decoding a plurality of baseband digital signals from the output signal of the demultiplexing means.

A seventeenth invention is an apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, provided for each of the plurality of baseband digital signals. A plurality of encoders for converting a digital signal into a digital signal of a DC-balanced code rule and outputting the signals; and a plurality of encoders provided for each of the plurality of encoders. A plurality of filters that band-limit the area with different cutoff frequencies, a multiplexing unit that multiplexes output signals from each filter and outputs them as a frequency multiplexed signal, and transmits a frequency multiplexed signal output from the multiplexing unit And a transmission unit for transmitting the data on the road.

An eighteenth invention is an apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates, wherein the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. Encoding means for converting a baseband digital signal other than the above into a DC-balanced code-law digital signal and outputting the converted signal, and band-limiting a high-frequency region of the baseband digital signal having the lowest transmission rate. Filter means for band-limiting the high frequency region of the output digital signal, a multiplexing unit for multiplexing the output signal from the filter means and outputting the multiplexed signal as a frequency multiplexed signal, and a frequency multiplexed signal output from the multiplexing unit And a transmission unit for transmitting the data on a transmission path.

A nineteenth aspect of the present invention is an apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, and converting the plurality of baseband digital signals into a DC balanced digital signal of a code rule. Encoding means for converting and outputting, and a high frequency region of a digital signal corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among a plurality of digital signals output from the encoding means. Filter means for band limiting, a digital signal output from the encoding means, a digital signal corresponding to a baseband digital signal having the highest transmission rate, and an output signal from the filter means, A multiplexing unit that outputs a frequency multiplexed signal and a frequency multiplexing signal that is output from the multiplexing unit And a transmission unit for transmitting on the transmission line a.

As described above, according to the fourteenth to nineteenth aspects, a plurality of baseband digital signals can be multiplex-transmitted with a simple circuit configuration using an encoder and a filter. Further, since multiplexing processing is performed within the signal band of the baseband signal, a circuit element that operates at high speed is not required. Furthermore, since a plurality of baseband digital signals are handled as one frequency multiplexed signal, there is no need to provide a plurality of transmission lines unlike the conventional spatial multiplexing method, and signal transmission can be realized at low cost.

[0034]

(First Embodiment) FIG. 1 is a block diagram showing a configuration of a signal transmission system according to a first embodiment of the present invention. In FIG. 1, a signal transmission system according to the present embodiment includes a signal input unit 10 and a signal transmission unit 20.
, Transmission path 30, signal receiving section 40, signal output section 10
0.

The signal input unit 10 includes signal sources 10a to 10c
including. These signal sources 10a to 10c output baseband digital signals 11a to 11c having different transmission rates (that is, different clock periods). Here, the baseband digital signal is, as is well known, a digital signal having a base band (baseband).

The signal transmitting section 20 includes a differentiating section 21, a filter section 22, a multiplexing section 23, and a transmitting circuit 24. The differentiating stage 21 includes a differentiator 21a having different time constants.
To 21c. Filter stage 22 includes filters 22a-
22c. Each of the filters 22a to 22c is configured by a high-cut filter that blocks a signal having a frequency equal to or higher than a predetermined frequency.
a, 22b, and 22c increase in this order.
The digital signals output from the filters 22a to 22c are multiplexed (multiplexed) by the multiplexing unit 23,
4 to the transmission path 30. As the transmission path 30, an electric signal wire transmission path, a wireless transmission path, an optical fiber transmission path, a spatial light transmission path, or the like is used according to a signal transmission mode adopted by the transmission circuit 24.

The signal receiving section 40 includes a receiving circuit 42, a branching section 43, a demultiplexing stage 45, an amplifying stage 46, and a signal reproducing stage 4.
7 is included. The splitting stage 45 includes splitters 45a to 45c, the amplifying stage 46 includes amplifiers 46a to 46c, and the signal reproducing stage 47 includes signal regenerators 47a to 47c. In addition, from the signal output unit 100, the reproduced signals 100a to 100a are output.
0c is output.

