JPH03208488A - Optical video signal transmission equipment - Google Patents

Abstract

PURPOSE:To obtain a stable video signal by transmitting an electric video signal with its dark level side as the bright side of a light and making the size of the dark level side constant. CONSTITUTION:In the range where the linearity of an electrooptical conversion element constituting an electrooptical conversion circuit 2 is satisfied, a composite video signal which is the output of an amplifier circuit 1 is converted to an optical signal by the electrooptical conversion circuit 2. When this converted optical signal is transmitted to a receiver R, the dark level side of the video signal is made to be the bright side of the light and transmitted. The size of the dark level side of the output of an automatic gain control amplifier circuit 4 is detected by an automatic gain control voltage detection circuit 5, and in order to make this detection value constant, by the output of the automatic gain control voltage detection circuit, the size of the dark level side of the video signal of the automatic gain control amplifier circuit 4 is amplified and controlled to be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical video signal transmission device used in measuring instruments and video printers, computers and video printers, computers and display devices, and the like.

[Prior Art] Conventionally, as a video signal transmission device that transmits a video signal from a transmitting device to a receiving device, electric video signal transmission that uses a coaxial cable to transmit the video signal is used for applications where the transmission distance is relatively short. For applications involving long transfer distances, optical video signal transmission devices are used that transmit video signals using optical fibers.

[Problems to be Solved by the Invention] The former electric video signal transmission device uses a coaxial cable and the transmitting device and receiving device are electrically coupled, so there are problems with noise and safety. There are sexual issues.

On the other hand, the latter optical video signal transmission device can improve the problems of the electrical video signal transmission device.

However, in the case of optical video signal transmission equipment, it is necessary to transmit harmonic modulated data, compress data, digitally encode it, demodulate it, frequency modulate it, and further demodulate it. It is necessary to perform Kao reproduction of a special video signal. As a result, peripheral circuits become complex, signal processing becomes complex, and the device itself becomes larger.
It has the disadvantage of being 1.

The present invention can solve the noise and safety problems caused by the drawbacks of electric video signal transmission devices, and eliminates the need to repeat the process of creating a special video signal, which is a drawback of optical image signal transmission devices. The object of the present invention is to provide a compact, highly reliable, and inexpensive optical video FD signal transmission device.

[Means for Solving the Problems] In order to achieve the above object, the present invention converts the dark level side of the electric video signal on the transmitting device side into an optical video signal on the optical body side and transmits it via an optical transmission system. In an optical video signal transmission device that transmits an optical video signal to a receiving device, converts the optical video signal into an electrical video signal on the receiving device side, and outputs this electrical video signal by a video output device, the receiving device is directly connected to an optical electrical conversion amplifier. It is composed of an amplifier, and inputs the electric video signal converted on the receiving device side to an automatic gain control means that keeps the magnitude of the dark level constant, and inputs this output to the video output device. It is composed of

[Sakukawa] According to the present invention, before inputting an electric video signal to a video output device, the transmitting device side transmits the electric video signal with the dark level side as a light body side, and the receiving device side This system is designed to keep the size of the dark level side of the electrical video signal converted by Thus, a highly reliable and inexpensive optical video signal transmission device can be obtained.

Example c] Examples of the present invention will be described below. FIG. 1 and FIG. 2 are block diagrams showing a transmitting device T and a receiving device R, respectively, showing a first embodiment of the present invention. The transmitting device T includes an amplifier circuit 1 which inputs a video signal (?a air signal) and a synchronization signal (electrical signal), composes and amplifies these signals, and optically transmits the composite video signal amplified by the amplifier circuit 1. It consists of an electrical-to-optical conversion circuit 2 that converts into a signal and outputs it.

Note that when a composite video signal in which the video signal includes a synchronization signal is input to the amplifier circuit 1 as a video signal, there is no need to input the synchronization signal, and the synchronization {j? In the case of a video signal that does not need to be transmitted, there is no need to input a synchronizing signal to the amplifying circuit 1. The electrical-to-optical conversion circuit 2 includes an electrical-to-optical conversion element, such as a current-to-optical conversion element shown in FIG. 4(a),
Alternatively, it is configured by either a voltage-light conversion element.

The receiving device R inputs a photoelectrical conversion circuit 3 composed of a photodiode, a pin photodiode, etc. that converts optical input into an electrical signal, and a video electrical signal converted by the photoelectrical 9A conversion circuit 3. An automatic gain 4fI111 (AGC) amplification circuit 4, an automatic gain control (AGC)@pressure detection circuit 5, and an automatic gain control amplification circuit constitute automatic gain control means for keeping the magnitude of the dark level side of the video electrical signal constant. It consists of a video signal detection circuit 6 which receives the output of the circuit 4 and detects a video signal, and a synchronization signal detection circuit 7 which receives the output of the automatic gain control amplifier circuit 4 and detects a synchronization signal. The synchronization signal detection circuit 7 is not required when the video signal is output as a composite video signal containing a synchronization signal or when a video signal not containing a synchronization signal is output. The transmitting device T and the receiving device R are optically connected by an optical signal transmission system consisting of an optical fiber.

The operation of the optical video signal transmission apparatus configured as described above will be explained below. As shown in FIG.
A planking period) b exists periodically and corresponds to the dark level of the image signal. If the signal input to the amplifier circuit 1 is separated into a video signal and a synchronization signal as shown in FIG. 1, the dark level of the video signal, or A composite video signal can be obtained in which a synchronizing signal is inserted at a constant rate during the blanking period b.

