JPS62161290A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce skew distortion by providing a switching circuit that switches and selects the output of a variable delay circuit and the output of a fixed delay circuit according to switching of the output of a main head and an auxiliary head. CONSTITUTION:The output of each head is inputted to head amplifiers 2a-2d, and after amplification, inputted to the first switching circuits 3a, 3b, and further, passed through the second switching circuit 4, and supplied to a demodulating circuit 6. After demodulation and reproduction, the output passes through a variable delay circuit 9 and the fourth switching circuit 15, and outputted from a video signal output end 13. The output of a variable delay circuit 9 is inputted also to a fixed delay circuit 14 and the output is supplied to the fourth switching circuit 15. When the output X of a controlling circuit 8 switches the second switching circuit 4, the fourth switching circuit 15 selects the output of the fixed delay circuit for a fixed time from rising of the switching pulse, and after stabilizing the output of the variable delay circuit, controlled by a switching signal Z to change the output of the variable delay circuit. Thereby, skew of a reproduced picture can be eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a helical scan type magnetic recording and reproducing bag (hereinafter referred to as VTR), and particularly when the device reproduces at a speed different from the normal speed. This relates to the reduction of generated noise.

[Conventional technology]

FIG. 2 shows a conventional example. FIG. 5(a) is a diagram showing the attachment of the head, and FIG. 2(b) is a block diagram. In the figure,
la, lc are main heads (SP-R, 5P-L), 1
b.

1d are auxiliary heads (BP-R, EP-L) each having an azimuth opposite to that of the adjacent main head, and these four heads are attached to the hend drum cylinder 14 as shown in FIG. 2 (al). The outputs of the heads 1a to 1d are amplified by head amplifiers 2a to 2d, and then amplified by the first switch circuits 3a, 3b and the switch circuit 4 of $2.
The signal is then modulated by i degrees in the demodulation circuit 6 and outputted from the video signal output terminal 13. 5 is a drum flip-flop pulse indicating which side of the head is in contact with the tape, and this pulse 5 causes the first switch circuit 3 to
a.

3b is switched. 7 is a comparator for comparing the outputs of adjacent heads with opposite azimuths, for example, heads 1a and 1d; 8 is a comparator for comparing the outputs of the heads 1a and 1d; 8, the output of the comparator 7 causes the second switch circuit 4 to select the output of the two heads that is larger; The second switch circuit 4
This is a control circuit that controls the

Next, the operation will be explained using standard mode fast-forward playback of a VH3 system VTR as an example.

FIG. 3(a) shows a trace pattern of 5x fast-forward playback. The 5P-L head 1c traces the track L1 from bottom to top. At this time, the first switch 3a
is switched to the head amplifier 2c side, and the first switch 3
b is also switched to the head 2b side at the same time. At this time,
Even if the BP-R head 1b traces the track L1, there is no output due to azimuth loss. Therefore, in accordance with the output of the comparator 7, the control circuit 8 causes the second switch circuit 4 to select the output of the head 1c which has a large output. switch 3a
Switch to the side. As the trace progresses, 5P-L head 1c
starts tracing the track R1, the output of the head amplifier 2c becomes low due to the azimuth loss, and the output of the EP-R head 1b increases instead. Switch the switch circuit 4 to the switch 3b side.

In this way, by switching between adjacent heads with different azimuths, such as heads 1c and 1b or heads la and ld, noise generated when tracks with different azimuths are crossed during fast-forward playback is removed.

[Problem that the invention seeks to solve]

However, conventional VTRs have a drawback in that when switching between adjacent heads, the horizontal synchronizing signal interval becomes discontinuous due to a shift in the head position, causing skew distortion in the reproduced screen. This situation is shown in FIG. 3(b). EP-
When the output of the R head tracing the R azimuth track becomes smaller than the output of the 5P-L head tracing the L azimuth trunk, the heads are switched. For simplicity, assuming that the outputs switch at the same time, EP-R
When the head is at the horizontal synchronization signal position of the R azimuth trunk, the 5P-L head is at a position 2.9 μm behind the synchronization signal position of the L azimuth trunk. When converted into time, this corresponds to approximately 0.5 μsec. Therefore, EP-
When switching from R head to 5P-L head, 0°5μ
sec signal is delayed, and this appears as skew distortion on the TV screen.

