JP2673598B2 - Video signal transmission system - Google Patents

Description

Description: (1) Technical Field of the Invention The present invention relates to a twisted pair cable (twisted pair wire) in a doorphone with a television function (hereinafter referred to as a television doorphone) and a video signal transmission system for transmitting other video signals. The present invention relates to a transmission method that can use a cable and can provide a free wiring form.

(2) Conventional Technology and Its Problems i) In the conventional TV door intercom, one door intercom monitor is used for one camera intercom and a coaxial cable is generally used. However, in this case, the coaxial cable is thick and low in flexibility, which causes a problem in construction. Especially when replacing a device with a normal voice-only intercom to a TV intercom, it is not possible to use an existing pair of twisted pair cables (twisted pair cables), and replacement work to a coaxial cable is required. In some cases, the coaxial cable could not be replaced, and it was sometimes impossible to switch to a TV door phone.

ii) Also, in order to avoid the drawbacks of thick coaxial cables, there are TV doorphones that transmit video signals over a short distance using bare cables, but in this case, one camera doorphone and one doorphone monitor are used. The doorphones and doorphone monitors are directly connected, and multiple connections cannot be made. The twisted-pair wire was used exclusively for directly interconnecting a specific camera doorphone and a specific doorphone monitor.
Therefore, it was not possible to arbitrarily connect using a plurality of camera doorphones and toaphone monitors.

iii) In addition, when multiple monitors or multiple television cameras (hereinafter referred to as television cameras) are used to arbitrarily switch between camera selections and monitor selections, the so-called exchange function is to be implemented, and transmission is performed between them. A switching function is required to switch between the roads and these. In order to realize this function, a changeover switch device is required, and the bus connection between the TV camera and the changeover switch device and between the changeover switch device and the monitor cannot be performed as described in ii) above. Is required. Therefore, the television camera and the changeover switch device, and the changeover switch device and the monitor must be connected by star wiring, which is disadvantageous in terms of economy, operability, workability, and freedom of installation.

iv) In addition, there is a method of connecting a plurality of monitors to one TV camera by a coaxial cable, but in this case, since a video signal is supplied to the terminal from the coaxial cable, it is necessary to use a branching device. Moreover, in this case, a branching device must be used for each branching, which causes problems in economic efficiency and workability.

v) If you try to connect more than one TV camera, there is a method of using two coaxial cables for going up and down, using a branching device and a head end, and putting it on the carrier wave of VHF.
This method had restrictions on workability, equipment price, and system flexibility.

As mentioned above, there was no method for transmitting a baseband video signal by connecting a plurality of TV cameras and a plurality of monitors with bus wiring using a pair cable and setting a video line between arbitrary devices. .

Especially in a home telephone system in which a plurality of extension telephones are connected to one or two telephone lines, it is the same as the telephone system when a high-performance type TV intercom system is provided with a plurality of TV cameras and a plurality of TV monitors. Transmission of video signals was difficult due to bus wiring using a pair cable of the wiring system. That is, conventionally, it is necessary to wire a coaxial cable in addition to the pair cable for transmitting a video signal, and it is difficult to connect a plurality of cameras and monitors.

FIG. 1 shows a system configuration in the case of using a plurality of television cameras and television monitors according to the conventional method. For example, when an attempt is made to connect the camera doorphone 1a and the doorphone monitor 100b, a video signal of a subject is generated by the image sensor 2a, A video signal is sent to a coaxial cable 10a, which is a video signal transmission path, via a process amplifier 3a for adding a synchronization signal and the like and a video signal transmitter 4a. This signal is transmitted to the switch device 21 and is connected to the coaxial cable 19b by closing the video signal switch 22b. This makes the camera door phone 1
The video signal from a is connected to the doorphone monitor 100b and forms a signal transmission path. In the intercom monitor 100b, the receiver 12
b, and the image display element 14 via the image amplification circuit 13b.
Displayed in b. Since audio often uses the same wiring system as the transmission path of the video signal, the audio signal from the microphone 8a of the camera doorphone 1a passes through the amplifier 9a and the audio signal from the 2-wire to 4-wire conversion circuit (HYB) 7a. Out on line 11a.
This signal is also sent by the switch device 21 to the audio signal switch 23.
By closing b, the 2 line of the doorphone monitor 100b-4
It is transmitted to the line conversion circuit (HYB) 7d and is output as an acoustic signal from the speaker 16b via the amplifier 15b. Similarly, an audio signal from the doorphone monitor 100b to the camera doorphone 1a is similarly transmitted via the audio signal switch 23b. As described above, for the transmission of the video signal, a method of forming a dedicated transmission line between the transmission side and the reception side each time is generally used.