FIG. 2 is a frequency spectrum diagram of signals of respective parts of the signal transmission system shown in FIG. In FIG. 2, (a) shows the frequency spectrum of the baseband digital signals 11a to 11c input from the signal input unit 10, and (b) shows the frequency spectrum of the output signal of the encoding stage 21. (C) shows the frequency spectrum of the output signal of the equalization stage 22, and (d) shows the frequency spectrum of the output signal of the multiplexing unit 23. Hereinafter, the operation of the signal transmission system of FIG. 1 will be described with reference to FIG.

As shown in FIG. 1, the baseband digital signals 11a to 11c from the signal input unit 10 are input to the signal transmission unit 20. As shown in FIG. 2A, the frequency bands of the baseband digital signals 11a to 11c are different from each other. Here, the frequency band of the baseband digital signal 11a is the narrowest, the frequency band of the baseband digital signal 11b is an intermediate width,
The frequency band of the baseband digital signal 11c is the widest. In other words, the transmission rate of each signal is
The baseband digital signal 11a is the lowest and increases in the order of the baseband digital signals 11b and 11c.

Next, in the signal transmitting section 20, the baseband digital signals 11a to 11c are differentiated by differentiators 21a to 21c, respectively, and the time difference between the rising and falling times of the baseband digital signal pulses on the time axis. It is converted to the corresponding positive / negative differential sign. At this time, each of the differentiators 21a to 21c operates as a kind of high-pass filter on the frequency axis. Therefore, the baseband digital signals 11a to 11c are differentiated from the differentiators 21a to 2c.
After passing through 1c, each low frequency region is suppressed, and each frequency spectrum becomes as shown in FIG. 2 (b).

Each differential code output from the differentiators 21a to 21c is subjected to a band by filters 22a to 22c for suppressing high frequency components in order to reduce interference between signals on the frequency axis generated when the signals are multiplexed. Limited (Fig. 2 (c)
reference). Each signal output from the filters 22a to 22c is multiplexed by the multiplexing unit 23 and is supplied to the transmission circuit 24 as a frequency multiplexed signal. Here, the output of the multiplexing unit 23 has a spectrum arrangement as shown in FIG. According to such a spectrum arrangement, each signal component corresponding to the baseband digital signals 11a to 11c has a certain degree of overlap, but is clearly separated on the frequency axis. Therefore, on the receiving side, the baseband digital signal 1
Signal components corresponding to 1a to 11c can be separated. The transmission circuit 24 sends out the frequency multiplexed signal given from the multiplexing unit 23 to the transmission line 30 as a multiplexed signal 32.

Next, the multiplexed signal 32 transmitted by the transmission line 30 is received by the receiving circuit 42, and then branched by the branching unit 43, and divided into baseband digital signals 11a to 11c by the branching units 45a to 45c. Each is split as a corresponding differential code. Each of the separated signals is supplied to an amplifier 4
After being amplified by 6a-46c, the signal regenerators 47a-47
c, and the baseband signals 11a to 11
The signal is output from the signal output unit 100 as reproduction signals 100a to 100c corresponding to c.

FIG. 3 is a block diagram showing an example of the configuration of the signal regenerator 47a shown in FIG. The signal regenerator 4
The configuration and operation of 7b and 47c are also similar to those of signal regenerator 47.
It is pointed out in advance that this is the same as the configuration and operation of a. In FIG. 3, the differential sign, which is a positive / negative pulse train input to the signal regenerator 47a, is separated into positive and negative pulses in comparison circuits 91 and 92. By turning ON / OFF the RS flip-flop 93 using these positive and negative pulses as a set pulse and a reset pulse, the DC component of the differential code is reproduced.

As described above, according to the first embodiment,
Multiple baseband digital signals can be multiplexed and transmitted with a simple circuit configuration using a differentiator and a filter. Further, since multiplexing processing is performed within the signal band of the baseband signal, a circuit element that operates at high speed is not required.
Furthermore, since a plurality of baseband digital signals are handled as one frequency multiplexed signal, there is no need to provide a plurality of transmission lines unlike the conventional spatial multiplexing method, and signal transmission can be realized at low cost.

