JPS642269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronization signal transmission system used in an image signal transmission system that encodes an image signal having horizontal synchronization signals whose occurrence time intervals are indefinite.

In recent years, commercially available video equipment such as cassette VTRs (video tape recorders) have become popular. These general video devices do not necessarily have sufficient synchronization frequency stability, and in particular, in VTRs, the synchronization interval inevitably expands or contracts due to uneven rotation during the recording and playback process. For this reason, devices are used to correct such synchronization intervals, but because they are expensive, in general video services such as ITV (industrial television), image signals with insufficient synchronization frequency stability are not used as they are. We are using.

On the other hand, such image signals cannot be encoded using the so-called frame synchronization encoding method, which performs encoding by synchronizing the phase of the encoding clock with the image signal, so it is encoded using a clock system independent of the image signal. This is done using a so-called frame asynchronous encoding method.

Generally, in the above-mentioned frame synchronous and asynchronous encoding systems, in order for the receiving side to accurately decode the code from the transmitting device, the transmitting side inserts word synchronization bits indicating code breaks into the encoded signal at a predetermined period. However, the word synchronization bit is detected on the receiving side to establish word synchronization. However, in order to deal with such word synchronization, the hardware for detecting the word synchronization bit and establishing word synchronization in the receiving device becomes complicated, and there are disadvantages in that it takes time to establish word synchronization.

SUMMARY OF THE INVENTION An object of the present invention is to provide a synchronization signal transmission method for an image transmission system that eliminates the above-mentioned drawbacks and allows word synchronization to be easily established.

Next, the present invention will be explained in detail with reference to the drawings.
FIG. 1 is a block diagram of an encoding device for explaining one embodiment of the present invention, and FIG. 2 is an operational waveform diagram of the circuit shown in FIG. 1. In FIG. 1, the encoding device includes an input terminal 1 that receives a decoded image signal including a horizontal synchronization signal with an indefinite time interval, and a synchronization separation circuit 2 that separates and outputs the horizontal synchronization signal from the decoded image signal. Analog/digital (A/D) converts the input image signal into a PCM (pulse code modulation) signal.
D) Differentially encode the PCM signal with the conversion circuit 3
A DPCM (differential code modulation) encoding circuit 4 and a control circuit that generates a special code (word) for word synchronization and an encoding stop signal on signal lines 51 and 52 in response to a horizontal synchronization signal applied from a signal line 21. 5, a holding circuit 6 that holds the value of the PCM signal input from the signal line 31 immediately before the encoding is stopped;
A conversion circuit 7 that divides the transmission line code (word) into the DPCM encoded output, a switching circuit 8 that switches the data sent to the transmission line, and a conversion circuit 8 that converts the code word input from the signal line 80 into a serial code series. A parallel-to-serial conversion circuit (S/P conversion circuit) 9 for sending signals, and a clock generation circuit 1 for supplying a sampling clock and a transmission line clock to signal lines 11 and 12 from a built-in clock source.
It is composed of 0. Note that it is also possible to provide an unequal length encoding circuit in the S/P conversion circuit and further encode the output of the switching circuit 8. Here, as the DPCM encoding circuit 4, a DPCM encoding circuit having a configuration consisting of a memory 44 and an adder 45 as shown in FIG. 8a is used. In a DPCM encoding circuit with such a configuration,
In order to accurately decode the received signal into the original image signal in the DPCM decoding circuit shown in FIG. 8b,
Contents of memory 44 of DPCM encoding circuit and DPCM
It is necessary to match the contents of the decoding circuit memory 44'. Therefore, in the encoding device shown in FIG.
As will be described later, the contents of the memory 44 and the memory 4
A PCM signal is sent to match the contents of 4'.

Next, the operation of the encoding device shown in FIG. 1 will be explained.

