JPS63275061A - Rewriting device for control signal - Google Patents

Abstract

PURPOSE:To prevent the generation of a whisker form pulse by shorting both the ends of a control head for a prescribed time in a timing for turning off the connection of the control head from a rewriting signal supply system for a prescribed period in the vicinity of a control signal of a reference. CONSTITUTION:A switch means 4 for shorting both the ends of the control head 14 in the timing for turning off the connection of the control head from the rewriting signal supply system for recording the new control signal is provided. Namely, the switch means 4 shorts both the ends of the control head in the timing for turning off the connection of the control head from the rewriting signal supply system. Accordingly, when the rewriting signal supply system is turned off from the control head 14, a back electromotive force generated from the coil of the control head 14 is self-discharged through the switch means 4. Thereby, the generation of the whisker pulse can be removed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides control coding methods (VISS, V
Video tape recorder (VTR) that uses ASS'
This invention relates to a control (CTL) signal rewriting device.

(Prior Art) Generally, in a VTR, a signal synchronized with the rotation of a rotating head is recorded as a control signal during recording, and during playback, the rotating head is controlled to correctly trace the video track based on the reproduced control signal. King Sabo is hung. Further, the recording control signal is a rectangular wave signal, and during reproduction, it is extracted in a differentiated state, that is, as positive and negative pulses, and the reference pulse signal is used for tracking servo.

The control coding method uses the other pulse signal, which is never used, and uses the time difference (duty ratio) from the reference pulse as information to make it possible to locate the beginning of a recorded portion. In other words, with this control coding method, during recording, it is possible to change the duty of the control signal for a predetermined period of time at the start part, or to rewrite the control signal at a predetermined location on the already recorded magnetic tape and change the duty ratio to detect that part. That's what I do.

When rewriting a control signal recorded on a VTR, the VTR is set to a playback mode, normal playback is performed, and the control signal is rewritten at a desired scene position while viewing the screen. In other words, the reference pulse used for the tracking servo is regenerated normally, the duty ratio of the other pulse is rewritten, the control head is set to the regeneration operation state, and a gate change signal is supplied to it via a switch. , the switch is turned off at the timing when the reference pulse is regenerated.

However, when reproducing and rewriting the control signal, the supply of the rewriting signal to the control head is turned on and off, so at the switching point, a pulse-shaped A beard appears. When this pulse-like whisker is input to the CTL amplifier circuit and the CTL Schmitt circuit, these circuits malfunction, making it impossible to reproduce the normal control signal, and the pulse-like pulse becomes a control residual number i. The disadvantage was that it would be recorded.

(Problem to be Solved by the Invention) When a control coding type VTR reproduces a control signal from a tape and records a new control signal on the tape based on this, rewriting is performed on the control head. The disadvantage is that the whisker-like pulses generated when the signal supply is turned on and off cause malfunctions in the circuit, and the control signal cannot be recorded in a normal coding format. Therefore, the present invention aims to eliminate the above-mentioned drawbacks, and is capable of absorbing the back electromotive force generated when turning on and off the supply of the rewriting signal to the control head, thereby eliminating the generation of whisker-like pulses. The purpose is to provide equipment. - [Structure of the invention] (Means for solving the problems) The present invention provides acI! In a video tape recorder using a control coding method, a control head normally plays back a control signal from a tape, and a new control signal with a changed duty ratio of the control signal is recorded by the control head. The configuration includes a switch means that short-circuits both ends of the control head for a predetermined period of time at the timing when the connection of the control head is turned off from a rewrite signal supply system for recording.

(Function) In the control signal rewriting device of the present invention, the switch means shorts both ends of the control head for a predetermined period of time at the timing when the connection of the control head is turned off from the rewriting signal supply system. As a result, when the rewrite signal supply system is turned off from the control head, the back electromotive force generated from the coil of the control head is self-discharged via the switch means.

(Example) An example of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of a control head reproducing and rewriting system equipped with a control head back electromotive force discharging circuit according to the present invention. A switch 1 turns on and off the recording pulse 100 supplied to the control head 14, and is turned on and off by the inverter output of the CTL guard pulse 200. 2 is the control head 14
This switch extracts only the reference CTL pulse reproduced from the reference CTL pulse 300, and is turned on and off by the reference CTL protection pulse 300. 4 is a switch that turns on and off the supply of the rewrite pulse 400 to the control head 14; 9 is a CTL;
an inverter for inverting the polarity of the guard pulse 200; 13;
14 is a control head (CTL head) that records and reproduces control pulses; 15 is an amplifier 16 that amplifies the reference CTL pulse; and 16 is a logic CTL head that shapes the waveform of the pulse from the amplifier 15. This is a waveform shaping circuit with a pulse (base $CTL pulse) of 500.

