KR940008846B1 - Magnetic reproducing apparatus and magnetic recording/reproducing apparatus - Google Patents

Abstract

No content.

Description

Magnetic playback device and magnetic recording playback device

1 is a block diagram showing the configuration of an FM modulation system in a recording system of a magnetic recording and reproducing apparatus according to an embodiment of the present invention.

2A is a block diagram showing the principle configuration of an FM demodulation system in a reproduction system of a magnetic recording and reproducing apparatus according to an embodiment of the present invention.

2B is a block diagram showing a more practical configuration of the FM demodulation system in the reproduction system of the magnetic recording and reproducing apparatus according to the embodiment of the present invention.

3 is a block diagram showing the configuration of an FM modulation system of a recording system and an FM demodulation system of a reproduction system in a conventional magnetic recording and reproducing apparatus.

4 is a waveform diagram of inputs and outputs of the signal processing circuit shown in FIG.

5 is a spectral waveform chart of the FM carrier spectrum of each part of the FM demodulation system shown in FIG.

FIG. 6 is a waveform diagram for explaining the multiplication demodulation operation in the pulse count type FM demodulator shown in FIG.

FIG. 7 shows that when the video signal has a constant phase with respect to the horizontal sync pulse, and when the FM carrier has a phase shift with respect to the horizontal sync pulse like a dotted line, a bead pattern is generated so that the phase of the FM carrier is horizontal as with a solid line. When fixed with respect to the synchronous pulse, the bit line generation component is a waveform diagram for explaining that the video signal is not just identical but is not bit lined.

* Explanation of symbols for main parts of the drawings

31: signal processing circuit 35: magnetic tape

35: head amp 37: Equalize

38: first low pass filter 39: doubler

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording and reproducing apparatus, and more particularly, to a magnetic recording and reproducing apparatus for recording and reproducing broadband video signals such as HDTV (High Definition Tele-vision) signals.

In FM recording and reproduction of a conventional video signal, there is no correlation between the phase of the video signal and the phase of the carrier (hereinafter referred to as FM carrier) FM-modulated with the video signal. Therefore, at the time of reproduction, even if a part of the lower band of the FM carrier leaks less in the band of the FM demodulated video signal, it becomes a bit line and impairs the screen stability. That is, a so-called bead pattern flows on the screen.

When the human movement is skewed, the sensitivity of detecting the bit line is extremely high, for example, it is the cause caused by the bit line.

A bead pattern is detected in an amplitude (peak-peak value) of a portion of the lower band of the leaked FM carrier at about 1/200 (0.5% -46 dB) of the amplitude (peak-peak value) of the video signal.

In general, the acceptable limit for a product as a home VTR is that the Desired-to-Undesired Signal Ratio (DU ratio) is around 35 dB.

Here, with reference to the waveform diagram of FIG. 7, a bead pattern is generated in detail as the difference between the phase of the FM carrier and the phase of the horizontal synchronization signal changes.

In general, when the carrier is FM-modulated by the video signal e (t), it is known that an infinite number of side bands are generated for each frequency wp, as shown in the following equation.

e (t) _FM = A _n ∑J _N (m) cos [wc + Nwp) + α]

However, in the above equation, J _N (m) is the first kind of cell function, wp is each frequency of the video signal, wc is each frequency of the FM carrier, α is the leading edge or the trailing edge of the horizontal synchronization pulse. A value of the phase of the FM carrier (frequency) signal is measured based on (後 緣; trailing edge), and N means an integer from -∞ to + ∞.

Fig. 7 (a) shows the reference phase of the granular phase of the leading edge or the trailing edge of the horizontal synchronous pulse.

7B shows the waveform of the video signal.

The video signal is always synchronized with the horizontal sync pulse.

The solid line in Fig. 7C shows the waveform of the FM carrier at the reference phase, i.e. The fundamental and spectrum of the FM carrier are as shown in Fig. 7 (d).

The first lower band and the first upper band of the FM carrier are as shown in Figs. 7E and 7F, respectively.

As apparent from Figs. 7 (d) to (f), the phases of the first lower band and the first upper band of the fundamental spectrum of the FM carrier are all synchronized with the reference phase of the leading edge or the trailing edge of the horizontal synchronization signal. . Therefore, if this phase relationship is always maintained, the spectral phase of the lower band where the bead pattern is caused is synchronized with the horizontal synchronizing pulse, and the bead pattern does not [flow] on the screen.

