JPS62274896A - Secondary beat cancel circuit - Google Patents

Abstract

PURPOSE:To cancel a secondary beat component over a wide range in a vertical non-correlation interval by supplying the secondary beat component and a non- correlation luminance signal outputted from a subtraction circuit to a limiter amplifier through a differentiation circuit. CONSTITUTION:In the subtraction circuit 3, a reproducing luminance signal before one horizontal period is subtracted from a present reproducing luminance signal, thereby, the secondary beat component and the non-correlation luminance signal included in the reproducing luminance signal are detected and outputted. The output of the subtraction circuit 3 is supplied to the differentiation circuit 4, the direct current component of the non-correlation luminance signal is substantially removed, the non-correlation luminance signal and the secondary beat component having only an edge part and a form of a differential pulse are supplied to the limiter amplifier 5 and the peak level of the non-correlation signal of the differential pulse form is regulated and the secondary beat component presenting except the edge part is amplified in a linear range. Thereby, the secondary beat component can be cancelled completely even in the vertical non-correlation interval.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention provides two suitable methods for application to a VTR that records a low frequency converted carrier color signal together with a luminance signal. This relates to a next beat cancellation circuit.

[Summary of the invention]

This invention is a secondary beam I-cancellation circuit used for V""R, etc., which records a low-pass converted carrier color signal together with a luminance signal. is supplied to the cane control circuit via a differentiating circuit and a limiter amplifier, and in an interval where a non-correlated color signal is detected from the envelope detection output of the carrier color signal, for example, compared to an interval where no uncorrelated color signal is detected, Limiter with 6dB level increased by -l
The output of the amplifier is supplied to a switch circuit, and when a chrominance signal is present, the differentiated uncorrelated luminance signal and the secondary beat component are supplied to a half-wave correlator, and when a chrominance signal is not present, a mute signal is supplied. By doing this, the output of only the second-order beat component is obtained from the half-wavelength correlator, without deteriorating the edge part of the reproduced luminance signal, and even in the vertical uncorrelation section, the second-order beat component is sufficiently suppressed. The beat component can be canceled to prevent deterioration of the 1iIiii quality.

[Conventional technology]

In a VTR that records a low-frequency converted carrier color signal together with a luminance signal, the tape/rotating magnetic head system has non-linear characteristics, so the secondary beat component of the low-frequency converted carrier color signal is recorded on the reproduced FM. Mixed into the modulated luminance signal.

When such a reproduced FM modulated luminance signal is demodulated, a secondary beat component centered around 2fc (fc is the low frequency conversion frequency) is also demodulated together with the reproduced luminance signal, and this secondary heat component causes the screen to change. A diagonal bead IK appears on the top, and the image quality is significantly degraded. For this reason, conventional VT
In R, a secondary beat canceling circuit for canceling secondary beat components is provided in the reproduction system.

For example, the conventional secondary beat cancellation circuit
After demodulating the modulated luminance signal, the reproduced luminance signal delayed by 1H is subtracted from the reproduced luminance signal to decode the secondary beat component contained in the reproduced luminance signal and the uncorrelated luminance signal generated during vertical uncorrelation. Detected as a correlated signal, this uncorrelated signal is supplied to a level control circuit composed of an AM modulator via a bandpass filter and a limiter.
The level of the non-correlation signal is controlled by the envelope output of the fastest color signal, and the level control is performed by subtracting the rolled non-correlation signal from the reproduced luminance signal that is fed via the delay circuit for time adjustment. Cancels the next beat component.

However, in the conventional secondary beat cancellation circuit described above, when a reproduced luminance signal without vertical correlation is supplied,
A non-correlated luminance signal is detected together with the secondary beat component and output as a non-correlated signal.

Therefore, when the uncorrelated signal including the uncorrelated luminance signal is level-controlled based on the envelope detection output of the carrier color signal and subtracted from the reproduced luminance signal, the level is reduced even at the edges of the reproduced luminance signal, and the edges are The problem arises that parts deteriorate.

As a secondary beat canceling circuit for preventing the deterioration of the edge portion that occurs during such secondary beat canceling processing, the applicant of the present application has previously proposed Japanese Patent Application No. 159461/1982 or Japanese Patent Application No. 22353/1982. The following are proposed.

This secondary beat canceling circuit is configured to prohibit the secondary beat canceling operation when there is a non-correlated luminance signal obtained in the vertical non-correlating section. This is to prevent deterioration of the edge portion of the reproduced luminance signal.

[Problem that the invention seeks to solve]

However, this secondary beat cancellation circuit prohibits the secondary beat cancellation operation in all vertical non-correlation sections, so the signal and the secondary beat components are not canceled in most sections where the secondary beat components are canceled. There is a problem in that the difference from the signal in the vertical non-correlation section becomes large, and the secondary beat component in the vertical non-correlation section is visually emphasized relatively.

In order to solve this problem, the vertical uncorrelated luminance signal is extracted, double-wave rectified, subtracted from the envelope detection output of the carrier color signal, and AM modulated based on the obtained signal. A secondary beat canceling circuit has been proposed that controls the level of a non-correlated signal by lowering the modulation degree of the section.