In the first embodiment, the baseband digital signal 11c having the widest frequency band has no other signal in a frequency region higher than the frequency band. Interference does not occur. Therefore, the baseband digital signal 11
The filter 22c for suppressing the high frequency component of c is not always necessary.

In the first embodiment, the other baseband digital signals 11b and 11c are prevented from entering the band of the baseband digital signal 11a having the narrowest frequency band. When the band limitation of the baseband digital signal 11a can be performed in the low frequency region, interference between the signals is not generated. Therefore, in this case, the differentiator 21a and the signal regenerator 47a are not always necessary.

In the multiplexed signal transmitted from the signal transmitting unit 20, if there is an empty area on the frequency axis, another signal is multiplexed and transmitted using such an empty area. May be. In this case, other signals that can be multiplex-transmitted need to have band characteristics so that they can be arranged in the empty area on the frequency axis. As such a signal, for example, a signal having no limited baseband and having a limited band (hereinafter, referred to as a passband signal) such as a QAM signal, a pilot carrier signal of a fixed frequency, and a modulated analog signal ). Note that, in the case of the first embodiment, the empty region includes a high-frequency region that is high-cut by the filter 22c. When the transmission rates of the adjacent baseband digital signals on the frequency axis are largely separated from each other, the signal bands after being filtered by the filter stage 22 do not overlap with each other. Become. An embodiment in which the passband signal is further multiplexed and transmitted using the vacant area on the frequency axis of the multiplexed signal will be described below as a second embodiment.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
It is a block diagram which shows the structure of the receiving side of the signal transmission system which concerns on embodiment. The configuration of this embodiment is the same as that of the first embodiment shown in FIG. 1 except for the following points.
Corresponding parts have the same reference characters allotted, and detailed description thereof will not be repeated.

In FIG. 4, the second signal input unit 12
Signal sources 12a to 12c are included. These signal sources 12a-1
2c outputs passband signals 13a to 13c, respectively. The multiplexing unit 25 includes a plurality of signals output from the filter stage 22 and a passband signal 1 from the signal input unit 12.
And 3a to 13c. The output signal of the multiplexing unit 25 is
The signal is transmitted onto the transmission line 30 by the transmission circuit 24. The signal transmitted on the transmission path 30 is received by the receiving circuit 42 and is split by the splitter 43 into a plurality of signals. The demultiplexers 48a to 48c included in the second demultiplexer 48 extract the reproduction signals 101a to 101c corresponding to the passband signals 13a to 13c, respectively.
Output to 01. Other configurations and operations of this embodiment are the same as those of the first embodiment shown in FIG.

(Third Embodiment) FIG. 5 shows a third embodiment of the present invention.
It is a block diagram which shows the structure of the receiving side of the signal transmission system which concerns on embodiment. In this embodiment, the configuration on the transmitting side may be the same as that of the first embodiment shown in FIG. 1, and the configuration on the receiving side is the same as that of the first embodiment. And the detailed description thereof is omitted.

In FIG. 5, in the present embodiment, the signal receiving section 40 includes a variable amplifying stage 50 instead of the amplifying stage 46 in the signal receiving section of the first embodiment. The variable amplification stage 50 includes amplifiers 51a to 51a that can adjust the gain.
1c and AGC circuits 52a to 52c. The signals split by the splitting stage 45 are amplified by the amplifiers 51a to 51c. The AGC circuits 52a to 52c detect output amplitudes of the amplifiers 51a to 51c, respectively, generate control signals based on the detection results, and feed back these control signals to the amplifiers 51a to 51c. Thereby, the gains of the amplifiers 51a to 51c are controlled so that the amplitudes of the output signals of the amplifiers 51a to 51c are always constant. Therefore, even when the transmission path or the like changes over time, the amplitude of the signal input to the signal reproducing stage 47 is always constant, and accurate signal reproduction in the signal reproducing stage 47 becomes possible.

