JPH077542B2 - Helical scan magnetic recording / reproducing device - Google Patents

Description

The present invention relates to a helical scan magnetic recording / reproducing apparatus such as a video tape recorder.

[Conventional technology]

In a helical scan magnetic recording / reproducing apparatus typified by a video tape recorder, in addition to normal reproduction for reproducing an information signal recorded by running a magnetic tape at a predetermined speed, for example, still reproduction, frame advance reproduction, etc. In some cases, special reproduction is performed in which the running of the magnetic tape is stopped and the information signal is continuously reproduced from one predetermined main track.

FIG. 3 is a block diagram of a portion for such special reproduction in a conventional helical scan magnetic recording / reproducing apparatus.
In the figure, reference numeral 1 denotes a low-pass filter, which separates and extracts a tracking pilot signal, which is recorded by being superimposed on a television video signal, from a reproduction signal of a rotary head (not shown). Reference numeral 2 denotes a multiplication circuit which multiplies the pilot signal generated by the pilot signal generation circuit 3 in synchronization with the edge of the switching pulse (SWP) for switching the head with the output of the low pass filter 1. Reference numerals 4 and 5 denote bandpass filters, which output the frequency f _H from the output of the multiplication circuit 2.
And the 3f _H component are extracted and output to the detectors 6 and 7 (f _H is the frequency of the horizontal synchronizing signal). A differential amplifier 8 outputs a difference between the outputs of the detectors 6 and 7, that is, a tracking error signal. Reference numeral 9 is a comparison circuit, which compares the output of the differential amplifier 8 with the reference potential output from the reference potential generation circuit 10 and outputs the result to the detection circuit 11.

During normal playback, the magnetic tape runs at normal playback speed,
The reproduction signal from the rotary head is supplied to the low pass filter 1. The low-pass filter 1 extracts the tracking pilot signals f _{1 to} f ₄ from the reproduced signal and supplies them to the multiplication circuit 2. Here, the frequencies of the pilot signals f _{1 to} f ₄ are set to 6.5f _H , 7.5f _H , 10.5f _H , and 9.5f _H , respectively. On the other hand, the pilot signal generating circuit 3 synchronizes the pilot signals of frequencies f _{1 to} f ₄ with 1
Output sequentially for each field. As a result, in the multiplication circuit 2, the pilot signal (the pilot signal reproduced from the main track and the adjacent track) included in the reproduced signal,
The multiplication with the pilot signal input from the pilot signal generation circuit 3 is performed, and the beat component is output. Then, the components of the frequencies f _H and 3f _H are extracted from the output of the multiplication circuit 2 by the bandpass filters 4 and 5, respectively, rectified and smoothed by the detectors 6 and 7, and converted into a direct current level. The tracking error signal is output from the differential amplifier 8. For example, the rotation of a capstan (not shown) is controlled according to this tracking error signal.

On the other hand, for example, when playing back frame by frame, the magnetic tape is temporarily stopped
As shown in FIG. 4, assuming that the main track on which the pilot signal of frequency f ₁ is recorded is traced by the rotary head, two rotations of the same azimuth are generated by the switching pulse as shown in FIG. 5 (a). The heads A and B'are switched alternately to obtain an RF signal envelope as shown in FIG. 5 (b) (where the rotary head B'is mainly used together with the rotary head A when reproducing a still image). The azimuth rotary head B different from the rotary head A used with the rotary head A during normal reproduction
Is provided corresponding to). At this time, the pilot signal generation circuit 3 generates a pilot signal having a frequency different from the frequencies f ₂ and f _{4 of the} pilot signal recorded on the track adjacent to the main track by f _H and 3f _H , that is, the frequency f ₁ The pilot signal of is fixed and output.
In other words, the same pilot signal as that recorded on the main track is continuously output. As a result, the differential amplifier 8 outputs a tracking error signal as shown in FIG. This tracking error signal is compared with the reference potential (zero potential) generated by the reference potential generation circuit 10, and the comparison circuit 9 compares positive when it is larger than the reference potential as shown in FIG. Output a signal. The level of the RF signal reaches its peak (maximum or minimum) when the tracking error signal becomes zero. Therefore, the detection circuit 11 can detect the stop position of the magnetic tape by detecting the phase difference between the rising edge of the switching pulse and the rising edge of the comparison signal.

[Problems solved by the invention]

However, in such a conventional device, since the tracking error signal similar to that in the normal reproduction is obtained during the special reproduction, the width of the rotary head is narrowed,
Alternatively, when there is little crosstalk from adjacent tracks due to differences in the recording density characteristics of the magnetic tapes, it is difficult to accurately detect the stop position of the magnetic tapes.

