JPH01295571A - Pulse generating circuit - Google Patents

Abstract

PURPOSE:To prevent production of color flicker or sag on the upper part of a pattern by constituting a clamp pulse generating circuit by the 1st pulse generating means receiving a composite synchronizing signal and a special signal and generating the 1st pulse, the 2nd to 8th pulse generating means and a gate circuit. CONSTITUTION:A composite synchronizing signal extracted from a synchronizing separator circuit 4 is fed to a retriggerable monostable multivibrator(MM) 17 and triggered at its front ridge. Then the 1st pulse is outputted from the MM 17. The 8th pulse with a shorter width than the pulse width of the 1st pulse (g) obtained by retarding the 1st pulse (g) from the MM 13 is extracted and converted into a pulse (k) at a 3-input AND circuit 22 and outputted as a clamp pulse clamping a pedestal level. Thus, the burst detection is always operated normally and then color flicker caused in a conventional circuit at the upper part of the pattern is eliminated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a pulse generation circuit, and particularly to a pulse generation circuit that generates a burst gate pulse for separating a color burst signal superimposed on a video signal, a clamp pulse for clamping a pedestal level, etc. This invention relates to a pulse generation circuit that generates pulses.

Home VTRs, which have become widely popular in recent years, usually have both recording and playback functions, allowing you to personally record and play back any television broadcast program or image signal from a television camera. can do. On the other hand, household V
Recorded magnetic tapes and recorded video discs with various information contents have come to be widely available on the market in large quantities for the purpose of being played back on TR and video disc players.

For this reason, video signals reproduced from recorded recording media such as commercially available recorded magnetic tapes and recorded video disks are easily duplicated (dubbed) on home VTRs. With the spread of home VTRs, this issue has come to the fore as a copyright issue.

In this way, recorded information on recorded recording media can be easily accessed from home V
The plagiarism and creation of copies by TR will cause great damage to copyright holders and other related industries. Therefore, when such theft is carried out, even if the recorded edge video signal of the recorded magnetic tape that is the copy is played back, the image quality will be unwatchable, for example. There is a method in which a copy guard signal is recorded in advance in a specific period within the vertical blanking period of a video signal.

Such copy guard signals include, for example, signals with three types of waveforms shown in FIGS. 4(A), 4(B), and 4(C), and others. In Fig. 4 (A) to (C), H and S are regular horizontal synchronization signals, C and B are color burst signals,
At a position that avoids these signal positions, a balsue ~■ with a predetermined peak value and a pseudo horizontal synchronization signal P are placed as copy guard signals.
, H, and S are alternately synthesized, five each in total.

In addition, in FIGS. 4(A) to 4(C), 100 IRE indicates the white peak level.

When a recorded magnetic tape on which such copy guard signals are pre-recorded is stolen, the AGC circuit installed in the luminance signal recording system of the home VTR automatically detects a predetermined signal immediately after the pseudo-horizontal synchronizing signals P, H, and S. Since the signal with the peak value of 2 is operated to be the signal of the normal sync tip level, the video signal portion other than the vertical blanking period is recorded at a level different from the original signal level. As a result, when the recorded signal of this magnetic tape is reproduced, the brightness of the screen appears to be different to an extent that is unbearable for viewing, and copy protection is achieved. Note that if the types of copy guard signals are changed at regular intervals, the copy guard effect will be even greater.

On the other hand, if a user who has legitimately purchased a pre-recorded magnetic tape on which the above-mentioned copy protection signal is pre-recorded plays it back, the playback system of a home VTR is not equipped with a 〇G circuit. The signal is ignored, and reproduction is performed almost without any trouble, similar to a recorded magnetic tape on which no copy guard signal is recorded.

When reproducing a recorded signal from a recorded recording medium on which a special signal such as a copy guard signal is superimposed on the video signal, color flicker or sag may occur due to the special signal. To avoid deterioration of image quality,
It is important to generate burst gate pulses, clamp pulses, etc.

