JPS63224492A - Regenerating circuit for subcarrier signal - Google Patents

Abstract

PURPOSE:To reduce the influence of transmission distortion, etc., and to prevent malfunction by regenerating the reference phase of a subcarrier according to the phase relation of a chrominance subcarrier when the subcarrier has a maximal or minimal value. CONSTITUTION:When digital signal processing is performed at the time of sampling a received signal at 4fsc four times as high as the chrominance subcarrier, a received television signal is converted by an A/D converting circuit 1 into a digital signal of 4fsc. A timing extracting circuit 8, on the other hand, extracts fsc and 4fsc, and horizontal and vertical synchronizing signals HD and VD necessary for signal processing. A line control circuit 4 specifies scanning lines of the HD and VD signal where the subcarrier mu0 is inserted and a mu0 regenerating circuit 5 generates a subcarrier mu0 in said period according to the phase relation between the maximal point of the subcarrier mu0 and fsc. A decoder circuit 3 uses those signals to generate a luminance signal Y and color difference signals I and Q by demodulation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a subcarrier signal reproducing circuit, and in particular, to a subcarrier signal reproduction circuit suitable for reproducing high definition information of a high definition television that is compatible with current televisions. Related to signal regeneration circuits.

[Conventional technology]

There is a method described in Japanese Patent Application No. 58-044238 to create a high-definition television that is compatible with current televisions, transmission paths, and receivers. In this method, a signal component exceeding the video signal band of current televisions, for example, a brightness high frequency component YH (4.2 MHz or more), is converted to a low frequency component Y)l' (4,2 MHz or more) by carrier suppression amplitude modulation using a subcarrier μo.
(frequency components of 2 MHz or less) and is transmitted by superimposing it on the current television signal using a frequency interleaving method.

On the image receiving side, the low frequency component Y H/ is separated and the original luminance high frequency component Y■ is demodulated by synchronous detection. On the image receiving side, subcarriers necessary for coherent detection are reproduced from the transmitted subcarrier μo. However, since μo is inserted into a part of a specific scanning line in each frame, less information is sent.
Japanese Patent Application No. 61-30829 discloses a method for reproducing subcarriers with high accuracy based on this information.

In this method, a reference phase is recovered by comparing the amplitude values of the subcarrier μo every period of the subcarrier fsc.

[Problem that the invention seeks to solve]

In the conventional technology described above, no consideration is given to the influence of transmission distortion, etc., and for example, if a phase error due to transmission distortion occurs between the color subcarrier fsc and the subcarrier μo, an incorrect phase may occur. There were problems with playback, etc. Further, the influence of noise and the like is not taken into account, and there are problems such as malfunctions in poor S/N ratios.

The purpose of the present invention is to reduce the influence of transmission distortion, noise, etc.
Another object of the present invention is to provide a subcarrier signal regeneration circuit that is easy to configure.

[Means for solving problems]

The above purpose is based on the phase relationship of the color subcarrier fsc when the subcarrier μo takes a local maximum value or a polar value.
This is achieved by regenerating the reference phase of

[Operation] The present invention will be explained in detail using an example in which the subcarrier μo is 315 fsc.

FIG. 3(a) shows the color subcarrier fsc, and FIG. 3(b) shows the maximum value detection gate signal generated from the color subcarrier μo.

On the other hand, (c) is the subcarrier μo when there is no phase distortion. Point X1 in the same figure. Xz, Xa.

X s' and Xx' indicate points that take local maximum values. The points that take these maximum values are determined by the maximum value detection gate signal.
, Xl' is selected, and Xt, XI
Phase recovery is performed with time a corresponding to ', a' as a point at the reference phase π/2 of μo.

On the other hand, as shown in (d), in the subcarrier μo that has undergone phase distortion due to the influence of transmission distortion, the local maximum values are X 1 , X 2 , Xs + Xt' + Xx, respectively.
' is the point. Then, the maximum points of Xz and Xz' are selected by the maximum value detection gate signal, and the phase of μo is recovered using these maximum points as the reference phase.

That is, in the present invention, the reference phase is set by selecting the maximum μo value described above.

Subcarrier regeneration that is less susceptible to transmission distortion, etc. is possible.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This embodiment shows a case of digital signal processing in which a received signal is sampled at 4 fsc, which is four times the color subcarrier.

