JPH0265582A - Pseudo vertical synchronizing signal additional circuit for vtr - Google Patents

Abstract

PURPOSE:To prevent disturbance of vertical synchronization even at the special reproduction by quickening the head switching time more than the substantial timing if a time is shorter than a prescribed time till a vertical synchronizing signal is detected at the normal reproduction and when the special reproduction mode is selected. CONSTITUTION:A comparison signal generating circuit 4 generates a comparison signal S3 being at a high level till a vertical synchronizing signal S2 is sent at the switching of an H.SW.P signal S1 at normal reproduction. Moreover, a reference signal generating circuit 6 outputs a reference signal S4 being at a high level for a period 2H from switching of the H.SW.P signal S1. If the period of high level of the comparison signal S3 is shorter than that of the reference signal S4, a vertical synchronizing signal discrimination circuit 7 goes to a high level. When the special reproduction is started, a flip-flop circuit 9 is set by a high output of the vertical synchronizing signal discrimination circuit 7 and the special reproduction mode signal and the delay time of the H.SW.P generating circuit 1 depending on a resistor R1 and a capacitor C1 mounted externally is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to VTR [video tape rec]
The present invention relates to a pseudo vertical synchronization signal adding circuit that adds a pseudo vertical synchronization signal to a reproduced video signal so that the vertical synchronization signal is not impaired by a noise band during special playback in [order].

[Conventional technology]

In special playback of a VTR, the envelope of the frequency-modulated playback video signal is periodically narrowed because playback is performed at a tape running speed different from that during recording. Noise bands occur in areas where this envelope is narrower than a certain level, making the screen difficult to see. However, at least in the case of still playback, predetermined slow playback, or double-speed playback, there is only one noise band, so the tracking servo is used to change the phase of tape travel, and the position of this noise band is set during the vertical blanking period. You can prevent it from appearing on the screen by pushing it.

However, when the noise hand is moved during the vertical blanking period in this manner, the vertical synchronization signal is impaired by this noise band, and the vertical synchronization is disturbed, which may cause vertical shaking on the screen.

Therefore, conventionally, a pseudo vertical synchronization signal was formed based on the head switching pulse from the rotary head, and this was added to the reproduced video signal to prevent vertical synchronization disturbance.

This conventional pseudo vertical synchronization signal addition circuit is shown in Figures 3 and 4.
This will be explained based on the diagram.

In the reproduced video signal Sl+, as shown in FIG. 4, the vertical synchronization signal is distorted by a noise band. Further, a PC (pulse generator) provided in the rotary head emits a PC output that detects when the head is switched.

This PG output is sent to the H, SW, P generation circuit 21 as shown in FIG. In response to the trigger of this PC output, the H, SW, P generation circuit 21 generates H, SW, and P signals Sl□ (head switching pulse signal) delayed by a predetermined time determined by an external resistor R0 and a capacitor C0. The signal is sent to the FV generation circuit 22.

The FV generation circuit 22 is a circuit that receives a special playback mode signal issued during the special playback mode and forms an FV signal 513 (pseudo vertical synchronization signal). As shown in FIG. 4, this FV signal SI1 is
, P signal SI2 is delayed by a predetermined time Tl+ determined by the external resistor R1□ and the capacitor C+z, and is output as a pulse signal spanning several H.

The FV signal 3+1 output from the FV generation circuit 22 is FV
It is sent to the V addition circuit 23. The FV adding circuit 23 is a circuit that inputs the reproduced video signal S11, adds the F■ signal s+3 to it, and outputs it as the FV added video signal SI4.

Here, as shown in Figure 4, the reproduced video signal Sl+ includes a vertical synchronization signal at a position delayed by 3 to 8H (5H in the figure) from the switching of the H, SW, and P signals S1□ based on the VH3 standard. recorded. However, since the delay time Tl+ in the FV generation circuit 22 is set to 2 to 3H (2H in the figure), the FV signal 5lff in the FV additional video signal SI4 is added before the original vertical synchronization signal. It turns out.

Therefore, if the video is played back based on this FV added video signal SI4, even if the original vertical synchronization signal is impaired by the noise band as shown in FIG.
Since the signal SI3 is detected as a vertical synchronization signal first, vertical synchronization can be ensured.

