JPS58129846A - Television optical repeater - Google Patents

Abstract

PURPOSE:To eleminate the need for a video converting circuit and a high freqency band converting circuit, by imposing intensity modulation directly on a light emitting diode by an input television signal and sending out the resulting signal, converting the received light into an electric signal on a photodetection side, and thus regenerating a television signal. CONSTITUTION:An input signal from an antenna 23 is passed through an input terminal 22 and an input attenuator 41 and demultiplexed into two by a demultiplexer 42; a trunk line output is supplied to a band-pass filter 43 and the other is sent to a monitor terminal 44. The output of the filter 43 is demultiplexed by a demultiplexer 47 to an LED driving circuit 50 and to the AGC amplifying circuit consisting of an AGC amplifier 49 after passing through a diode 45 and an amplifier 46. The signal of an LED25 driven by the circuit 50 is received by a photodiode 33, whose output is passed through a receiving amplifier 62, demultiplexer 63, band-pass filter 64, amplifier 65, diode 66, and amplifier 67 and demultiplexed into two, i.e. to the AGC circuit consist of an AGC amplifier 70 and to an output terminal 35 via a filter 71 and an atenuator 72 by a demultiplexer 68.

Description

[Detailed description of the invention] The present invention relates to a television optical repeater.

Recently, optical repeaters that do not require line installation are increasingly being used when relaying television waves for CATV and the like. A conventional television optical repeater is constructed as shown in FIG. That is, a high frequency band television signal broadcast from a television broadcasting station is received by an antenna 2 in a light transmitter 1 and sent to a video conversion circuit 1. This video conversion circuit 3 selects and detects a channel desired to be relayed from among the broadcast waves, and converts the signal into a male/video signal C2. This video signal is transmitted to the FM modulation circuit 4
The signal is modulated and sent to the light emitting diode drive circuit 5. This light emitting diode drive circuit 5 superimposes the input video signal and DC current to drive the light emitting diode Pg.
Generates modulated light. The modulated light output from this light emitting diode is converted into parallel light beams by an optical system r and radiated into space. On the other hand, the light receiver 11 is placed at a remote point from the light transmitter 1, and transmits the transmitted light from the light transmitter 1 to the optical system 1.
2, the light is optically detected by a PIN photodiode 1'Jj, and converted into an electrical signal. This electrical signal is amplified by an amplifier 14 and then demodulated into a video signal by a demodulation circuit 11. This video signal is further frequency-converted into a high-frequency band signal by ζ=high-frequency band conversion circuit 1σ, and is sent to a telef receiver or a CATV circuit.

As mentioned above, in conventional television optical repeaters,
Since the high frequency band television signal is converted into a video signal and then modulated, the video conversion circuit 1
The optical receiver 11 requires a demodulation circuit 15 and a high frequency band conversion circuit 1#, which causes problems such as a complicated circuit configuration, significant image quality deterioration, and possibly increased cost. Ta.

The present invention has been made in view of the above points, and an object of the present invention is to provide an optical repeater for a television set that can obtain good image quality with a simple circuit configuration, and is highly stable and reliable.

An embodiment of the present invention will be described below with reference to the drawings. @2
In the figure, 21 is a light transmitter, and a broadcast wave band high frequency television signal received by an antenna 23 is input to an input terminal 22 of the light transmitter. In addition, high frequency television signals for independent broadcasting can also be input to this input terminal 22.

The television signal input to the input terminal 22 is
The signal is sent to a light emitting diode drive circuit 24 whose details will be described later. The light emitting diode drive circuit 24 modulates the light intensity of the light emitting diode 25 using the input high frequency television signal, converts it into visible light or near infrared light, and outputs the signal. As this light emitting diode 25, for example, a near infrared light emitting diode (I RED ) having broadband frequency characteristics is used. The signal optically modulated by the light emitting diode j5 is converted into parallel light beams by the optical system 2c and radiated into space. Accordingly, a light receiver 3 is disposed at a remote point, for example, several hundred meters away from the light transmitter 21. This light receiver 31 collects the transmitted light sent from the light transmitter 21 with an optical system 32, and connects it to a high-speed PIN.
The photodiode 13 optically detects the signal and converts it into an electrical signal. This electrical signal is sent to the receiving amplifier 34 (details of which will be described later), is reproduced as a high-frequency television signal at a predetermined level, and is output to the outside from the output terminal 35. A television receiver or a CATV circuit is connected to the output terminal 35.