When the image signal is being encoded, the switching circuit 8
The contact 83 is closed, and the image signal applied to the input terminal 1 is converted into a PCM signal by the A/D conversion circuit 3 and then applied to the DPCM encoder 4. The encoded output of the DPCM encoder 4 is sent to the conversion circuit 7
The signal is converted into a transmission line code, provided to the parallel-to-serial conversion circuit 9 via the switching circuit 8, and supplied to the output terminal 91 as serial data. When a horizontal synchronizing signal is input to the input terminal 1, the horizontal synchronizing signal is separated by the synchronization separation circuit 2 and is provided to the control circuit 5. When the control circuit 5 receives the horizontal synchronization signal, it sets a predetermined encoding stop period using the clock on the signal line 91 and sends the encoding stop signal via the signal line 52.
Switches 42 and 43 of DPCM encoding circuit 4
(FIG. 8a), and at the same time, a special code word for word synchronization is output to the signal line 51. At this time
The PCM signal value is given to the holding circuit 6, and after a predetermined time, it is sent to the contact 8 via the signal line 61.
given to 2. When the special code arrives on the signal line 51, the switching circuit 8 immediately selects the contact 81, and the special code word is sent to the output line 80. When the sending of the word synchronization code is completed, contact 82 is selected,
The PCM signal value is output on output line 80.

The operation of the circuit of FIG. 1 will be further explained with reference to FIG. Waveform 101 is an image signal waveform input to terminal 1, and waveforms 511, 611 and 711
are the waveforms of signal lines 51, 61 and 71 in FIG. 1, respectively. A waveform 801 represents the output waveform of the output line 80.

When the horizontal synchronization signal of waveform 101 arrives at the input terminal 1, the encoding of the DPCM encoder 41 is stopped by the control of the signal line 52 at the bottom of the horizontal synchronization signal, and at the same time, the waveform 51 is transmitted via the signal line 51 and contact 81.
A special code S shown in 1 is sent out. Next, waveform 6
The PCM signal value P shown in 11 is transmitted via the signal line 61.
Switch 42 of DPCM encoding circuit 4 (Fig. 8a)
and is sent out via contact 82. When the transmission of these signals is completed, the contact 83 is selected and at the same time the encoder 4 resumes encoding, so the waveform 71
The encoded data shown in 1 is transmitted to the signal line 71 and the contact point 8.
3.

As explained above, normally the contact 83 is selected and encoded image signal data is output, but each time a horizontal synchronization signal arrives, the contact changes from 83 to 8.
1 → 82 → 83 and return signal line 80 has waveform 8 which is a combination of waveforms 511, 611 and 711.
01 is sent out and sent out to the transmission line via the parallel-to-serial conversion circuit 9.

FIG. 3 shows a specific circuit of the control circuit 5, and the fourth
The figure is a waveform diagram. The horizontal synchronizing signal input to the signal line 21 is read into the shift register 50 by the clock 111 of the signal line 11, and the two
In combination with the NAND gate, signal lines 51 and 5
2, a special code generation pulse 511-0 and an encoding stop pulse 521 are generated. The waveforms of signal lines 53, 54 and 55 are shown as 531, 541 and 55 in FIG.
Shown in 1. In the example shown here, we assume that the PCM signal has 8 bits per sampling and the DPCM encoder output has 4 bits per sampling.
In addition to prohibiting the assignment of specific codes (for example, "00000000" for PCM and "0000" for DPCM) as output codes of DPCM, for example, 24-bit codes of 111100...001111 are used as special codes. If the number of bits to be sent per sampling period is 4 bits to match the DPCM, this special code will be transferred to the shift register 5.
A pattern generator 56 controlled by tap outputs from the first stage to the sixth stage of 0 outputs it to the signal line 51-1-4 as 4-bit parallel codes (511-1 to 511-4) during six sampling periods. . If two sampling periods are allocated to transmitting the PCM signal, the encoding stop period will be a total of eight sampling periods.

Next, the configuration of the holding circuit 6 and its waveform diagram are shown in FIGS. 5 and 6. The PCM signal 311 applied to the 8-bit parallel signal line 31 is 8-bit at the leading edge of the code stop control pulse 521 applied to the signal line 52.
bits are stored in parallel registers 60 and signal line 6
A PCM signal 611 held at 1 is output.