On the other hand, even if the phase of the video signal is synchronized with the phase of the horizontal synchronizing signal, the phase of the FM carrier is 90 ° (α = 90) with respect to the reference phase of the horizontal synchronizing pulse as shown by the broken line in FIG. °) If off, the phase of the spectrum of the first lower band and the spectrum of the spectrum of the first upper band deviate by 90 °, as shown by the broken lines in Figs. 7 (d), (e), and (f), respectively. As a result, when the spectrum of the first lower band is mixed into the band of the demodulated video signal, a bead pattern appears on the screen due to the variation of the phase α. The video signal is always synchronized with the horizontal synchronizing signal as shown in FIG.

Here, with reference to Figs. 3 to 6, a method for preventing beading in a conventional FM demodulation system in a VTR (Video Tape Recorder) in MUSE (Multiple Sub-Nyquist Sampling Encoding) It demonstrates below.

3 is a block diagram showing a schematic configuration of a conventional FM modulation demodulation system for MUSE and VTR.

The input MUSE signal is fed to the signal processing circuit 31 and the FM modulator 32 having an AFC (automatic frequency control) circuit after the addition of the negative synchronization signal and the reference burst signal and time axis compression are performed. Is modulated by FM so that the recording amplifier 33 and the magnetic head are sandwiched between and recorded on the magnetic tape 35.

In addition, various timing pulses necessary for the operation of the signal processing circuit 31 and the FM modulator 32 are generated by the timing pulse generator 34 based on the MUSE signal.

By the way, since the MUSE signal adopts positive polarity synchronism, it cannot be recorded on magnetic tape as it is (refer to FIG. 4 (a)). In order to allow the MUSE signal to be recorded on the magnetic tape, for example, as shown in FIG. 4B, the MUSE signal is time-compressed 9/10 times in the signal processing circuit 31 for each period of the horizontal synchronization signal. .

The time-compressed MUSE signal is inserted into the negative electrode synchronization signal and the reference burst signal in the blank time (about 2.9 µsec) generated by the time compression and recorded on the magnetic tape 35. In addition, the arrow in FIG.4 (a), (b) has shown the phase in which a positive electrode synchronization is performed.

On the other hand, during reproduction, after the jitter 44 of the reproduction signal is corrected by the TBC (time base, collect) circuit 43 based on the negative synchronization signal and the reference burst signal, the reproduction signal is reproduced by the time axis expansion circuit 44. 10/9 times the time axis extension processing is performed to reproduce the first MUSE signal.

The band of the MUSE signal input to the signal processing circuit 31 is 8.1 MHz, but as a result of the 9/10 times time compression processing, the required band becomes 9 MHz.

As shown in Fig. 5 (a), if the carrier is FM-modulated by the MUSE signal in which the modulation frequency fp of 9 MHz is superimposed on the intermediate gray level and recorded on the magnetic tape 35, the FM carrier is in the process of FM demodulation during reproduction. The spectrum of is as shown in Fig. 5B. That is, during reproduction, the recording information from the magnetic tape 35 is input to the equalizer 37 with the head amplifier 36 interposed therebetween.

The spectrum of the FM carrier output from the equalizer 37 is as shown in FIG. 5 (b), and the FM modulation parameter is the frequency of Fe of the center carrier of 16 MHz, the frequency shift ΔF of ± 4 MHz, The modulation frequency Fp is set at 9 MHz modulation index m, which is 0.44.

As shown in FIG. 3, the cutoff frequency of the first low pass filter 38 is determined by the frequency characteristic of the output of the magnetic head, but is referred to herein as 36 MHz for convenience.

As shown in Fig. 5 (b), the components of the second lower band (-2MHz, 2.4% of the carrier ratio) of the FM carrier are returned to the positive frequency range and demodulated as they are and the video signal band (9MHz) It is mixed with. Also, in general, the band of the demodulated video signal (hereinafter referred to as the "corridor video band") is handled from -9MHz to + 9MHz.

