JPH0516664Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement of a magnetic recording/reproducing device called an 8mm video.

<Summary of the invention> This invention is a magnetic recording/reproducing device that complies with the 8mm video standard, in which head switching pulses are created based on the FG signal and PG signal used to control the rotation of a rotating drum, and after-recording (hereinafter referred to as "after recording") is performed. This generates sampling pulses that are effective for tracking servo during post-recording.

<Prior Art> In recent years, a standard for a magnetic recording and reproducing method called 8 mm video has been decided upon, and some commercialized products have recently become available on the market. The recording tape format of this 8mm video is as shown in Figure 3.
The main difference from the conventional general tape format is that a PCM audio recording track is provided as an extension of the video recording track recorded by a helical scan type rotating head, and a tracking servo is also provided on these video recording tracks and the PCM audio recording track. For this purpose, four pilot signals having different frequency components from those of adjacent tracks are sequentially and repeatedly superimposed and recorded.

Therefore, in a magnetic recording and reproducing device that conforms to the 8mm video standard, as shown in Figure 4, a magnetic tape 2 is wound around a rotating drum 1 for approximately 220°, and 180° of the tape is used as a video recording area. 36°min
A PCM audio area was used, and a time-axis compressed PCM audio signal was recorded in this PCM audio area.

<Problems to be solved by the invention> However, when attempting to after-record only the PCM audio signal onto a recorded tape in the above-mentioned magnetic recording/reproducing device, crosstalk occurs between the recorded PCM audio signal and the reproduced video signal. There was a risk of interference.

That is, in the post-recording mode, for example, as shown in FIG. 4, while the first rotary head 3a is recording PCM audio, the second rotary head 3b is simultaneously reproducing the video signal. The signal leaks to the second rotary head 3b side and interferes with the reproduced video signal. The biggest problem in this case is that the pilot signal included in the reproduced video signal is affected by this crosstalk interference, making it impossible to perform accurate tracking servo.

<Means for solving the problem> The present invention was developed in view of the above points, and aims to eliminate the influence of crosstalk interference during dubbing mode. In a magnetic recording/reproducing device that detects a signal level and applies a tracking servo to the playback head according to the detected level, the level of the beat signal immediately before the period in which crosstalk occurs is sampled and held, especially in the dubbing mode, and this hold signal is used. Based on this, the tracking servo is applied during that period.

Furthermore, in the present invention, a head switching pulse is generated based on the FG signal and PG signal used for controlling the rotation of the rotating drum, and at the same time, a sampling pulse for the dubbing mode is generated.

<Example> The present invention will be described below according to an example shown in the drawings. FIG. 1 shows a block diagram of an embodiment of the present invention, and FIG. 2 shows signal waveform diagrams of various parts of the same embodiment.

In FIG. 1, 1 is a rotating drum, 3a and 3b are first and second rotating heads, and 4 and 5 are rotating drums 1.
FG and PG detectors are used to extract the FG signal and PG signal for controlling the rotational speed of the rotary drum 1. When the rotating drum 1 is rotating, the PG detector 5 outputs the FG signal and the PG signal according to the rotational speed of the drum 1. A PG pulse signal as shown in FIG. 2a is obtained, and an FG pulse signal as shown in FIG. 2b is obtained from the FG detector 4. FG pulse signal is sent to amplifier 6 and delay circuit 7
The signal is amplified and its phase is slightly delayed as shown in FIG. 2c before being supplied to the frequency divider 8. Further, the PG pulse signal is amplified by the amplifier 9 and then applied to the reset terminal of the frequency divider 8.
Here, the frequency divider 8 has a 1/2 frequency division output terminal and a 1/4 frequency division output terminal, and each frequency division output terminal has a second frequency division output terminal.
Frequency-divided outputs as shown in Figures f and d are obtained. Second
The 1/2 frequency divided output shown in Figure d is the flip-flop 10
At this time, the flip-flop 10 outputs a rectangular wave pulse as shown in FIG. 2e. This rectangular wave pulse is supplied to the signal switching circuit 11 as a head switching signal.

