KR920000566Y1 - For vtr (video tape record) at reverse search mode horizontal synchronization frequency compensation circuit - Google Patents

Abstract

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Description

Horizontal Synchronization Correction Circuit in Reverse Search Mode in Video Recorder

1 is a block diagram according to the present invention.

2 is a concrete circuit diagram of FIG.

3 is an operating waveform diagram of each part of FIG.

* Explanation of symbols for the main parts of the drawings

10: drum speed control unit 20: drum phase control unit

30: speed voltage converter 40: phase voltage converter

50: error voltage comparison generation unit

The present invention relates to a relative speed control (circuit) of a video tape recorder (hereinafter referred to as a VTR), and in particular, in a reverse search mode (reverse searoh mode), the relative speed generated between the video head and the tape is reduced to The present invention relates to a circuit capable of correcting synchronization.

In general, the running speed of the tape in the search mode is considerably faster than that in the playback mode or the recording mode. Here, the relative speed refers to a relative speed between the magnetic tape and the video head speed, which is expressed as follows.

Magnetic Tape and Relative Speed (m / sec) f _v = Feed Frequency (Hz) ℓ = 1 Video Track Length of Feed (mm) ø = Cylinder (Drum) Diameter v _t = Travel Speed of Magnetic Tape (mm / sec) In general, the relative speed of normal picture playback is defined as 5.8m / sec in VHS type VTR.However, the relative speed in search mode is higher than the rotational speed of the drum. It is several times faster than the relative speed at normal screen playback. That is, in the reverse search mode, the rotation of the drum motor is rotated in the counterclockwise direction, and the running of the tape is controlled so that the tape wound on the take-up reel side is transferred to the supply reel side. Therefore, in the reverse search mode, the conveying direction of the tape is conveyed from right to left as described above, and the running speed of the tape is several times speed in the normal mode. Therefore, in reverse search mode, the rotational direction of the drum and the running direction of the tape are reversed, so that the relative speed becomes faster. For example, in the 9x search mode, this is 9 times the normal tape travel speed. In this case, in reverse search mode, the video head must traverse nine tracks during one track period in normal mode. If the video head fails to diffract 9 tracks precisely due to the increase of the tape speed and the drum rotation speed, the track position is shifted when the video head tracks the track in the next state. Ham phenomenon will occur.

Therefore, due to the change of the relative speed between the video head and the tape during reverse picture search mded, the video head cannot scan the video signal recorded on the tape properly. As a result, the horizontal sync signal is displaced. Skew phenomenon that the upper part is bent, and in severe cases there was a problem that the synchronization is unstable.

Therefore, an object of the present invention is to provide a circuit capable of reproducing a stable screen by controlling the rotational speed of the drum in the reverse screen search mode by adding a horizontal synchronization correction circuit to the drum servo circuit of the video recorder.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of the present invention, and inputs a drum frequency generator (FG) signal generated when the drum mode is rotated to pass a speed comparator to obtain a first pulse width modulation (PWM). Drum phase control unit 10 for outputting a signal and a drum pulse generator (PG) signal generated when the drum motor rotates to output a second pulse width modulation signal through a phase comparator The control unit 20, the speed voltage converter 30 for inputting the first PWM output of the drum speed controller 10 to convert the DC voltage, and the second PWM output of the drum phase controller 20 for inputting the DC voltage And a phase voltage converter 40 for depressurizing a phase voltage level for the horizontal synchronization frequency correction upon receiving a reverse search mode signal, and the speed voltage converter 30 and the phase voltage converter 40. Comprising an error voltage of the drum motor by inputting the output, and supplies it to the drum motor and is composed of an error voltage comparison generator 50 controlled by a predetermined output of the drum motor drive control circuit.

Based on the above configuration, the present invention will be described in detail with reference to FIG.

The rotation speed (rpm) of the drum motor is fixed at 1800 rpm in the normal mode (Play back mode or record mode) in the VHS standard.

In this case, the tape running speed is controlled by the capstan servo in the high speed screen search function, but the drum servo controls the drum in the same manner as in the normal mode. The speed of rotation is constant.

At this time, in the reverse search mode, the moving direction of the tape is reversed to have a tape running speed of several times speed, and the rotating direction of the drum is counterclockwise, so that the rotating direction of the drum and the moving direction of the tape are reversed. It will be much faster. In this case, when the relative speed between the tape and the drum increases and the video head cannot read the track accurately, the horizontal synchronization is turned off. In order to prevent such horizontal synchronization, manual synchronization may be turned off if the video head cannot read the track accurately by slowing down the relative speed between the tape and the drum. To prevent this horizontal synchronization, the video head should track the track accurately by slowing down the relative speed between the tape and the drum.

