JPH03289790A - Receiver for optically transmitted digital image signal - Google Patents

Abstract

PURPOSE:To prevent a clear noise on the screen of a monitor and the flicker on the screen from occurring by providing a detecting means and a means to input a digital signal of prescribed pattern to a digital-analog converter when detecting the fact that no normal image reproduction can be performed by the detecting means. CONSTITUTION:The detecting means 5 which detects the presence/absence of the input of an optical signal for a receiver B from a transmission line 4 and/or the fact that signal conversion processing from the optical signal to an analog image signal is performed normally, and the means 10 which inputs the digital signal of prescribed pattern to the digital-analog converter 8 when it is detected that no normal image reproduction can be performed by the detecting means 5 are provided. Therefore, the receiver B can output an image signal to the monitor 9 based on the digital signal of specific pattern even when the abnormality of a receiving state such as the interruption of a transmission signal or frame step out, etc., occurs. In such a way, it is possible to prevent the clear noise on the screen of the monitor and the flicker on the screen from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a receiver for optically transmitted digital image signals. More specifically, the present invention particularly reduces deterioration of reproduced images in a receiver that receives a digitized image signal as an optical signal, converts it into an electrical signal, converts it into an analog signal, and outputs it as an analog image signal. Regarding new configurations that can be implemented.

BACKGROUND OF THE INVENTION FIG. 2 is a diagram showing a typical configuration of an image signal optical transmission system including a conventional receiver.

As shown in the figure, this system is a system in which an image signal is transmitted from a transmitter A side to a receiver B side connected via an optical fiber 4 and reproduced on a monitor 9.

Here, the transmitter A includes an analog/digital converter (hereinafter referred to as an A/D converter) 1 that converts an input analog image signal into a parallel digital image signal, and an A/D converter 1. A parallel/serial converter (hereinafter referred to as a P/S converter) 2 that converts the output into a serial signal, and an optical signal that converts the electrical signal output from the P/S converter 2 into an optical signal and serves as an optical transmission path. It also includes an optical transmitter (electrical/optical converter) 3 that transmits data to a fiber 4.

On the other hand, receiver B is an optical receiver (optical/electrical converter) that converts the optical signal transmitted via the optical fiber 4 into an electrical signal.
5, a frame synchronization circuit 6 that extracts a frame synchronization signal from the image signal output from the optical receiver 5, and a serial/parallel circuit that converts the received signal into a parallel signal based on the frame synchronization signal extracted by the frame synchronization circuit 6. A converter (hereinafter referred to as an S/P converter) 6 and a digital/analog converter (hereinafter referred to as a D/A converter) that converts the digital image signal output from the S/P converter 6 into an analog signal. ) 8, and is configured to output an analog image signal output from the D/A converter 8 to an external monitor 9.

In the optical transmission system configured as described above, the image signal input to the transmitter A is converted into a digital image signal by the A/D converter 1, and then converted into a serial signal by the S/P converter 2. The signal is then sent to the optical fiber 4 as an optical signal via the optical transmitter 3. On the other hand, at the receiver, the optical signal input from the optical fiber 4 is converted into a serial digital signal by the optical receiver 5, and then the timing is adjusted by the frame synchronization circuit 6.
The P conversion circuit 7 converts it into a parallel digital image signal, and the D/A converter 8 reproduces the analog image signal.

Problems to be Solved by the Invention In the conventional receiver in the system as described above, when the transmitter A is not transmitting an optical signal, or when the optical transmission line is interrupted for some reason, the optical signal input to the receiver is interrupted. When the signal is interrupted, the optical/electrical converter of the optical receiver 5 often oscillates. In such a case, the optical receiver 5 generates random noise, this noise is processed by the S/P converter 7 and the D/A converter 8, and the noise is also input to the monitor 9. In addition, even when optical signals are being transmitted, if frame synchronization occurs, the D/
No valid image signal is output from the A converter 8.

If such an abnormal signal is output from the D/A converter 8, clear noise such as large flickering will appear on the screen of the monitor 9.

Therefore, the present invention solves the above-mentioned problems of the prior art, and when an abnormality occurs in optical signal transmission or frame synchronization,
The purpose of this invention is to provide a new receiver configuration in which no noise that can be seen on the screen is output from the D/A converter 8.

According to the present invention, a digital image signal is received as an optical signal, the received optical signal is converted into an electrical signal, and then converted into an analog image signal to reproduce the image. ,
A receiver used in an optical transmission system, which detects whether an optical signal is input to the receiver from a transmission path and/or whether signal conversion processing from an optical signal to an analog image signal is being performed normally. and means for inputting a digital signal of a predetermined pattern to a digital/analog converter when the detection means detects that normal image reproduction cannot be performed. A receiver for optically transmitted digital image signals is provided.