The reproduction signals reproduced by the two rotary heads 3a and 3b are alternately switched by a signal switching circuit 11 and supplied to a video circuit and also to a beat signal extraction circuit 12. At this time, the beat signal extracting circuit 12 converts only the pilot signal components, especially the beat signals of adjacent tracks, into a DC level and extracts them as shown in FIG. 2g. When in the normal reproduction mode, this beat signal is supplied to the tracking servo circuit via the signal switching circuit 14. Further, the 1/2 frequency divided output as shown in FIG. From Figure 2 h
A hold voltage as shown in is output. Here, this hold voltage is supplied to the tracking servo circuit via the signal switching circuit 14 only when in the post-recording mode, thereby controlling the rotating head 3.
Tracking servos a and 3b are applied.

In this embodiment, as mentioned above, from one frequency divider 8,
Since the 1/4 frequency-divided output and 1/2 frequency-divided output of the FG pulse signal are taken out, and based on these, the head switching pulse and the sampling pulse for dubbing are generated, the phases of both are as shown in Figure 2 e and f. As can be seen by comparing the waveform diagrams, there is a correlation between the two, and especially during the period when crosstalk occurs during post-recording mode, that is, one rotary head plays back the video signal and the other rotary head records the PCM audio signal. (shown as the crosstalk period in Figure 2)
Tracking servo is always applied using the hold voltage sampled and held at the immediately preceding sampling pulse. Therefore, there is no risk that the tracking of the rotary head during video playback will be disturbed due to crosstalk interference during this time.

In the above embodiment, the frequency divider 8 is 1/
I am using one with a 2 frequency division output terminal and a 1/4 frequency division output terminal, but this is done by setting an appropriate frequency division ratio of 1/m, taking into account the period of the FG signal, the crosstalk period, etc.
What is necessary is to use one having a ratio of 1/n.

<Effects of the invention> As described above, the magnetic recording and reproducing apparatus of the invention can be used for controlling the rotation of a rotating drum.
Since the head switching signal and the sampling pulse are generated based on the FG signal and the PG signal, an accurate phase relationship is always obtained between the two, and there is no crosstalk interference even during post-recording.

Furthermore, with this invention, the sampling pulse during dubbing can be obtained from the middle stage of the frequency divider that obtains the head switching signal, so the head switching can be performed using a frequency divider consisting of a single chip of IC, without having to build individual circuit configurations. It is possible to obtain the signal and the sampling signal at the same time, and the cost advantage is also large.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention;
The figures are signal waveform diagrams of various parts of the same embodiment, Figure 3 is a diagram showing the recording tape format of 8 mm video, and Figure 4 is a diagram showing the recording tape format of 8 mm video.
The figure is a schematic diagram showing the state in which the tape is wound around the rotating drum in the same 8mm video. 1... Rotating drum, 3a, 3b... Rotating head, 4... FG detector, 5... PG detector, 8...
Frequency divider, 12... Beat signal extraction circuit, 13...
Sampling hold circuit.

Claims (1)

[Scope of utility model registration request] A PCM audio recording track is provided as an extension of the video recording track, and a pilot signal with a frequency component different from that of the adjacent track is superimposed and recorded on both tracks for tracking servo, and the beat signal of this pilot signal is detected during playback. In a helical scan type magnetic recording/reproducing device that performs tracking control of the reproducing head according to the detection signal, the FG signal is reset based on the PG signal for controlling the rotation of the rotating drum, and the FG signal is adjusted to 1/m and 1/m. /n (where m and n are positive integers in the relationship m>n);
means for obtaining a head switching signal based on the 1/m frequency divided output from the frequency dividing means; a beat signal extracting means for extracting a beat signal of a pilot signal reproduced by the rotary head; means for sampling and holding the beat signal based on the /n frequency divided output, and in the after-recording mode, the tracking servo of the rotary head is applied based on the beat signal held by the sampling and holding means. A magnetic recording/reproducing device characterized by: