JPS61198461A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain the switching of a reference signal formed from an output of a framing detection circuit and an output of a field discrimination circuit out affected by skew by comparing the framing detection circuit and the field discrimination circuit for their outputs to detect the skew and providing a changeover switch. CONSTITUTION:When no skew exists, a Q' output of a D flip-flop 2 is outputted as a reference signal and even when a skew takes place, since an output of a field discrimination circuit 5 is a correct framing signal, D and B signals are compared by an exclusive OR gate 9 to form a signal (c). Only when the skew takes place, an output of an integration filter 10 goes to an H level. On the other hand, an output of a D flip-flop 2 is inputted to a monostable multivibrator 7, its output signal D latches the signal B to form a signal E. The signal is susceptible to noise but immune to the effect of skew, and when a skew takes place, a switch 11 is changed over to the position C to output a signal F as a reference signal. Thus, a framing servo function immune to either noise or skew is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording and reproducing apparatus such as a video tape recorder for broadcasting and business use (hereinafter abbreviated as VTR).

2. Description of the Related Art In recent years, editing VTRs have introduced a framing servo function to ensure the connection between screens at editing points on a field-by-field basis. Two fields are discriminated, and as a result, the reproduced video signal is free from disturbances caused by turbulence.

The conventional framing servo function will be described below with reference to the drawings.

FIG. 6 shows a block diagram of the conventional system, and FIG. 6 shows its timing chart. In the figure, (a) is the 5YNC portion of the video signal, (b) is a signal synchronized with the horizontal synchronization signal created from the video signal, and (c) is a signal synchronized with the vertical synchronization signal created from the video signal. .

The detector 18 in FIG. 5 detects that if the rising edge of the VD pulse (C) in FIG. If there is, it is a detector that becomes H level, and with this,
1st. A reference signal that becomes H level in the third field is obtained.

However, with this alone, the correct reference signal cannot be obtained if there is noise in the 5YNC section, and the H3YNC that creates the HD to be compared is instantaneously disturbed or is shifted from its original position due to sink noise, etc. This causes the continuity of the cylinder servo to be disrupted during recording. In order to avoid this problem, a D flip 70 knob 19 is provided,
When there is no noise, the switch 20 is set to the b side, the D flip-flop 19 is used as a simple frequency divider, and its Q output is used as a reference signal. An exclusive OR gate 21 detects whether the signal is a correct reference signal. When there is no noise, the detector 18 outputs a correct reference signal, so if the D flip-flop 19 outputs an incorrect reference signal, the output of the exclusive OR gate 21 will be at H level, and will remain for a certain period of time. If the H state continues, the output of the integrating circuit 24 becomes L, and the output of the comparator 23 becomes H.
Otherwise, the switch 2o is switched to the a side, and the D flip-flop 19 operates in the same way as the D flip-flop 70 knob 18, so that a correct reference signal can be obtained. Then, the output of the exclusive OR gate 21 becomes L level, the output of the comparator 23 becomes L level, and the D flip-flop 19 becomes a mere frequency divider again.

Furthermore, even if 5H3YNC is disturbed by noise and the detector 18 outputs an erroneous signal, it will return to normal within a certain period determined by the time constant of the integrating circuit 22 and the threshold value of the comparator 23. If the signal changes to a false signal, the output of the comparator 23 remains at L level, and the false signal is ignored.

As described above, this framing servo device has the first . It has the advantage that it faithfully produces a reference signal that detects the second field, and is not affected by noise, tape dropout, or lack of H3YNC due to bouncing that occurs when switching input signals.

Problems to be Solved by the Invention Conventional framing servo devices have the above-mentioned characteristics, but when the width between equivalent pulses in VSYNC changes over a certain period of time due to fluctuations in the time axis of H3YNC, The reference signal output will be different from the original reference signal. From now on, this time axis fluctuation of H3YNC will be referred to as skew, but the conventional 7-raming servo device has the drawback of being susceptible to the influence of skew.

In view of the above-mentioned problems, the present invention provides a magnetic recording and reproducing apparatus equipped with a framing servo device that is not affected by skew as well as noise in the input video signal.

Means for Solving the Problems In order to solve the above problems, the magnetic recording/reproducing device of the present invention has a conventional framing detection circuit that is not affected by noise, and a field detection circuit that is weak against noise but not easily affected by skew. It has a discrimination circuit that detects skew by comparing the outputs of both, and uses a switch to generate a reference signal created from the output of a conventional framing detection circuit and the output of a field discrimination circuit that is not affected by skew. It is equipped with a configuration that switches between the two.

Operation The present invention has the above configuration so that when there is no skew, the output of the conventional framing detection circuit is used as a reference signal.
When a skew occurs, the skew detection circuit operates and the output of the field discrimination circuit, which is not affected by the skew, is passed through a synchronization circuit and taken out as a reference signal.0 Embodiment of the present invention Before describing one embodiment, the field discrimination circuit used in this embodiment will be explained with reference to the drawings. This field discrimination circuit is characterized in that it is easily affected by noise, but not easily affected by skew. Its block diagram is shown in FIG. 3, and its timing chart is shown in FIG. 4.

If, 5YNC signal is used by the vSYNC separation circuit 13 to generate a signal like a. The pulse width is o, s
At e H, input to the retriggerable digital monomulti 14 to create a signal like b.

