JPH06335021A - Chrominance subcarrier elimination circuit - Google Patents

Abstract

PURPOSE:To eliminate a chrominance carrier component included in a composite video signal fed to a trap circuit by making a center frequency of a trap charac teristic match with a chrominance subcarrier frequency. CONSTITUTION:A phase adjustment means 50 receives a reference signal and a low pass component for a blanking period and gives a phase difference signal having phase difference information of two signals to a trap circuit 44 via a signal feeding line 54. When the information is positive, mutual conductance of 1st and 2nd gm amplifiers 45, 46 is increased and when negative, the mutual conductance is decreased. A phase difference between a reference signal and a low pass characteristic signal is -90 deg.. That is, an interrupt frequency of the low pass characteristic signal being the output of the amplifier 45 and a center frequency of the trap characteristic signal being the output of the amplifier 46 are made match with the chrominance subcarrier frequency. Furthermore, a switch 52 is turned off for a video period and the result of multiplication with the low pass component of a composite color video signal is not fed to the amplifiers 45, 46 and a potential of a capacitor 53 is used as a control signal and given to the amplifiers 45, 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for removing a color subcarrier from a composite video signal, and more particularly to an NTSC (Nation)
al Television System Committee) color television receivers, video tape recorders (VTRs), and other devices that process video signals, and the color sub-carriers included in the composite video signals supplied to this device. The present invention relates to a circuit for removing a luminance signal.

[0002]

2. Description of the Related Art A composite video signal is a burst signal and a luminance signal (0 to 4.2) together with a horizontal synchronizing signal and a vertical synchronizing signal.
MHz) and color subcarrier signals, etc., and since these various signals are included, a color television or V
The signal used in TR is also called a composite video signal. Of the signals included in the composite video signal, the color subcarrier signal is used to superimpose and transmit a color signal on a monochrome (monochrome) television signal.
In the SC system, the frequency of this color subcarrier is 3.57.
It is set to 9545 MHz. The reproduction of the color signal from the composite color video signal of the NTSC system is performed as follows. First, the luminance signal is extracted from the composite color video signal by passing it through a 3.58 MHz removal trap, and separately from this, from the high frequency components of the composite color video signal, 3.
The color subcarrier is extracted by a band filter of 58 MHz ± 0.5 MHz. From the color subcarrier, a carrier color signal is taken out by an amplification stage that is cut off only during a color blanking period including a horizontal back porch period. Separately from this, a burst signal is extracted from the color subcarrier by an amplification stage that conducts only during the horizontal back porch period. Since the composite video signal is processed by the basic operation described above, the chrominance subcarrier signal and the luminance signal may exist in the same frequency band, and when the 3.58 MHz removal trap is applied, the luminance signal At the same time, a part of the color subcarrier signal may be extracted. In this case, dot noise appears on the screen of the reproduced image, making it difficult to see the screen. Therefore, it is necessary to remove the color subcarrier signal contained in the luminance signal extracted from the composite color video signal.

Conventionally, various methods have been proposed to remove the color subcarrier signal. The first color subcarrier removing circuit is a trap circuit composed of an inductor and a capacitor, and is shown in FIG. In FIG. 5, the color subcarrier removing circuit 1 includes an input terminal 2 for inputting a composite color video signal, an output terminal 3 for outputting a luminance signal from which a color subcarrier is removed, an input terminal 2 and an output terminal 3. An inductor 4 connected in between, a capacitor 5 connected in parallel with the inductor 4, a connection point between the capacitor 5 and the inductor 4, a connection point between the output terminal 3 and a ground potential. It is composed of a damping resistor 6. The first color subcarrier removing circuit 1 includes an inductor 4
The frequency of the color subcarrier (3.57
9545 MHz), and determines the center frequency that resonates at at least 15 MHz by the resistance component of the damping resistor 6.
The color subcarrier is removed by attenuating it in the range of -20 dB. Since this first color subcarrier removing circuit 1 uses an inductor, a capacitor, a resistor, etc., it is easily affected by temperature changes, and its accuracy is not reliable, and it also changes over time due to long-term use. There is a problem in that the resonance points are displaced and the center frequencies cannot be correctly matched. In addition, the inductor is an integrated circuit for video signal processing (hereinafter referred to as IC-Integr
ated Circuit. ) Had the problem that it could not be built into.

