JPH0568920B2 - - Google Patents

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Outline of the invention C. Prior art (Figs. 2 to 5) D. Problem to be solved by the invention E. Means for solving the problem (Fig. 1) F. Effect G. Implementation Example (FIG. 1) H Effects of the Invention A Field of Industrial Application The present invention relates to a receiving device that receives a broadcast signal containing a spread signal.

B. Summary of the Invention The present invention relates to a receiving device that receives a broadcast signal containing a spread signal, and is capable of obtaining good and quick synchronization by cutting off the spread signal removal signal when the reception is asynchronous. It is.

C. Conventional technology As a new transmission method for so-called high-definition television
MUSE (Multiple Sub-Nyquist Sampling
Encoding) method has been proposed (Preliminary of the Foundation Commemoration Lecture, "New Transmission Method for High-Definition Television (MUSE)", Yuichi Ninomiya, June 6, 1980,
NHK Research Institute of Technology/Basic Broadcasting Science Research Institute).

That is, in this method, when a luminance signal Y and color difference signals C _N and C _W as shown in FIG. 2 A to C are received on the transmitting side, the color difference signal
The time axis of C _N and C _W is compressed to 1/4, respectively, and inserted into the horizontal blanking period at the leading end of each corresponding luminance signal Y in line order to form a TCI signal as shown in FIG. This TCI signal is as shown in figure E.
Sampling is performed at 64.8 MHz, and one sample is extracted every four samples of this sampling data to form a sub-Nyquist sampling signal that is dot-interleaved with each other and goes around in four fields as shown in FIG. Therefore, the frequency of sub-Nyquist sampling becomes 16.2MHz, which allows the baseband signal bandwidth, which was originally 20MHz, to be compressed to 8.1MHz. This signal is frequency modulated (FM) and transmitted via a broadcasting satellite or the like.

On the receiving side, on the other hand, the received signal is demodulated and the above-mentioned
Extract the 8.1MHz Sapnyquist sampling signal. Sample this signal at 16.2MHz,
This sampling data is written to the memory as shown in E of the above figure, and further, these data and the data of the non-sampling points indicated by blanks are converted and interpolated as shown in G of the same figure, and then written as D in the above figure. Restore the TCI signal as shown. From this signal, a luminance signal Y and color difference signals C _N and C _W as shown in A to C in the above-mentioned figure can be extracted.

MUSE high definition TV signal in this way
Depending on the method, it is possible to transmit data using one channel of satellite broadcasting with a bandwidth of, for example, 27 MHz.

By the way, in the satellite broadcast transmission mentioned above,
In order to prevent interference with existing terrestrial microwave lines, etc., it has been considered to superimpose and transmit so-called spread signals. In that case, the above
As shown in Figure 3, the spread signal in the MUSE system is at a predetermined level during the period of the horizontal synchronization signal HD, rises during the period of the color difference signal C that follows, and then falls during the period of the luminance signal Y, so that it lasts for one horizontal period. The complete waveform was used to transform this spread signal.
It will be added to the MUSE signal, then modulated, and transmitted.

Therefore, when receiving such signals,
It is necessary to perform inverse conversion of the MUSE method after removing the above-mentioned spread signal, and for this reason, a device as shown in FIG. 4 has been proposed.

In the figure, the above-mentioned received and demodulated MUSE
A signal of the system is supplied to the input terminal 1. This signal is supplied to the adder 2, and the diffusion removal signal generation circuit 3
The above-mentioned spread signal from and a cancellation signal of opposite polarity are added to remove the spread signal.

Further, this signal is supplied to a clamp circuit 4 and clamped to a predetermined level, and this clamped signal is supplied to an AD conversion circuit 5. For example, a signal converted into an 8-bit digital signal is taken out to an output terminal 6 and output to a subsequent stage. The signal is supplied to a MUSE type inverse conversion circuit (not shown) such as a memory. The digitally converted signal is also supplied to a synchronization detection circuit 7, and the detected synchronization signal is supplied to a basic clock generation circuit 8 to form a basic clock signal. Furthermore, an internal horizontal synchronizing signal formed from this basic clock is supplied to the spreading cancellation signal generating circuit 3.

Note that the clamp circuit 4 normally uses a pedestal clamp circuit 41 that uses a predetermined level in the horizontal synchronization signal as a reference, but such clamping cannot be performed when the horizontal synchronization signal is not synchronized. , an average value clamp circuit 42 is provided in parallel, and front and rear switches 43 and 44 are switched by a control signal indicating whether synchronization of the horizontal synchronization signal from the generation circuit 8 has been obtained.

By the way, in the MUSE system signal, the synchronization signal is the video signal (luminance signal Y, color difference signal C _N ,
C _W ) is inserted with the same polarity (positive polarity).
For example, when using a synchronization signal with opposite polarity as in the NTSC system, the overall amplitude of the signal expands.
This is especially to prevent the band from widening when transmitting FM signals.

A frame synchronization signal corresponding to a vertical synchronization signal of a normal video signal is configured as follows.
That is, FIG. 5A shows a frame synchronization pattern provided at, for example, the 605th among 1125 horizontal periods of high-definition television.

