JPH114458A - Adaptive comb-line filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a circuit to have provision for both the PAL and NTSC systems with a small circuit configuration by using three BPFs that are placed to a pre-stage of a correlation detection circuit and have a broad frequency band characteristic through which subcarrier frequencies of the PAL/NTSC signals pass, so as to cut off the DC components and using a BPF placed to a post-stage of the detection circuit for selecting the center frequency for the PAL/NTSC systems. SOLUTION: A video signal and video signals delayed by line memories 11, 12 are given to BPS (1) 13-15, through which chroma signal band components pass, and the components are given to a BPF (2) 17 via a correlation detection circuit LOGIC 16. The center frequency of the BPF (2) 17 is changed between PAL demodulation and NTSC demodulation times by changing the filter configuration such that the center frequency comes to the actual center frequency of the respective TV systems, based on the overall characteristic of the BPF (1) 13-15 and the BPF (2). The circuit can cope with both the PAL/NTSC systems by having only to select the center frequency of the BPF (2) 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a comb filter circuit for a television receiver (International Patent Classification H04N9 / 7).
8) In particular, the present invention relates to an adaptive comb filter circuit that adaptively selects a line memory based on a correlation between upper and lower lines using a line memory.

[0002]

2. Description of the Related Art A conventional adaptive comb filter of a television receiver uses a line memory to detect upper and lower correlations by using a line memory in order to reduce cross luminance generated particularly at upper and lower boundaries of color signals. Cross luminance was reduced by operating the line and comb. In a conventional adaptive comb filter, as shown in Japanese Patent Application Laid-Open No. 2-9755, cross-luminance is reduced by detecting upper and lower correlations using two line memories and performing a comb operation with a line having a high correlation. Was.

An example in the case of a conventional digital filter will be described with reference to the drawings. FIG. 2 is an example of a conventional adaptive comb filter.

[0004] In FIG. 2, a digitally encoded video signal is input to a first line memory 21. The first
The output of the line memory 21 is input to the second line memory 22. The digitally encoded video signal is input to a first band pass filter 23 (hereinafter, referred to as BPF). The output of the first line memory 21 is input to a second BPF 24. The output of the second line memory 22 is input to a third BPF 25. The output of the first BPF 23, the output of the second BPF 24, and the output of the third BPF 25 are respectively input to a correlation detection circuit 26, and the correlation detection circuit 26 outputs two inputs having a high correlation among the three inputs. By selecting and taking the difference between the two signals, the luminance signal is suppressed, and the chroma component is extracted. The output of the correlation detection circuit 26 and the output of the first line memory 21 are input to an addition circuit 27.

With the above arrangement, a chroma signal is obtained at the output of the correlation detection circuit 26, and a luminance signal is obtained at the output of the addition circuit 27.

[0006]

When such an adaptive comb filter is constructed by digital signal processing, the sampling frequency is an integer multiple of the color subcarrier frequency. Has been advantageous and has been used frequently. However, PAL, NTS
In a television receiver that handles both types of C, since the color subcarrier frequency differs between both types, it is necessary to switch the sampling clock when changing the type.
A special procedure and a protection circuit are required for clock switching, and the circuit configuration is complicated.

On the other hand, regardless of the PAL / NTSC system,
A system that handles both systems with the same system clock has also been proposed. However, in this system, it is necessary to change the circuit configuration due to the difference in the ratio between the system clock and the subcarrier frequency by PAL / NTSC, which increases the circuit scale. There was an adverse effect.

When the sampling clock in the above example uses a clock frequency other than an integer multiple of the color subcarrier frequency, the change in the center frequency of the BPF is
This is necessary according to the NTSC system, and the configuration of the BPF needs to be changed. In the above configuration, each of the first BPF 23, the second BPF 24, and the third BPF 25
Has to be changed to the method, and the hardware scale is sometimes increased.

[0009]

In order to solve the above-mentioned problems, an adaptive comb filter circuit according to the present invention has three BPFs before a correlation detection circuit and one BPF after a correlation detection circuit. The BPF has a wide band characteristic that only the PAL / NTSC subcarrier frequency can pass through. After blocking the DC component by these three BPFs, a correlation process is performed by a correlation detection circuit, and a chroma signal is supplied to the BPF to be added. give. In the post-BPF, the center frequency is switched by the PAL / NTSC system, and the front BPF and post-BP
The composition frequency of F is configured to be the center frequency of the selected method.

According to the present invention, the PAL / NTS can be realized by simply switching the center frequency of one BPF by the above configuration.
It is possible to provide an adaptive comb filter circuit compatible with both C types.