(Fourth Embodiment) FIG. 6 shows a fourth embodiment of the present invention.
It is a block diagram which shows the structure of the receiving side of the signal transmission system which concerns on embodiment. In this embodiment, the configuration on the transmitting side may be the same as that of the first embodiment shown in FIG. 1, and the configuration on the receiving side is the same as that of the first embodiment. And the detailed description thereof is omitted.

In FIG. 6, in the present embodiment, the signal receiving section 40 includes a variable amplifying stage 53 instead of the amplifying stage 46 in the signal receiving section of the first embodiment. The variable amplifying stage 53 includes amplifiers 51a to 51a whose gain can be adjusted.
1c and an AGC circuit 54. The signals split by the splitting stage 45 are amplified by the amplifiers 51a to 51c. The AGC circuit 54 detects the output amplitude of the amplifier 51a as a representative, generates a control signal based on the detection result, and feeds back the control signal to the amplifiers 51a to 51c. As a result, the amplifiers 51a to 51c are controlled so that the amplitudes of the output signals are always constant.
To 51c are controlled. As described above, in the present embodiment, the signal amplitude is detected by one AGC circuit 54, and the output amplitudes of all the amplifiers 51a to 51c are controlled based on the detection result. Accurate signal reproduction is possible with a smaller number of parts.

(Fifth Embodiment) In the second and third embodiments described above, since the amplitude of the differential code is detected in the AGC circuit, it is difficult to accurately detect the signal amplitude depending on the signal pattern. There is. Therefore, an embodiment in which more accurate amplitude control can be performed without depending on the signal pattern of the differential sign will be described below.

FIG. 7 is a block diagram showing the configuration on the receiving side of the signal transmission system according to the fifth embodiment of the present invention. The configuration of this embodiment is the same as that of FIG. 1 except for the following points.
Is the same as that of the first embodiment shown in FIG. 1, and the corresponding parts are denoted by the same reference numerals and detailed description thereof will be omitted.

In FIG. 7, a signal source 14 outputs a pilot carrier signal 15 having a constant frequency. In the signal transmission unit 20, the multiplexing unit 25 multiplexes the band-limited baseband digital signal group output from the filter stage 22 and the pilot carrier signal 15. However, when frequency-multiplexing the pilot carrier signal 15, it is necessary to arrange the pilot carrier signal 15 in its free band so as not to overlap the band-limited baseband digital signal group on the frequency axis.

In the signal receiving section 40, the multiplexed signal 32 propagated through the transmission path 30 is received by the receiving section 42, then branched by the branching section 43, and separated by the branching section 45 into the baseband digital signals 11a to 11c and the pilot. The signal is split as a signal corresponding to the carrier signal 15. These split signals are supplied to the amplifiers 51 a to 51 a included in the variable amplification stage 55.
Amplified by 51d. The AGC circuit 56 detects the amplitude of the output signal of the amplifier 51d corresponding to the pilot carrier signal 15, generates a control signal based on the detection result, and feeds back the control signal to the amplifiers 51a to 51d. As a result, the amplifiers 51a to 51d are controlled such that the amplitudes of the output signals are always constant.
To 51d are controlled.

As described above, in the fifth embodiment, the amplitude of the signal corresponding to pilot carrier signal 15 is
Since the output amplitude of all the amplifiers 51a to 51d is controlled based on the detection result by the circuit 56, the stable signal amplitude can be always detected without being affected by the disturbance of the differential sign signal pattern. And more accurate signal reproduction becomes possible.

(Sixth Embodiment) FIG. 8 shows a sixth embodiment of the present invention.
It is a block diagram showing the composition of the signal transmission system concerning an embodiment. The configuration of this embodiment is the same as the configuration of the first embodiment shown in FIG. 1 except for the following points. Corresponding portions are denoted by the same reference numerals, and detailed description thereof will be omitted. It shall be.