However, this type of secondary beat cancellation circuit suffers from problems such as excessive or insufficient cancellation due to the nonlinearity of the AM modulator, and noise due to carrier leakage when no modulation is applied, and the circuit becomes more complex. However, the canceling effect of the secondary beam I component in the vertical uncorrelation interval is insufficient.

Therefore, an object of the present invention is to cancel secondary beats that can sufficiently cancel secondary beat components even in vertical non-correlation sections without deteriorating the edge portions of reproduced luminance signals with a simple circuit configuration. The purpose is to capture the circuit. In particular, a sufficient cancellation effect can be obtained even when there is vertical correlation in luminance signals but no correlation in color signals.

[Means for solving problems]

The present invention provides a secondary beam 1-1 for removing a frequency component twice the low frequency carrier frequency of a color signal from a reproduced luminance signal.
In the 1-Yansel circuit, there is a subtraction circuit 3 that subtracts the output signal of the delay circuit 2 having a delay amount of IH or 2I+ from the reproduced luminance signal, and the output signal of the subtraction circuit 3 is and a means 11 for forming a discrimination signal corresponding to the presence or absence of a color signal from the envelope detection output of the carrier color signal, and detecting a non-correlated color signal to form a control signal corresponding to the generation section of the non-correlated color signal. 1.2.]3゜14.16, the gain controller 1 to roll circuit 6 which controls the gain of the output signal of the differentiator circuit 4 by a control signal, and the output signal of the cane controller 1-1 coil circuit 6 correspond to the discrimination signal. a switch circuit 7 for turning on/off the
2, characterized in that it comprises a delay circuit 21 for delaying the reproduced luminance signal, and a circuit 22 for adding the reproduced luminance signal passed through the delay circuit 2 and the output signal of the switch circuit 7 in opposite phases. This is the next beat cancel circuit.

[Effect]

The reproduced luminance signal is supplied to the subtraction circuit 3, and at the same time, the reproduced luminance signal is supplied to the subtraction circuit 3 via the H delay circuit 2. By subtracting , the secondary heat component included in the reproduced brightness signal and the uncorrelated brightness signal are detected and output. The output of the subtraction circuit 3 is the differential circuit 4
The DC component of the uncorrelated luminance signal is almost removed and only the edge portion is left as a differentiated pulse-like uncorrelated luminance signal and the secondary beat component is supplied to the misotor amplifier 5, which generates a differentiated pulse-like uncorrelated signal. The beam level of the signal is limited, and the secondary beam 1-component existing outside the edge portion is sufficiently amplified in a linear range and supplied to the gain control circuit 6. The gain control circuit 6 is controlled based on a control signal corresponding to the generation section of the uncorrelated color signal formed from the uncorrelated color signal detected from the enrobe detection output of the first fastest color signal, and controls the output from the limiter amplifier. For example, the level of the section where non-correlated color signal No. 3 is detected is amplified by 6 dB compared to the section where no non-correlated color signal is detected, and the level of the secondary beat component is kept constant and supplied to the switch circuit 7. The switch circuit 7 is controlled by a discrimination signal indicating the presence or absence of a color signal in synchronization with the reproduced luminance signal, and only in the section where the color signal is present, the output of the gain control circuit 6 is controlled by the λ/2 delay circuit 17.19 and the correlation signal. is supplied to a half-wavelength correlator constituted by a device 20 etc.
Muting is performed in a section where no color signal is present. In the correlator 20, the differential pulse-shaped uncorrelated luminance signal, which is only the edge portion, is removed because there is no horizontal correlation, and only the secondary heat component is supplied to the adder circuit 22 and then supplied via the delay circuit 21. By adding it to the reproduced luminance signal in reverse phase, the secondary beat component is canceled without deteriorating the edge portion of the reproduced luminance signal.

〔Example〕

a. Overall configuration of one embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, and in FIG. 1, reference numeral 1 indicates an input terminal. For example, a reproduced RF signal from a magnetic head is supplied to a bypass filter to separate a reproduced FM modulated luminance signal, and the reproduced FM modulated luminance signal is demodulated into a reproduced luminance signal. This reproduced luminance signal is supplied to the input terminal 1 as the input signal Sl.

Further, a reproduced RF signal from the magnetic head is supplied to the terminal 8.

An input signal s1 from the input terminal 1 is supplied to the IH delay circuit 2 and the delay circuit 21, and is also supplied to one input terminal of the subtraction circuit 3. In the 1H delay circuit 2, the input signal S1 is delayed by one horizontal period to form an output signal S2, and this output signal S2 is supplied to the other input terminal of the subtraction circuit 3.

In the subtraction circuit 3, the output signal S2 is subtracted from the input signal S1 to form an output signal s3.