This invention was made in order to solve the above-mentioned problems, and provides a magnetic recording and reproducing device that can reduce skew distortion caused by head switching during playback screens that are not at normal speeds, such as during fast-forward, double-reverse playback, etc. The purpose is to obtain.

[Means for solving problems]

A VTR according to the present invention includes: a variable delay circuit whose delay time is determined by a clock frequency supplied to the output of a demodulation circuit; a clock generating means for supplying a clock of a predetermined frequency to the variable delay circuit; A fixed delay circuit connected to the output and a switch circuit for switching between the variable delay circuit output and the fixed delay circuit output are provided.

[Effect]

In this invention, the delay time of the variable delay circuit is changed by switching the clock frequency in synchronization with switching between heads with different adjacent azimuths, absorbing the discontinuity in the synchronization signal interval due to head switching, and furthermore, the variable delay Until the corrected signal appears at the output of the circuit, a signal that is a fixed delay of the signal before the head is switched is output, and when the clock frequency of the variable delay circuit is switched, the clock that remains in the variable delay circuit is To eliminate discontinuity in synchronization signal intervals caused by outputting a signal before switching.

〔Example〕

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

FIG. 1 shows a VTR according to an embodiment of the present invention. FIG.

It is a figure which shows the timing relationship of Y and Z. Standard mode R azimuth head 5P-R (1a), L azimuth head 5P-L (1c,), and 3x mode R azimuth head EP-R (1b), L azimuth head UP-L (1d), As shown in FIG. 1 (al), each is attached to the head drum cylinder 14.

The spacing between adjacent mutually opposite azimuthal heads is chosen to be an integer multiple of the distance corresponding to the horizontal synchronization time. The output of each head is input to head amplifiers 2a to 2d, and after being amplified,
The signal is input to the first switch circuits 3a and 3b. Furthermore, this signal passes through a second switch circuit 4, is supplied to a demodulation circuit 6, is demodulated and reproduced, and is then demodulated and reproduced by a variable delay circuit 9. The signal passes through the fourth switch circuit 15 and is output from the video signal output terminal 13. Further, the output of the variable delay circuit 9 is the fixed delay circuit 1.
4, and its output is also input to the fourth switch circuit 1.
5. Further, 5 is a drum flip-flop pulse indicating which side of the head is in contact with the tape, and the first switch circuits 3a and 3b are switched by this pulse. Reference numeral 7 denotes a comparator that compares the outputs of adjacent heads with opposite azimuths, and the control circuit 8 causes the second switch circuit 4 to select the head with the larger output according to the output of the comparator 7. The switch circuit 4 is switched by the switch switching signal X so that 1). 12 are different frequencies fl
, [1st . second oscillation circuit, 1
The first . Second oscillation circuit 1). This is a third switch circuit that switches the output of the variable delay circuit 9, thereby changing the clock frequency supplied to the variable delay circuit 9.

The fourth switch circuit 15 is configured such that the output X of the control circuit 8 is
When switching the switch circuit 4, select the fixed delay circuit output for a certain period of time from the rising edge of the switching pulse,
After the variable delay circuit output becomes stable, it is controlled by a switching signal Z to switch to the variable delay circuit output.

Next, the operation will be explained.

As explained in the conventional example, when the outputs of adjacent heads are switched during high-speed playback every time the heads cross a track and the magnitude of each output is switched, the horizontal synchronization signal interval changes due to a shift in the head position. Let this change time be ΔL. Now, with the variable delay circuit 9, the first oscillation circuit 1
) when the output frequency f1 of ) is used as a clock, the delay time t
1. Let t2 be the delay time when the output frequency r2 of the second oscillation circuit 12 is used as a clock.

fl and f2 are selected so that tl-t2=Δt (tl>t2.f2>fl), and the control output Y of the control circuit 8 to the third switch circuit 10 is
The third switch circuit 10 selects the output of the first oscillation circuit 1) when the head is in R azimuth, and selects the output of second oscillation circuit 12 when the head is in L azimuth. The variable delay circuit 9 can eliminate discontinuity in the horizontal synchronizing signal interval caused by head switching, and skew distortion in the reproduced screen can be eliminated.

