JPH0148716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a filter circuit suitable for color television image monitor devices and the like.

[Prior art and problem to be solved by the invention] In the NTSC color television system, the luminance and chromaticity components of a composite video signal are mixed using a frequency interpolation method in order to prevent beats, crosstalk, etc. has been done. That is, a subcarrier carrying a chrominance component signal is inserted into a frequency spectrum space where no luminance component signal energy exists. When demodulating such composite video signals, the luminance and chrominance components are typically separated using a bandpass/notch filter or a comb filter.

FIG. 1 shows a conventional bandpass/notch filter for separating luminance and chrominance component signals. The composite video signal is input to a bandpass filter 2 and a phase equalizer 4. A chromaticity component signal near the subcarrier frequency (including a frequency-interpolated luminance component) is obtained from the bandpass filter 2, and the phase of the output signal of the bandpass filter 2 is adjusted by the phase equalizer 4 to produce a composite image. A luminance component signal is obtained by subtracting from the signal. However, in this luminance component and chromaticity component separation method, although the vertical resolution is good, the signal that has passed through the bandpass filter 2 contains high-frequency components of the luminance component whose frequency has been interpolated. Therefore, a so-called cross-color problem occurs, and the horizontal resolution of the luminance component signal output from the subtracter 6 is degraded because high-frequency components near the subcarrier frequency are removed.

FIG. 2 is a block diagram showing a conventional comb filter for separating luminance and chrominance components. The composite video signal is input to a delay means 10, a subtracter 12, and an adder 14, respectively. The delay means 10 delays the input signal by one horizontal line period (approximately 63.5 μs). Composite video signals of two adjacent lines are generally similar signals (they are said to have line correlation) with only the chromaticity components phase inverted, so
By subtracting the composite video signal of the next line from the composite video signal delayed by one horizontal line period, a chromaticity component signal with the luminance component removed in a comb shape is obtained. When the line composite video signals are added, a comb-shaped luminance component signal from which the chromaticity component has been removed is obtained. In this comb-type filter, the adder 14 also passes the high frequency component of the luminance component, so the horizontal resolution is good, but the arithmetic processing between two adjacent lines eliminates the influence of the correlation between the lines. low correlation between adjacent lines in the image (no line correlation)
In this case, the vertical resolution is significantly degraded.

Color television image monitoring equipment is used when producing programs, when recording/playing on a VTR (video tape recorder), or when switching television signals from various signal sources in the main control room. Since it is used to evaluate whether or not the actually reproduced image is appropriate, it needs to have high resolution for accurate visual evaluation. Therefore, in order to take advantage of the respective advantages of the above-mentioned two types of filters, it is desirable to provide both types of filters and use them selectively. However, when both filters are switched, the separation characteristics and bandwidth of the luminance component and chrominance component are different due to the difference in filter characteristics, and furthermore, the image is shifted due to the difference in delay time of the luminance signal path.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a filter circuit that does not cause image shift when switching between operating modes corresponding to a comb filter and a bandpass/notch filter, respectively.

[Means for Solving the Problems] According to the filter circuit of the present invention, there is provided a series circuit including a delay means for delaying an applied composite video signal by a time corresponding to one horizontal line and a bandpass filter, and this series circuit. a switch means for selectively generating an output signal, and receiving the composite video signal and generating a first output signal that is band-passed around the subcarrier frequency and a second output signal that is delayed by a predetermined time from the composite video signal. transversal
When the filter means and the switch means generate the output signal of the series circuit, they receive the output signal and the first output signal, cancel out the luminance components of these two signals, and output only the chromaticity component signal; a first arithmetic means for receiving the first output signal and outputting only the first output signal when the switch means blocks generation of the output signal of the series circuit;
A filter circuit is provided that includes a second calculation means that receives an output signal and an output signal of the first calculation means, cancels out the chromaticity components of these two signals, and outputs only the luminance component.

