JPH1013814A - Bi-directional digital signal transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a transmittable distance by compensating a loss in a transmission line and providing a switch preventing a bi-directional signal from forming a loop at a repeater part provided in the middle of a cable. SOLUTION: A video and speech signal transmitted and received mutually between a camera head part 1 and a camera control part 2 is digitized, time- base-compressed and then bi-directionally and alternately transmitted by a time division multiplexing system through a single coaxial cable 2. The repeater part 7 provided in the middle of the cable 2 sends a signal, which is inputted to a terminal 8, to a camera control part 2 from a terminal 9 through amplifiers 5a and 4a and a signal inputted to the terminal 9, from the camera control part 2 is sent to the camera head part 1 through amplifiers 5b and 4b. Then a switch 10a is connected only when a signal from the camera head part 1 to a camera control part 2 exists, a switch 10b is connected only when a signal from the camera control part 2 to the camera head part 1 exists.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable relay device required for digitally and bidirectionally transmitting video, audio, control signals, and the like using a single transmission line (cable). .

[0002]

2. Description of the Related Art In general, a television camera device used for broadcasting generally includes a camera head unit for converting an optical image into an electric signal, and a camera control unit for controlling the camera head unit by performing various shaping processes on the electric signal. CCU: Camera Control
Unit). Here, a video signal, an audio signal, and the like generated by the camera head unit are transmitted from the camera head unit to the camera control unit. On the other hand, an image for monitoring by the camera head unit is transmitted from the camera control unit to the camera head unit. A signal, a voice signal for communication, and the like are transmitted. These signals can be transmitted by using a triple coaxial cable, called a triax cable. In this case, it is necessary to multiplex these signals. Conventionally, these analog signals are modulated, frequency-division multiplexed, and transmitted bidirectionally.

As a recent example, a camera head unit and a camera control unit connected by one coaxial cable digitize analog video and audio signals, respectively, and perform time division multiplexing and time axis compression. Then, a transmission signal consisting of a repetition of a signal period and a no-signal period is generated, and during the no-signal period of the transmission signal from one, the transmission signal from the other is transmitted to each other, so that both signals are transmitted by one cable. "Digital video signal multiplex transmission method and apparatus" (Japanese Patent Application Laid-Open No. 7-203399) has been proposed, which enables two-way transmission. FIG. 2 shows an example of the configuration of this transmission system in which a video signal and an audio signal are digitized, time-division multiplexed and bidirectionally transmitted between a camera head unit and a camera control unit. The form is shown. An analog luminance signal Y, chrominance signals Pr and Pb, an audio signal A1, and the like are given to a transmission unit 1 installed on the camera head side, and are converted into digital signals by an A / D converter 1-1. You. These signals are multiplexed by the multiplexer 1-2 ((a) of FIG. 4), the time axis is compressed by the compressor 1-3, and an intermittent signal period and a non-signal period are repeated. A digital transmission signal ((b) in FIG. 4) is transmitted to the cable 2 via the line interface 1-4 (FIG. 4).
(c)). The transmission unit 3 installed on the camera control unit side
Is received via the line interface 3-1.
The time-axis-compressed and multiplexed digital signal is expanded in the time axis by an expander 3-2, separated into a luminance signal Y, color signals Pr and Pb, and an audio signal A1 by a separator 3-3.
The signal is converted into an analog signal by the / A converter 3-4.

On the other hand, the analog return video signal M and the audio signal A2 supplied to the transmission unit 3 are converted by an A / D converter 3
The signal is converted into a digital signal by -5, multiplexed by a multiplexer 3-6 ((e) in FIG. 4), data is compressed by a compressor 3-7, and a time axis is further compressed by a compressor 3-8. An intermittent digital transmission signal ((d) in FIG. 4) consisting of a repetition of a signal period and a no-signal period becomes a period during which no reception signal from the camera head unit exists via the line interface 3-1. It is sent to the cable 2 (FIG. 4 (c)). And
The time-axis-compressed and multiplexed digital signal received by the transmission unit 1 via the line interface 1-4 is time-expanded by the decompressor 1-5, and demultiplexed by the demultiplexer 1-6. The video signal M is returned to the video signal M and the audio signal A2, and is converted into an analog signal in the D / A converter 1-7. Here, the line interfaces 1-4 and 3-
3 is shown in FIG. It comprises a transmitting amplifier 4 for transmitting a signal to a line, a receiving amplifier 5 for receiving a signal from the line, and an equalizer 6 for compensating for distortion in the received signal caused by cable characteristics.

[0005] As described above, this transmission system is composed of a video signal and an audio signal transmitted from the camera head to the camera controller, and a video signal and audio transmitted from the camera controller to the camera head. As shown in FIG. 4, signals are transmitted so as to occupy different times with a time gap therebetween, so that a single cable enables two-way transmission without mutual interference. Here, in this transmission system, the state of each transmission signal at an intermediate point of the cable 2 connecting the camera head unit and the camera control unit is as shown in FIG. 4C. That is,
The values of the time gaps τ ₁ , τ ₂ between the two transmission signals are equal and τ. At the end of the cable 2 on the camera head side, the time gap τ ₁ is 2τ and the time gap τ ₂ is 0. At the end of the cable 2 on the camera control section side, the time gap τ ₁ is 0 and the time gap is 0. τ ₂ is 2τ
Becomes At any point on the cable 2, the sum of these time gaps is 2τ.

[0006]

When a plurality of video signals and audio signals are digitized and time-division multiplexed, the bit rate becomes extremely high. For example, the luminance signal of the video signal transmitted from the camera head side is 13.5 MHz.
z, when two types of color signals are sampled at 6.75 MHz and quantized by 10 bits, the total bit rate becomes 270 Mb
ps. In addition, since a slight deterioration in image quality can be tolerated in the video signal transmitted from the camera control unit, the bit rate is 54 Mbps, for example, even if a signal compressed to 1/5 is assumed. When a sound signal of several channels is added to these, the total bit rate becomes 33
It will exceed 0 Mbps. When such high-speed digital data is transmitted through a coaxial cable, the loss in the cable is large, and the transmittable distance is limited. This depends on the cable loss compensation method, for example,
The transmission distance is about 300 meters. In the transmission between the camera head unit and the camera control unit, in a normal case, even about 300 meters can be tolerated. However, in order to expand the application, an increase in the transmission distance is a major problem. In view of these problems, the present invention compensates for cable loss in a system for transmitting video signals, audio signals, and the like bidirectionally between a camera head unit and a camera control unit using a single cable. The aim is to increase the possible distance.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a video device connected to both ends of a transmission line to time-division multiplex, digitize video and audio signals, etc. Axial compression, to generate a transmission signal consisting of repetition of a signal period and a no-signal period, in a no-signal period of the transmission signal from one end of the transmission path, in a transmission system that mutually transmits the transmission signal from the other end, In the middle of the transmission path, there is provided at least one relay means for compensating for a loss caused by the transmission path, and the relay means prevents the bidirectional transmission signal from forming a loop. This is a bidirectional digital signal transmission device configured to include switch means. In addition, one of the transmission signals is a video signal whose information amount is compressed, and controls a compression ratio of the video signal according to a transmission distance of the transmission path according to the number of stages of the relay unit. The sum of the time during which each of the transmission signals does not exist on the transmission path is maintained at least twice the delay time of the transmission path. With this relay device, cable loss is compensated and transmission distance is extended. In the above example, if n repeaters are inserted every 300 meters, the transmission distance becomes n × 300 meters, and the transmittable distance is expanded n times.

[0008]

FIG. 1 shows the most basic configuration of the present invention, and the operation will be described below. In this configuration, a relay unit 7 of the present invention is inserted between a transmission unit 1, a cable 2, and a transmission unit 3 on a camera control unit side, which are equivalent to those shown in FIG. The transmission signal transmitted from the transmission unit 1 or 3 via the cable 2 is compensated for the loss of the cable 2 by the relay unit 7 and transmitted to the next cable 2 again. In the cable 2, transmission signals are respectively transmitted from the camera head unit and the camera control unit. Therefore, the relay unit 7 must receive, compensate, and transmit these two-way transmission signals. The detailed configuration of the relay unit 7 having these functions is shown in FIG. 5 and will be described below. Here, it is assumed that the two input / output terminals of the relay unit 7 are 8,9. The transmission signal input from the terminal 8 is received by the reception amplifier 5a.
, And the loss of the cable 2 is compensated for by the equalizer 6a, and output to the terminal 9 via the transmission amplifier 4a.

On the other hand, the transmission signal input from the terminal 9 is
The signal is amplified by the reception amplifier 5b, compensated for cable loss by the equalizer 6b, and output to the terminal 8 via the transmission amplifier 4b. By the way, the signal input from the terminal 8 is amplified by the receiving amplifier 5a, the cable loss is compensated by the equalizer 6a, the signal is amplified by the receiving amplifier 5b through the sending amplifier 4a, and the cable loss is reduced by the equalizer 6b. When compensated and returned to the receiving amplifier 5a via the sending amplifier 4b, a loop is formed, and an oscillation phenomenon occurs. However, since the transmission signals input to the terminals 8 and 9 do not exist at the same time as shown in FIG. 4, the oscillation can be prevented by inserting a changeover switch in this loop. . In FIG. 5, the switch units 10a and 10b are connected to the output units of the transmission amplifiers 4a and 4b, respectively. Since the purpose of this is to break the loop, for example, the switch unit 10a may be anywhere between the transmission amplifier 4a, the reception amplifier 5a, and the equalizer 6a. The same applies to the switch section 10b.

