JPH02252171A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To effectively cancel a cross modulation component contained in a demodulation signal by providing a 2-step multiplication circuit for 2nd-step-multiplying an output of a filter for subtracting a 2nd modulation wave component and a subtractor for subtracting an output of the 2-step multiplication circuit from the demodulation signal obtained by FM-demodulating a 1st modulation wave. CONSTITUTION:An inputted video signal is recorded by a head 6, and at the time of reproducing, a regenerative signal regenerated by the head 6 is signal-processed by luminance and chrominance signal reproducing systems 8 and 9 respectively, and a demodulation video signal is outputted from an adder 10. Then, the regenerative signal from a head amplifier 7 is slightly adjusted in frequency characteristics in order to make a reproducing level smaller than a reproducing level of fc by an equalizer circuit 25 of a moire canceler circuit 11. This regenerative signal is limited by a limiter circuit 26, and an output is processed by the filter 12, and then an output frequency is given to the 2-step multiplication circuit 13, and consequently a 2-step multiplication frequency component 2F1 is adjusted in phase and gain by a phase adjusting circuit 14 and a gain adjusting circuit 15, and then a moire component 2f1 is cancelled from the demodulation video signal by the subtractor 16 to output the signal without moire.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetic recording/reproducing device such as a VTR.

Conventional technology In home VTRs, the color signal of the video signal is converted to low frequency,
A so-called color under recording method is used in which the signal is mixed with an FM modulated luminance signal and recorded and reproduced.

Here, if the FM carrier frequency is fc and the low frequency converted color signal frequency is f, cross-modulation occurs at the fc 2f+ frequency due to the characteristics of the electromagnetic conversion system during reproduction, and the reproduced luminance signal after demodulation is 2f. , component cross-modulation moiré occurred, which had a large negative impact on image quality.

Conventionally, by keeping the color signal recording current low,
Although the occurrence of cross-modulation moiré was suppressed to below an acceptable ratio, this resulted in a deterioration of the S/N of the color signal.

Further, as a method for removing the cross-modulation moiré of the 2f+ component, there is a method proposed by the present inventor in Japanese Patent Application No. 181529/1982. This is a moiré cancellation circuit that filters 11 components of the reproduced signal with a low-pass filter, generates a 2f+ component with a doubling circuit, and subtracts it from the luminance demodulated signal, and is quite effective.

However, further investigation revealed the following problems.

Problem to be Solved by the Invention Even if the fl level and fc 2f+ level in the reproduced signal are constant, the level of the cross-modulation component 2f included in the demodulated luminance signal varies.

This means that when a luminance signal is FM-modulated with a carrier fc, there is a deviation of several MHz, but the reproduced output f C1- on the lower frequency side of the deviation is the reproduced output f C1- on the higher frequency side with a lot of various losses. Since the playback output level is higher than fcl+, even if the temperature is 871 (fc
Even if the level of the 2fI) component is constant, the 2fI) component after demodulation
f, the level of the component fluctuates.

This is shown in FIG. FIG. 4(A) is a spectrum diagram of the reproduced FM signal, in which the solid line shows the low frequency carrier rct and the dotted line shows the high frequency carrier fcl+. It can be seen that the reproduction level of fCL is higher than the reproduction level of fCM. (B) is a demodulated signal obtained by demodulating fc, and shows a cross-modulation component 2f. Here, as the carrier level fc changes, the cross modulation level 2f
, shows that it also changes.

However, conventionally, in the moire canceling circuit proposed by the present inventor, fl is filtered from the reproduced output by a low-pass filter, and the resultant 2f, which is the sum of the two, does not depend on the carrier level fc, and the reproduced output level f, If it is constant, it is constant, and there was a problem that cross modulation could not be canceled sufficiently after all.

