JPS63181592A - Video tape recorder - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the picture quality of a reproduced video and to correctly demodulate a desired signal superimposed during a vertical blanking period by removing an information signal component mixed in the reproduced signal based on a control signal and the output signal of a level detecting circuit. CONSTITUTION:The title recorder is constituted of a low pass filter circuit 11 for extracting the information signal component STC from the reproduced signal SPB, the level detecting circuits 12, 13 for detecting the signal level of the output signal STC of the low pass filter circuit 11, pulse signal generating circuits 18, 19, 25 for outputting the control signals SC1, ST3 having a prescribed pulse duration during the vertical blanking period and information signal component removing circuits 15-17, 20, 27 for removing the information signal component mixed in the reproduced signal SPB based on the control signals SC1, ST3 and the output signal ST1 of the level detecting circuits 12, 13. Thereby, signals SC, SY except the information signal component STC can be effectively demodulated and the information signal component STC mixed in the luminance signal SY and the chroma signal SC can be removed.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A: Industrial field of application B: Outline of the invention C: Prior art (Figs. 3 to 6) D: Problems to be solved by the invention (Fig. 7) E: Means for solving the problems (Fig. 1) ) F Effect (Fig. 1) G Embodiment (Figs. 1 and 2) H Effect of the invention This invention is suitable for application to a VTR configured to play back a magnetic tape on which time code information is recorded.

B Summary of the Invention The present invention performs vertical blanking in V'rR by operating for a predetermined period an information signal component removal circuit that removes information signal components mixed into the luminance signal and chroma signal of the reproduced signal. This system is designed to reliably reproduce text information etc. superimposed on a period, and to prevent deterioration of the image quality of the reproduced video.

C. Prior Art Conventionally, some VTRs of this type have been designed to record time code information using a fixed head along with video signals in order to perform editing operations efficiently.

That is, as shown in FIG. 3, a recording track 2 is formed by sequentially recording diagonally low frequency converted chroma signals and frequency modulated luminance signals on a magnetic tape 1 using a rotary head.

Furthermore, frequencies 1.2 (KHz) and 2.2 (KHz) representing time code information are added to an area 3 on the scanning start end side of the recording track 2 where signals during the vertical blanking period of the video signal are recorded.
By deep recording the time code signal composed of a 4 KHz pulse train using a fixed head, the time code information can be recorded while avoiding deterioration of the S/N ratio of the video signal except during the vertical blanking period. It is designed to be recorded.

However, even if the time code information is deep recorded during the vertical blanking period in this way, during playback, the time code signal recorded using a fixed head is reproduced using a rotating head, so that the frequency f + (1
29 (KHz)) and f2 (25B (KH2))
There is a problem in that a time code signal converted into a pulse train signal (hereinafter referred to as a reproduced time code signal) mixes in during the vertical blanking period of the video signal, deteriorating the reproduced video.

That is, as shown in FIG. 4, the frequency characteristics of the reproduced signal SPH obtained through the rotary head are such that the low-frequency converted chroma signal SC is distributed on the low frequency side of the frequency-modulated luminance signal SY, and A reproduced time code signal STC having an amplitude level 4 to 6 times that of the burst signal of the chroma signal SC is distributed superimposed on the low frequency side of the chroma signal SC which has been converted to a low frequency band.

Therefore, the reproduced time code signal STC is mixed into the chroma signal SC separated from the luminance signal SY using a low-pass filter circuit, and as a result, ACC (automatic
There was a problem that the chroma 1 level control) circuit malfunctioned and the quality of the reproduced video deteriorated.

Furthermore, since the electromagnetic conversion system of the VTR has nonlinearity, third-order high-frequency distortion occurs in the reproduced signal SPB, and the beat consists of a signal multiplied by the demodulated precision signal, the reproduced time code signal, and the frequency-modulated luminance signal. Signals are mixed. Therefore, during the period when the beat signal is mixed into the demodulated luminance signal (that is, during the vertical blanking period), the S/N ratio of the demodulated luminance signal deteriorates, and as a result, the video signal output from the VTR is When monitoring with a television receiver, there was a risk that the synchronization circuit of the television receiver would malfunction.

For this reason, as shown in FIG. 5, in the conventional VTR 5, a reproduced time code signal detection circuit is used to detect the reproduced time code signal by extracting a signal component in the frequency band during the vertical blanking period. By detecting and removing this, deterioration of the image quality of the reproduced video is prevented.

That is, the reproduction signal SPB output from the rotary head 7 via the amplifier circuit 6 is received by the low-pass filter circuit 8,
After extracting the reproduced time code signal STC and chroma signal SC, they are outputted to a delay circuit 10 and a low-pass filter circuit 1) via an amplifier circuit 9.

