JPH04243395A - Video signal processing circuit for digital television receiver - Google Patents

Abstract

PURPOSE:To reduce the effect of noise by allowing a standard/non-standard detection circuit to extract a synchronizing signal and a color burst signal from a luminance signal and a chrominance signal from a comb-line filter so as to discriminate the standard/non-standard input signal. CONSTITUTION:A comb-line filter 102 separates an inputted composite video signal into a luminance signal and a chrominance carrier signal and a color demodulation circuit 106 demodulates the chrominance carrier signal into a color difference signal, which is outputted. Moreover, a line lock PLL 120 extracts a synchronizing signal from the video signal from the filter 102, generates and outputs the synchronized line clock. Furthermore, a burst lock PLL 119 extracts a color burst signal from the video signal inputted from a terminal 101 and generates and outputs a synchronized burst lock clock. Then a standard/non-standard detection circuit 121 based on them decides whether or not the inputted video signal satisfies the NTSC system and decides it to be the standard signal when satisfied and it to be the non-standard signal when not satisfied.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit for a digital television receiver.

0002

[Prior Art] As a conventional technology, for example,
There is a publication No. 4-001389. This prior art is a VTR
etc., non-standard signals that do not meet the specifications of the NTSC system are subjected to optimal processing in the same way as standard signals that meet the specifications of the NTSC system.

This prior art will be explained using FIG. 2. FIG. 2 is a block diagram showing a conventional video signal processing circuit.

In the figure, 101 is a video input terminal;
102 is a line comb filter, 103 and 104 are switches, 105 is a band pass filter (hereinafter abbreviated as BPF) and an ACC circuit, 106 is a color demodulation circuit, 107, 1
08 is an A/D converter, 109 is a frame comb filter, 110 is a line comb filter, 111 is a switch,
112 is a mixing circuit, 113 is a luminance signal output terminal, 114
1 is a line comb filter, 115 is a frame comb filter, 116 is a switch, 117 is a mixing circuit, 118 is a color difference signal output terminal, 119 is a burst lock PLL, 1
20 is a line lock PLL, 121 is a standard/non-standard detection circuit, and 122 is a switch. Further, 123 represents a comb filter for luminance signals, and 124 represents a comb filter for color signals.

The line lock PLL 120 extracts a synchronization signal from the video signal input from the video input terminal 101, generates and outputs a line lock clock synchronized with the synchronization signal. Furthermore, the burst lock PLL 119 extracts a color burst signal from the video signal input from the video input terminal 101, generates and outputs a burst lock clock synchronized with the color burst signal.

On the other hand, the standard/non-standard detection circuit 121 extracts a synchronization signal and a color burst signal from the video signal input from the video input terminal 101, and based on them, determines whether the input video signal satisfies the NTSC system. (standard/non-standard determination), and based on this determination result, switches 103, 104, 122, 111, 116
Switch.

That is, in the case of the NTSC system, between the color subcarrier frequency fSC, horizontal scanning frequency fH, and vertical scanning frequency fV, fSC=(455/2)・fH, fH=(52
A predetermined frequency relationship of 5/2)·fV is accurately managed. A signal that satisfies the NTSC system is called a standard signal. For such standard signals, between frames,
Since the phase relationship of color subcarriers between lines is accurately managed and an inversion relationship is established, the optimal process is to use this property to separate the luminance signal and color signal using a comb filter. Become.

[0008] Therefore, if it is determined that the input video signal is a standard signal, switches 103, 104, 12
2,111,116 close on the side marked STD. That is, if the input video signal is determined to be standard (that is, satisfies the NTSC system), the output of the burst lock PLL 119 (burst lock clock) is used as the system clock, and the A/D converters 107 and 108
In this case, a signal that does not pass through the line comb filter 102 is introduced, and instead, the line comb filter 110,
The signal via 114 is guided to mixers 112 and 117.

On the other hand, in the case of home VTRs, personal computers, or television broadcast signals with poor reception conditions, the above frequency relationship is not accurately managed. A signal that does not satisfy the NTSC system is called a non-standard signal. In particular, regarding such non-standard signals,
When there is a long time difference, such as between frames, the luminance signal and color signal cannot be separated accurately, which may actually cause deterioration of image quality. Therefore, in the case of a non-standard signal, the signal that has passed through the line comb filter beforehand is input to the frame comb filter, and the frame comb filter is used only for the purpose of removing crosstalk components between the luminance signal and color difference signal. This is the optimal process.

