JPH0262905B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a magnetic recording/reproducing device (hereinafter referred to as a VTR), and in particular, it superimposes a pilot signal on a video signal, records it on a video track on a magnetic tape, and reproduces it. The present invention relates to a VTR which is sometimes configured to perform tracking control based on the above-mentioned pilot signal and has a function of detecting whether the above-mentioned tracking control is being performed satisfactorily.

[Prior Art] FIG. 1 is a schematic block diagram showing the configuration of a conventional VTR that performs tracking control using a pilot signal.

First, the configuration of a conventional VTR tracking control means will be explained with reference to FIG. In the figure, the magnetic head 8 is mounted on a rotating head drum (not shown). The magnetic head 8 rotates with the rotation of the head drum, and diagonally scans a magnetic tape (not shown). A head switch signal inputted to the head switch signal input terminal 1 and representing the timing of switching of the rotating magnetic head is applied to the cyclic frequency generator 2 and the switch 18. Cyclic frequency generator 2 sequentially generates a pilot signal in response to the leading and trailing edges of the head switch signal described above.

During recording, a video signal is input to the video signal input terminal 4, and after being superimposed on the pilot signal described above,
It is amplified via a recording amplifier 5. Further, the changeover switch 6 is connected to the REC side, and the output of the recording amplifier 5 is supplied to the magnetic head 8 via the rotary transformer 7 and recorded on the magnetic tape.

On the other hand, during playback, the selector switch 6 is
Switched to the PLAY side, the video signal including the pilot signal read out by the magnetic head 8 is input to the regenerative amplifier 9 via the rotary transformer 7 and the changeover switch 6, and is amplified. The output of the regenerative amplifier 9 is applied to a low pass filter 10, and a pilot signal component is extracted from the regenerated signal. This pilot signal component and the aforementioned pilot signal (hereinafter referred to as
During playback, it is called a carrier signal and its frequency is f _CR
) is input to the mixer 11, and a signal component having a frequency corresponding to the frequency difference between both signals is output. The output of the mixer 11 is simultaneously connected to a bandpass filter 12 with a passband of 16kHz and 46kHz.
and a bandpass filter 13 having a passband of . The signal that has passed through the bandpass filter 12 is subjected to envelope detection by a detector 14, and its output is given to a subtracter 16. On the other hand, the signal that has passed through the bandpass filter 13 is envelope-detected by a detector 15, and its output is also given to a subtracter 16. The output of the subtracter 16 can be output as a signal of the same polarity by a switch 18 which is switched in response to the head switch signal, or can be output by an inverting amplifier 17.
A signal of opposite polarity is outputted to the tracking error signal output terminal 19 via the tracking error signal output terminal 19.

FIG. 2 is a diagram showing video tracks formed obliquely in the longitudinal direction of the magnetic tape 20 and a pilot signal recorded on each video track in a manner superimposed with a video signal.

Next, the operation of the tracking control means of the VTR shown in FIG. 1 will be explained with reference to FIG.
During recording, the cyclic frequency generator 2 switches and generates pilot signals of four different frequencies f ₁ , f ₂ , f ₃ , and f ₄ for each field in response to the leading and trailing edges of the head switch signal. For example, when recording an NTSC video signal, these four frequencies are f ₁ = 102kHz, f ₂ = 118kHz, f ₃ =
164kHz, f ₄ = 148kHz, so that the frequency difference α between f ₁ and f ₂ is equal to the frequency difference between f ₄ and f ₃ , and f ₄
The frequency difference between and f ₂ is set to be approximately twice α. These pilot signals are superimposed on the video signal, and are recorded by the magnetic head 8 on the magnetic tape 20 by forming a video track inclined in the longitudinal direction of the magnetic tape 20 in field order, as shown in FIG. In FIG. 2, video tracks F ₁ , F ₂ , F ₃ , F ₄ have frequencies f ₁ , f ₂ ,
This shows that the pilot signals of f ₃ and f ₄ are recorded.

During playback, the magnetic head 8 reads a signal from the video track on the magnetic tape 20, and the playback signal is input to the playback amplifier 9 via the rotary transformer 7 and the changeover switch 6, where it is amplified. The output of the regenerative amplifier 9 is applied to a low pass filter 10, and the pilot signal component contained in the regenerated signal is extracted.