The low-pass filter circuit 1) has a cutoff frequency of approximately 300
(Kllz), and as a result, as shown in FIG.
During the vertical blanking period shown in (Fig. 6(A)), the reproduced time code signal STC (Fig. 6(A)) rises in signal level.
B)) is extracted and sent to the comparison circuit 13 via the amplifier circuit 12.
is output to.

The comparison circuit 13 converts the reproduced time code signal STC into 2 based on the signal level of the reproduced time code signal STC.
After converting the pulse signal STI into the pulse train of the value 5TI (FIG. 6(C)), the pulse signal STI is sent to the monomulti circuit 14.
and output to the switch circuit 15.

The mono multi circuit 14 is composed of a retriggerable mono multi circuit, and based on the pulse signal STI, the pulse width is approximately two fields of the video signal S■, and the pulse signal ST
Pulse signal ST2 that rises at the timing of the rise of I
(FIG. 6(D)) and outputs it as a signal for setting the mono multi-circuit 16, it is possible to eliminate noise that may be mixed in, for example, when time code information is not recorded on the magnetic tape 1. This prevents the monomulti circuit 16 from malfunctioning.

In this way, the amplifier circuit 12 and the comparison circuit 13 constitute a level detection circuit that detects the signal level of the reproduced time code signal.

On the other hand, the switch circuit 15 becomes a closed circuit in response to the vertical blanking pulse SVB (FIG. 6(E)).
By outputting the pulse signal STI to the OR circuit 17 during the rising period of the vertical blanking pulse SVB,
It is designed to prevent the OR circuit 17 from malfunctioning when removed during the vertical blanking period due to noise or the like.

Further, the OR circuit 17 passes through the differentiating circuit 18 and the slicing circuit 19 a period TI from the rise of the pulse signal STI.
The pulse signal ST3 (Fig. 6 (F)) which rises at the timing of the rise of the vertical blanking pulse SVB (approximately 100 (nsec)) earlier is received, and the pulse signal S
By obtaining a logical product with TI, a pulse signal 5T4 (see Fig. 6 (G )
) is output.

Based on the pulse signal ST4, the monomulti circuit 16 rises at the timing of the rise of the pulse signal ST4, and approximately the period T2 (200
(μsec) ) falls at a timing delayed by (
In other words, the signal level of the reproduced time code signal STC is 0.
A detection signal SCC of the reproduced time code signal STI (which falls after reaching [V]) is formed and outputted to the muting circuit 20 and a filter circuit (not shown).

The muting circuit 20 operates only during the period in which the detection signal SCC rises, and the ACC circuit 21 operates during the period when the chroma signal SC is mixed with the reproduced time code signal S.
The TC prevents malfunctions.

Similarly, the filter circuit operates only during the period in which the detection signal SCC rises to remove the beat signal contained in the demodulated luminance signal.

Therefore, during the vertical blanking period, the reproduction time code signal STC is detected and the muting circuit 20
By operating the filter circuit and the filter circuit, it is possible to prevent the image quality of the reproduced video from deteriorating, and it is also possible to easily perform the &g collection operation based on the time code information obtained through the fixed head.

D Problems to be Solved by the Invention In recent years, in video signals, for example, VTTS (vertical 1nter
V ITC (vert test signal) signal, time code information used between broadcasting equipment.
ical 1nterval timecode) signal etc. during the vertical blanking period! Text information is superimposed and broadcast during the vertical blanking period, such as in 1 tatami, text multiplexing, and the captain system.

However, when a video signal with a signal superimposed during the vertical blanking period is played back, the conventional VTR 5 has a problem in that the playback time code signal detection circuit malfunctions and the playback video is distorted.

In other words, as shown in FIG. 7, when a high frequency, for example, multiverse VITS signal S signal S is added to the video signal SVI (FIG. 7 (A)), the VITS signal ST is frequency modulated together with the luminance signal. The sideband of the signal component falls within the band of the low-pass filter circuit 1), and the VIT consisting of this sideband is added to the reproduced time code signal STC.
Output signal mixed with S signal multiplication signal TS (Figure 7 (D))
is obtained via the low-pass filter circuit 1).

Therefore, even during the period in which the VITS signal is superimposed other than the period in which the signal level of the reproduced time code signal STC rises, the mono multi-circuit 16 operates, and the detection signal SCC ( whose signal level rises even in the period in which the VITS signal is superimposed) FIG. 7(C)) is obtained.

As a result, in the chroma signal SC output via the ACC circuit 21, no burst signal is obtained during this period, and on the television receiver side, the A P C (au
There has been a problem in that the image quality of the reproduced video deteriorates due to malfunction of the (tomatic phase control) circuit.

Furthermore, in the demodulated luminance signal, during the period,
There was a problem in that the low-pass filter circuit operated, and as a result, a correctly demodulated VMTS signal could not be obtained.

