JPS62305Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is based on a tape guide drum that has one rotating magnetic head built in, and a magnetic tape that is guided around the entire circumference of the drum. The present invention relates to a noise removal circuit for a magnetic recording/reproducing device which forms a trajectory on a magnetic tape obliquely with respect to its longitudinal direction.

In this type of magnetic recording/playback device, one rotating magnetic head records one field or one frame of a video signal so as to form one locus diagonally to the longitudinal direction of the magnetic tape. ,
Also, when playing back one recording trajectory and then playing the next trajectory, the reproduced video signal may be lost or its level may be attenuated during playback. . If the reproduced video signal is an FM modulated signal, the
When an FM modulated video signal is demodulated, noise is generated in that portion in response to a dropout or a drop in the level of the reproduced signal, and this causes flicker in the reproduced image.

For this reason, in the past, recording was performed so that the noise at the joint position of the video signal was as close as possible to the vertical synchronization signal, but this still prevented the above-mentioned flicker on the playback screen. I couldn't do it.

In view of this, the present invention provides a magnetic recording and reproducing device of the above-mentioned type that can effectively remove noise at the joint position of the reproduced video signal of the magnetic recording and reproducing device and obtain a flicker-free reproduction screen. The purpose of this paper is to propose a noise removal circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. First, a first embodiment of the present invention will be described with reference to FIG. In a magnetic recording/playback device, a magnetic tape is guided by a tape guide drum containing one rotating magnetic head so as to be wound α. The tape guide drum is designed to form a trajectory on the
It consists of an upper drum and a lower drum, the lower drum being fixed, the upper drum rotating, and the rotating magnetic head rotating together with the rotating upper drum. The rotating magnetic head is arranged to face the outside in the gap between the upper drum and the lower drum. Further, the video signal is FM modulated and recorded on a magnetic tape, and the reproduced signal is amplified and supplied to a limiter circuit, and then supplied to an FM demodulation circuit where it is demodulated to the original video signal.

In FIG. 1, _t1 is the input terminal to which the demodulated video signal is supplied. 1 is this input terminal.
A reproduced video signal from _t1 is supplied, and the leading edge level of the signal is clamped to a predetermined clamp level during the vertical sync signal interval.
FM modulated video signal, W is the signal missing part,
The left side shows a field with a video signal, and the right side shows the signal of the following field, with the reproduced signal level dropping before and after the signal missing portion W. This reproduced FM modulated video signal is then supplied to an FM demodulation circuit (not shown) and demodulated into a video signal as shown in Fig. 2B, which is then supplied to the above-mentioned input terminal _t1 . In Fig. 2, _TVB indicates a vertical blanking interval, and S _V in Fig. 2B and below indicates a vertical synchronizing signal. In this case, before and after the number H of vertical synchronizing signals S _V (H is the horizontal period),
In this case, the FM modulated video signal is recorded on the magnetic tape so that the joint of the video signal occurs during the vertical blanking interval _TVB . In this case, the signal loss interval W occurs exactly after the number H of vertical sync signals S _V , in this case 1 to 2H later, and noise N occurs due to this signal loss. First, the specific configuration of this clamp circuit 1 will be explained.

The video signal supplied to input terminal _t1 is connected to a capacitor.
It is supplied through C ₁ to the base of emitter follower transistor Q ₁ . . The voltage of the power supply +B is divided by a series circuit of resistors R ₂ and R ₃ and is applied to the base of the transistor Q ₁ as a base voltage. The collector of transistor _Q1 is the power supply +B
and its emitter is grounded through load resistor _R4 . Furthermore, an emitter follower transistor Q ₃ is provided, and the emitter of the transistor Q ₁ is connected to the transistor Q ₃ through a capacitor C ₃ .
connected to the base of The collector of transistor _Q3 is connected to the power supply +B, and its emitter is grounded through a load resistor _R7 . In this case, the capacitance of capacitor C ₃ is set to 10 MF, for example, and the input impedance of transistor Q ₃ is set to 1 MΩ, and the time constant of the low-pass waveformer determined by the input impedance seen from the base of capacitor C ₃ and transistor Q ₃ is increased. do. Furthermore, a transistor Q ₂ is provided,
Its collector is connected to the base of the transistor Q ₃ , and its emitter is connected to the midpoint of its connection of the series circuit of resistors R ₅ and R ₆ connected across the supply +B, and its base is connected through the capacitor C ₂ . Connect to the input terminal t ₂ and ground the input terminal t ₂ through the resistor R ₁ . Further, the base of the transistor _Q2 is grounded through a protective diode D. Furthermore, the cathode of diode D is a transistor.
This is the base side of _Q2 . Then, the voltage obtained by dividing the voltage of the power supply +B by resistors R ₅ and R ₆ is set as a clamp level (clamp voltage). Then, the pulse signal of, for _example , 60 Hz generated in connection with the rotation of the rotating magnetic head of the magnetic recording/reproducing device is delayed by a predetermined amount by, for example, a monostable multivibrator to the input terminal t2, and the vertical synchronizing signal shown in FIG. A clamp pulse P _C as shown in FIG. 2E, which occurs in the interval S _V , is obtained and is supplied to the input terminal t ₂ .
Also, a smoothing capacitor _C4 is connected between both ends of the resistor _R6 .
is connected.

When a video signal as shown in FIG. 2B is supplied to the input terminal t ₁ and a clamp pulse P _C as shown in FIG. ₂ E is supplied to the input terminal t 2, the clamp pulse P _C is supplied to the transistor Q ₂ . At this point, the transistor Q ₂ turns on, and the voltage at the midpoint of the connection between the resistors R ₅ and R ₆ is applied as a clamp voltage to the base of the transistor Q ₃ , which causes the vertical synchronization signal S _V
The tip level of is clamped to this clamp voltage.