[Problem to be solved by the invention]

However, so-called self-recorded VTR tapes recorded with equipment other than the equipment used for playback contain H, SW, and P signals S+Z.
In some cases, a vertical synchronizing signal is recorded at a position delayed by 1 to 2 hours from the time of switching. Even with such a VTR tape, no problem occurs during normal playback.

However, during special playback, the delay time T of the added FV signal 5lff becomes longer than this, so the original vertical synchronization signal corrupted by the noise band is detected first.

Therefore, with the conventional pseudo vertical synchronization signal addition circuit of a VTR, when performing special playback of a VTR tape in which the vertical synchronization signal is recorded at an early position, it is not possible to prevent vertical synchronization disturbance, and the vertical synchronization signal appears on the screen. There was a problem that this occurred.

[Means for Solving the Problems] In order to solve the above problems, the pseudo vertical synchronization signal adding circuit of the VTR according to the present invention delays the playback video signal by a predetermined time from the head switching time during special playback. In a pseudo vertical sync signal adding circuit of a VTR that adds a pseudo vertical sync signal, there is a vertical sync signal detection means for detecting a vertical sync signal from a reproduced video signal during normal playback, and a head switching time is detected from the output of a pulse generator of a rotary head. head switching detection means for detecting head switching, comparison means for comparing whether the time from when head switching is detected to when a vertical synchronization signal is detected during normal playback is shorter than a predetermined time; The present invention is characterized in that it includes a shift means that advances the timing of head switching earlier than the original timing when switching to special reproduction mode when the time until the synchronization signal is detected is shorter than a predetermined time.

[For production]

First, during normal playback, the vertical synchronization signal detection means detects the vertical synchronization signal from the reproduced video signal. During normal playback, the vertical synchronization signal is not affected by noise bands, so it can be detected normally.

Further, the head switching time detection means detects the head switching time from the output of the pulse generator of the rotary head. and,
The comparing means compares a predetermined time period with a time period from when the head switching detecting means detects the time of head switching until when the vertical synchronizing signal detecting means detects the vertical synchronizing signal. This predetermined time is set to be equal to or slightly longer than the delay time from head switching when adding the pseudo vertical synchronization signal. Therefore, if it is detected that the detection time of the vertical synchronization signal is shorter than the predetermined time by comparison using this comparison means, it is determined that the vertical synchronization signal was recorded earlier than the standard due to so-called other recordings. It can be determined that it is a VTR tape.

Next, during special playback, since there is a risk that the vertical synchronization signal of the reproduced video signal may be impaired, a pseudo vertical synchronization signal delayed by a predetermined time from the head switching time detected by the head switching detection means is added.

However, during normal playback, if the comparison means determines that the VTR tape is a VTR tape in which the vertical synchronization signal was recorded earlier than the standard, the shift means will detect when the head changeover is detected by the head changeover detection means. earlier than the original timing.

The time advanced by this shift means is appropriately determined within a range shorter than the delay time of the pseudo vertical synchronization signal. In this way, when the head switching time is advanced by the shift means, the timing at which the pseudo vertical synchronization signal is added is also advanced.

Therefore, the present invention adds a pseudo vertical synchronization signal before the original vertical synchronization signal that has been damaged by the noise band even when performing special playback on a VTR tape in which the vertical synchronization signal was recorded earlier than the standard. can do.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 and 2.

The PG ratio output from a PC (pulse generator) provided in a rotary head (not shown) is input to the H, SH, and P generation circuit 1. The II, SW, and P generation circuit 1 is configured by a one-shot multi-by-break. Then, in response to a trigger from the PC output, H becomes "old GH" for a certain period of time at a timing delayed by a predetermined period determined by external resistor R5 and capacitor CI.
, SW, outputs the P signal S1. The output of this H, SW, P generation circuit 1 is connected to an FV generation circuit 2. Further, this FV generation circuit 2 is provided with an "old Gl+
The FV generating circuit 2 is a circuit that outputs an FV signal S when the special playback mode signal is input.This FV signal S, is a pseudo vertical synchronizing signal that rises with a delay of a predetermined time T1 determined by an external resistor R2 and capacitor C2 from the switching of H, SW, and P signal S, and whose "HIGH" period is several H. The output of the FV generation circuit 2 is connected to the FV addition circuit 3.A reproduced video signal is input to this FV addition circuit 3.The FV addition circuit 3 is connected to the FV addition circuit 3. Signal S keeps the reproduced video signal “LOW” only during the “old GH” period.
” level, and apply the FV signal S to this reproduced video signal.

This is a circuit that adds

The above configuration is the same as the conventional pseudo vertical synchronization signal adding circuit. Therefore, when a special playback mode signal is input to the FV generation circuit 2 during normal VTR tape playback, H, SW,
The FV signal S is sent to the FV addition circuit 3 based on the H, SW, and P signals S1 generated by the P generation circuit 1, and an FV addition video signal similar to the conventional one is generated.

In this embodiment, the output of the above-mentioned 1.5W, P generation circuit 1 is also connected to the comparison signal ordering circuit 4 and the reference signal generation circuit 5. Further, the reproduced video signal is also input to the vertical synchronization signal layering circuit 6. The vertical synchronization signal separation circuit 6 is a circuit that separates and outputs the vertical synchronization signal S2 from the reproduced video signal during normal playback. This vertical synchronization signal separation circuit 6 is connected to the comparison signal generation circuit 4. Comparison signal generation circuit 4 is constituted by a flip-flop. And 11. sW,P
By inputting the H, SW, and P signals S1 from the generation circuit 1 as set pulses and inputting the vertical synchronization signal S2 from the vertical synchronization signal separation circuit 6 as a reset pulse, when switching Il, SW, and P signals S1, Vertical synchronization signal S
The reference signal generation circuit 5 is a circuit configured with a one-shot multi-high break. 11.sW, P signal SI from Il, SW, P generation circuit 1 is manually inputted as a trigger pulse, and 28 (1
Reference signal S4 becomes “old GH'” only for a period of 28ms)
generate.

The outputs of the comparison signal generation circuit 4 and reference signal generation circuit 5 are connected to a vertical synchronization signal discrimination circuit 7, respectively. The vertical synchronization signal determination circuit 7 compares the period (duty) of "'HIG11" in the comparison signal S from the comparison signal generation circuit 4 and the reference signal generation circuit 5 and the reference signal S, and determines whether the comparison signal S3 is If it is less than 2H, ``Old Gl! ``This is a circuit that outputs level.

The output of this vertical synchronization signal discrimination circuit 7 is connected to a set terminal of a flip-flop circuit 9 via one input of an AND circuit 8. The other input of the AND circuit 8 is
The special reproduction mode signal is input. Further, the output of the vertical synchronization signal discrimination circuit 7 is connected to the reset terminal of the same flip-flop circuit 9 via an inverter circuit 0. Therefore, the flip-flop circuit 9 is set only when the vertical synchronization signal discrimination circuit 7 is at the "HIG11 level" and the special reproduction mode signal is issued. Note that when special playback is started, the vertical synchronization signal discriminating circuit 7 stops the comparison operation, and the previous output state is maintained.

The output of this flip-flop circuit 9 is connected via a bumper amplifier 11 and a resistor R1 between an external resistor R8 and a capacitor CI in the H, SW, P generating circuit 1.

The operation of the pseudo vertical synchronization signal adding circuit having the above configuration will be explained.

First, during normal playback, the comparison signal generation circuit 4 outputs H, SW.
, the H, SW, and P signals S output from the P generation circuit 1 and the vertical synchronization signal S2 output from the vertical synchronization signal separation circuit 6.
As shown in FIG. 2, H.

The comparison signal S becomes “'')IIG)I” from the time of switching SW and P signal S until the vertical synchronization signal S2 is sent.
.

generate. Also, in the reference signal generation circuit 5, based on the H3S and P signals S1, the reference signal S becomes the "old GH" for a period of 2H from the time of switching of the H, SW and P signals S1.
Outputs 4. Then, as in the case illustrated in FIG. 2, when the period of "FIIGH" of the comparison signal S is shorter than that of the reference signal S4, the vertical synchronization signal discrimination circuit 7 becomes 'old GH', and in this case In this case, it is determined that the VTR tape being played back has the vertical synchronization signal S2 recorded earlier than specified.

