JPS62272795A - Secondary beat cancel circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the edge part of a reproduction luminance signal and moreover to securely cancel a secondary beat component even in a vertical non-correlative interval by adding a secondary beat component, the one of a non-correlation luminance signal and the secondary beat component which are included in the reproduction luminance signal, to the reproduction luminance signal in an opposite phase. CONSTITUTION:The reproduction luminance signal is inputted from a terminal 1, and the secondary beat component and non-correlation luminance signal are detected in a subtraction circuit 3 and supplied to a differentiation circuit 4. Then the differential pulse state of non- correlation luminance signal and the secondary beat component which are set only the edge part are supplied to a limitter amplifier 5 and as the peak level of the non-correlation signal is limitted, the secondary beat component which exists except in the edge part is amplified and supplied to a switch circuit 6. The switch circuit 6 is controlled by a discrimination signal supplied from a comparator 12 and only in the interval to which a chrominance signal exists the output on the amplifier 5 is supplied to a half-wave correlator consisting of lambda/2 delay circuit 13 and 15 and a correlator 16, etc., so as to remove the non-correlation luminance signal and only the secondary beat component is supplied to an addition circuit 18 and added in the opposite phase to the reproduction luminance signal supplied through a delay circuit 17.

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]

The present invention provides a secondary beat canceling circuit used in a VTR or the like that records a carrier color signal subjected to low frequency conversion together with a luminance signal, in which a differential circuit and a secondary beat component are used to separate a detected uncorrelated luminance signal and When a chrominance signal is present, the differentiated uncorrelated luminance signal and the secondary beat component are supplied to a half-wave correlator through a limiter amplifier, and when a chrominance signal is absent, the differentiated uncorrelated luminance signal and secondary beat component are supplied to a half-wave correlator. By performing muting to obtain the output of only the secondary beat component from the half-wave correlator, the edge portion of the reproduced luminance signal is not degraded (but it is also sufficiently This system is designed to prevent deterioration of image quality by making it possible to cancel secondary beat components.

[Conventional technology]

In a VTR that records a low-band converted carrier color signal together with a luminance signal, the tape/rotating magnetic head system has nonlinear characteristics, so the secondary beat component of the low-band converted carrier color signal is recorded in 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 beat component causes the screen to change. Diagonal beat stripes appear on the top, significantly degrading the image quality. For this reason, conventional VTRs are provided with a secondary beat canceling circuit in the reproduction system for canceling secondary beat components.

For example, the conventional secondary beat cancellation circuit
After demodulating the M modulated luminance signal, the IH
The delayed reproduced luminance signal is subtracted to detect the secondary beat component included in the reproduced luminance signal and the uncorrelated luminance signal generated during vertical uncorrelation as an uncorrelated signal, and this uncorrelated signal is passed through a bandpass filter. and A via the limiter
The level of the uncorrelated signal is controlled by the enrove output of the carrier chrominance signal supplied to a level control circuit composed of an M modulator, and the level is controlled from the reproduced luminance signal supplied via a delay circuit for time adjustment. The secondary beat component is canceled by subtracting the uncorrelated signal.

However, in the conventional secondary beat cancellation circuit described above, when a reproduced luminance signal (Jt) having no vertical correlation is supplied, an uncorrelated luminance signal is detected together with the secondary beat component and output as an uncorrelated 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 cancel circuit for preventing the deterioration of the edge portion that occurs during such secondary heat cancel processing, the applicant of the present application has previously disclosed Japanese Patent Application No. 58-19748 or Japanese Patent Application No. 51-21210. 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 1 to cancel circuit prohibits the secondary beat canceling operation in all vertical non-correlation sections, so the signal in most sections where the secondary beat component is canceled and the secondary beat component are There is a problem in that the difference between the signal and the signal in the vertical non-correlation section that is not canceled becomes large (becomes thick), and the secondary Be 1-component in the vertical non-correlation section is visually relatively emphasized.

To solve this problem, we extract the uncorrelated luminance signal, double-wave rectify it, subtract it from the envelope detection output of the carrier chrominance signal, and perform M modulation based on the obtained signal. A secondary beat cancellation circuit has been proposed that controls the level of a non-correlated signal in such a way as to lower the degree of modulation in the correlation 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 beat 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 provide circuits.