As described above, according to the present invention, it is possible to configure an adaptive comb filter circuit compatible with both PAL and NTSC with a smaller circuit configuration.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

According to the first aspect of the present invention, in a digital signal processing television, a video signal is delayed by delaying video signal information using a line memory and a correlation between lines is measured to selectively output each line memory. In the comb filter to be switched, a BPF section is provided before and after the correlation detection circuit, and the frequency characteristic of the BPF section provided after the correlation detection circuit is switched according to the difference between the PAL and the NTSC system. Having.

According to a second aspect of the present invention, in a digital signal processing television, a first line memory to which a digitally encoded video signal is inputted, and a second line memory to which an output of the first line memory is inputted. A first band pass filter (hereinafter referred to as BPF) for inputting the digitally encoded video signal, a second BPF for inputting the output of the first line memory, A third BPF to which the output of the second line memory is input, the output of the first BPF, the output of the second BPF, and the output of the third BPF. A correlation detection circuit for selecting two inputs having a high correlation, a fourth BPF for receiving an output of the correlation detection circuit, and changing a frequency characteristic thereof according to a control signal, And an adder circuit to which the output of the first line memory is input. The fourth BPF provided after the correlation detection circuit switches the frequency characteristic according to the difference between the PAL and the NTSC system. / NTSC has the effect of corresponding to both types.

An embodiment of the present invention will be described below with reference to FIG. (Embodiment 1) FIG. 1 illustrates a block diagram of an adaptive comb filter circuit according to claim 1 of the present invention. In FIG. 1, in a digital signal processing television, a video signal is input to line memories 11 and 12 to delay video signal information by 1H or 2H. The video input signal and the output of the line memory are respectively supplied to a first band-pass filter (hereinafter, referred to as BPF (1)) 13, 1
After passing through lines 4 and 15, a correlation detection circuit 1 for measuring the correlation between lines and selectively switching the output of each line memory
Enter 6 The output of the correlation detection circuit 16 is input to a second band-pass filter (hereinafter, referred to as BPF (2)) 17, and the frequency characteristic of the BPF (2) 17 provided after the correlation detection circuit depending on the PAL or NTSC system. Switch. The output of the BPF (2) 17 is added by the adder 18 to the video signal passed through the line memory.

Next, the operation will be described. In FIG. 1, an input video signal is delayed by 1H or 2H in a line memory, and then three BPFs (1) 13, 14, and 15 are output.
To pass the chroma signal band signal component. The outputs of the signals are detected by the correlation detection circuit 16 to output signals having high correlation in the upper and lower lines from the correlation detector.
Input to BPF (2) 17. In BPF (2) 17, P
The center frequency is changed by changing the filter configuration between AL demodulation and NTSC demodulation, so that the respective center frequencies come to the center at the time of demodulation of each system based on the overall characteristics of BPF1 and BPF2. A chroma signal is obtained from the output of BPF2. Further, the luminance signal is extracted by adding the chroma signal to the video signal whose time has been adjusted by delaying the input video signal by the line memory.

With the above configuration, the present invention provides a PAL / NT
This makes it possible to configure an adaptive comb filter corresponding to both types of SC.

A second embodiment of the present invention will be described in further detail with reference to an embodiment of the configuration of the adaptive comb filter. FIG. 1 shows a block diagram of an embodiment according to the second aspect of the present invention. In FIG. 1, a digitally encoded video signal is input to a first line memory 11. The first line memory 1
1 is input to the second line memory 12. Also,
The digitally encoded video signal is input to a first bandpass filter 13 (hereinafter, referred to as BPF). The output of the first line memory is input to a second BPF. The output of the second line memory 12 is the third BP
Input to F15. The output of the first BPF 13, the output of the second BPF 14, and the output of the third BPF 15 are respectively input to a correlation detection circuit 16, and the correlation detection circuit 1
6, two inputs having a high correlation among the three inputs are selected to perform the comb operation. The output of the correlation detection circuit 16 is input to a fourth BPF 17 whose frequency characteristic is changed by a control signal. The output of the fourth BPF 17 is input to the addition circuit 27 together with the output of the first line memory 11.

With the above configuration, a chroma signal is obtained at the output of the correlation detecting circuit 26, and a luminance signal is obtained at the output of the adding circuit 27.

(Embodiment 2) In claim 3, claim 1
In the more specific configuration of the line memory described in
An embodiment of a line memory suitable for switching between the NTSC and NTSC will be described. FIG. 3 is a block diagram showing a third embodiment of the present invention. In FIG. 3, a video signal is input to a first line memory 111 to delay the video signal for one horizontal period. The output of the first line memory 111 is input to the second line memory 112 and delays the video signal for one horizontal period. First line memory 111 and second line memory 1
Twelve outputs are input to the selector 113 and are switched by an external control signal. The output of the selector 113 is input to the third line memory 121 to delay the video signal for one horizontal period. The output of the third line memory 121 is input to the fourth line memory 122 to delay the video signal for one horizontal period. Outputs of the third line memory 121 and the fourth line memory 122 are respectively input to the selector 123 and are switched by an external control signal.