In FIG. 8, in the signal transmission system of the present embodiment, an encoding stage 26 is provided instead of the differentiation stage 21 in FIG. The encoding stage 26 includes encoding units 26a to 26c. Here, the encoding units 26a to 26
c converts the coding rules of the baseband digital signals 10a to 10c input from the signal sources 10a to 10c into predetermined coding rules, respectively. Here, the predetermined coding rule may be a coding rule with DC balance, and examples thereof include a 4B5B code, an 8B10B code, and a CMI code. Further, in the sixth embodiment, a decoding stage 49 is provided instead of the signal reproduction stage 47 in FIG.
This decoding stage 49 includes decoding sections 49a to 49c.
These decoding units 49a to 49c respectively include an amplifier 4
Encoding units 26a to 26c for output signals of 6a to 46c
The original baseband digital signals 11a to 11c are reproduced by performing a coding rule conversion reverse to that of c. The other configurations and operations of the eighth embodiment are the same as those in FIG.

As described above, the baseband digital signals 11a to 11c are converted into the DC balanced digital signal using the coding units 26a to 26c, thereby converting the DC component of the baseband digital signal. Can be suppressed. That is, the encoding units 26a to 26
c operates as a kind of high-pass filter on the frequency axis, like the differentiators 21a to 21c. The differentiator 21
a to 21c are replaced by encoders 26a to 26c, and the signal reproducers 47a to 47c are replaced by decoding units 48a to 48c.
The substitution with can be performed not only in the first embodiment but also in other embodiments.

In the first to fifth embodiments described above, the baseband digital signal to be multiplexed and transmitted may be a binary baseband digital signal or a multilevel baseband digital signal. There may be. However, when a binary baseband digital signal and a multilevel baseband digital signal are multiplexed and transmitted, the transmission rate of the multilevel baseband digital signal is higher than the transmission rate of the binary baseband digital signal. Preferably it is slow.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a signal transmission system according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of a signal of each unit of the signal transmission system shown in FIG.

FIG. 3 is a block diagram showing an example of a configuration of a signal regenerator shown in FIG.

FIG. 4 is a block diagram illustrating a configuration on a receiving side of a signal transmission system according to a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration on a receiving side of a signal transmission system according to a third embodiment of the present invention.

FIG. 6 is a block diagram illustrating a configuration on a receiving side of a signal transmission system according to a fourth embodiment of the present invention.

FIG. 7 is a block diagram illustrating a configuration on a receiving side of a signal transmission system according to a fifth embodiment of the present invention.

FIG. 8 is a block diagram illustrating a configuration of a signal transmission system according to a sixth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Signal input part 10a-10c ... Signal source 11a-11c ... Baseband digital signal 20 ... Signal transmission part 21 ... Differentiation stage 21a-21c ... Differentiator 22 ... Filter stage 22a-22c ... Filter 23 ... Muxing unit 24 ... Transmission circuit 30 ... Transmission path 32 ... Multiple signal 40 ... Signal receiving unit 42 ... Receiving circuit 43 ... Branching unit 45 ... Demultiplexing stage 45a-45c ... Diplexer 46 ... Amplifying stage 46a-46c ... Amplifier 47 ... Signal reproducing stage 47a- 47c: signal regenerator 100: signal output unit 100a to 100c: reproduced signal 91, 92: comparator 93: RS flip-flop 12: second signal input unit 12a to 12c: signal source 13a to 13c: pass band signal 25: Multiplexing section 48: second demultiplexing stage 48a to 48c demultiplexing section 101 second signal output section 101a to 101c reproduced signal 5 ... variable amplification stages 51a to 51c ... amplifiers 52a to 52c ... AGC circuits 53 ... variable amplification stages 54 ... AGC circuits 13 ... signal sources 14 ... pilot carrier signals 55 ... variable amplification stages 56 ... AGC circuits 26 ... coding stages 26a to 26c ... Encoding unit 49 ... Decoding stages 49a to 49c ... Decoding units

Continued on the front page (72) Inventor Jun Hirano 1006 Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 5K022 AA01 AA12 AA22

Claims (19)