In other words, by subtracting the reproduced luminance signal one horizontal period before from the reproduced J luminance signal, a secondary beat component included in the reproduced luminance signal and a non-correlated luminance signal are detected and output. The non-correlated luminance signal is detected and output only when there is no vertical correlation between the currently reproduced luminance signal and the reproduced luminance signal one horizontal period before. In addition, in an interval where there is a vertical correlation between the current reproduced luminance signal and the reproduced luminance signal one horizontal period before, the secondary beat component is added to approximately twice the level, and the uncorrelated luminance In the vertical uncorrelation interval in which the signal is detected, the level of either the secondary beat component included in the current reproduced luminance signal or the reproduced luminance signal one horizontal period before is determined, and the correlation interval and the vertical uncorrelated interval There is a level difference of approximately 6 dB between the two. The output signal S3 of the subtraction circuit 3 is supplied to the differentiation circuit 4.

In the differentiating circuit 4, the output signal S3 is differentiated. If there is a vertical correlation between the current reproduced luminance signal and the reproduced luminance signal one horizontal period before, and the output signal S3 is only a secondary beat component, only the secondary beat component is limintered almost unchanged. It is supplied to amplifier 5. In addition, when there is no vertical correlation and an uncorrelated luminance signal is included in the output signal S3, the uncorrelated luminance signal is differentiated, the DC component is almost removed, and a differentiated pulse-like non-correlated signal with only the edge portion is generated. The correlated luminance signal and the secondary beat component are supplied to the sharp mister amplifier 5.

The limiter amplifier 5 limits the level of input signals that are above a predetermined amplitude level, and increases the level of input signals that are below a predetermined amplitude level to generate an output signal S4. Form. In other words,
In addition to limiting the peak level of the uncorrelated luminance signal that includes only the edge portion, the secondary beat component is sufficiently amplified within a linear range. Output signal s4 of limiter amplifier 5
is supplied to the input terminal of the gain control circuit 6.

By the way, the reproduced RF signal supplied to the terminal 8 is supplied to the low-pass filter 9 to separate the low-pass converted carrier color signal, and this carrier color signal is passed through the amplifier 10 to be at a predetermined level and subjected to envelope detection. It is supplied to the circuit 11. In the envelope detection circuit 11, envelope detection of the carrier color signal is performed to form an output signal S5, and this output signal S5 is supplied to the clamp/comparison circuit]2, and also to one of the 1H delay circuit 13 and the subtraction circuit 14. is supplied to the input terminal of

In the 1H delay circuit 13, the envelope detection circuit 11
The output signal S5 from the subtraction circuit 14 is delayed by one horizontal period to form an output signal S6, which is supplied to the other input terminal of the subtraction circuit 14. In the subtraction circuit 14,
Output signal S6 is subtracted from output signal s5 to obtain output signal S
7 is formed. That is, by subtracting the envelope detection output of the carrier color signal one horizontal cycle ago from the envelope detection output of the current carrier color signal, a non-correlated color signal is detected and output. The output signal S7 of the subtraction circuit 14 is supplied to a double wave rectification circuit 15.

In the double wave rectifier circuit 15, the output signal s7 is double wave rectified, and the rectified output is supplied to the clamp/comparison circuit 16.

After the rectified output of the uncorrelated color signal is clamped and level-shifted to a predetermined level, it is compared with a reference level, and the clamp/comparison circuit 16 detects the generation section of the uncorrelated color signal to form an output signal 88. be done. For example, an output signal S8 is formed in the clamp/comparison circuit 16, which is at a high level when an uncorrelated color signal is detected, and which is at a low level when no uncorrelated color signal is detected. A signal S8 is supplied to the control terminal of the gain control circuit 6.

Further, the output signal S5 of the envelope detection output 11 supplied to the clamp/comparison circuit 12 is clamped and level-shifted to a predetermined level, and then compared with a reference level,
In the clamp/comparison circuit 12, input signals M, S 1
An output signal indicating the presence or absence of a color signal is formed in synchronization with the color signal. For example, if the envelope detection output of the clamped carrier color signal is above the reference level, it is determined that a color signal exists and is set to high level, and if it is below the reference level, it is determined that no color signal exists. is set to low level. An output signal indicating the presence or absence of a color signal is supplied as a control signal to a control terminal of a switch circuit 7, which will be described later, in synchronization with the input signal S1.

The gain control circuit 6 controls the signal level of the output signal S4 of the limiter amplifier 5 supplied to the input terminal based on the output signal of the clamp/comparison circuit I6 supplied to the control terminal. Either amplify the signal level of the section where the color signal is detected by 6 dB compared to the section where the uncorrelated color signal is not detected, or change the signal level of the section where the uncorrelated color signal is not detected to the section where the uncorrelated color signal is detected. By attenuating the signal by 6 dB, the signal level of the secondary beat component is kept constant and output.

For example, the specific configuration of the gain control circuit that keeps the signal level of the secondary beat component constant is shown in Figures 2A and 2.
Shown in Figure B. The gain control circuit as an example shown in FIG.
7 and a switch circuit 38.

