A video tape recorder

Abstract: A video tape recorder (10) includes first and second magnetic heads (12a, 12b) to which reference pilot signals f₁ and/or f₃ produced by a programmable counter (14a) and reference pilot signals f₂ and/or f₄ produced by a programmable counter (14b) are applied, respectively, in a recording mode. In a reproducing mode, the reference pilot signals are reproduced and applied to mixers (28a, 28b) to which the reference pilot signals reproduced by the programmable counters (14a, 14b) are also applied. Therefore, frequency reference signals between the reproduced reference pilot signals and the produced reference pilot signals are outputted from the mixers (28a, 28b) and applied to amplitude detectors (34a, 34b, 34c, 34d) via bandpass filters (30a, 30b, 32a, 32b). A level difference between levels detected by the amplitude detectors (34a, 34b) is evaluated by an operational amplifier (38a), and a level difference between levels detected by the amplitude detectors (34c, 34d) is evaluated by an operational amplifier (38b). On the basis of the level differences, it is possible to determine whether or not index signals are recorded.

Description: BACKGROUND OF THE INVENTION Field of the invention The present invention generally relates to a video tape recorder. More specifically, the present invention relates to a video tape recorder such as an 8mm VTR having a tracking function of a 4-frequency pilot system. Description of the prior art With referring to Figure 4, in a conventional video tape recorder 1 of a 4-frequency pilot system, when a portion indicated by slanting lines in Figure 5 is traced by a magnetic head in a reproducing mode, pilot signals f 1 , f 2 and f 3 are derived by a bandpass filter 2, and then, inputted to a mixer 3. On the other hand, a reference pilot signal f 2 is reproduced by a programmable counter 4, and then, inputted to the mixer 3. Therefore, a difference signal (f 2 - f 1 ) and a difference signal (f 3 - f 2 ) are outputted from the mixer 3, and then, wave-shaped by an f H bandpass filter 5 and a 3f H bandpass filter 6, respectively. Thereafter, levels of the difference signals (f 2 - f 1 ) and (f 3 - f 2 ) are detected by amplitude detectors 7a and 7b, and a level difference between the both levels is evaluated by an operational amplifier 8. Accordingly, an ATF error signal is outputted from the operational amplifier 8 so that a rotation speed and a phase of a Capstan motor (not shown) are controlled, whereby a tracking can be automatically adjusted. A prior art very similar to Figure 4 prior art is disclosed in, for example, Japanese Patent Publication No. 59-31795 published for opposition on August 4, 1984 (FR-A-7807298). In the above described conventional video tape recorder, no PCM signal is recorded, and therefore, PCM areas or tracks becomes to be full-empty areas. On the other hand, in such video tape recorders, there is no control signal such as a signal which is utilized in a VHS system, and therefore, there was a problem that in order to write or record an index, it was required to provided a large-scaled circuitry similar to a circuitry used in a VSC (video subcode) system. US-A-5 115 324 shows a recording apparatus for recording an information signal on a recording medium which has a timer for automatically renewing the date and a circuitry for providing a mark on the recording medium when recording starts after the date is changed by the timer. Means for generating a mark switches pilot signal generation means in response to a control signal, so that the size of the region in which the pilot signal is recorded in each track is different from the size for another period in response to that control signal. Therefore it is a principle object of the present invention to provide a video tape recorder capable of writing or recording an index easily. This object is solved by the features of claim 1. Further advantageous features are mentioned in the subclaims. First, second, third and fourth reference pilot signals are recorded in respective first areas of the first, second, third and fourth tracks. On the other hand, any one of the first and third reference pilot signals is recorded in respective second areas of the first and third tracks by the first recording means, and any one of the second and fourth reference pilot signals is recorded in respective second areas of the second and fourth tracks by the second recording means. When the first track is traced by a first magnetic head included in the first recording means, the fourth reference pilot