Here, for example, as shown in FIG.
Considering the case where F ₁ is being tracked, the pilot signal component detected by the magnetic head 8 includes, in addition to the pilot signal of frequency f ₁ superimposed on the video track F ₁ , the side lead effect, Also included is a pilot signal superimposed on both adjacent video tracks (video track F ₂ and video track F ₄ in the example of FIG. 2) due to crosstalk or the like. The magnitude of the pilot signal detected from these adjacent video tracks increases as the amount of positional deviation of the magnetic head 8 from the center of the video track it is tracking increases. When tracking the video track _F1 , the above-mentioned pilot signal component extracted by the low-pass filter 10 and the frequency generated by the circulating frequency generator 2
The carrier signal of f _CR = f ₁ is input to the mixer 11,
The frequency of the pilot signal f ₂ = 118kHz and the frequency of the carrier signal f _CR of one adjacent video track F ₂
= f ₁ = 102 kHz, and the difference between _{the pilot signal frequency f 4 =} 148 kHz and the carrier signal frequency f _CR = f ₁ = 102 kHz. A signal component with a frequency of 46kHz is obtained. These 16kHz and
The 46 kHz signal component is further extracted separately by a band pass filter 12 having a pass band of 16 kHz and a band pass filter 13 having a pass band of 46 kHz. The output of the bandpass filter 12 is subjected to envelope detection by the wave detector 14, and the output level represents the amount of positional shift of the magnetic head 8 to the adjacent video track _F2 on the right side. On the other hand, the output of the bandpass filter 13 is subjected to envelope detection by the wave detector 15, and the output level represents the amount of positional deviation of the magnetic head 8 to the adjacent video track _F4 on the left side.
By passing these two outputs through the subtracter 16, the amount of positional deviation of the magnetic head 8 from the center of the video track _F1 can be obtained.

However, when the magnetic head 8 is tracking video track F ₁ or F ₃ and when it is tracking video track F ₂ or F ₄ , the relationship between the frequency difference with the adjacent video tracks on the left and right is reversed. Therefore, the output of the subtracter 16 has the opposite polarity. Therefore, by providing an inverting amplifier 17 for reversing the polarity and switching the switch 18 by the head switch signal, the magnetic head 8
When tracking video track _F2 or _F4 , it is necessary to invert the polarity of the output of subtractor 16.

In this way, a signal having a voltage corresponding to the amount of positional deviation of the magnetic head 8 from the center of the video track is outputted to the tracking error signal output terminal 19, and this signal is fed back to the capstan motor. A servo control system is formed, and good tracking is performed.

However, with conventional VTRs, it takes time for the capstan motor control system to stabilize and perform good tracking after playback starts, and during that time, both the reproduced image and audio are distorted. The dot was hot. Therefore, during the above-mentioned period, it is necessary to take measures such as not displaying the reproduced image and muting the audio signal, and to perform tracking control by recording the control signal on a dedicated control track and reproducing it. With VTRs, it is possible to determine the period of poor tracking and take the above-mentioned countermeasures accurately. However, with a VTR that uses the aforementioned pilot signal to perform tracking control, it is not possible to detect the period of poor tracking, and the above-mentioned The drawback was that countermeasures could not be taken in a timely manner.

[Summary of the Invention] This invention was made to eliminate the drawbacks of the conventional ones, and therefore, the main purpose of the invention is to provide tracking during playback using a pilot signal recorded superimposed on a video signal. To provide a device with a relatively simple configuration for determining whether a tracking state is good or bad in order to determine a period for performing muting or the like immediately after the start of playback in a VTR configured to perform control.

To summarize this invention, during playback, after envelope-detecting and adding the 16 kHz component and 46 kHz component from the frequency difference components obtained by mixing the pilot signal and the carrier signal, the signal has an appropriate threshold value. This magnetic recording and reproducing apparatus is configured to be able to determine whether the tracking state is good or bad based on the magnitude of the above-mentioned addition output by feeding it to a comparator.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

[Embodiment of the Invention] FIG. 3 is a schematic block diagram showing the configuration of a VTR which is an embodiment of the invention. The embodiment shown in FIG. 3 is the same as the conventional VTR tracking control means shown in FIG. 1 except for the following points. That is, the detector 14 and the detector 15
The output is given to the subtracter 16 and also to the newly provided adder 21. The output of the adder 21 is applied to a low-pass filter 22 to absorb the output portion during the transient response time, and then a comparator 23 having a threshold voltage value V _T for determining whether tracking is being performed satisfactorily. is input. Comparator 23
The output is output from the servo lock detection signal output terminal 24.

FIG. 4 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 3. A is a diagram showing the output level of the detector 14 that performs envelope detection of the video track tracked by the magnetic head 8 and the corresponding 16 kHz frequency component.
Figure b shows the output level of the detector 15 that envelope-detected the 46kHz frequency component, and the adder 2 that adds the outputs of the detectors 14 and 15
A diagram showing the output level of 1 is c. In the figure, the horizontal axis is the distance in the longitudinal direction of the magnetic tape.

Now, assume a period in which the carrier signal has a frequency f ₁ =102kHz. When good tracking is performed, that is, as shown in FIG. 2, the frequency f ₁
A video track with a pilot signal superimposed on it.
When tracking F ₁ well, the pilot signal component with frequency f ₂ = 118 kHz and the _pilot signal component with frequency f ₄ = 148 kHz from both adjacent video tracks are minute, and the pilot signal component with frequency f ₁ = 102 kHz is small. The signal components with a frequency difference of 16 kHz and 46 kHz from the carrier signal are minute. At this time, as can be seen from FIG. 4, the outputs of the bandpass filter 12 with a passband of 16kHz and the bandpass filter 13 with a passband of 46kHz are minute, and these are enveloped by the detector 14 and the detector 15, respectively. The detected output level is minute, and the output level of adder 21, which is the sum of the outputs of detector 14 and detector 15, is also minute. On the other hand, if good tracking is not performed and the tracking shifts toward video track _F2 , as can be seen from Figure 4,
The pilot signal component with a frequency f ₂ =118 kHz increases, the signal component with a frequency difference of 16 kHz increases, and the output level of the detector 14 increases. At this time, the pilot signal component with frequency f ₄ = 148kHz disappears,
The signal component with the frequency difference of 46 kHz disappears, and the output level of the detector 15 becomes the minimum, but the output level of the adder 21, which is the sum of the outputs of the detectors 14 and 15, increases. Also, video tracks
If tracking shifts toward F ₄ , frequency f ₄ =
The 148 kHz pilot signal component increases, the 46 kHz frequency difference signal component increases, and the output level of the detector 15 increases. At this time, frequency f ₂ = 118kHz
The pilot signal component disappears, the signal component with the frequency difference of 16 kHz disappears, and the output level of the detector 14 becomes the minimum. However, the output level of the adder 21, which is the sum of the outputs of the detectors 14 and 15, is increase Therefore, in FIG. 4c, an appropriate threshold voltage value _VT is set, and good tracking is performed during the period when the output level of the adder 21 is less than or equal to the threshold voltage value _VT . It is determined that the output level of the adder 21 is the threshold voltage value.
The configuration may be such that it is determined that tracking is not performed satisfactorily for a period longer than V _T and corresponding processing such as muting is performed.

Note that even when video track F ₃ is being tracked well, the pilot signal component at frequency f ₂ = 118 kHz and the pilot signal component at frequency f ₄ = 148 kHz are very small, indicating that video track F ₁ is being tracked well. As in the case, the output level of the adder 21 is small, but since the servo control system operates to stably track the video track _F1 , the output level of the adder ₂₁ is The level becomes minute because it is transient. Therefore, after absorbing the output of the adder 21 during this transient response time with the low-pass filter 22, by applying it to the comparator 23 of the threshold voltage value V _T mentioned above,
A signal indicating whether tracking is being performed satisfactorily is output from the servo lock detection signal output terminal 24.

Also, the frequency f _CR of the carrier signal is the frequency f ₂ ,
Even in the periods f ₃ and f ₄ , if good tracking is being performed, the output level of the adder 21 will be small, and if good tracking is not being done, the output level of the adder 21 will increase. A signal indicating whether tracking is being performed satisfactorily is outputted from the comparator 23 to the servo lock detection signal output terminal 24.

Note that in the above embodiment, the detector 14 and the detector 1
5 is added by an adder 21, and the output level is compared with the threshold voltage value V _T by a comparator 23.
A similar effect can be obtained by comparing the magnitudes of the output levels of 5 using comparators each having an appropriate threshold voltage value V _T and then calculating the logical product of these comparator outputs.

[Effects of the Invention] As described above, according to the present invention, a signal component corresponding to the frequency difference between a carrier signal and a pilot signal is extracted, and the sum of the signal levels is compared with a preset threshold voltage value. I configured it like this,
With a simple circuit configuration, it can be determined whether tracking is being performed well or not, and necessary countermeasures such as muting can be taken in a timely manner when tracking is defective, such as in a linear chain at the start of regeneration.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the configuration of a conventional VTR that performs tracking control using a pilot signal. FIG. 2 is a diagram showing a video track formed on a magnetic tape and a magnetic head. Figure 3 shows a VTR that is an embodiment of this invention.
FIG. 2 is a schematic block diagram showing the configuration of the device. Figure 4 shows
4 is a waveform chart for explaining the operation of the embodiment shown in FIG. 3. FIG. In the figure, 2 is a circulating frequency generator, 7 is a rotary transformer, 8 is a magnetic head, 9 is a regenerative amplifier, 10 and 22 are low-pass filters, 11 is a mixer, 12 and 13 are band-pass filters, 14 and 1
5 is a detector, 20 is a magnetic tape, 21 is an adder,
23 indicates a comparator. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A magnetic tape on which a plurality of pilot signals having different frequencies are sequentially and repeatedly recorded for each signal track is reproduced by a rotating magnetic head, and the running of the magnetic tape is determined based on the extracted pilot signals. A magnetic recording and reproducing apparatus for controlling the magnetic recording and reproducing apparatus, comprising: a signal generating means for sequentially and repeatedly generating a plurality of signals each having the same frequency as the pilot signal in synchronization with a signal indicating switching of the rotating magnetic head; first and second level detection means for comparing the frequencies of the extracted pilot signal with a plurality of signals sequentially and repeatedly generated by the means, and detecting the level of a signal component responsive to the difference between the frequencies; , a magnetic recording and reproducing apparatus comprising: an addition means for adding the outputs of the first and second level detection means; and a comparison means for comparing the output of the addition means with a preset threshold value. . 2. The magnetic recording according to claim 1, wherein the plurality of pilot signals are obtained by recording signals generated by the signal generating means on the signal track by the rotating magnetic head. playback device.