The collector of the transistor 33 is connected to the power supply terminal 32, and the input terminal 31 is connected from the base of the transistor 33 to the input terminal 31.
is derived. The emitter of transistor 33 is grounded via resistors 34 and 35 connected in series. One end of a capacitor 36 is connected to the connection point between the emitter 7 of the transistor 33 and the resistor 34, and the other end of the capacitor 36 is connected to one input terminal 38a of the switch circuit 38. One end of a capacitor 37 is connected to the connection point between the resistor 34 and the resistor 35, and the other end of the capacitor 37 is connected to the switch circuit 3.
8 is connected to the other input terminal 38b.

An output terminal 4o is led out from the output terminal of the switch circuit 38. The switch circuit 38 has a control terminal 39,
For example, when the control terminal 39 is at a high level, one input terminal 38a and the output terminal are connected, and when the control terminal 39 is at a low level, the other input terminal 38b and the output terminal are connected. ing.

A limiter is connected to the input terminal indicated by 31 in Fig. 2A.
The output signal S4 of the amplifier 5 is supplied, and the output signal s8 of the clamp/comparison circuit 16 is supplied to a control terminal indicated by 39 in FIG. The emitter output of the transistor 33 is connected to the switch circuit 3 via the capacitor 36.
At the same time, the emitter output of the transistor 33 is voltage-divided by the resistors 34 and 35, and the emitter output, which has a level of 2 compared to the capacitor 36 side, is connected to the switch circuit via the capacitor 37. 3
8 is supplied to the other input terminal 38b.

When the control terminal 39 is set to a high level in a section where a non-correlated color signal is detected, one input terminal 38a and the output terminal of the switch circuit 38 are connected, and the transistor 33
The emitter output of the capacitor 36 and the switch circuit 38
It is taken out from the output terminal 40 as it is via the. In addition, when the control terminal 39 is set to a low level in an interval in which no uncorrelated color signal is detected, the other input terminal 38b and the output terminal of the switch circuit 38 are connected, and the emitter of the transistor 33 whose voltage is divided into two is connected. Output is capacitor 37
and is taken out from the output terminal 40 via the switch circuit 38.

Further, the gain control circuit as another example shown in FIG. 2B includes three NPN type L transistors 43, 48,
50, two resistors 45 and 47 having the same resistance value, a capacitor 46, and the like.

The collector of the transistor 43 is connected to the power supply terminal 42, and the input terminal 31 is connected from the base of the transistor 43 to the input terminal 31.
is derived. The emitter of the transistor 43 is the resistor 44
grounded via. One end of a resistor 45 is connected to the connection point between the emitter of the transistor 43 and the resistor 44;
The other end is connected to the base of a transistor 50 whose collector is connected to the power supply terminal 42 . The emitter of the transistor 50 is grounded via a resistor 51, and the output terminal 5 is connected to the connection point between the emitter of the transistor 50 and the resistor 51.
2 is derived. Further, a capacitor 46 and a resistor 4 are connected in series at the connection point between the resistor 45 and the transistor 50.
7 to the collector of a transistor 48 whose emitter is grounded. A control terminal 49 is led out from the base of transistor 48 .

A limiter is connected to the input terminal indicated by 41 in Fig. 2B.
When the output signal S4 of the amplifier 5 is supplied, the signal S4 shown in FIG.
An output signal S8 of the clamp/comparison circuit 16 is supplied to a control terminal indicated by 49, for example, via an inverter (not shown). The emitter output of transistor 43 is supplied to the base of transistor 50 via resistor 45,
The emitter output of transistor 50 is taken out from output terminal 52.

When the output signal S8 is set to high level in the section where the non-correlated color signal is detected and the control terminal 49 is set to low level by passing through the inverter, the transistor 4
8 is turned off, the emitter output of the transistor 43 via the resistor bC45 is directly supplied to the base of the transistor 50, and the emitter output of the transistor 50 is connected to the output terminal 5.
He is taken out from 2. In addition, in a section where no uncorrelated color signal is detected, the output signal S8 is set to a low level, and when the control terminal 49 is set to a high level by passing through an inverter, the 1-transistor 48 is turned on.
The emitter output of the Laran jitter 4 is voltage-divided into two by resistors 45 and 47, and is supplied to the bases of transistors 1 to 50. Therefore, the emitter output of the transistor 50 is 2 compared to when the transistor 48 is off, and the output terminal 52
taken from.

In the gain control circuit 6, the formed output signal S9 is supplied to one input terminal 7a of the switch circuit 7, the other input terminal 7b of which is grounded via a bypass capacitor 24. The switch circuit 7 performs a switching operation based on the output signal of the clamp/comparison circuit 12 supplied to the control terminal. For example, when the control terminal is set to a high level, one input terminal 7a and the output terminal are switched. is connected and the control terminal is set to low level, the other input terminal 7b and the output terminal are connected.

