Magnetic tape reproducing system having analogue digital compatibility

Abstract: There is disclosed, an analog/digital compatible reproducing system, particularly a stationary head system using a digital recorded magnetic tape having a plurality of, n, digital data recorded tracks, and an analog recorded magnetic tape having a first analog recorded track (TA 1 ) and a second analog recorded track (TA 2 ) between which a guardband (W GB ) of a certain width is provided, so as to reproduce signals from the digital recorded magnetic tape by driving n reproduce magnetic head elements (h 1 -h 8 ) respectively corresponding to the n digital data recorded tracks, and to reproduce the analog recorded magnetic tape by driving a plurality of, m, reproduce magnetic head elements of said n reproduce magnetic head elements (h 1 -h 3 , h 5 -h 7 ), corresponding to the first and second recorded tracks so that common outputs can be produced from the m reproduce magnetic head elements. There is also disclosed a tape cassette used in such system.

Description: Background of The Invention The present invention relates to a magnetic tape reproducing system having analog/digital compatibility. Recently, the digital recording audio tape recorder DAT has achieved remarkable development and popularization. However, since the usual cassette tape, or compact cassette audio tape has so far been extremely spread, the general users have a large number of recorded compact cassette tapes and thus use conventional analog tape recorder and DAT. This brings very inconvenience particularly for the user of the portable tape recorder of pocket-size or the like. In fact, an S-DAT (stationary head digital audio tape recorder ) has substantially the same construction, or hardware as does the conventional analog cassette system (player and recorder) except it has a multitrack head and is able to reproduce the analog signal recorded on the conventional compact cassette or record an analog signal on the compact cassette, and further record and reproduce a digital signal, or is constructed to have the compatibility for both digital and analog recording/reproduction. In this case, the cassette tape exclusively used for the S-DAT is produced according to the same specification as the conventional compact cassette B shown in Fig. 20 which is exclusively used for the analog recording as will be understood from the above description. Therefore, particularly a reel hub 122 shown in Fig. 21, around which a magnetic tape 121 is wound has 6 ratchets 124 provided at an equal pitch on the inner wall of a cylindrical body 123 so as to project towards its center in the same way as in the conventional compact cassette B. A reel table 125 provided in the tape cassette holding portion of the S-DAT is matched with the shape of the reel hub 122. As shown in Fig. 22, this reel table has a reel shaft 126 at its center and this reel shaft 126 has 3 engaging projections 127 integrally provided around the reel shaft 126 at an equal pitch as in the conventional analog cassette system. The three engaging projections 127 are inserted in recesses 128 which are formed between the ratchets 124 of the reel hub 122, when a tape cassette exclusively used for the S-DAT is loaded in the tape cassette holding portion of the S-DAT, or when the reel hub 122 is fitted on the reel table 125. When the reel table 125 is rotated in one direction as a rotating shaft 129 rotates, the reel hub 122 is rotated while the engaging projections 127 of the reel table 125 engage with the ratchets 124 of the reel hub 122. Thus, when this reel hub 122 ratchets, the magnetic tape 121 is wound on the other reel hub 122, and transported past the head so that, for example, analog and digital reproduction is automatically made. Since the specification of the S-DAT tape cassette is the same as that of the conventional compact cassette B, the tape cassette for S-DAT has a mark (for example, detection hole or the like) provided for mechanically or electrically distinguishing from the conventional compact cassette. The tape cassette exclusively used for S-DAT which has been discussed can be loaded in the normal analog cassette system since it has same specification as the conventional compact cassette B. When the S-DAT tape cassette is recorded with a digital signal, however, the digital signal cannot be reproduced by the normal analog cassette system. Thus, the general user will inevitably load the S-DAT tape cassette in the normal analog cassette system without knowing it. Thus, in order to distinguish the S-DAT tape cassette from the conventional tape cassette, the general user will have to put an identification mark on the label, and finally will have no choice but to try to load the tape cassette in the analog cassette system and to reproduce it, thus probably getting confused in using tape cassettes. Moreover, since the idea of the compatibility for the digital and analog recording/reproduction is not yet fully understood by the general user, the S-DAT tape cassette may be mistaken for the compact cassette. In that case, since the S-DAT type cassette cannot be reproduced, it my be regarded as being defective. EP-A-0 381 266 being state of the art for the purpose of Article 54 (3) EPC for all designated contracting states describes an analog/digital compatible reproducing system. In this system, the information is reproduced from a tape divided into two halves in the widthwise direction for reproduction in two transport directions. Digital information is reproduced by a plurality of digital reproduction heads, while analog information is reproduced by a dedicated analog reproduction head. OBJECTS AND SUMMARY OF THE INVENTION In view of the above aspect, this invention is to provide an analog/digital compatible reproducing system capable of at least reproducing both analog recorded tape and digital recorded tape on a single tape recorder with the compatibility for both tapes. According to the present invention, a magnetic tape