signal and a signal obtained when the first magnetic head traces the second area of the first track (which signal includes a signal corresponding to one of the first and third reference pilot signals and a signal reproduced from the second area of the fourth and second tracks which are adjacent to the first track) are mixed by a mixer, for example, so that two frequency difference signals are obtained. The two frequency difference signals are applied to a 46 kHz bandpass filter and a 16 kHz bandpass filter, for example. A level outputted from one of the bandpass filters is subtracted by a level of the other of the bandpass filters by an operational amplifier, for example. When the second track is traced by a second magnetic head included in the second recording means, the first reference pilot signal and a signal obtained when the second magnetic head traces the second area of the second track (which signal includes a signal corresponding to one of the second and fourth reference pilot signals and a signal reproduced from the second area of the first and third tracks by which the second track is sandwiched) are mixed by a mixer, for example, so that two frequency difference signals are obtained. The two frequency difference signals are applied to a 46 kHz bandpass filter and a 16 kHz bandpass filter, for example. A level outputted from one of the bandpass filters is subtracted by a level of the other of the bandpass filters by an operational amplifier, for example. When the third track is traced by the first magnetic head included in the first recording means, the second reference pilot signal and a signal obtained when the first magnetic head traces the second area of the third track (which signal includes a signal corresponding to one of the first and third reference pilot signals and a signal reproduced from the second area of the fourth and second tracks which are adjacent to the first track) are mixed by a mixer, for example, so that two frequency difference signals are obtained. The two frequency difference signals are applied to a 46 kHz bandpass filter and a 16 kHz bandpass filter, for example. A level outputted from one of the bandpass filters is subtracted by a level of the other of the bandpass filters by an operational amplifier, for example. When the fourth track is traced by the second magnetic head included in the second recording means, the third reference pilot signal and a signal obtained when the second magnetic head traces the second area of the second track (which signal includes a signal corresponding to one of the second and fourth reference pilot signals and a signal reproduced from the second area of the third and first tracks by which the fourth track are sandwiched) are mixed by a mixer, for example, so that two frequency difference signals are obtained. The two frequency difference signals are applied to a 46 kHz bandpass filter and a 16 kHz bandpass filter, for example. A level outputted from one of the bandpass filters is subtracted by a level of the other of the bandpass filters by an operational amplifier, for example. Thus, signals from respective operational amplifiers are utilized as a signal for determining whether or not there is an index. In accordance with the present invention, only by recording a predetermined reference pilot signal in the second area of each track as necessary, it is possible to add an index without a large-scaled and complex circuitry. The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram showing an embodiment according to the present invention; Figure 2 is an illustrative view showing one example of a recording format of a magnetic tape; Figure 3 is a timing chart showing an operation of Figure 1 embodiment, where Figure 3(A) shows a heat switching signal Figure 3(B) and Figure 3(C) show pilot signals, and Figure 3(D) shows an index signal; Figure 4 is a block diagram showing a prior art; and Figure 5 is an illustrative view showing a recording format of a magnetic tape in the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With referring to Figure 1, a video tape recorder 10 of this embodiment shown includes first and second magnetic heads 12a and 12b. In a recording mode, reference pilot signals f 1 and/or f 3 produced by a programmable counter 14a is applied to the first magnetic head 12a via a bandpass filter 16a and a switch 18a at every timing of 180 degrees rotation of the first magnetic head 12a. On the other hand, at every timing of 180 degrees rotation of the second magnetic head 12b, reference pilot signals f 2 and/or f 4 produced by