JPH0253246A - Control signal writing circuit - Google Patents

Abstract

PURPOSE:To gradually increase and decrease a current to a control coil by providing a charging switch connected to a first path to link a control driver and the control coil and turned on when rewriting is started and discharging switch connected to a second path and turned on in the case of rewriting is ended. CONSTITUTION:The title device is equipped with a control coil 10, a control driver 12, a charging switch SW1, a discharging switch SW2, and a capacitor C1. Further, when a control signal is to be rewritten, a prescribed current is supplied to the control coil 10 by the control driver 12. At this time, when a rewriting current rises, the charging switch SW1 is turned on, charging to the capacitor C1 is executed through the switch SW1, and the rise of the writing current is weaken. On the other hand, when the rewriting current falls, the discharging switch SW2 is turned on, discharging from the capacitor C1 is executed through the switch SW2, and the fall of the rewriting current can be weakened. Thus, the current can be changed gradually.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control signal writing circuit, and particularly to improvements in rewriting cue signals.

[Background Art] The spread of video tape recorders in recent years has been remarkable, and their functions have become more sophisticated and diversified. and,
One such function is a cueing function.

This cueing function places some sort of mark at the starting point of recording on the tape, detects it during fast forwarding or rewinding, and automatically stops the recording. If you have this feature, you can fast forward or rewind to find the beginning of a program when you have recorded multiple programs.

This cueing function uses VISS (VH8Index).
5earch System) and VASS (VH
There are various types such as 3^ddres 5earch System). The former records the cue position and automatically stops at that position, while the latter records the cue position as a predetermined address, and by specifying that address, auto-stops at the specified cue position. It is something.

Here, the recording of the cueing signal in this cueing function is as follows.
- This is done by changing the duty ratio of the control signal written in the control track of the videotape.

That is, a control track is provided on the negative side of the tape, and a control signal for synchronizing video signals and the like stored in the video track is recorded on this control track. An on/off signal with a fixed duty ratio is used as the control signal, but since this control signal only specifies the position of a video track or the like, there is no problem even if the duty ratio is changed. Therefore, by changing the duty ratio of this control signal, cueing and recording of the signal is performed.

As described above, the cueing function is convenient because it allows you to specify the recording start location, but it would be even more convenient if you could record or change the cueing mark at an arbitrary position. Therefore, devices having such functions are beginning to become popular.

In order to write or change such a cue signal, it is necessary to rewrite the control signal, but in this case, since the video signal etc. are not rewritten, the part related to synchronization of the control signal is The duty ratio of the control signal must be changed in such a way that it has no effect on the control signal. Therefore, it is necessary to rewrite only the portion related to the duty ratio of one of the control signals.

Here, writing and reading of control signals to and from the control track during normal recording is performed by a control coil. Writing is performed by DC recording by switching the current direction. Therefore, when writing a control signal, the current direction is switched at predetermined intervals, and the direction of magnetization of the magnetic material in the control track is reversed at predetermined intervals.

Next, such rewriting of the control signal will be explained based on FIG. 3.

As shown in FIG. 3(A), in a normal state, a control signal with a duty ratio of about 60% is written in the control track. Furthermore, at the cue location, a control signal with a duty ratio of about 27.5% is written as shown in FIG. 3(B).

When erasing the cue signal, a current as shown in FIG. 3(C) is passed through the control coil. By flowing such a current, it is possible to rewrite the control signal recorded on the control track, which indicates cueing, into a signal with a normal duty ratio of about 60%.

On the other hand, when rewriting the cue signal, as shown in Fig. 3 (D
) Flow the current shown in the control coil. As a result, a normal control signal with a duty ratio of about 60% can be rewritten into a cueing signal with a duty ratio of about 27.5%.

In this way, the position of the falling part of the control signal can be changed without rewriting the rising part of the control signal.

[Problems to be Solved by the Invention] The rewriting of the control signal is performed as described above, and this rewriting is performed by rewriting a part of the signal that has already been written. For this reason,
There may be a difference in the degree of magnetization on the tape between the control signal that has already been written and the signal that has been rewritten.

Particularly when rewriting control signals written by another video tape recorder, it is inevitable that slight differences will appear in the degree and position of magnetization.

Therefore, a difference in level occurs in the control signal at the start and end of rewriting. That is, the originally written signal and the rewritten signal are connected at the locations where rewriting begins and ends on the control track, but a discontinuous point occurs in the magnitude of magnetization at this point.

For this reason, when the control coil reads out the control signal during playback, the rewriting start point and end point are mistakenly recognized as the rising edge of the control signal as the falling edge.
Problems such as loss of synchronization may occur.

By the way, in order to solve this problem, it is conceivable to gradually increase or decrease the current flowing through the control coil at the start and end of rewriting. In this way, current changes in the readout signal by the control coil during reproduction are suppressed, and the possibility of misidentification of the control signal during reproduction is greatly reduced.