[Function] In this filter circuit, two operation modes are selected by the switch means. In the comb filter operation mode selected when there is line correlation,
An output signal is generated from the series circuit, and the luminance component of this output signal and the first output signal from the transversal filter means are canceled by the first calculation means to obtain a comb-shaped chromaticity component signal. The chromaticity component signal and the chromaticity component of the second output signal from the transversal filter means are canceled by the second calculation means to obtain a comb-shaped luminance component signal.

In the bandpass/notch filter operation mode selected when there is no line correlation, no output signal is output from the series circuit, and the first calculation means receives only the first output signal of the transversal filter means; This is output as is as a chromaticity component signal. The first output signal of the transversal filter means is a signal mainly consisting of a chromaticity component signal band-passed around the subcarrier frequency, but also includes a frequency-interpolated luminance component. 1st
The output signal of the arithmetic means and the second output signal of the transversal filter means are inputted to the second arithmetic means, and the chromaticity components of these two signals are canceled out to produce a luminance component signal in which the components near the subcarrier frequency are removed. is output. Note that the second calculation means operates as a notch filter.

In the above two operation modes, the first and second output signals of the transversal filter means are used in common, and when switching the operation mode, each bandwidth of the output chromaticity component signal and luminance component signal is It is possible to eliminate changes in the luminance component signal and delay time of the luminance component signal.

[Example] FIG. 3 is a block diagram for explaining the principle of the present invention. The NTSC composite video signal is applied to the delay means 16, and is delayed by one horizontal line period, similar to the delay means 10 in FIG. The output end of the delay means 16 is connected to a bandpass filter 18, and its connection midpoint is connected to a movable contact of a single pole double throw switch 17. The switch 17 passes the video signal to the latter stage when the movable contact is connected to the fixed contact C1 (comb filter operation mode), and when the movable contact is connected to the fixed contact C2 (band pass/notch filter operation mode).・When in filter operation mode),
Prevents the video signal from passing to the subsequent stage. switch 1
7 is on the contact C1 side, the band pass filter 18 passes the signal component near the subcarrier of about 3.58 MHz. That is, the bandpass filter 18
passes the harmonic components of the luminance signal, and
A chromaticity component signal inserted between the harmonics (that is, frequency interpolated) is also passed. A composite video signal is also applied to the input end of the transversal filter means 20. This transversal filter means 20 includes delay means 22 with taps T1 to Tn.
and addition/subtraction means 24, and the output signals of the taps T1 to Tn of the delay means 22 are weighted by weighting coefficients K1 to Kn, respectively.
After weighting, addition and subtraction are performed by the addition and subtraction means 24. The transversal filter means 20, as is well known, weights the signals from the plurality of taps and applies the signals to the addition/subtraction means 24.
A second output signal is generated by delaying the added and subtracted first output signal and composite video signal by a predetermined time. Note that the delay time of this second output signal is much shorter than one horizontal line period. By appropriately selecting these weighting coefficients K1 to Kn, the transversal filter means 20 is given a linear phase characteristic, and as described later, the subcarrier frequency (approximately
A first output signal that is band-passed around a frequency (3.58 MHz) can be generated. That is, the first output signal is a signal in which a luminance component and a chromaticity component near the subcarrier frequency are frequency-interpolated, but the first output signal is a signal mainly composed of the chromaticity component.

Bandpass filter 18 and transversal filter 18
The first output terminal of the filter means 20 (the addition/subtraction means 24
(output terminal) are respectively connected to the non-inverting input terminal and the inverting input terminal of the first calculation means 26, which is a subtracter. The first calculation means 26 is a means for canceling the luminance components from two input signals in the comb filter operation mode, and in FIG. 3, the phase relationship of the luminance components of the two input signals is the same. It is assumed that the phase is the same. As will be described later, if the luminance components of the two input signals have opposite phases, an adder is used as the first calculation means. First calculation means 26
applies its output signal to the output terminal A (terminal for extracting the chromaticity component signal) and to the circuitry 28. The output terminal of the circuit network 28 and the output terminal (tap Tn) of the delay means 22 are connected to the second arithmetic means 30, which is a subtracter.
are connected to the inverting input terminal and non-inverting input terminal of the inverting input terminal, respectively. The second calculation means 30 is a means for canceling the chromaticity components from the two input signals, and is based on the premise that the chromaticity components of the two input signals are in the same phase. Of course, if the chromaticity components of the two input signals have opposite phases, an adder is used as the second calculation means. The output signal of the second calculation means 30 is taken out from an output terminal B (a terminal from which a luminance component signal is taken out).