a programmable counter 14b are applied to the second magnetic head via a bandpass filter 16b and a switch 18b. In addition, although not shown in Figure 1, a video signal and a sound signal are also applied to the first and second magnetic heads 12a and 12b through other signal systems. Therefore, on respective tracks of a magnetic tape 20, as shown in Figure 2, 3(B) and Figure 3(c), the video signal and the sound signal are sequentially recorded on video tracks, and reference pilot signals f 1 , f 2 , f 3 and f 4 for performing a tracking of a 4-frequency pilot system are periodically or cyclically recorded in accordance with an order of the respective video tracks. Furthermore, reference pilot signals described below are recorded in second areas of respective tracks, that is, PCM tracks in this embodiment shown. More specifically, any one of the reference pilot signals f 1 and f 3 produced by the programmable counter 14a is recorded on the first and third tracks. In this embodiment shown, the reference pilot signal f 3 is recorded on the first track, and the reference pilot signal f 1 is recorded on the third track. On the other hand, any one of the reference pilot signals f 2 and f 4 produced by the programmable counter 14b is recorded on the second and fourth tracks. In this embodiment shown, the reference pilot signal f 2 is recorded on the second track, and the reference pilot signal f 2 is recorded on the fourth track. In the present invention, by writing or recording the reference pilot signals for performing a tracking of a 4-frequency pilot system in the second areas of the respective tracks as necessary, it becomes possible to add an index in arbitrary tracks without any specific circuitry. In addition, in an NTSC system, for example, the programmable counter 14a and 14b can produce the respective reference pilot signals f 1 , f 2 , f 3 and f 4 having frequency relationship shown in Figure 2 on the basis of a clock 378f H and in response to 2-bit signals "00", "01", "10" or "11" provided by a microcomputer (not shown). In a PAL system, however, instead of the clock 378f H , a clock 375f H is utilized. Furthermore, the switches 18a and 18b are switched in accordance with a recording mode/reproducing mode changing signal outputted from the microcomputer (not shown) in response to instructions from a remote controller (not shown). In a reproducing mode, when the first track, for example, shown in Figure 2 is traced by the first magnetic head 12a, not only the reference pilot signal f 3 is reproduced from the second area, that is, the PCM track of the first track, but also the reference pilot signal f 2 is reproduced from respective second areas of the fourth and second tracks by which the first track is sandwiched. Furthermore, not only the video signal, the sound signal and the reference pilot signal f 1 are reproduced from the first area, that is, the video track of the first track, but also the reference pilot signals f 4 and f 2 are reproduced from the respective first areas of the fourth and second tracks by which the first track is sandwiched together with the video signal and the sound signal of that tracks. In a similar manner, when the third track, for example, shown in Figure 2 is traced by the first magnetic head 12a, the reference pilot signals f 1 , f 2 and f 3 are reproduced from the PCM tracks, and the reference pilot signals f 3 and f 4 are reproduced from the video tracks together with respective video signals and sound signals. When the second track, for example, shown in Figure 2 is traced by the second magnetic head 12b, not only the reference pilot signal f 2 is reproduced from the second area, that is, the PCM track of the first track, but also the reference pilot signals f 3 and f 1 are reproduced from respective second areas of the first and third tracks by which the second track is sandwiched. Furthermore, not only the video signal, the sound signal and the reference pilot signal f 2 are reproduced from the first area, that is, the video track of the first track, but also the reference pilot signals f 1 and f 3 are reproduced from the respective first areas of the first and third tracks by which the second track is sandwiched together with the video signal and the sound signal of that tracks. In a similar manner, when the fourth track, for example, shown in Figure 2 is traced by the second magnetic head 12b, the reference pilot signals f 2 , f 3 and f 1 are reproduced from the PCM tracks, and the reference pilot signals f 4 , f 3 and f 1 are reproduced from the video tracks together