The present invention has been made in consideration of the above points, and even in a video signal on which a desired signal is superimposed during the vertical blanking period, the reproduced time code signal component mixed in the luminance signal and chroma signal can be reliably removed. The present invention attempts to propose a VTR that can effectively prevent deterioration of the image quality of reproduced video and accurately demodulate the desired signal superimposed during the vertical blanking period.

E Means for Solving Problems In order to solve these problems, in the present invention, a rotary head is used to magnetically record the chroma signal along with the frequency-modulated brightness signal SY by converting the chroma signal to a low frequency range, and the vertical recording of the brightness signal SY is performed. In a video tape recorder for playing back a magnetic tape 1 in which information signals ST are deeply recorded using a fixed head in an area 3 in which signals during a blanking period are recorded, information signals ST are obtained through a rotating head. playback signal S
A low-pass filter circuit 1) that extracts the information signal component STC from PB, and an output signal S of the low-pass filter circuit 1)
Level detection circuit 12.1 that detects the TC signal level
3, a pulse signal generation circuit 18.19.25 that outputs a control signal SCI, Sr1 having a predetermined pulse width during the vertical blanking period, and an output signal of the control signal SCI, ST3 and level detection circuit 12.13. Information signal component removal circuits 15.16.17.2o, 2 that remove the information signal component STC mixed into the reproduced signal SPB based on STI
7.

F action control signal SCI, Sr1 and level detection circuit 12.13
Based on the output signal STI of the information signal component removal circuit 15
．． By operating 16.17.20 and 27, it is possible to reliably demodulate signals sc and sy other than the information signal component STC, and also to demodulate the luminance signal SY and chroma signal SC.
The information signal component STC mixed in can be removed.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. 5 are given the same reference numerals, the logic level rises at a timing synchronized with the rising edge of the vertical blanking pulse SVB, and then the logic level falls after a predetermined period has elapsed. The signal S01 is generated by the monomulti circuit 25, and the switch circuit 15 is controlled using the control signal SCI.

For this reason, the monomulti circuit 25 receives the vertical blanking pulse SVB, rises at a timing synchronized with this, and continues for a period T3 until the signal level of the reproduced time code signal STC rises (for example, during the horizontal synchronization period). During a period 13TH), a control signal SCI is output to maintain the logic level.

As a result, as shown in FIG. 2, the signal level of the reproduced time code signal STC returns to 0 (V) during the horizontal synchronization period T.
In the case of reproducing the video signal SVI (Fig. 2 (A)) in which the VITS signal S is multiplied on the horizontal synchronization period HI and the horizontal synchronization period TH separated by a period 6 TH from the horizontal synchronization period TH, the low-pass filter circuit 1) via V
Even when the reproduced time code signal STC (FIG. 2 (B)) mixed with the ITS signal S multiplied sideband component STS is obtained, the pulse signal ST output from the comparator circuit 13
l, vertical blanking pulse SVB (Fig. 2 (C)
) during the period in which the control signal SCI (FIG. 2 (D)) with a shorter pulse width than during the vertical blanking period T
3 (that is, during the period in which the reproduced time code signal STC is obtained) can be supplied to the OR circuit 17.

Therefore, it is possible to prevent the OR circuit 17 from malfunctioning due to the sideband component STS of the VITS signal superimposed on the horizontal synchronization period TH2 of the horizontal synchronization periods 'rHI and TH2, and even during the period TH2. ,
Detection signal SC2 (second
Figure (E)) can be obtained.

Therefore, by operating the muting circuit 20 in accordance with the detection signal SC2, even when the VITS signal S is superimposed, the vi'FS signal is superimposed during the period (horizontal in FIG. 2). During the synchronization period TH2), a burst signal can be obtained, and malfunctions of the APC circuit can be effectively avoided and deterioration of the image quality of the reproduced video can be prevented.

In particular, the VITS signal S superimposed on the horizontal synchronization period THI
In the double code, since it is reproduced superimposed on the reproduced time code signal STC, the muting circuit 20
By operating the ACCrgJ path 21, malfunction of the ACCrgJ path 21 is prevented with priority over the APC circuit to the extent that the APC circuit does not malfunction in practice.

Furthermore, when the VITS signal S is not superimposed, the logic level of the pulse signal STI output from the comparator circuit 13 falls earlier by the amount that the VIST signal disappears during the horizontal synchronization period THI, and the logic level falls earlier by that amount. A falling detection signal SC2 (FIG. 2(F)) is obtained.

On the other hand, a filter circuit (not shown) that processes the demodulated luminance signal rises in synchronization with the rising timing of the vertical blanking pulse SVB (Fig. 2 (C)), and the equivalent pulse of the video signal ends. The control signal SC3 (Fig. 2 (G)) and the detection signal SC2 fall at the timing of
(Figure 2 (E) and (F)) logical sum signal SC4 (second
Use the diagram (■()) to control it.