The reason for this is that if a video signal is to be transmitted in a domestic bus wiring that also allows branch connection, there is no method for solving this problem due to the deterioration of the image due to the reflected wave of the video signal. This is because there is only one individual wiring system or a combination system of a switch circuit and star wiring.

Usually, a coaxial cable is used for transmitting a video signal, but when transmitting a video signal from an arbitrary transmission point to an arbitrary reception point, a method using two up and down coaxial cables is generally used. Is. This is shown in FIG. In FIG. 2, the coaxial cable 32 of the upstream video line is transmitted from the video signal transmitting terminal 30 via the video signal branching device 34 in the connection box 35.
The video signal is superimposed on the carrier wave and transmitted. This signal is converted to a downlink signal at the head end 33 (generally, carrier frequency conversion), and is retransmitted as a video signal 4 on the coaxial cable 31 of the downlink video line. This signal is branched and received by the branching device of the receiving terminal 36. In a conventional system of this type, a video signal is placed on a carrier wave and converted at the head end 33 into a carrier wave of another frequency. In this way, when video equipment is connected to the bus to configure an arbitrary video transmission channel, conventionally, two thick coaxial cables are used, each terminal uses a branching device, and the head end uses an up / down frequency conversion circuit. Was necessary and there was a problem in terms of workability and economy.

(3) Object of the Invention The present invention eliminates the above-mentioned drawbacks and arbitrarily transmits video between a plurality of transmitters such as a TV camera and an intercom camera and a plurality of receivers such as a TV monitor with a simple device as needed. It is an object of the present invention to provide a video signal transmission system which constitutes a channel and is capable of putting into practice a communication means having a high degree of freedom that enables high-quality video signals to be transmitted and received between arbitrary devices.

(4) Configuration and Operation of the Invention In order to achieve this object, a video signal transmission system according to the present invention comprises a bus signal transmission line composed of twisted pair wires,
A bus video signal transmission system is configured using one or more baseband video signal transmitters and one or more baseband video signal receivers, and the twisted pair is provided at the end of the bus signal transmission line. A terminating impedance having an impedance equal to the characteristic impedance of the line is connected, and each output end of the transmitter is connected to the bus signal transmission line via a signal transmission line composed of a twisted pair line. And transmitting the baseband video signal, and when not transmitting the baseband video signal, a switching means for connecting to the signal transmission line a terminating impedance having an impedance equivalent to the characteristic impedance of the twisted pair. The bus signal transmission line is provided at each input end of the receiver via a signal transmission line composed of a twisted pair wire. Connection means is provided for connecting the input end and connecting a terminating impedance having an impedance equivalent to the characteristic impedance of the twisted pair to the signal transmission line to receive the baseband video signal; and Each of the receivers has a configuration provided with automatic gain control means for adjusting the reception level of the received baseband video signal to a constant level signal.

Next, the configuration and operation of the present invention will be described in detail. FIG. 3 shows an embodiment of the present invention, in which 24a to 24d are video channel switches built in the video terminal, 25a to 25d are also audio channel switches, and 26b and 26c are equipped with an automatic gain control function using a synchronization signal. The video signal receiver 27 is a terminator that terminates the baseband video signal transmission path using a pair cable. The video signal receivers 26b and 26c have higher input impedance than the terminator 27, and automatic gain adjustment for supplying the received baseband video signal to the video amplifier circuits 13a and 13b at a required signal level. Has a function (AGC circuit). Since the transmitted video signal is a baseband signal in this AGC circuit, there is no reference carrier (carrier wave). Therefore, a method of performing AGC using a synchronization signal whose signal level is known is applied. There are various schemes for this, which are known per se.

