JPH04263157A - Drum servo apparatus of video tape recorder - Google Patents

Abstract

PURPOSE:To suppress jitter, which is the fluctuation of a time axis in a playback image signal, in a helical system video tape recorder. CONSTITUTION:A drum motor 2 for the rotation of a drum 1 is driven by a drum motor control circuit 12. A frequency error correction signal is supplied from an FG generator 10 to the drum motor control circuit 12 through a revolution error detecting circuit 8 and a phase error correction signal is supplied from a PG generator 11 to the drum motor control circuit 12 through a phase error detecting circuit 9. Further, a signal corresponding to the jitter of a horizontal synchronous signal separated from an image output is supplied from a synchronous signal phase error detecting circuit 7 to the drum motor control circuit 12 through a low-pass filter 24 and the motor 2 is so controlled as to suppress the jitter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drum servo control device for correcting errors caused by fluctuations in the time axis called jitter contained in a reproduced video signal in a video tape recorder employing a helical scanning system.

0002

2. Description of the Related Art A typical prior art drum servo device for such a video tape recorder is shown in FIG.

The servo device in the helical scanning video tape recorder is composed of a drum servo device for controlling the rotation of the drum 1 and a capstan servo device for controlling the feeding of the tape 14.

Among these, the outline of the control system of the drum servo device is as follows:
The frequency signal of the drum motor 2 and the frequency of a fixed reference oscillator are input to the rotation speed error detection circuit 8, and a rotation speed correction signal corresponding to the rotation speed error is derived, thereby controlling the rotation speed of the drum motor 2. A phase signal of the PG generator 11 which is applied to the control circuit 12 and which is also attached to the drum 1;
The rotation of the drum motor 2 is controlled by inputting the reference synchronous frequency of 30 Hz for driving the drum motor 2 to the phase error detection circuit 9, deriving a phase correction signal corresponding to the phase error, and giving it to the drum motor control circuit 12. It is for controlling.

[0005]

[Problems to be Solved by the Invention] Conventional drum servo systems rely on the motor 2 that controls the motor 2 or the drum 1 itself that is integrated with the motor 2 to provide control information. No correction can be made for errors such as processing accuracy of the drum 1, frequency accuracy of the FG generator 10, etc. Therefore, such errors are called jitter in the reproduced video signal. This will be included as a time axis error.

[0006] Furthermore, with tapes recorded on other video decks, due to slight differences in performance between models such as linearity, the reproduced video signal may be distorted even though the motor 2 is rotating normally. contains jitter, and there is a problem that the jitter cannot be corrected reliably.

An object of the present invention is to reduce jitter by focusing on the problems that conventional drum servo devices have, and by detecting final information on time axis errors using simple means and providing it as a feedback signal to the drum motor. The object of the present invention is to provide a drum servo device that allows the user to perform the following tasks.

[0008]

[Means for Solving the Problems] The present invention provides a helical scanning video tape recorder that includes a drum motor control circuit that controls the rotational speed of a drum motor, and a drum motor that detects the rotational speed of a drum driven by the drum motor. An FG generator that derives a frequency signal, a PG generator that detects the rotational phase of the drum and derives a phase signal, a video signal demodulation circuit that demodulates a playback signal from the video head into a video signal, and an FG generator. A rotation speed correction feedback circuit that compares the frequency signal from the oscillator with the frequency from the reference oscillator to derive a rotation speed correction signal corresponding to the error in the rotation speed and supplies it to the drum motor control circuit, and a phase correction signal from the PG generator. A phase correction feedback circuit that compares the signal with the phase of the reference synchronization frequency and derives a phase correction signal corresponding to the phase error and supplies it to the drum motor control circuit, and horizontal synchronization from the video signal from the video signal demodulation circuit. Separate the signal,
A drum servo for a video tape recorder, comprising: a jitter correction feedback circuit that detects time fluctuations in the period of a horizontal synchronization signal, derives a jitter correction signal corresponding to a time axis error, and provides the jitter correction signal to a drum motor control circuit. It is a device.