This is because the synchronization signal exists during the blanking period b of the video signal, so a composite signal can be obtained. If transmission of the synchronization signal is unnecessary, or if the video signal is originally a composite video signal, there is no need to combine the synchronization signal and the image signal.

As shown in FIG. 4(a), the video signal is converted to Figure 4(b)
As shown in FIG. 2, the composite image f4, which is the output of the amplifier circuit 1, is converted into an optical signal by the electrical-to-optical conversion circuit 2.

When transmitting this converted optical signal to the receiving device R, it is transmitted with the dark level side of the video signal on the optical side. This optical signal is then converted into an electrical signal in the optical-to-electrical conversion circuit 3 of the receiving device R. This converted electrical signal is input to the automatic gain control amplifier circuit 4, and the magnitude of the dark level side of the output of the automatic gain control amplifier circuit 4 is detected by the automatic gain control voltage detection circuit 5, and this detected value is The output of the automatic gain control voltage detection circuit 5 is amplified and controlled so that the magnitude of the dark level side of the video signal of the automatic gain control amplifier circuit 4 is constant.

The optical to electrical conversion circuit 3, the automatic gain control amplification circuit 4, and the automatic gain control voltage detection circuit 5 are DC-coupled as a direct-coupled amplifier. In this way, the signal whose dark level (bright level of light) of the video signal is made constant is input to the video signal detection circuit 6 and the synchronization signal detection circuit 7, where the video signal and the synchronization signal are detected and output. If the output of the synchronization signal is unnecessary or if the composite video signal is originally output, the synchronization signal detection circuit 7 is not necessary.

The automatic interest II4 control voltage detection circuit 5 detects the peak value (peak I
f1) It is composed of a detection circuit, etc., and the responsiveness of the circuit can be controlled by adjusting the charging/discharging time of this detection port.

As mentioned above, focusing on the fact that the dark level of the video signal always exists periodically, the dark level side of the video signal is transmitted to the optical body side, and the automatic gain control amplifier circuit 4 on the receiving device side
and an automatic gain control voltage detection circuit 5 to perform automatic gain control so as to keep the dark level of the video signal constant, thereby performing automatic gain control of the video signal. It solves the noise and safety issues that are disadvantages of video signal transmission equipment, eliminates the need for special video signal processing and reproduction, which is a drawback of optical video signal transmission equipment, and is small, highly reliable, and inexpensive. An optical video f= signal transmission device can be provided.

In addition, even if the video signal and the synchronization signal are separated, the transmitting device T transmits it as a composite video signal in which the synchronization signal is combined with the dark level side during the retrace period b of the video #j signal. This composite video signal can be transmitted to the receiving device R.
can be easily separated into a video signal and a synchronization signal. Furthermore, since the transport system for the video signal and synchronization signal input to the transmitting device T passes through substantially the same circuit, the time difference (skew) between the video signal and the synchronization signal can be reduced. Also,
Since the receiving device R is DC-coupled, there is no need for DC regeneration, and it is practical to simply divide the DC offset of the transmitted video signal.

The embodiments described above are for monochromatic image signals, but
In the case of R (red), G (It color), and B (blue) video signals, the video signals can be similarly transmitted by providing three circuits of the above-described length embodiment. moreover,
In the case of digital RGB video signals, three circuits of the above-described embodiments may be used, or a single circuit may be used that combines the RGB video signals, transmits them as one video signal, and then regenerates the RGB signals. It can also be transmitted by

In addition, in a video signal in which a synchronization signal is not inserted, I,
The iJ period signal is combined with the dark level side of the video signal during the blanking period of the video signal and transmitted, and the receiving device R separates the video signal and the synchronization signal and reproduces and outputs them,
It can also be transmitted together with a synchronization signal and a video signal.

[Effects of the Invention] According to the present invention described above, by transmitting the dark level side of the electric video signal as the light body side, there is no need to perform special DC reproduction in the receiving device, and the electric video signal is It is designed to obtain a stable video signal by keeping the size of the dark level constant, eliminating the need for special video signal processing and playback that was required with conventional optical video signal transmission equipment. A compact, highly reliable, and inexpensive optical video signal transmission device can be obtained.

[Brief explanation of drawings]

ml diagram and FIG. 2 are block diagrams of a transmitting device and a receiving device, respectively, in an embodiment of the optical video signal transmission device according to the present invention, and FIG. 3 is a diagram for explaining the relationship between a video signal and a synchronization signal in the embodiment of the same. , FIG. 4 is a diagram for explaining the function of the electrical-to-optical conversion circuit according to the same example. T... Transmitting device, 1... Amplifying circuit, 2... Electrical-to-optical conversion circuit, R... Receiving device, 3... Optical-to-electrical converting circuit, 4... Automatic gain control amplifier circuit, 5... Automatic gain control voltage detection circuit, 6... Video signal detection circuit, 7.
...I, iJ period fd issue detection.

Claims (1)

[Claims] Converts the dark level side of the electrical video signal on the transmitting device side into an optical video signal on the optical body side, transmits it to the receiving device via the optical transmission system, and converts the optical video signal into an electrical video signal on the receiving device side. However, in an optical video signal transmission device that outputs this electrical video signal with a video output device, the receiving device includes an optical-to-electrical conversion amplifier that is a direct-coupled amplifier, and the electrical video signal converted on the receiving device side is An optical video signal transmission device configured to input the signal to an automatic gain control means for keeping the magnitude of the dark level constant, and input the output to the video output device.