JP2917093B2 - Optical modem device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modem device suitable for transmitting an image signal between an information processing device such as a computer and an image display device.

[0002]

2. Description of the Related Art In recent years, in order to transmit an image signal output from an information processing device such as a computer to an image display device, an optical modem device configured as shown in the block diagram of FIG. 3 is frequently used. . This optical modem device 1 has an E / O
The converter 5 and the O / E converter 11 are connected to the optical fiber cable 4
It is configured with a connection. And the information processing device 2
The transmission of image signals between the image display device 3 and the image display device 3 is performed by the optical modem device 1 as follows. That is, the image signal (NTSC, RGBHV, etc.) of the electric signal output from the information processing device 2
The optical signal is transmitted to the I / O converter 5, converted into an image signal of an optical signal by the E / O converter 5,
The data is transmitted to the converter 11. In the O / E conversion unit 11, the light is converted into an electric signal by the light receiving element 6 driven by the constant current circuit 7, which is a known circuit. The output signal of the light receiving element 6 is amplified by the amplifier circuit 8, and an image signal of an electric signal is output from the O / E converter 11 via the current buffer circuit 10 and transmitted to the image display device 3 by the metal cable 13. It had been.

[0003]

When an image signal is transmitted using the optical modem device 1 configured as described above, the optical fiber cable 4 is disconnected, or a failure occurs on the E / O conversion unit 5 side. When this occurs, a state occurs in which the image signal of the optical signal is not input to the O / E conversion unit 11, and only the dark current of the light receiving element 6 is amplified by the amplifier circuit 8 as it is. Therefore, there is a problem that only noise is output as an image signal from the O / E conversion unit 11 and transmitted to the image display device 3. If the state where only the noise is transmitted to the image display device 3 continues for a long time, it may cause a malfunction or a failure of the image display device 3 and may cause a great risk of deteriorating the image quality.

SUMMARY OF THE INVENTION It is an object of the present invention to transmit a signal which adversely affects an image display device, such as noise due to dark current of a light receiving element, to the image display device when no optical signal is input to the O / E converter. There is no attempt to provide an optical modem device.

[0005]

An E / O converter for inputting an electric signal output from an information processing apparatus and converting the input optical signal into an optical signal, and an image display apparatus for converting the input optical signal into an electric signal. In an optical modem device comprising an O / E converter connected to an optical fiber cable, the O / E converter 11 includes a light receiving element 6, a constant current circuit 7 for driving the light receiving element 6, and a light receiving element. Amplifying circuit 8 for amplifying the output current of element 6
A light detection circuit 9 that detects the presence or absence of an optical signal input from the output of the amplifier circuit 8 to the O / E converter and outputs a high-level or low-level signal in accordance with the presence or absence of the optical signal;
A current buffer circuit with a switch function of turning on and off an output of an electric signal input from the amplifier circuit according to the output of the photodetector circuit, and when the optical signal is not input to the O / E converter. Configures the optical modem device so as not to output an image signal from the O / E converter 11 to the image display device 3.

[0006]

According to the present invention, the presence / absence of an optical signal input to the O / E converter is determined by O /
The light is detected by a light detection circuit provided in the E conversion unit, and a high-level or low-level signal is output from the light detection circuit in accordance with the presence or absence of an optical signal. This output signal is applied to a switch pin of a current buffer circuit having a switch function, thereby turning on and off the output of the current buffer circuit, and converting the image signal into an image only when an optical signal is input to the O / E converter. It can be transmitted to a display device.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an optical modem device according to the present invention, and FIG. 2 is an explanatory diagram illustrating a main configuration of an O / E conversion unit according to the present invention. In the figure, 1 is an optical modem device, 5 is an E / O conversion unit having a built-in light emitting element driving circuit composed of a known circuit,
Reference numeral 4 denotes an optical fiber cable that transmits an optical signal output from the E / O converter 5 to the O / E converter 11.

The O / E converter 11 includes a light receiving element 6, a constant current circuit 7 including a known circuit for driving the light receiving element 6, and an amplification circuit 8 including a known circuit for amplifying an output of the light receiving element 6.
And a known circuit that detects the presence or absence of an optical signal input from the output of the amplifier circuit 8 to the O / E converter 11 and outputs a high-level or low-level signal in accordance with the presence or absence of the optical signal. ON / OFF so that the image signal input from the amplification circuit 8 is transmitted to the image display device only when the output of the circuit 9 and the light detection circuit 9 are applied and the optical signal is input to the O / E conversion unit 11. A current buffer circuit 10 having a switch function and having a well-known circuit is provided.