[0009]

[Operation] The control voltage derived by the drum motor control circuit is
Frequency error correction by rotation speed correction feedback circuit,
In addition to the phase error correction by the phase correction feedback circuit, this control is performed because the voltages correspond to the three input elements, which include a correction signal obtained from the time axis error present in the reproduced signal based on the jitter correction feedback circuit. The voltage is the output that contains the final jitter information, so it is possible to control the drum motor to reduce jitter.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a servo control device according to an embodiment of the present invention.

An FG generator 10 and a PG generator 11 are provided in association with the helical scanning drum 1 in which the tape 14 is wound around more than half of the circumference and runs diagonally.
The control bed 2 is brought into contact with the running tape 14.
2 and a pinch roller 23 are provided. A drum motor 2 is connected to the drum 1, and the rotation of the drum motor 2 is controlled by applying a control voltage derived from a drum motor control circuit 12. A capstan 26 is arranged opposite to the pinch roller 23. The capstan 26 is connected to the capstan motor 4, and the rotation of the capstan motor 4 is controlled by applying a control voltage derived from the capstan motor control circuit 13.

The FG generator 10 detects a pulse signal corresponding to the rotation speed of the drum 1, derives a frequency signal, and inputs the frequency signal to a rotation speed error detection circuit 8 realized by a frequency discrimination circuit.

The frequency discrimination circuit 8 compares the frequency oscillated by a fixed reference oscillator with the frequency signal of the FG generator 10, derives a rotation speed correction signal corresponding to the frequency error, and outputs a rotation speed correction signal to the drum motor control circuit 12. Input to. This frequency discrimination circuit 8 constitutes an element of a rotation speed correction feedback circuit in the drum motor 2 control system.

The PG generator 11 detects a pulse signal having a timing corresponding to the rotational phase of the drum 1, derives a phase signal, and inputs the phase signal to the phase error detection circuit 9.

The phase error detection circuit 9 compares the frequency with a reference synchronous frequency of 30 Hz for driving the drum motor 2, derives a phase correction signal corresponding to the phase error, and inputs it to the drum motor control circuit 12. This phase error detection circuit 9
constitutes an element of a phase correction feedback circuit in the drum motor 2 control system.

A playback signal derived from the video head 3 in contact with the tape 14 wound around the drum 1 during playback operation is input to the video signal demodulation circuit 5.

The video signal demodulation circuit 5 demodulates the video signal such as the carrier color signal and outputs it from the output terminal.
Due to uneven rotation of the video head 3, expansion and contraction of the video tape 14, changes in tape running speed, etc., the demodulated video signal contains jitter components of time axis errors.

The video signal derived by the video signal demodulation circuit 5 is input to a synchronization separation circuit 6, and a horizontal synchronization signal is derived from the synchronization separation circuit 6.

The horizontal synchronizing signal naturally contains a jitter component, and this is input to the synchronizing signal phase error detection circuit 7 and compared with the phase of the reference frequency.

FIG. 2 is a block diagram of the synchronizing signal phase error detection circuit 7. As shown in FIG. The detection circuit 7 is composed of a phase-locked loop frequency synthesizer (PLL circuit), and includes a voltage-controlled oscillator (VCO) 15, a frequency dividing circuit 16, a phase comparison circuit 17, and a low-pass filter (LPF) 1.
For example, 15.734KH, which is obtained by dividing the horizontal synchronization signal SH derived by the synchronization separation circuit 6 and the frequency oscillated by the voltage controlled oscillator 15 by the frequency division circuit 16.
The phase comparison circuit 17 compares the phase with the comparison frequency of z, and outputs a jitter correction signal 25 corresponding to the phase difference.
By supplying the voltage controlled oscillator 15 as a control voltage via
The voltage controlled oscillator 15 is controlled to oscillate at an output frequency that approaches .