Since the higher order sideband of the FM carrier decreases its spectral intensity, it is necessary to perform the demodulation process when the frequency of the center carrier Fc is shifted to the higher frequency side as much as possible to prevent bit interference.

In order to realize this, conventionally, (a) a doubler for multiplying the frequency of the FM carrier before the FM demodulation process, and (b) a carrier doubled demodulator such as a pulse count type is adopted, and (a) and ( The multiplication and demodulation of the FM carrier is performed by cascading the circuit of b).

For example, as shown in FIG. 3, the output of the first low pass filter 38 is input to the doubler 39, where the frequency of the FM carrier is doubled.

As shown in Fig. 5 (c), the doubler 39 performs a multiplication process, and the modulation parameters of the FM carrier are 32 MHz for the center carrier Fc2, ΔF2 for ± 8 MHz, and modulation index m ₂ for 0.89. Are converted respectively.

Therefore, the second lower band of the FM carrier is converted to 14 MHz and deviates from the demodulated video band (10 MHz). Therefore, bit interference does not occur.

However, each component of the third lower band (5 MHz, large carrier ratio of 1.2% -38 dB) and the fourth lower band (-4 MHz, carrier ratio of 0.15% -56 dB) of the FM carrier is mixed into the demodulated video band. come.

Thus, as shown in FIG. 3, a high pass filter 40 is provided to cut off components of the third lower band and the fourth lower band of the FM carrier. In addition, the cutoff frequency of the high pass filter 40 is 10 MHz or more.

The output of the high pass filter 40 is input to a pulse count double-modulation FM demodulator (hereinafter referred to as a "pulse count-type FM demodulator") 41 and demodulated twice.

Like the doubler 39, the pulse count type FM demodulator 41 multiplies the frequency of the center carrier Fc, the frequency shift ΔF, and the modulation index m by about two. The FM carrier component is output as it is mixed with the demodulated video signal component. Thus, a second low pass filter 42 is provided to remove the main FM carrier component and extract the video signal.

That is, as shown in FIG. 3, the output of the pulse count type FM demodulator 41 is sent to the 2nd low pass filter 42. As shown in FIG. However, at this time, part of the lower band of the FM carrier enters the demodulated video band and causes bit interference when its level is above a predetermined allowable limit level.

On the other hand, if the FM carrier is quadrupled demodulated by the cascade connection between the doubler 39 and the pulse count type FM demodulator 41, the modulation parameters of the FM carrier have a frequency of Fp of 9 MHz and a main carrier Fc4. Is 64 MHz, the frequency shift ΔF4 is ± 16 MHz, and the modulation index m4 is about 1.78.

Therefore, entering the demodulated video band cannot be seen below the detected bit line in the seventh lower band (1 MHz, carrier ratio of about 0.01%) of the FM carrier (see FIG. 5 (e)).

In such ideal operation, even if the frequency of the center carrier Fc of the FM modulation is lowered to 12 MHz, the fifth lower band (3 MHz, carrier ratio of 0.4%) of the FM carrier, which is a problem in the multiplication demodulation, is a bit detection limit level. It becomes the level of neighborhood. As a result, the pulse counted FM demodulator 41 is essentially unnecessary.

By the way, the analog multiplier (multiplier) for the doubler structure which is generally available now, and the broadband thing contains a considerable error component by the output from the input FM carrier etc. at the output.

In short, as shown in FIG. 5 (d), at the output of the doubler 39, the leakage component Fc from the input FM carrier is present about 20% of the center carrier portion Fc2 doubled by the doubler 39. It is common to do it.

In this case, the leakage component of the first lower band (7 MHz to leakage carrier ratio of 21%) reaches 4% of the doubled center carrier component, which causes the generation of bit strings.

Here, the conditions under which the multiplication demodulation is satisfied in the pulse counter FM demodulator 41 will be described below with reference to FIG. Further, a monomultivibrator (not shown) is triggered at the zero cross point of the input carrier, and the output pulse (the pulse shown in Figs. 6A to 6C) is transferred to the second low pass filter 42. The video signal is demodulated by averaging.

In the pulse count type FM demodulator 41, the exact conditions under which the doubled demodulation is established are shown in Fig. 6 (a). , And low harmonic skew components.