In order to make such a gradual change in current, it is usually considered to connect a capacitor to the circuit leading to the control coil to slow down the rise and fall. However, this requires two capacitors, one for rising and one for falling, which poses a problem in that it becomes an obstacle to the integration of the control signal writing/reading/accepting circuit.

This invention was made to solve the above-mentioned problems, and its purpose is to gradually increase and decrease the current to the control coil during rewriting using one capacitor. An object of the present invention is to provide a control signal writing circuit.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a video tape in which a duty ratio of a control signal stored in a control track of a video tape can be rewritten, and a cue signal can be rewritten. In a control signal writing circuit of a recorder, there is a control coil that writes and reads control signals on a control track of a videotape, a control driver that switches the direction of current to the control coil, and controls writing of a control signal to the control track, and a control A charging switch connected to a first path connecting the driver and the control coil and turned on when rewriting starts; a discharging switch connected to a second path connecting the control driver and the control coil and turned on when rewriting ends; is connected to both the charging switch and the discharging switch, and receives current supply via the charging switch when the rewriting current rises in the control coil, and supplies current via the discharging switch when the rewriting current falls. , and is characterized in that the current is gradually changed at the rise and fall of the rewrite current of the control fill.

[Operation] The control signal writing circuit according to the present invention has the above-described configuration and operates as follows.

That is, when rewriting the control signal, a predetermined current is supplied to the control coil by the control driver.

Here, since the charging switch is turned on when the rewrite current rises, the rise of the write current can be slowed down by charging the capacitor via this charging switch. On the other hand, since the discharge switch is turned on when the rewrite current falls, the capacitor is discharged via this discharge switch, thereby making it possible to slow down the fall of the rewrite current.

This makes it possible to significantly reduce noise at the start and end of rewriting when reading a rewritten control signal.

[Embodiment] Next, a control signal writing circuit according to an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment.

The control coil 10 is a video tape (not shown)
The video tape is placed at a position facing the control track of the video tape in the loading state. A control signal can be written to the control track by passing a current through this control coil 10. In addition, during playback, this control coil 1
The control signal is read by 0.

Further, the control driver 12 controls the write current to the control coil 10 . That is,
The control driver 12 is supplied with a gate signal G and a write signal R.
2 supplies a current corresponding to the write signal R to the control coil 10 when the gate signal G is on. In the figure, the upper output end 12a of the control driver 12 is connected to one end T of the control coil 10 via the REC(+) end.
1, and the lower output end 12b is connected to the other end T2 of the control coil 10 via the RFC(-) end. The control driver 12 then reverses the direction of the DC current at the output terminals 12a, 12b depending on the high level or low level of the write signal.

Therefore, the control coil 10 has a current flowing from the top to the bottom (TI-T2) and from the bottom to the top (T2-T2) according to the high level and low level of the write signal R.
A current flows through TI). As a result, control signals whose magnetization directions are sequentially reversed are stored in the control tracks of the video tape facing the control coil 12.

Further, the upper output end 12a of the control driver 12
A switch sv is connected to the RCE (+) terminal.
A switch Sv2 is connected to a path connecting the lower output end 12b of the control driver 12 and the RCE (10) terminal. And these switches S
The other ends of ν1 and Sν2 are connected to the capacitor C1 via the trapezoidal wave terminal WT.

Note that the output lines L1 and L2 connected to both ends of the control coil 10, respectively, are for outputting the read signal of the control coil 12 during reproduction, and the switches sv3. It is connected to the reproducing circuit 20 via sw4.

Next, regarding the case of rewriting the control signal in such a control signal writing circuit, the second
This will be explained based on the diagram.

FIG. 2(A) shows the state of the control signal currently written in the control track. The rise point of the rectangular wave is necessary for synchronizing video signals and the like. Then, the duty ratio of the control signal is determined from the location of the fall, and it is recognized whether the signal is a cueing signal or not. In this example, the 1.4th control signals are normal signals, and the 2.3.5th control signals are cue signals. In the figure, several cue signals and several normal signals are shown for explanation, but normally several dozen cue signals are formed in succession.
Represents one cue.

FIG. 2(B) shows a signal recognized by the reproducing circuit 20 when the signal shown in FIG. 2(A) is read out as is by the control coil 10. In this way, the rising edge and falling edge of the control signal are recognized.

FIG. 2C shows the write signal R when rewriting the cue signal. In response to this write signal R, the control driver 12 writes a control signal corresponding to this write signal R to the control track after rewriting. Therefore, this write signal R corresponds to the control signal after rewriting.

FIG. 2(D) is a signal for controlling on/off of the input of the reproduction signal to the reproduction circuit 20. When this signal is on, the control coil 10 operates as a reading coil, and as shown in FIG. 2(E). A synchronizing signal as shown is obtained in the reproducing circuit 20. Since it is sufficient to detect the rise of the control signal, in this example, it is turned on for 10% to 10% of one cycle.