Therefore, the output signal S9 from the gain control circuit 6 is outputted via the switch circuit 7 only when a color signal is present and the output of the clamp/comparison circuit 12 is at a high level. Further, when there is no color signal and the output of the clamp/comparison circuit 12 is at a low level, the output signal S9 from the gain control circuit 6 is not output from the switch circuit 7, Output is muted to ground level. That is, in the signal section where no color signal exists, there is no secondary beat component in the input signal S1, so there is no need to extract the secondary beat component, and by muting the output of the switch circuit 7 to the ground level, Noise accompanying secondary beat extraction etc. is made substantially equal to zero.

The output signal SIO formed by the switching operation in the switching circuit 7 is supplied to a half-wave correlator.

The half-wavelength correlator is composed of, for example, a λ/2 delay circuit 17, 19, which delays the secondary beat component by a half-wave of the wavelength λ, a correlator 20, and the like.

The output signal SIO to the switch circuit 7 is supplied to the λ/2 delay circuit 17 and also to the correlator 20. λ
In the /2 delay circuit 17, an output signal delayed by λ/2 is formed, and this delayed output is sent to the λ/2 delay circuit 1.
9, and is also supplied to the correlator 20 through an inverter I8 as a negative phase output. λ/
In the 2-delay circuit 19, the delayed output from the λ/2 delay circuit 17 is further delayed by λ/2 and supplied to the correlator 20.

The correlator 20 is configured as an AND circuit, detects the horizontal correlation of each signal supplied to the correlator 20, and extracts only signals with horizontal correlation. Only the continuous secondary beat component is extracted in such a manner that the differential pulse-like non-correlated luminance signal, which is only a partial portion, is removed, and an output signal Sll is formed. For example, if the secondary beat component included in the output signal S10 is shown to the third player, the correlator 2o will have the signal shown in FIG. 3A and the inverter 18 shown in FIG. 3B.
The signal from the λ/2 delay circuit 17 supplied through the λ/2 delay circuit 17 and the signal from the λ/2 delay circuit 19 shown in FIG. is extracted and output. Therefore, the differential pulse-like non-correlated luminance signal containing only the edge portion is removed and not output because there is no horizontal correlation. The output signal Sll from the correlator 20 is supplied to one input terminal of the adder circuit 22.

The input signal s1 is supplied to the other input terminal of the addition circuit 22 via the delay circuit 21 for time adjustment, and the output signal Sll is added to the input signal s1 in the opposite phase in the addition circuit 22. As a result, the secondary beat components are uniformly canceled without deteriorating the edge portions of the reproduced luminance signal. The output of the adder circuit 22 is taken out via the output terminal 23, and a reproduced luminance signal with the secondary heat component canceled is obtained at the output terminal 23.

Details of b2 operation For example, a signal with a high brightness level and many color components in the first half of one horizontal period, a signal with a low brightness level and almost no color components in the second half, and a signal with high brightness over the entire period of one horizontal period. A signal with a low level and almost no color components is continuously reproduced by a magnetic head, and the reproduction R
A case in which the F signal is supplied to the terminal 8 and a reproduced luminance signal obtained from the reproduced RF signal is supplied to the input terminal 1 in the above-described embodiment will be described with reference to FIGS. 4A to 4K.

The gain control circuit 6 is configured to amplify the signal level of the section where the uncorrelated color signal is detected by 6 dB compared to the section where the uncorrelated color signal is not detected.
The reproduced luminance signal for 5 horizontal periods shown in the fourth doujin is supplied to the 1H delay circuit 2 and the delay circuit 2 as the input signal S1.
1 and is also supplied to one input terminal of the subtraction circuit 3. A secondary beat component exists in the signal section indicated by the O mark in FIG. 4A, and Hl, H2°H
A secondary beat component exists in the first half of the horizontal period indicated by H3 and H5.

The input signal S1 supplied to the IH delay circuit 2 is delayed by one horizontal period to form the output signal S2 shown in FIG. 4B, and this output signal S2 is supplied to the other input terminal of the subtraction circuit 3. . In the subtraction circuit 3, the output signal S2 is subtracted from the input signal S1 to form an output signal S3, not shown in FIG. 4C. As shown in Figure 4C, Hl, H4, H5
In the first half of the horizontal period indicated by H2 and H6 (indicated by a circle in the figure), the uncorrelated luminance signal and the secondary beat component are detected and output, and in the first half of the horizontal period indicated by H2 and H3. At (indicated by a mark ◎ in the figure), a secondary beat component whose level is doubled by being added is output. This output signal S3 is supplied to the differentiating circuit 4.

In the differentiating circuit 4, the output signal S3 is differentiated into Hl,
The DC component of the uncorrelated brightness signal existing in the first half of the horizontal period indicated by H4, H5, and H6 is almost removed and only the edge portion is left. ] to l-16) are supplied to the sharp misotor amplifier 5. In the Rimisoku amplifier 5, the peak level of the differential pulse-shaped non-correlated luminance signal which is limited to the edge portion is limited, and the peak level of each horizontal frequency! 1Jl (■11~I-
The secondary beat component present in the first half of T6) is sufficiently amplified in a linear range, and the output signal S (not shown in the fourth diagram) is
4 is formed. This output signal S4 is supplied to the gain controller 1 to roll circuit 6.