The second color subcarrier removing circuit is shown in FIG. 6 and is a so-called comb filter. The second color subcarrier removing circuit 7 is composed of a charge coupled device (CCD-Charge Coupled Device) delay device, a glass delay line or the like and delays the input composite color video signal by one horizontal scanning period (1H). The delay means 8 and the addition means 9 for adding the 1H delay output by the delay means to the composite color video signal input from the input terminal 2 are provided. Examples of the 1H delay line include the CCD delay line used in a signal processing device that detects the correlation of color in the vertical direction and adaptively switches the operating characteristics of the filter, the glass delay line also called an ultrasonic delay line, and the like. . This second color subcarrier removing circuit has a problem that the CCD delay element and the glass delay element cannot be built in the IC for video signal processing.

The third color subcarrier removing circuit is shown in FIG. 7, and is a so-called biquad system trap circuit. This third color subcarrier removal circuit 10
Is a band elimination filter (BEF-B) that outputs a luminance signal by eliminating a component or signal in the band of ± 0.5 MHz of the frequency of the color subcarrier (3.579545 MHz).
and Elimination Filter) 11, a controller 12 for adjusting a transconductance (hereinafter, referred to as gm if necessary) of a current output type amplifier used for a band elimination filter and outputting a control signal to the band filter 11, It is composed of a variable resistor 13 for adjusting the input / output of the controller 12, and an input terminal 14 for supplying a reference bias signal to the variable resistor 13. One end of the variable resistor 13 is connected to the input terminal 14, while the other end is connected to the ground potential.

The current output type amplifier has at least two input terminals and one output terminal, and an output current (io) proportional to an input voltage (vi) applied between one and the other of the input terminals. ) Is output from the output terminal, and a change amount of the output current (io) with respect to the change of the input voltage (vi) is called a transconductance (gm), and has a relation of “gm = io / vi”. This third color subcarrier removing circuit is provided with a variable resistor 13 which is an external component.
Since the input and output of the controller 12 is adjusted using
There is a problem in that the adjustment of the center frequency is required to be the same as the frequency of the color subcarrier, and this adjustment is complicated.

Therefore, a fourth conventional example has been proposed to compensate for the problems of the first to third color subcarrier removing circuits. The fourth color subcarrier removal circuit is shown in FIG. In FIG. 8, a color subcarrier removing circuit 15 includes a trap circuit 16 that inputs a composite video signal, removes a color subcarrier and outputs a luminance signal, and a center frequency control circuit that supplies a control signal to the trap circuit 16. 21 and more. The trap circuit 16 includes a first gm amplifier 17 and a second gm amplifier 17.
Gm amplifier 18, a first capacitor 19, and a second capacitor 20. The center frequency control circuit 21 provides an input terminal 22 for inputting a reference signal having the same frequency fs as the burst signal, and gives different phase changes to the reference signal input from the input terminal 22, and cuts off the phase. First and second low-pass filters 23 and 30 whose frequencies match the center frequency of the trap circuit 16 are provided. The first low-pass filter 23 includes a third and a fourth gm amplifiers 24 and 25 and a third and a fourth capacitor.
It is composed of 26 and 27. 4th gm amplifier 25
Is also one of the differential inputs of the third gm amplifier 24 and is also supplied to the multiplier 28, which multiplies the reference signal by the output of the fourth gm amplifier 25. . The second low-pass filter 30 has a fifth gm and a sixth gm.
Amplifiers 31 and 32 and fifth and sixth capacitors 33 and 34
And are equipped with. The output of the sixth gm amplifier 32 is supplied as one of the differential inputs of the fifth gm amplifier 31 and is also supplied to the multiplier 35. The multiplier 35 supplies the reference signal and the sixth gm amplifier. It is multiplied with the output of amplifier 32. The outputs of the first and second low-pass filters 23 and 30 are multiplied by the multipliers 28 and 35, respectively, and after the ripple component is removed by the capacitor 36, they are supplied to the transconductance adjusting circuit 37. The transconductance adjusting circuit 37 detects a phase error of the outputs of the first and second low pass filters 23 and 30 with respect to the reference signal, and outputs a correction signal for correcting this error. The correction signal output by the transconductance adjusting circuit 37 is the center frequency control circuit 21.
Third to sixth gm amplifiers 24, 25, 31 provided on the side
And 32, and also to the first and second gm amplifiers 17 and 18 provided in the trap circuit 16. As a result, the trap circuit 16 constituted by the gm amplifiers 17 and 18 can favorably remove the color subcarrier contained in the input composite video signal.