Therefore, the vertical blanking signal SVB is received by the mono multi-circuit 26, and after forming the control signal SC3, it is output to the AND circuit 27 together with the detection signal SC2.

In this way, only when the reproduced time code signal STC is superimposed on the reproduced signal SPB and output, it is possible to prevent the reproduced time code signal STC from being mixed in during the equivalent pulse period, which is sufficient for practical use. By preventing the synchronization circuit from malfunctioning within a certain range, and by stopping the operation of the filter circuit outside of this period, it is possible to obtain an accurately demodulated ITS signal S double.

Therefore, a switch circuit 15, a monomulti circuit 16
, the OR circuit 17, the muting circuit 1520, the AND circuit 27, and the filter circuit reproduce the reproduced time code signal component mixed into the luminance signal and chroma signal according to the control output SC1, the pulse signal ST3, and the output signal STI of the monomulti circuit 14. An information signal component removal circuit is configured to remove an information signal component consisting of:

As described above, according to the present invention, since the reproduced time code signal is detected during the predetermined period between the vertical blanking periods, the detection period is used as the chroma signal.
The VIT of the reproduction time code signal detection circuit is set during the period in which the reproduction time code signal is obtained, and in the case of the luminance signal, by setting it during the period of the equivalent pulse.
Malfunctions caused by the S signal can be prevented.

As a result, it is possible to correctly demodulate the VrTS signal and prevent malfunctions of the APC circuit.
Deterioration of the image quality of the reproduced video can be prevented.

In the above-mentioned embodiment, a case was described in which a video signal superimposed with a VrTS signal was reproduced, but the present invention is not limited to this.
The present invention can be widely applied to VTRs that reproduce video signals on which text information or the like is superimposed during the vertical blanking period.

Further, in the above embodiment, a case has been described in which a filter circuit that removes a reproduced time code signal component from a demodulated luminance signal is operated during an equivalent pulse period, but the present invention is not limited to this. In short, on the television receiver side, the filter circuit should operate within the range where the synchronization circuit does not malfunction and during the vertical blanking period other than when the VITS signal etc. are superimposed. , the rising period of the control signal SC3 output from the monomulti circuit 26 can be set to various values.

Furthermore, in the embodiments described above, time code information was recorded as an information signal using a fixed head. The present invention is applicable not only to the reproduction of time code information but also to the reproduction of magnetic tapes in which various information signals are recorded in the area between the vertical blanking periods using a fixed head. Can be widely applied.

H Effects of the Invention As described above, according to the present invention, only the information signal components mixed in the luminance signal and chroma (No. , it is possible to accurately demodulate the desired signal superimposed during the vertical blanking period.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the VTR according to the present invention, FIG. 2 is a signal waveform diagram for explaining its operation, and FIG.
The figure is a plan view showing the recording format on a magnetic tape, Figure 4 is a characteristic curve diagram showing its frequency characteristics, Figure 5 is a block diagram showing a conventional VTR, and Figures 6 and 7 are explanations of its operation. FIG. 1...magnetic tape, 7...rotating head, 9.12...amplifier circuit, 1)...low-pass filter circuit, 13...・Comparison circuit, 14
．． 16.25.26...Mono multi circuit, 15
...Switch circuit, 17...OR circuit, 20...Muting circuit, 27...
...AND circuit. Video recorder No. 75A Signal ST type A1 Format of data No. 3 Figure 6 Video recorder No. 5 SL type Figure 6

Claims (2)

[Claims] (1) A rotary head is used to magnetically record the chroma signal along with a frequency-modulated luminance signal, and a fixed head is used to record information in the area where the signal during the vertical blanking period of the luminance signal is recorded. A video tape recorder that plays back magnetic tape on which signals are recorded deep includes a low-pass filter circuit that extracts the information signal component from the playback signal obtained through the rotary head, and a low-pass filter circuit that extracts the information signal component from the playback signal obtained through the rotary head, and an output signal of the low-pass filter circuit. a level detection circuit that detects a signal level; a pulse signal generation circuit that outputs a control signal having a predetermined pulse width during the vertical blanking period; based on the control signal and the output signal of the level detection circuit; A video tape recorder comprising: an information signal component removal circuit for removing information signal components mixed into the reproduced signal. (2) the pulse signal generation circuit includes first and second pulse signal generation circuits that output first and second control signals each having a predetermined pulse width during the vertical blanking period; The information signal component removal circuit removes the information signal component mixed into the low frequency converted chroma signal of the reproduced signal based on the first control signal and the output signal of the level detection circuit, and The video tape recorder according to claim 1, wherein information signal components mixed into the luminance signal obtained by demodulating the reproduced signal are removed based on the control signal of the control signal and the output signal of the level detection circuit. .