Next, the light emitting diode drive circuit 24 and the reception amplifier 3
The details of 4 will be explained with reference to Fig. 3 and Fig. 4. Third
The figure shows details of the light emitting diode drive circuit 24.
First, the broadcast wave band high frequency television signal input to the input terminal 22 is as follows.

A predetermined level, for example, 95±5 dBμ, is set by the input attenuator 41.
It is adjusted so that Then, the input signal adjusted by the input attenuator 41 is branched into two via the 1-brancher 42,
The main output is sent to the band F wave filter 43 for the input channel, and the branched output is taken out at a level lower by 10 dB, for example, and sent to the input monitor terminal 44. The band MP wave generator 43 removes unnecessary signals other than the input channel, and prevents generation of interference waves such as spurious waves due to nonlinearity of the light emitting diode 25. Here, if necessary, a voice canceller may be inserted to lower the voice carrier wave level. Then, the television signal of a predetermined channel taken out via the band r wave filter 43 is amplified by an amplifier 46 via a PIN diode 45. A part of the output of this amplifier 4# is branched by a branching device 41.

After being detected by the diode 48, it is inputted to the PIN diode 45 as a gain adjustment signal via the %AGO amplifier 49. That is, the diode 48 detects the peak value of the video synchronization signal.

By amplifying the signal with an AGO amplifier 49 and applying it to the PIN diode 45, attenuation is applied when the input is high, and attenuation is reduced when the input is low, so that the gain can be automatically adjusted. The output of the amplifier 46 is maintained at a constant high output level by the AGO circuit, and the output is
The signal is sent to the ED drive circuit 50. Also, this LEDy
The LED drive circuit 50 is supplied with a high frequency current from the amplifier 46 using the current value from the constant current circuit 51 as a reference. The light emitting diode 25 is driven by superimposing the television signal.As a result, the light emitting diode 2
σ converts the high frequency TV V signal into light intensity and outputs it.

FIG. 4 shows the details of the receiving amplifier 34. A signal converted from light to electricity by the photodiode 33 is input to the input terminal 61, and is amplified to a high impedance by the receiving amplifier 34.

The signal amplified by the receiving anzoro 2 is branched into two by a single splitter 63, the main line output is input to a band F wave generator 64, and the branch output is input to a received light level monitor terminal 66. The signal input to the band-wave converter 64 has unnecessary frequency components removed and is amplified by an amplifier 65.
The signal is sent to the amplifier 61 via the N diode 66.

A part of the output of this amplifier 67 is branched by a brancher 68, and a diode II! After being detected by I, it is input as a gain adjustment signal to PIN diode C# via huC amplifier 70. An f# by the above A00 circuit
1 is kept constant and sent to the band p-wave converter 11 via a splitter 68.

Unnecessary frequency components are removed again. Then, the output of the bandpass filter 71 is adjusted to the required output signal level by an output attenuator 72 having a variable range of, for example, O to 10 dB.
The main line output is branched into two via the splitter 73 and sent to the output terminal 35 as the light receiver 31, and the five-branch output is, for example, 20.
The signal is extracted at a dB lower level and sent to the output monitor terminal 74. At the monitor terminal CD, 74 and the monitor terminal 44 of the light transmitter 21, C2 monitoring is easily possible with a commercially available television controller.