In the figure, a blank period of arbitrary length is provided consecutively to the horizontal synchronizing signal HD, and after that, 17.5 pairs of pulses that are inverted between the highest and lowest levels of the signal are provided every four clock periods. This is followed by a pulse of the highest or lowest level for 16 clock periods, followed by a pulse that is the inverse of the previous portion of 8 clock periods.
Immediately after the pulse of this 8 clock period, the horizontal synchronizing signal HD of the next horizontal period continues. The frame synchronization signals are provided in the 605th and 606th horizontal periods inverted from each other, and the leading edge of the pulse in 16 clock periods of the frame synchronization signals is used as a reference for phase synchronization.

In order to obtain synchronization from the above signal, first detect the above frame synchronization pattern in the signal,
This detection signal is used to pull in synchronization within a ±1 clock period, and then the horizontal synchronization signal HD is used to apply phase synchronization.

By the way, when the above-mentioned spread signal is superimposed, this superimposed frame synchronization pattern becomes as shown in B of the above-mentioned figure. Therefore, the spread signal can be removed by adding to this signal a removal signal of opposite polarity to the spread signal as shown in C in the above diagram.

However, in this case, normal removal can only be performed after synchronization of the horizontal synchronizing signal is obtained, and before that, the removal signal from the generation circuit 3 is generated asynchronously. For this reason, for example, there is a possibility that a removal signal (shown by a broken line) corresponding to the color difference signal portion is added to the luminance signal portion, and in this case, the level change due to the spread signal will be increased.

Although the level change due to the spread signal is schematically enlarged in the figure, it is actually about several percent of the amplitude of the video signal. If the level change is only a few percent, there is no problem in detecting the frame synchronization pattern after AD converting this signal, but if this level change is doubled, for example, Since the duty of the pulse signal during that time is changed, normal detection cannot be performed. For this reason, there is a possibility that normal synchronization detection cannot be performed and an extremely long time is required until synchronization is obtained.

D Problems to be Solved by the Invention The conventional device was configured as described above. For this reason, when the spread signals are asynchronous, the frame synchronization pattern cannot be detected well, resulting in problems such as a large amount of time being required until synchronization is achieved.

E. Means for Solving the Problems The present invention provides a receiving device that receives a broadcast signal containing a spread signal, including a generating circuit 3 that generates a signal for removing the spread signal, and a generation circuit 3 that generates a signal for removing the spread signal, and a generation circuit 3 for generating a signal for removing the spread signal. A constant voltage circuit 11 that generates a voltage, a switch 12 that switches between a removal signal from the generation circuit and a voltage from the constant voltage circuit, and a signal from this switch as a reception signal of the broadcast signal (input terminal 1) The switch is switched (control signal) according to the state of synchronization with the received signal, and when synchronization with the received signal cannot be obtained, the voltage from the constant voltage circuit is changed. In the receiving device, the removed signal from the generating circuit is added to the received signal, and when synchronization with the received signal is obtained, the removed signal from the generating circuit is added to the received signal.

F Effect According to this device, since spreading cancellation is not performed when synchronization with respect to the received signal cannot be obtained, it is possible to always detect good frame synchronization, and furthermore, this makes it possible to detect synchronization. Since the number of times is increased, the time for convergence of synchronization can be significantly shortened.

G. Embodiment In FIG. 1, a constant voltage circuit 1 that generates a voltage equal to the voltage in a period corresponding to the horizontal synchronization period of the removal signal is provided in parallel with the above-mentioned diffusion removal signal generation circuit 3.
1 is provided, and the voltage from the constant voltage circuit 11 and the removal signal from the generation circuit 3 are switched by a switch 12 and supplied to the adder 2. The switching of this switch 12 is performed by a control signal from the basic clock generating circuit 8, similar to the switching of the clamp circuit 4 described above. The rest is the same as the conventional device.

Therefore, according to this device, until synchronization with the received signal is obtained, a constant voltage corresponding to the synchronization period from the constant voltage circuit 11 is added to the received signal, and the erroneous cancellation signal is Therefore, there is no risk that the level change will be increased. Therefore, the number of times synchronization is detected is increased, and the stability of the PLL etc. of the basic clock generation circuit 8 is increased, so that the synchronization convergence time is shortened.

H. Effects of the Invention According to the present invention, since spreading cancellation is not performed when synchronization with respect to the received signal cannot be obtained, good frame synchronization can always be detected, and furthermore, this makes it possible to detect synchronization. Since the number of detections is increased, the time for synchronization to converge can be significantly shortened.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an example of the present invention, Figures 2 to 5
The figure is a diagram for explaining a conventional device. 1 is an input terminal, 2 is an addition circuit, 3 is a diffusion removal signal generation circuit, 4 is a clamp circuit, 5 is an AD conversion circuit, 6 is an output terminal, 7 is a synchronization detection circuit, 8 is a basic clock generation circuit, 11 is a constant The voltage circuit 12 is a switch.

Claims (1)

[Scope of Claims] 1. A receiving device that receives a broadcast signal containing a spread signal, comprising: a generation circuit that generates a signal for removing the spread signal; and a constant voltage circuit that generates a voltage equal to the synchronization period of the removal signal. and a switch for switching between the removal signal from the generation circuit and the voltage from the constant voltage circuit, and an addition circuit for adding the signal from the switch to the received signal of the broadcast signal, The switch is changed according to the synchronization state, and when synchronization with the received signal cannot be obtained, the voltage from the constant voltage circuit is added to the received signal, and when synchronization with the received signal is obtained, the voltage from the generator circuit is added. A receiving device configured to add a removed signal from the received signal to the received signal.