[0010] Therefore, if it is determined that the input video signal is a standard signal, switches 103, 104, 12
2,111,116 close to the side marked NSTD. In other words, the input video signal is non-standard (that is, NTSC
If it is determined that the line lock PLL 120 does not satisfy the system clock, the output of the line lock PLL 120 is used as the system clock, and the signal via the line comb filter 102 is guided to the A/D converters 107 and 108. Instead,
Signals that do not pass through line comb filters 110 and 114 are guided to mixers 112 and 117. By doing this, even non-standard signals from VTRs etc. that do not satisfy the NTSC system can be handled without deterioration in image quality.
Optimal processing similar to that for standard signals is possible.

[0011]

Generally, standard/non-standard determination is an important technique for achieving high image quality, and the performance of this determination determines the performance of the entire system. However, in the above-mentioned conventional technology, sufficient consideration has not been given to the noise contained in the input video signal, so there is a problem that it is easy to make a mistake in determining whether the signal is standard or non-standard when noise increases.

[0012]Also, although the line comb filter 102 is expensive, it is used only for non-standard signals, and therefore has a problem of low usage efficiency. The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a video signal processing circuit that can improve the accuracy of standard/non-standard determination and improve the efficiency of using a comb filter.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a comb filter that inputs a composite video signal, separates the composite video signal into a luminance signal and a carrier color signal, and outputs the separated signals. and a color demodulation circuit that demodulates the carrier color signal from the comb filter into a color difference signal and outputs the same, and inputs the composite video signal and the luminance signal from the comb filter, and selects one of them. a sampling device that inputs the composite video signal or the luminance signal and carrier color signal from the comb filter, and generates and outputs a sampling clock signal based on a specific reference signal included in the input signal; a clock generation circuit; and a first analog/digital converter that receives an output signal from the switch, converts the signal from an analog signal to a digital signal based on a sampling clock signal from the sampling clock generation circuit, and outputs the signal. and a second analog/digital converter that inputs the color difference signal from the color demodulation circuit, converts the color difference signal from an analog signal to a digital signal based on the sampling clock signal from the sampling clock generation circuit, and outputs the digital signal. a spatio-temporal processing circuit which inputs the output signals from the first and second analog/digital converters, performs spatio-temporal processing on the signals and outputs them, and a luminance signal from the comb filter; a determination circuit that receives a carrier color signal and determines whether the composite video signal is a regular signal of a predetermined signal system based on the input signal (that is, determines whether it is standard or non-standard); When the determination circuit determines that the composite video signal is a regular signal (that is, a standard signal), the switch selects and outputs the composite video signal, and the composite video signal is not a regular signal. (In other words, when it is determined that it is a non-standard signal),
The switch selects and outputs the luminance signal from the comb filter.

[0014]

[Operation] When separating the composite video signal into a luminance signal and a carrier chrominance signal, the comb filter uses signal components (particularly,
To reduce noise components without deteriorating a synchronization signal included in a luminance signal or a color burst signal included in a carrier color signal. Therefore, in the present invention, since the judgment circuit inputs the luminance signal and the carrier color signal from the comb filter, the standard/non-standard judgment in the judgment circuit is less susceptible to noise. Even when the number increases, there is no error in determining standard/non-standard. For example, when a line comb filter is used as the comb filter, the determination accuracy is 3 dB in terms of S/N ratio.
It can be improved to some extent.

Furthermore, in the present invention, the carrier color signal output from the comb filter is always used, so instead of using the expensive comb filter only for non-standard signals as in the past. , will be used all the time, thus increasing the efficiency of using the comb filter. Furthermore, it becomes possible to eliminate a part of the color signal comb filter conventionally used as a spatio-temporal processing circuit, which is advantageous in terms of cost. Note that even if such deletion is performed, no deterioration in performance can be detected in color signal processing because the difference in performance between digital and analog comb filters is very small.

[0016]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram showing a video signal processing circuit as an embodiment of the present invention.

In the figure, 101 is a video input terminal;
102 is a line comb filter, 103 is a switch, 1
05 is a band pass filter (hereinafter abbreviated as BPF) and ACC circuit, 106 is a color demodulation circuit, and 107 and 108 are A
/D converter, 109 is a frame comb filter, 110
1 is a line comb filter, 111 is a switch, 112 is a mixing circuit, 113 is a luminance signal output terminal, 115 is a frame comb filter, 117 is a mixing circuit, 118 is a color difference signal output terminal, 119 is a burst lock PLL, 120 is a line Lock PLL, 121 is a standard/non-standard detection circuit,
122 is a switch. Further, 123 represents a comb filter for luminance signals, and 124 represents a comb filter for color signals.