reproducing system having analog/digital compatibility for using a digital magnetic tape having a plurality of n digital data recording tracks and an analog magnetic tape having a first and a second analog recording track between which a guard-band of a certain width is provided, wherein said system comprises means for reproducing signals from said digital magnetic tape by means of n magnetic reproducing head elements, respectively corresponding to said n digital data recording tracks said system comprising means for reproducing signals from said analog magnetic tape by means of two sets of m magnetic head elements among said n magnetic reproducing head elements corresponding to said first and second analog recording tracks so that common outputs can be produced from each of said sets of m magnetic head elements. According to an advantageous development, the magnetic reproducing head elements are formed of reproducing head elements having magneto-resistance effect magneto-sensitive portions, said system further comprises switching means for applying a high-frequency bias magnetic field to said magneto-sensitive portions when reproduction is made by said magnetic head elements from said analog recorded magnetic tape and for applying a dc bias magnetic field to said magneto-sensitive portions of said magneto-resistance effect head elements when reproduction is made from said digital recorded magnetic tape. According to a further advantageous development, the magnetic tape reproducing system in accordance with the present invention, divides said analog magnetic tape and said digital magnetic tape, respectively, into a first half and a second half in their widthwise direction and said analog magnetic tape and said digital magnetic tape are transported in one direction and in the opposite direction so that each of the first and second halves can be reproduced, wherein upon transport in said one direction, a recorded area is included on the first half of said analog magnetic tape and on the second half of said digital magnetic tape, while upon transport in said opposite direction, a recorded area is included on said second half of said analog magnetic tape and on said first half of said digital magnetic tape. A tape cassette, which can be advantageously used comprises reel hubs each having cut-outs provided to oppose engaging projections of a reel table that has provided at its centre a reel shaft around which said engaging projections are integrally provided, and blocking portions to block said reel shaft from being inserted in said reel hub. Brief Description of the Drawings Figs. 1 and 2 show the relations between the tracks and the head elements of one embodiment of a system of the invention, Figs. 3, 9 and 10 are circuit diagrams of embodiments of a system of this invention, Figs. 4A and 4B are perspective views of magnetic tape cassettes, Fig. 5 is a diagram of an alternative arrangement of magnetic head elements not belarging to the present invention, Fig. 6 is a cross sectional diagram of a magnetoresistance effect magnetic head element, Fig. 7 is a schematical circuit diagram thereof, Fig. 8 is a graph of a resistance-magnetic field characteristic curve, Fig. 11 is a diagram of the arrangement of magnetic head elements, Fig. 12 shows the relation between erase head elements and the magnetic head elements, Fig. 13 is a circuit diagram of a conventional magnetoresistance effect magnetic head, and Fig. 14 is a waveform diagram useful for the explanation thereof. Fig. 15 is a plan view of a tape cassette useable in this embodiments, Fig. 16 is a plan view of the structure of the reel hub of this embodiments, Figs. 17A and 17B are a plan views and side views of a reel table adapted to a reel hub of Fig. 16, Fig. 18 is a plan view of another example of the reel hub, Figs. 19A and 19B are a plan view and side view of another example of the reel table adapted to the reel hub of Fig. 18, Fig. 20 is a plan view of a conventional compact cassette, Fig. 21 is a plan view of the normal reel hub, and Figs 22A and 22B are a plan view and side view of the normal reel table. DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention employs the stationary head type DAT, or S-DAT (stationary head digital audio tape recorder), and the recorded digital magnetic tape takes the same format as for example, the analog recorded magnetic tape, or the compact cassette format. According to this invention a positional relation between the magnetic tape and magnetic head element is provided as shown in Figs. 1 and 2. The analog/digital compatible reproducing system using a recorded digital magnetic tape 1D (see Fig. 1) having a plurality of n digital by recorded data tracks T D1 , T D2 , T D3 ... and a recorded analog magnetic tape 1A having a first recorded analog track TA₁ and a second recorded analog track TA₂ between which a guardband 2 of a certain width W G8 is provided, so as to reproduce signals from the digital magnetic tape 1D by driving n magnetic reproducing head elements h₁, h₂, h₃ ..., respectively opposite to the n digital data recording tracks T D1 , T D2 , T D3 ... and to reproduce the analog magnetic tape 1A by driving a plurality of m magnetic reproducing head elements of the n magnetic reproducing head elements, for example h₁ to h₃, and h₅ to h₇ of the magnetic reproducing head elements h₁, h₂, h₃ ... opposite to the first and second recorded analog tracks TA₁ and TA₂ so that common outputs OUT₁ and OUT₂ can respectively be produced from the two groups of m magnetic reproducing head elements. According to this invention there is also provided an analog/digital compatible reproducing system according to the above system as shown by the circuit example in Fig. 3 wherein the magnetic reproducing head elements h₁, h₂, h₃ ... are formed of magnetoresistance effect head elements having magnetosensitive portions MR₁, MR₂, MR₃ ..., and in this case the system further comprises switching means 3 for applying a high frequency bias magnetic