In other words, as shown in the diagram (a), if the intervals between the zero cross points are equally spaced in the FM carrier (the zero cross point of the fundamental wave carrier and the zero cross point of the input carrier coincide). The leakage component from the input carrier is eliminated, and the mixing of the lower band component in the FM demodulated video band is reduced.

In Fig. 6A, the waveforms of the input FM carriers are indicated by solid lines for convenience, and the waveforms of the basic and carriers are indicated by broken lines.

On the other hand, when the applied FM carrier contains a second harmonic skew component, for example, as shown in Fig. 6B, the intervals between the zero cross points disappear at equal intervals (zero cross point of the fundamental wave carrier). The zero cross point of the second harmonic skew and the zero cross point of the input carrier are all different).

The input leakage component increases or decreases according to the degree of deviation between the zero roll cross points from the equal intervals.

In the case where the center component Fc2 doubled by the doubler 39 contains the leakage component Fc '(1/2 low harmonic skew component) from the input FM carrier not doubled (FIG. 6 ( In the same manner as described above, the interval between the zero cross points disappears at equal intervals, so that the input leakage component is increased or decreased depending on the degree to which the distance between the zero cross points deviates from the equal interval.

The spectrum of the leak component Fc '(refer to FIG. 5 (d)) is converted by the pulse count type FM demodulator 41 to convert the leak component Fc2 from the input carrier as shown in FIG. The three lower bands (5MHz, leakage carrier ratio 1.4%) enter the FM demodulated video band.

In addition, in the pulse counter type FM demodulator 41, intermodulation of the upper and lower harmonic spectra of the main carriers, and intermodulation of each harmonic of the main carrier and the leak component are also performed.

2 MHz component (vs. main carrier) by intermodulation of the second lower band (14 MHz, major carrier ratio of 9%) and 20% leak component Fc (16 MHz, major carrier ratio of 20%) of dual menyl carrier Fc2 Ratio 9 × 20 / (2 × 100)% = 0.9%), resulting in a bead pattern. To avoid this, the output of the doubler 39 is directed to the high pass filter 40 with a cutoff frequency of 14 MHz.

The leak component Fc 'is attenuated by the high pass filter 40 to prevent the occurrence of bit strings.

However, in the conventional configuration, the modulation index m1 is large and the spread spectrum is large in the upper and lower bands of the FM carrier spectrum.

Therefore, when a part of the lower band of the FM carrier spectrum is cut off by the high pass filter 40, the upper and lower bands are unbalanced, and it is easy to cause inversion (tailing noise) in the FM demodulation output.

Therefore, by reducing the modulation index m1 and preventing the frequency shift from ΔF by ± 2 MHz, it is possible to reduce the spectral spread of the upper and lower bands to prevent inversion, but it is difficult to improve the SN ratio of the demodulated video signal. I have a different problem.

In addition, installing the high pass filter 40 to prevent bit lines complicates the configuration of the apparatus and at the same time causes an increase in cost.

It is therefore an object of the present invention to provide a simple and inexpensive magnetic reproducing apparatus and a magnetic recording / reproducing apparatus so as to prevent bit strings without using a high pass filter to cut off a portion of the lower band of the spectrum.

A magnetic reproduction apparatus according to the present invention reproduces a video signal from a magnetic recording medium on which an FM carrier obtained by FM modulation of a carrier with a video signal is recorded.

In recording, the phase of the FM carrier is reset to the reference phase of the leading edge of the horizontal sync pulse in the video signal and is fixed to the reference phase every one period of the horizontal sync pulse.

The magnetic reproduction apparatus according to the present invention includes pickup means for picking up an FM carrier from a magnetic recording medium, and FM demodulation means for FM demodulating the picked-up FM carrier and converting it into a video signal.

FM demodulating means is the frequency of the pick-up FM carrier 2 ^M a (M is a positive integer) by holding FM demodulating the output of the drain end chaebae means of times the frequency is again 2 ^N (N is a positive integer) baedoen video signal And an FM demodulator with a sampling function for converting.

The output of the multiplication means is directly put into the FM demodulator having a multiplication function, and a high pass filter is not provided between the multiplication means and the FM demodulator having a multiplication function.