Therefore, when performing optical relay using the above-mentioned optical repeater, 1, for example, the first dejannel and '@3? In Jiboku, where Yannel is broadcast, the second channel (96-102
When broadcasting is carried out on adjacent channels, as in the case of optical relay using MH1, each band-width transmitter is used with a steep band characteristic so as not to interfere with each other. Then, the output attenuator 12 is adjusted so that the output of the receiving amplifier 31 is the same as the signal level of the adjacent channel. In general, optical repeaters have a large amount of attenuation due to rain and fog, so the signal level may change greatly.
By configuring the output so that it remains at a constant level even when the input fluctuates by dB or more, interference from adjacent channels can be prevented. Also, the second-order distortion between the video carrier wave and the audio carrier wave is 4.5MHz for each carrier wave! Since these interference waves are generated at distant locations, these interference waves are transmitted to the band wave transmitters 43, 64, . It can be removed by '11. However, since color cross modulation occurs in the own channel, it is necessary to use the operating range of the light emitting diode 25 with good linearity to eliminate it, and for this purpose, the level of the carrier wave is adjusted by the input attenuator 41. Furthermore, in order to prevent the above-mentioned cross-modulation, it is necessary to lower the level of the audio carrier wave to 1/10 to 1/1000 compared to the level of the audio carrier wave. The level of this audio carrier wave must be lowered to such an extent that disturbances such as path sounds do not occur. In the case of independent broadcasting, it would be sufficient to create a level difference when combining video* and audio carrier waves.

In the case of general broadcast waves, the band in the transmitter 21 - the wave transmitter 4
By adding a Knopp filter for audio attenuation to 3, it is possible to easily create a level difference between the two carrier waves.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment shows an example in which multi-stage optical repeating is performed on an 0ATV line. The high frequency television signal from the line is branched by a splitter 81111, one of which is sent to CATV 8211 and the other to the light emitting diode drive circuit shown in FIG. It is input to d&. Then, the light emitting diode drive circuit 24a drives the light emitting diode 25a placed at the focal position of the reflection @83 to emit parallel light into space. On the other hand, on the light receiving side, the transmitted light is received by the Fresnel lens 84, and the photodiode 33 &
The received light is collected and processed by the reception amplifier 3411 shown in FIG. The high frequency television signal regenerated by this reception amplifier 34 is branched by a 5-brancher 81b, one of which is 0AT.
VJiJ b, the other is the light emitting diode drive circuit 24b
is input. The light emitting diode zsb is driven by the light emitting diode drive circuit 24b6. Then, the modulated light output from the light emitting dion 25b is transmitted to the optical system 2.
The light is inputted to the optical fiber #85 via the optical fiber 6, transmitted to a remote location several kilometers away, and inputted to the photodiode 33b on the light receiving side. The received light is converted into an electrical signal by the photodiode 33b, and processed by the receiving amplifier 34b.
It is reproduced as a high frequency television signal. This high frequency television signal is then sent out to the next line. In this way, multi-stage optical repeating is performed, and all frequencies except intensity modulation of the light are unified at the frequency of the input channel, for example, the frequency of the second channel, and extremely high stability and reliability can be obtained.

As described above, according to the present invention, the intensity of the light emitting diode is directly modulated by the input broadcast wave band high frequency television signal, the modulated light is sent to the light receiving side, and the received light is converted into a TP signal on the light receiving side. Since the system reproduces high-frequency television signals by using
It is possible to provide a television optical repeater that eliminates the need for a high frequency band conversion circuit, simplifies the circuit configuration, provides good image quality, and provides high stability and reliability.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional optical repeater. '＠Figure 2 is a diagram showing a schematic configuration of the present invention, fJII3 is a circuit configuration diagram showing details of the light emitting diode drive circuit in Figure 2: ;, and Figure 4 is a circuit showing details of the receiving amplifier in Figure 2. The configuration diagram, Figure W&5, is a diagram showing an example of a configuration when multi-stage optical relay is performed. 21... Light transmitter, 24... Light emitting diode drive circuit, 25... Light emitting diode %26.32... Optical system, II-... Light receiver, 33... Photodiode, 3
4...Reception amplifier, 41°12...Attenuator, 42$
4269, Lll, 71... Turnout, 4B, 64°1
1...Band V wave device.

Claims (1)

[Claims] A light transmitter that amplifies a broadcast wave band high-frequency television signal with an amplifier to directly intensity-modulate a light emitting diode, and sends out the modulated light through an optical system; A television optical repeater comprising: a light receiver that receives light through a system, optically detects it with a photodiode, converts it into a high frequency signal, amplifies it with an amplifier and regenerates it into a high frequency television signal of a predetermined level. .