Operation In the receiver according to the present invention, if an abnormality occurs in the process of converting the optical signal received on the receiver side into an analog image signal, the digital signal of the specific pattern is
/A converter.

Therefore, even if noise occurs in the reproduced image due to transmission signal interruption or frame synchronization, the receiver will monitor the image signal based on a specific pattern of digital signals. Therefore, no clearly visible noise appears on the monitor screen, and phenomena that are unpleasant to the user, such as flickering on the screen, do not substantially occur.

Hereinafter, the present invention will be described in more detail with reference to the drawings, but the following disclosure is merely one embodiment of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 is a block diagram schematically showing a specific example of the configuration of an optical transmission system for digital image signals including a receiver according to the present invention. In this figure, the same reference numerals are given to the same components as those of the optical transmission system shown in FIG. 2.

As shown in the figure, this system also includes a transmitter A and a receiver connected via an optical fiber 4. Transmitter A has the same configuration as the transmitter of the conventional system shown in FIG. 2, so a description thereof will be omitted. Receiver B also
The basic signal processing system composed of an optical receiver 5, an S/P converter 6, and a D/A converter 7 is the same as the conventional system shown in FIG. However, in this system, the output of the S/P converter 7 is input to the D/A converter 8 via an AND circuit group 10.

That is, one input terminal of each AND circuit constituting the AND circuit group 10 is connected to each output of the S/P converter 7, and the output of the AND circuit 10 is connected to the input of the D/A converter 80. has been done. In addition, the other input of each AND circuit has a signal CD indicating the presence or absence of an input signal in the optical receiver 5.
I is input respectively.

This signal CI)I is configured to output an "H" level when the optical receiver 5 is receiving an optical signal, and to output an "L" level when the optical receiver 5 is not receiving an optical signal. ing. Therefore, in this system, when no optical signal is input to the optical receiver 5, an "L" level signal is input to one input of each AND circuit. No signal is input to 8. Therefore, even if the optical/electrical converter of the optical receiver 5 oscillates and the S/P converter 7 outputs random noise, this noise will not cause flickering in the image on the monitor.

In the above example, only the signal CDI indicating the input state to the optical receiver 5 is input to the AND circuit 10, but as shown by the dotted line in FIG. The signal CD2 for detecting deviation is sent to the AND circuit 9.
It can also be configured to input That is, this signal CD2 is #H'' when frame synchronization is achieved.
This is a signal that becomes "L" level when a level shift or out-of-synchronization occurs. AND such signal CD2
By inputting the signal into the circuit, even if an optical signal is input to the optical receiver 5, the output of the image signal detection signal can be suppressed when a loss of synchronization occurs and normal image signal reproduction cannot be performed. I can do it.

In this embodiment, an AND gate is connected to each input of the 1D and /A converter 8, but the present invention is not limited to this. For example, the S/P converter 7 It is also possible to configure only one AND gate to be connected to the data input of.

In this case, the output of the optical receiver 5 is connected to one input of the AND gate, and each detection signal CDI and/or CD2 is connected to the other input. Therefore, when CDl and/or CD2 go to "L" level, S/
The input signal to the P converter 7 is fixed, and no random signal is output from the D/A converter 8.

As described in detail of the invention, in the optical transmission system for digital image signals using the receiver according to the present invention, even if an abnormality in the reception condition such as signal interruption or frame synchronization occurs, the receiver can Since an image signal based on a digital signal with a pattern of It will no longer occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a specific configuration example of an optical transmission system for digital image signals including a receiver according to the present invention, and FIG. FIG. 1 is a block diagram showing a typical configuration of a transmission system. [Main reference numbers] 1... Analog/digital converter, 2... Parallel/serial converter, 3... Optical transmitter, 4... Optical fiber, 5... Optical receiver, 6 ...Frame synchronization circuit, 7.Serial/parallel converter, 8.Digital/analog converter, 9.Monitor, 9.AND circuit

Claims (1)

[Claims] A receiver used in an optical transmission system that receives a digital image signal as an optical signal, converts the received optical signal into an electrical signal, and then converts it into an analog image signal to reproduce the image. a detection means for detecting whether or not an optical signal is input to the receiver from the optical path and/or whether signal conversion processing from the optical signal to an analog image signal is being performed normally; and normal image reproduction by the detection means. and means for inputting a digital signal of a predetermined pattern to a digital/analog converter when it is detected that the image signal cannot be transmitted.