with respective video signals and sound signals. Respective reproduced signals are inputted to bandpass filters 24a and 24b via a preamplifiers 22a and 22b. Therefore, when the first track is traced by the first magnetic head 12a, reproduced reference pilot signals f 3 and f 2 from the PCM track and reproduced reference pilot signals f 4 , f 1 and f 2 from the video track are outputted from the bandpass filter 24a. Furthermore, the second track is traced by the second magnetic head 12b, reproduced reference pilot signals f 2 , f 3 and f 1 from the PCM track and reproduced reference pilot signals f 1 , f 2 and f 3 are outputted from the bandpass filter 24b. Respective signals outputted from the bandpass filters 24a and 24b are inputted to mixers 28a and 28b via amplifiers 26a and 26b, respectively. Furthermore, when the third track is traced by the first magnetic head 12a, reproduced reference pilot signals f 1 and f 2 from the PCM track and reproduced reference pilot signals f 3 , f 2 and f 4 from the video track are outputted from the bandpass filter 24a. Furthermore, the fourth track is traced by the second magnetic head 12b, reproduced reference pilot signals f 2 , f 1 and f 3 from the PCM track and reproduced reference pilot signals f 4 , f 3 and f 1 are outputted from the bandpass filter 24b. Respective signals outputted from the bandpass filters 24a and 24b are inputted to mixers 28a and 28b via amplifiers 26a and 26b, respectively. The reference pilot signal produced by the programmable counter 14a is further inputted to the mixer 28a. More specifically, when the PCM track of the first track is traced, that is, during a period that the reproduced reference pilot signals f 2 and f 3 are inputted to the mixer 28a, the reference pilot signal f 4 which is the same as the reference pilot signal f 4 which has been recorded on the proceeding fourth track is inputted to the mixer 28a, and when the video track of the first track is traced, that is, during a period that the produced reference pilot signals f 4 , f 1 and f 2 are inputted to the mixer 28a, the reference pilot signal f 1 for the first track is applied to the mixer 28a. Furthermore, when the reproduced reference pilot signals f 1 and f 2 which are reproduced from the PCM track by tracing the third track are inputted to the mixer 28a, the reference pilot signals f 2 for proceeding second track is applied to the mixer 28a, and when reproduced reference pilot signals f 3 , f 2 and f 4 that are reproduced from the video track of the third track are applied to the mixer 28a, the mixer 28a further receives the reference pilot signal f 3 for the third track. In a similar manner, the reference pilot signal produced by the programmable counter 14b is further inputted to the mixer 28b. More specifically, when the PCM track of the second track is traced, that is, during a period that the reproduced reference pilot signals f 3 , f 2 and f 1 are inputted to the mixer 28b, the reference pilot signal f 1 which is the same as the reference pilot signal f 1 which has been recorded on the proceeding first track, and when the video track of the second track is traced, that is, during a period that the produced reference pilot signals f 1 , f 2 and f 3 are inputted to the mixer 28a, the reference pilot signal f 2 for the second track is applied to the mixer 28b. Furthermore, when the reproduced reference pilot signals f 2 , f 1 and f 3 which are reproduced from the PCM track by tracing the fourth track are inputted to the mixer 28b, the reference pilot signals f 3 for proceeding third track is applied to the mixer 28b, and when reproduced reference pilot signals f 4 , f 3 and f 1 that are reproduced from the video track of the fourth track are applied to the mixer 28b, the mixer 28b further receives the reference pilot signal f 4 for the fourth track. Therefore, if the PCM track of the first track is traced by the first magnetic head 12a, two frequency difference signals (f 3 - f 4 : 16 kHz) and (f 4 - f 2 : 29 kHz) are outputted from the mixer 28a, and then, one frequency difference signal (f 3 - f 4 : 16 kHz) is derived by an f H bandpass filter 30a. Furthermore, if the video track of the first track is traced by the first magnetic head 12a, two frequency difference signals (f 2 - f 1 : 16 kHz) and (f 4 - f 1 : 49 kHz) are outputted from the mixer 28a, and then, respective frequency difference signals are derived by the f H bandpass filter 30a and a 3f H bandpass filter 32a. If the PCM track of the second track is traced by the second magnetic head 12b, two frequency