JPS6238387Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field] The present invention is a so-called power supply superimposed type video information signal transmission system in which power is supplied superimposed on the same cable as a coaxial cable for video signal transmission. It is related to.

[Background technology]

Recently, as society has become more and more information-oriented, there has been a remarkable development of information systems in apartments, buildings, homes, etc., such as home computers and CATV systems. Under these circumstances, information is transmitted and received via a single cable such as a coaxial cable or optical fiber, such as audio signals from intercoms and door phones, TV intercoms and monitor TVs, and security information data such as crime prevention and fire prevention. Transmission systems are becoming more popular. Therefore, in such an information transmission system, when considering the video information signal transmission system, generally speaking, as the video information signal transmission distance from the TV camera 1 to the monitor TV receiver 3 as shown in Fig. 1 increases,
Due to the influence of the distributed constant of the cable 2, the high frequency components of the transmission signal are reduced. As the high-frequency components deteriorate, the sharpness of the image substantially decreases. Therefore, in order to compensate for the deterioration of this high frequency component, the current method is to emphasize the high frequency component by adding appropriate preshoot and overshoot to the step response waveform of the image signal on the TV camera 1 side. transmitting a signal. In other words, in the image signal frequency characteristics shown in Figure 2, the longer the signal transmission distance, the more
The high-frequency components deteriorate in this order. Therefore, the level of the high-frequency components is raised in advance and transmitted as shown in a in the same figure. More specifically, for a normal image signal waveform as shown in Figure 3a, appropriate preshoot and overshoot are added in advance to the step response waveform of the image signal as shown in Figure 3b, and this is transmitted. Conventionally, the degree of high frequency compensation has been set to an appropriate value depending on the transmission distance. Note that FIG. 3c shows a waveform when the high frequency component is degraded. In addition, in the conventional example in Fig. 1, 4 is a DC power supply, and a monitor
This is the power supply for driving the TV camera 1 installed on the TV receiver 3 side, and is supplied to the TV camera 1 side through the same cable 2 as the video signal transmitted as a baseband signal in order to reduce wiring costs. Therefore, the transmission signal on the cable 2 becomes a power superimposed image signal as shown in FIG.

Thus, in the conventional example described above, there is a problem in that the degree of high-frequency compensation of the transmitted video signal must be set each time according to the transmission distance from the TV camera to the monitor TV receiver, making the installation work complicated. There was a problem that if this initial setting was incorrect, it might not be possible to send a clear image.

[Purpose of invention]

This invention automatically detects the length of the transmission distance and performs high-frequency compensation according to this transmission distance, making it possible to always monitor clear images and simplify the installation work for video information signals. The purpose is to provide a transmission system.

[Disclosure of invention]

FIG. 4 shows a block diagram of an embodiment of the present invention, in which, like the conventional example shown in FIG.
The operating power is sent from the DC power supply 4 on the TV receiver 3 side to the TV camera 1 via the cable 2, and the image signal output from the TV camera 1 is sent via the cable 2 to the monitor TV receiver 3 side. At this time, the longer the transmission distance by the cable 2, the more the DC voltage component in the power superimposed image signal detected by the TV camera 1 on the cable 2 as shown in Figure 5 will decrease due to voltage drop. This DC voltage drop is detected by the power supply detection circuit 6 to determine the transmission distance of the video signal, and the output of this power supply detection circuit 6 controls the image quality adjustment circuit 5, which determines the transmission distance. The longer the , the higher the preshoot and overshoot levels are to compensate for the high frequency components.

An embodiment of the present invention shown in FIG. 6 will be described. First, the image quality adjustment circuit 5 obtains a second-order differential waveform of the TV camera 1 output by an inductance Lo and a capacitor Co connected to the collector of the transistor Tr, and divides this by resistors R ₁ and R ₂ . Press to get the output of ~. At this position, a step response waveform with large preshoot and overshoot levels is obtained, at position , a similar waveform is obtained although smaller than in the above case, and at position , a response with no waveform distortion is obtained. It's made so that you can get it. Therefore, the output waveforms from these ~ positions are converted to analog switches.
By controlling SW ₁ , SW ₂ , and SW ₃ , the output is divided into long distance, medium distance, and short distance, respectively. Next, in the power supply detection circuit 6 which inputs the power supply superimposed signal as shown in FIG. 5, the low peak hold circuit 16 first detects the direct current voltage (DCV) in the signal waveform shown in FIG. _The comparator ₇ ^,
8 and 9, and if the DC voltage (DCV) value is V ₃ or higher, it is determined that the distance is close and the analog switch SW ₁ is set.
, and when the DC voltage (DCV) is V ₂ to _{V 3} , it is determined that the distance is medium, and analog switch SW ₁ is turned on, and when the DC voltage (DCV) is V ₁ to _{V 2} , it is determined that the distance is medium. These judgment control operations are performed by a gate circuit ₁ consisting of two inverters 10, 11 and two AND gates 12, 13.
4. Note that 15 in the figure is a reference voltage generating section, which generates the aforementioned reference voltages V ₁ to V ₃ . In addition, in the above-mentioned embodiment, the image quality can be adjusted from far to medium.
Although switching is performed in three stages of short distance, the image quality may be adjusted in appropriate stages, such as by further dividing into multiple stages.

[Effect of idea]

Since the present invention is configured as described above, even if the transmission distance of the video signal varies depending on the installation condition, etc., signal transmission can be performed with adjustment and compensation always performed according to the transmission distance at that time. This has the effect of making it possible to always monitor clear images without complicating installation work.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a frequency characteristic diagram of an image signal, and FIGS. 3 a to 3 are waveform diagrams of a normal image signal, a high-frequency component compensated image signal, and a high-frequency component degraded image signal, respectively. FIG. 4 is a block diagram of an embodiment of the present invention, FIG. 5 is a waveform diagram of a power supply superimposed image signal, FIG. 2 is a cable, 3 is a monitor TV receiver, 4 is a power supply detection circuit, and 5 is an image quality adjustment circuit.

Claims (1)

[Scope of utility model registration request] A power supply superimposed image display in which a video signal is transmitted from a TV camera to a monitor TV receiver via a single cable, and power to the TV camera is supplied from the monitor TV receiver via the cable. In information signal transmission systems,
A power supply detection circuit for detecting a voltage drop in the transmission power supply and an image quality adjustment circuit for adjusting the sharpness of the transmitted image are provided on the TV camera side, and the transmission distance is determined from the voltage drop detected by the power supply detection circuit and the transmission is performed. A video information signal transmission system characterized in that the image quality adjustment circuit automatically adjusts and compensates for the sharpness according to the distance.