Next, a description will be given of the circuit operation when the movable contact of the switch 17 is located on the C2 side (that is, the bandpass/notch filter operation mode is suitable when the line correlation is low). In this case, no signal is applied from the bandpass filter 18 to the non-inverting input terminal of the first calculation means 26, and the addition/subtraction means 24 applies only to the inverting input terminal.
to the first of the transversal filter means 20
An output signal is applied. This first output signal is a signal mainly composed of chromaticity components band-passed around the subcarrier frequency, but also includes a luminance component whose frequency is interpolated between the chromaticity component signals. This first
Since the output signal is input to the inverting input terminal of the first calculation means 26, it is inverted and sent to the output terminal A and the circuit network 2.
8. The circuit network 28 includes the first calculation means 2
6 and, if necessary, remove components having a frequency three times the subcarrier frequency due to spurious responses of the transversal filter means 20. By appropriately selecting the delay time of the network 28, the phase of the chromatic component of the output signal of the network 28 and the chromatic component of the second output signal of the transversal filter means 20 (output of tap Tn) can be adjusted. The phases become in-phase. The second output signal of the transversal filter means 20 is substantially the same as the original composite video signal, except that the composite video signal is delayed by a predetermined period of time. This second output signal and the chromaticity component of the output signal of the circuit network 28 are canceled out by the second calculation means 30, which is a subtracter, and a luminance component signal is output from the output terminal B. This second calculation means 30
When designed so that the phase relationship between the chromaticity components of two input signals is opposite, an adder is of course used to cancel out the chromaticity components. As will be described later, since the first output signal subjected to bandpass processing by the transversal filter means 20 has excellent phase linearity, the chromaticity components are canceled out from the first output signal and the second output signal. The phase linearity of the obtained luminance component signal also becomes good.

Next, the circuit operation when the movable contact of the switch 17 is on the C1 side (that is, the comb filter operation mode suitable when the line correlation is high) will be described. In this case, the output signal of the bandpass filter 18 is delayed by one horizontal line period by the delay means 16. Furthermore, the chromaticity components of the composite video signal of the next adjacent horizontal line are in opposite phase. As a result, the output signal of the bandpass filter 18 and the first output signal of the transversal filter means 20 are signals corresponding to two horizontal lines adjacent to each other, and the luminance components of these two signals are in phase. , on the other hand, the chromaticity components are in opposite phase. Furthermore, an adjustment circuit (not shown) included in the bandpass filter 18 allows the bandpass filter 1
The luminance component and transversal of the output signal of 8.
The amplitudes of the luminance components of the first output signal of the filter means 20 are made equal. This allows the first
The calculation means 26 cancels out the luminance component and doubles the amplitude of the chromaticity component. As described above, when the luminance components of these two input signals are designed to have opposite phases, an adder is used as the first calculation means. When viewed in the frequency domain, the NTSC composite video signal includes harmonic signal components of the luminance signal at intervals of 15.734 KHz, and chromatic components are located between these luminance components, that is, at a position 7.87 KHz different from the frequency of the luminance component. A signal is inserted. Therefore, in this case, the chromaticity component signal output from output terminal A is
This results in a signal having comb-shaped frequency components as shown in FIG. 4A. The dotted line in the center of FIG. 4A indicates the position of the subcarrier frequency (3.58MHz). The frequency interval between adjacent teeth of this comb-shaped chromaticity component signal is
It is 15.734KHz. On the other hand, the second calculation means 30, which is a subtracter, uses the transversal filter means 2
The output signal of network 28 is subtracted from the second output signal of zero to cancel out the chrominance component and provide a luminance component signal to output terminal B. That is, the two signals input to the second calculation means 30 are adjusted so that the chromaticity components are in the same phase. Therefore, from output terminal B,
A comb-shaped luminance component signal as shown in FIG. 4B is obtained. The valley portion of one of the chromaticity and luminance component signals shown in FIGS. 4A and 4B corresponds exactly to the tooth portion of the other.