Next, FIG. 2(F) shows the gate signal G that controls the operation of the control driver 12, and FIG. 2(E)
It is turned on for a certain period of time after a predetermined period of time has elapsed from the rising time shown in . When this gate signal G is on, the control coil 10 is in the write mode, and is set so as not to overlap with when the reproduction on signal shown in FIG. 2(D) is on. In addition, the time when this gate signal G turns on must be before the fall of the control signal that indicates cueing, and the time when the gate signal G turns off is after the time when the normal control signal falls. It must be.

This allows any originally stored control signal to be rewritten into a rewrite signal.

In this example, the gate signal G is turned on for 15% to 85% of one cycle based on the rising edge of the control signal.

Then, if the gate signal G is turned on and the write signal R at this time is at a high level, the control;
A forward current (T14T2) begins to flow. However, as shown in FIG. 2(G), the charging switch Sw1 is turned on at the same time as this current gate signal G is turned on.

Therefore, the circuit on the RED(+) terminal side is connected to the capacitor C.
It will be connected to 1. Therefore, this capacitor C
REC (
The voltage change at the +) terminal will be blunted and gradually rise as shown in FIG. 2 (H).

Then, when the write signal R goes low, the control driver 12 reverses the current supply at its output. The direction of the current in the control coil 10 is therefore reversed.

Here, in this example, FIGS. 2(G) and (1)
As shown in FIG. 3, at the same time as this reversal of the current supply direction, the charging switch Svl is turned off and the discharging switch Sv2 is turned on. Therefore, the location where capacitor C1 is connected at the same time as the current reversal is I? The EC(+) end is changed to RIEC(-). Therefore, this capacitor C1 is connected to a location having the same potential, and its charged state is maintained.

In this state, the control coil 10 writes a signal corresponding to the low level state of the control signal, but this writing must be completed by the next rise of the originally written control signal. It won't happen. In this invention, FIG. 2 (J)
As shown in FIG. 3, the current flowing through the control coil 10 from TI to T2 is stopped by the rewrite end signal ED. This rewrite end signal ED is supplied to the control driver 12, and the control driver thereby stops supplying current.

Then, as shown in FIG. 2 (1) and (J), when this rewriting end signal ED falls, the discharge switch Sv2
is still on. Therefore, as shown in FIG. 2(K), the potential at the REC(-) terminal gradually decreases due to the flow from the capacitor C1.

The rewrite end signal ED is set to turn off at 70% from the rise of the control signal so that the originally written control signal can be rewritten even with a normal signal with a duty ratio of 60%.

Further, the switch Sw needs to be turned off when the discharge by the capacitor C1 is finished and before entering the regeneration mode, and in this example, it is turned off at 85% of the time.

Incidentally, the voltage change at the trapezoidal wave terminal W□ in such an operation is as shown in FIG. 2 (L).

As described above, according to the circuit of this embodiment, the rise of the current flowing through the control coil 10 during rewriting,
The fall can be done gradually.

Therefore, even if there is a slight difference in magnetization between the originally written control signal and the rewritten signal, the change will occur gradually, and no large peak will occur in the reproduced signal. Therefore, noise in the rewritten control signal can be significantly reduced. Such an operation can be performed by charging and discharging one capacitor.

[Effects of the Invention] As explained above, according to the control signal writing circuit according to the present invention, when only the control signal is rewritten, the rise and fall of the write current can be slowed down, and the change in current can be slowed down. can be done gradually. Therefore, noise generation in the control signal can be prevented. Furthermore, since only one capacitor is required to slow down the change in the rewrite current, the circuit can be significantly simplified and can be easily integrated.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a control signal writing circuit according to an embodiment of the present invention, FIG. 2 is a timing chart in the same embodiment, and FIG. 3 is an explanatory diagram of conventional control signals, etc. 'f Ohhiikuri's C! Figure 1 Control Coil Control Driver Charging Switch Discharging Switch Capacitor

Claims (1)

[Claims] (1) In a control signal writing circuit of a video tape recorder that can rewrite the duty ratio of the control signal stored in the control track of the video tape and rewrite the cue signal, the control signal is written in the control track of the video tape. A control coil that performs reading, a control driver that switches the direction of current to the control coil and controls writing of control signals to the control track, and a first circuit that connects the control driver and the control coil.
A second charging switch connects the control driver to the control coil and is turned on when rewriting starts.
A discharging switch is connected to the path of the control coil and is turned on when the rewriting is completed, and one end is connected to both the charging switch and the discharging switch, and when the rewriting current in the control coil rises, the current is supplied via the charging switch, and the rewriting is completed. a capacitor that supplies current via a discharge switch when the writing current falls, and the control signal writing is characterized in that the current gradually changes when the rewriting current of the control coil rises and falls. circuit.