[Conventional technology]

FIG. 5 shows a circuit diagram of an example of a conventional pulse generating circuit. In the figure, the composite video signal (color video signal or luminance signal) input to input terminal 1 is filtered by a low-pass filter (LPF).
2 removes unnecessary high frequency components and noise, and then is supplied to the synchronous separation circuit 4 through the clamp circuit 3.
Here, only the composite synchronization signal is separated and output. When the output composite video signal of the LPF 2 is immediately after the start of the second field, as shown by al in FIG. Immediately after, it becomes as shown by bl in the figure. In addition, in the composite video signal al # al, for example, the image shown in FIG. 4 (
The copy guard signals Cg+ to CQy shown in A) are superimposed over seven horizontal scanning periods.

The composite synchronization signals t)+ and bl are supplied to a retrigger pull monostable multivibrator (hereinafter referred to as M) via an inverter 5.
(denoted as M) 6, and is triggered at the falling timing (the rising timing of the output of the inverter 5) to generate a pulse with a width of approximately 40 μsec. Here, one horizontal scanning period (1H) is approximately 63.5 μs.
ec, and the pulse interval of the equalization pulse is approximately 31.75μ
sec t”, the output pulses of M, M, and 6 are the 6th
As shown by C in the figure, the waveform remains at a high level during the equalization pulse period and the copy guard signal transmission period. In the waveform shown by C in FIG. 6, the broken line portion is the waveform when the composite synchronization signal b2 is input manually, and the solid line portion is the waveform when b+ is input.

The D-type flip-flop 7 latches the above signal C at the rising edge of the composite synchronization signal b+,l)z, thereby outputting a signal with the waveform shown in FIG. 6 from its Q output terminal, and , outputs a signal d having the opposite phase to the signal d from its σ output terminal.

On the other hand, 8.9.12 and 13 are monostable multivibrators (M, M,), respectively.

A composite synchronization signal b+ or bl is supplied to 8 and 9, respectively, and is triggered at the rising edge of the signal, and from M, M, and 8, approximately 4 μS
A pulse of width aC is taken out, M, M.

9, a pulse with a width of approximately 6 μsec is extracted.

Each output pulse width of M, M, 8.9 is inverter 10.1
1 separately to M, M, 12.13, which is triggered to supply about 5 from M, M, 12 as shown by e in FIG.
A pulse with a width of μsec is output, and a pulse with a width of about 3.5 μsec having substantially the same waveform as the pulse e is outputted from M, M, and 13. M.

If one of the output pulses M, 12, and 13 is used as the burst gate pulse as it is, the burst gate pulse will also be output during the equalization pulse period and the vertical synchronization pulse period where no color burst signal exists, so the input pulse will not be used during this period. The burst detection circuit will operate even though there is no color burst signal, and the burst detection circuit will malfunction due to noise, and even if the color burst signal starts to be input again, it will not be able to immediately follow the detection operation and will not be able to recover. it takes time. This causes color flickering at the top of the screen.

Furthermore, if the other of the output pulses M, M, 12 and 13 is used as a clamp pulse, the pulse generated during the vertical synchronization pulse will raise the sync tip level to the pedestal level, causing synchronization flow and sag.

Therefore, conventionally, the pulse d and the pulse e are supplied to the AND circuit 14, and the pulses in the vertical synchronization pulse period and the 3H equalization pulse periods before and after the vertical synchronization pulse period are removed, as shown by f in FIG. A pulse is generated and output as, for example, a burst gate pulse. Also, at the same time, the pulse d,! :M,M.

13 output pulses are supplied to an AND circuit 15, from which a pulse having a waveform similar to the pulse shown by f in FIG. 6 is extracted and outputted as, for example, a clamp pulse.

[Problem to be solved by the invention]

However, in the above conventional circuit, AND circuits 14 and 15
As shown by f in FIG. 6, the pulses output from the above can solve the above problem because no pulses are output during the vertical synchronization pulse period and each 3H equalization pulse period before and after the vertical synchronization pulse period, but the above-mentioned copy guard Similarly, no pulses are generated during the transmission period of the signals CQ+ to Cg7.