A magnetic recording and reproducing apparatus according to the present invention includes a recording system for recording a video signal on a magnetic recording medium and a playback system for reproducing a video signal from a go recording medium.

The recorder includes FM modulating means, reset means and magnetic recording means.

The FM modulating means FM modulates the carrier with a video signal and outputs an FM carrier.

The reset means resets the FM modulation means to the reference phase of the horizontal synchronization pulse every one period of the horizontal synchronization pulse in the video signal, thereby resetting the phase of the FM carrier corresponding to the horizontal synchronization pulse front end by the reference phase every one period of the horizontal synchronization pulse. Secure in.

The magnetic recording means magnetically records the phase fixed FM carrier on the magnetic recording medium.

The regeneration system has the same configuration as the magnetic regeneration device of the present invention described above.

According to the present invention, since the phase of the FM carrier of the horizontal sync pulse is fixed at the reference phase at the leading edge of the horizontal sync pulse at the time of recording, for example, part of the FM carrier spectrum is leaked in the band of the FM demodulated video signal at the time of reproduction. Even if the disturbance signal caused by the leak appears to be distorted (distorted) in the reproduced image synchronized with the video signal, the human detection sensitivity can be lowered compared to the bit lines flowing out of synchronization with the video signal.

As a result, even if the frequency bias amount of the FM carrier is increased, the level of the disturbance signal can be suppressed to a practical level without causing the high pass filter to cut off a part of the lower band of the FM carrier spectrum.

Therefore, the SN ratio of the FM demodulated video signal can be improved without causing an inversion phenomenon (tailing noise) of the FM demodulated video signal.

The omission of the high pass filter simplifies the configuration and reduces the cost.

One embodiment of the present invention will be described below with reference to FIGS. 1, 2 and 2B.

1 shows a configuration example of a modulation system, and FIG. 2 shows a configuration example of a demodulation system.

The phase of the FM carrier corresponding to the horizontal synchronous pulse tip at the leading edge of the pulse at each cycle of the horizontal synchronous pulse of the video signal to be recorded with reference to FIG. 1 will be described below.

1 is a block diagram showing an example of an FM modulation system in a recorder of a magnetic recording / playback apparatus according to an embodiment of the present invention.

As shown in FIG. 1, the FM modulation system mainly includes a signal processing circuit 1, a DC amplifier 2, an FM modulator 3, a timing signal generator 4, and a frequency discriminator 5. As shown in FIG.

The signal processing circuit 1 is input with a recording video signal (e.g., MUSE signal).

The output of the signal processing circuit 1 is given to the DC amplifier 2.

The frequency discriminating error signal (DC voltage) is input to the signal processing circuit 1 from the frequency discriminator 5.

In the signal processing circuit 1, the frequency discriminating error signal is superimposed on the recorded video signal to emphasize the high frequency component again.

In the DC amplifier 2, the output of the signal processing circuit 1 is DC-amplified over a wide band and sent to the FM modulator 3.

The first and second reset pulses are input to the FM modulator 3 from the timing signal generator 4.

In the timing signal generator 4, for example, a clock signal Fck and a horizontal synchronization pulse FH of 9.72 MHz are input.

It is assumed here that a condition of Fck = n · FH (n is an integer) is established.

The timing signal generator 4 outputs the AFC reference clock signal AFC gate pulse and the first and second reset pulses based on these signals Fck and FH.

In addition, the reference clock signal for the AFC has a clock signal Fck to the frequency (9,72MH _Z) of the same frequency as the carrier frequency F _H of the horizontal pulse corresponding to the leading end.

The gate pulse for the AFC is a signal instructing the frequency discriminator 5 to make a frequency comparison only for a period corresponding to the leading end of the horizontal synchronization pulse FM in the recorded video signal.

The first and second reset pulses are forcibly reset the phases of the FM carriers corresponding to the front end portions of the horizontal synchronization pulses to the reference phase.

The pulse for resetting the phase of the FM carrier of the FM modulator 3 may be essentially one reset pulse.

However, when there is only one reset pulse, it is preferable that there are two or more reset pulses in order to alleviate the phase change since a sudden change in the phase of the FM carrier occurs and a large pulse noise occurs during FM demodulation.

That is, only when there are two reset pulses as in the present embodiment, the timing signal generator 4 outputs the first reset pulse when it is near the reference phase, resets the phase of the FM carrier corresponding to the tip, When it reaches, the second reset pulse is output to reset the phase of the FM carrier corresponding to the tip portion.

As a result, the FM carrier corresponding to the horizontal synchronous pulse tip can be reliably reset to the reference phase with high accuracy, so that waveform distortion (pulse noise) caused by the FM demodulated video signal can be reduced.

The output of the FM modulator 3 is sent to the frequency discriminator 5.

The frequency discriminator 5 compares the frequency of the AFC reference clock signal with the frequency of the FM carrier output from the FM modulator 3 only for the predetermined period.

According to the above configuration, the frequency of the FM carrier output and the frequency of the AFC reference clock signal are compared by the frequency discriminator 5 and fed back to the signal processing circuit 1 a frequency discrimination error signal which changes according to the frequency difference.

In the signal processing circuit 1, the frequency discriminating error signal is superimposed on the recorded video signal to emphasize the high frequency of the video signal.

The output of the signal processing circuit 1 is amplified at an appropriate amplification factor in the DC amplifier 2 and then superimposed on the base bias voltage of the FM modulator 3.

Then, the frequency of the FM carrier rises (or falls) as the direct current component of the base bias voltage rises (or falls) in the FM modulator 3.

As a result, the FM carrier modulated with the video signal is output from the FM modulator 3.

At this time, the first and second reset pulses from the timing signal generator 4 are used to reset the FM carrier corresponding to the horizontal synchronization pulse tip to the reference phase with high accuracy, thereby reducing the excessive distortion caused by the reset.

Instead of the modulation system shown in FIG. 1, a modulation system such as that disclosed in Japanese Patent Application Laid-Open Nos. 63-185177 or 63-274290 may be used in this invention.

Next, with reference to FIG. 2A, a more principle example of the FM demodulation operation during reproduction will be described below.

The FM carrier reproduced by the magnetic head is input to the doubler 9 (double multiplier) and gate circuit 17 of the FM demodulator 50.

In the FM demodulator 50, the output of the doubler 9 is directly input to the pulse count type FM demodulator 11.

That is, in the reproduction system of FIG. 2A, the high-pass filter 40 for preventing the bite pattern disposed between the doubler 39 and the pulse count FM demodulator 41 is omitted in the conventional example (see FIG. 3). .

The output of the FM demodulator 50, that is, the FM demodulated video signal, is output as the video signal with the TBC time base collect circuit 13 interposed therebetween and is input to the horizontal synchronous pulse detector 16.

The horizontal synchronous pulse detector 16 separates the horizontal synchronous pulse from the FM demodulated video signal.

The separated horizontal synchronization pulses are input to the gate circuit 17 and the write trigger pulse generator 18.

The gate circuit 17 pulls out a certain frequency portion from the FM carrier as a burst signal by gated the FM carrier in synchronization with the leading edge of the horizontal synchronization pulse.

The write trigger pulse generator detects a specific zero cross point of the burst signal in synchronization with the trailing edge of the horizontal synchronization pulse and outputs a write trigger pulse to the TBC circuit 13 based on the detection result.

In synchronization with the write trigger pulse, the FM demodulated video signal and the lower band of the FM carrier spectrum which are mixed in the demodulated video band are written into the memory in the TBC circuit 13.

Next, a more practical example of the FM demodulation operation at the time of reproduction according to FIG. 2B will be described below.

The following two items (1) and (2) can be given roughly as differences from the principle circuit configuration shown in FIG. 2A.

Except for the following two items, since the circuit configurations of FIGS. 2A and 3 are essentially the same, detailed description thereof is omitted here.

(1) The head amplifier 6, the equalizer 7, the first low pass filter 8, the second low pass filter 12, and the time axis extension circuit 14 are provided in the same manner as the conventional example shown in FIG. .

(2) The dedicated FM demodulator 15 is provided for the burst signal processing system.

This is because the frequency characteristics of the FM demodulator 11 of the video signal demodulator are changed in the equalizer 7 in a wide band, and therefore sag occurs at the leading edge or the trailing edge of the horizontal synchronization pulse, which is not suitable for the horizontal synchronization pulse detection. Because.

Furthermore, since the FM demodulator 15 is relatively good in a narrow band, it is sufficient to use only one low-cost general-purpose IC used for the current home VTR.

As described above, by resetting the phase of the FM carrier for each horizontal synchronization pulse in synchronization with the reference phase at the leading edge of the horizontal synchronization pulse, the FM carrier can be synchronized with the video signal on the screen.

Therefore, the lower band of the FM carrier spectrum that has been mixed in the demodulated video band also appears apparently on the screen.

However, the sensitivity of human detection of the flowing bead pattern on the screen is extremely high, and the bead pattern is detected even when the amplitude of the undesired signal causing the bit line is 1/200 times the amplitude of the video signal.

Therefore, the tolerance of DU ratio in home video is said to be around 35dB.

However, when the bead pattern stops on the screen, the bit line appears as a skewed image of the reproduced image, so the detection sensitivity by the human is lowered.

Therefore, even if a still bit line of about 1/20 is mixed in the reproduced video, the screen stability is not deteriorated.

Therefore, even if the high pass filter connected to the output of the conventional doubler is not used, there is no problem, and even if the frequency shift is increased ΔF, the FM spectral band is widened, and even if the lower wave component is forced into the video band, no bit interference occurs. Do not.

Claims (10)

A magnetic reproducing apparatus for reproducing a video signal from a magnetic recording medium on which an FM carrier modulated using the video signal is recorded; The phase of the FM carrier portion carrying the synchronization signal is reset to the reference phase at the leading edge of the horizontal synchronization pulse in the video signal every period of the horizontal synchronization pulse width in the zero signal at the time of recording; The leading edge is fixed to the reference phase every period of the horizontal synchronous pulse width; The magnetic reproduction apparatus includes pickup means for picking up the FM carrier from the magnetic recording medium, and FM demodulation means (50) for FM demodulating the FM carrier picked up by the pickup means to generate the video signal; ; The FM demodulation means has a multiplication means 9 for multiplying the frequency of the FM carrier picked up by the pick-up means by 2 ^M (M is a positive integer) and a frequency-doubling fuction as an output. The FM carrier further includes an FM demodulator 11 for superimposing the demodulated video component and the FM carrier component multiplied by 2 ^N (N is a positive integer) times, and when FM demodulating the output of the multiplication means, And an output of the multiplication means is directly input to the FM demodulator having a frequency multiplication function. The frequency multiplier according to claim 1, wherein the multiplication means comprises a frequency doubler circuit (9) that multiplies the frequency of the FM carrier picked up by the pickup means, and the FM demodulator (11) has a frequency doubled function, And an FM signal of an output of the frequency doubler circuit as an output is superimposed on a 4-multiplied FM carrier component multiplied by two again and a demodulated video signal. 2. The apparatus according to claim 1, further comprising: jitter detecting means (15 to 18) for carrying a synchronization signal and detecting jitter in the portion of the FM carrier picked up by the pick-up means by an FM carrier, and in response to the detection output of the jitter detecting means. And a time axis correction means (13) for removing jitter components from the video signal by correcting the time axis of the reproduced video signal provided as an output from the FM demodulation means. 4. The horizontal synchronous pulse detecting means (16) according to claim 3, wherein the jitter detecting means includes a horizontal synchronous pulse detecting means (16) for detecting a horizontal synchronous pulse from an output of the FM demodulating means and providing the output as an output. Burst signal extracting means (17) for carrying out a synchronization signal in response to a pulse and extracting a portion of the FM carrier portion picked up by the pick-up means by the pick-up means as a reference burst signal, and from said horizontal synchronous pulse detecting means; And time axis control signal detection means (18) for outputting a time axis control signal to said time axis correction means by detecting a predetermined zero cross point in said reference burst signal based on the trailing edge of said horizontal synchronization pulse. Magnetic regeneration device. 