FIG. 7 is a specific circuit diagram of the switching circuit 8. Special code (8 bits), PCM signal (8 bits) and
It receives a DPCM code (4 bits) and outputs a 4-bit parallel signal. The 4-bit output lines (80-1 to 80-4) each have one input from the four inputs.
A switch is provided to select the input (1 out of 4). Normally, contacts 83-1 to 83-4 are selected and 4-bit DPCM is supplied from signal line 71.
Output lines 80-1 to 80-4 whose code is the sampling period
However, when the special code 511-0 is input to the signal line 51-0, the contacts 81-1 to 8
1-4 are selected and sequentially "1111", "0000",
Send "0000", "0000", "0000", "1111".
In the next sampling period, the contacts 82-1a to 82-4
a is selected, the upper 4 bits of the PCM signal are sent out, and the contacts 82-1b to 82- are selected during the next sampling period.
4b is selected and the lower 4 bits are sent out.

Figures 8a and 8b are block diagrams showing a DPCM encoder and decoder. The principles of the DPCM encoder and decoder are well known, so a detailed explanation will be omitted here. Among these, switching circuit 4
I would like to add some additional information regarding 2.43. Usually the switching circuit 42
42a is closed, the memory circuit 44 and the addition circuit 45
(each dart number corresponds to the other on the receiving side). However, the contact 42b is closed by the encoding stop signal on the signal line 52, and the PCM signal value held through the signal line 61 is input to the storage circuit 44. be done. A similar operation is performed in the receiving section,
The integrator is reset to the same level as the transmitter.
The switching circuit 43 is also controlled by the signal line 52, and code transmission is stopped during the coding stop period.

Note that on the receiving side, a shift register and a special code generation circuit composed of a gate circuit are provided, and the encoded output sent from the encoding device is input to the shift register, and the input encoded output and the above coded output are input to the shift register. The special code can be easily detected by comparing it with the special code from the special code generating circuit, and word synchronization can thereby be established. Furthermore, by extracting a PCM signal from the encoded output and resetting the contents of the memory 44' of the decoding circuit shown in FIG. The contents of memory can be matched.

In the above embodiment, the DPCM encoding circuit 4
but instead of this DPCM encoding circuit,
It is possible to use a DPCM encoding circuit having a configuration in which a multiplier for multiplying the output of the adder 45 by a coefficient is provided before the memory 44 of the DPCM encoding circuit. In this case, the contents of the encoding circuit memory 44 and the decoding circuit memory 44' as shown in the waveform 611 of FIG.
PCM as described above to match the contents of
There is no need to send out a signal. It is also possible to directly send out the output signal of the A/D conversion circuit 3 after the special code word without using the DPCM encoding circuit 4.

As described above, in the present invention, word synchronization can be easily established by transmitting a special code word when a horizontal synchronization signal is input and detecting this special code word on the receiving side.

[Brief explanation of the drawing]

1 and 2 are block diagrams and operational waveform diagrams for explaining one embodiment of the present invention, and FIGS. 3 and 4 are specific circuits of the control circuit used in the device shown in FIG. 1. 5 and 6 are specific circuit diagrams and operation waveform diagrams of the holding circuit used in the device of FIG. 1, and FIGS. 7 and 8 a and b are FIG. 3 is a specific circuit diagram of a switching circuit and a DPCM encoding/decoding circuit used in the device shown in the figure. In FIG. 1, 2... synchronous separation circuit, 3...
A/D conversion circuit, 4...DPCM encoding circuit, 5
... Control circuit, 6 ... Holding circuit, 7 ... Conversion circuit, 8 ... Switching circuit, 9 ... Parallel-serial conversion circuit.

Claims (1)

[Claims] 1. An image signal containing a horizontal synchronization signal with an indefinite time interval is sampled and encoded in response to a first clock generated from a clock source independent of the horizontal scanning period of this signal, and a plurality of code words are sampled and encoded. In a synchronizing signal transmission method for an image signal transmission system, the encoded data consisting of:
When the horizontal synchronization signal of the image signal appears on the transmitting side, a special code word different from each word forming the encoded data is transmitted as a synchronization signal for the transmission system, and the receiving side detects the special code word. A synchronous signal transmission method for an image signal transmission system, characterized in that synchronization with a transmitting side is established by