JPH0648806B2 - Signal multiplexer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal multiplexing device that multiplexes sub-signals in television signal transmission that adopts the vestigial sideband transmission method.

2. Description of the Related Art In recent years, it has become popular to multiplex various signals with television signals to provide more advanced services. Text-multiplexed broadcasting is one example, but generally in urban CATV, it is necessary to multiplex various signals such as a scramble relation to a television signal.

There are roughly two types of conventional signal multiplexers. There are a time multiplex system such as a character multiplex broadcast for multiplexing information in a synchronization signal section, or a frequency multiplex system widely used in a voice multiplex broadcast.

As an example of such a conventional signal multiplexing apparatus, a signal multiplexing apparatus for character multiplex broadcasting will be described below with reference to the drawings.

FIG. 3 shows a block diagram of a signal multiplexing apparatus for character multiplex broadcasting. 51 is a video signal input terminal, 52 is a character signal superimposing device, 53 is a waveform shaping filter, 54 is a character signal (sub signal) input terminal, 55 is a carrier wave input terminal, 56 is an amplitude modulator, and 57 is a vestigial sideband filter. The transmission system 514 is configured as described above. Reference numeral 58 is a transmission path. Further, 59 is a detector, 510 is a video signal output terminal, 511
Is a sync separation circuit, 512 is a character signal extracting circuit, 513
Is a character signal (sub signal) output terminal.
15 are configured.

The operation of the signal multiplexer configured as described above will be briefly described below with reference to FIG.

In the transmission system 514, the character signal as the sub signal is burst-multiplexed in the vertical blanking interval by the character signal superimposing unit 52. On the other hand, in the receiving system 515, after being detected by the detector 59, the sync separating circuit 511 separates the sync signal, and the character signal extracting circuit 512 separates the sub signal based on this sync signal. (For example, "Broadcasting Technology" Vol. 36 NO.
10pp105-111) On the other hand, there are roughly two types of signal multiplexers that perform frequency multiplexing.
It is divided into two. One is a method of multiplexing a signal in a spectrum gap in a channel of a television signal, and the other is a method of multiplexing a signal outside the channel of a television signal. The former includes multiplex voice broadcasting and multiplex facsimiles. The latter corresponds to the case where a data transmission band is provided separately from the television signal band, as is often used in CATV.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the conventional configurations as described above, the configurations are complicated (especially in a demodulation system), and in the case of frequency-multiplexing a signal outside the channel of a television signal, the spectrum utilization efficiency is also increased. Not preferable.

In view of the above problems, the present invention provides a signal multiplexing device that has a simple structure, has a high spectrum utilization efficiency, and multiplexes sub-signals.

Means for Solving the Problems In order to solve the above problems, the signal multiplexer of the present invention includes an amplitude modulator for a video signal, a 90 ° phase shifter for shifting a carrier by 90 °, and a sub-signal. A band limiting filter, a balanced modulator that amplitude-modulates a carrier having a 90 ° phase difference from a video signal carrier by the sub-signal that has passed through the band limiting filter, and an output signal of the amplitude modulator and the balanced modulator. It is provided with a combiner for combining and a residual sideband filter for cutting off a part of the sideband of the output signal of the combiner.

With the above-described configuration, the present invention multiplexes the sub-signal on the axis orthogonal to the modulation axis of the video signal, so that it is possible to multiplex signals with good spectrum utilization efficiency without increasing the occupied spectrum. In addition, since the signal can be easily separated by using the synchronous detection, the structure is simplified especially in the demodulation system.

Embodiment Hereinafter, a signal multiplexer according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit configuration diagram of a signal multiplexing apparatus in a first embodiment of the present invention. In FIG. 1, 1 is a carrier wave input terminal, 2 is an amplitude modulator, 3 is a video signal input terminal, 4 is a 90 ° phase shifter, 5 is a balanced modulator, 6 is a sub signal input terminal, and 7 is a multiplexer. , 8 are vestigial sideband filters, 19 is a sub-signal band limiting filter, and the transmission system 20 is constituted by the above. Reference numeral 9 is a transmission line. Further, 10 and 14 are balanced modulators, 11 is a -90 ° phase shifter, 12 is a video signal filter, 13 is a sub-signal filter, 15 is a VCO (voltage controlled oscillator), 16 is a loop filter, and 17 is a video. A signal output terminal, reference numeral 18 is a sub signal output terminal, and the reception system 21 is constituted by the above.

The operation of the signal multiplexer configured as described above will be described below with reference to FIG.

First, in the transmission system 20, the carrier wave input from the carrier wave input terminal 1 is first divided into two systems, one of which is 90
The 90 ° phase shifter 4 shifts the 90 ° phase. Two orthogonal carrier waves are subjected to amplitude modulation by the amplitude modulator 2 and the balanced modulator 5 by the video signal and the sub signal, respectively, and are combined by the multiplexer 7. The quadrature-modulated wave is transmitted by removing a part of the sideband by the residual sideband filter 8. The sub-signal band limiting filter 19
Limits the band of the sub-signal.