By the way, based on the reproduced RF signal supplied to the terminal 8, the carrier color signal that has been low-pass converted is subjected to enrobe detection in synchronization with the input signal S1, and the enrobe detection circuit 1
1, Figure 4 F? An output signal S5 as shown in , is formed. This output signal S5 is the clamp/comparison circuit 1
2, and is also supplied to one input terminal of the 1H delay circuit 13 and the subtraction circuit 14.

In the 1H delay circuit 13, the output signal 85 is delayed by 85 horizontal cycles to form the output signal S6 shown in FIG.
This output signal S6 is supplied to the other input terminal of the subtraction circuit 14. In the subtraction circuit 14, the output signal s6 is subtracted from the output signal S5 to form the output signal S7 shown in FIG. 4G.

As shown in FIG. 4G, uncorrelated color signals are detected and output in the first half of the horizontal period indicated by H1, H4, H5, and H6.

The output signal S7 formed in the subtraction circuit 14 is supplied to the double-wave rectification circuit 15 and rectified, and the output signal S8 shown in FIG. 4H is formed in the clamp/comparison circuit 16. As shown in FIG. 4H, in the first half of the horizontal period indicated by H1, H4, H5, and H6, the output signal s8, which is set to high level corresponding to the generation period of the non-correlated color signal, is output from the clamp/comparator circuit. 16 and is supplied to the control terminal of the gain control circuit 6.

Further, the presence or absence of a color signal is detected in synchronization with the input signal S1 based on the output signal S5 (not shown in FIG. 4H) supplied to the clamp/comparison circuit I2, and , +(3 and H5, an output signal η which is set to a high level is formed in the first half of the horizontal period, and the switch is switched.

It is supplied to the control terminal of the child circuit 7.

In the gain control circuit 6, the signal level of the output signal S4 is controlled based on the output signal S8 of the clamp/comparison circuit 16, and an output signal S9 is formed (not shown in FIG. 4). In the first half of the horizontal period indicated by H1, H4, H5, and H6, the gain is controlled to be twice that of the other periods, and as shown in FIG.
It is assumed that the signal level of the secondary beat component existing in the first half section (indicated by ◎ in the figure) of H] to H6) is constant. An output signal S9 formed in the gain control circuit 6 is supplied to one input terminal 7a of the switch circuit 7.

The switch circuit 7 is controlled by the output signal of the clamp/comparison circuit 12, and the control terminal becomes high level H1, H2.
, H3, and H5, the input terminal 7a and the output terminal are connected, and in the other sections, the input terminal 7b, which is grounded via the capacitor 20, is connected to the output terminal. Therefore, by the switching operation of the switch circuit 7, muting is performed in the latter half of the horizontal period indicated by H1, H2, H3, and H5, and in the entire horizontal period indicated by H4 and H6, and the fourth
The output signal SIO shown in FIG. J is formed. As shown in FIG. 4J, the differential pulse-like non-correlated luminance signal H1 includes only the edge portions present at the beginning of the horizontal period indicated by H1 and H5.

The secondary beat components present in the first half of the horizontal period (indicated by ◎ in the figure) indicated by H2, H3, and H5 are output as the output signal SIO by the λ/2 delay circuit 17°19 and the correlator 20.
The signal is supplied to a half-wavelength correlator constructed by the following.

In the correlator 20 of the half-wave correlator, the output signal 310 and the λ/2 delay circuit 17 are supplied via the inverter 18.
The horizontal correlation between the delayed output of the λ/2 delay circuit 19 and the delayed output of the λ/2 delay circuit 19 is detected, and only continuous secondary beat components are extracted to form the output signal Sll shown in FIG. 4H. As shown in FIG. 4H, the differential pulse-shaped uncorrelated luminance signal, which was only the edge portion that existed at the beginning of the horizontal period indicated by Hl and H5, is removed, and Hl, H2, H3 and H5 are removed. The first half of the horizontal period shown by (indicated by ◎ in the figure)
Only the secondary beat component present in is supplied to one input terminal of the adder circuit 22 as the output signal Sll. In the adder circuit 22, the input signal S1 shown in FIG.
After the output signal Sll shown in is at a level of, for example, %, it is added in reverse phase, and the secondary beat components existing in the first half of the horizontal period shown by H1, H2, H3, and H5 are constantly canceled. Ru. Therefore, from the output terminal 23, a reproduced luminance signal is obtained in which the secondary beat components are equally canceled over the entire interval, and the edge portions are not degraded.

Also, in the first half of one horizontal period, the brightness level is high and there are almost no color components, and in the second half the brightness level is low and there are almost no color components, and in the first half of one horizontal period, the brightness level is high. A signal with a high luminance level and many color components present, and a signal with a low luminance level and almost no color components in the latter half is continuously reproduced by the magnetic head, and the reproduced RF signal is supplied to the terminal 8, and this reproduced RF signal In the case where the reproduced luminance signal obtained from the above is supplied to the input terminal l in the above-mentioned embodiment, that is, when the luminance signal is vertically correlated but the chrominance signal is uncorrelated, FIG. This will be explained with reference to A to K.