4. The FM demodulation means (15) according to claim 3, wherein the jitter detecting means has a narrow band basically and obtains horizontal synchronization pulses by demodulating the FM carrier picked up by the pickup means, and the horizontal pulses. Horizontal synchronous pulse detection means 16 for accurately detecting and outputting the horizontal synchronous pulse from the output of the dedicated FM demodulation means, and horizontally from the output of the pickup means in response to the horizontal synchronous pulse provided from the horizontal synchronous pulse detection means. A burst signal extracting means 17 for extracting a part of the FM carrier corresponding to the synchronous pulse leading end as a reference burst signal, and the reference burst signal based on a trailing edge of the horizontal synchronous pulse provided from the horizontal synchronous pulse detecting means; When outputting a time axis control signal to the time axis correction means by detecting a predetermined zero cross point And a reduction control signal output means (18). A magnetic recording / reproducing apparatus having a recording system for recording a video signal on a magnetic recording medium and a reproduction system for reproducing the video signal from the magnetic recording medium; The recorder comprises an FM modulating means (3) for FM-modulating a carrier with the video signal and outputting an FM carrier, and the reference signal at the leading edge of a horizontal sync pulse at every period of the horizontal sync pulse width in the video signal. Reset means (4) for fixing the phase of the leading edge of the FM carrier portion carrying the synchronous signal in the reference phase at each period of the horizontal synchronization pulse width by resetting the FM carrier portion carrying the Magnetic recording means for magnetically recording on the magnetic recording medium the FM carrier of the FM carrier portion carrying the synchronization signal in a corrected phase; The reproduction system comprises pickup means for picking up the FM carrier from the magnetic recording medium, and FM demodulation means (50) for FM demodulating the FM carrier picked up by the pickup means and generating the video signal therefrom; The FM demodulation means has a multiplication means 9 for multiplying the frequency of the FM carrier picked up by the pick-up means by 2 ^M (M is a positive integer) and a frequency doubled function in FM demodulating the output of the multiplication means. And an FM demodulator 11 having an FM carrier as an output and superimposing the demodulated image component with an FM carrier component multiplied by 2 ^N (N is a positive integer) times further; And the output of said multiplication means is directly input to said FM demodulator having a multiplication function. 7. The multiplier according to claim 6, wherein the multiplication means comprises a frequency doubled circuit (9) for doubling the frequency of the FM carrier picked up by the pickup means, and the FM demodulator has a frequency doubled function, A magnetic recording and reproducing apparatus characterized by superimposing and outputting a demodulated video signal with an FM carrier frequency of the output of the multiplication circuit being multiplied by 2 again. The jitter detecting means (15 to 18) according to claim 6, wherein the reproducing system carries a synchronization signal and detects jitter of the portion of the FM carrier picked up by the pick-up means by the FM carrier, and the jitter detecting means is detected. And a time axis correction means (13) for removing jitter components from the video signal by correcting the time axis of the video signal output from the FM demodulation means in response to the output. 9. The jitter detecting means according to claim 8, wherein the jitter detecting means comprises a horizontal synchronizing pulse detecting means (16) for detecting and outputting a horizontal synchronizing pulse from an output of the FM demodulating means, and the horizontal synchronizing pulse provided from the horizontal synchronizing pulse detecting means. A burst signal extracting means (17) which carries a synchronous signal in response and extracts the portion of the FM carrier picked up by the pickup means as a reference burst signal, and the horizontal synchronous pulse provided from the horizontal synchronous pulse detecting means; And a time axis control signal detection means (18) for outputting a time axis control signal to said time axis correction means by detecting a predetermined zero cross point in said reference burst signal based on a trailing edge of the magnetic field. Device. 9. The FM demodulating means (15) according to claim 8, wherein said jitter detecting means has a narrow band, and horizontal demodulation-only FM demodulating means (15) for demodulating said FM carrier picked up by said pick-up means to obtain a horizontal synchronizing pulse basically; Accurately detect the horizontal synchronizing pulse from the output of the pulse-only FM demodulating means to detect the synchronizing signal from the output of the pickup means in response to the horizontal synchronizing pulse detecting means 16 and the horizontal synchronizing pulse provided from the horizontal synchronizing pulse detecting means. A burst signal extracting means 17 for outputting a part of the FM carrier carrying a as a reference burst signal and a predetermined burst in the reference burst signal based on a trailing edge of the horizontal sync pulse provided from the horizontal sync pulse detecting means. Time axis control signal output means for outputting a time axis control signal to the time axis correction means by detecting a zero cross point And a magnetic recording and reproducing apparatus, characterized in that (18).