field and a DC bias magnetic field to the magnetosensitive portions MR1, MR2, MR3..., when reproduction is made from the recorded analog magnetic tape 1A by the magnetic head elements h₁, h₂, h₃ ..., and for applying a DC bias magnetic field to the magnetoresistance effect magnetosensitive portions MR₁ , MR₂ , MR₃ ... when reproduction is made from the recorded digital magnetic tape 1D. Fig. 4A show a perspective view of the recorded analog magnetic tape 1A and tape cassette 4A, and Fig. 4B shows the tape cassette 4D for the digital recorded magnetic tape 1D. There is also provided an analog/digital compatible reproducing system using the recorded analog magnetic tape 1A and the recorded digital magnetic tape 1D each of which is divided into one half 1A₁, 1D₁, and the other half 1A₂, 1D₂ in the widthwise direction and transported in one direction indicated by arrow-a and in the other direction indicated by arrow-b so that each of the halves can be reproduced, wherein upon transport in the a-direction the recorded area of the so-called A-side is included in the first half 1A₁ of the recorded analog magnetic tape 1A and on the other half 1D₂ of the recorded digital magnetic tape 1D, while upon transport in the b-direction a recorded area of the so-called B-side is included on the other half 1A₂ of the analog recorded magnetic tape 1A and on the first half 1D₁ of the digital recorded magnetic tape 1D. Accordingly, there is provided as shown in Fig. 4 an analog/digital compatible reproducing system using an analog magnetic tape 1A and a digital magnetic tape 1D each of which is divided into one half 1A₁, 1D₁ and the other half 1A₂, 1D₂ in the widthwise direction and transported in one direction-a and the other direction-b so as to be reproduced, wherein as shown in Fig 5 an analogly recorded area and a digitally recorded area are reproduced by a digital reproducing head which comprises analog reproduce head elements H₁, and H₂ disposed to oppose each of the halves 1A₁ and 1A₂ of the analog magnetic tape 1A, and digital reproducing head elements h₁, h₂, h₃ ... disposed to oppose a plurality of digital data tracks of a digital magnetic tape 1D having opposite halves 1D₂, 1D₁ to those of tape analog magnetic 1A, as if is described above in view of Figs. 4A and 4B. According to the system of this invention a tape recorder can be used to reproduce not only a digitally recorded magnetic tape ,but also an analogly recorded compact cassette tape which has been widely used so far. An embodiment of a system of this invention will be described with reference to Figs. 1 and 2. As shown in Fig. 1, a plurality of n tracks, in this embodiment, 7 digitally recorded data tracks T D1 - T D7 and, for example, one signal recorded track T D8 are formed on a digital recorded magnetic tape 1D, and magnetic head elements h₁ to h₇ are arranged to oppose the tracks T D1 to T D7 , and one magnetic head element h₈ is provided to oppose track T D8 . Among the n=7 magnetic head elements h1 to h 7, two sets of m, for example 3 magnetic head elements h₁ to h₃ and h₅ to h₇ are, as shown in Fig. 2, opposed to, for example, the left-and right-channel signal recording tracks of an analog magnetic tape 1A, or first and second analog recorded tracks T A1 and T A2 , and output signals out₁ and out₂ are respectively produced from the two sets of the elements h₁ to h₃, h₅ to h₇ by driving, or operating the head elements. In other words, when two sets of three magnetic head elements are respectively opposed to the first and second analog recorded tracks T A1 and T A2 of the analog magnetic tape 1A of, for example, the normal compact cassette, the three adjacent magnetic head elements h₁ to h₃ are opposed to the track T A1 , the next magnetic head element h₄ to a guardband 2, and the following three adjacent magnetic head elements, h₅ to h₇ are opposed to the other track T A2 . In this case, since the tracks T A1 and T A2 on the analog recorded magnetic tape of the normal compact cassette have a width W of 0.61mm, and the guardband 2 between the tracks T A1 and T A2 has a width W GB of 0,325mm, all the magnetic head elements h₁ to h₈, particularly h₁ to h₇ can form tracks of an equal width T W , for example, T W =160µm, on the tracks T A1 and T A2 so that no cross talk is caused therebetween In addition, the distance B₁ between the elements h₁ to h₃ and between h₅ to h₇ is selected to be 65µm, and the distance B2 between the elements h₄ within the guardband 2 and the opposed edges of the analog audio tracks is selected to be 82.5µm. The magnetic head element h₈ for the recorded cue signal track T D8 is opposed to the guardband on the center-0 side of the tape 1D. These magnetic head elements can also be formed of an inductive type head structure not only for reproduction but also for, for example, digital recording. Only for reproduction, these head elements can be formed of MR type magnetic head elements which comprise magnetosensitive portions having the magnetoresistance effect. The magnetoresistance effect head element can be constructed as, for example, shown in Fig. 6 which is a cross-sectional diagram of one example thereof. That is, on a magnetic base 11 made of, for example, Ni-Zn based ferrite or Mn-Zn based ferrite, this base 11 having an electrical conductivity, there is formed through an insulating layer 12 of SiO₂ or the like a bias conductor 13 which is formed of a band-shaped conductive film in which a current is to be flowed, producing a bias magnetic field against the magnetoresistance effect magnetosensitive portion which will be described later. On this conductor 13, is formed through an insulating layer 14 a magnetosensitive portion MR is formed of a magnetoresistance effect thin file made of, for example, Ni-Fe based alloy or Ni-Co based alloy. On this magnetosensitive portion MR are formed through a thin insulating layer 16 a pair of magnetic layers 17 and 18 so that the opposite ends of these layers are formed over the top of the magnetosensitive