difference signals (f 2 - f 1 : 16 kHz) and (f 3 - f 1 : 63 kHz) are outputted from the mixer 28b, and then, one frequency difference signal (f 2 - f 1 : 16 kHz) is derived by an f H bandpass filter 30b. In addition, if the video track of the second track is traced by the second magnetic head 12b, two frequency difference signals (f 2 - f 1 : 16 kHz) and (f 3 - f 2 : 46 kHz) are outputted from the mixer 28b, and then, respective frequency difference signals are derived by the f H bandpass filter 30b and a 3f H bandpass filter 32b. When the first track is traced, levels of the frequency difference signals (f 3 - f 4 : 16 kHz) and (f 2 - f 1 : 16 kHz) which are obtained from the f H bandpass filter 30 are detected by an amplitude detector 34a, and the frequency difference signal (f 4 - f 1 : 46 kHz) obtained from the 3f H bandpass filter 32a is detected by an amplitude detector 34b. Furthermore, when the second track is traced, a level of the frequency difference signal (f 2 - f 1 : 16 kHz) obtained from the f H bandpass filter 30b and a level of the frequency difference signal (f 3 - f 2 : 46 kHz) obtained from the 3f H bandpass filter 32b are respectively detected by amplitude detectors 34c and 34d. Then, outputs of the amplitude detectors 34a and 34b are inputted to an operational amplifier 36a so as to be subtracted from each other. Furthermore, outputs of the amplitude detectors 34c and 34d are inputted to an operational amplifier 36b so as to be subtracted from each other. Therefore, during a period of the PCM track of the first track, a negative level of the frequency difference signal (f 3 - f 4 : 16 kHz) is outputted from the operational amplifier 36a, and during a period of the PCM track of the second track, a positive level of the frequency difference signal (f 2 - f 1 : 16 kHz) is outputted from the operational amplifier 36b. During a period of the video track of the first track, a level signal which is obtained by subtracting a level of the frequency difference signal (f 2 - f 1 : 16 kHz) from a level of the frequency difference signal (f 4 - f 1 : 46 kHz) is outputted from the operational amplifier 36a, and a level signal obtained by subtracting a level of the frequency difference signal (f 3 - f 2 : 46 kHz) from a level of the frequency difference signal (f 2 - f 1 : 16 kHz) is outputted from the operational amplifier 36b. The level signals are applied to a switch circuit through amplifiers 38a and 38b, respectively, and then, an output of a period of the PCM track is outputted from the switch circuit 40 as an index signal, and an output of a period of the video track is outputted as an ATF error signal. A rotation speed and a phase of a capstan motor (not shown) is controlled in accordance with the ATF error signal. Furthermore, as shown in Figure 3(D), the index signal becomes the low level because the level signal is a negative signal during the first track, and the high level because the level signal is a positive signal during the second track. Therefore, it is possible to determine that the index is added in the second track, in this embodiment shown. In addition, by combining the index signals thus reproduced in a direction of a time axis, it is possible to record a complex code such as a time code. Furthermore, since the pilot signals are recorded on the magnetic tape 20 at timings of Figure 3(B) and 3(C), the switch circuit 40 is switched by a head switching signal (RFSW) as shown in Figure 3(A). That is, if the head switching signal RFSW shown in Figure 3(A) is the high level, the switch 40a is connected to a contact C2, and the switch 40b is connected to a contact C3. When the low level, the switches 40a and 40b are connected to contacts C1 and C4, respectively. Therefore, during a period of the high level of the switching signal RFSW, the video track of the second track or the fourth track is traced by the second magnetic head 12b, and therefore, the ATF error signal is outputted through the contact C3. At the same time, since the PCM track of the first track or the third track is traced by the first magnetic head 12a, the index signal is outputted through the contact C2. On the other hand, during a period of the low level of the head switching signal, the video track of the first track or the third track is traced by the first magnetic head 12a, and therefore, the ATF error signal is outputted through the contact C1, and the PCM track of the second track or the fourth track is traced by the second magnetic head 12b, and therefore, the index signal is outputted through the contact C4.

