JPH0440194A - Digital decoder system for composite video signal - Google Patents

Abstract

PURPOSE:To unnecessitate the conversion of sampling conversion and to prevent the deterioration of picture quality by holding the interchangeability of a horizontal effective picture element number while turning the frequency to 910 times that of the horizontal synchronizing frequency fH at the time of an NTSC and turning to 916 times that of the horizontal effective picture element number at the time of a PAL as a sampling clock. CONSTITUTION:A horizontal synchronization signal made by frequency-dividing the output of a voltage control oscillation circuit 5 by frequency dividers 6 and 7 and a signal with the identical frequency are inputted to a phase comparator 4. The sampling clock of 910fH or 916H can be obtained by the 1/2 frequency divider 6 when turning the oscillation frequency of the voltage control oscillation circuit 5 to 1820fH when the input is NTSC, and to 1832fH when the PAL. Thus, the conversion of the sampling frequency conventionally necessary is unnecessitated since the sampling frequency is common in both systems and turned to be the integral multiple of the horizontal synchronization frequency. Therefore, the deterioration of picture quality accompanied by the conversion of the sampling frequency can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a digital decoder system for performing luminance signal and color signal separation and color demodulation of a composite video signal in digital TV (television) equipment.

(Prior art) As is well known, NTS is the world-famous color TV system.
There are C system and PAL system. In either system, the device takes means to separate the composite video signal into a luminance signal (Y) and a color signal (C).

There are two ways to do this: an analog method, and an A/D method.
There is a method in which conversion is performed using a digital filter after conversion, but the latter method is becoming mainstream in digital TV equipment.

A typical method for Y/C separation using a digital filter is the literature, ``Digital Signal Processing of Images'' by Takahiko Fukinuki.
Published on May 25, 1981, Nikkan Kogyo Shimbun series, P10
6 to 112, etc., and the outline is as follows.

The sampling frequency is set to four times the color subcarrier frequency fac, and the composite video signal is A/D converted, bandpass filtered by a digital filter, and Y/C Perform separation.

The separated color signals are demodulated into color difference signals R-Y and B-Y signals by multiplication with color subcarriers. If the sampling frequency is set to 4flc as described above, a relatively simple circuit can be realized without requiring a multiplier in the structure of the pantone filter used for Y/C separation or the color demodulation circuit.

Next, as mentioned earlier, TV systems include NTSC and P
There is an AL system, and the Y/C separation system in a TV system converter that converts between these systems will be described.

Figure 2 shows the configuration of the decoder section as an example. When a composite video signal is input, it first performs A/D conversion (3
1), then Y/C min ml! (34) Do. The separated C (color signal) is color demodulated (35) to become R-Y and B-Y signals, which together with the Y signal are once D/A converted (3B) and then A/D converted (37). As mentioned earlier, if the sampling frequency is set to 4f, (32) the circuit configuration becomes simpler, but the sampling frequency differs greatly between the NTSC system and the PAL system. Also, when converting TV formats,
The number of scanning lines and the number of fields are converted for the digitized luminance signal and R-Y%B-Y signal, but in order to maintain compatibility with the signal in the line direction, NT
In order to obtain the same number of effective pixels in the SC and PAL systems, and because it requires a sampling clock that is phase-synchronized with the horizontal synchronization signal, the sampling frequency is 13.58. (33)
Power S is generally chosen. Therefore, when applying Y/C separation to such a device, the separated luminance signal Y, R-Y, B-Y signals are converted once (36) to A/A conversion, and then converted back to analog signals (13). .5H2 A/D conversion (
37), or the sampling frequency must be converted by performing D-D conversion on the digital signal as it is.

(Problems to be Solved by the Invention) None of the methods described above can prevent image quality deterioration or horizontal resolution deterioration due to an increase in quantization error due to sampling frequency conversion.

On the other hand, in output signals of home VTRs, etc., the phase relationship between the color subcarrier and the horizontal synchronization signal may not satisfy the standard specifications, so sampling with phase synchronization with the color subcarrier is required for such signals. If a clock is used, there is a problem that the Y/C female branch circuit will not provide sufficient characteristics and the image quality will deteriorate.

The present invention provides a method for eliminating image quality deterioration caused by sampling clock conversion in TV type equipment that shares such different TV systems. Furthermore, the present invention also provides a method for obtaining good Y/C separation characteristics even for non-standard signals such as home-use YTR.

(Means for Solving the Invention) In order to solve the above problems, the present invention provides a digital TV device that uses both the NTSC system and the PAL system.
As a sampling clock, in the case of NTSC, the frequency is 910XI' which is phase-locked to the horizontal synchronization frequency fH, and in the case of PAL, the same frequency is 916Xf'.
, (the value is different from f□ in the case of the NTSC system), thereby maintaining compatibility in the number of horizontal effective pixels and eliminating the need for conversion of the sampling frequency.

In addition, the color subcarrier required for demodulating the color signal is reproduced in an analog manner and then digitized at the sampling frequency, so that color demodulation can be performed regardless of the phase relationship between the sampling clock and the color subcarrier. I made it happen.

(Operation) By taking the above measures, it becomes unnecessary to convert the sampling frequency, which was necessary in the past, and it is possible to eliminate image quality deterioration caused by the conversion.