A slicing circuit 2 is connected to the subsequent stage of the clamp circuit 1 for slicing the output video signal at a predetermined slice level that is approximately equal to a predetermined clamp level. This slice circuit 2 will be explained. A transistor Q 4 is provided, which constitutes a differential amplifier circuit 3 with a transistor Q ₃ and a resistor R ₇ . The collector of _{the transistor Q 4 is} connected to the power supply +B, and the emitter of the transistor Q 4 is connected to the emitter of the transistor Q ₃ . The midpoint of the connection between resistors R ₅ and R ₆ is connected to the base of transistor Q ₄ through resistor R ₈ , and the base of transistor Q ₄ is grounded through a parallel circuit of capacitor C ₅ and semi-fixed resistor R ₉ . Ru. The resistor _R8 and capacitor _C5 constitute a low-pass wave filter. Thus, the base of the transistor Q ₄ is given a voltage approximately equal to the potential at the midpoint of the connection between the resistor R ₅ and the resistor R ₆ , that is, the predetermined clamp voltage, and the emitters of the transistors Q ₃ and Q ₄ are thus , a predetermined slice level, ie, a slice voltage, which is lower than this base voltage by the base-emitter voltage of the transistor is applied. Therefore, when a video signal as shown in FIG. _2B is supplied to the input terminal t1, the transistor _Q3 is turned off for the part of the noise N of the video signal that is lower than the predetermined slice voltage. A slice voltage is obtained as an output voltage from the emitter of transistor _Q3 . Therefore, at the emitter of the transistor _Q3 , as shown in FIG. 2C, a video signal having a noise N' with a portion smaller than the slice voltage of the noise N removed is obtained.

Further, on the output side of this slice circuit 2, an emitter follower type transistor _Q5 for output is provided. The emitter of transistor _Q3 is connected to the base of transistor _Q5 through resistor _R11 , the collector of transistor _Q5 is connected to power supply +B, and its emitter is grounded through resistor _R12 .
And its emitter is capacitor _C6 and resistor
Connected to the output terminal t ₃ through a series circuit of R ₁₃ . In this way, at the output terminal _t3 , a video signal with part of the noise removed as shown in FIG. 2C is obtained.

Next, another example of the present invention will be described with reference to FIG. 3, and parts corresponding to those in FIG. 1 will be denoted by the same reference numerals and repeated explanation will be omitted. In the noise removal circuit of FIG. 1, noise N' still remains above the slice level as shown in FIG. 2C.
Therefore, in the embodiment shown in FIG. 3, a subless circuit 4 is further provided in the noise removal circuit shown in FIG. 1 to further suppress the noise N'. To explain this noise elimination circuit, the collector of transistor Q ₄ is connected to load resistor R ₁₄
Connect this resistor to the power supply +B through
Connect a capacitor C ₇ across R ₁₄ to detect the level of the noise below the above-mentioned slice voltage from the collector of this transistor Q ₄ and supply it to the base of the transistor Q ₆ whose emitter is grounded. . In this case, transistors Q ₁ to _{Q 5} are all
Although it is an NPN type, transistor Q ₆ is a PNP type, and the emitter of transistor Q ₆ is connected to the power supply +B, and its collector is connected to a resistor.
Ground through _R10 and connect its collector to the capacitor
Connect to the base of transistor _Q5 through _C8 .

In this way, when a video signal as shown in FIG. 2B is supplied to the input terminal _t1 , if the noise N is smaller than the slice voltage, the transistor _Q6 is turned on, and the collector-emitter of the transistor _{Q3 is} turned on. The transistor Q ₃ is short-circuited, thereby reducing the noise N′ as shown in FIG.
At the emitter of the transistor Q5 or the emitter of the transistor _Q5 , that is, the output terminal _t3 , a video signal having a noise N'' whose level is further reduced as shown in FIG. 2D is obtained.

According to the present invention described above, a magnetic tape is placed on a tape guide drum incorporating one rotating magnetic head.
In a magnetic recording/reproducing device in which a rotating magnetic head is guided as if it is wound and travels, forming a locus obliquely to the longitudinal direction of the magnetic tape, it is particularly important to By effectively reducing or removing the noise generated in the playback screen, it is possible to effectively suppress flicker on the playback screen.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a waveform diagram, and FIG. 3 is a circuit diagram showing another embodiment of the present invention. 1 is a clamp circuit, 2 is a slice circuit, 3 is a differential amplifier circuit, and 4 is a suppress circuit.

Claims (1)

[Scope of utility model registration request] A magnetic tape is wound and guided around almost the entire circumference of a tape guide drum containing one rotating magnetic head, and the one rotating magnetic head guides the magnetic tape in its longitudinal direction. On the other hand, in a magnetic recording/reproducing apparatus which is configured to form track trajectories diagonally, the track trajectories on the magnetic tape are controlled so that the joints of the track trajectories on the magnetic tape occur in the vertical retrace interval of the reproduced video signal, and the rotating magnetic A clamp circuit that uses pulses generated in relation to the rotational position of the head to clamp the tip level of the reproduced video signal to a predetermined clamp level in the vertical synchronization signal section; a slicing circuit that is connected to the slicing circuit and slices the output video signal at a predetermined slice level substantially equal to the predetermined clamp level, and the slicing circuit outputs a video signal from which noise has been removed. noise removal circuit.