[0008]

However, even with the color subcarrier removing circuit according to the fourth conventional example described above,
There were the following problems. As shown in FIG. 8, the circuit according to the fourth conventional example has a large number of gm in addition to the trap circuit.
It is necessary to provide a center frequency control circuit having a complicated structure including an amplifier, which causes an increase in manufacturing cost due to an increase in the number of circuits. Further, an error occurs in the circuit constant between the trap circuit and the center frequency control circuit for adjusting the trap circuit, and this error causes an error between the center frequency of the trap circuit and the frequency of the color subcarrier, There is also a problem that a high color subcarrier removal rate cannot be obtained.

Therefore, an object of the present invention is to provide a color subcarrier removing circuit which can be incorporated in a video signal processing IC without using external individual circuit parts or a center frequency control circuit having a complicated structure. It is in.

[0010]

In order to solve the above problems, a color subcarrier removing circuit according to the present invention removes a color subcarrier signal from a composite video signal including a burst signal, a luminance signal and a color subcarrier signal. In the circuit for extracting the luminance signal by selecting the composite video signal from the reference signal having the same frequency as the color subcarrier signal and the composite video signal, the composite video signal is selected during the blanking period and the reference signal is selected during the blanking period. A signal switching means for selecting and outputting, and two output signals having a filtering (low-pass) characteristic and a filtering (trap) characteristic, respectively, using the output of the signal switching means as an input signal, and at the same time, the cut-off frequency of the filtering characteristic and the removal are removed. The defocusing means for matching the center frequency of the wave characteristic and the phase difference between the reference signal and the output signal having the filtering characteristic in the debanding means are detected and the frequency difference is detected. And a, a phase adjusting means for supplying to said reject means as a signal for adjusting the characteristics.

[0011]

With the above construction, the output signal having the wave-removing (trap) characteristic in the wave-removing means is output from the output terminal as a luminance signal and is used for the subsequent video signal reproduction processing. The signal switching means switches the signal path so that a reference signal having the same frequency as the burst signal is supplied to the trap circuit as the wave removing means during a blanking period that does not affect the video signal. The trap circuit is composed of, for example, a two-stage gm amplifier, and the phase adjusting means extracts a low-pass (low-pass) signal having a low-pass characteristic output from the first gm amplifier. The phase adjusting means is composed of, for example, a multiplier, a switch, a smoothing capacitor and the like, and the multiplier multiplies the low pass signal and the reference signal. The phase-detected output is passed through a switch that is closed only during the blanking period during which a low-pass signal is output, and is converted to a direct current by a smoothing capacitor, and then the first and second gm of the trap circuit are used. It is supplied to the amplifier to control these. By controlling the transconductance of the gm amplifier using such a DC-converted phase detection output, the amount of phase shift of the low-pass signal is always adjusted to -90 degrees with respect to the input signal, and the center frequency of the trap characteristics is adjusted. Corresponds to the frequency of the input reference signal, that is, the color subcarrier frequency. As a result, the color subcarrier component contained in the composite video signal supplied to the trap circuit is satisfactorily removed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a color subcarrier removing circuit according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the basic concept of the present invention. In the figure, the color subcarrier removing circuit 40 is
A first input terminal 41 for inputting a composite color video signal, a second input terminal 42 for inputting a reference signal having the same frequency as the burst signal, and an input from the first terminal 41 during the video period A signal switching means 43 for switching the two signals so as to receive the reference signal inputted from the second terminal 42 during the blanking period by taking in the composite color video signal, and a trap circuit composed of, for example, a gm amplifier or the like. The wave means 44 and the low-pass (low-pass) signal detected by the wave removing means 44 are taken into the blanking period and multiplied by the reference signal to detect a predetermined phase difference, and the wave removing means 44 mutually Phase adjusting means 50 for controlling the conductance or capacitance, and the wave removing means 44
It is composed of an output terminal 55 for outputting the luminance signal taken out by removing the color subcarrier.

Next, the circuit according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 showing the basic concept of the present invention.
Does not show the detailed construction of the wave removing means 44 and the phase adjusting means 50, but FIG. 2 shows the detailed construction of these circuits. The wave removing means is composed of a so-called biquad type trap circuit 44. This trap circuit 44 uses the output of the signal switching means 43 as one differential input to the first gm.
An amplifier 45, a second gm amplifier 46 having the output of the first gm amplifier 45 as one differential input, and a first and a second gm amplifier 46.
a first capacitor 47 interposed between a connection point between the m-amplifiers 45 and 46 and the ground potential, and the first gm amplifier 45.
A second capacitor 48 inserted in the branch output line of the second gm amplifier 46 which is fed back to the one differential input of
It is composed of The branch output of the second gm amplifier 46 is fed back as the other differential input of the first and second gm amplifiers 45 and 46. The phase adjusting means 50 inputs the potential of the connection point between the first capacitor 47 and the second gm amplifier 46, and applies this connection point potential to the reference signal input from the second input terminal 42. The multiplier 51 to be multiplied, the switch 52 for turning on / off the output of the multiplier 51 in synchronization with the signal switching operation of the signal switching means 43, and the output of the multiplier 51 when the switch 52 is closed. It is composed of a smoothing capacitor 53 for removing the ripple component.

The operation of the color subcarrier removing circuit according to the first embodiment having the above configuration will be described. In FIG.
The composite video signal is input from the first input terminal 41, and is supplied to the trap circuit 44 during the video period because the movable contact of the signal switching means 43 closes the circuit on the terminal 41 side. On the other hand, the reference signal is input through the second input terminal 42 and branched by the branch terminal, one of which is the signal switching means.
While being supplied to 43, the other is supplied to the phase adjusting means 50. The signal switching means 43 switches the movable contact so as to supply the composite color video signal input from the terminal 41 to the trap circuit 44 during the video period as described above, and is input through the terminal 42 during the blanking period. The movable contact is switched so as to supply the reference signal to the trap circuit 44. The trap circuit 44 outputs the low-pass component of the reference signal and the multiplier 51 of the phase adjusting means 50 via the signal supply line 49.
Supply to. The phase adjusting means 50 receives the reference signal and the low-pass component of the reference signal (reference low-pass signal) in the blanking period and outputs a signal (phase difference signal) having phase difference information of these two signals via the signal supply line 54. Is supplied to the trap circuit 44.

In the trap circuit 44, the mutual conductance gm1 of the first and second gm amplifiers 45 and 46 is
And gm2 and the capacitance values c ₁ and c _{2 of} the first and second capacitors 47 and 48, the luminance signal which is the output of the trap circuit 44 and the low-pass characteristic which is the output of the first gm amplifier 45. The transfer functions f _t1 and f _t2 of and are obtained by equations (1) and (2), respectively.