Next, the operation of this embodiment will be explained. The line comb filter 102 is connected to the video input terminal 101.
The input video signal is separated into a luminance signal and a color signal and output. The line lock PLL 120 extracts a synchronization signal from the luminance signal output from the line comb filter 102, generates and outputs a line lock clock synchronized with the synchronization signal. Furthermore, the burst lock PLL 119 extracts a color burst signal from the color signal output from the line comb filter 102, and generates and outputs a burst lock clock synchronized with the color burst signal.

On the other hand, the standard/non-standard detection circuit 121 extracts a synchronization signal and a color burst signal from the luminance signal and color signal output from the line comb filter 102,
Based on these, it is determined whether the input video signal satisfies the NTSC system (standard/non-standard determination),
Based on this determination result, switches 103, 122, 111
Switch.

That is, if it is determined that the input video signal is a non-standard signal, the switches 103, 122,
111 closes on the side marked NSTD. Then, the line lock clock from the line lock PLL 120 is used as the system clock. Furthermore, the luminance signal output from the line comb filter 102 is input to the A/D converter 107, where it becomes a digital signal. On the other hand, the color signal output from the line comb filter 102 is input to the A/D converter 108 as a color difference signal via the BPF/ACC circuit 105 and the color demodulation circuit 106, where it becomes a digital signal.

The luminance signal output from the A/D converter 107 is sent to the mixer 11 via a frame comb filter 109.
2, and directly input to the mixer 112 as is. The frame comb filter 109 removes the color signal component and extracts only the luminance signal by summing the input and output of the internal memory, thereby removing crosstalk from the color signal.

Further, the mixer 112 mixes the two input luminance signals and outputs the mixed signal. At this time, the frame comb filter 109 calculates the difference between the input and output of the internal frame memory, and if the difference is small, it determines that it is a still image, and outputs more luminance signals from the frame comb filter 109. The mixing ratio of the mixer 112 is controlled so that. Conversely, if the difference is large, it is determined that it is a video, and the A/D
The mixing ratio of the mixer 112 is controlled so that a large amount of the direct luminance signal from the converter 107 is output.

The color difference signal output from the A/D converter 108 is input to the mixer 117 via the frame comb filter 115, while the color difference signal is directly input to the mixer 117 as it is.
is input. The frame comb filter 115 removes the luminance signal component and extracts only the color difference signal by summing the input and output of the internal memory, thereby removing crosstalk from the luminance signal.

Further, the mixer 117 mixes the input luminance signals and outputs the mixed signal. At this time, the frame comb filter 115 calculates the difference between the input and output of the internal frame memory, and if the difference is small, determines that it is a still image, and outputs more color difference signals from the frame comb filter 115. The mixing ratio of the mixer 117 is controlled so that. Conversely, if the difference is large, it is determined that the image is a moving image, and the mixing ratio of the mixer 117 is controlled so that more color difference signals directly from the A/D converter 108 are output.

[0025] If it is determined that the input video signal is a standard signal, switches 103, 122, 111 are set to ST.
Close on the side marked D. Then, the burst lock clock from the burst lock PLL 119 is used as the system clock. Further, the video signal inputted from the video input terminal 101 is inputted as is to the A/D converter 107, where it becomes a digital signal. On the other hand, in the A/D converter 108, as in the case of non-standard signals,
The color signal output from the line comb filter 102 is B
The signal is input as a color difference signal via the PF/ACC circuit 105 and the color demodulation circuit 106, where it becomes a digital signal.

The luminance signal output from the A/D converter 107 is sent to the mixer 11 via a frame comb filter 109.
2 and input to a mixer 112 via a line comb filter 110. The frame comb filter 109 and the line comb filter 110 remove the color signal component and extract only the luminance signal by summing the input and output of each internal memory, thereby removing crosstalk from the color signal. It is carried out.

Further, the mixer 112 mixes the two input luminance signals and outputs the mixed signal. At this time, the frame comb filter 109 calculates the difference between the input and output of the internal frame memory, as in the case of a non-standard signal, determines that it is a still image if the difference is small, and filters the frame comb filter 109. The mixing ratio of the mixer 112 is controlled so that more luminance signals from the mixer 109 are output. Conversely, if the difference is large, it is determined that the image is a moving image, and the mixing ratio of the mixer 112 is controlled so that more luminance signals are output from the line comb filter 110.