Next, in the receiving system 21, the balanced modulator 14, the sub-signal filter 13, the loop filter 16 and the VOC 15 constitute a PLL, and the carrier wave is regenerated. Since the carrier wave of the video signal is not suppressed, the phase of the reproduced carrier wave is locked at a position shifted by 90 ° from the video signal demodulation axis, that is, the phase of the sub-signal demodulation axis. When the balanced modulator 14 performs synchronous detection on the reproduced carrier wave, the sub-signal is demodulated. This reproduced carrier wave is moved by -90 ° phase shifter 11
If the phase is shifted by 90 °, it becomes the video signal demodulation axis. Therefore, the video signal is demodulated by the synchronous detection by the balanced modulator 10. Since the reproduction of the carrier wave is fixed based on the phase of the video signal carrier wave, it is not necessary to perform differential encoding on the sub signal. Further, the loop filter 16 functions to remove the component of the sub signal in the control signal supplied to the VCO 15 and reduce the phase jitter of the reproduced carrier.

All or part of the horizontal or vertical blanking interval is selected as the sub-signal multiplex interval, and the sub-signal is non-signal other than this interval. By doing so, it is possible to reduce interference with the image due to orthogonal distortion. The sub-signal may be a digital signal. In this case, the sub-signal is multiplexed at a lower level, and error correction technology is introduced to further prevent mutual interference between the sub-signal and the video signal. Can be reduced.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit configuration diagram of a signal multiplexing apparatus showing a second embodiment of the present invention. In the figure, 1 is a carrier wave input terminal,
2 is an amplitude modulator, 3 is a video signal input terminal, 4 is a 90 ° phase shifter, 5 is a balanced modulator, 6 is a sub-signal input terminal, 7 is a multiplexer, 8 is a vestigial sideband filter, and 19 is The transmission system 20 is configured by the sub-signal band limiting filter. Reference numeral 9 is a transmission line. Also, 10 and 14 are balanced modulators, 11 is -90 °.
A phase shifter, 12 is a video signal filter, 13 is a sub signal filter, 15 is a VCO (voltage controlled oscillator), 16 is a loop filter, 17 is a video signal output terminal, 18 is a sub signal output terminal, and a receiving system 21 Is configured. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 1 is that a gate switch 22 is provided between the sub-signal band limiting filter 19 and the balanced modulator 5 in the transmission system 20.

The operation of the signal multiplexing apparatus configured as described above will be described below. Similar to the first embodiment, the sub-signal is multiplexed on the modulation axis orthogonal to the modulation axis of the video signal. The difference from the first embodiment is that the gate switch 22 makes the switch conductive in all or part of the horizontal or vertical blanking period. By doing so, it is possible to reduce the interference of the video signal due to the response of the sub-signal band limiting filter 19 or the noise of the sub-signal system.

As described above, by providing the gate switch 22 between the sub-signal band limiting filter 19 and the balanced modulator 5, it is possible to further reduce the interference with the video signal.

In the second embodiment, the gate switch 22 is 9
It may be installed before or after the 0 ° phase shifter 4, after the balanced modulator 5, or before the sub-signal band limiting filter 19.

As described above, according to the present invention, the amplitude modulator for the video signal, the 90 ° transporter for transporting the carrier by 90 °, the band limiting filter for the sub signal, and the sub signal passing through the band limiting filter, A balanced modulator that amplitude-modulates a carrier whose phase is 90 ° different from that of the video signal carrier, a combiner that combines the output signals of the amplitude modulator and the balanced modulator, and a sideband of the output signal of the combiner. It is equipped with a vestigial sideband filter that removes a part of the spectrum, and all or part of the horizontal or vertical blanking interval is multiplexed on the axis that is orthogonal to the modulation axis of the video signal. It is possible to perform signal multiplexing with high utilization efficiency and a simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a signal multiplexing device according to a first embodiment of the present invention, FIG. 2 is a circuit configuration diagram of a signal multiplexing device according to a second embodiment of the present invention, and FIG. 3 is a conventional signal multiplexing device. It is a circuit block diagram of an example of an apparatus. 1 ... Carrier input terminal, 2 ... Amplitude modulator, 3 ... Video signal input terminal, 4 ... 90 ° phase shifter, 5,10,14 ...
… Balanced modulator, 6 …… Sub signal input terminal, 7 …… Combiner,
8 ... Residual sideband filter, 9 ... Transmission line, 11 ...-
90 ° phase shifter, 12 ... Video signal filter, 13 ...
Sub-signal filter, 15 ... Voltage controlled oscillator (VC
O), 16 ... Loop filter, 17 ... Video signal output terminal, 18 ... Sub signal output terminal, 19 ... Sub signal band limiting filter, 20 ... Transmission system, 21 ... Reception system, 22 ...
... gate switch.

Claims (3)

[Claims] 1. In television signal transmission using the vestigial sideband transmission method, an amplitude modulator for a video signal, a 90 ° phase shifter for shifting a carrier by 90 °, a band limiting filter for a sub signal, and the band. A balanced modulator that amplitude-modulates a carrier that is 90 ° out of phase with the carrier for the video signal in the sub-signal that has passed through the limiting filter; and a multiplexer that combines the amplitude modulator and the output signal of the balanced modulator. A residual sideband filter for removing a part of sidebands of the output signal of the multiplexer, and all or some of the horizontal blanking interval and the vertical blanking interval for the sub-signal. Multiplexer for signal multiplexing. 2. The signal multiplexing apparatus according to claim 1, wherein the sub signal is a digital signal. 3. The signal multiplexing apparatus according to claim 1 or 2, wherein the television signal transmission is television signal transmission in a CATV transmission system.