[Means for solving problems]

The present invention provides a secondary beat cancellation circuit for removing a frequency component twice the low carrier frequency of a color signal from a reproduced luminance signal, which reproduces an output signal of a delay circuit 2 having a delay amount of IH or 2H. A subtraction circuit 3 for subtracting from a luminance signal, a differentiation circuit 4 to which an output signal of the subtraction circuit 3 is supplied, means 10, 11 and 12 for forming a discrimination signal corresponding to the presence or absence of a low frequency conversion color signal, and a differentiation circuit 4. a switch circuit 6 for turning the output signal ON10 F F in response to the discrimination signal; a delay circuit 17 for delaying the reproduced luminance signal; and a reproduction luminance signal passed through the delay circuit 17 and the output of the switch circuit 6. This is a secondary beat canceling circuit characterized by comprising a circuit 18 that adds signals in opposite phase.

[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 1H delay circuit 2, and in the subtraction circuit 3, 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 3 is supplied to a differentiating circuit 4, which substantially removes the DC component of the uncorrelated luminance signal, and outputs the differentiated pulse-shaped uncorrelated luminance signal, which is used as an edge part, and the secondary beat component to a pointed minotaur amplifier 5. supplied,
The peak level of the differential pulse-like uncorrelated signal is limited, and the secondary beat components present in areas other than the edge portions are sufficiently amplified within a linear range and supplied to the switch circuit 6. The switch circuit 6 is controlled by a discrimination signal indicating the presence or absence of a color signal in synchronization with the reproduced luminance signal supplied from the comparator circuit 12, and the output of the limiter amplifier 5 changes to λ/2 only in the section where the color signal is present. Delay circuit 13. ] 5 and a correlator 16, and muting is performed in an interval where no color signal exists. In the correlator 16, the differential pulse-like uncorrelated luminance signal, which is only the edge portion, is removed because there is no horizontal correlation, and only the secondary beat component is supplied to the adder circuit 18 and then supplied via the delay circuit 17. By adding the reproduced luminance signal in reverse phase, the reproduction luminance signal processing
The secondary beat component is canceled without deteriorating the digital part.

〔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 input terminal 1 as input signal S1.

In addition, a reproduced RF signal from the magnetic heel is supplied to the terminal 7.

The input signal S1 from the input terminal 1 is supplied to the ]H delay circuit 2 and the delay circuit 17, and is also supplied to one input terminal of the subtraction circuit 3. In the IH delay circuit 2, the input signal Sl is delayed by one horizontal period to form an output signal S2, which 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.

That is, by subtracting the reproduced luminance signal of one horizontal period previous from the current reproduced 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. The output signal S3 is supplied to the differentiating 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 sent to the limiter 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 a limiter 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, thereby forming an output signal S4. do. In other words,
The peak level of the non-correlated luminance signal which is only the edge portion is limited, and the secondary beat component is sufficiently amplified within a linear range. Output signal S4 of limiter amplifier 5
is one input terminal 6a of the switch circuit 6, the other input terminal 6b of which is grounded via a bypass capacitor 20.
supplied to

The switch circuit 6 has a control terminal, and performs a switching operation based on a control signal supplied to the control terminal. For example, when the control terminal of the switch circuit 6 is set to the noise level, one input terminal 6a and the output terminal are connected and the output signal S4 from the limiter amplifier 5 is outputted via the switch circuit 6. Ru. Further, when the control terminal of the switch circuit 6 is set to low level, the other input terminal 6b
Muting is performed by connecting the output terminal and the output terminal.

By the way, the reproduced RF signal supplied to the terminal 7 is supplied to the low-pass filter 8 to separate the low-pass converted carrier color signal, and this carrier color signal is passed through the amplifier 9 to be at a predetermined level and subjected to envelope detection. is supplied to the circuit 10. In the envelope detection circuit 10, envelope detection of the carrier color signal is performed, and the detection output is sent to the clamp circuit 1.
1. An envelope detection circuit for a carrier color signal whose level has been shifted to a predetermined level by being passed through a clamp circuit 11 is supplied to a comparator circuit 12 .

In the comparison circuit 12, the output from the clamp circuit 11 is compared with a reference level, and an output signal S5 indicating the presence or absence of a color signal is formed in synchronization with the input signal S1. For example, when the output from the clamp circuit 11 is above the reference level, it is determined that a color signal exists and is set to high level, and when the output from the clamp circuit 11 is below the reference level, no color signal is present. It is determined that the level is low. An output signal S5 indicating the presence or absence of a color signal is supplied as a control signal to a control terminal of the switch circuit 6 in synchronization with the input signal S1.

The switch circuit 6 is controlled and switched by the output signal S5, and the output signal S4 from the limiter amplifier 5 is outputted via the switch circuit 6 only when a color signal is present. When there is no color signal, the output signal S4 from the limiter amplifier 5 is not output from the switch circuit 6, and the output of the switch circuit 6 is muted to the 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 6 to the ground level, Noise accompanying secondary beat extraction etc. is made substantially equal to zero.