[0017]

[Equation 1] If the reference signal input to the trap circuit 44 during the blanking period can be expressed as sin ωt, and the low-pass characteristic output of the first gm amplifier 45 can be expressed as Asin (ωt−θ), these two signals can be input. The output of the multiplier 51 of the phase adjusting means 50 has the relationship as shown in equation (3).

[0018]

[Equation 2] During the blanking period, since the switch 52 of the phase adjusting means 50 is closed, the output of the multiplier 51 is the signal supply line.
It is supplied to the 54 side. At this time, since the capacitor 53 removes the ripple component, the AC component “A / 2cos (2
ωt−θ) ”is attenuated and only the direct current component“ A / 2cos θ ”remains, and this direct current component is the first and second gm amplifiers 45.
And 46 as control signals.

The control signal supplied to the trap circuit 44 via the signal supply line 54 is controlled so as to increase the transconductance of the first and second gm amplifiers 45 and 46 when it is positive, and is negative when it is negative. Control to lower the mutual conductance of the amplifiers 45 and 46, and finally "A / 2.cos"
“θ” converges to “0”. At this time, the phase difference between the reference signal and the low-pass characteristic signal is −90 degrees. That is, the first
The cutoff frequency of the low-pass characteristic signal that is the output of the gm amplifier 45 and the center frequency of the trap characteristic signal that is the output of the second gm amplifier 46 match the frequency of the color subcarrier.

The switch 52 of the phase adjusting means 50 is opened during the video period, and the result of multiplication with the low-pass component of the composite color video signal cannot be supplied to the first and second gm amplifiers 45 and 46. Absent. During this video period, the potential stored in the capacitor 53 is given to the trap circuit 44 as a control signal for the first and second gm amplifiers 45 and 46. The capacitor 53 can be incorporated in an integrated circuit device for video signal processing by using the technique described in "Detection circuit" disclosed in Japanese Patent Laid-Open No. 2-145003.

Next, a color subcarrier removing circuit according to the second embodiment of the present invention will be described with reference to FIG. The circuit shown in FIG. 3 is different from the circuit shown in FIG. 2 in that the trap circuit 44
The output side of the second gm amplifier 46 and the output terminal 55 of the luminance signal
And a buffer 60 provided between the first and second embodiments and a reference signal which is limited to a predetermined condition in the first embodiment, and is not particularly limited. Since there is no particular difference from the first embodiment of FIG. 1, its detailed description is omitted. This buffer 60 has a sufficiently high input impedance and a voltage amplification factor of "1".
Therefore, the frequency characteristic of the trap circuit 44 is prevented from becoming unstable. The frequency characteristic of the trap circuit 44 becomes unstable because the input impedance of the differential input of one of the first and second gm amplifiers 45 and 46 and the luminance to which the output signal of the color subcarrier removing circuit is supplied. This is due to the influence of the input impedance of the signal processing circuit. Further, in the first and second embodiments, the concrete circuit configuration of the phase adjusting means 50 can be implemented by a circuit having the same or corresponding configuration as that of the first embodiment shown in FIG. Detailed description of the configuration and operation will be omitted.

Finally, a color subcarrier removing circuit according to the third embodiment of the present invention will be described with reference to FIG. In both the first and second embodiments, the phase adjusting means 50 is used.
The control signal generated by the above is configured to control the transconductance of the first and second gm amplifiers that form the trap circuit as the wave removing means. However, the present invention is not limited to this, and the transfer function is The capacitance value as another component to be determined may be configured to be controlled by the control signal. In FIG. 4, the phase adjusting means 50 has the same configuration as that of FIG. 2 showing the first embodiment, and the control signal supplied to the trap circuit 64 via the signal supply line 54 is the first and second control signals. It controls capacitors 67 and 68.
The configuration in which the trap circuit 64 includes the first and second gm amplifiers 65 and 66 is the same as that of the trap circuit 44 of the first embodiment shown in FIG. The first and second capacitors 67 and 68
For example, a circuit having any configuration may be used as long as it is a capacitance varying means such as a reverse bias diode and a varicap. The circuit for controlling the capacitance value, which is the method of the third embodiment, is more difficult to implement than the embodiment for controlling the transconductance, which is another factor of the transfer function, but it is theoretically sufficient. Are included in the technical idea of the present invention.