Therefore, during the 7-day period during which the copy guard signals CQ+ to Cg7 are transmitted, the burst detection circuit stops detection operation because no burst gate pulse is input even though the color burst signal is input. Immediately after the transmission period, image transmission begins and even if the burst gate pulse is input again, it cannot be followed immediately, causing color flickering at the top of the screen.

In addition, since the clamp pulse is not generated for several days before the vertical synchronization signal and during the above 7H period, for example, when clamping the pedestal level with this clamp pulse, there is a level difference before and after the vertical synchronization signal and before and after the above 7-day period. Another drawback is that a type of sag (a kind of sag) occurs, and this appears in the vertical scanning period.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a pulse generation circuit that can prevent color flicker and sag from occurring at the top of the screen.

[Means to solve the problem]

To achieve the above object, the present invention provides a composite synchronization signal separated from a composite video signal on which a special signal, which is a pulse train of a constant period, is superimposed within a predetermined horizontal scanning period and a special signal. The device is constructed of a first pulse generating means for generating one pulse, second to eighth pulse generating means, and a gate circuit.

The first pulse generating means has a first pulse generating means that is longer than the fixed period of the special signal and shorter than the period between the leading edge of the first pulse in the special signal and the leading edge of the horizontal synchronizing signal immediately before the leading edge of the first pulse in the special signal.
When the composite synchronization signal and special signal are input at an interval within the first time width, the previous state is maintained; when the composite synchronization signal and special signal are input at an interval longer than the first time width, the previous state is maintained. A first pulse having a first time width is generated with reference to a leading edge of the composite synchronization signal or the special signal.

The second pulse generating means generates the first pulse at intervals within a second time width that is longer than the period of the equalization pulse and shorter than the maximum value of the first time width from one horizontal scanning period. When a pulse is input, the previous state is maintained,
When the first pulse is input at an interval equal to or longer than the second time width, a second pulse having the second time width is generated with the leading edge of the first pulse as a reference.

Similarly, the third. The fifth pulse generating means maintains the previous state when pulses are input at intervals within the 3.5th time width; When pulses are input at intervals longer than the fifth time width, the third. Generate a fifth pulse. here,
The third time width is longer than one horizontal scanning period and shorter than three horizontal scanning periods. The fifth time width is longer than the constant period, but shorter than the period from the trailing edge of the last pulse in the special signal to the leading edge of the horizontal synchronizing signal immediately thereafter.

Further, the fourth pulse generating means is supplied with the second pulse, and with the leading edge of the second pulse as a reference, the fourth pulse generating means generates a signal between the leading edge of the first pulse in the special signal and the leading edge of the horizontal synchronizing signal immediately before it. A fourth pulse having a fourth time width longer than the period and shorter than the period of the equalization pulse is generated.

Further, the sixth pulse generating means latches the fifth pulse at each leading edge of the composite synchronization signal and the special signal to generate the sixth pulse, and the seventh pulse generating means generates the sixth pulse by latching the fifth pulse at each leading edge of the composite synchronization signal and the special signal. A seventh pulse is generated by performing a logical operation on each of the six pulses.

Furthermore, the gate circuit outputs a gate pulse.

[Effect]

The first pulse is supplied to a second pulse generating means to generate a second pulse.
, and is supplied to an eighth pulse generating means to generate an eighth pulse. Here, the first pulse is a pulse that has a predetermined logical value in each of the horizontal synchronization signal transmission period and the special signal transmission period. Further, the second pulse is a pulse that has a predetermined logical value in each of the equalization pulse period, the vertical synchronization pulse period, the horizontal synchronization signal transmission period, and the special signal transmission period; is supplied to generate the third and fourth pulses. This third pulse becomes a pulse whose state does not change (maintains at a predetermined logical value) until immediately before the vertical synchronization pulse. Further, the fourth pulse is a pulse that is phase-synchronized with the horizontal synchronization signal except for the vertical synchronization pulse period and the equalization pulse periods before and after the vertical synchronization pulse period.

The fifth pulse has a predetermined logical value at least during the special signal transmission period, and has a different logical value from the horizontal synchronization signal transmission period. Therefore, by latching the fifth pulse at the leading edge of the composite synchronization signal and the special signal by the sixth pulse generating means, a sixth pulse having a width corresponding to at least the transmission period of the special signal can be generated. I can do it.