The output signal S6 formed by the switching operation in the switching circuit 6 is fed to a half-wave correlator.

The half-wavelength correlator is composed of, for example, a λ/2 delay circuit 13, 15, a correlator 16, etc., which delays the secondary beat component by a half-wavelength of the wavelength λ.

The output signal S6 from the switch circuit 6 is sent to the λ/2 delay circuit 1.
3 and also to the correlator 16. λ/
In the 2-delay circuit 13, an output signal delayed by λ/2 is formed, and this delayed output is sent to the λ/2 delay circuit 15.
It is also supplied to the correlator 16 through the inverter 14 as a negative phase output. λ/2
In the delay circuit 15, the delayed output from the λ/2 delay circuit 13 is further delayed by λ/2 and supplied to the correlator 16.

The correlator 16 is configured as an AND circuit, and detects the horizontal correlation of each signal supplied to the correlator 16, and extracts only the signals with horizontal correlation. Only continuous secondary beat components are extracted in such a manner that the differential pulse-like uncorrelated luminance signal is removed, and an output signal S7 is formed. For example, if the secondary beat component included in the output signal S6 is as shown in FIG. 3A, the correlator 16 has the signal shown in FIG. 3A and the inverter shown in FIG. 3B. 14 and a signal from the λ/2 delay circuit 15 shown in FIG. 3C,
Only the continuous signals shown in the third diagram with horizontal correlation are 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. Output signal S7 from correlator 16
is supplied to one input terminal of the adder circuit 18.

The input signal S1 is supplied to the other input terminal of the adder circuit 18 via the delay circuit 17 for time adjustment, and the output signal S7 is added to the input signal S1 in the opposite phase in the adder circuit 18. As a result, the secondary beat component is canceled without deteriorating the edge portion of the reproduced luminance signal.

The output of the adder circuit 18 is taken out via the output terminal 19, and a reproduced luminance signal with the secondary beat component canceled is obtained at the output terminal 19.

b. Details of operation. For example, in the first half of one horizontal period, the brightness level is high and there are many color components, and in the second half, the brightness level is low and there are almost no color components. A signal with a low luminance 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 7 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. 2A to 2G.

A reproduced luminance signal for 5 horizontal periods shown in FIG. shall be carried out. ○ in Figure 2
A secondary Be] component exists in the signal section indicated by the mark, and H
1, H2, H3, and) (A secondary beat component exists in the first half of the horizontal period indicated by 5.

The input signal S1 supplied to the 1H delay circuit 2 is delayed by one horizontal period to form the output signal S2 shown in FIG. 2B, 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 the output signal S3 shown in FIG. 2C. As shown in Figure 2C, each horizontal period (H1
~H6)), the secondary beat component is output in the first half (indicated by a circle in the figure), and the uncorrelated luminance signal is output in the first half of HiH4, H
5, H6 is detected and output in the first half of the horizontal period. 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. The secondary beat component existing in the first half of H6) is supplied to the limiter amplifier 5. In the limiter amplifier 5, the peak level of the differential pulse-like uncorrelated luminance signal that is only the edge portion is limited, and the secondary beat components present in the first half of each horizontal period (H1 to H6) are linearized. The output signal S4 is sufficiently amplified within a certain range, and an output signal S4 shown in the second diagram is formed. This output signal S4 is supplied to one input terminal 6a of the switch circuit 6.

By the way, the presence or absence of a color signal is detected in synchronization with the input signal S1 based on the reproduced RF signal supplied to the terminal 7,
In the comparator circuit 12, an output signal S5, not shown in FIG. 2E, is formed. As shown in FIG. 2E, an output signal S5, which is at a high level only during the first half of the horizontal period indicated by H1, H2, H3, and H5, is output from the comparison circuit 12 and supplied to the control terminal of the switch circuit 6. Ru.

The switch circuit 6 is controlled by the output signal S5, and the input terminal 6a and the output terminal are connected in the first half section of the horizontal period indicated by H1, H2, H3, and H5 when the output signal S5 is at high level, and in the other sections. The grounded input terminal 6b and the output terminal are connected via the capacitor 20.

Therefore, due to the switching operation of the switch circuit 6, Hl.

1-12. Muting is performed in the latter half of the horizontal period indicated by H3 and H5 and in the entire horizontal period indicated by H4 and H6, resulting in the output signal S shown in FIG. 2F.
6 is formed. As shown in FIG. 2F, a differential pulse-shaped uncorrelated luminance signal with only edge portions existing at the beginning of the horizontal period indicated by H1 and H5 and H], 11
2. The secondary beat components existing in the first half of the horizontal period (indicated by circles in the figure) indicated by T(3 and H5) are outputted to the λ/2 delay circuits 13 and 15 and the correlator 1 as the output signal S6.
6, etc., to a half-wavelength correlator.