[0023]

As described in detail above, according to the color subcarrier removing circuit of the present invention, the color subcarrier signal is removed from the composite video signal including the burst signal, the luminance signal and the color subcarrier signal. The color subcarrier removing circuit for extracting the luminance signal selects the composite video signal from the reference signal having the same frequency as the color subcarrier signal and the front and rear composite video signals within the video period, and within the blanking period. A signal switching means for selecting and outputting the reference signal from the two signals, and two output signals having a filtering (low-pass) characteristic and a wave removing (trap) characteristic with the output of the signal switching means as an input signal. Rejecting means for outputting the respective signals and matching the cut-off frequency of the filtering characteristics with the center frequency of the removing characteristics, and an output signal having the filtering characteristics of the reference signal and the removing means. And a phase adjusting means for supplying the signal to the wave removing means as a signal for adjusting the frequency characteristic of the phase difference detecting means and the phase adjusting means for adjusting the transfer function factor. It becomes possible to do. This makes it possible to reduce the circuit scale as a whole and to eliminate the error or inconsistency between the center frequency and the frequency of the color subcarrier caused by the error of the circuit constant of the wave removing means, thereby achieving a good color subcarrier removal rate. A achievable circuit can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic concept of a color subcarrier removing circuit according to the present invention.

FIG. 2 is a circuit diagram showing a specific circuit of a color subcarrier removing circuit according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a color subcarrier removing circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a specific circuit of a color subcarrier removing circuit according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a first example of a conventional color subcarrier removing circuit.

FIG. 6 is a circuit diagram showing a second example of a conventional color subcarrier removing circuit.

FIG. 7 is a circuit diagram showing a third example of a conventional color subcarrier removing circuit.

FIG. 8 is a circuit diagram showing a fourth example of a conventional color subcarrier removing circuit.

[Explanation of symbols]

 43 Signal switching means 44 Rejection means (trap circuit) 45 First gm amplifier 46 Second gm amplifier 47 First capacitor 48 Second capacitor 50 Phase adjusting means 51 Multiplier 52 Switch 53 Smoothing capacitor 64 Rejection Means (trap circuit) 65 First gm amplifier 66 Second gm amplifier 67 First capacitor 68 Second capacitor

Claims (3)

[Claims] 1. A chrominance subcarrier removing circuit for removing a chrominance subcarrier signal from a composite video signal including a burst signal, a luminance signal and a chrominance subcarrier signal to extract a luminance signal. A signal switch for selecting a composite video signal from a composite video signal and a reference signal having the same frequency as the color subcarrier signal, and selecting and outputting a composite reference signal from the two signals during a blanking period. Means for outputting the two output signals having the filtering characteristic and the filtering characteristic using the output of the signal switching means as an input signal and for making the cutoff frequency of the filtering characteristic and the center frequency of the filtering characteristic coincide with each other. Means for detecting the phase difference between the reference signal and the output signal having the filtering characteristic in the wave removing means, and supplying this to the wave removing means as a signal for adjusting the frequency characteristic. Color characterized by comprising an adjustment means, a sub-carrier removal circuit. 2. The wave removing means comprises first and second transconductance amplifiers for filtering the composite video signal or the reference signal, and first and second capacitors provided on the output sides of these transconductance amplifiers, respectively. The color subcarrier removing circuit according to claim 1, further comprising: 3. The phase adjusting means comprises a first capacitor and a second capacitor.
A multiplier for multiplying the low-pass signal between the transconductance amplifier and the reference signal and outputting a control signal containing an AC component and a DC component, and the reference signal is supplied in synchronization with the signal switching means. 3. The color subcarrier removing circuit according to claim 2, further comprising: a switch that allows the control signal to be supplied only during a blanking period and a capacitor that removes an AC component included in the control signal. .