[Claims] 1. A system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein the system is provided corresponding to each of the plurality of baseband digital signals. By differentiating, a plurality of differentiators that output a differential code corresponding to each baseband digital signal, and a plurality of differentiators are provided corresponding to each of the plurality of differentiators, and a high frequency region of an output signal of each differentiator is provided. A plurality of filters for performing band limiting at different cutoff frequencies, a multiplexing unit that multiplexes output signals from the filters and outputs the multiplexed signals as a frequency multiplexed signal, and a frequency multiplexed signal output from the multiplexing unit on a transmission line. A transmitting unit that transmits the frequency multiplexed signal transmitted on the transmission path; and a receiving unit that receives the frequency multiplexed signal transmitted on the transmission path. A branching unit for branching the received frequency multiplexed signal into a plurality of frequency multiplexed signals; provided in correspondence with each of the plurality of frequency multiplexed signals branched by the branching unit; A plurality of demultiplexers for demultiplexing a signal corresponding to a digital signal; and a plurality of signal regenerators provided corresponding to each of the plurality of demultiplexers and reproducing the baseband digital signal from respective output signals. A signal transmission system comprising: 2. The multiplexing section, in addition to the output signals from each of the filters, at least one or more passband signals frequency-arranged in an empty area on the frequency axis that does not interfere with the output signals of these filters. Multiplexed and output as the frequency multiplexed signal, and among the plurality of demultiplexers, some of the demultiplexers correspond to the plurality of baseband digital signals from the frequency multiplexed signal split by the splitter. The signal transmission system according to claim 1, wherein a signal to be transmitted is demultiplexed, and a remaining demultiplexing unit demultiplexes the passband signal. 3. An output signal of each demultiplexing unit is provided between each of the demultiplexing units and each of the signal regenerators, and amplifies an output signal of each demultiplexing unit before an output signal of the demultiplexing unit is supplied to each of the signal regenerators. The signal transmission system according to claim 1, further comprising a plurality of amplifiers. 4. An amplifier provided corresponding to each of the plurality of amplifiers, detecting an amplitude of an output signal of each amplifier, generating a control signal based on the detection result, and feeding back the control signal to the corresponding amplifier. A plurality of AGC circuits, wherein the gain of each of the amplifiers is controlled based on a control signal from the corresponding AGC circuit.
The signal transmission system according to claim 3. 5. An AGC circuit for detecting an amplitude of an output signal of any one of the plurality of amplifiers, generating a control signal based on the detection result, and feeding back the control signal to each amplifier. The signal transmission system according to claim 3, wherein the gain of each of the amplifiers is controlled based on a control signal from the one AGC circuit. 6. The multiplexing unit multiplexes, in addition to the output signals from the respective filters, a pilot carrier signal of a constant frequency arranged in an empty area on the frequency axis that does not interfere with the output signals of the filters. And outputting as the frequency multiplexed signal, any one of the plurality of demultiplexing units demultiplexes the pilot carrier signal, and the other demultiplexing unit outputs the plurality of baseband digital signals. A signal corresponding to a signal is demultiplexed, provided between each of the demultiplexing units and each of the signal regenerators, and before the output signal of each demultiplexing unit is given to each of the signal regenerators, A plurality of amplifiers for amplifying the output signal of the plurality of amplifiers, among the plurality of amplifiers, detecting an amplitude of an output signal of the amplifier for amplifying the pilot signal, generating the control signal based on the detection result, and To each amplifier. 2. The signal transmission system according to claim 1, further comprising one AGC circuit for performing feedback, wherein each of the amplifiers has a gain controlled based on a control signal from the one AGC circuit. . 7. A system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein a base other than the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. A differentiating means for outputting a differential code corresponding to the band digital signal; and a band limiting for a high frequency region of the baseband digital signal having the lowest transmission rate, and a band limiting for a high frequency region of the differential signal output from the differentiating means. A multiplexing unit that multiplexes an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal, and a transmission unit that sends out the frequency multiplexed signal output from the multiplexing unit onto a transmission path. A receiving unit for receiving the frequency multiplexed signal transmitted on the transmission path; A branching unit for branching the received frequency multiplexed signal into a plurality of frequency multiplexed signals, and, from the plurality of frequency