FIG. 5 is a circuit diagram showing one embodiment of the filter circuit of the present invention. In FIG. 5, blocks corresponding to those in FIG. 3 are given the same reference numerals. Composite video signals can be output from input terminals IN,
The signal is applied to the bandpass filter 18 via the buffer amplifier 31 and the delay means 16. The bandpass filter 18 includes an amplifier 32, a capacitor 34, a transformer 36, an operational amplifier 38, and its peripheral elements (variable inductor 4).
4, variable resistor 48, etc.). In the bandpass filter 18, the output terminal of the amplifier 32 is connected to one terminal of the transformer 36 via the capacitor 34, and the amplifier 32 provides the transformer 36 with a low source impedance. The other terminal of the transformer 36 is connected to one terminal of each of a capacitor 42 , a variable inductor 44 , and a resistor 46 via a resistor 40 . The other terminals of the capacitor 42 and the variable inductor 44 are connected to the non-inverting input terminal of the operational amplifier 38 and grounded via the variable resistor 48, and the other terminal of the resistor 46 is connected to the inverting input terminal of the operational amplifier 38. connected to the end. The output terminal of the operational amplifier 38 is connected to the inverting input terminal via a feedback resistor 50. The variable inductor 44 is
The variable resistor 48 is for adjusting the phase of the output signal of the band pass filter 18.
Transversal filter means 2
This is for group delay adjustment to match the delay time of the first output signal of 0. The output signal of the bandpass filter 18 is supplied to the inverting input terminal of the first arithmetic means 26, which is an operational amplifier, after appropriately adjusting the phase and delay time, and forms part of the transversal filter means 20. It is added to the first output signal from the addition/subtraction means 24. That is, the first calculation means 26 constitutes an adder together with resistors 80, 82, and 84. Note that while the first calculation means 26 in the case of FIG. 3 is a subtracter, the first calculation means 26 in FIG.
The reason why an adder is used as the calculation means 26 is as follows.
The design is such that when the output signal of the bandpass filter 18 and the first output signal of the transversal filter means 20 are compared, the luminance component signal is in opposite phase and the chrominance component signal is in the same phase. By adjusting the variable resistor 82, the amplitudes of the luminance components of opposite phases that are canceled by addition are equalized. As described above, it should be noted that in the case of FIG. 5, the phase relationship between the chromaticity component and the luminance component of the two signals input to the first calculation means 26 is different from the case of FIG. 3.

The transversal filter means 20 includes delay means 52 and 54 such as delay lines having a delay time of 140 ns, which is much shorter than one horizontal line period, an addition/subtraction means 24 which is an operational amplifier, an operational amplifier 56,
It includes a buffer amplifier 58, resistors 60 and 62, and the like. The connection midpoint of the input side of the resistor 60 and the delay means 52 is connected to the output end of the buffer amplifier 31. The composite video signal is applied to the inverting input of the adding/subtracting means 24 via a resistor 60. Since the half period of the subcarrier frequency is approximately 140 ns, the delay means 5
It should be noted that when a subcarrier frequency signal is input to 2 and 54, the phase of the output signal differs by 180 degrees from the input signal and becomes an opposite phase. Operational amplifier 56 and resistors 62 and 64 constitute an inverting amplifier 66. The output terminal of the inverting amplifier 66 is connected to the inverting input terminal of the adding/subtracting means 24 via a variable resistor 68. When the slider of the variable resistor 68 is placed in the center position, the variable resistor 68 and the resistor 60 have substantially equal resistance values. Inverting amplifier 66
The output of is further applied to the delay means 54,
Delayed by 140ns. The output of the delay means 54 is
The voltage is applied via the buffer amplifier 58 to the other end of the variable resistor 74 whose one end is grounded.
The output signal of 4 is applied to the non-inverting input terminal of the addition/subtraction means 24. Resistor 76 is a feedback resistor for addition/subtraction means 24 . The delay means 52 and 54
Corresponding to the delay means 22 with taps in the figure, the weighting factors of the taps are determined by resistors 60 and 76, variable resistors 68 and 74, and inverting amplifier 66.