The received television signal is converted to 4fsc by A/D conversion circuit 1.
is converted into a digital signal. On the other hand, in the timing extraction circuit, fsc=4fsc required for signal processing.
, as well as horizontal and vertical synchronization signals HD.

Extract the VD. The HD and VD signals are sent to the line control circuit 4.
In this period, the scanning line in which the subcarrier μo is inserted is specified, and during this period, the μo reproducing circuit 5 detects the reproduced subcarrier μo based on the maximum point of the subcarrier μo according to the method described above and the phase relationship with J sc. Generate μo.

The decoder circuit 3 uses these signals to demodulate the original luminance signal Y into two color differences T and Q. Since this function has no particular relation to the present invention, a description thereof will be omitted.

FIG. 2 shows a specific embodiment of the μo regeneration circuit 5 shown in FIG. The data series of the A/D conversion circuit 1 is converted into three adjacent data by a latch circuit 6 using a clock of 4 fsc.
Latch pixel data A, B, and C. On the other hand, the magnitude comparison circuit 7 compares B and A or C, and outputs 1 if BAA or B>C, and O otherwise. Therefore, when the outputs of the magnitude comparison circuit 7 are all 1, this corresponds to B taking the maximum value.

The determination circuit 8 uses the extreme value detection gate signal generated from fsc, the line information for subcarrier μo insertion, and the large/
The reference phase point of the reproduced subcarrier is determined from the output signal of the J% comparison circuit 7. FIG. 4 shows a time chart for determining the reference phase point when the subcarrier μo has no phase distortion as shown in FIG. 3(c).

As shown in FIG. 4, the reference phase point occurs every 20 clock cycles, but there is a possibility that this reference phase point will be erroneously determined due to the influence of noise and the like. Therefore, the reference phase point delayed by 20 clocks by the 20 clock delay circuit 9 is taken by the AND circuit 10, and the period of the reference phase point is 3.
The phase information generating circuit 1
Set the initial value of 1 to π/2. This processing can significantly reduce malfunctions caused by noise and the like. As shown in FIG. 5, the phase information generating circuit 11 changes the phase to 3π/1 every 4 fsc clocks based on π/2 corresponding to the phase information AO.
An address corresponding to a phase advanced by 0 is generated at 20 clock cycles, and the μo generation circuit 12 generates the subcarrier signal shown in FIG. 5 in accordance with this address. Note that this function can be easily implemented using a ROM or the like.

〔Effect of the invention〕

According to the present invention, a highly accurate subcarrier regeneration circuit that is less susceptible to transmission distortion and less likely to malfunction due to noise etc. can be realized with a simple configuration, and the effects are great.

Note that in the present invention, the subcarrier μo is the color subcarrier f
Although we have explained the case of 315 times sc, in general μ
It is clear that it is also valid even if o is proportional to Q/m fsc (Q, m integer).

Further, although the present invention has been described in the case of digital signal processing, it is clear that the present invention is similarly applicable to analog signal processing.

Furthermore, in the present invention, explanations are given using local maximum values as an example, but it is clear that the same thing holds true even for local minimum values.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a conceptual diagram of the present invention; FIG. 4 is a time chart of the μo regeneration circuit; and FIG. 5 is phase information of the regenerated carrier wave. . 1... A/D conversion circuit, 2... Timing extraction circuit. 3... Decoder circuit, 4... Line control circuit, 5...
... μo regeneration circuit, 6 ... latch circuit, 7 ... magnitude comparison circuit, 8 ... judgment circuit, 9 ... 20 clock delay circuit, 10 ... AND circuit, 11 ... phase information Generation circuit, 12...μo generation circuit,
7-Agent, Patent Attorney, Masaru Koyōh') ＼3. / Figure 2

Claims (1)

[Claims] 1. When performing multiplex transmission by amplitude modulating significant information with a subcarrier μo, the subcarrier μo is set to be in a proportional relationship with the color subcarrier fsc, and the position of the maximum value or minimum value of the subcarrier μo is 1. A reproducing circuit for a subcarrier signal, comprising means for regenerating the phase of a subcarrier μo based on its phase relationship with a color subcarrier fsc.