multiplexed signals branched by the branching unit, demultiplexing the baseband digital signal having the lowest transmission rate, A demultiplexer for demultiplexing a signal corresponding to another baseband digital signal; and reproducing the other baseband digital signal from a signal corresponding to the other baseband digital signal demultiplexed by the demultiplexer. A signal transmission system comprising: 8. A system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein a derivative corresponding to each baseband digital signal is obtained by differentiating the plurality of baseband digital signals. A differential means for outputting a code; and a filter means for band-limiting a high frequency region of a differential code corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among the plurality of differential codes. A multiplexing unit that multiplexes a differential code corresponding to a baseband digital signal having a high transmission rate and an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal; and a frequency output from the multiplexing unit. A transmitting unit for transmitting a multiplexed signal on a transmission line; and a frequency transmitted on the transmission line. A receiving unit that receives the multiplexed signal; a branching unit that branches the frequency multiplexed signal received by the receiving unit into a plurality of frequency multiplexed signals; and the plurality of basebands from the plurality of frequency multiplexed signals branched by the branching unit A signal transmission system, comprising: a demultiplexer for demultiplexing a signal corresponding to a digital signal; and a signal reproducer for reproducing the plurality of baseband digital signals from an output signal of the demultiplexer. 9. An apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, provided for each of the plurality of baseband digital signals. By differentiating, a plurality of differentiators that output a differential code corresponding to each baseband digital signal, and a plurality of differentiators are provided corresponding to each of the plurality of differentiators, and a high frequency region of an output signal of each differentiator is provided. A plurality of filters for band limiting at different cutoff frequencies; a multiplexing unit that multiplexes output signals from the filters and outputs the multiplexed signals as a frequency multiplexed signal; And a transmission unit for transmitting the signal to the signal transmission device. 10. The multiplexing unit, in addition to the output signals from each of the filters, at least one or more passband signals frequency-arranged in an empty area on the frequency axis that does not interfere with the output signals of these filters. The signal transmitting apparatus according to claim 9, wherein the signals are multiplexed and output as the frequency multiplexed signal. 11. The signal transmitting apparatus according to claim 10, wherein the passband signal is a pilot carrier signal having a constant frequency. 12. An apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein a base other than the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. A differentiating means for outputting a differential code corresponding to the band digital signal; and a band limiting for a high frequency region of the baseband digital signal having the lowest transmission rate, and a band limiting for a high frequency region of the differential signal output from the differentiating means. A multiplexing unit that multiplexes an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal, and a transmission unit that transmits the frequency multiplexed signal output from the multiplexing unit onto a transmission path. A signal transmission device. 13. An apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, comprising differentiating the plurality of baseband digital signals to obtain a differential signal corresponding to each baseband digital signal. A differential means for outputting a code; and a filter means for band-limiting a high frequency region of a differential code corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among the plurality of differential codes. A multiplexing unit that multiplexes a differential code corresponding to a baseband digital signal having a high transmission rate and an output signal from the filter unit and outputs the multiplexed signal as a frequency multiplexed signal; and a frequency output from the multiplexing unit. A transmission unit for transmitting a multiplexed signal onto a transmission path. 14. A system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein the system is provided corresponding to each of the plurality of baseband digital signals. DC
A plurality of encoders that convert and output digital signals of a balanced coding rule, and are provided corresponding to each of the plurality of encoders, and each of the high frequency regions of the output signal of each encoder is A plurality of filters for performing band limiting at different cutoff frequencies, a multiplexing unit that multiplexes output signals from the filters and outputs the multiplexed signals as a frequency multiplexed signal, and a frequency multiplexed signal output from the multiplexing unit on a transmission line. A transmitting unit that transmits the frequency multiplexed signal transmitted on the transmission path; a branching unit that divides the frequency multiplexed signal received by the receiving unit into a plurality of frequency multiplexed signals; A plurality of frequency-division multiplexed signals branched by the section, and a signal for demultiplexing a signal corresponding to the plurality of baseband digital signals from each frequency-division multiplexed signal; Min and wave portion provided corresponding to each of the plurality of the branching portion, and a from each of the output signals and a plurality of decoding portions for decoding the baseband digital signal, the signal transmission system. 