The operation of the transversal filter means 20 will be explained. In order to analyze the phase characteristics of this filter means 20, it is convenient to use the so-called T-pulse signal shown in FIG. 6a. Figures 6a to 6d
Each waveform in the figure shows the waveform at the positions a to d circled in FIG. 5 when the T pulse signal is applied to the transversal filter means 20. The T pulse of FIG. 6a applied to point a of FIG. 5 is delayed by 140 ns by the delay means 52 and inverted by the inverting amplifier 66 (FIG. 6b). The outputs of the inverting amplifier 66 are added at the connection point between the resistor 60 and the variable resistor 68, and are input to the inverting input terminal of the adding/subtracting means 24. The output of the inverting amplifier 66 is further
It is delayed by 140 ns by the delay means 54 (Fig. 6c),
The signal is inputted to the non-inverting input terminal of the adding/subtracting means 24 via the buffer amplifier 58 and the variable resistor 74. As a result, the signal obtained by adding the signal in FIG. 6a and the signal in FIG. 6b is subtracted from the signal in FIG. 6c, and the signal in FIG.
The signal shown in the figure is generated at the output end of the addition/subtraction means 24 at point d. The waveform in FIG. 6d is symmetrical,
This shows that the linearity of the phase characteristics of the transversal filter means is good.

Returning again to FIG. 5, first, a case will be described in which a signal at a subcarrier frequency (3.579545 MHz to be exact) is applied to the transversal filter means 24. As mentioned above, this subcarrier frequency signal undergoes a phase inversion each time it passes through the delay means 52 and 54. Transversal filter means 20
Assume that the relative amplitude of the input signal is 1 at the input end of . This input signal is phase-inverted by the delay means 52 and further phase-inverted by the inverting amplifier 66, so that the phase of the output signal of the inverting amplifier 66 is in phase with the phase of the input signal, and its relative amplitude is 1. ing. The input signal and the output signal of the inverting amplifier 66 are added via the resistor 60 and the variable resistor 68, respectively, and the relative amplitude 2/
It is supplied as a signal of 3. In addition, the inverting amplifier 6
The output signal of No. 6 is further phase-inverted by the delay means 54, and sent to the non-inverting input terminal of the addition/subtraction means 24 via the buffer amplifier 58 and the variable resistor 74 with a relative amplitude of −1/3.
(The negative sign indicates the opposite phase).
As a result, the output signal of the adding/subtracting means 24 is -1/3-2/3=-1 because the signal at the inverting input terminal is subtracted from the signal at the non-inverting input terminal, and the absolute value with respect to the input signal is The result is a signal whose phase is equally inverted.
The above is the response to the subcarrier frequency signal, and this transversal filter means 20
the first output signal (output signal of the addition/subtraction means 24)
becomes a signal that is band-passed around the subcarrier frequency and whose phase is inverted with respect to the input signal. That is, when a composite video signal is input, the first output signal of the transversal filter means 20 shown in FIG. The phase is opposite to that of the composite video signal. Please note that this phase is different from that of the embodiment shown in FIG. On the other hand, switch 17 is C1
side, the output signal of the bandpass filter 18 is 1
Due to the delay in the horizontal line period, the luminance component is in the same phase as the composite video signal of the adjacent line, and only the chromaticity component is in the opposite phase. Therefore, in FIG. 5, when the output signal of the bandpass filter 18 and the first output signal of the transversal filter means 20 are compared, the luminance component is in opposite phase and the chromaticity component is in the same phase, so both signals are By adding , the luminance component is canceled out, and a chromaticity component signal with the luminance component removed can be obtained in a comb shape as shown in FIG. 4A. Further, when the switch 17 is on the C2 side, the first output signal of the transversal filter means 20 is output as it is as a band-passed chromaticity component signal. In the case of FIG. 3, a subtracter was used as the first calculation means 26, but in short, depending on the phase relationship between the luminance component and the chromaticity component of the two signals input to the first calculation means, Either an adder or a subtracter may be used to cancel out the luminance components.