In order to slow down the relative speed as described above, it is necessary to slow down the running speed of the tape or slow down the rotation speed of the drum. At this time, since the running speed of the tape is already determined, the relative speed is slowed down by varying the rotational speed of the drum through the drum servo. That is, since the rotational direction of the drum and the running of the tape are reversed, it can be seen that the relative speed decreases by decreasing the rotational speed of the drum.

When the reverse search mode is set, the drum frequency generator generates a drum FG signal according to the rotation of the drum motor, and the drum pulse generator generates a drum PG signal. Then, the drum speed control unit 10 for receiving the drum PG signal compares the rotational speed of the drum by the drum FG signal, and generates a first PWM signal according to a corresponding state. Then, the speed voltage converter 30 receives the first PWM signal, converts it into a DC voltage, and outputs it to the error voltage generator 50.

And the drum phase control unit 20 for receiving the drum PG signal compares the phase according to the rotation of the drum and generates a second PWM signal according to the state.

Then, the phase voltage converter 40 receives the second PWM signal and converts it into a DC voltage. In this case, the reverse voltage mode controls the second PWM signal to reduce the level of the DC voltage. This is to reduce the driving voltage of the drum motor to reduce the rotation of the drum.

Then, the error voltage generator 80 inputting the output of the speed voltage converter 30 and the phase voltage converter 40 compares the two input voltages and decompresses the error voltage which is the driving voltage of the drum motor to control the system. Apply to the microcomputer side. Then, the control micom drives the drum motor with the reduced drive error voltage to reduce the rotational speed of the drum, thereby slowing the relative speed between the tape and the drum. Thus, as the relative speed is slowed, the video head can accurately track the track even in reverse search mode.

FIG. 2 is a detailed circuit diagram of FIG. 1, which includes a drum speed control unit 10 including a drum speed comparator 11 and a first PWM generator 12, a drum phase comparator 21, and a second PWM generator 22. As shown in FIG. Phase voltage controller 20, speed voltage converter 30 composed of resistor R1 and capacitor C1, resistor R2, capacitor C2, phase voltage composed of diode D1 and transistor Q2. An error voltage comparison generator 50 composed of a converter 40, a comparator COM1, a capacitor C2, a diode D1, and a transistor Q1.

3 is an operation waveform diagram of each part of FIG. 2, 3A is a waveform of a first PWM signal outputting the first PWM generator 12, and 3B is a first waveform outputting the speed voltage converter 30. FIG. (3C) is the waveform of the second PWM signal by the reverse search mode signal, (3D) is the DC voltage waveform of the second PWM signal outputting the phase voltage converter 40, ( 3E) is a waveform of the reverse search mode signal, 3F is a waveform of the drum motor control signal, and 3G is a waveform of the drum motor drive signal outputting the comparator COM1 in the reverse search mode.

Based on the configuration of FIG. 2 described above, the present invention will be described in detail with reference to the waveform diagram of FIG. 3.

First, in the normal mode (play or record mode), the reverse search mode signal such as 3E has a ″ low ″ level logic, which causes the transistor Q2 to remain turned off. The drum motor control signal always has a low level logic except for a stop mode as shown in 3F, so that the transistor Q1 also maintains a turn-off state.

At this time, the drum PG signal generated according to the rotation of the drum is applied to the drum speed comparator 11, and the drum speed comparator 11 compares the rotational speed of the received drum with a predetermined reference speed and then outputs a result signal. 1 PWM generator 12 is applied. The first PWM generator 12 then generates a first PWM signal, such as 3A, by the output of the drum speed comparator 11. Then, the first PWM signal is rectified by the resistor R1 and the capacitor C1 and is generated in the form of a DC voltage corresponding to the rotational speed of the drum as shown in 3B.

In addition, the drum PG signal is applied to the drum phase comparator 21, and the drum phase comparator 21 compares the received drum PG signal with a predetermined reference signal, and then outputs the signal to the second PWM generator 22. Is authorized. The second PWM generator 22 then generates a second PWM signal, such as 3C, by the output of the drum phase comparator 21. At this time, since the reverse search mode signal is a ″ low ″ logic state such as (3E), the second PWM signal such as (3C) is applied to the phase voltage converter 40 as it is, thereby causing the resistor R2 and the capacitor C2. Is generated in the form of direct current voltage corresponding to the phase of the drum as in (3D). At this time, since the second PWM signal is directly converted into a DC voltage form, the voltage applied to the non-inverting terminal of the comparator COM1 is not affected.

At this time, the comparator COM1 compares a speed voltage such as 3B and a phase voltage such as 3D to generate an error voltage such as 3G to output the driving signal of the drum motor. Therefore, it can be seen that the drum motor rotates at a constant speed of 1800 rpm.