Claims: A video tape recorder of a 4-frequency pilot system wherein each of first, second, third and fourth tracks includes a first area (A) and a second area (B), and first, second, third and fourth pilot signals (f1 to f4) are inherently recorded on first areas of first, second, third and fourth tracks, whilst pilot signals are recorded on the second areas in dependence of an index signal the video tape recorder comprising pilot signal producing means (14a, 14b) for producing said first, second, third and fourth pilot signals; first recording means, including a first magnetic head (12a), for recording any one of said first and third pilot signals (f1, f3) on said second area of each of said first and third tracks; second recording means, including a second magnetic head (12b), for recording any one of said second and fourth pilot signals (f2, f4) on said second area of each of said second and fourth tracks; the selection between the first and third pilot signal and between the second and fourth pilot signal being in response to the index signal index detecting means (28a-38a, 28b-38b) for detecting the index for each track on the basis of one of the pilot signals produced by said pilot signal producing means and at least of one signal reproduced from said second area by said one of said first magnetic head and said second magnetic head at a time that said second area (B) of each track is traced by one of said first magnetic head and said second magnetic head; wherein said first track and said third track can be traced by said first magnetic head, and said second track and said fourth track can be traced by said second magnetic head, and said index detecting means includes first frequency difference signal producing means (28a) for receiving one of the reference pilot signal being produced by said pilot signal producing means and different from said first and third pilot signals, and signals reproduced from said second area (B) of one of said first and third tracks by said first magnetic head, and for producing first two frequency difference signals on the basis of signals received by said first frequency difference signal producing means; second frequency difference signal producing means (28b) for receiving one of the reference pilot signals produced by said pilot signal producing means and different from said second and fourth pilot signals, and signals reproduced from said second area of one of said second and fourth tracks by said second magnetic head, and for producing second two frequency difference signals on the basis of signals received by said second frequency difference signal producing means; first level difference detecting means (36a) for outputting a first level difference signal on the basis of said first two frequency difference signals; and second level difference detecting means (36b) for outputting a second level difference signal on the basis of said second two frequency difference signals; and the outputs of the first and second level difference detecting means during the period of the second area forming the index signal. A video tape recorder according to claim 1, wherein each of said first level difference detecting means includes first bandpass filter means (30a; 30b) for filtering the frequency difference signals with a first predetermined frequency pass-band; second bandpass filter means (32a; 32b) for filtering the frequency difference signals with a second predetermined frequency pass-band; first amplitude detecting means (34a; 34c) for detecting and amplitude of an output of said first bandpass filter means; second amplitude detecting means (34b; 34d) for detecting an amplitude of an output of said second bandpass filter means; and difference evaluating means (36a) for evaluating a difference between amplitudes detected by said first amplitude detecting means and said second amplitude detecting means, an output signal of said difference evaluating means being said first level difference signal or said second level difference signal. A video tape recorder according to claim 1, further comprising ATF error detecting means for detecting an ATF error for each track on the basis one of the pilot signals produced by said pilot signal producing means and at least one signal reproduced from said first area by said one of said first magnetic head and said second magnetic head at a time (RFSW) that said first area of each track is traced by one of said first magnetic head and said second magnetic head. A video tape recorder according to claim 1, further comprising ATF error detecting means for detecting an ATF error for each track on the basis one of the pilot signals produced by said pilot signal producing means and at least one signal reproduced from said first area by said one of said first magnetic head and said second magnetic head at a time that said first area of each track is traced by one of said first magnetic head and said second magnetic head. A video tape recorder according to claim 4, wherein signals outputted by said first level difference signal producing means and said second level difference signal producing means become to be ATF error signals at a timing when said first area of said each track is traced by said first magnetic head or said second magnetic head.

Inventors: TABUCHI JUNICHIRO, TABUCHI, JUNICHIRO
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO., LTD.
Application year: 1993
Main classification: G11B27
IPC codes: G11B27, G11B15