portion and extend across the bias conductor 13 and magnetosensitive portion MR, these magnetic layers 17, 18 being made of, for example, Mo permalloy and serving as magnetic cores of part of the magnetic circuit. To the base 11 is bonded a protective base 20 through a nonmagnetic insulation holding layer 19. A nonmagnetic gap spacer layer 21, which is formed of, for example, an insulating layer 16 and having a necessary thickness, is interposed between the magnetic layer 17 and the front end of the base 11, thus producing a front magnetic gap g. Then, the front end surfaces of the base 11, gap spacer layer 21, magnetic layer 17, protective layer 19 and protective base 20 are grinded and polished to form a touching face 22 which is to be brought in contact with the magnetic recording medium. The back end of the magnetic layer 17 which makes the magnetic gap g together with the magnetic base 11, and the front end of the other magnetic layer 18 are formed on the insulating layer 16 so as to cross the magnetosensitive portion MR which underlies the insulating layer, but a discontinuous portion 23 is formed between the opposite ends of the magnetic layers 17, 18. The back end of the magnetic layer 17 and and the front end of the magnetic layer 18 are electrically insulated by the insulating layer 16 on both sides of the magnetoresistance effect magnetosensitive portion MR, but magnetically coupled. The discontinuous portion 23 between the magnetic layers 17 and 18 is magnetically bridged by the magnetosensitive portion MR, so that a magnetic circuit is formed to make a closed magnetic path from the base 11-magnetic gap g-magnetic layer 17-magnetosensitive portion MR-magnetic layer 18 to the base 11. The magnetic head elements h₁ to h₈ of this magnetoresistance effect head structure are simultaneously formed in parallel on the same base 11 or through a non-magnetic material on the same base 11, and the bias conductor 13 for the elements h₁ to h₈ is formed common to the elements h₁ to h₈ . In this magnetoresistance effect magnetic head, the signal magnetic flux from the front gap g made in contact with the magnetic medium is flowed in the magnetic circuit so that the resistance value of the magnetosensitive portion MR in the magnetic circuit is changed by this signal magnetic flux, or external magnetic field. Thus, this resistance change is detected as a voltage change across this magnetosensitive portion MR by flowing a detection current in the magnetosensitive portion MR, so that the recorded signal on the magnetic tape can be reproduced. In this case, in order to operate the magnetosensitive portion MR as a magnetic sensor linearly and with high sensitivity, it is necessary to magnetically bias the magnetosensitive portion MR. This bias magnetic field includes the magnetic field produced by flowing a current in the bias conductor 13 and the field which the magnetosensitive portion MR produces itself by the detected current therein. In this kind of MR-type magnetic head assembly, as schematically shown in Fig. 2 in relation to Fig. 7, a magnetic field is applied to the magnetosensitive portion MR by flowing a certain DC current i₈ in the bias conductor 13, and under this condition a predetermined detection current i MR is applied with a bias field H B , or the field produced by flowing a current in the bias conductor 13 and the magnetic field produced by flowing the detection current in the magnetosensitive portion MR. Under this conduction, the signal magnetic field H s from the magnetic tape as described above is applied. The voltage across the magnetosensitive portion MR based on the resistance change due to this signal magnetic field H s , or the change of the potential at point A is amplified by an amplifier 24, fed to an output terminal 25 and detected. Shown at 26 is a low-frequency blocking capacitor. Fig. 8 is a diagram of an operational characteristic curve showing the relation between the magnetic fields H and resistance value R, of this magnetosensitive portion MR. From this figure, it will be seen that in the range, - H BR to + H BR in which the absolute value of the magnetic field H is small, this curve is a quadratic curve with a maximum resistance value R max and that as the magnetization of the MR magnetic thin film at its center starts to saturate in the magnetic circuit direction, the resistance R gradually approaches a certain value R Min away from the quadratic curve. In this connection, the maximum value R max of the MR magnetic thin film is all magnetized in the current direction. In the characteristic portion of the quadratic curve of this operational characteristic curve, the bias magnetic field H B is applied, and under this condition, a signal magnetic field is applied from the magnetic tape as indicated by reference number 67 in Fig. 8. The signal output is obtained by the resistance change shown by reference numeral 68 in the Fig. 8. In this case, however, upon reproduction of analog signal, or when the signal magnetic field is applied from a recorded analog signal, the second-order harmonic distortion increases with increasing signal field. Moreover, the potential at point A (refer to Fig. 7) in the MR-type magnetic head assembly as shown in Fig. 2 is determined by the resultant resistance of the fixed portion and the variable portion of the resistance of the magnetoresistance effect magnetosensitive portion. In this case, since the fixed portion is about 98% of the total resistance and has a great temperature dependency, the temperature drift of the potential at point A is large enough to have an adverse effect on the analog reproduction. In order to solve the problem with the analog reproduction in the MR magnetic head, a magnetoresistance effect head assembly was proposed as, for example, disclosed in Japanese Patent Laid-open Gazette No. 182503/1985 which was filed by this applicant. This head assembly will be mentionned with the circuit arrangement of Fig. 13. In Fig. 13, like elements