When attempting to transmit a video signal from the camera intercom 1a to the intercom monitor 100b, a video signal of the subject is generated by the image sensor 2a, the process amplifier 3a, the video signal transmitter 4a, and by closing the video signal switch 24a. The video signal is sent to the pair cable 28 which is the transmission path of the video signal. This signal is transmitted to the doorphone monitor 100b. In the doorphone monitor 100b, the video signal switch 24b is closed, the video signal receiver 26b and the pair cable 28 are connected, and the baseband video signal is received. The transmission distance of the pair cable 28, which is the transmission path of the video signal, differs for each communication, and the received signal level at the video signal receiver 26b is not constant, and the level is high in a short distance and low in a long distance. If this signal is supplied to the image display element 14b as it is, an image having high brightness and high contrast at a short distance, an image having low brightness and low contrast at a long distance, and further synchronization disturbance due to a decrease in the synchronization signal level occur.

For this reason, when trying to build a system that connects multiple video signal transmission sources and multiple video signal reception sources with this type of bus connection, it is necessary to manually adjust the brightness and contrast for each communication on the receiving side. It was not the target.

On the other hand, in the present invention, the video signal receiver 26b with the automatic gain control function of the baseband (26c for the intercom monitor 100a)
By using, it is possible to always see an image of constant quality even if the signal level differs for each communication.

Furthermore, the configuration of the video signal transmission circuit, the reception circuit, and the pair cable will be described. In a normal home bus (including branch) wiring configuration, the information channel is open for the purpose of transmitting an audio signal, and the end of the wiring is open. Therefore, when transmitting an image signal, signal reflection occurs at the end of the wiring. , Degradation of received image (ghost interference) occurs. Therefore, in the present invention,
As shown in FIG. 4, a terminator 27 equivalent to a pair cable is inserted at the end of the wiring that does not connect any terminal, and the transmitting terminal 39
In non-communication, a non-reflective termination condition is set by using the switching means 41 for inserting the terminating impedance 37 equivalent to that of the pair cable into the pair cable, and at the time of communication, the transmitting terminal 39 has a transmitting circuit having an output impedance equivalent to that of the pair cable (video). Terminal) 38 and the receiving terminal 40 has a connecting means 43 for connecting to a receiving circuit (video terminal) 42 having an input impedance equivalent to that of a pair cable, so that a baseband video signal can be received without being deteriorated. It becomes possible to transmit. By this method, the terminal can be connected to an arbitrary position on the bus wiring.

Further, when it is used only for the bus wiring and not for the branch wiring, the terminating impedance 37 of the transmitting terminal 39 and the receiving terminal 40 is omitted, and the transmitting circuit (38) having a high input impedance and a high output impedance, the receiving circuit. It is also possible to use (42).

Further, when such a transmission circuit and a reception circuit having high input impedance and high output impedance are used, since the transmission of the video signal is not affected, the video switch built in the device can be omitted.

Furthermore, as shown in FIG. 5, the video terminal 42 or
When connecting 38, since the terminator 27 is already connected to the wiring system, the terminator 27 in this case is the video terminal 42 or 38.
Has a structure of a relay connector so that the terminating impedance 37 is connected in parallel inside. At the same time, the internal impedance of the video terminal 42 or 38 is a high impedance circuit. With such a configuration, the video terminal 42 or 38 can be arbitrarily connected either in the middle or at the end of the wiring system. In addition,
In the case of the video terminal 42 or 38 in which the internal impedance cannot be high impedance, by using the video switch 24, the video signal can be transmitted and received even if the internal impedance is low.

In the same way as the video signal, the communication of the audio signal is converted into an electric signal by the microphone 8a, and the microphone output amplifier 9a
Hybrid circuit that separates the received audio signal that is amplified by
By closing the audio signal switch 25a via 7a, the video signal is sent to the pair cable 11 which is the transmission path of the audio signal. This signal is transmitted to the doorphone monitor 100b, and the doorphone monitor 100b captures the audio signal by closing the audio signal switch 25b. This audio signal is separated by the hybrid circuit 7d as an input to the speaker amplifier 15b. In this way, the audio signal is also transmitted with the same configuration as the wiring configuration of the video signal.