The equalizer 88 compensates for the phase and group delay of the luminance component signal, and includes an operational amplifier 86, a resistor 90 connected to its inverting input terminal, and a resistor 90 connected between its non-inverting input terminal and ground. Variable resistor 92, its non-inverting input terminal and operational amplifier 2
6, and a capacitor 96 connected in parallel to the variable inductor 94. Variable resistor 92 and variable inductor 94 are adjusted to have the proper phase and group delay when the chrominance component signals are applied to operational amplifier 30. A bandpass filter 98 consisting of a capacitor 100 and a variable inductor 102 connected in series reduces the output of the equalizer 88 to 3.58M.
Pass the band with Hz as the center frequency. Furthermore, a capacitor 104 and an inductor 1 are connected in series.
06 is for reducing the frequency of the spurious response of the transversal filter means 20 (10.7 MHz: a frequency three times the subcarrier frequency). Variable inductor 102 and inductor 106
The connection point of is grounded via a resistor 103.

The second calculation means 30, which is an operational amplifier, constitutes a subtracter together with associated resistors 108-114. That is, when the second output signal of the transversal filter means 20 outputted from the buffer amplifier 58 is compared with the output signal of the equalizer 88, it is found that the chromaticity component signals of both signals are adjusted to be in the same phase. Therefore, by subtracting both signals, the chromaticity component is canceled out, and a luminance component signal is output. Of course, when the chromaticity components to be canceled are designed to have opposite phases, an adder is used as the second calculation means 30. As mentioned above, when the switch position of the switch 17 is C1 (comb filter operation mode), the signals output from the output terminals A and B are as follows.
They are a comb-shaped chromaticity component signal and a luminance component signal, respectively, and when the switch position of switch 17 is C2 (bandpass/notch filter operation mode), the signals output from output terminals A and B are subcarrier signals, respectively. A chromaticity component signal is band-passed around the frequency, and a luminance component signal is obtained by removing components near the subcarrier frequency by a notch filter.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described herein, and various modifications and changes can be made as necessary without departing from the gist of the present invention. It is clear to those skilled in the art that this can be done.

[Effects of the Invention] According to the present invention, the chromaticity component signal and the Since the luminance component signal is obtained, when switching between the two operation modes, it is possible to eliminate the effects of changes in the bandwidth of each output signal, changes in the delay time of the luminance component signal, etc. Furthermore, by using transversal filter means, conventional bandpass/
The circuit configuration can be made simpler than when both a notch filter and a comb filter are used selectively.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional bandpass/notch filter, FIG. 2 is a block diagram of a conventional comb filter, and FIG. 3 is a block diagram for explaining the principle of a filter circuit according to the present invention. Figure 4 is
5 is a circuit diagram of one embodiment of the present invention, and FIG. 6 is a waveform diagram for explaining the operation of the transversal filter means. 16: Delay means, 17: Switch means, 18:
Bandpass filter, 20: transversal filter means, 26: first calculation means, 30: second calculation means.

Claims (1)

[Claims] 1. A series circuit to which a composite video signal is applied, which has a delay means for delaying the composite video signal by a time corresponding to one horizontal line, and a bandpass filter connected to the output terminal of the delay means. , a switch means for selectively generating an output signal in the series circuit; and a first output signal that receives the composite video signal and is band-passed around the subcarrier frequency, and a second output signal that delays the composite video signal by a predetermined time. transversal filter means for generating an output signal; and when the switch means generates the output signal of the series circuit, it receives the output signal and the first output signal and cancels the luminance components of both signals to produce a color. a first calculation means that receives the first output signal and outputs only the first output signal when the switch means blocks generation of the output signal of the series circuit; 2 output signal and the output signal of the first calculation means, a second calculation means for canceling the chromaticity components of these two signals and outputting only the luminance component.