An object of the present invention is to provide a helical scan magnetic recording / reproducing apparatus capable of accurately detecting a magnetic tape stop position during reproduction of a still image without depending on crosstalk of a recording pilot signal.

[Means for solving problems]

FIG. 1 shows a block diagram of a helical scan magnetic recording / reproducing apparatus of the present invention. In the figure, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. In the present invention, the pilot signal generation circuit 3 is controlled by the control circuit 21 such as a microcomputer, and at the time of frame advance reproduction, it is not the same frequency as the pilot signal recorded on the main track,
A pilot signal having a frequency different by f _H or 3f _H , that is, a pilot signal having a frequency f ₂ or f ₄ is output. In other words, the pilot signal having the same frequency as the pilot signal recorded on either one of the adjacent tracks is output. Other configurations are basically the same as those in FIG.

[Operation] The operation will be described with reference to FIG. During normal reproduction, the control device 21 causes the pilot signal generation circuit 3 to output pilot signals of frequencies f _{1 to} f ₄ in synchronization with the timing of the edge of the head switching pulse. Therefore, tracking control is performed by the tracking error signal output from the differential amplifier 8 as in the case of FIG.

Next, at the time of frame advance reproduction, with magnetic tape is temporarily stopped at a predetermined position, f _H or 3f _H only different frequency pilot signal is a pilot signal generation circuit with respect to the pilot signal recorded on the main track It is output from 3. For example, as shown in FIG. 4, when the rotary head traces the main track on which the frequency f ₁ is recorded, the pilot signal of frequency f ₂ (or f ₄ ) is output. Since the frequency of the pilot signal included in the reproduced signal from the rotary head is _{f 1, f 2, f 4} , the frequency of the beat _{component, f 2 -f 1 (= f} H), f 2 -f 2 (= 0), f ₄ −f ₂
(= 2f _H ). Since the band pass filters 4 and 5 pass only the signal of frequency f _H or 3f _H , f ₂
Only the -f ₁ beat component is extracted by the bandpass filter 4, detected by the detection circuit 6, and input to the non-inverting terminal of the differential amplifier 8. Since the input to the inverting terminal is zero, the output of the differential amplifier 8 is as shown in FIG. 2 (c). That is, when the two rotary heads A and B'are alternately switched by the head switching pulse as shown in FIG. 2 (a), the envelope of the reproduced RF signal is changed to the main track as shown in FIG. 2 (b). It becomes maximum when the rotating head A of the matched azimuth is located substantially in the center of the magnetic tape (when the overlap of the trace track of the rotating head A with the main track is the largest), and decreases slightly when it is located at both ends. . This is the same when the rotary head B'traces because the azimuths are the same. On the other hand the level of the beat component of the frequency f ₂ -f ₁ is changed in response to the level of the frequency f ₁ of the pilot signal in the reproduced signal, since the pilot signal is independently reproduced azimuth rotary heads A and B The level of the beat component of frequency f ₂ −f ₁ becomes maximum when the overlap of the trace locus of ′ with the main track is the largest. In other words, the position of the maximum value (peak value) of this beat component corresponds to the position of the peak value (maximum value or minimum value) of the envelope of the RF signal. Therefore, when the reference potential output from the reference potential generation circuit 10 is set to a value slightly smaller than the peak value of the output of the differential amplifier 8, the second value in the comparison circuit 9 is set.
It is possible to obtain a peak detection pulse as shown in FIG. When a pilot signal of frequency f ₄ is generated by the pilot signal generation circuit 3, a signal obtained by inverting the signal shown in FIG. 2 (c) is obtained, and in this case, a negative peak value is detected. You can do it like this. The position of the peak value of the RF signal can be detected by obtaining the center of the pulse in the detection circuit 11 and obtaining the phase difference from the rising edge of the head switching pulse, for example. The center or phase difference of such a pulse can be easily calculated by counting a predetermined clock or the like.

The detection signal of the peak value of the RF signal thus obtained is used as follows. That is, the magnetic tape is temporarily stopped, one main track is reproduced as a still image, the magnetic tape is slightly moved, and the next main track is reproduced as a still image, thereby repeating frame-by-frame reproduction. But,
When the stop position of the magnetic tape during reproduction of a still image is correct, the overlap of the portion traced by the rotary head A (B ') with the main track is the largest. In other words, as shown in FIG. 4, the area where the trace locus of the rotary head A and the main track overlap (the hatched portion in the figure) is the largest. In such a case, the RF signal level is the highest and the noise that appears on the screen is small. On the other hand, when the stop position of the magnetic tape deviates, the trace track of the rotary head A (B ') and the main track overlap each other (the hatched part in the figure).
Area becomes smaller, the RF signal level becomes smaller,
The noise that appears on the screen increases. The deviation of the stop position of the magnetic tape corresponds to the deviation of the peak value of the RF signal. That is, if the magnetic tape stop position is correct, RF
The peak value of the signal is generated when the rotary head A (B ') is in the approximate center of the main track (and therefore in the approximate center of the head switching pulse), but if the stop position is shifted, the position where the peak value occurs is correspondingly generated. The magnetic tape is displaced toward the lower end or the upper end. Therefore, when the still image reproduction of one screen is completed and a frame advance command is issued so that the next screen is reproduced as a still image, the transfer amount of the magnetic tape is changed according to the detected deviation, The deviation is reduced in the next main track.

If the pilot signal output from the pilot signal generation circuit 3 and the pilot signal recorded on the main track are immediately matched when the magnetic tape is changed from the stopped state to the running state during such special reproduction, the differential amplifier The signal output from 8 can be supplied to a tracking servo circuit (not shown) as a phase servo signal. However, if the signals output from the differential amplifier 8 are supplied to the tracking servo circuit as they are in a state where they cannot be matched, the tracking state is disturbed. Therefore, during special playback, for example, the output of a frequency generator that rotates in conjunction with the capstan is compared with a predetermined reference value, and only so-called frequency servo is performed to control the rotation of the capstan in response to the error signal. You can

Although the peak value of the RF signal is detected by comparing the output of the differential amplifier 8 with the fixed reference potential in the above, the reference potential is an average value signal obtained by rectifying and smoothing the output of the differential amplifier 8. You can also In this way, even if the DC level of the output of the differential amplifier 8 changes, the reference potential also changes following the change, and the detection operation is stabilized. It is also possible to sample and hold the output of the differential amplifier 8 with a clock having a predetermined short interval and detect the largest hold value as its peak value. Furthermore, the input and output of such a sample hold circuit may be compared by the comparison circuit 9. In this case, so to speak, whether the slope of the output of the differential amplifier 8 is positive or negative, that is, the polarity is detected, and the polarity is inverted at the peak value. For example, as shown in FIG. , RF
A pulse with an edge rising at the peak value of the signal can be obtained. Also, for example, the output of the differential amplifier 8 is A / D
Alternatively, the peak value may be detected digitally by conversion.

〔effect〕

According to the present invention, attention is paid to the fact that there is little noise appearing on the screen when the reproduction signal level is maximum, and that there is a fixed correlation between the reproduction signal level and the pilot signal level. Since the maximum position of the reproduction signal level is detected based on the beat component of the signal and the internally generated pilot signal of the same frequency as the recording pilot signal of the adjacent track, it does not depend on the crosstalk of the recording pilot signal and stops. The magnetic tape stop position can be accurately detected during image reproduction. Then, by feeding back the detection signal to the magnetic tape running control system as a tape position correction signal and reflecting it at the next still image reproduction command operation, it is possible to obtain a reproduction screen with less noise.

[Brief description of drawings]

FIG. 1 is a block diagram of a helical scan magnetic recording / reproducing apparatus of the present invention, FIG. 2 is a timing chart thereof, FIG. 3 is a block diagram of a conventional helical scan magnetic recording / reproducing apparatus, and FIG. FIG. 5 is a schematic plan view showing a track in FIG.
The figure is the timing chart. 1 ... Low-pass filter, 2 ... Multiplier circuit 3 ... Pilot signal generation circuit 4, 5 ... Bandpass filter 6, 7 ... Detector, 8 ... Differential amplifier 9 ... Comparison circuit 10 ... Reference potential Generation circuit 11 …… Detection circuit, 12 …… Control device

Claims (1)

[Claims] 1. A superimposed signal composed of an information signal recorded by a rotary head on a plurality of recording tracks that are inclinedly arranged with respect to the longitudinal direction of a magnetic tape, and a recording pilot signal for tracking having a different frequency for each recording track. Is reproduced, the beat component between the internal pilot signal generated from the built-in pilot signal generating means and the recording pilot signal included in the reproduction superimposed signal is detected, and tracking control is performed based on the detected beat component. And a special reproduction operation for reproducing the information signal on the main track of the reproduction target specified by the frequency of the recording pilot signal included in the superimposed signal in a state where the running of the magnetic tape is stopped. In a helical scan magnetic recording device capable of performing the above, during the special reproduction operation, the built-in pad Control means for causing the ilot signal generating means to generate an internal pilot signal having the same frequency as a recording pilot signal of one of the tracks adjacent to the main track; and the pilot signal generating means during the special reproduction operation. A tape position detection that detects the phase of the maximum value or the minimum value of the beat component based on the beat component of the output internal pilot signal and the recording pilot signal of the main track, and outputs this detection signal to the tracking control system. And a helical scan magnetic recording device.