JP2501563B2 - Optical image transmission method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for multiplexing an auxiliary signal such as a voice signal in an analog baseband optical transmission method for transmitting a video signal.

(Prior Art) As a system using a conventional optical video transmission method, there is a system shown in FIG.

In the figure, VIN is an input video signal, AIN is an input audio signal, MOD is an FM modulation circuit, MIX is a mixing circuit, E / O is an electro-optical conversion circuit, OF is an optical fiber, O / E is an opto-electric conversion circuit, LPF is a low pass filter circuit, VOUT is an output video signal, HPF is a high pass filter circuit, DEM is an FM demodulation circuit, and AOUT is an output audio signal.

The input video signal VIN is composed of a composite color video signal, and the mixing circuit MIX superimposes the signal modulated by the FM modulation circuit MOD of the input audio signal AIN on the input video signal VIN as shown by the chain line to form a multiplexed video signal. To output the modulation current I. The electro-optical conversion circuit E / O converts the modulation current I into a transmission optical signal P. FIG. 3 shows a characteristic example of the optical output P with respect to the modulation current I when a light emitting diode is used as the electro-optical conversion element of the electro-optical conversion circuit E / O of FIG. C
Is the characteristic curve of the modulation current vs. optical output. In the same figure, the modulation current I and the optical output P are also shown with respect to the time t, but the respective operating points are set in the portion where the linearity of the modulation current-optical output characteristic is good.

In these methods, the differential gain (DG) and differential phase (DP) of the video transmission characteristics are improved, as described in "Video analog transmission technology" in 0 PLUS E, January 1985. There is a need.

(Problems to be Solved by the Invention) However, in the above method, the video transmission characteristic (D
In order to improve (G, DP), it is necessary to set the portion from the peak of the video signal to the tip of the synchronization signal in the linear portion of the modulation current vs. optical output characteristics, so the video signal level cannot be increased. That is, try to improve the video transmission characteristics
There was a problem that the S / N ratio became worse.

Further, since the auxiliary signal such as the audio signal is mixed in the video signal period, there is a problem that the video signal and the auxiliary signal interfere with each other.

It is an object of the present invention to provide an optical video transmission method that improves the S / N ratio, improves video transmission characteristics, and eliminates the problem of interference between a video signal and an auxiliary signal.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an analog baseband optical transmission using a composite color video signal and an auxiliary signal for transmitting in parallel with the composite color video signal. In the method, a composite color video signal including a color video signal, a sync signal and a color burst signal is input, and the sync signal is a sync burst signal composed of a high frequency signal outside the band of the color video signal modulated by the auxiliary signal. The synchronous burst signal and the color burst signal are converted and superimposed on a DC level approximately in the middle of the color video signal to synthesize a transmission electric signal together with the color video signal, and the transmission electric signal is converted into a transmission optical signal. Convert and transmit light,
The composite color video signal and the auxiliary signal are reproduced on the receiving side.

(Function) The sync signal is a signal converted into a high frequency signal (sync burst signal) modulated by the auxiliary signal and superimposed on the color burst signal at a DC level approximately in the middle of the color video signal. A waveform having a predetermined amplitude is formed around the middle of. Therefore, this transmission signal is used when the conventional sync signal and the color burst signal have an amplitude in a range that exceeds the amplitude of the color video signal, centering on a level deviating from the intermediate level of the color video signal. On the other hand, it acts in the direction of reducing the amplitude in the above-mentioned range, and the entire amplitude range is reduced.
In transmitting each of these signals, when setting the level of each signal to the linear portion of the modulation current vs. optical output characteristics and converting, the modulation current is increased by the amount corresponding to the decrease in the total amplitude range. The output can be set to high.

The video signal and the auxiliary signal are optically transmitted as independent signals.

(Embodiment) FIG. 1 is a block configuration diagram showing an embodiment of a system using the optical video transmission method of the present invention.
This is based on an analog baseband optical transmission method using a color video signal.