Means for Solving the Problems In order to solve the above problems, the present invention subjects an I-th signal to FM modulation at a carrier frequency (fc) to form a first modulated wave, and a second signal at the frequency (fc). fc) An apparatus that modulates in a lower frequency region to produce a second modulated wave, mixes the first modulated wave and the second modulated wave, records the mixture on a recording medium, and reproduces it from the recording medium, an equalization circuit that adjusts frequency characteristics such that a reproduction level of a second modulated wave of the reproduction signal is lower than a reproduction level of the first modulated wave; a limiter circuit that limits an output of the equalization circuit; and the limiter circuit. a filter that filters a second modulated wave component from the output of the filter, a doubler circuit that multiplies the output of the filter by two, and subtracts the output of the doubler circuit from the demodulated signal obtained by FM demodulating the first modulated wave. The configuration is such that it is equipped with a subtractor that performs the following steps.

As a result, no matter how much the reproduced output level of the FM carrier frequency fc changes, the cross-modulation component 2f1 can be canceled very effectively.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to screens.

FIG. 1 shows a block diagram of an embodiment of the present invention.

The video signal input from terminal 1 is sent to luminance signal recording system 2,
After the signals are processed by the color signal recording system 3, they are added by the adder 4, and are recorded by the head 6 through the recording amplifier 5. During reproduction, the reproduced signal reproduced from the head 6 passes through the head amplifier 7, undergoes signal processing in a luminance signal reproduction system 8 and a color signal reproduction system 9, and is converted into a decoded video signal by an adder 10. Conventionally, the information is output as is, and the explanation of the embodiments up to now is completely the same as in the prior art. Now, in the present invention, the head amplifier 7
A reproduction signal from the moire canceling circuit 11 is sent to the moire canceling circuit 11.

The moire canceling circuit 11 is a circuit that cancels cross-modulation moiré 2f caused by cross-modulation generated in the luminance signal reproduction system 8.

The playback signal is processed by the equalization circuit 25 so that the playback level of f is f.
After the frequency characteristics are slightly adjusted so as to be lower than the reproduction level of c, the frequency characteristics are limited by the limiter circuit 26. The output of the limiter circuit 26 is input to the filter 12 which filters the low frequency conversion color signal f1.

Filter 12 is a low-pass filter or a band-pass filter. The output of the filter 12 is divided into two multipliers 1
Sent to 3. In the 2 multiplier circuit 13, the frequency f is 2
2f is obtained. The phase and gain of the 2ft frequency component are adjusted by a phase adjustment circuit 14 and a gain adjustment circuit 15, and then sent to a subtracter 16. In the subtracter 16,
Only the moire component 2f is canceled from the decoded video signal, and a moire-free signal is output to the terminal 17.

Here, the subtracter 16 does not need to be located after the adder 10, but may be located anywhere after the FM demodulator in the luminance signal reproduction system 8.

The second subtracter 16 is located within the luminance signal reproducing system 8.
A block diagram of this embodiment is shown in FIG. The luminance signal reproduction system 8 includes an equalizer circuit 18 that filters only the luminance signal component of the reproduced FM signal and compensates for the frequency characteristics, and an equalizer circuit 18 that filters only the luminance signal component of the reproduced FM signal and compensates for the frequency characteristics.
It is comprised of a demodulator 19 for demodulating, a low-pass filter 20 for filtering signal components from its output, a de-emphasis circuit 21 for de-emphasis, and a non-linear de-emphasis circuit 22. Subtractor 16 is inserted between low-pass filter 20 and de-emphasis 21.

This has the advantage that noise components leaking from the moiré canceller circuit are reduced by the de-emphasis circuit 21 and the non-linear de-emphasis circuit 22 compared to the first embodiment. The explanation of the operation of the luminance signal reproduction system is well known and will therefore be omitted.

Here, the operation of the limiter circuit 26, which is the key point of the present invention, will be explained.

As mentioned in the conventional example, even if the reproduction signal f, fc2f+ is at a constant level, if the reproduction level of fc changes,
The level of the demodulated cross-modulation component 2f also fluctuates. This is because the level of the 2f+ component after demodulation is determined by the ratio between the level of the carrier frequency fc and the level of fc 2f+ in the reproduced signal.

Therefore, the present invention attempts to normalize the level of the frequency f at the input of the moiré canceling circuit by the carrier frequency fc. In other words, limiting at the carrier frequency fc means normalizing the frequency levels other than the fc base at the level of the carrier frequency fc.

