JPS63164591A - Secondary beat canceling circuit - Google Patents

Abstract

PURPOSE:To cancel a secondary beat signal without deteriorating the resolution of a luminance signal by canceling a secondary beat signal to be superposed to a demodulated luminance signal by means of a signal component with twice frequency of a low frequency conversion chroma signal and a secondary higher harmonic signal. CONSTITUTION:A reproduced signal SPB outputted from an adder 6 is sent to an LPF circuit 7 and a chroma signal converted at its low frequency is separated. After correcting the phase and amplitude characteristics of the chroma signal, the signal is outputted to a frequency converting circuit 11 to form a secondary higher harmonic signal, which is outputted to an adder 14 through a BPF circuit 12. On the other hand, a luminance signal SFY separated by an HPF 20 is demodulated by a demodulator 22 through a limiter 21. Since a secondary beat signal superposed to the demodulated luminance signal SY becomes twice higher harmonic component of the chroma signal whose center frequency is converted into a low frequency level, a secondary higher harmonic component is formed by a secondary beat canceling circuit 30, inverted and amplified and the obtained component is added to the luminance signal SY by an adder 26.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a secondary beat cancellation circuit, and is particularly suitable for application to a video tape recorder (VTR).

B. Summary of the Invention The present invention provides a secondary beat canceling circuit that generates a chroma signal that is formed from a signal component with a frequency twice that of the carrier wave of a low-frequency converted chroma signal extracted from a demodulated luminance signal and a low-frequency converted chroma signal. By canceling the secondary beat signal superimposed on the demodulated luminance signal using the next harmonic signal, the secondary beat signal can be reliably canceled with a simple configuration without reducing the resolution of the luminance signal. This is what I did.

C. Conventional technology Conventionally, in a VTR, the chroma signal is converted to low frequency
Some devices are designed to perform magnetic recording together with M-modulated luminance signals.

In such a VTR, since the magnetization characteristics of the magnetic tape are nonlinear, it is unavoidable that odd-order harmonic distortion occurs in the reproduced signal obtained through the magnetic head. There was a problem that the large third-order harmonic component deteriorated the image quality of the reproduced video.

In other words, if the frequency of the carrier wave of the low-frequency converted chroma signal is f, and the carrier frequency of the FM-modulated luminance signal is fY, then among the third harmonic components, the second-order of the low-frequency converted chroma signal The multiplied signal of the harmonic signal and the FM-modulated luminance signal becomes a signal component with a frequency fV±2fc,
It mixes within the frequency band of the FM-modulated luminance signal.

Therefore, when the luminance signal is demodulated, the second harmonic signal of the chroma signal that has been low frequency converted by the multiplication signal is superimposed on the luminance signal as a second beat signal with a frequency of 2fc, and as a result, the reproduction There was a problem in which beat stripes appeared on the video and the image quality of the reproduced video deteriorated significantly.

In order to solve this problem, conventionally, a comb-shaped filter circuit composed of an IH delay circuit is used to extract a secondary beat signal, and then this is used to cancel the secondary beat signal of the luminance signal. A beat cancellation circuit has been proposed (Japanese Patent Laid-Open No. 56-96590, Japanese Patent Application No. 61
-116899, Japanese Patent Application No. 61-116900, Japanese Patent Application No. 118347-1983).

D Problems to be Solved by the Invention However, in this type of secondary beat canceling circuit, not only the secondary beat signal is combed from the luminance signal, but also the luminance signal components of portions that have no correlation in the vertical and horizontal directions. 2 in the luminance signal because it is extracted by the filter circuit.
There is a problem in that when canceling the next beat signal, the signal level of the luminance signal in the uncorrelated portion decreases, resulting in a decrease in the resolution of the reproduced video.

Therefore, in this type of secondary beat canceling circuit, it is necessary to detect uncorrelated parts of the luminance signal and prevent the resolution of these parts from decreasing. It was inevitable that it would become a composition.

In addition, in a part where the chroma signal has no correlation in the vertical direction, the signal level of the secondary beat signal obtained via the comb filter circuit changes with respect to the signal level of the secondary beat signal superimposed on the luminance signal. As a result, there was a problem in that the secondary beat signal could not be completely canceled in this part.

Therefore, in this type of secondary beat canceling circuit, it is necessary to detect the correlation of the chroma signals and control the signal level of the secondary beat signal obtained from the comb filter circuit according to the detection result. There is an unavoidable problem that the next beat canceling circuit as a whole has a more complicated configuration.