In the figure, SV1 is an input video signal, and as shown in FIG. 4A, a synchronizing signal S2 having a predetermined level in the negative direction from the reference level 0 and a predetermined amplitude centered on the reference level 0. Color burst signal S3 and reference level 0
It is mainly composed of a composite color video signal including a color video signal S4 in a predetermined level range extending in the plus direction. SA
Reference numeral 1 denotes an input auxiliary signal, which is a digitized input voice signal in this embodiment.

PRCt is a signal processing unit on the transmitting side, which FM-modulates the input audio signal SA1 and, in response to the synchronizing signal S2 of the input video signal SV1, outputs the synchronizing burst signal S6 as shown in FIG. 4B.
Then, the sync burst signal S6 and the color burst signal
S3 and S3 are superimposed on the DC level N which is the center level of the color video signal S4, and a signal S7 which is a combination of these signals S6, S3 and S4 is output, and as shown in FIG. The first processing circuit PRCt1 on the transmission side, the second processing circuit PRCt2 on the transmission side, and the third processing circuit PRCt3 on the transmission side.

The processing circuit PRCt1 separates the input video signal SV1 into a sync signal S2, a color burst signal S3, and a color video signal S4.

The processing circuit PRCt2 converts the synchronization signal S2 into the synchronization burst signal S6.
And a pulse signal S5 having a level equal to the DC level N for converting the sync burst signal S6 and the color burst signal S3 in level is generated over a period including the generation period of each of these signals S6, S3. Yes, as shown in FIG. 6, it comprises a polarity inversion circuit INV1, a mono-multi MM1, a buffer memory MEMt, an FM modulation circuit MOD, and an OR gate OR1.

The input video signal SV1 includes an equalizing pulse and a vertical synchronizing pulse in a pause period of generation of a composite color video signal such as the color video signal S4, that is, a vertical blanking period, as shown in FIG. 9 described later. And processing circuit
The sync signal S2 output from the PRCt1 is composed of a horizontal sync signal S21 during the generation period of the composite color signal, a vertical sync pulse S22 having a half cycle of the horizontal sync signal S21 during the pause period of the composite color signal, and the like.

The polarity inverting circuit INV1 inverts the level of the synchronization signal S2 and outputs an inversion signal ▲ ▼. The mono-multi MM1 uses the sync signal S2 shown in FIG.
(S21 in FIG. 9) occurrence period τ2 and color burst signal S
The signal S10 of the period τp (see (B) of FIG. 4 and FIG. 9) including the generation period τ3 of 3 is output.

The OR gate OR1 serves as a signal for level conversion
The logical sum signal S5 of ▼ and S10 is output. The level of this signal S5 is made to coincide with the level of the DC level signal N shown in FIG. It should be noted that the signal S5 becomes the signal ▲ ▼ because the period of the signal ▲ ▼ (see FIG. 9) exceeds the period τp during the generation period of the vertical synchronizing pulse.

The buffer memory MEMt temporarily stores the input audio signal for one horizontal scanning period and sends out the stored signal within the period of the synchronizing signal S2. The FM modulation circuit MOD receives the output of the buffer memory MEMt and the synchronization signal ▲ ▼ as input, and generates a synchronization burst signal S6 FM-modulated by the input audio signal SA1.

The processing circuit PRCt3 is a color bust signal S3 shown in FIG.
, The color video signal S4, the level conversion signal S5, and the synchronization burst signal S6 are combined to output a transmission electric signal S7. FIG. 4B shows the combined transmission electric signal S7 of the composite color video signal.

E / O is an electro-optical conversion circuit that converts the transmission electric signal S7 into a transmission optical signal for optical transmission. OF is an optical fiber,
The optical signal for transmission is transmitted.

FIG. 7 is a characteristic diagram of the optical output P with respect to the modulation current I of the electro-optical conversion circuit E / O, and is shown by using the same modulation current-optical output characteristic curve C as that of the conventional FIG. In the figure, the modulation current I composed of the electric signal S7 and the modulation current I shown in FIG. 3 are made equal in amplitude range to correspond to the straight line portions of the characteristic curve C. The amount of change in each part of the output P is greater in FIG. 7 than in FIG. 3, and this improves the S / N ratio.

O / E is an opto-electric conversion circuit that converts the transmission optical signal transmitted by the optical fiber OF into an electric signal, and outputs an electric signal S7 having the same waveform as the transmission electric signal S7.