Furthermore, when switching the output of the first oscillation circuit 1) and the second oscillation circuit 12, the variable delay circuit 9 does not immediately output a signal with the horizontal synchronization signal interval corrected; The signal remaining in the variable delay circuit 9 inputted to the clock frequency is outputted at a different clock frequency, and the signal is outputted at a different clock frequency.

The horizontal synchronizing signal interval becomes discontinuous by the time taken by the variable delay circuit 9 every time the frequency is switched.

To prevent this, the signal before switching is delayed by a fixed delay circuit 14 for a certain period of time at the point of clock switching, and this signal is output.

After that, the variable delay circuit 9 in which the horizontal synchronization signal interval is corrected
If you select , the horizontal synchronization signal interval of the reproduced signal will always be constant. In this case, the delay time of the fixed delay circuit 14 is longer than the maximum delay time of the variable delay circuit 9, and is selected to be an integral multiple of one horizontal opening period.

In the above embodiment, the clock frequency supplied to the variable delay circuit is switched by switching between two oscillation circuits, but this may also be done by varying the oscillation frequency of the voltage controlled oscillator.

〔Effect of the invention〕

As described above, according to the magnetic recording and reproducing apparatus according to the present invention, a variable delay circuit is provided at the output of the demodulation circuit to delay the demodulated output by a predetermined period of time, and the clock frequency supplied to the variable delay circuit is switched by the head. Since the delay times are different in synchronization with each other, that is, the delay times are different, discontinuity in the horizontal synchronizing signal interval that occurs when switching heads can be removed by the delay time difference, and skew in the playback screen can be removed. Further, by providing a fixed delay circuit at the output of the variable delay circuit, it is possible to eliminate discontinuity in the horizontal synchronization signal interval that occurs until the output of the variable delay circuit becomes stable.

[Brief explanation of drawings]

FIG. 1 (al) is a diagram showing the state of the head installation of a VTR according to an embodiment of the present invention, FIG. 1 (b) is a block diagram of the VTR, and FIG. 1 (C) is a control circuit of the VTR. FIG. 2(a) is a diagram showing the state of the head installation of a conventional VTR, FIG. 2(b) is a block diagram of a conventional VTR, and FIG. Figure (a) is a diagram showing a trace pattern during fast-forward playback, and Figure 3 (bl is a diagram showing a tape pattern and head position when switching heads. 1a to 1d: head, 6: demodulation circuit) , 8...
Control circuit, 9... variable delay circuit, IO... third switch circuit, 1). 12...1st. a second oscillation circuit,
14... Fixed delay circuit, 15... Fourth switch circuit. Note that the same parts in the figures indicate the same or equivalent parts.

Claims (3)

[Claims] (1) Using the helical scan method, signals are recorded in adjacent recording tracks with different recording azimuths, and when reproducing the signals, a pair of opposite azimuths is placed near a pair of opposing main heads, respectively. In a magnetic recording and reproducing apparatus, an auxiliary head is provided, the output of the main head and the auxiliary head is switched and selected, and the output is demodulated according to the clock frequency connected to and supplied to the output of the demodulation circuit. a variable delay circuit for determining a delay time; a clock generating means for switching and supplying clocks of first and second frequencies to the variable delay circuit in synchronization with switching of the outputs of the main head and the auxiliary head; A fixed delay circuit connected to the variable delay circuit output; and a switch circuit for switching and selecting the variable delay circuit output and the fixed delay circuit output in response to switching between the outputs of the main head and the auxiliary head. A magnetic recording/reproducing device characterized by: (2) The clock generation means includes first and second oscillation circuits having different oscillation frequencies, and a switch circuit that selects and outputs either the output of the first or second oscillation circuit. A magnetic recording and reproducing device according to claim 1, characterized in that: (3) The magnetic recording and reproducing apparatus according to claim 1, wherein the clock generating means is a voltage controlled oscillator whose oscillation frequency changes depending on the input voltage.