Note that the low-pass filter 18 is for ensuring operation as a PLL circuit, and is a necessary element for obtaining the jitter correction signal 9 in direct current after phase comparison, and the waveform line in FIG. As is clear from the figure, the phase error pulse signal obtained by comparing the phases of input A and input B can be converted into direct current by the low-pass filter 18.

The jitter correction signal 25 derived by the synchronization signal phase error detection circuit 7 in this manner is input to the drum motor control circuit 12 via the low-pass filter 24. These synchronization separation circuit 6 and synchronization signal phase error detection circuit 7 constitute elements of a jitter correction feedback circuit in the drum motor 2 control system.

Note that the low-pass filter 24 is a filter used to determine the response characteristics of the drum servo system as a whole.

The loop from the control bed 22 to the capstan motor control circuit 13 is a capstan servo device, and the F
The frequency signal corresponding to the rotation speed of the capstan 26 derived by the G generator 21 is input to the frequency discrimination circuit 20, where it is compared with the frequency oscillated by a fixed reference oscillator, and a rotation speed correction signal corresponding to the frequency error is generated. Once derived, it is input to the capstan motor control circuit 13.

On the other hand, the phase detection circuit 19 compares the phase of the control signal reproduced by the control bed 22 with a 30Hz synchronization signal obtained by dividing the frequency signal of the FG generator 21, and detects the phase error. When the phase correction signal corresponding to the phase correction signal is derived, it is input to the capstan motor control circuit 13.

As explained above, in the drum servo control system, rotation speed correction, phase correction, and jitter correction are jointly feedback-controlled, while in the capstan servo control system, rotation speed correction and phase correction are jointly controlled. Feedback controlled.

[0027]

As described above, according to the present invention, when performing drum rotation control during playback operation, the time axis error included in the playback video signal of the video tape recorder is derived and this is used to control the drum rotation of the drum motor 2. By using it as a feedback signal element, errors in the final stage are detected and the drum motor 2
It is possible to perform rotation control, and it is possible to reduce jitter.

Furthermore, the present invention can improve the jitter of a video tape recorder by adding a circuit with a simple structure such as a PLL circuit, so it is excellent in economical efficiency, and in addition to increasing its value as a general-purpose product. It has great effects.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram according to an embodiment of the present invention.

FIG. 2 is a block diagram of the synchronization signal phase error detection circuit 7 in FIG. 1.

FIG. 3 is a waveform diagram illustrating the operation of the synchronization signal phase error detection circuit 7.

FIG. 4 is a block diagram of the prior art.

[Explanation of symbols]

1 Drum 2 Drum motor 5 Video signal demodulation circuit 6 Synchronous separation circuit 7 Synchronous signal phase error detection circuit 9 Phase error detection circuit 10 FG generator 11 PG generator 12 Drum motor control circuit 14 Tape 15 Voltage controlled oscillator 16 Frequency divider circuit 17 Phase comparison circuit 18 Low pass filter

Claims (1)

[Claims] 1. A helical scanning video tape recorder comprising: a drum motor control circuit that controls the rotational speed of a drum motor; and an FG that detects the rotational speed of a drum driven by the drum motor and derives a frequency signal.
a PG generator that detects the rotational phase of the drum and derives a phase signal, a video signal demodulation circuit that demodulates the playback signal from the video head into a video signal, and a frequency signal from the FG generator; The rotation speed correction feedback circuit derives a rotation speed correction signal corresponding to the rotation speed error by comparing the frequency from the reference oscillator and supplies it to the drum motor control circuit, and the phase signal from the PG generator serves as a reference. The horizontal synchronization signal is separated from the video signal from the phase correction feedback circuit and the video signal demodulation circuit, which derives a phase correction signal corresponding to the phase error by comparing the phase of the synchronization frequency and gives it to the drum motor control circuit. A drum servo device for a video tape recorder, comprising a jitter correction feedback circuit that detects time fluctuations in the period of a synchronization signal, derives a jitter correction signal corresponding to a time axis error, and supplies the jitter correction signal to a drum motor control circuit. .