In the correlator 16 of the half-wavelength correlator, the horizontal correlation between the output signal S6 and the delayed output of the λ/2 delay circuit 13 and the delayed output of the λ/2 delay circuit 15, which are supplied via the inverter I4, is detected. Only the secondary beat components are extracted,
An output signal S7 shown in FIG. 2G is formed. As shown in FIG. 2G, the differential pulse-shaped uncorrelated luminance signal, which was only the edge portion that existed at the beginning of the horizontal period indicated by I-11 and H,5, is removed, and H1, H2 , H3, and I-+5, only the secondary beat components present in the first half of the horizontal period (indicated by ○ in the figure) are included in the output signal S7.
The signal is supplied to one input terminal of the adder circuit 18 as a signal. In the adder circuit 18, the output signal S7 shown in FIG. 2G is added to the input signal S1 not shown in FIG.
The secondary beat components existing in the first half of the horizontal period indicated by 2, H3, and H5 are canceled. Therefore,
From the output terminal 19, a reproduced luminance signal is obtained in which the secondary beat components are canceled and the edge portions are not degraded.

In one embodiment of the present invention, a case has been described in which, for example, NTSC system signals are input that are correlated every two horizontal periods. Even when a signal is input,
The 1H delay circuit 2 may be applied as a 2H delay circuit.

〔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, leaving only the edge portion, and the differentiated pulse-shaped uncorrelated luminance signal and the secondary beat component are supplied to the limiter amplifier. is,
The peak level of the differential pulse-like non-correlated luminance signal is limited, and the secondary beat components present outside the edge portion are sufficiently amplified within a linear range and supplied to the switch circuit. The switch circuit is controlled by a discrimination signal indicating the presence or absence of a color signal in synchronization with the reproduced luminance signal supplied from the comparator circuit, and the output of the Rimisocou amplifier is supplied to the half-wave correlator only in the section where the color signal is present. Muting is performed in sections where no signal is present.

In the half-wave correlator, the differential pulse-like uncorrelated luminance signal, which was only the edge part, is removed because there is no horizontal correlation.
Only the secondary beat component is supplied to the adder circuit, where it is added in reverse phase to the reproduced luminance signal supplied via the delay circuit, and the secondary beat component is canceled without deteriorating the edge portion 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, 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 no secondary beat components are present. 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,
It is possible to cancel the secondary beat component in a manner linearly corresponding to the level of the inputted secondary beat component, and is effective for all levels of the secondary beat component.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of this invention, Fig. 2 is a waveform diagram used to explain the operation of an embodiment of this invention, and Fig. 3 is an illustration of a half-wave correlator in an embodiment of this invention. It is a waveform diagram used. Explanation of main symbols in the drawing ■ = input terminal, 2: 1H delay circuit, 3: subtraction circuit,
4: Differential circuit, 5: Rimisotar amplifier, 6: Suinochi circuit, 7: Terminal into which the reproduced RF signal is input, 8:
Low-pass filter, 10: Envelope detection circuit,
11: Clamp circuit, 12: Comparison circuit, 17:
Delay circuit, 18 two-adder circuit, 19: Output terminal. Agent Patent Attorney Masaaki Sugiura Written amendment of written procedure June 23, 1985 Patent Application No. 116899 of 1988 2 Title of invention Secondary beat cancellation circuit 3 Relationship with the case of the person making the amendment Patent applicant address No. 6-7-35, Kitashinyo, Tokyo Parts Ward Name (2
1El) Sony Corporation Representative Director Norio Oga 4, Agent address 1-48-10-6, Higashiikebukuro, Toshima-ku, Tokyo, ? !
Column for detailed description of the invention in the positive subject specification (in 11 specifications, page 5, lines 2 and 3, “Patent Application 1982-
19748 specification” is corrected to “Japanese Patent Application No. 58-159461 specification.” (2) Same page, box 3 and 4 lines, “Patent Application 1986-2121
"Specification No. 0" is corrected to "Specification of Japanese Patent Application No. 59-22353."

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 for subtracting from the reproduced luminance signal; a differentiation circuit to which the output signal of the subtraction circuit is supplied; means for forming a discrimination signal corresponding to the presence or absence of a low-frequency conversion color signal; Turns on in response to the discrimination signal
/OFF, a delay circuit for delaying the reproduced luminance signal, and a circuit for adding the reproduced luminance signal passed through the delay circuit and the output signal of the switch circuit in opposite phases. A secondary beat cancellation circuit characterized by comprising: