JPH0771262B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording / reproducing apparatus, and particularly in a so-called special reproduction mode in which a helical scan video tape recorder (hereinafter referred to as VTR) reproduces at a speed other than normal reproduction. The present invention relates to reduction of generated distortion.

[Conventional technology]

FIG. 3 is a view showing a mounting arrangement of the video head,
Four SP-R ', EP-R, SP-L', EP-L video heads 1a
1d are fixed to the rotary drum 10 in the arrangement shown in the figure for the purpose of reducing noise during special reproduction. The two heads 1a, 1d (or 1b, 1c) arranged close to each other have mutually opposite azimuth angles.

FIG. 4 shows a block diagram of the reproducing system. Reference numerals 2a to 2d are head amplifiers provided corresponding to the heads 1a to 1d, respectively, and outputs of the heads 1a to 1d are input to the head amplifiers 2a to 2d via a rotary transformer (not shown). And the playback output is these head amplifiers 2a-2d
After being amplified by, the signal passes through the first switch circuits 3a, 3b and the second switch circuit 4, is FM demodulated by the demodulation circuit 6, and is output to the output terminal 9. The first switch circuit 3a, 3b
Is switched by a drum flip-flop pulse 5 indicating which head is in contact with the tape.
Further, the outputs of the heads having mutually opposite azimuth angles adjacent to each other are amplitude-compared by the comparator 7, and the control circuit 8 which receives the comparison result selects the head having the larger output from the second switch circuit 4 described above. Switch control.

Next, the noise reduction operation will be described by taking the fast-forward reproduction in the VHS standard mode as an example.

The track locus is shown in FIG. SP-L 'head 1c
It is assumed that the L ₁ ′ track is used as the starting point and tracing is performed as shown in the figure. At this time, the first switch 3a is switched to the head amplifier 2c side by the pulse 5, and the switch 3b is also switched to the amplifier 2b side corresponding to the head 1b adjacent to the head 1c. At this time, even if the head 1b traces the L ₁ ′ track, there is no output because the azimuth angle is reversed, so the second switch circuit 4 is switched to the switch 3a side by the comparator 7 and the control circuit 8, and therefore The reproduction output of the head 1c is demodulated by the demodulation circuit 6. And SP
-L 'head 1c is R _1' opposite to eliminate the output of the head amplifier 2c is the above and according to the track, the output of the EP-R head 1b is increased, by switching the second switching circuit 4 to the switch 3b side The reproduction output of the head 1b is demodulated by the demodulation circuit 6.

By switching the adjacent heads having the opposite azimuth angles in this way, it is possible to remove the noise generated when tracing tracks having different azimuth angles.

[Problems to be solved by the invention]

However, in the conventional VTR, when the adjacent heads are switched, the horizontal sync signal interval becomes discontinuous due to the displacement of the head position, which causes a skew distortion in the reproduced image.

This will be explained with reference to FIG. 6. When the EP-R head is at the horizontal synchronizing signal position of the R'azimuth track as shown in the figure, both heads of the SP-L 'head are 15 .mu.m apart from the lower end of the head.
Since they are mounted at 2H intervals (740 μm) based on the position of m, the position is 2.9 μm behind the horizontal synchronizing signal position of the L'azimuth track. This corresponds to about 0.5 μs in terms of time, and the sync signal becomes discontinuous at the time of switching the head, which disturbs the synchronization of the monitor TV and appears as so-called skew distortion.

Therefore, the inventor of the present invention has developed a time axis correction circuit capable of eliminating this skew distortion. This is to perform a phase comparison between a horizontal synchronizing signal including a time axis fluctuation and a reference horizontal synchronizing signal to obtain an error voltage according to the comparison result, and control a delay time of a clock having a frequency according to the error voltage to a variable delay line. The clock signal is supplied as a clock for the composite video signal, whereby the composite video signal is delayed by a time corresponding to the time-axis variation, and the time-axis variation is corrected.

However, during a transition such as mode switching, there is a gap between the speed correction of the capstan motor that feeds the tape and the speed correction of the drum motor that rotates the head, which causes the relative speed between the tape and the head to change. However, since the cycle of the horizontal synchronizing signal largely deviates from the normal reproduction state, it may exceed the control range of the time axis correction circuit. In such a case, if the correction is performed by the time axis correction circuit, the time axis correction circuit does not operate normally, so that erroneous control is performed, and the reproduction screen is more disturbed than when the correction is not performed.

The present invention has been made to solve the above problems, and can reduce the skew distortion that occurs during special playback such as fast-forwarding and rewinding playback, and also enables playback screens during transition such as mode switching. It is an object of the present invention to obtain a magnetic recording / reproducing device in which the magnetic field does not disturb.

[Means for solving problems]

A magnetic recording / reproducing apparatus according to the present invention includes a horizontal sync signal separating circuit for separating a horizontal sync signal from a composite video signal including a time base fluctuation, a horizontal sync signal generating circuit for generating a reference horizontal sync signal, and the separated horizontal sync signal. A phase comparator that outputs an error voltage by performing a phase comparison between a signal and a reference horizontal synchronizing signal, a voltage controlled oscillator that generates a clock having a frequency according to the error voltage, and a composite that receives the clock as a control clock. A time axis correction circuit that has a variable delay line that delays the video signal for a predetermined time and that corrects the time axis fluctuation of the input composite video signal, and the time axis correction circuit that was corrected in the steady state during special playback. For the composite video signal, select the original composite video signal that is not corrected during the transition until the relative speed of the tape and head shifts to the steady state when switching the mode. A switch circuit for outputting is provided.

[Action]

In the present invention, the phase comparison between the horizontal synchronizing signal including the time base fluctuation and the reference horizontal synchronizing signal is performed, the error voltage is output according to the comparison result, and the clock having the frequency corresponding to the error voltage is delayed by a variable delay. It is supplied to the line as a clock for delay time control, whereby the composite video signal is delayed by a time corresponding to the time-axis variation, and the time-axis variation is corrected.

Also, when transitioning from normal playback to special playback mode, the signal indicating mode transition is used to switch and output the original video signal that has not been time-axis corrected until a steady state is reached.
It is possible to prevent the playback screen from being disturbed by a rapid time axis fluctuation during a transition such as the mode transition.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a time axis correction circuit and a switch circuit of a magnetic recording / reproducing apparatus according to an embodiment of the present invention. In the figure, numeral 21 indicates a video signal or the like which is input according to the frequency of an input control clock. It is a variable delay line capable of arbitrarily changing the delay time of a signal. Reference numeral 22 denotes a horizontal sync signal separation circuit (hereinafter referred to as a horizontal sync separation circuit) that extracts only the horizontal sync signal from the composite video signal input to the variable delay line 21.
23 is a pulse generation circuit that inputs the horizontal synchronization signal separated by the horizontal synchronization separation circuit 22 and generates a pulse at a predetermined timing using the input horizontal synchronization signal, and 24 is a horizontal synchronization signal that uses a crystal or the like. Generator and pulse generator
The pulse generated by 23 is used, and the generation of the horizontal synchronizing signal is reset by the pulse. twenty five
Is a phase comparison between the reference horizontal sync signal generated by the horizontal sync signal generator 24 and the horizontal sync signal of the input video signal separated by the horizontal sync separation circuit 22, and outputs an error voltage according to the phase error. And a phase comparator (including a sample hold circuit). Reference numeral 26 is a voltage controlled oscillator that changes the oscillating frequency according to the error voltage output from the phase comparator 25, and the delay time of the variable delay line 21 is changed by the clock frequency output from the voltage controlled oscillator 26. ing. Reference numeral 27 is a switch circuit that switches between the output of the variable delay line 21 and a signal that does not pass through the delay line 21, and 29 is a terminal to which a switching pulse from a switch control circuit (not shown) that controls the switch circuit 27 is input.

Next, the operation will be described.

The input composite video signal is input to the horizontal sync separation circuit 22 and divided by the separation circuit 22. One of them is input to the pulse generation circuit 23. This pulse generator 23
Uses this synchronization signal to generate a pulse at a predetermined timing determined externally. The predetermined timing is a timing at which the generation of the synchronization signal generator 4 is reset, and the reset timing is performed before the phase error of the phase comparison circuit 5 is accumulated and exceeds the dynamic range of the phase comparison. It must be done in the blanking interval which is the vertical sync signal interval. Therefore, a reset pulse may be generated for several H periods after the vertical synchronizing signal, but 1 / 2H is generated due to interlacing, so in reality, resetting is performed every two fields.

The horizontal sync signal generator 24 oscillates using a crystal oscillator or the like, and resets the generation of the sync signal by an external reset pulse, that is, a reset pulse from the pulse generator 23. The phase comparison circuit 25 compares the phase of the reference horizontal synchronization signal created by the horizontal synchronization signal generation circuit 24 with the horizontal synchronization signal input by receiving a time axis fluctuation from the outside, and samples and holds the phase error. Output as an error voltage using a circuit. The voltage controlled oscillator 26 oscillates a frequency corresponding to the output voltage of the phase comparator 25, thereby changing the delay time of the variable delay line 21, and the output has the time axis fluctuation corrected.

Here, from the switching pulse input terminal, switch circuit 27
A signal for switching control is input, whereby the switch circuit 27 is controlled at the timing shown in FIG. That is, the output of the variable delay line 21 is switched to the output of the variable delay line 21 by the pulse that has received the delay time of ΔT after the speed search is turned on, and the original uncompensated composite video signal is output during the transition such as mode switching. Prevents video signals disturbed beyond the dynamic range from appearing on the screen due to abrupt changes in the time axis during transition.

Therefore, in such an embodiment, in the steady state of special reproduction, the phase comparison between the reference horizontal synchronization signal and the input horizontal synchronization signal is performed to perform time axis correction according to the comparison result, and a stable image is obtained. In addition, even when there is a rapid time-axis change that exceeds the dynamic range (correction control range) during a transition such as mode switching, the disturbed video signal due to incorrect control does not appear on the screen. .

〔The invention's effect〕

As described above, according to the present invention, the phase comparison between the reference horizontal synchronization signal and the horizontal synchronization signal including the time base fluctuation is performed, and the delay time of the input video signal is corrected according to the comparison result. When switching between the corrected composite video signal and the original composite video signal, output the original video signal instead of the correction signal during transition until the relative speed of the tape and head shifts to a steady state when switching modes, etc. Therefore, it is possible to eliminate the discontinuity of the horizontal synchronizing signal that occurs when the head is switched, eliminate skew distortion, and prevent the playback screen from being disturbed by the rapid time axis fluctuation that occurs when the mode is switched. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing a time axis correction circuit and a switch circuit of a magnetic recording / reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a switching pulse timing diagram for explaining a switching operation, and FIG. 3 is a video head. FIG. 4 is a diagram showing a mounting state, FIG. 4 is a block diagram showing a reproducing system of a VTR, FIG. 5 is a diagram showing a relationship between a head and a track when special reproduction is performed, and FIG. 6 is an explanation that skew distortion occurs. FIG. 21 ... Variable delay line, 22 ... Horizontal sync signal separation circuit, 23 ...
... Pulse generation circuit, 24 ... Horizontal synchronization signal generation circuit, 25 ...
… Phase comparison circuit, 26 …… Voltage controlled oscillator, 27 …… Switch circuit, 29 …… Switching pulse. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A variable delay circuit to which a composite video signal having a time base fluctuation is input, and the delay time of the signal can be controlled by the frequency of a control clock supplied from the outside, and the composite video input to the variable delay circuit. A horizontal synchronizing signal separating circuit for separating a horizontal synchronizing signal from a signal, a pulse generating circuit for generating a pulse at a predetermined timing by using the separated horizontal synchronizing signal, a reference horizontal synchronizing signal and a pulse generating circuit from the pulse generating circuit. A synchronization signal generation circuit in which the generation timing of the reference horizontal synchronization signal is reset by a pulse, a phase comparison is performed between the horizontal synchronization signal separated by the horizontal synchronization signal separation circuit and the reference horizontal synchronization signal, and the phase error is an error voltage. And a clock having a frequency corresponding to the error voltage for controlling the variable delay circuit. A time-axis correction circuit for correcting the time-axis fluctuation of the input video signal, and a composite video signal corrected by the time-axis correction circuit and an original composite video that is not corrected. The dynamic range of the above-mentioned time axis correction circuit is exceeded due to the switch circuit that switches and outputs the signal and the rapid time axis fluctuation that occurs at the time of transition until the relative speed of the tape and head shifts to a steady state when switching modes. And a switch control circuit for controlling the switch circuit so as to select the original composite video signal for a period of time.