15. A system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein a base other than the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals. Encoding means for converting the band digital signal into a digital signal having a DC-balanced coding rule and outputting the signal; and band-limiting a high-frequency region of the baseband digital signal having the lowest transmission rate, and outputting from the encoding means. Filter means for band-limiting the high frequency region of the digital signal to be obtained, a multiplexing unit for multiplexing an output signal from the filter means and outputting the multiplexed signal as a frequency multiplexed signal, and a frequency multiplexing output from the multiplexing unit. A transmission unit for transmitting a signal on a transmission path; and a frequency multiplexed signal transmitted on the transmission path. Receiving unit, a branching unit that branches the frequency multiplexed signal received by the receiving unit into a plurality of frequency multiplexed signals, and from the plurality of frequency multiplexed signals branched by the branching unit, the lowest transmission rate A demultiplexing unit that demultiplexes a baseband digital signal and also demultiplexes a signal corresponding to another baseband digital signal; a signal corresponding to the other baseband digital signal demultiplexed by the demultiplexing unit And a decoding means for decoding the other baseband digital signal. 16. A system for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, comprising: converting the plurality of baseband digital signals into a DC balanced digital signal of a code rule. Encoding means for outputting, and band limiting a high frequency region of a digital signal corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among a plurality of digital signals outputted from the encoding means Filter means, a digital signal output from the encoding means, a digital signal corresponding to a baseband digital signal having the highest transmission rate, and multiplexing the output signal from the filter means, A multiplexing unit that outputs as a frequency multiplexed signal; A transmitting unit for transmitting a frequency multiplexed signal on a transmission line; a receiving unit for receiving a frequency multiplexed signal transmitted on the transmission line; a frequency multiplexed signal received by the receiving unit is split into a plurality of frequency multiplexed signals A branching unit; a branching unit that branches a signal corresponding to the plurality of baseband digital signals from the plurality of frequency multiplexed signals branched by the branching unit; and the plurality of basebands from an output signal of the branching unit. A signal transmission system comprising: decoding means for decoding a digital signal. 17. An apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein the apparatus is provided in correspondence with each of the plurality of baseband digital signals. DC
A plurality of encoders that convert and output a digital signal of a balanced coding rule, and are provided corresponding to each of the plurality of encoders; A plurality of filters for band limiting at different cutoff frequencies; a multiplexing unit that multiplexes output signals from the filters and outputs the multiplexed signals as a frequency multiplexed signal; And a transmission unit for transmitting the signal to the signal transmission device. 18. An apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, wherein a base other than the baseband digital signal having the lowest transmission rate among the plurality of baseband digital signals is provided. Coding means for converting the band digital signal into a digital signal of a DC-balanced coding rule and outputting the converted signal; and band-limiting a high-frequency region of the baseband digital signal having the lowest transmission rate, and outputting from the coding means. Filter means for band-limiting a high frequency region of the digital signal to be obtained, a multiplexing unit for multiplexing an output signal from the filter means and outputting the multiplexed signal as a frequency multiplexed signal, and a frequency multiplexing output from the multiplexing unit. A transmission unit for transmitting a signal onto a transmission path. 19. An apparatus for frequency-multiplexing and transmitting a plurality of baseband digital signals having different transmission rates from each other, comprising converting the plurality of baseband digital signals into a digital signal having a DC-balanced code rule. Encoding means for outputting, and band limiting a high frequency region of a digital signal corresponding to a baseband digital signal other than the baseband digital signal having the highest transmission rate among a plurality of digital signals outputted from the encoding means Filter means, a digital signal output from the encoding means, a digital signal corresponding to a baseband digital signal having the highest transmission rate, and multiplexing the output signal from the filter means, A multiplexing unit that outputs as a frequency multiplexed signal, and a frequency that is output from the multiplexing unit. The number multiplexed signal and a transmitter for sending on a transmission line, the signal transmission apparatus.