Further, the color difference signal outputted from the A/D converter 108 is inputted to the mixer 117 via the frame comb filter 115, as in the case of the non-standard signal.
It is directly input to the mixer 117 as it is. The frame comb filter 115 removes the luminance signal component and extracts only the color difference signal by summing the input and output of the internal memory, thereby removing crosstalk from the luminance signal.

Further, the mixer 117 mixes the input luminance signals and outputs the mixed signal. At this time, the frame comb filter 115 calculates the difference between the input and output of the internal frame memory, and if the difference is small, determines that it is a still image, and outputs more color difference signals from the frame comb filter 115. The mixing ratio of the mixer 117 is controlled so that. Conversely, if the difference is large, it is determined that the image is a moving image, and the mixing ratio of the mixer 117 is controlled so that more color difference signals directly from the A/D converter 108 are output.

Now, there are two features of this circuit. One is
Burst lock PLL119, line lock PLL12
0, the output of the line comb filter 102 is used as the input of the standard/non-standard detection circuit 121. It is known that in the line comb filter 102, since there is an operation for calculating the sum between lines, the signal component does not change, but the noise component increases by 1/(square root of 2). Therefore, it is less susceptible to the influence of noise.

Another reason is that for color signal processing, the output of the line comb filter 102 is always used, and compared to the conventional method, two switches and one line comb filter are used.
One thing has been deleted. Regarding the luminance signal, if the output of the line comb filter 102 is always used, the resolution in the diagonal direction will deteriorate and ringing will occur. A method that switches between standard time and non-standard time is better. However, for color signals, such defects are at an undetectable level, so the output of the line comb filter 102 may always be used.

[0032]

According to the present invention, since the standard/non-standard determination circuit inputs the luminance signal and carrier color signal from the comb filter, the standard/non-standard determination in the determination circuit is free from the influence of noise. Therefore, even when noise increases, there is no error in determining standard/non-standard. For example, when a line comb filter is used as the comb filter, the determination accuracy is converted into an S/N ratio of 3d
It can be improved by about B.

Furthermore, according to the present invention, the carrier color signal output from the comb filter is always used, so unlike the conventional method, the expensive comb filter is used only for non-standard signals. Therefore, the comb filter can be used more efficiently. Furthermore, it becomes possible to eliminate a part of the color signal comb filter conventionally used as a spatio-temporal processing circuit, which is advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional video signal processing circuit.

[Explanation of symbols]

102, 110...Line comb filter, 105...BP
F.ACC circuit, 106...color demodulation circuit, 119...burst clock PLL, 120...line clock PLL, 1
21...Standard/non-standard detection circuit, 115...Frame comb filter 112, 117...Mixer.

Claims (1)

[Claims] 1. A comb filter that inputs a composite video signal, separates the composite video signal into a luminance signal and a carrier color signal, and outputs the separated signal; and a comb filter that demodulates the carrier color signal from the comb filter into a color difference signal. a color demodulation circuit for outputting the composite video signal and the luminance signal from the comb filter; a switch for inputting the composite video signal and the luminance signal from the comb filter; and a switch for selecting and outputting either the composite video signal or the luminance signal from the comb filter; a sampling clock generation circuit that receives a luminance signal and a carrier color signal, generates and outputs a sampling clock signal based on a specific reference signal included in the input signal; a first analog/digital converter that converts the signal from an analog signal to a digital signal based on a sampling clock signal from the sampling clock generation circuit and outputs the converted signal; a second analog/digital converter that converts the analog signal into a digital signal based on the sampling clock signal from the sampling clock generation circuit and outputs the digital signal;
and a spatio-temporal processing circuit which inputs the output signals from the second analog/digital converter, subjects the signals to spatio-temporal processing and outputs the respective signals, and inputs the luminance signal and carrier color signal from the comb filter. and a determination circuit that determines whether or not the composite video signal is a regular signal of a predetermined signal system based on the input signal, and the composite video signal is determined to be a regular signal by the determination circuit. When the switch selects and outputs the composite video signal, and when it is determined that the composite video signal is not a regular signal, the switch selects and outputs the luminance signal from the comb filter. A video signal processing circuit for a digital television receiver, characterized in that: