JPH0510721B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a magnetic recording/reproducing device for overlapping recording of, for example, a video signal and a PCM audio signal.
In particular, it relates to a rotary transformer that connects a magnetic head and a reproduction head preamplifier. [Background of the Invention] In a two-head helical scan VTR (for example, a home VTR) that records and plays back video signals,
The luminance signal is used as the FM modulation signal, and the chromaticity signal is used as the FM modulation signal.
FM modulation signal is recorded and played back by converting it to a lower frequency band. Recently, as an extension of the track pattern of the magnetic tape on which these video signals are recorded, for example, PCM
converted audio signal (hereinafter abbreviated as PCM audio signal)
An overlap recording method has been proposed in which the video data is recorded and played back using a video head. The overlap recording method will be briefly explained using FIGS. 1 and 2. FIG. 1 shows a loading diagram in the above recording method. In the figure, 1 is a magnetic tape, 2 is a cylinder, 3 is a guide post, 4 and 5 are magnetic heads, 6 is the rotating direction of the cylinder, and 7 is the traveling direction of the magnetic tape. In this device,
The magnetic tape 1 is wrapped around the cylinder 2 by about 210 degrees. Then, about 30 degrees on the tape entry side.
PCM audio is recorded, and approximately 180 degrees of remaining video signals are recorded. In this apparatus, since the magnetic tape 1 is wound over 180 degrees or more as described above, a situation occurs in which the two heads 4 and 5 are positioned simultaneously on the magnetic tape as shown in the figure. FIG. 2 shows a tape format diagram of the above recording method. 8 and 9 in the figure are respectively magnetic tapes,
The moving direction of the video head, numerals 10 and 11, indicate recording patterns. Also, 1 of recording patterns 10 and 11
0a, 11a are video signal recording parts, 10b, 1
1b shows the recorded portion of the PCM audio signal. The positions of the video heads 4, 5 correspond to FIG. As is clear from the figure, head 5
When the head 4 is reproducing the PCM audio signal 11b, the head 4 will reproduce the video signal 10a. Next, crosstalk in conventional home VTRs will be briefly explained. As is well known, the winding angle of the magnetic tape around the cylinder is approximately 185 degrees, with an overlapping portion of approximately 5 degrees. This corresponds to a very small portion of the screen, and the crosstalk interference in this overlapping area was tolerable in terms of performance. On the other hand, in the VTR using the overlap recording method explained above, two different signals are played back at the same time in an interval of about 30 degrees (corresponding to about 1/5 on the screen), so crosstalk interference between them occurs. It becomes a big problem. The inventors have determined that the permissible limit for the amount of crosstalk caused by PCM audio signals that interferes with video is
We have confirmed that it is -38dB on the recording side and -28dB on the playback side. The above-mentioned crosstalk can be broadly classified into crosstalk on the circuit side and crosstalk on the rotary transformer that magnetically couples the magnetic head and the recording/reproducing circuit. Next, a conventional technique for reducing crosstalk in a rotary transformer will be explained. Figure 3 shows the structure of the rotary transformer. A is a plan view of the rotor side, and B is a cross-sectional view when both the rotor and stator are opposed to each other. In a rotary transformer used in a home VCR, as shown in FIGS. 1A and 2B, a rotor core 15 and a stator core 19 face each other in a plane while maintaining an air gap 22. 16 and 17 are wire rods wound around the winding grooves of the rotor core 15, and 20 and 21 are wire rods wound around the winding grooves of the stator core 19. For the sake of explanation here,
The inside (windings 16, 20) is ch1, the outside (winding 1
7, 21) is called ch2. Crosstalk between ch1 and ch2 can be sufficiently suppressed by digging a groove between ch1 and ch2 and inserting metal ring members (referred to as short rings) 18 and 23. For example, in a rotary transformer with a diameter of 30 mm, if there is no shot ring, the crosstalk between channels is approximately -
Approximately 25dB, if there is a shot ring -
It can be reduced to about 40 to -50dB. However, by inserting the short ring, the coupling coefficient K, which indicates the degree of magnetic coupling between the rotor and the stator, decreases and signal transmission loss in the rotary transformer increases. As explained above, in the case of a two-head VTR, by providing a short ring in the two-channel rotary transformer used therein, the crosstalk interference caused by the rotary transformer can be sufficiently suppressed, and the system can be applied to an overlap recording type VTR. However, in an overlap recording type VTR having three or more magnetic heads, the structure of the rotary transformer, the connection method between the magnetic head and the rotary transformer, and the connection method between the rotary transformer and the recording/reproducing circuit are required to reduce crosstalk. There are no known examples, and it is of great significance to provide optimal means regarding them. [Object of the Invention] The object of the present invention is to develop a new structure of the rotary transformer, connection with the magnetic head, and connection method between the rotary transformer and the recording/reproducing circuit in an overlap recording type VTR having three magnetic heads. The object of the present invention is to provide a magnetic recording and reproducing device that is free from crosstalk interference between video signals and PCM audio signals. [Summary of the Invention] The present invention is characterized in that, in a VTR that has two recording/playback heads and a playback head dedicated to field still, and uses an overlap recording method, three grooves corresponding to each head and a shortening groove are provided. In this 4-channel rotary transformer, which has a total of 4 grooves, the connection between the rotor side and the head, and the connection between the fixed side and the 3-channel playback head preamplifier and recording amplifier are optimized, and the connection between the video signal and the PCM audio signal is optimized. The point is to suppress crosstalk between the two. [Embodiments of the Invention] A first embodiment of the present invention will be described below. FIG. 4 shows the positional relationship of the heads in a three-head VTR. 24 is a cylinder, 25, 26,
27 is a video head. FIG. 5 shows the positions of the video heads 25, 26, and 27 when the recorded pattern on the magnetic tape 1 is reproduced. During normal playback, azimuth channel 1 head 25
and azimuth ch2 head 26, and azimuth ch1 head 25 and azimuth ch1 head 25 during field still.
Uses ch3 head 27. Track 1 in Figure 5
The hatching above 0 and 11 indicates the azimuth; the azimuth of heads 25 and 27 corresponds to that of track 10, and the azimuth of head 26 corresponds to that of track 11. Also, the PCM signal is recorded in the overlap section (hereinafter referred to as overlap section).
VTRs (abbreviated as PCM) can output high-quality audio even during double-speed playback by taking advantage of the PCM signal, which performs signal processing by time companding. However, for example, when playing at double speed,
The video head plays back recorded tracks every other track. Therefore, when reproducing with two heads (25 and 26 in FIG. 4) having different azimuths, a stable reproduction output cannot be obtained continuously. At this time, if the two heads 25 and 27 having the same azimuth are used for reproduction, a continuous and stable reproduction output can be obtained.
It is also possible to output high-quality double-speed audio. In principle, this can be applied when the speed is an even number. As explained above, in VTRs using the overlap recording method that provide high-quality double-speed audio, the fourth
As shown in the figure, a three-head configuration in which two heads having both azimuths are placed at one end of the cylinder is effective. Next, crosstalk occurring in a three-head VTR will be explained using FIG. First, the case where PCM signals are recorded in the overlap areas 10b and 11b will be described. Considering normal playback, the video signal recording section 10 on the track 10
When the ch1 head 25 is reproducing a, the ch2 head 26 is reproducing the PCM signal recording section 11b, so the amount of crosstalk between ch1 and ch2 is as follows.
The detection limit during playback must be kept below -28dB. In addition, the overlap area (Fig. 5 10b, 1
The signal recorded in 1b) is the PCM described above.
In addition to signals, for example, a signal obtained by frequency multiplexing a pilot signal used as a tracking control signal and a video signal can be considered. This is a tracking method (ATF method; A
When inserting a video using automatic T rack indexing ), the overlap area (10
While reproducing pilot signals of areas 10a and 11b, video signals are recorded in areas 10a and 11a. The video signals recorded in the overlap areas 10b and 11b have the function of acting as an alternating current bias during recording with respect to a relatively low-frequency pilot signal in the vicinity of 100 KHz to 200 KHz. Therefore, during normal playback, when the head 25 of channel 1 is playing back the video signal recording section 10a on the track 10,
The ch2 head 26 may simultaneously reproduce the video signal recorded in the channel 11b. ch at this time
The detection limit for crosstalk between channel 1 and channel 2 is approximately -
The inventors have confirmed that it is 32 dB. Therefore, considering both the crosstalk from the PCM signal to the video signal and the crosstalk from the video signal to the video signal as explained above, the amount of crosstalk during playback in the overlap section should be at least -32 dB.
Must be kept below. In FIG. 5, since the azimuth of the head 27 of ch3 and the azimuth of the track 11 are different, the amount of frosttalk from ch3 to ch1 due to azimuth loss is determined by the signal components from the track 11 and the adjacent track. For example, the track width of the ch3 head 27 is 28 μm, and the track pitch is 20 μm.
In this case, the signal reproduced by the head 27 from the adjacent track is a signal of 8 μm, which is approximately -8 dB of the signal reproduced by the heads 25 and 26 of ch1 and ch2.
Therefore, since the detection limit during reproduction is -32 dB, it is necessary to suppress the amount of crosstalk between ch1 and ch3 to at least -24 dB or less. Also, ch
The heads 26 and 27 of channels 2 and 3 are generally separated by about 1H to 3H, and when the amount of crosstalk between them increases, interference similar to a ghost occurs on the image. The detection limit for crosstalk interference between video signals is approximately -32dB.
This is even more difficult than converting a PCM signal to a video signal. As explained above, the signal reproduced by the head 27 of ch3 is about -8 dB compared to the signal reproduced by the head 26 of ch2.
2. The amount of crosstalk between ch3 is at least -
It is necessary to keep it below 24dB. Even during field still playback, it is necessary to reduce the amount of crosstalk between each channel, just as during normal playback. During recording, as can be seen from the positional relationship of the heads shown in FIG.
7 follows the ch2 head 26, and the head 27 exerts an erasing effect on the signal recorded by the head 26. Therefore, when recording, ch3 head 2
It is necessary to prevent current from flowing through 7. From what has been said so far, if a VTR using the overlap recording method is configured with three heads, the rotary transformer connecting the head and preamplifier will need at least three channels.
As explained in the prior art section, the biggest challenge is to reduce crosstalk between the three channels during playback, and the structure of the low retransmission and connection with the head and recording/playback circuits are as follows. It is best to do so. This will be explained below using FIGS. 6 and 7. FIG. 6 shows a cross-sectional view of the rotary transformer,
28 is a rotor core, 29 is a stator core, 30,3
2 and 33 are the windings of ch1, ch3, and ch2, respectively, and 31
is a shot ring. Figure 7 is similar to Figure 8.
Recording/playback circuit compatible with ch1, ch2, ch3,
25, 26, 27 are video heads, 37, 38,
39, 40, 49, 50, 51, 63 are switches, 41, 42, 43 are reproduction head preamplifiers,
44, 45 are recording amplifiers, 52 is an inverter circuit, 54 is an amplifier circuit, 55 is a PCM decoder, 5
6 is a video signal processing circuit, 57 is a band pass filter (hereinafter abbreviated as BPF), 58 is a servo circuit, 4
6, 47, 48, 53, 59, 60, 61, 62
is a signal terminal. Generally, to reduce crosstalk between the channels of a rotary transformer, increase the diameter and increase the distance between the channels. The diameter of the channel is also limited, and crosstalk between adjacent channels can only be ensured at around -10 to -15 dB. Therefore, the present invention provides a circuit configuration that suppresses the above-mentioned inter-channel crosstalk using a rotary transformer having four grooves. The embodiments shown in FIGS. 6 and 7 are cases in which a sufficient coupling coefficient (K) of the rotary transformer can be ensured by using a high-quality core material, a narrow gap, etc. Conventionally used rotary transformers generally have a coupling coefficient (K) of about 0.97. The ch1 winding 30 is placed in the outermost groove of the rotary transformer, and the shot ring 31, ch3 winding 32, and ch2 winding are placed inside it to reduce crosstalk between ch1, ch2, and ch3. Here, it is possible to use only the short ring 31a or only 31a, as it is sufficiently effective. The present invention can also be applied to the case where ch2 and ch3 are replaced. Next, the operation of the circuit shown in FIG. 7 will be briefly explained. Recording amplifiers are installed only in ch1 (44) and ch2 (45), and ch3 operates only for reproduction. switch 49
selects the output of preamplifier 43 of ch 2 during normal playback, and selects the output of preamplifier 43 of ch 2 during field still or double speed playback.
The output of the preamplifier 42 of No. 3 is selected and connected to a channel switch 50 for the video FM signal and a channel switch 51 for the PCM signal.
The switch 50 receives a 30Hz head pulse input from the terminal 53, and the switch 51 causes the inverter 5 to
They are switched in conjunction with each other by the head pulses inverted in step 2. The video FM signal that has passed through the switch 50 is further amplified by an amplifier circuit 54 to reduce crosstalk interference from the PCM signal, and then processed by a video signal processing circuit 56 and sent to a terminal 61.
is output as a video signal. In addition, the pilot signal frequency multiplexed with the video signal is BPF
After passing through 57, the signal is input to a servo circuit, and a tracking error signal indicating a tracking error is outputted to a terminal 62. After passing through the switch 51, the PCM signal undergoes processing such as D/A conversion in the PCM decoder 55 and is outputted to terminals 59 and 60 as a 2ch signal (stereo signal). Next, in addition to the short ring 31 in the recording and reproducing circuit of FIG. 7, switches 37, 38, 39, 40,
Table 1 shows the switching for each mode of 49 and 63.

[Table] During recording, switch 63 is connected to the b side to form an equivalent short ring in order to prevent the erase effect due to leakage current flowing to the ch3 head. Further, the switch 49 may be connected to either the a or b side, but in consideration of interlocking with the switch 63 by the control signal input from the terminal 48, it is preferable to connect it to the b side. During normal reproduction, the ch1 head 25 and ch2 head 26 are used, and by connecting the switch 63 to the b side, the stator side of the rotary transformer 32 of ch3 that is not needed is shot, forming an equivalent shot ring. This makes it possible to sufficiently reduce the crosstalk component that enters ch2 from ch3 via the rotary transformer. Next, as mentioned above, it is effective to use the ch1 head 25 and ch3 head 27 of the same azimuth during field still/double speed reproduction. In order to sufficiently suppress the crosstalk component that enters the channel 3 from the unused channel 2 head 26 via the rotary transformer, both switches 39 and 40 are connected to b to form an equivalent short ring. By shortening the stator side of the rotary transformer connected to heads that are not used for normal playback, field still playback, and double-speed playback (forming an equivalent short ring), the amount of crosstalk leaking into adjacent channels can be reduced from the usual -15 dB. It can be reduced to about -35dB. As explained above, in this embodiment (Figs. 6 and 7), the shot rings 31 are used to connect ch1 and ch1.
By reducing the crosstalk between ch2 and ch3 to a level of -40dB or less, and making unused channels equivalently short rings, ch2,
Crosstalk between channels 3 can be reduced to about -35dB. However, since there are equivalently two shot rings, the resultant coefficient K of the rotary transformer is slightly lower than when there is only one shot ring, but as mentioned earlier, the quality of the core material and the narrow gap reduce this deterioration. This is applicable when almost all the amount of water can be absorbed. In the present invention, in FIG. 6, the windings are arranged in order from the inside of the core to channel 1 (30), short ring 3,
1, ch3 (32), and ch2 (33). Next, a second embodiment of the present invention will be described. FIG. 8 shows a cross-sectional view of the rotary transformer,
72 is a rotor core, 73 is a stator core, 74, 7
6 and 77 are the windings of ch1, ch3, and ch2, respectively, and 75
is a shot ring. Figure 9 is the channel of Figure 8.
78 with recording and reproducing circuits compatible with 1, ch2, and ch3
indicates a switch, and everything else is the same as in FIG. This embodiment reduces crosstalk and minimizes the decrease in the coupling coefficient K when the coupling coefficient (K) of the rotary transformer is approximately 0.97, which is approximately the same as that used in conventional home VTRs. It is something to suppress. Next, Table 2 shows the relationship between the short ring, coupling coefficient, inductance, and transmission loss of a 4-channel rotary transformer with 4 grooves in a rotary transformer with a diameter of about 30 to 35 mm used in a small diameter cylinder of about 40 mm. show.

[Table] As shown in Table 2, the inventors of the present invention found that when there is one shot ring, the transmission loss increases by about 0.4 dB compared to the case where there is no shot ring, whereas when there are two shot rings, the transmission loss increases by about 0.4 dB. It has been experimentally confirmed that the loss increases by approximately 1 dB. Figure 8 shows the outermost groove 74 of the rotary transformer.
ch1, the winding 75 is arranged on the stator side inside it,
A switch 78 is provided at the terminal. Furthermore, windings 76 and 77 are provided as ch3 and ch2 on the inside thereof.
In FIG. 9, switches 37, 38, 39, 4
Table 3 shows the switching between 0, 49, 63, and 78.

〔Effect of the invention〕

The present invention provides an overlap recording system VTR with three
By configuring it as a head type, it is possible to output a temporally stable and high-quality double-speed audio signal during double-speed playback. In addition, by using a rotary transformer with four grooves, crosstalk between all channels corresponding to three heads can be sufficiently reduced for both recording and playback, preventing image quality deterioration due to crosstalk and sound quality deterioration of PCM audio. It has the effect of

[Brief explanation of the drawing]

Fig. 1 is a plan view showing loading, Fig. 2 is a tape pattern diagram showing recording patterns on the magnetic tape, Fig. 3A is a plan view of the rotary transformer, Fig. 3B is its sectional view, and Fig. 4 is a tape pattern diagram showing the recording pattern on the magnetic tape. 5 is a tape pattern diagram showing the position of the heads on the tape pattern, FIG. 6 is a sectional view of the rotary transformer of the present invention, and FIG. 7 is a diagram of the recording/reproducing circuit of the present invention. FIG. 8 is a sectional view of the rotary transformer of the present invention, and FIG. 9 is a block diagram of the recording/reproducing circuit of the present invention. 25, 26, 27...video head, 28, 7
2... Rotor core of rotary transformer, 29,7
3... Stator core of rotary transformer, 31...
Shot ring, 49, 63, 78... switch, 55... PCM decoder, 58... servo circuit, 56... video signal processing circuit.

Claims (1)

[Claims] 1. A magnetic tape is wound around the cylinder by more than 180 degrees, and a first magnetic head is mounted on a rotating cylinder; a second magnetic head having a different azimuth angle from the first magnetic head; A magnetic recording/reproducing device having a third magnetic head having the same azimuth angle as the magnetic head, the first and second magnetic heads being arranged 180 degrees apart from each other, and the second and third magnetic heads being arranged adjacently. In the apparatus, a first magnetic head, a shot ring, a third magnetic head, and a second magnetic head are connected in order from one end on the rotor side of a rotary transformer having four grooves, and the first and second magnetic heads are connected in order from one end on the rotor side. During recording and normal playback, the stator side of the channel of the rotary transformer connected to the third magnetic head is short-circuited, and during playback using the first and third magnetic heads, the rotary transformer connected to the second magnetic head is short-circuited. A magnetic recording/reproducing device characterized by comprising a switch circuit that short-circuits a stator side of a channel of a transformer.