Since this monomulti 14 detects the trailing edge of VSYNC, it is not affected even if the width between equivalent pulses in VSYNC changes due to skew. Next, input the signal b to the digital monomulti 16 with a pulse width of 2H,
Create a signal C, and the pulse width will be o, se H
The digital monomulti 16 generates a pulse like d, and the field is determined based on whether H3YNC is present within this pulse width.In the first field, a pulse like e is used to generate a pulse like D.
Flip-flop 17 is set, and in the second field, D flip-flop 70 is set at the rising edge of the C pulse.
7 is reset and a framing signal is created.

Next, the framing servo device used in the present invention will be explained with reference to the drawings.

FIG. 1 shows a block diagram of a framing detector in an embodiment of the present invention, and FIG. 2 shows its timing chart. In FIG. 1, the 6.1 degree integral filter is a combination of the integral circuit 22 and comparator 23 in FIG.

When there is no skew, the output of the integral filter 10 is at L level, the switch 11 is on the d side, and the d output of the D flip-flop 2 is output as a reference signal. Since this operation is exactly the same as the conventional method, the explanation will be omitted.

Next, the operation when skew occurs will be explained. Even when skew occurs, the output of the field discrimination circuit 6 is a correct framing signal, so the exclusive OR gate 9 compares the D signal and the B signal to generate a signal C. However, if this is done alone, a pulse will be generated due to the phase difference between the input signal and the B signal, and the phase relationship between the A and B signals may be reversed for a short time due to noise.
These are compensated for, and the output of the integral filter 10 becomes H level only when skew occurs.

On the other hand, the output of the D flip-flop 2 is input to a monomulti 7 which is triggered by both edges, and a signal pE is created by latching the B signal with the output signal. Although this signal is easily affected by noise, it is not affected by skew and is the same signal as the normal reference signal. When skew occurs, switch 11 is switched to the C side, and the F signal is Output as a reference signal. The above means avoids the problem that the phase of the reference signal is reversed when skew occurs.

Furthermore, when a skew occurs, the output of the integral filter 6 also becomes H level, and if this is sent as a control signal to the switch 3, the D flip-flop 2 will output an incorrect signal, so the skew will be reduced. When this happens, the gate circuit 12 forces the cisinch 30 control signal to go low.
level, and the D flip-flop 2 is made into a simple frequency divider.Thus, even when the switch 11 is switched from the C9 side to the d side, there is no disturbance of the reference signal.As described above, according to this embodiment, the reference signal is not disturbed. , it faithfully creates a reference signal by detecting the first and second fields of the input video signal, and also eliminates H due to noise and dropouts.
Ignoring disturbances in the reference signal due to lack of sync, etc., and when further skew occurs, the skew detection device operates and outputs the output of the framing detection circuit, which is not affected by skew, as the reference signal. This makes it possible to realize a framing servo function that is not affected by noise or skew.

Note that in this embodiment, a circuit having a configuration as shown in FIG. 3 was adopted as the field discrimination circuit 5 in FIG.
Any material that is not easily affected by skew is sufficient. In addition, as the basic framing detection section, we adopted a method using D flip-flops as shown in 1 and 2 in Figure 1, but by combining a 1/2 frequency divider, an integral filter for noise removal, and a switch, , as long as it has the above functions.

Effects of the Invention As described above, according to the present invention, the reference signal taken out from the switch 11 in FIG. This has the excellent effect of being able to extract a continuous framing reference signal that corrects not only the absence and disturbance of the horizontal synchronization signal due to dropouts, but also the effects of changes in the width between equivalent pulses due to skew.

Furthermore, when recording or editing a video signal that has been played back from a tape with many disturbances in the synchronization signal due to the effects of noise and skew, the framing may be distorted due to the disturbance in the synchronization signal, and therefore the recording This has the effect of solving the conventional problem of the servo being disturbed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a framing servo device in an embodiment of the present invention, FIG. 2 is a timing chart thereof,
FIG. 3 is a block diagram of the field discrimination circuit used in this embodiment, FIG. 4 is a timing chart thereof, FIG. 5 is a block diagram of a conventional 7-raming servo device, and FIG. 6 is a timing chart thereof. 1.2.8...D flip-flop, 4,9.
...Exclusive OR gate, 3, 11...
...Switch, 6...Field discrimination circuit, 6,1o...Integral filter, 8...
Mono multi, 12... gate circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 Figure 4 '1 enemy γ゛

Claims (1)

[Claims] A synchronization signal separation circuit separates a horizontal synchronization signal and a vertical synchronization signal of the video signal, and compares the vertical synchronization signal separated by the synchronization signal separation circuit with the horizontal synchronization signal to separate the first and second fields of the video signal. A first, a second, and a third generating a framing signal that detects the field.
The first means has a vertical synchronizing signal of 1/2.
A first changeover switch that can be converted into a frequency divider that divides the frequency by two is provided, and the output when the first changeover switch is on the frequency divider side is compared with the output of the second means. and a first integrating circuit that integrates the comparison output, and is configured to operate the first switch with the integrated output, and detects a trailing edge of the vertical synchronization signal. a second comparator for comparing the phases of the output of the third means and the output of the second means; a second integrating circuit for integrating the comparison output; 1st
It has a synchronization circuit that produces a reference signal synchronized with the output of the means, and is characterized by comprising a switch for switching between the output of the first means and the output of the synchronization circuit according to the output of the second integrating circuit. A magnetic recording and reproducing device.