corresponding to those in Fig. 7 are identified by the same reference numerals and will not be described. In this case, an AC bias current i A of high frequency f c is flowed in the bias conductor 13, to produce a high-frequency magnetic field superimposed on a DC magnetic field, and applied to the magnetosensitive portion MR. The waveform of the AC bias current i A , and hence the waveform of the AC magnetic field may be a sine wave, rectangular wave or other useable waveforms. Thus, since an AC bias magnetic field is superimposed on the DC bias magnetic field and applied to the magnetosensitive portion MR, an AC signal of frequency f c is produced across the magnetosensitive portion MR, or at point A. The AC signal output is supplied through the capacitor 26 and through the preamplifier 24 which passes the component of frequency f c , to a multiplier 27 where this signal X is multiplied by the AC signal Y of frequency f c . Shown at 28 is a low-pass filter. Thus, the signal output according to the signal magnetic field H s from the magnetic tape appears at an output terminal 35 in this case, the frequency f c of AC current i A , if the final output at the output terminal 35 is required to have a band of, for example, 0 to 40 kHz, is selected to be triple or above the maximum frequency, or for example, f c = 140 kHz. Fig. 14A shows a field resistance characteristic curve of the magnetosensitive portion MR. When the magnetosensitive portion MR is applied with the superimposed field of the rectangular wave AC magnetic field H B (t) and the signal magnetic field H s (t), the magnetosensitive portion MR produces the output voltage V(t) as shown in Fig. 14C. The multiplier 27 multiplies this output voltage V(t) by the rectangular wave AC current shown in Fig. 14D, and the low-pass filter 68 produces, as shown in Fig. 14E, a signal output V ⊘ (t) corresponding to the signal magnetic field H s (t) shown in Fig, 14D. This magnetic head assembly has the advantages of excellent-linearity and small-distortion output, small temperature drift, small slide noise, large effective track width, and small track width, and capable of reducing the capacity of the capacitance, and increasing the dynamic range. Also, in some case, the permeability of the magnetic circuit can be avoided from being reduced. In this invention, when the magnetic head elements h₁ to h₈ are formed of MR type magnetic head elements, the reproduction of digital recording can be made substantially without a problem with output linearity, temperature drift and sliding noise, but when part of the magnetic head elements is used for the production of analog recording as described with reference to Fig. 2, the above-given problems occur and thus they are desired to be solved. Therefore, in this case, as shown in Fig. 3, the arrangement shown in Fig. 7 or the arrangement shown in Fig. 13 in which the switching means 3 is provided in accordance with Figs. 3, 9 and 10, is used for the magnetic head elements h depending on whether the reproduction is made of the digital recorded tape 1A. In Fig. 3, like elements corresponding to those in Figs. 7 and 13 are identified by the same reference numerals and will not be described. In Fig. 3, SW is the change-over switch for switching a DC bias source 40 and an AC bias to the bias conductor 13. In the illustrated example, a rectangular wave generator 30 for desired frequency f c is provides to produce a pulse, which is supplied through an amplifier 31 to the switch SW, by which it is switched and supplied to the common bias conductor 13 (Fig. 6) as an AC source. In this case, the magnetosensitive portions MR₁ to MR₈ of the magnetic head elements h₁ to h₈ are respectively connected through capacitors 26 and amplifiers 24 to output terminals 25₁ to 25₈ . The output ends of the amplifiers 24 of the respective sets of elements h₁ to h₃, h₅ to h₇ are connected to common change-over switches SW H1 and SW H2 , respectively. The change-over switches SW H1 and SW H2 are connected through multipliers 27H₁ and 27H₂ and low-pass filters 28H₁ and 28H₂ to output terminals 35H₁ and 35H₂ , respectively. The rectangular wave from the rectangular wave generator 30 is supplied to the multipliers 27H₁ and 27H₂ where it is multiplied by the output from the change-over switches SW H1 and SW H2 . The multiplied outputs are supplied to the filters 28H₁ and 28H₂ . Also, in Fig. 3 there is shown an analog/digital switching means 3. In the analog reproduction mode, the switch SW is changed to the AC supply portion, and the rectangular wave generator 30 is operated. Also, the positions of the change-over switches SW H1 and SW H2 are changed to the side of the multipliers 27H₁, 27H₂. Thus, the output terminals 35H₁ and 35H₂ are producing the outputs of the magnetosensitive portions MR₁ to MR₃, MR₅ to MR₇ of the magnetic head elements h₁ to h₃, h₅ to h₇, as described with reference to Figs. 13 and 14. In the digital reproduction mode, the position of the switch SW is changed to the side of the DC bias source 40, the rectangular wave generator 30 and so on are stopped from operation and the change-over switches SW H1 and SW H2 are opened. Thus, the signals from the magnetic head elements h₁ to h₈ are produced from the output terminals 25₁ to 25₈ as described with reference to Fig. 7. Another magnetoresistance effect magnetic head assembly is proposed as disclosed in Japanese Patent Laid-open Gazette No. 57012/1986 which this applicant filed. According to this head assembly, the multipliers 27H₁ and 27H₂ in Figs. 13 and 3 are replaced by a phase switching circuit 34 having inverters 33H₁ and 33H₂ as shown in Fig. 9. In Fig. 9, like elements corresponding to those in Fig. 3 are identified by the same reference numerals and will not be described. In this case, the control circuit 32 for switching the analog reproduction mode and digital reproduction mode, upon digital reproduction, controls the switch SW to be changed to the position leading to the DC power supply 40, and the