5. The present invention has been made in consideration of the above points, and proposes a secondary beat canceling circuit with a simple configuration that can reliably cancel the secondary beat signal without reducing the resolution of the luminance signal. This is what I am trying to do.

E Means for Solving the Problem In order to solve the problem, in the present invention, a low frequency converted chroma signal S magnetically recorded on a magnetic tape is used.
In the magnetic reproducing device 1 that reproduces the LC and the frequency-modulated luminance signal SFY, the low-frequency converted chroma signal S
Second-order harmonic signal forming circuits 31 and 32 that form the second-order harmonic signal 5LC2 of LC, and a frequency-modulated luminance signal S
A bandpass filter circuit 35 extracts a signal component 5fcz having a frequency fc2 that is twice the frequency of the carrier wave of the low-frequency converted chroma signal SLC from the luminance signal SY demodulated from FY.
and a level detection circuit 3 that detects the signal level of the signal component 5fcz obtained via the bandpass filter circuit 35.
6, and control circuits 33, 34, and 37 that control the signal/level of the second harmonic signal 5LC2 according to the detection result SD of the level detection circuit 36, and the demodulated luminance signal SY.
By subtracting the output SMC2 of the control circuits 33, 34, and 37 from the subtraction signal SMC2, the secondary beat signal SB superimposed on the demodulated luminance signal SY is canceled out.

A signal component Sf having a frequency f0 twice that of the carrier wave of the low-frequency converted chroma signal SLC extracted from the demodulated luminance signal SY, which is a second harmonic signal 5LC2 formed from the F-effect low-frequency converted chroma signal SLC; By controlling at the signal level of 2, it is possible to obtain a signal SMC2 proportional to the signal level of the secondary beat signal S B z.

Therefore, the luminance signal sy demodulated using this signal SMC2
By canceling the secondary beat signal SB2 of the luminance signal SY, it is possible to cancel only the secondary beat signal SBz of the luminance signal SY, thereby ensuring that the secondary beat signal SB2 of the luminance signal SY is canceled without reducing the resolution of the luminance signal SY. The signal SBz can be canceled.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, 1 indicates a VTR as a whole, and reproduced signals 5PBA and 5 obtained through magnetic heads 2 and 3.
PBB is received by an adder circuit 6 via amplifier circuits 4 and 5, respectively.

The low-pass filter circuit 7 separates the low-frequency converted chroma signal SLC from the reproduced signal SPB output from the adder circuit 6, and converts the low-frequency signal SLC through the equalizer circuit 8, ACC circuit 9, and differential gain control circuit 10. chroma signal SL
After correcting the phase characteristics and amplitude characteristics of C to predetermined characteristics,
It is output to the frequency conversion circuit 11.

As shown in FIG. 2, the frequency conversion circuit 11 frequency-converts the low frequency-converted chroma signal SLC (FIG. 2(A)) into a chroma signal SC, and converts the frequency of this chroma signal (sc) to a bandpass filter circuit. 12 and an amplifier circuit 13 to an adder circuit 14 .

On the other hand, the bypass filter circuit 20 separates the FM-modulated luminance signal SFY from the reproduced signal SPB and outputs it to the demodulation circuit 22 via the limiter circuit 21.

The demodulation circuit 22 demodulates the FM-modulated luminance signal SFY into a luminance signal SY (FIG. 2(B)) and outputs it to the delay circuit 25 via the low-pass filter circuit 23 and the amplifier circuit 24.

The delay circuit 25 delays the luminance signal SY by a predetermined time to correct the time delay of the chroma signal SC with respect to the luminance signal SY, and then outputs the luminance signal SY to the addition circuit 14 via the addition circuit 26. Accordingly, a video signal SV (FIG. 2(E)) can be obtained by superimposing the chroma signal SC on the luminance signal SY via the adder circuit 14.

Furthermore, the VTR 1 has a secondary beat canceling circuit 30, which uses the low frequency converted chroma signal SLC output from the differential gain control circuit 10 to cancel the secondary beat signal superimposed on the luminance signal SY. being done.

In other words, the low frequency converted chroma signal SLC is applied to the multiplier circuit 3.
1, the second harmonic signal 5L of the chroma signal SLC
C2 (FIG. 2(C)) and outputs it to the balanced modulation circuit 33 via the bandpass filter circuit 32.

The secondary beat signal superimposed on the demodulated luminance signal SY is
Since its center frequency is twice the harmonic component of the low frequency converted chroma signal, the center frequency of the second harmonic signal 5LC2 (Figure 2 (C)) is the center of the second beat signal SB. It becomes the same frequency as frequency rcz.

