JPS58118057A - Recording and reproducing device of magnetic tape - Google Patents

Abstract

PURPOSE:To eliminate completely the magnetized phenomenon of a control track head, by supplying a recording current having the attenuation of oscillation to record a signal, and to have the own AC demagnetizing effect. CONSTITUTION:When a negative pulse of input is supplied, a TR1 is turned off through a C1. A bias current flows to a TR2 through an R2 to turn on the TR2 just for a period equivalent to the width gamma of an input pulse. The collector of the TR2 is set at about -12V to charge a resonance circuit C2 and an L1. When the negative pulse period gamma is over, the TR2 is turned off with the area between the emitter and the collector of the TR2 set in an open state. Then the electric charge stored to the circuit C2 and the L1 cause the attenuated vibration in response to the own resonance frequency and the value of Q. Thus a signal having the burst type attenuation characteristics is obtained to be supplied to a control track head 5 in the form of a recording signal through coupling capacitors C3 and C4 in a recording mode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic tape recording/reproducing device (hereinafter referred to as a video tape recorder).

In general, it is necessary for video tape recorders of this type to operate in synchronization with a reference synchronization signal during recording and playback. ), which separates and generates a so-called frame synchronization signal from the reference signal during recording.
In this way, a signal to be controlled (hereinafter referred to as a control track signal) is formed and recorded on the control track, and at the time of playback, the control track signal is reproduced from the track, and this is synchronized with the reference signal for operation. A so-called servo circuit is configured to maintain synchronized tape running.

Traditionally, video tape recorders use a 4-head system.
Regardless of the helical scan method, the recording signal of the control track signal is as shown in Figure 1 (S + (11) +
(A square wave signal as shown in each figure.)

Pulse signals or sinusoidal signal waveforms were used, and these signals were recorded using a direct recording method without using bias.

When the number shown in Figure 1 is supplied to the control track head, recording is performed without bias, and recording is stopped, the head is slightly magnetized due to direct current excitation or transients when recording is stopped, and is so-called magnetized. It remains in the same state. If the head is left magnetized and played repeatedly, the recorded letter control track signal will be slightly erased due to the magnetism, causing deterioration of the control track signal and reducing the reliability of synchronous operation. There were drawbacks that impaired the

Furthermore, a video tape recorder performs so-called overlapping recording, in which a signal is first recorded on an audio trunk including a control track on the tape, and then a video signal is recorded on a video track formed obliquely on these audio tracks. When thinking about realizing this, since video tracks are generally formed only near the six sides of the tape magnetic layer, even a slight magnetization phenomenon of the audio head can cause repeated playback. The portion of the video track that overlaps with the audio track is relatively easily erased, resulting in a serious drawback in that the image quality of the video signal is impaired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic tape recording and reproducing apparatus that can prevent head magnetization and perform stable synchronous operation.

Another object of the present invention is to provide a magnetic tape recording and reproducing apparatus that can prevent erasure of video tracks and maintain stable video signal quality even in a video tape recorder that performs overwriting.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings of embodiments of the present invention. FIG. 2(a) is a diagram showing a control track recording signal according to the present invention, and L(b) shows a synchronization pulse. FIG. 3 is a diagram showing a system of a recording/reproducing circuit for control track signals of a video tape recorder, and 1 is a reference synchronization signal input to the apparatus. In response to this reference synchronization signal, the reference frame synchronization signal separation circuit 2 obtains a reference frame synchronization pulse P (same signal as in FIG. 2(b)).

3 is a control track recording signal generating circuit which generates an attenuated burst signal P as shown in FIG. 2(a) every time a pulse signal arrives. 4 is a switch circuit, which passes the signal P during recording and controls the control track head 5.
During playback, the output of the playback amplifier 6 is used as a controlled signal for synchronized servo control of tape running during playback.

Next, the control track recording signal generation circuit No. 3 will be explained in detail with reference to FIG. The input is shown in Figure 2 (b
), the negative pulse period has a defined time τ in the reference frame pulse.

The transistor TR1 is R before the arrival of the negative pulse.
1, a bias current flows and is in the on state, and the voltage at its collector is approximately -12Vnc, so the transistor TR2 is in the off state, and the resonant circuit composed of C2 and Ll is in the discharge state. be. Therefore T
The potential of the collector of R2 is at the Eastmi level through Ll. When a negative input pulse arrives, TR1 is turned off through CI, and a bias current flows through R2 to TR2, turning it on for a period of τ, which is the width of the manual pulse.

'r The collector of R2 becomes approximately -12V, and the resonant circuit C2
and charge Ll. When the negative pulse period τ ends, TR2 is turned off, and the emisometric collector 5- of TR2 is not in an open state, and the electric charge stored in the resonant circuit C2 and Ll changes according to its own resonant frequency and the saliva of Q. , a damped oscillation occurs, and a signal with a burst-like damping characteristic as shown in FIG. 2 is obtained at 9 points, and its amplitude smoothly converges toward zero. This signal is 03. The signal is led to a switch 4 through a recording current limiting resistor 3 through a coupling capacitor C4, and is supplied as a recording signal to a control track head 5 during recording.

By supplying a recording current that oscillates attenuated in this way, it is possible to record the polarization code and at the same time have an AC demagnetizing effect on its own, making it possible to eliminate the magnetization phenomenon of the rack head. be.

As is clear from the above explanation, the present invention is applicable to Figure 2 (
By recording the signal shown in a) on the control track as a control track recording signal and reproducing it,
Can completely prevent magnetization of the control track head.
It eliminates signal deterioration due to unnecessary erasure of control track playback signals during repeated playback, maintains stable synchronized operation, and also eliminates image quality deterioration of video signals in 6- overwriting type video tape recorders. This has the effect of maintaining stable playback image quality.

[Brief explanation of the drawing]

FIG. 1 shows a conventional control track recording signal. Figures 2 (al and b) show the control track recording signal and frame synchronization signal of the present invention. Figure 3 is a block diagram of an embodiment of the present invention, and Figure 4 is the circuit of the part shown in Figure @3. In the figure, 1... Reference synchronization signal, 2... Frame synchronization pulse separation circuit, 3... Control track recording signal forming circuit, 4... ...Switch circuit, 5...Control track head, 6
...Control track signal regeneration circuit. 7- IV Graduation 2nd Class 3rd Group

Claims (1)

[Claims] means for receiving a reference synchronization signal and generating a synchronization pulse signal having a constant repetition cycle; and a control track having a predetermined frequency and whose amplitude converges to zero each time the synchronization pulse signal arrives. 1. A magnetic tape recording and reproducing apparatus, comprising means for generating a signal, and recording the control track signal on the control track.