JPH05300403A - Comb line filter - Google Patents

Abstract

PURPOSE:To constitute the comb line filter by using difference between a current input chrominance signal and a 1H delayed chrominance signal when handling chrominance signals in a PAL system. CONSTITUTION:An oscillation circuit 6 generates a signal having a double frequency as high as the sub carrier frequency synchronized with a chrominance signal 100 inputted from an input terminal 1, and this signal is outputted to a multiplier 2 after the phase is shifted for a prescribed amount by a phase sifter 9. Thus, since the multiplier 2 multiplies a signal 200 inputted from the phase shifter 9 to the chrominance signal 100 inputted from the input terminal 1 and afterwards outputs this signal through an amplifier 3 to a low-pass filter 4, a chrominance signal 101 having the sub carrier frequency axially symmetric concerning the B-Y axis of the chrominance signal 100 is extracted from the low-pass filter. This chrominance signal 101 is 1H delayed by a 1H delay line 5 and afterwards inputted to a subtracter 8 and since the above-mentioned chrominance signal 100 is subtracted at this subtracter, a chrominance signal 103 removed the non-correlative signal component is outputted from the subtracter 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comb filter used for noise reduction or separation of a luminance signal and a chrominance signal in a video device handling a PAL video signal.

[0002]

2. Description of the Related Art Conventionally, the transmission of a color signal included in a video signal of the PAL system is performed by inverting the phase of the color signal for each horizontal scanning line (hereinafter referred to as 1H). It has the advantage that it is strong and has little hue change. However, since the color signal of the PAL system is transmitted with the phase inverted every 1H as described above, it is 1
The comb filter cannot be constructed by taking the difference with the color signal after H, and the comb filter has to be constructed by taking the difference with the color signal after 2H.

FIG. 3 is a block diagram showing such a conventional comb filter for a PAL system video signal. PAL
The system video signal 100 is input to the 2H delay line 31, the adder 32, and the subtractor 33. The 2H delay line 31 delays the input video signal 100 for 2H period and outputs it to the adder 32 and the subtractor 33. As a result, in the adder 32, P
The AL system video signal 100 and the PAL system video signal delayed by 2H are added, and as a result, a luminance signal Y having no correlation is obtained every 2H. Further, the subtractor 33 subtracts the currently input PAL system video signal from the 2H delayed PAL system video signal, and as a result, the uncorrelated luminance signal is removed every 2H to obtain the PAL system color signal C.

As described above, in the conventional comb filter for the PAL video signal, the video signal currently input and the delayed signal delayed by 2H are added or subtracted, so that the signal output from the filter is thereafter synthesized. When it is reproduced, there is a drawback that a color shift in the vertical direction of the screen due to 2H delay occurs, and when the color signal is demodulated into a color difference signal in the receiver, a 1H delay line is used. However, there was a drawback that the color dropped in the vertical direction. This drawback becomes more remarkable in the comb filter for the cyclic PAL video signal. Therefore, in the case of a color signal having no correlation in the vertical direction, it is often combined with a decorrelation detector in order to stop the comb operation or the cyclic operation. But,
Even with this configuration, when the input video signal has a small amplitude, it is vulnerable to noise, so the detection level cannot be set to a very small level. There is a drawback that it is not possible to suppress the color shift in the direction.

[0005]

As described above, the comb filter for the PAL system video signal is constructed by taking the difference between the color signal of the current input and the color signal delayed by 2H.
There is a drawback that color shift occurs in the vertical direction of the screen. In order to avoid this drawback, the comb-shaped operation is stopped when a color signal having no correlation in the vertical direction is input. Even with the configuration, since the detection level cannot be set very small, there is a drawback that it is not possible to suppress the color shift in the vertically downward direction of the light-colored portion.

In view of the above, the present invention eliminates the above-mentioned drawbacks, and when the color signal of the PAL system is handled, the color signal of 1
An object of the present invention is to provide a comb filter that can configure a circuit by using the difference from the H-delayed color signal.

[0007]

The comb filter according to the present invention is formed by an oscillator circuit which produces a signal having a frequency twice the carrier frequency of the input signal in synchronization with the carrier frequency of the input signal. A phase shift circuit that shifts the phase of the signal by a predetermined amount, a multiplication circuit that multiplies the signal output from the phase shift circuit and the input signal, and a filter that removes a high frequency component from the multiplication result of the multiplication circuit, It has a configuration including a delay circuit that delays the signal output from this filter for one horizontal scanning period, and an arithmetic circuit that adds or subtracts the delay signal delayed by the delay circuit and the input signal.