rectangular wave generator 30 to be stopped from operation. Thus, the outputs from the elements h₁ to h₈ are produced at the output terminals 25₁ to 25₈. In the analog reproduction mode, the position of the switch SW is changed to the side of the amplifier 31, the rectangular wave generator 30 is operated, and the phase switching circuit 34 is operated. In other words, the output from the amplifier 14 and the inverted output from the inverter 33 to which the output of the amplifier is applied are switched and supplied to the low-pass filters 28H₁ and 28H₂ by the switches SWH₁ and SWH₂ which are controlled by the rectangular wave signal. Thus, the signal outputs according to the signal magnetic field H s are produced from the output terminals 35H₁ and 35H₂ . Still another magnetoresistance effect magnetic head assembly is proposed as disclosed in Japanese Patent Laid-open Gazette No. 54005/1986 which this applicant filed. As shown in Fig. 10, the inverters 33H₁ and 33H₂ in Fig. 9 are replaced by sample-and-hold circuits 41H₁ and 41H₂ for sampling and holding the rectangular wave signal from the amplifiers 24, A/D converters 42H₁ and 42H₂ for converting the outputs of the sample-and-hold circuits 41H₁ and 41H₂, and digital filters 43H₁ and 43H₂, to which the digital signals from the A/D converters 42H₁ and 42H₂ are supplied. Thus, the digital filters 43H₁ and 43H₂ can supply to the output terminals 35H₁ and 35H₂, smooth digital signals which are code-inverted from one sample to each other sample and correspond to the signal magnetic field. The sample pulse signal formed on the basis of the pulse signal from the pulse generator 44 is synchronized with the rectangular wave signal from the rectangular wave generator 30 so as to generate a pulse signal of twice the frequency, or 2f c . In Fig. 10, like elements corresponding to those in Figs. 3 and 9 are identified by the same reference numerals. In this case too, the control circuit 32 for switching the analog reproduction mode and the digital reproduction mode controls, upon digital reproduction, the position of the switch SW to be changed to the side of the DC power supply 40, the rectangular wave generator 30 to be stopped and the switches SW H1 and SW H2 to be opened. Thus, the outputs from the magnetic head elements h₁ to h₈ are produced from the output terminals 25₁ to 25₈ . While in the examples, the magnetic head elements h₁ to h₈ are formed by the magnetoresistance effect head elements, they may be formed by an inductive type, for example, thin film type magnetic head. Moreover, in the above system of this invention the recorded analog magnetic tape 1A is reproduced by part of magnetic head elements h₁ to h₈, or sets of three magnetic head elements h₁ to h₃ , h₅ to h₇ which oppose the tracks T D1 to T D8 of the digital recording magnetic tape. In practice, since the shortest wavelength to be recorded in digital form is 1µm or below, the gap length of the digital magnetic head elements is selected to be 0.3 to 0.4µm, while the gap length of the analog magnetic head is preferably 0.8 to 1µm relative to the recorded wavelength. In the analog reproduction mode, since the digital magnetic head elements of small gap length are used and since a necessary distance is required between the elements h₁ to h₃ and between h₅ to h₇, the reproduction efficiency is low. In order to solve this low reproduction efficiency problem, it is desired to use different magnetic head elements having gap lengths, characteristics and track widths suitable for the reproduction of each of the analog magnetic recording tape 1A and digital magnetic recording tape 1D. According to another system not belonging to the present invention, as shown in Fig. 5, the tape recorder has, in addition to the magnetic head elements h₁ to h₈ for digital reproduction, first and second magnetic head elements H₁ and H₂ for analog reproduction to oppose the first and second analog recorded magnetic tracks T A1 and T A2 of the analog recorded magnetic tape 1A. On the other hand, as shown in Figs. 4A and 4B, the analog recorded magnetic tape 1A and digital recorded magnetic tape 1D of the tape cassettes 4A and 4D are provided, and the magnetic tapes 1A and 1D each have one halves 1A₁, 1D₁ and the other halves 1A₂, 1D₂ relative to the widthwise direction. The magnetic tapes 1A and 1D are used and transported in the a-direction and the b-direction so that the respective halves of the analog recorded magnetic tape 1A and digital record magnetic tape 1D are reproduced. When transported in one direction a, the analog recorded magnetic tap and the digital recorded magnetic tape have thereon the recorded areas, or one half 1A₁ and the other half 1D₂, respectively and when transported in the other direction b, the analog recorded magnetic tape 1A and the digital recorded magnetic tape 1D have formed thereon the recorded areas, or the other half 1A₂ and one half 1D₁, or the so-called A-side and B-side, respectively. As shown in Fig. 5, the analog reproducing magnetic head elements H₁, H₂ and digital reproducing magnetic head elements h₁ to h₈ are opposed to the one half 1A₁, 1D₁ of the tape 1A, 1D when the analog recorded magnetic tape cassette 4A or the digital recorded magnetic tape cassette 4D is loaded in the tape recorder. When the tape is transported in the a-direction, for example the so-called A-side can be reproduced. In this case, when the cassette 4A is loaded so that the analog recorded magnetic tape 1A is reproduced, the magnetic head elements H₁ and H₂ are operated. When the cassette 4D is loaded so that the digital recorded magnetic tape 4A is reproduced, the magnetic head elements h₁ to h₈ are operated. In this case, the circuits associated with the magnetic head elements h₁ to h₈ or H₁, H₂ which are not required to operate, are not supplied with power for the purpose of power saving. When the other half 1A₂, 1D₂ of the tape cassette 4A, 4D is to be reproduced, the cassette 4A, 4D is turned over, and loaded, and the