Other configurations are the same as those shown in FIG. Two
The 4-conversion circuit 27 and the like are the same as those in FIG. 3, and those using the same numbers are configured to realize the same functions.

(5) Effects of the Invention According to the configuration of the present invention as described above, the following effects can be obtained.

i) Wiring work is simple, flexible, and often already installed without the use of coaxial cables. Using paired cables, wiring equipment costs due to simplification of wiring work, housing construction and reconstruction It is possible to reduce the construction cost and the system price by deleting the video signal switch device.

ii) Enables bus connection or branch connection between a baseband video signal transmitting terminal such as a TV doorphone camera and a receiving terminal such as a TV doorphone monitor, and a conventional star wiring between the camera and the switching switch device, and the switching switch device and the monitor. It is possible to eliminate the congestion of the wiring due to the connection between the devices.

iii) A video transmission channel is arbitrarily configured between a plurality of transmitters such as a TV camera and a doorphone camera and a plurality of receivers such as a TV monitor, as necessary, so that an image by a reflected wave is transmitted between arbitrary devices. It is possible to provide a communication means with a high degree of freedom that enables transmission and reception of high-quality video signals without deterioration. At the same time, since the coaxial cable is not used for transmitting the video signal, it is possible to use a flexible cord from the bus wiring to the terminal. For this reason, it is possible to realize an extension terminal with high handleability, and the effect of the present invention is very high.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example in the case of connecting a plurality of TV doorphone cameras and TV doorphone monitors according to the conventional system, and FIG. 2 is a block diagram showing a configuration example of the conventional system for realizing bus connection using a coaxial cable, FIG. Is a block diagram showing an embodiment of the present invention, and FIGS. 4 and 5 are circuit configuration diagrams showing an embodiment of the present invention. 1a, 1b …… Camera door phone, 2a, 2b …… Imaging element, 3a, 3b
...... Process amplifier, 4a, 4b …… Video signal transmitter, 5a, 5
b, 16a, 16b ... speakers, 6a, 6b, 9a, 9b, 13a, 13b, 15a, 15
b, 18a, 18b ... Amplifier, 7a, 7b, 7c, 7d ... 2-wire to 4-wire conversion circuit (HYB), 8a, 8b ... Microphone, 10a, 10b, 19a, 19
b, 20a, 20b …… Coaxial cable, 11a, 11b …… Signal line, 12a,
12b ... Receiver, 14a, 14b ... Image display element, 21 ... Video signal switch device, 22a to 22d ... Video signal switch, 23
a to 23d ... audio signal switch, 24a to 24d ... video channel switch, 25a to 25d ... audio channel switch, 26a,
26c …… Video signal receiver, 27 …… Terminator, 28 …… Pair cable, 30 …… Sending terminal, 31,32 …… Coaxial cable, 33
...... Headend, 34 …… Video signal splitter, 35 …… Junction box, 36 …… Reception terminal, 37 …… Terminal impedance, 28,4
2 ... video terminal, 40 ... receiving terminal, 41 ... switching means, 43 ... connecting means, 100a, 100b ... door phone monitor.

Claims (1)

(57) [Claims] 1. A bus video signal using a bus signal transmission line composed of a twisted pair wire, one or more baseband video signal transmitters, and one or more baseband video signal receivers. A transmission system is configured, a terminating impedance having an impedance equal to the characteristic impedance of the twisted pair is connected to the end of the bus signal transmission line, and a twisted pair is formed at each output end of the transmitter. The baseband video signal is transmitted by connecting the output end to the bus signal transmission line via the signal transmission line, and the twisted pair is connected to the signal transmission line when the baseband video signal is not transmitted. A switching means is provided for connecting a terminating impedance having an impedance equal to the characteristic impedance of the line, and a twisted pair is provided at each input end of the receiver. Connecting the input end to the bus signal transmission line via a signal transmission line composed of, and connecting a terminating impedance having an impedance equivalent to the characteristic impedance of the twisted pair to the signal transmission line, A video is provided with connection means for receiving a baseband video signal, and each of the receivers is provided with automatic gain control means for adjusting the reception level of the received baseband video signal to a constant level signal. Signal transmission method.