In this way, the multiplier circuit 31 and the bandpass filter circuit 32 constitute a second harmonic generation circuit that forms a second harmonic signal.

Further, in the secondary beat canceling circuit 30, a signal component 5fcz of frequency fC2 is extracted from the luminance signal SY via a bandpass filter circuit 35 of frequency fc2, which is twice the carrier wave of the low-frequency converted chroma signal SLC. do.

The level detection circuit 36 detects the signal component 5 of the frequency fcZ.
Envelope detection is performed on fc2, and the detected signal SD (Fig. 2 (
D)) is output to the balanced modulation circuit 33 via the amplifier circuit 37.

Therefore, the signal component 5fc of the frequency f1.2 of the luminance signal sy
Second harmonic signal SMC2 amplitude modulated at the signal level of 4
is obtained via the balanced modulation circuit 33, and thus,
a second-order harmonic signal S proportional to the amplitude level of the second-order beat signal SB, which has the same frequency characteristics as the second-order beat signal 5B1L;
MC2 can be obtained.

As a result, this second harmonic signal SMC2 is inverted and amplified to a predetermined signal level via the level adjustment circuit 34, and added to the luminance signal SY in the addition circuit 26, thereby generating a second harmonic signal SMC2.
Video signal SV with only the next beat signal SB2 component canceled
(Fig. 2(E)) can be obtained.

According to the above configuration, the secondary beat signal can be completely canceled without using a comb filter circuit.
It is possible to prevent the resolution of the video signal from deteriorating even in uncorrelated parts.

Furthermore, according to the above embodiment, only the secondary beat signal can be canceled regardless of the presence or absence of the H correlation and the This eliminates the need for a secondary beat canceling circuit, which has a small and simple configuration as a whole, and thus allows the VTR as a whole to be made smaller and simpler.

Furthermore, in the above-described embodiment, in order to obtain the second harmonic signal SMC2 for canceling the second-order beat signal, the differential gain control circuit outputs the low-frequency conversion signal after being corrected to have predetermined phase characteristics and amplitude characteristics. 2 from the chroma signal SLC
By forming an order harmonic signal and modulating it with the signal level of a signal component of twice the frequency with respect to the carrier wave of the chroma signal obtained from the luminance signal and low frequency converted, it is possible to When using a magnetic tape, when playing back a magnetic tape recorded on a VTR with different characteristics, when the characteristics of the magnetic heads 2 and 3 are different, or when the magnetic head 2
Even in the case where the magnetic characteristics are changed due to wear of the second harmonic signal SMC2, it is possible to obtain the second harmonic signal SMC2 with the optimum signal level for canceling the second beat signal. In this way, the secondary beat signal can be completely canceled even in the above-mentioned case.

Note that in the above embodiment, the multiplication circuit 31 is used to
Although the case of forming a second-order harmonic signal has been described, the means for forming a second-order harmonic signal is not limited to this, and a wide range of nonlinear second-order system amplifier circuits can be used.

H Effects of the Invention As described above, according to the present invention, the secondary beat signal can be canceled without using a comb filter circuit, so the secondary beat signal can be reliably canceled without reducing the resolution of the luminance signal. It is possible to obtain a secondary beat canceling circuit with a simple configuration that can cancel out.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a secondary beat cancel circuit according to the present invention, and FIG. 2 is a signal waveform diagram for explaining its operation. 1...VTR, 2, 3...Magnetic head, 13.37...Amplification circuit, 3o...
Secondary beat cancel circuit, 31...Multiplication circuit, 32.35...Band pass filter circuit, 3
3... Balance modulation circuit, 34... Level adjustment circuit, 36... Level detection circuit.

Claims (1)

[Claims] In a magnetic reproducing device for reproducing a low-frequency-converted chroma signal and a frequency-modulated luminance signal magnetically recorded on a magnetic tape, a second harmonic of the low-frequency-converted chroma signal is provided. A second harmonic signal forming circuit that forms a wave signal, and a luminance signal demodulated from the frequency-modulated luminance signal, extracting a signal component having a frequency twice that of the carrier wave of the low-frequency converted chroma signal. a bandpass filter circuit that detects the signal level of the signal component obtained through the bandpass filter circuit; a level detection circuit that detects the signal level of the signal component obtained through the bandpass filter circuit; and a level detection circuit that detects the signal level of the second harmonic signal according to the detection result of the level detection circuit. and a control circuit for controlling the secondary beat, wherein the secondary beat signal superimposed on the demodulated luminance signal is canceled by subtracting the output of the control circuit from the demodulated luminance signal. cancellation circuit.