tape is travelled in the b-direction as shown in Fig. 4. For the so-called autoreverse operation, the magnetic head elements H₁, H₂ and h₁ to h₈ are inverted. Moreover, the analog reproducing magnetic head elements H₁, H₂ and digital reproducing magnetic head elements h₁ to h₈ can be formed by a bulk-type inductive head. In this case, the head elements H₁ and H₂ are spaced enough; as are the conventional magnetic heads, to reserve the space for the head winding. If a large number of very small magnetic head elements h₁ to h₈ are shifted in position against one another relative to the tape travel so as to be in two rows as, for example shown in Fig. 11, the adjacent elements in each row can be spaced to oppose every other tracks, and thus to keep the winding space. In this case, the delay due to the positional shift of every other elements can be corrected by digital signal processing and thus no problem occurs. If erase head elements 51 of the so-called tunnel erase 50 are provided between the head elements h₁ to h₈ and on both the outer sides of the head elements group so as to make overwriting relative to the tracks TD₁ to TD₈, arbitrary overwriting can also be made on the cue signal track TD₈ . In the above described system the magnetic head elements h₁ to h₈ are exclusively used for reproduction. As is apparent, they may be used for digital recording and reproduction, too. An embodiment of a tape cassette used in the invention will be described with reference to Figs. 2, and 15 to 19. Fig. 15 is a plan view of a tape cassette for exclusive use in the S-DAT. This tape cassette A has the same specification and construction as the normal audio cassette, or compact cassette, and has provided therein a magnetic tape 102, reel hubs 103 which are rotated to wind and unwind the tape, and though not shown, guide rollers, guide poles and a shield plate. The magnetic tape 102 wound on the reel hub 103 is transported through the guide rollers, guide poles, and shield plate past the head of a cassette recorder which will be described later. The cassette recorder used here is, for example, of a stationary head system such as S-DAT and has the compatibility for the digital and analog recording/reproduction. Particularly in this embodiment, as shown in Fig. 2 it has 8 heads h₁ to h₈ including a cue head h₈ of which a plurality of heads (three heads in this illustration) are disposed to oppose an analog track TA₁, TA₂ of R-channel, L-channel. The other hardware than the heads are the same as the normal analog cassette system. When the magnetic tape 102 is recorded with a digital signal, the 7 heads h₁ to h₇ except the cue head h₈ are used to form 7 multiple tracks. When the compact tape recorded by the normal analog cassette system is reproduced, each three heads h₅ to h₇, h₁ to h₃ is used to read, or reproduce the analog track TA₁, TA₂ on R-channel, L-channel. The reel hub 103, as shown in Fig. 16, has six poles 105 integrally formed on a cylindrical body 104 to extend in the radial direction. The six poles 105 are arranged at an equal pitch as are the ratchets 124 in the normal reel hub 122 (see Fig. 21). And holes, or cutouts 106 are provided at portions corresponding to the recesses 128 between the ratchets 124 of the normal reel hub 122. That is, the cutouts 106 are formed to oppose the engaging projections 127 around the reel shaft 126 of the normal reel table (see Fig. 22). The 6 poles 105 are connected at the center of the reel hub 103, and this connection portion 107, and the six poles 105 block the cassette not to be fitted with the reel shaft 126 of the normal reel table 125 (see Fig. 22). Since the hub 103 has the above construction, each of reel tables 110 mounted on the S-DAT tape cassette holding portion used in this embodiment has, as shown in Fig. 17, a plurality of (three in this figure) projections 112 provided to project from the upper surface of a base 111. The diameter of the projections 112 is smaller than the width of the openings of the cutouts 106 of the reel hub 103. The projections 112 are so arranged that when the tape cassette A is loaded on the tape cassette holding portion of the S-DAT, or when the reel hubs 103 are engaged on the reel tables 110, the three projections 112 are equidistantly inserted in three ones of the six cutouts 106 of each of the reel hubs 103 as shown in Fig. 16 by two-dot chain lines. Particularly in this embodiment, each three projections can also be inserted in the recesses 128 of the normal reel hub 122 (see Fig. 21). When the reel table 110 is rotated by the rotating shaft 113, the projections 112 and the poles 105 are engaged and the reel hub 103 is rotated. Thus, the magnetic tape 102 wound on the reel hubs 103 is continuously transported past the head as the reel hubs 103 are rotated, so that digital or analog recording/reproduction can be made. According to the above description, since the tape cassette A is so constructed that particularly in the reel hubs 103, the cutouts 106 are provided at the positions corresponding to the engaging projections 127 which are provided around the reel shaft 126 of the normal reel table 125 (see Fig. 22) and that the six poles 105 and the connection portion 107 are provided to block the reel shaft 126 not to engage, this cassette can be prevented from being loaded to the reel table 125 of the normal analog cassette system. Thus, the S-DAT tape cassette A can be prevented from being misloaded in the normal analog cassette, and the general user can easily understand that the S-DAT tape cassette A cannot be used on the normal analog cassette system, thus not getting confused upon using the tape cassettes (the S-DAT tape cassette and the conventional compact cassette). Moreover, the general user can understand the idea of the compatibility, or that the S-DAT has the compatibility for the digital and analog recording/reproduction whereas the normal analog cassette system does not have the compatibility for the digital recording/reproduction, thus