Furthermore, since the sampling clock and the color subcarrier are processed independently, stable operation can be achieved even with non-standard signals without considering the phase relationship between the horizontal synchronization signal and the color subcarrier.

(Embodiment) FIG. 1 is a block diagram of a decoder section of a TV system conversion apparatus showing an embodiment of the present invention. In the same figure, the input NT
The composite video signal of the SC system or the PAL system is band-limited by a low-pass filter 1, and then digitized by an A/D converter 2. The sampling clock input to this A/D converter 2 is phase-synchronized with the horizontal synchronization signal of the composite video signal, and for NTSC, it is 910f* (
As mentioned above, f□ is the frequency of the horizontal synchronizing signal), PAL
916fu (This fu is the frequency of the PAL horizontal synchronization signal, and the value is different from the above-mentioned NTSC f)
shall be. (This becomes 14.3Ml1.) The method for reproducing this sampling clock will be described below.

A horizontal synchronizing signal is extracted from the input composite video signal by a horizontal synchronizing signal separation circuit 3 and inputted to a phase comparator 4 . On the other hand, this phase comparator 4 is input with a signal having the same frequency as the horizontal synchronizing signal produced by dividing the frequency by the frequency divider 6.7 which is the output of the voltage controlled oscillation circuit 5 which is voltage controlled by the output of the phase comparator 4. .

The oscillation frequency of the voltage controlled oscillation circuit 5 is 1820f' when the input is NTSC, 1832f when the input is pAL, then the oscillation frequency of the voltage controlled oscillation circuit 5 is 910fh or 91
A 6fH sampling clock is obtained. The frequency divider circuit 7 is 1/910 when the input is NTSC, and 1/91 when the input is PAL.
It becomes 6.

Returning to the previous step, the composite video signal digitized by the A/D converter 2 is separated into color signals by the bandpass filter 15. In addition, the subtraction circuit 16 outputs a composite video signal (A/D
The luminance signal is separated by subtracting the output of the converter 2) from the color signal. Note that a two-dimensional or three-dimensional comb filter may be used as the band pass filter 15.

Next, a method for reproducing color subcarriers necessary for demodulating R-Y and B-Y signals from color signals will be described.

A bandpass filter 8 extracts a color signal from the input composite video signal, and a color subcarrier reproducing circuit 9 reproduces continuous color subcarriers. The output of the reproducing circuit 9 is input to a phase comparator 10. The output controls a voltage controlled oscillation circuit 11, and the output of the voltage controlled oscillation circuit LL is frequency-divided by a frequency dividing circuit 12 and input to a band pass filter 13 and also to a phase comparator IO. The frequency of that signal is the same frequency as the color subcarrier. The oscillation frequency of the voltage controlled oscillation circuit 11 was set to eight times the frequency of the color subcarrier, and the frequency dividing circuit 12 was set to be a frequency dividing circuit of l/8. The output of the frequency dividing circuit 12 is a rectangular wave signal, which is converted into a sine wave signal by a bandpass filter 13. The signal, ie, the color subcarrier signal, is input to an A/D converter 14 and digitized. It is assumed that the sampling clock of this A/D converter 14 is the same as the clock of the A/D converter 2 described above. That is, the output of the l/2 frequency divider 6 is used. A
The color subcarrier digitized by the /D converter 14 is converted to R-Y, B- by the demodulation coefficient generation circuit 17°18.
These are converted into coefficients necessary for demodulating each into a Y signal, and multiplied by a color signal by a multiplication circuit 19.2'0. The outputs are then demodulated through low-pass filters 21 and 22, respectively, to obtain R-Y and BY signals.

(Effects of the Invention) As explained above, according to the present invention, the NTSC system and P
In digital TV equipment that shares the AL system, the sampling frequency is set to 91 Of, 916 f,
Since it is common to both methods and is an integer multiple of the horizontal synchronization frequency, there is no need to convert the sampling frequency that was previously necessary.
Image quality deterioration due to sampling frequency conversion can be eliminated. In addition, since the sampling clock and color subcarrier are processed independently of each other, there is no need to consider the phase relationship between the horizontal synchronization signal and color subcarrier, and the system is stable even for signals whose phase relationship does not meet the standards. can perform various movements.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figure 2 is a conventional TV.
FIG. 2 is a configuration diagram of a decoder section of the system conversion device. 2---------A/D converter, 3-------1 horizontal synchronization signal separation circuit, 4.10-
-----One phase comparator, 5.1l---One voltage controlled oscillation circuit, 6------
---1/2 frequency divider, 7.12---1 frequency divider circuit.

Claims (1)

[Scope of Claims] A digital decoder device that performs A/D conversion of a composite video signal, digitally separates it into a luminance signal and a color signal, and performs color demodulation, wherein the sampling frequency of the A/D conversion is set to the NTSC system. 910 times the frequency of the horizontal synchronization signal of the composite video signal, PA
For the L method, it is multiplied by 916 times, and for the color subcarrier, the color signal is extracted from the composite video signal, the color subcarrier is reproduced in an analog manner, and then A/D conversion is performed using the sampling frequency to reproduce the same sample. 1. A digital decoder system for a composite video signal, characterized in that the composite video signal and color subcarrier signal digitized at a frequency are used to separate a luminance signal and a chrominance signal and demodulate a chrominance signal.