By replacing the line memory configured as described above with the first line memory 11 and the second line memory 12 of the first embodiment, the line memory is 1H (horizontal period) in NTSC. The PAL has a length and has a length of 2H, and a configuration of an adaptive comb filter circuit that can be switched according to the system is possible.

(Embodiment 3) In claim 4, claim 1
A more detailed configuration of the BPF described in claim 2 will be described. FIG. 4 is a block diagram showing a fourth embodiment of the present invention. In FIG. 4, the chroma signal is input to the first latch circuit 41 and is delayed by one unit time. The output of the first latch circuit 41 is input to the second latch circuit 42 and is delayed by one unit time. The output of the second latch circuit 42 is input to the inverting circuit 43 to invert the logic. The output of the inverting circuit 43 is input to the third latch circuit 44 and is delayed by one unit time. Third
The output of the latch circuit 44 and the input signal to the first latch circuit 41 are input to a first adder 45 and added. Also,
The output of the first latch circuit 41 and the output of the inverting circuit 43 are input to a second adder 46 and added. Second adder 46
Is input to the multiplier 47, and 1 is set to NTS at the time of PAL demodulation.
At the time of C demodulation, -0.5 is multiplied. The output of the first adder 45 and the output of the multiplier 47 are input to a third adder and added. The above configuration constitutes the first BPF 49. The output of the first BPF is input to a second BPF 50 having the same configuration as the first BPF, and is subjected to band limitation. Second B
The output of the PF 50 is input to the multiplier 51, which is 29/1024 for PAL demodulation and 300/1024 for NTSC demodulation.
Is multiplied by

The BPF configured as above is

[0024]

(Equation 2)

Having a transfer function of 1 and -0.5
By switching the coefficient of the first multiplier 47 built in the first BPF 49 and the second BPF 50, the center frequency can be changed. BPF above
Is used in the fourth BPF 17 described in the first embodiment, it is possible to configure an adaptive comb filter circuit compatible with both types by switching coefficients between PAL and NTSC.

[0026]

As described above, according to the adaptive comb filter circuit of the present invention, the BPFs are arranged before and after the correlation detection circuit, and the frequency characteristics of the BPF placed after the BPFs are changed, so that the PAL can be synchronized with the same clock. It is possible to provide an adaptive comb filter circuit compatible with both the NTSC and NTSC systems.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an invention relating to an adaptive comb filter circuit of the invention.

FIG. 2 is a block diagram showing a configuration of a conventional comb filter.

FIG. 3 is a block diagram showing a configuration of the invention according to claim 3 of the present invention.

FIG. 4 is a block diagram showing the configuration of the invention according to claim 4 of the present invention.

[Explanation of symbols]

 11, 12 Line memory 13, 14, 15, 17 BPF 16 Correlation detection circuit 18 Adder

Claims (4)

[Claims] A BPF section is provided before and after a correlation detection circuit in a comb filter for delaying video signal information of a video signal using a line memory, measuring the correlation between lines, and selectively switching the output of each line memory. , PAL
Alternatively, by changing the frequency characteristic of the BPF section provided after the correlation detection circuit due to the difference in the NTSC system, the PA
An adaptive comb filter circuit adapted to support both L / NTSC systems. 2. A first line memory for receiving a video signal, a second line memory for receiving an output of the first line memory, and a first band for receiving the digitally encoded video signal. A pass filter (hereinafter, referred to as a BPF), a second BPF for receiving an output of the first line memory, a third BPF for receiving an output of the second line memory, A correlation detection circuit that receives the output of the BPF, the output of the second BPF, and the output of the third BPF, and selects two of the three inputs having a high correlation by a correlation detection circuit; A fourth BPF in which an output of a circuit is input and the frequency characteristic of which is changed by a control signal;
And an adder circuit to which the output of the first line memory is input, and a fourth B provided after the correlation detection circuit.
In the PF, the frequency characteristics are switched according to the difference between the PAL and the NTSC system, so that the PAL / NTSC
An adaptive comb filter circuit that is compatible with both types. 3. The line memory is 1H in the NTSC system.
3. The adaptive comb filter circuit according to claim 2, having a length of (horizontal period), a length of 2H in the PAL system, and switching by these systems. 4. The fourth BPF is: 3. The adaptive comb filter circuit according to claim 2, wherein the center frequency is changed by switching the coefficient a between 1 and -0.5.