A reproduced luminance signal for four horizontal periods (not shown in FIG. 5A) is supplied to the input terminal 1, and is supplied to the 1H delay circuit 2 delay circuit 21 as the input signal S1. It is assumed that the signal is supplied to one input terminal of the subtraction circuit 3. In FIG. 4A, a secondary beat component exists in the signal section indicated by a circle, and a secondary beat component exists in the first half of the horizontal period, indicated by H2 and H3.

In the 1H delay circuit 2, the input signal is delayed by a horizontal period of 81 months to form the output signal S2 shown in FIG. 5B,
In the subtraction circuit 3, an output signal S3 shown in FIG. 5C is formed. As shown in FIG. 5C, uncorrelated luminance signals are detected in the first half of the horizontal period indicated by Hl and H5, and two uncorrelated luminance signals are detected in the first half of the horizontal period indicated by H2 and H4 (indicated by O in the figure). The next beat component is output, and at the same time, the second beat component whose level is doubled by being added in the first half section of the horizontal period (indicated by ◎ in the figure) indicated by H3 is output. This output signal S3 is passed through a differentiating circuit 4 and a limiter amplifier 5 to become an output signal S4 shown in FIG. This output signal S4 is supplied to the input terminal of the gain control circuit 6.

Incidentally, based on the reproduced RF signal supplied to the terminal 8, envelope detection of the carrier color signal that has been low-pass converted is performed in synchronization with the input signal S1, and the envelope detection circuit 1
1, an output signal S5 as shown in FIG. 5E is formed. In the 1H delay circuit 13, the output signal S5 is 1
An output signal S6 shown in FIG. 5F is formed after being delayed by a horizontal period, and an output signal S7 shown in FIG. 5G is formed in the subtraction circuit 14. As shown in FIG. 5G, uncorrelated color signals are detected and output in the first half of the horizontal period indicated by H2 and H4. This output signal S7 is passed through a double-wave rectifier circuit 5 to become an output signal S8 shown in FIG. H2 and H4 as shown in Figure 5H
An output signal S8 that is at a high level in the first half of the horizontal period indicated by is supplied to the control terminal of the gain control circuit 6.

In the gain control circuit 6, the signal level of the output signal S4 is controlled based on the output signal S8, and the signal level of the output signal S4 is controlled as shown in FIG.
An output signal S9 shown in is generated.

In the first half of the horizontal period indicated by H2 and H4, the gain is controlled to be twice as much as in the other sections.
As shown in FIG. I, the signal level of the secondary beat component existing in the first half of the horizontal period indicated by H2, H3, and H4 (indicated by ◎ in the figure) is constant. The output signal S9 formed in the gain control circuit 6 is supplied to one input terminal 7a of the SW7000 circuit 7.

The switch circuit 7 is controlled by a signal formed based on the output signal S5 (shown in FIG. 5E) of the enherobe detection circuit 11, and is connected to the input terminal 7a in the first half period of the horizontal period indicated by H2 and l-(3). The output terminal is connected,
Muting is performed in other sections. By the switching operation of the switch circuit 7, an output signal 510 shown in FIG. 5, I is formed. )−(2
The secondary beat component existing in the first half of the horizontal period (indicated by ◎ in the figure) indicated by H3 and H3 is the output signal S ], O
as a half-wavelength correlator.

In the correlator 20 of the half-wavelength correlator, the horizontal correlation is detected and only the continuous secondary beat components are extracted.
The output signal SIO from the circuit 7 is output almost unchanged as shown in FIG. 5K. Only the secondary beat components present in the first half of the horizontal period (indicated by ◎ in the figure) indicated by H2 and H3 are supplied to one input terminal of the adder circuit 22 as the output signal S],1. In the adder circuit 22, the output signal 311 shown in FIG. 5K is set to a level of 2, for example, to the input signal S1 shown to the fifth doujin, and then added in the opposite phase to the input signal S1 shown in the fifth doujin. The existing secondary beat components are constantly canceled even though they have no correlation with the color signal.

In one embodiment of the present invention, a configuration has been described in which the gain control circuit 6 is provided at a stage before the switch circuit 7. The level of the secondary beat component may also be controlled. Additionally, in one embodiment of the invention, the clamp/comparison circuit 16
Although we have described a configuration in which the double-wave rectifier circuit 15 is provided at the front stage of the subtraction circuit 14, the non-correlated color signal output from the subtraction circuit 14 is supplied as it is to the clamp/comparison circuit, and the average value plate of the output level of the subtraction circuit 14 is A similar effect can be obtained by providing a threshold for the level. Furthermore, in one embodiment of the present invention, a case has been described in which a signal of the NTSC system, for example, which has a correlation every horizontal period is input, but a signal of the PAL system, for example, which has a correlation every two horizontal periods, is input. Even in the case where a signal is inputted, the lH delay circuits 2 and 13 may be applied as the 21-1 delay circuits, respectively. Furthermore, in one embodiment of the present invention, ζ is
Although a configuration has been described in which a non-correlated color signal is detected from the envelope detection output of a carrier color signal, similar effects can be obtained by detecting a non-correlated color signal using the output of the clamp/comparison circuit 12.