The light detecting circuit 9 which is a feature of the present invention is, specifically, a resistor R1, R2, R3, R4, R5, R6, a transistor Q1, a diode D1, a capacitor C1,
Further, a comparator U1 is provided. And
The electric signal from the amplifier circuit 8 input to the photodetector circuit 9 is input via the resistor R1 to the base of the transistor Q1 whose power supply voltage is applied to the collector, and is DC-amplified. Next, the signal amplified and output by the transistor Q1 is connected to a resistor R2 connected in series between the power supply voltage and the ground.
Is output to the common connection point of the resistor R3 and the diode D1.
Is applied to a parallel circuit of a capacitor C1 and a resistor R4, one end of which is grounded, and smoothed.

Here, the smoothed voltage smoothed by the parallel circuit of the capacitor C1 and the resistor R4 is peak-held. On the other hand, since the light receiving element 6 is driven by the constant current circuit 7, the peak hold voltage when there is an optical signal input is smaller than the peak hold voltage when there is no optical signal input. Therefore, by applying the peak-held voltage to the negative terminal of the comparator U1 and applying the voltage previously set by the resistors R5 and R6 to the + terminal of the comparator U1, the O / E converter 11 The light detection circuit 9 is configured to output a high-level signal from the comparator U1 when there is an optical signal input, and the high-level output signal of the light detection circuit 9 is applied to the switch pin of the current buffer circuit 10 so that the current is reduced. The buffer circuit 10 can be turned on and off. Then, the current buffer circuit 10 is turned ON only when the optical signal is input to the O / E converter 11, and the current buffer circuit 1
The electric signal input to 0 is output to the image display device 3.

The comparator U1 detects that the voltage value peak-held by the capacitor C1 and the resistor R4 becomes smaller than the voltage value previously set by the resistors R5 and R6, and switches the high level signal. It functions so as to output to the switch pin of the current buffer circuit with function 10. When an optical signal is input to the O / E converter 11, the current buffer circuit 10 is turned on, the image signal from the amplifier circuit 8 is transmitted to the image display device 3, and when no optical signal is input, the current buffer circuit 10 is turned on. Since the circuit 10 is turned off, the image signal is not transmitted to the image display device 3. Therefore, when there is no optical signal input to the O / E converter 11, noise due to dark current of the light receiving element 6 is reduced by the image display device 3.
Will not be transmitted to

[0012]

As described above, in the optical modem device of the present invention, a state in which no optical signal is input to the O / E converter due to the disconnection of the optical fiber cable or the failure of the E / O converter occurs. In such a case, the image signal is O / E
It is possible to prevent transmission from the conversion unit to the image display device side. As a result, when there is no optical signal input to the O / E converter, noise due to dark current of the light receiving element is reduced by O / E.
A malfunction or failure of the image display device which is not output from the E-converter and is conventionally caused by input of noise is prevented, and practical effects such as improvement of image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical modem device according to the present invention.

FIG. 2 is an explanatory diagram illustrating a main configuration of an optical modem device according to the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional optical modem device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical modem device 2 information processing device 3 image display device 4 optical fiber cable 5 E / O conversion unit 6 light receiving element 7 constant current circuit 8 amplification circuit 9 photodetection circuit 10 current buffer circuit 11 O / E conversion unit 12, 13 metal cable

Claims (1)

(57) [Claims] 1. An E / O converter for inputting an electric signal output from an information processing device and converting it to an optical signal, and an O / O converter for converting the input optical signal to an electric signal and outputting the same to an image display device. In the optical modem device in which the / E converter is connected by an optical fiber cable, the O / E converter 11 has a light receiving element 6, a constant current circuit 7 for driving the light receiving element 6, and an output of the light receiving element 6. Amplifying circuit 8 for amplifying current, and amplifying circuit 8
And a photodetector circuit 9 for detecting the presence or absence of an optical signal input to the O / E converter from the output of the optical detector and outputting a high-level or low-level signal in accordance with the presence or absence of the optical signal. A current buffer circuit 10 with a switch function for turning on and off the output of the electric signal input from the amplifier circuit 8 in response to the input signal. When the O / E converter 11 has no optical signal input, the O / E conversion is performed. An optical modem device wherein an image signal is not output from the unit 11 to the image display device 3.