the S-DAT being promoted to be widely used. Particularly, since the reel hubs 103 each have 6 poles 105 extending to the center of the reel hub 103 unlike the reel hub of the conventional compact cassette, the S-DAT cassette can be distinguished at a glance from the normal compact cassette. Moreover, since the reel table 110 has three projections 112 provided equidistantly for each hub on the base 111, the reel hubs 103 can be engaged with the projections, or the projections can be inserted in the cutouts 106 of each of the reel hubs 103, and the reel hubs 122 of the conventional compact cassette B (see Fig. 21) can be engaged with the projections, or the projections can be inserted in the recesses 128. Therefore the S-DAT having this reel table 110 can accept not only the S-DAT tape cassette but also the conventional compact cassette. If the tape stopper of the cassette case within which the tape cassette is placed for the preservation and management is constructed in the same way as the reel table 110, the S-DAT tape cassette and the conventional compact cassette can be separately preserved and managed while being distinguished from each other. Also, if, as shown in Fig. 18, an insertion hole 115 is further provided at the connection portion 107 or at the center of the reel hub 103 where the six poles 105 are connected together, and if, as shown in Fig. 19, a projection 116 to be inserted in the insertion hole 115 is provided at the center of base 111 of each of the reel tables 110, the reel hubs 103 can be more effectively stabilized on the reel tables 110. While three projections 112 are provided on the base 111 of each of the reel tables, a single projection may be provided or two, four, five or six projections may arbitrarily be provided considering the stability of the reel hubs 103 on the reel tables. Since the system of this invention can reproduce the analog and digital recorded magnetic tapes compatibly, it can be applied to a digital tape recorder capable of reproducing the generally used compact cassette, particularly to a portable, pocket-size tape recorder, and has great advantages. Further since the reel hubs of the tape cassette proposed above each have cutouts provided to oppose the engaging projections of each of the normal reel tables having a reel shaft at its center and engaging projections integrally provided around the reel shaft, and blocking portions for blocking the reel shaft from being inserted in the cutouts, this tape cassette can be prevented from being loaded in the normal analog cassette system, so that a recorder of the type which has the compatibility for the digital and analog recording/reproduction (for example, S-DAT) and the other type having no compatibility (the normal analog cassette system) can be selected for this tape cassette without confusion. Moreover, the general user can easily understand the idea of the compatibility.

Claims: Magnetic tape reproducing system having analog/digital compatibility for using a digital magnetic tape (1D) having a plurality of n digital data recording tracks (TD1-TD8) and an analog magnetic tape (1A) having a first and a second analog recording track (TA1,TA2) between which a guard-band (2) of a certain width (WGB) is provided, wherein said system comprises means for reproducing signals from said digital magnetic tape (1D) by means of n magnetic reproducing head elements (h1-h8), respectively corresponding to said n digital data recording tracks (TD1-TD8), said system comprising means for reproducing signals from said analog magnetic tape by means of two sets of m magnetic head elements (h1-h3 and h5-h7) among said n magnetic reproducing head elements (h1-h8) corresponding to said first and second analog recording tracks (TA1, TA2) so that common outputs can be produced from each of said sets of m magnetic head elements. The magnetic tape reproducing system according to claim 1, wherein said magnetic reproducing head elements (h1-h8) are formed of reproducing head elements having magneto-resistance effect magneto-sensitive portions, said system further comprises switching means for applying a high-frequency bias magnetic field to said magneto-sensitive portions when reproduction is made by said magnetic head elements from said analog recorded magnetic tape and for applying a DC bias magnetic field to said magneto-sensitive portions of said magneto-resistance effect head elements when reproduction is made from said digital recorded magnetic tape. The magnetic tape reproducing system in accordance with claim 1, wherein said analog magnetic tape (1A) and the digital magnetic tape (1D) are respectively divided into a first half (1A1, 1D1) and a second half (1A2, 1D2) in their widthwise direction and transported in one direction (a) and in the opposite direction (b) so that each of said first and second halves can be reproduced wherein upon transport in said one direction (a), a recorded area (A) is included on the first half (1A1) of said analog magnetic tape (1A) and on the second half (1D2) of said digital magnetic tape (1D), while upon transport in said opposite direction (b) a recorded area (B) is included on said second half (1A2) of said analog magnetic tape (1A) and on said first half (1D1) of said digital magnetic tape (1D). The magnetic tape reproducing system according to one of the preceding claims, wherein said system uses a tape cassette comprising reel hubs each having cut-outs provided to oppose engaging projections of a reel table that has provided at its centre a reel shaft around which said engaging projections are integrally provided, and blocking portions to block said reel shaft from being inserted in said reel hub.

Inventors: FUJIWARA KEISUKE, FUKUYAMA MUNEKATSU, SEKIYA TETSUO, SEKO SATORU, SODA YUTAKA, YADA HIROAKI, FUJIWARA, KEISUKE, FUKUYAMA, MUNEKATSU, SEKIYA, TETSUO, SEKO, SATORU, SODA, YUTAKA, YADA, HIROAKI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1990
Main classification: G11B5
IPC codes: G11B5, G11B23, G11B15