〔Effect of the invention〕

In this invention, the reproduced luminance signal is supplied to the subtraction circuit, and the reproduced luminance signal is also supplied to the subtraction circuit via the 1H delay circuit, and in the subtraction circuit, the reproduced luminance signal one horizontal period before the current reproduced luminance signal is By subtracting, the secondary beat component included in the reproduced luminance signal and the uncorrelated luminance signal are detected and output. The output of the subtraction circuit is supplied to a differentiating circuit, and the DC component of the uncorrelated luminance signal is substantially removed, and the differentiated pulse-shaped uncorrelated luminance signal and the secondary beat component are supplied to a sharp misotor amplifier.
The peak level of the differential pulse-like uncorrelated luminance signal is limited, and the secondary beat component present in the edge portion 1 is sufficiently amplified within a linear range and supplied to the gain control circuit.

The gain control circuit is controlled based on a control signal corresponding to the generation section of the uncorrelated color signal formed from the uncorrelated color signal detected from the envelope detection output of the carrier color signal, and The level of the section where the correlated color signal is detected is amplified by 6 dB compared to the section where the uncorrelated color signal is not detected, and the level of the secondary beat component is kept constant and supplied to the switch circuit. The switch circuit is controlled by a discrimination signal that indicates the presence or absence of a color signal in synchronization with the reproduced luminance signal, and the output cuff of the gain control circuit is supplied to the half-wave correlator only in the section where the color signal is present. Muting is performed in the interval where the signal is not transmitted. In the half-wave correlator, the differential pulse-shaped non-correlated luminance signal, which is only the edge part, is removed because there is no horizontal correlation, and only the secondary beat component is supplied to the adder circuit and reproduced by being supplied via the delay circuit. It is added to the luminance signal in reverse phase, and the secondary beat components are constantly canceled without deteriorating the edge portions of the reproduced luminance signal.

Therefore, according to the present invention, the secondary beat component and the non-correlated luminance signal outputted from the subtraction circuit are supplied to the limiter amplifier via the differentiating circuit, so that the non-correlated luminance signal is limited in the limiter amplifier. In sections other than the edge portions of the luminance signal, secondary beat components are not lost, and
Secondary beat components can be canceled over a wide range even in the vertical non-correlation interval.

Further, according to the present invention, a control signal corresponding to the generation section of the uncorrelated color signal is formed from the en-rope detection output of the carrier color signal, and the gain of the gain control circuit is switched based on this control signal. For example, the level of the secondary beat component in the section where the uncorrelated color signal is detected is twice the level in the section where the uncorrelated color signal is not detected, and the amount of cancellation is kept constant. The secondary beat components can be equally canceled over substantially the entire section regardless of signal correlation, and a sufficient canceling effect can be obtained even in the vertical non-correlation section.

Further, according to the present invention, the presence or absence of a color signal is determined from the envelope detection output of the carrier color signal, and the switch circuit is switched based on this determination signal to ensure that the mute signal is not muted in the section where the secondary beat component does not exist. Because of this, it is possible to extract the secondary beat component with a high S/N without being affected by noise compared to the case where it is passed through an AM modulator, and because it is not passed through an AM modulator,
The secondary beat component can be canceled in a manner linearly corresponding to the level of the input secondary beat component, and is effective for all levels of the secondary beat component.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a connection diagram of a specific example of a gain control circuit in an embodiment of the invention, and a connection diagram of another example, and FIG. 3 is an embodiment of the invention. FIGS. 4 and 5 are waveform diagrams used to explain the half-wavelength correlator in the example, and FIGS. 4 and 5 are waveform diagrams used to explain the operation of an embodiment of the present invention. Explanation of main symbols in the drawings 1: Input terminal, 2.13; 1H delay circuit, 3゜14
2 subtraction circuit, 4: Differential circuit, 6: Gain control circuit, 7: Switch circuit, 8: Terminal to which reproduced RF signal is input, 11: Envelope detection output,
12. ] 6: Clamp/comparison circuit, 21: Delay circuit, 22: Adder circuit, 23: Output terminal.

Claims (1)

[Claims] In a secondary beat cancellation circuit for removing a frequency component twice the low carrier frequency of a color signal from a reproduced luminance signal, the output signal of the delay circuit having a delay amount of 1H or 2H is a subtraction circuit that subtracts from the reproduced luminance signal; a differentiation circuit to which the output signal of the subtraction circuit is supplied; a gain control circuit for controlling the gain of the output signal of the differentiating circuit using the control signal; a switch circuit for turning ON/OFF in response to a discrimination signal; a delay circuit for delaying the reproduced luminance signal; and a switch circuit for inverting the reproduced luminance signal passed through the delay circuit and the output signal of the switch circuit. 1. A secondary beat canceling circuit comprising: a phase-based addition circuit;