Next, when special playback is started, the flip-flop circuit 9 is set by the "old GH" output of this vertical synchronization signal discrimination circuit 7 and the special playback mode signal.Then, the output voltage of this flip-flop circuit 9 causes The delay time of the H, SW, and P generation circuit 1, which was determined by the external resistor R7 and capacitor C, is shortened.

As a result, as shown in FIG. 2, the H, SW, and P signals S1' during special playback are switched at an earlier timing than the original H, SW, and P signals SI. Therefore, this )1
．． SW, P signal 3. The FV generating circuit 2 to which + is input also outputs the FV signal S with a delay of time T1.

The timing will be earlier than usual. Then, the FV addition circuit 3 receives this FV signal S.

is added to the playback video signal. For this reason, FV addition circuit 3
In the FV-added video signal output from the FV signal S, the original vertical synchronization signal S2 will not be detected earlier than the FV signal S.

When playing back a normal VTR tape, the output of the vertical synchronization signal discrimination circuit 7 becomes "LOW" and the flip-flop circuit 9 is reset, so that the FV signal S is output at the same timing as in the conventional case.

is added.

〔Effect of the invention〕

As described above, the VTR pseudo vertical synchronization signal adding circuit according to the present invention adds a pseudo vertical synchronization signal delayed by a predetermined time from head switching to a reproduced video signal during special playback. The signal addition circuit includes vertical synchronization signal detection means for detecting a vertical synchronization signal from the reproduced video signal during normal playback, head switching detection means for detecting head switching from the output of the pulse generator of the rotary head, and head switching detection means for detecting the vertical synchronization signal from the reproduced video signal during normal playback. a comparison means for comparing whether the time from when switching is detected until the vertical synchronization signal is detected is shorter than a predetermined time; and the time from when the vertical synchronization signal is detected during normal playback to the predetermined time. If the head is shorter than the original timing, when switching to the special reproduction mode, the shift means is configured to advance the timing of head switching earlier than the original timing.

This makes it possible to add a pseudo vertical sync signal before the original vertical sync signal that has been damaged by the noise band, even when performing special playback on a VTR tape where the vertical sync signal was recorded earlier than the standard. can.

Therefore, according to the present invention, since the pseudo vertical synchronization signal is always detected before the original vertical synchronization signal, vertical synchronization is not disturbed even during special playback.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention, in which FIG. 1 is a block diagram of a pseudo vertical synchronization signal adding circuit;
FIG. 2 is a time chart showing the operation of the pseudo vertical synchronization signal adding circuit. 3 and 4 show a conventional example, in which FIG. 3 is a block diagram of a pseudo vertical synchronizing signal adding circuit, and FIG. 4 is a time chart showing the operation of the pseudo vertical synchronizing signal adding circuit. 1 is an H, SW, P generation circuit (head switching detection means);
6 is a vertical synchronization signal separation circuit (vertical synchronization signal detection means);
7 is a vertical synchronization signal discrimination circuit (comparison means), and 9 is a flip-flop circuit (shift means). Figure 3 PG output

Claims (1)

[Claims] 1. V that adds a pseudo vertical synchronization signal delayed by a predetermined time from the time of head switching to the reproduced video signal during special reproduction.
The pseudo vertical synchronization signal addition circuit of the TR includes vertical synchronization signal detection means for detecting a vertical synchronization signal from a reproduced video signal during normal playback, and head switching detection means for detecting head switching from the output of a pulse generator of a rotating head. , a comparison means for comparing whether the time from when head switching is detected to when a vertical synchronization signal is detected during normal playback is shorter than a predetermined time; and until the vertical synchronization signal is detected during normal playback. 1. A pseudo vertical synchronizing signal adding circuit for a VTR, comprising a shift means for advancing head switching timing earlier than the original timing when switching to a special reproduction mode when the time is shorter than a predetermined time.