[0008]

In the comb filter of the present invention, the oscillator circuit produces a signal having a frequency twice the carrier frequency of the input signal in synchronization with the carrier frequency. The phase shift circuit shifts the phase of the signal generated by the oscillator circuit by a predetermined amount.
The multiplication circuit multiplies the signal output from the phase shift circuit by the input signal. The filter removes high frequency components from the multiplication result of the multiplication circuit. The delay circuit delays the signal output from the filter by one horizontal scanning period. The arithmetic circuit adds or subtracts the delay signal delayed by the delay circuit and the input signal.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a comb filter according to the present invention. Reference numeral 1 is an input terminal to which a PAL color signal 100 is input, and 2 is a color signal 100 input from the input terminal 1 and the color signal 100 input from the phase shifter 9.
A multiplier 3 that multiplies a signal 200 having a frequency twice the subcarrier frequency of 3 with an amplifier that doubles the output of the multiplier 2 and a low-pass filter that removes high frequency components from the output of the amplifier 3 ( LPF), 5 is a 1H delay line that delays the output color signal 101 obtained from the low-pass filter 4 by 1H into a 1H delayed color signal 102, and 6 is a subcarrier frequency of the PAL color signal 100 input from the input terminal 1. A burst gate 6 for extracting a burst signal by an oscillation circuit that generates a signal 200 having a frequency twice this frequency in synchronization with
1. A phase comparator 62 that compares the phases of the burst signal and the signal output from the frequency divider 65 and outputs a difference voltage corresponding to the difference, and a low-pass that smoothes the difference voltage output from the phase comparator 62. The filter 63, the voltage-controlled oscillator 64 that changes its oscillation frequency by the control voltage output from the low-pass filter 63, and the frequency divider 6 that divides the frequency of the output signal of the voltage-controlled oscillator 64 into 1/2.
Have five. Reference numeral 7 is a delay line that delays the input signal by the signal processing delay time of the multiplier 2, the amplifier 3, and the low-pass filter 4, and 8 is 1 from the color signal input from the delay line 7.
A subtracter for subtracting the 1H delayed color signal 102 input from the H delay line 5, and a phase shifter 9 for shifting the phase of the signal output from the oscillation circuit 6 by a predetermined amount.

Next, the operation of this embodiment will be described. The color signal 100 input from the input terminal 1 is input to the multiplier 2, the oscillation circuit 6 and the delay line 7. The burst gate 61 of the oscillator circuit 6 extracts a burst signal, that is, a color subcarrier signal from the input color signal and outputs it to the phase comparator 62. On the other hand, the voltage controlled oscillator 64 oscillates a signal having a frequency twice the frequency of the color subcarrier signal and outputs it to the phase shifter 9 and the frequency divider 65. The frequency divider 65 sets the frequency of the input oscillation signal from the voltage controlled oscillator 64 to 1
After the frequency is divided into / 2, it is output to the phase comparator 62.
As a result, the phase comparator 62 compares the phase of the color subcarrier signal input from the burst gate 61 with the phase of the oscillation signal input from the frequency divider 65, and outputs the difference voltage to the low pass filter 63. The low-pass filter 63 smoothes the differential voltage input from the phase comparator 62, and then outputs it to the voltage controlled oscillator 64. The voltage controlled oscillator 64 adjusts its oscillation phase so that the input differential voltage becomes zero. As a result, the oscillation signal 200 output from the oscillation circuit 6 is synchronized with the subcarrier frequency of the color signal 100 input from the input terminal 1 and has a frequency twice that of the color subcarrier signal. Become.

The phase shifter 9 shifts the phase of the oscillation signal 200 input from the oscillation circuit 6 by a predetermined amount and outputs this phase shift signal to the multiplier 2. As a result, in the multiplier 2, the input terminal 1
The phase-shifted signal 20 to the color signal 100 input from
0 is multiplied, and the multiplication result is doubled by the amplifier 3 and then input to the low-pass filter 4. The low-pass filter 4 passes only the target low-frequency component from the input signal and outputs it to the 1H delay line 5.
Here, the signal output from the low-pass filter 4 is a color signal having a sub-carrier frequency that is the axis target of the B-Y axis with respect to the color signal 100 input from the input terminal 1.
Hereinafter, this signal is referred to as a color signal 101. The 1H delay line 5 receives the color signal 101 input from the low-pass filter 4 for 1H.
The delayed color signal 102 is delayed by the period and is used as the subtractor 8
Output to. On the other hand, the delay line 7 delays the color signal 100 input from the input terminal 1 by the signal processing time of the multiplier 2, the amplifier 3, and the low-pass filter 4, and outputs it to the subtractor 8. As a result, the subtractor 8 subtracts the delayed color signal 102 from the color signal input from the delay line 7, and as a result, the uncorrelated noise component is removed from the color signal input from the delay line 7, and the noise component Reduced color signal 103
Is output.

Here, P input from the input terminal 1
The AL type color signal 100 is given by the following equation. EP = ± (ER-EY) cosω sc t + (EB-EY) sinω sc t ... (1) However, in the ω _sc = 2πf _sc, f _sc shows the color subcarrier frequency, moreover (1) of The code of the first term alternates every 1H. Here, the phase shift signal 20 output from the phase shifter 9
0 is a signal that has a frequency twice that of the color subcarrier signal and is phase-shifted by a predetermined amount. This is expressed as 2f _sc -cosω _sc t, and when this is multiplied by the equation (1) by the multiplier 2, , (2)
The formula is obtained.

