JPS6256584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capstan servo circuit employed in 8 mm video that records a tracking pilot signal on a video track without forming a control track.

8mm video records four types of tracking pilot signals on the video track and PCM track instead of the control track.
This enables the DTF servo to control the vertical position of the video head and the ATF servo (capstan servo) to control the tape speed. The DTF servo operates so that the video head correctly scans the center of the track during normal playback and scans a single track during special playback. The ATF servo also controls the rotational phase of the capstan motor according to the tracking error output obtained by reproducing the tracking pilot signal. For normal VTRs, when performing high-speed playback, the divided output of the playback control signal is used as the comparison signal of the capstan servo, but the tracking error output of the ATF servo for 8mm video is used. used. This tracking error output uses the difference frequency between four types of tracking pilot signal frequencies, and the difference frequency with the tracking pilot signal of the adjacent track is 16KHz for one and 46KHz for the other.
The frequency is selected so that That is, the frequency of the tracking pilot signal is ₁ = 102KHz for the first signal, and ₂ = 118KHz for the second signal.
Then, the third signal is ₃ = 164KHz, and the fourth signal is
₄ = 148KHz, and the frequency is cyclically switched at the field period. During reproduction, in order to reproduce these tracking pilot signals and obtain a tracking error output, an injection signal with the same frequency as the tracking pilot signal of the track to be scanned is input to a multiplier circuit together with the reproduced tracking pilot signal. However, the multiplication output may be separated by a 16K filter and a 46K filter, and the comparison output obtained by comparing the levels may be used as the tracking error output. The tracking control principle described above is well known, and further explanation will be omitted.

For 8mm video, an ATF servo is essential, but a DTF servo is not essential, just like a normal VCR. Therefore, when realizing ATF for 8mm video without DTF servo, it is as follows. FIG. 1 is a diagram illustrating the switching of scanning traces and injection signals for a track pattern. The numbers in the figure are the identification numbers of the tracking pilot signals of the corresponding track, and are the same as those of the first to fourth signals described above. handle. As is clear from the figure, in the normal reproduction scan trace P _A on the track pattern, the tracking pilot signal is switched in sequence for each field, but in the triple-speed reproduction scan trace P _B , the tracking pilot signal is switched three times in one field. Switch. Furthermore, in the triple reverse reproduction scan trace P _C , the tracking pilot signal is switched five times in one field, and the switching order is also discontinuous for each field. Therefore, switching the injection signal during normal playback is easy as shown in A, but switching during triple speed playback requires complicated setting of switching timing in the field as shown in B. Furthermore, when switching during triple reverse playback, not only the setting of the switching timing but also the selection of the injection signal becomes complicated, as shown in C.

Therefore, compared to the injection signal switching operation of an 8mm video that also has a DTF servo mechanism, the present invention has the following advantages:
Considering that the injection signal switching operation for 8mm videos that only have an ATF servo mechanism is complicated and costly, we developed an injection signal switching circuit for 8mm videos that only have an ATF servo mechanism and a DTF servo mechanism. The purpose of this paper is to propose a new and effective capstan servo circuit that can be used to standardize the injection signal switching circuit.

The present invention takes into account that the desired tracking state at the middle point of the video track is the same for both 8mm videos with a DTF servo mechanism and 8mm videos without a DTF servo mechanism. It is characterized by being configured to detect a tracking error to be input to the capstan servo at an intermediate point.

A simple injection signal switching order for an 8mm video with a DTF servo mechanism will be explained below. Generally, the multiple for double-speed playback is selected to be an odd number because the recording track performs azimuth recording. It has been confirmed that there are only two types of switching order in odd-numbered double speed playback. That is, ..., -
In the case of 7x, -3x, 1x, 5x, 9x, etc., the switching order is...→ ₁ → ₂ → ₃ → ₄
→... becomes a positive order, and..., -9 times, -5 times, -1
In the case of times, three times, seven times, etc., the switching order is...→
The order is reversed: ₄ → ₃ → ₂ → ₁ →...
Therefore, it is only necessary to switch the injection signal for each field in the forward or reverse direction depending on the multiple of the double speed reproduction. Generally, when the multiple is 4n+1 (where n is an integer and the sign indicates the direction), the switching order may be in the positive direction, and when the multiple is 4n+3, the switching order may be in the reverse direction.

Hereinafter, the present invention will be explained according to an illustrative embodiment. In this embodiment, the injection signal switching circuit described above is
This is used for 8mm videos that only have an ATF servo mechanism. FIG. 2 shows a circuit according to an embodiment of the present invention, and FIG. 3 shows a waveform diagram of its essential parts.
In the following explanation, for convenience of explanation, only the tracking pilot signal weighted on the video track is taken out to perform the ATF servo.

First, in this embodiment, a tracking pilot signal is separated from a reproduced video signal obtained after switching by a low-pass filter 1 having a passband of 200 KHz or less. On the other hand, a 2-bit reversible counter 2 which receives the RF switching pulse RF for switching the head output as a counting input performs addition or subtraction counting in accordance with the index output D issued in accordance with its multiple. In the case of 3x reverse playback, the reversible counter 2 performs subtraction counting, and its bit output is...
It changes as 4 → 3 → 2 → 1 → 4... The injection signal switching circuit 3 which receives this count output as input is...→ ₄ →
Switch the signal in the order of ₃ → ₂ → ₁ →...
This injection signal and the filter output are input to the multiplication circuit 4. This multiplication output is 16K filter 5 and 46K
After being input to the filter 6, the signal is input to the first and second detection circuits 7 and 8. Both detection outputs are input to a switching circuit 9 which uses the lower bit output of the reversible counter 2 as a switching input, and switches the input to the comparison circuit 10 for each field. The tracking error output obtained by comparison becomes as shown in CP3 in FIG. ₃ during triple speed reproduction, and as shown in CP _-3 in FIG. 3 during triple reverse reproduction. For each output waveform in the figure, the dotted lines indicate when the phase is leading;
The one-dot chain line represents each output waveform during a slow phase, and the solid line represents each output waveform during normal operation. As is clear from these waveform diagrams, the output level at the center of the video track corresponds to a tracking error. Therefore, in this embodiment, the RF switching pulse RF is input to the sampling pulse generation circuit 11, and the sampling pulse SP (see FIG. 3) obtained by delaying the RF switching pulse RF by 1/2 field is sent to the sample hold circuit 12. I am typing. Note that the sampling pulse generation circuit 11 includes a variable monomulti, and the sampling timing can be changed. The output obtained by sampling and holding the comparison output is input to a well-known capstan control circuit 13, which controls the rotation of the capstan motor to run the tape at a predetermined running speed.

As described above, according to the present invention, the 8 mm video capstan servo circuit can be shared with a simple circuit regardless of the presence or absence of a DTF servo mechanism, and the effect is great.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional capstan servo, FIG. 2 is a circuit block diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of an error output waveform. Explanation of main figure numbers, 2... Reversible counter, 3...
Injection signal switching circuit, 4...multiplication circuit, 12...sample hold circuit.

Claims (1)

[Claims] 1. A 2-bit reversible counter that adds or subtracts RF switching pulses according to the double speed in 8 mm video that sequentially switches four types of tracking pilot signals and records them superimposed on the video signal, and the reversible counter. 4. Make the frequency the same as that of the tracking pilot signal according to the count value of 4.
An injection signal generation circuit that generates various types of injection signals, a multiplication circuit that multiplies the reproduction tracking pilot signal and the injection signal, and a 16KHz component during the multiplication output.
A comparison circuit that compares the levels of the 46KHz component and generates an error output, a sample and hold circuit that samples the tracking error output at the center of the video track, and controls the rotation of the capstan motor based on the sample and hold output. A capstan control circuit and a capstan servo circuit that enable double-speed playback.