This sixth pulse is supplied to the seventh pulse generating means together with the third pulse, and is converted into a seventh pulse that has a predetermined logical value only during a period when a special signal is transmitted.

Therefore, the gate circuit controls at least the fourth . A gate pulse can be output using the fifth and eighth pulses. This gate circuit has no pulses only during the vertical synchronization pulse period and the equalization pulse period, and can output pulses that are phase-synchronized with the horizontal synchronization signal at other times.

〔Example〕

FIG. 1 shows a circuit diagram of an embodiment of the present invention.

In the figure, the same components as those in FIG. 5 are denoted by the same reference numerals, and the explanation thereof will be omitted. In this embodiment, for example, in the reproduction system of a VTR, the copy guard signal GO
~Guy is a pulse generation circuit that generates burst gate pulses and clamp pulses from a composite video signal that is synthesized in time series with a composite synchronization signal. Note that FIG. 2 is a time chart for explaining the operation of FIG. 1, and the same signals as in FIG. 6 are denoted by the same reference numerals, and the explanation thereof will be omitted.

In FIG. 1, a composite synchronization signal (indicated by b2 in FIG. 2) taken out from the synchronization separation circuit 4 is supplied to a retriggerable monostable multivibrator (hereinafter referred to as FM, M, and J) 17. , triggers on its leading edge (here the rising edge).

M, M, 17 are five additional pulses obtained by synchronously separating a horizontal synchronizing signal with a width of 4.7 μsec and a subsequent copy guard signal (p in b1 in Figure 2, and p1 to p1 in Figure 3).
The time constant is set to be longer than 7.5μ5f3C and shorter than 9.4μsec in order to distinguish between

That is, as mentioned above, the copy guard signal has other types of waveforms as shown in FIGS. 4(A) to (C), but they all differ only in the wave n value of the positive pulse portion, The pulse interval is constant regardless of the type. Therefore,
The copy guard signal in the output signal of the synchronization separation circuit 4 is
Regardless of the type, the result will always be as shown in FIG. This is a constant set.

In Figure 3, regular horizontal synchronizing signals H, S+ to H, S
3 has a width of 4.7 μsec each, whereas the period of each of the five additional pulses p1 to p5 is constant at 7.5 μsec, and the first additional pulse immediately after the rising edge of the horizontal synchronizing signal 8.82 The time width until the rise of p1 is approximately 9.4 μsec, and the final additional pulse ps
The period from the trailing edge (here, the falling edge) to the immediately following rising edge of the horizontal synchronizing signals H and Ss is approximately 22.1 μs.
It is ec.

Therefore, for the reason mentioned above, the time constant of M, M, 17 is 7.
It is set between 5 μsec and 9.4 μsec, and here it is set to 9 μsec as an example. This allows M
, M, 17 output a first pulse having a waveform as shown by Q in FIG.

8 and 9 respectively, while M in FIG.

M, 18, which is triggered on its rising edge.

The time constants of M, M, and 18 are equalization pulse and additional pulse p1~
In order to distinguish p5 from horizontal synchronization signals in other sections, the first
The period of 1H (Lr
63.5μsec) minus 9.4μsec, and the period of the equalization pulse ("F31.75
It is set to be longer than ps6(), for example, about 40 μsec. As a result, M, M.

18, as shown by i in Fig. 2, in the normal horizontal synchronization signal transmission period longer than about 40 μsec, the transmission period is about 40 μsec.
sec time width and a total of 9H period consisting of the vertical synchronization pulse period and the equalization pulse period is at least high level, and the copy guard signal and the immediately preceding horizontal synchronization signal transmission period are also high level. A pulse is extracted.

This second pulse i is M, M, 19 and M, M.

20 respectively, and these are triggered at the rising edge. The time constants of M, M, and 20 are longer than the 1H period (ave3.sμsec) and longer than the vertical synchronization pulse mrai of 38 ('v 19G, 5μsec) so as to generate a pulse whose state does not change until immediately before the vertical synchronization pulse. It is set to a short time, for example, about 180 μsec.

As shown in Fig. 2, the second pulse i has a one-day period for the most part, but it becomes longer by 9.4 μsec at the point where the additional pulse begins to appear.
Also, since there is no rising edge during the equalization pulse period, by setting the above time constants of M, M, and 20, as shown by j in Fig. 2, the vertical synchronization pulse remains high until immediately before the vertical synchronization pulse. After that, a third pulse at a low level is taken out from M, M, 20 only during the equalization pulse period and the period of about 40 μsec after that. are supplied to the circuits 22, respectively.

Further, the time constants of M, M, and 19 are based on the rising edge of the second pulse i, and the rising edge of the first additional pulse p+ among the five additional pulses p1 to Ds and the rising edge of the horizontal synchronizing signals H and S2 immediately before that. The fourth period width is set to, for example, 11 μsec, which is longer than the period between the equalization pulses (i.e., about 9.4 μsec) and shorter than the period of the equalization pulse (i.e., about 31.75 μsec).

Therefore, as shown by 0 in FIG. 2, M, M, and 19 are in phase synchronization with the horizontal synchronization signal of the composite synchronization signals b+ and bz, and there is a vertical synchronization pulse period and equalization pulse periods before and after it. The fourth pulse that does not (i.e. corresponds to the color burst signal transmission period) is taken out and the 3-power A
It is supplied to one input terminal of the ND circuit 26.

On the other hand, the composite synchronization signal and additional pulse bI.

bz is applied to M, M, 24 through inverter 23 to trigger them. M, M, 24 have a time of less than 1.5 μsec based on the falling edge of the composite synchronization signal in order to generate pulses of a constant level only during the transmission period of the five additional pulses D(p+-1)s). In addition, approximately 2 times as shown in Fig.
A time constant of less than 2.1 .mu.sec is selected, here - by way of example, approximately 11 .mu.sec.

, As a result, the fifth pulse as shown by 2 in FIG. It is latched at the rising edge of the signal and additional pulses b+ and bz. Therefore, the Q of flip 70 and knob 25
A sixth pulse having a waveform as shown by m in FIG. 2 is taken out from the output terminal. The broken line portions of the pulses m and Il show the waveforms of the composite synchronization signal b2 when it is manually operated. Further, a pulse 100 having an opposite phase to the pulse m is taken out from the σ output terminal of the flip 70 and the knob 25.

This pulse m is supplied to the AND circuit 21 together with the pulse j, and an additional pulse p(p+-
ps) is converted into a high-level seventh pulse.

On the other hand, from M, M, 13, the first
An eighth pulse with a width shorter than the pulse width of the first pulse 9 obtained by delaying the pulse Q of is extracted, and the three-man ANDI
It is logically ANDed with other pulses j and stones in the illil path 22 and converted into a pulse as shown at k in FIG. This pulse is also extracted in synchronization with the horizontal synchronizing signal immediately before the copy guard signal, and is output as a clamp pulse that clamps the pedestal level.

In addition, pulses substantially similar to the eighth pulse h (therefore, this is also referred to as the eighth pulse) are taken out from M, M, and 12, and are ANDed with the pulses 5 and O, respectively, by the three-man AND circuit 26. Be taken. As a result, a pulse shown as p in FIG. 2 is extracted from the AND circuit 26, which has a waveform in which there is no pulse of equalization pulse transmission JflrM before the vertical synchronization pulse among the pulses shown as k in FIG. Output as burst gate pulse. This burst gate pulse p is output immediately after the horizontal synchronizing signal during the period in which the color burst signal exists, and is used as the copy guard signal CQ+ to CQ7.
Since it is also output in phase synchronization with the horizontal synchronization signal immediately before each transmission period, it is possible to eliminate the phenomenon of color flicker occurring at the top of the screen as in the conventional circuit.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can also be applied to a recording system of a VTR. Furthermore, since the copy guard signal can be detected using pulse n or the like, this can be used to make the operation more reliable.

Further, to obtain the third pulse j, the rising edge of the second pulse 1 may be used to set a time width longer than one day and shorter than three days.

(Effects of the Invention) As described above, according to the present invention, pulses can be generated in phase synchronization with the horizontal synchronization signal even during the horizontal scanning period when a special signal and a color burst signal are present. Therefore, the burst detection operation can always be operated normally, and therefore the color flicker that has conventionally been present at the top of the screen can be removed. Since clamp pulses can be generated even during signal transmission, the occurrence of sag can be significantly reduced, and special signals can be detected, which can be used to improve the original behavior of special signals. can be made certain,
Furthermore, since it can be constructed entirely using digital circuits, it has many advantages such as being able to be constructed in a small size and at low cost by forming a gate array.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG.
3 is a signal waveform diagram for explaining the main parts of the circuit system shown in FIG. 1, FIG. 4 is a waveform diagram showing examples of copy guard signals, and FIG. FIG. 6 is a circuit system diagram of an example of a conventional circuit, and is a time chart for explaining the operation of FIG. 1...Composite video signal input terminal, 4...Synchronization W1 circuit, 17.18.19.20.24...Retrigger pull monostable multivibrator (M, M,'), 7゜2
5...D type flip-flop, 21, 22° 26
...AND circuit. Patent applicant: Victor Japan Co., Ltd. 2' Figure 4? ',M,b

Claims (1)

[Scope of Claims] A composite synchronization signal separated from a composite video signal on which a special signal that is a pulse train of a constant period is superimposed within a predetermined horizontal scanning period and the special signal are supplied, and the special signal is the composite synchronization signal and the special signal at intervals within a first time width that is longer and shorter than the period between the leading edge of the first pulse in the special signal and the leading edge of the immediately preceding horizontal synchronizing signal; is input, the previous state is maintained, and when the composite synchronization signal and special signal are input at intervals equal to or longer than the first time width, the leading edge of the composite synchronization signal or special signal is referenced. a first pulse generating means for generating a first pulse having a first time width, the first pulse being supplied with a period longer than the period of the equalization pulse in the composite video signal and one horizontal period; When the first pulse is input at an interval within a second time width shorter than a period obtained by subtracting the maximum value of the first time width from the scanning period, the previous state is maintained and the second time width is a second pulse generating means that generates a second pulse having the second time width using the leading edge of the first pulse as a reference when the first pulse is input at an interval equal to or greater than the width; When a second pulse is supplied and the second pulse is input at an interval within a third time width that is longer than one horizontal scanning period and shorter than three horizontal scanning periods, the previous state is maintained; a third pulse that generates a third pulse of the third time width with the trailing edge of the second pulse as a reference when the second pulse is input at intervals equal to or longer than the third time width; generating means, wherein the second pulse is provided and equalized for a period longer than the period between the leading edge of the first pulse in the special signal and the leading edge of the immediately preceding horizontal synchronization signal, with respect to its leading edge; fourth pulse generating means for generating a fourth pulse having a fourth time width shorter than the period of the pulse; the composite periodic signal and the special signal being supplied; When the composite synchronization signal and special signal are input at an interval within the fifth time width, which is shorter than the period from the trailing edge of the last pulse in the signal to the leading edge of the immediately following horizontal synchronization signal, state is maintained, and when the composite synchronization signal and the special signal are input at intervals longer than the fifth time width, a fifth pulse of the fifth time width with the trailing edge of the composite periodic signal as a reference. a fifth pulse generating means for generating a sixth pulse; a sixth pulse generating means for generating a sixth pulse by latching the fifth pulse at each leading edge of the composite synchronization signal and the special signal; a seventh pulse generating means for generating and outputting a seventh pulse having a predetermined logical value only during the transmission period of the special signal, which is supplied with the third pulse and the sixth pulse, and performs a logical operation on both; 1 pulse is supplied, and the eighth pulse generating means delays the first pulse to generate and output an eighth pulse having a time width shorter than the first time width; A pulse generating circuit comprising a gate circuit that outputs a gate pulse based on at least the fourth, fifth, and eighth pulses of the pulse and the eighth pulse.