This will be explained using FIGS. 3(A) to 3(E).

(A) is the input signal of the limiter circuit 26, (B) is the output signal of the limiter circuit 26, (C) is the output signal of the moire canceling circuit, (D) is the 2f1 component in the demodulated signal, (E)
is the demodulated signal after moiré cancellation.

Here, when the playback level of the solid line fC is high, the dotted line is fc
This indicates when the playback level is low.

It can be seen that even if the reproduction level of fc fluctuates, the moiré component of 2f is sufficiently removed.

Although the present embodiment deals with a color signal whose frequency is f and whose acid component is low-frequency converted, the present invention is not limited to this. For example, it may be a signal obtained by line-sequentially FM modulating a color difference signal such as R-Y, B-Y or ■, Q signal, it may be a signal obtained by FM modulating the color difference signal after time axis compression, or it may be a signal obtained by FM modulating the color difference signal after time axis compression. It may be an FM-modulated signal, or it may be a variety of pilot signals.

Further, the equalization circuit 25 is necessary because there is an inconvenience that it cannot be limited around fc when the level of f is higher than the level of fc, but it is not necessary if the reproduced output level is originally f<fc.

Further, the doubler circuit 13 is simply constructed of a balanced modulator and a filter that filters the doubler component.

Further, the phase adjustment circuit 14 and the gain adjustment circuit 15 may not be provided.

Effects of the Invention As described above, the present invention allows the first signal to be adjusted to the carrier frequency (
A second signal is modulated in a frequency region lower than the frequency (f c) to form a second modulated wave, and the first modulated wave and the first modulated wave are An apparatus for mixing two modulated waves, recording them on a recording medium, and reproducing them from the recording medium, wherein the reproduction level of the second modulated wave of the reproduction signal is lower than the reproduction level of the first modulated wave. an equalizer circuit that adjusts the frequency characteristic to 1, a limiter circuit that limits the output of the equalize circuit, a filter that filters a second modulated wave component from the output of the limiter circuit, and a filter that multiplies the output of the filter by 2. The device is configured to include a doubler circuit and a subtracter that subtracts the output of the doubler circuit from a demodulated signal obtained by FM demodulating the first modulated wave, thereby increasing the FM carrier frequency fc.
This provides the effect that the cross-modulation component 2f can be canceled extremely effectively no matter how much the reproduced output level changes.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating a first embodiment of the present invention;
FIG. 2 is a block diagram illustrating a second embodiment of the present invention;
FIG. 3 is a spectrum diagram for explaining the present invention, and FIG. 4 is a spectrum diagram for explaining the conventional example. 11... Moire canceller circuit, 12...
...filter, 13...2 multiplier circuit, 14
・Old: Phase adjustment circuit, 15: Gain adjustment circuit, ]6: Subtractor, 25: Equalize circuit, 26: Old: Limiter circuit.

Claims (4)

[Claims] (1) The first signal is FM modulated at the carrier frequency (fc) to become the first modulated wave, and the second signal is FM-modulated at the carrier frequency (fc).
c) An apparatus that modulates in a lower frequency region to produce a second modulated wave, mixes the first modulated wave and the second modulated wave, records the mixture on a recording medium, and reproduces it from the recording medium, an equalization circuit that adjusts frequency characteristics such that a reproduction level of a second modulated wave of the reproduction signal is lower than a reproduction level of the first modulated wave; a limiter circuit that limits an output of the equalization circuit; and the limiter circuit. a filter that filters a second modulated wave component from the output of the filter, a doubling circuit that multiplies the output of the filter by 2, and an FM filter that filters the first modulated wave.
A magnetic recording/reproducing apparatus comprising: a subtracter for subtracting the output of the doubling circuit from the demodulated signal. (2) The magnetic recording and reproducing apparatus according to claim (1), wherein the first signal is a luminance signal of a video signal. (3) Claim (1) characterized in that the second modulated wave is a low frequency converted color signal obtained by modulating the color signal of the video signal to a low frequency range.
) magnetic recording and reproducing device. (4) The magnetic recording/reproducing apparatus according to claim (1), wherein the second modulated wave is an FM modulated color difference signal.