In the configuration of the error voltage generator 50, capacitor C4 is for high frequency compensation, capacitor C3 and resistor R2 are feedback elements of comparator COM1, and resistors R4-R5 are system control. This is a bias resistor for turning on and off the transistor Q1 by receiving the stop of the drum motor or the drive control signal output from the microcomputer. At this time, the mode is switched to the reverse search mode at the time T1 of FIG. 3, and the system control microcomputer transitions the reverse search mode signal to the ″ high ″ level logic as shown in (3E). Receiving the reverse search mode signal to the gate terminal, the transistor Q2 is then turned on by a reverse search mode signal of the ″ high ″ level. In addition, since the drum motor control signal has a logic of "low" level in the reverse search mode as in (3F), the transistor Q1 is kept turned off.

At this time, the drum FG signal generated according to the rotation of the drum is applied to the drum speed comparator 11, and the drum speed comparator 11 compares the rotation speed of the received drum with a predetermined reference speed and then outputs a result signal. 1 PWM generator 12 is applied. The first PWM generator 12 then generates a first PWM signal, such as 3A, by the output of the drum speed comparator 11. Then, the first PWM signal is rectified by the resistor R1 and the capacitor C1 and is generated in the form of a DC voltage corresponding to the rotational speed of the drum as shown in 3B.

The drum PG signal applied to the drum phase drum phase comparator 21 is compared with a predetermined reference signal, and a comparison result signal is applied to the second PWM generator 22. Then, the second PWM generator 22 pulse-modulates the output of the drum phase comparator 21 to generate a second PWM signal according to the drum. However, at this time, since the transistor Q2 is turned on due to the ″ low ″ logic reverse search mode signal as described above (3E), the second PWM signal outputting the second PWM generator 22 generates the diode D1. Bypass is bypassed from the collector of transistor Q2 to the emitter. Accordingly, it can be seen that in the reverse search mode, the second PWM signal is generated only as much as the on voltage V _DE of the diode D1 as shown in (3C). That is, in the reverse search mode, the second PWM signal is decompressed by the on voltage V _DE of the diode D1, and the second PWM signal is converted into a direct current form. Therefore, in the reverse search mode, the second PWM signal generated by the transistor Q2 and the diode D1 as (3C) is converted into the DC voltage form by the resistor R2 and the capacitor C2 as (3D). The voltage is reduced to the V _DE on voltage level of the diode D1.

At this time, the comparator COM1 receives the speed voltage as shown in the above (3B) and the phase voltage as shown in the above (3D) to generate a drum motor driving signal. Likewise, the drum motor driving signal is reduced. Therefore, since the driving voltage of the drum motor is depressurized, the rotational speed of the drum is reduced, so that the relative speed between the tape and the drum is lowered. Since the advancing direction of the tape and the rotational direction of the drum are reversed as described above, in order to lower the relative speed between the tape and the drum, it is necessary to lower the running speed of the tape or lower the rotational speed of the drum. Therefore, it can be seen that the relative speed can be lowered by reducing the rotational speed of the drum by reducing the phase voltage in the reverse search mode. By lowering the relative speed between the tape and the drum as described above, the video head can accurately track the magnetic track, and thus, the horizontal synchronization can be accurately achieved to prevent skew or loss of synchronization.

As described above, when the reverse search mode is implemented in the VTR, a horizontal synchronizing correction function is inserted into the drum servo to reduce the driving voltage of the drum motor, thereby preventing the upper ham or synchronization loss of the search screen due to an increase in the relative speed between the tape and the drum. There is an advantage that can be prevented to play a stable screen.

Claims (1)

A drum speed control unit 10 receiving the output of the drum frequency generator to generate a first pulse width modulation signal according to the rotational speed of the drum, and a second pulse width modulation according to the rotational phase of the drum by receiving the drum pulse generator output A horizontal synchronous signal correction circuit of a video recorder provided with a drum phase control unit 20 for generating a signal, comprising: a speed voltage converter 30 for receiving the first pulse width modulation and converting the signal to a speed voltage of a DC level; And receiving a second pulse width modulated signal at all times, switching by the reverse search mode signal to reduce the second pulse width modulated signal to a predetermined voltage level, and converting the decompression level into a phase voltage of a DC level. Receiving the output of the unit 40, the speed voltage converter 30 and the phase voltage converter 40, for driving the drum motor with the speed voltage and the reduced phase voltage The error voltage generating unit 50 generates an error voltage and outputs it to the drum motor. In reverse search mode, the rotation speed of the drum is reduced to lower the relative speed between the drum and the tape. A horizontal synchronization correction circuit in reverse search mode in a video recording recorder, characterized in that it is operated to keep track of a magnetic track.