Next, the operation of this embodiment will be explained according to the operation time chart shown in FIG. First, when the cue write signal shown in FIG. 2(A) is outputted from a microcomputer (not shown), the CTL guard pulse 200 shown in FIG. 2(D) is outputted. First, when the CTL guard pulse 200 rises, switch 4 is turned off and switch 1 is turned on. Next, this CTL guard pulse 20
The reference CTL protection pulse 300 shown in FIG. 2(C) created from 0 becomes high level, the switch 2 is turned on, and the CTL head 14 reproduces the reference CTL protection pulse 300 shown in FIG. 2(B).
The reference CTL signal among the CTL signals shown in is the amplifier 15.
The signal is further waveform-shaped by the waveform shaping circuit 16 to become a logic CTL pulse 500 shown in FIG. 2(H), which is then supplied to a servo system (not shown). Next, CT
When the L guard pulse 200 falls, the switch 4 is turned on and at the same time the switch 1 is turned off by the output of the inverter 9. At the same time, the rewrite pulse 400 shown in FIG. 2(E) is output and supplied to the CTL head 14, and this pulse 400 is written on the tape. Note that this rewrite pulse 400 is generated from the CTL guard pulse 200. FIG. 2(G) is an example of a CTL pulse after rewriting. Here, in synchronization with the rise of the CTL guard pulse 200, a whisker removal pulse 600 is generated as shown in FIG. 2(F), and this pulse turns on the transistor 13. This allows CTL
Both ends of the head 14 are short-circuited via the transistor 13. Therefore, when the switch 4 is turned off by the rise of the CTL guard pulse 200, both ends of the CTL head 14 are short-circuited.
The back electromotive force generated in the CTL head 14 when it is turned off is self-discharged via the transistor 13, and the CTL head 14
As shown in Figure 2 (I), the "whiskers" that occur in the past can be removed after rewriting.
It will no longer be on the TL pulse.

FIG. 3 is a circuit diagram showing a detailed example of the circuit shown in FIG. 1, and the same parts as in FIG. 1 are denoted by the same reference numerals. When the CTL guard pulse 200 rises as shown in FIG.
is turned off. This CTL guard pulse 200 is input to the monomulti 12, and this monomulti 12
Figure 4 (B) synchronized with the rise of guard pulse 200.
) is output. This whisker removal pulse 600 is input to the monomulti 11, where it passes through the signal forms shown in FIGS. 2(C) and (D), and becomes the reference CTL protection pulse 300 shown in FIG. 4(E). Turn switch 2 on and off. This reference CTL protection pulse 300 is output so as to match the negative pulse of the CTL signal shown in FIG. 4(H), and the switch 2 is turned on by the rise of this pulse 300 and turned off by the fall of this pulse 300. On the other hand, the hair removal pulse 600 output from the monomulti 12 is input to the transistor 13, and turns on the transistor 13 during its high level period.

On the other hand, the pulse 800 shown in FIG.
is the drive signal, and the period when the reference CTL signal does not exist,
The switch 3 is turned on and the positive input of the amplifier 15 is grounded via the transistor 8. C.T.L.
The guard pulse 200 is also input to the monomulti 10 at the same time, and the monomulti 10 receives the CTL as shown in FIG. 2(F).
A rewrite pulse signal 700 synchronized with the rising edge of the guard pulse 200 is output to the transistor 7, and this transistor 7 is turned on and off by the signal 700, and when the switch 4 is turned off and on, the rewrite pulse as shown in FIG. 4(G) is output. A write pulse 400 is provided to control head 14 to write a new CTL signal to the tape. FIG. 4(I) shows the CTL pulse after rewriting.

Note that at the falling edge of rewrite pulse 400 (when the current changes in the opposite direction), a new pulse is written to the tape. Since the same level of current flows thereafter, the positive component of the original control pulse is erased. Note that the transistor 5 is used to adjust the time constant of the monomulti 10, and by adjusting the time constant to 60% or 27.5%, the write timing of the rewrite pulse 400 is adjusted. The transistor 6 is controlled by the index signal shown in FIG. 4(J), and prevents the switch 2.3 from being controlled by the output of the monomulti 11 when the control signal is not written. The transistor 8 is a switch that is always on and grounds one end of the control head 14.

According to this embodiment, when the switch is turned off to cut off the supply of the rewrite signal to the control head 14 at a timing near when the reference control pulse is obtained in the cue write mode, the transistor 13 is turned off by the whisker removal pulse 600. By turning on, both ends of the control head 14 are temporarily short-circuited.
When the switch 4 is turned off, the back electromotive force generated in the coil of the control head 14 can be self-discharged.

Therefore, the whisker-like pulse that was generated due to the back electromotive force when the switch 4 is turned off disappears, and the whisker-like pulse is used as a reference CTL pulse by the amplifier 15 and the waveform shaping circuit 1.
This eliminates the possibility of malfunctions and prevents whisker-like pulses from being recorded as residual signals on the tape.

. [Effects of the Invention] As described above, the control signal rewriting device of the present invention absorbs the back electromotive force generated when turning on and off the supply of the rewriting signal to the control head, thereby preventing the generation of whisker-like pulses. There is an effect that can be removed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a control head reproducing and rewriting system equipped with the control signal rewriting device of the present invention, and FIG. 2 is an operation time chart of the circuit shown in FIG. Fig. 3 is a circuit diagram showing a detailed example of the circuit shown in Fig. 1, and Fig. 4 is an operation time chart of the circuit shown in Fig. 3. 1.2.3.4...Switch 5. 6, 7, 8, 9.13...transistor 10, 1
1.12...Monomulti 14...Control head 15...Amplifier 16...Waveform shaping circuit Representative Patent attorney Noriyuki Chika Yudo Hiroshi Uji (A) Figure 2

Claims (1)

[Claims] (1) In a control coding type video tape recorder in which a control head normally reproduces a reference control signal from a tape and a new control signal with a changed duty ratio of this control signal is recorded by the control head, The rewriting of the control signal is characterized in that a switch means is provided for short-circuiting both ends of the control head for a predetermined period of time in the vicinity of the control signal, at the timing of turning off the connection of the control head from the rewriting signal supply system. writing device.