The switch unit 10a is conductive during a time period when a transmission signal from the camera head unit side to the camera control unit side is present as shown in FIG. 4, and is non-conductive during other time periods. Control is performed such that conduction occurs during a time period during which a transmission signal from the control unit to the camera head unit exists, and non-conduction occurs during other time periods. Here, the conduction time may enter the time gaps τ ₁ and τ ₂ shown in FIG. 4, but it is important that the two switch units 10
a and 10b are not conducting at the same time. As a result, the loop is always interrupted, and no oscillation phenomenon occurs. The switch control units 11a and 11b realize such switching control. The switch control units 11a and 11b determine a signal break from the signal sequence shown in FIG. 4 equalized by the equalizers 6a and 6b, and there is a transmission signal from the camera head unit to the camera control unit. And a time zone in which a transmission signal from the camera control unit to the camera head unit exists, and switches the switch units 10a and 10b. FIG. 1 shows an example in which one relay unit 7 is inserted between the cables 2. As shown in FIG. 6, two relay units 7 may be inserted, or three or more relay units may be inserted. Thereby, the total transmission distance can be increased.

By the way, the time gap τ shown in FIG. 4 must be a value exceeding the delay time generated at the time of cable transmission. This is determined by the condition that bidirectional signals are not simultaneously present at both ends of the cable 2 in FIG. Therefore, when the transmission distance is increased and the delay time is increased by the relay unit 7 of the present invention, it is necessary to increase the time gap τ accordingly. Of course, the maximum transmission distance may be assumed, and the time gap τ satisfying the maximum transmission distance may be set as a fixed value from the beginning. However, in this case, since the value is used even when the transmission distance is short,
Transmission efficiency decreases. In other words, the time gap is a useless time zone during which no signal is sent, and if this is large,
Transmission volume decreases. Therefore, if the transmission distance changes due to the insertion of the relay unit 7, it is desirable to always set the necessary minimum time gap accordingly. However, changing the amount of signals that can be transmitted by changing the setting of the time gap leads to an overall change in the signal transmission format. Further, it is not easy to change the transmission format every time the number of relay sections to be inserted changes.

Therefore, the present invention focuses on the fact that the transmission signal from the camera control section to the camera head section is mainly a compressed video signal, and deals with this as follows. That is, when the transmission distance increases due to the insertion of the relay unit 7 and the transmission amount decreases, the compression rate of the transmission signal from the camera control unit to the camera head unit is increased by allowing a certain degree of deterioration of the transmission image quality. A video signal is transmitted with a smaller transmission code amount than ever. The floating time by this,
The increase in the time gap τ is applied. Conversely, when the relay unit 7 is removed and the transmission distance is reduced, the compression rate of the video signal transmitted from the camera control unit to the camera head unit is reduced, and the video signal with a larger transmission code amount and good image quality is used. Is transmitted. The required time is covered by the reduced time gap τ.

[0013]

As described above, with the transmission device using the relay unit of the present invention, video, audio,
When a control signal or the like is transmitted bidirectionally, cable loss can be compensated and the transmittable distance can be set arbitrarily.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a transmission device according to the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional transmission device.

FIG. 3 is a block diagram showing a configuration of a line interface unit of a conventional transmission device.

FIG. 4 is a diagram showing a form of a signal transmitted in the present invention.

FIG. 5 is a block diagram showing a configuration of a relay unit of the transmission device of the present invention.

FIG. 6 is a block diagram showing another configuration of the transmission device of the present invention.

[Explanation of symbols]

1,3: transmission unit, 2: cable, 1-2, 3-6: multiplexer, 1-3, 3-7, 3-8: compressor, 1-4, 3-
1: line interface, 1-5, 3-2: decompressor, 1
-6, 3-3: separator, 4a, 4b: sending amplifier, 5
a, 5b: reception amplifier, 6a, 6b: equalizer, 7: relay unit, 8, 9: input / output terminal, 10a, 10b: switch unit, 11a, 11b: switch control unit.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H04N 7/18

Claims (3)

[Claims] A video device connected to both ends of a transmission path,
The digitalized video and audio signals are time-division multiplexed and time-axis compressed to generate a transmission signal consisting of a repetition of a signal period and a no-signal period. , A transmission system for mutually transmitting transmission signals from the other end, in the middle of the transmission path, at least one stage of relay means for compensating for a loss caused by the transmission path, and the relay means A bidirectional digital signal transmission device comprising switch means for preventing the bidirectional transmission signal from forming a loop. 2. One of the transmission signals is a video signal in which the amount of information is compressed, and the compression ratio of the video signal is set in accordance with the transmission distance of the transmission path according to the number of stages of the relay means. 2. The bidirectional digital signal transmission apparatus according to claim 1, wherein the control unit controls the transmission signal so that the total time during which both of the transmission signals are not present on the transmission path is at least twice the delay time of the transmission path. 3. The bidirectional digital signal transmission device according to claim 1, wherein said one video device is a television camera head unit and said other video device is a television camera control unit. .