PRCr is a signal processing unit on the receiving side, which converts the electric signal S7 into an output video signal SV10 and an output audio signal SA10 having the same waveforms as the input video signal SV1 and the input audio signal SA1, respectively, as shown in FIG. , A receiving side first processing circuit PRCr1 and a receiving side second processing circuit PRCr2.

The processing circuit PRCr1 receives the electrical signal S7 and receives the synchronization signal S2.
And a video signal S9 with color burst. As shown in FIG. 8, the high-pass filter circuit HPF extracts the synchronous burst signal S6 from the signal S7, and the pulse generator circuit PRG outputs the same signal S6. The synchronizing signal S2 for the period is output. Then, the low pass filter circuit LPF outputs a signal S8 shown in FIG. 9 which is composed of the color burst signal S3 and the color video signal S4 from the signal S7. Then, the polarity inverting circuit INV2 receives the synchronization signal S2 and outputs a signal ▲
▼ is output, the mono-multi MM2 outputs the signal S10 of the period τp at the leading edge of the signal ▲ ▼, and the OR gate OR2 outputs the level conversion signal S by the logical sum of the signal ▲ ▼ and the signal S10.
5, and the polarity reversing circuit INV3 outputs a signal ▲ ▼ for returning only the superimposed DC level N. The adder circuit MIX adds the signals ▲ ▼ and S8 and outputs the video signal S9 with color burst shown in FIG.

The demodulation circuit DEM demodulates the audio signal compressed in the synchronous burst signal S6. The buffer memory MEMr temporarily stores the demodulated audio signal, reads it in one horizontal scanning period, and reproduces the same output audio signal SA10 as the input audio signal SA1.

The processing circuit PRCr2 adds the synchronization signal S2 and the color burst added video signal S9 to reproduce the same output video signal SV10 as the input video signal SV1.

(Effects of the Invention) As described above, according to the present invention, since the synchronizing signal of the composite color video signal is moved inward in the amplitude range of the color video signal, each level of the composite color video signal is changed. It is possible to transmit without increasing the linearity even if is increased. Therefore S / N and video transmission characteristics (DG, DP)
Can be expected to improve.

Further, since the information of the auxiliary signal is multiplexed with the synchronization burst signal, interference between the auxiliary signal and the video signal does not occur.

Further, the high frequency burst signal for transmitting the synchronizing signal can be used as a pilot signal for automatic gain control in the optical transmission system by controlling the peak value to be constant.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a system using the optical image transmission method of the present invention, and FIG. 2 is a block diagram showing an example of a system using the conventional optical image transmission method.
FIG. 3 is a characteristic diagram of modulation current vs. optical output in the conventional method shown in FIG. 2, FIG. 4 is an explanatory diagram of conversion of a composite color video signal in the method of the present invention shown in FIG. 1, and FIG. First
FIG. 6 is a detailed view, FIG. 6 is a detailed view of an essential part of FIG. 5, FIG. 7 is a modulation current vs. optical output characteristic diagram in the method of the present invention shown in FIG. 1, and FIG. 8 is an essential part of FIG. Detailed drawings and FIG. 9 are waveform charts of respective portions in FIGS. 1, 5, 6, and 8. SV1… Input video signal SA1… Input audio signal (auxiliary signal) S2… Sync signal S3… Color burst signal S4… Color video signal S6… Sync burst signal S7… Electrical signal for transmission E / O… Electro-optical conversion circuit

Claims (1)

(57) [Claims] 1. An analog baseband optical transmission system using a composite color video signal and an auxiliary signal for transmitting the composite color video signal in parallel, the composite color including a color video signal, a synchronizing signal and a color burst signal. The video signal is input and the sync signal is converted into a sync burst signal composed of a high frequency signal outside the band of the color video signal modulated by the auxiliary signal, and the sync burst signal and the color burst signal are substantially equal to those of the color video signal. An optical video transmission method comprising: superimposing on an intermediate DC level, synthesizing an electrical signal for transmission together with the color video signal, converting the electrical signal for transmission to an optical signal for transmission, and optically transmitting.