[Equation 1] The signal expressed by the equation (2) is input from the multiplier 2 to the low-pass filter 4 via the amplifier 3. Low-pass filter 4 is a signal of frequency omega _sc is passing, for 3 [omega] _sc prevents the signal output from the low pass filter 4 when the 2E _out, which has the form as shown in (3) ing.

[Equation 2]

The shape of the color signal 100 output from the low-pass filter 4 represented by the equation (3) is different from the shape of the color signal 100 input from the input terminal 1 represented by the equation (1). Only the sign of one item is reversed, and the rest has the same shape. That is, the color signal obtained by the equation (3) becomes a color signal having a subcarrier frequency that is symmetrical with respect to the color signal 101 with respect to the BY axis. The details of the above process are described in detail in Japanese Patent Application Publication No. 62-33797. Therefore, since there is an axial symmetric correlation between the delayed color signal 102 output from the low pass filter 4 and the color signal output from the delay line 7, the color signal output from the delay line 7 is converted into the low pass filter 4. By subtracting the 1H-delayed color signal output from, only the noise of the non-correlation component is removed.

According to this embodiment, from the color signal 100 input from the input terminal 1, the color signal 1 is output from the multiplier 2, the amplifier 3, the low pass filter 4, the oscillator circuit 6 and the phase shifter 9.
00, a color signal 101 having a sub-carrier frequency of the B-Y axis target is created, the color signal 101 is delayed by 1H to create a delayed color signal 102, and the color signal input from the input terminal 1 is generated. The delay color signal 102 is subtracted from the delay color signal 102 from the
It is possible to configure a comb filter without delaying 2H with respect to 0, and it is possible to reduce a color shift in the vertical direction that occurs when a color signal is reproduced by passing through the comb filter.

FIG. 2 is a block diagram showing another embodiment of the present invention, in which the same parts as those of the previous embodiment are designated by the same reference numerals.
This example constitutes a recursive comb filter. The noise signal input from the amplifier 12 is removed from the color signal 100 input from the input terminal 1 by the subtractor 8 to obtain the color signal 1
10 is input to the multiplier 2, the amplifier 3, the low pass filter 4, the oscillation circuit 6 and the adder 10. The multiplier 2, the oscillator circuit 6 and the phase shifter 9 perform the same operation as in the previous embodiment to create the color signal 120 of the subcarrier frequency which is the axis target of the color signal 110 with respect to the BY axis, and this is generated for 1H. Output from the low-pass filter 4 to the delay line 5. The 1H delay line 5 delays the color signal 120 for 1H period and outputs it to the adder 10. In the adder 10, the color signal 110 and the color signal 120 delayed for the 1H period are added to leave only a noise component having no correlation, and the noise component is amplitude-limited by the limiter 11 and then subtracted via the amplifier 12. Input to the container 8. Therefore, the subtractor 8 removes the noise component from the color signal 100 input from the input terminal 1 and outputs the removed color signal 110 to the next stage or the like. Also in this example, 2H is applied to the PAL system color signal input from the input terminal 1.
Since no delay is performed, it is possible to suppress the occurrence of color shift in the vertical downward direction of the screen in the same manner as described above.

[0016]

As described above, according to the comb filter of the present invention, when a PAL system color signal is handled, a circuit can be constructed by using the difference between the color signal of the current input and the color signal delayed by 1H. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a comb filter according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing an example of a conventional comb filter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input terminal 2 ... Multiplier 3 ... Amplifier 4 ... Low-pass filter 5 ... 1H delay line 6 ... Oscillation circuit 7 ... Delay line 8 ... Subtractor 9 ... Phase shifter

Claims (2)

[Claims] 1. An oscillating circuit for producing a signal having a frequency twice as high as the carrier frequency of an input signal, and a shift for shifting a phase of the signal produced by the oscillating circuit by a predetermined amount. A phase circuit, a multiplication circuit for multiplying the signal output from the phase shift circuit by the input signal, a filter for removing high frequency components from the multiplication result of the multiplication circuit, and a signal output from the filter for one horizontal scanning. A comb filter, comprising: a delay circuit for delaying for a period; and an arithmetic circuit for adding or subtracting the delay signal delayed by the delay circuit and the input signal. 2. A subtraction circuit for subtracting a non-correlation component from an input signal, and an oscillating circuit for producing a signal having a frequency twice the carrier frequency in synchronization with the carrier frequency of the input signal.
A phase shift circuit that shifts the phase of the signal created by the oscillator circuit by a predetermined amount, a multiplication circuit that multiplies the signal output from the phase shift circuit by the input signal, and a high frequency from the multiplication result of the multiplication circuit. A filter for removing components, a delay circuit for delaying a signal output from this filter for one horizontal scanning period, an adder circuit for adding the delayed signal delayed by this delay circuit and the input signal, and an adder circuit An amplitude limiting circuit for limiting the amplitude of an output non-correlation component and outputting it to the subtraction circuit.