THIN-FILM MAGNETIC HEAD

Abstract: One of the preferred embodiments of the present invention provides a thin-film magnetic-head assembly for a digital-signal recording/reproducing system using multiple tracks comprising: electronic-circuit components including a combined capacitor (25)/resistor (27), a constant-current source (31), an amplifier (30), and an analogue-signal multiplexer (30), all located inside a casing (18, 19) that surrounds the thin-film magnetic-head (21). While those electronic circuits present on the upper and lower surfaces of the casing are connected by means of an elastomer (28) so that these circuits are integrally connected to the thin-film magnetic head. Reflecting the preferred format, the thin-film magnetic head of the casing is bent and extended so that electronic-­ circuit components can be mounted to it.

Description: The present invention relates to an improved thin-film magnetic head device, and more specifically to a thin-film magnetic head of the type which reproduces digitally recorded signals from magnetic tape. Conventional pulse code modulation (PCM) devices used to reproduce pulse-coded modulation signals recorded on multiple tracks require many electronic-circuit components in the periphery of the magnetic head assembly unit. Fig. 1 shows a typical example of a conventional device used to reproduce PCM signals recorded on multiple tracks. The PCM signals recorded on magnetic tape 1 are reproduced by the playback head 2, and are then amplified to the needed level by amplifier circuit 3. The amplified PCM signals are then subjected to waveform equalization by the waveform equalizer circuit 4 after which they are sent to level detection circuit 5 and then converted into digital pulse signals by decoding circuit 6. This digital information is then input to the digital signal processing circuit 7, where it is demodulated and subjected to phase correction. These demodulated signals are then converted to analogue signals by D/A converter 8 and output at audio signal output terminal 9. Thus, in the device shown in Fig. 1, it is necessary to have a number of circuits following amplifier circuit 3 which corresponds with the number of tracks present in the tape. Taking this into account, one device of the prior art proposed a circuit format in which a number of circuits are inserted between tracks so that the number of circuits can be reduced to a minimum. Fig. 2 represents a typical circuit configuration found in one apparatus of the prior art. Fig. 2 is a block diagram of circuits in the periphery of the magnetic reproducing head used to execute a time-sharing process. In this process, constant-current source 10 delivers constant current to the yoke-type magnetic resistor (YMR) 11 (in this case the reproducing thin-film magnetic head itself), and as a result, a specific voltage signal is generated by the varied magnetic resistance. A high-pass filter composed of capacitor 12 and resistor 13 filters out the DC components, and the resultant AC signal is then amplified by amplifier circuit 3. These AC signals, reproduced and amplified by multiple tracks, are then selected in sequence by analogue multiplexer 14, and converted again into digital signals by A/D converter 15. These digitalized signals are then processed by digital waveform equalizer circuit 16 to eventually generate signal 17. Nevertheless, as shown in Fig. 2, even when the time-sharing process is executed, the conventional configuration must still include those circuits arranged between the yoke-type magnetic resistor (yoke-type magnetic head) 11 and the signal switching circuit 14; in other words, circuits corresponding in number to the number of tracks. Conventionally, those circuits beyond the constant-current source 10 and capacitor 12 are located outside the casing of the magnetic head 11 (YMR), and these circuits are connected to each other by means of wires or a flexible printed circuit board (hereinafter called FPC). The resulting high number of circuit wires degrades the quality of the signals due to the number of tracks, with an extremely minimal level of output signal, and a poor signal-to-noise (S/N) ratio. A high date error rate results, hampering adeqate use. Fig. 3 is a sectional view of a conventional magnetic head assembly. In Fig. 3, a yoke-type magnetic resistance is generated inside ferrite substrate 21 and protection glass 20. To strengthen protection and increase magnetic shielding, the magnetic heads are mounted inside metal casings 18 and 19. Connection between the magnetic heads and the external reproducing circuits is achieved by bonding the flexible printed circuit board 23 with metal casing 19. The magnetic head and flexible printed circuit board 23 are connected by wire bond or other form of wire 22. The magnetic heads are connected in turn to external circuits by means of the flexible printed circuit board. Space inside metal casings 18 and 19 is filled with molded resin 32. The conventional head-installation method described above could potentially generate many errors due to low output signals and a poor S/N ratio for all data. This unwanted phenomenon as mentioned earlier, increases in proportion to the number of tracks in the tape, thus resulting in critical problems in actual use. FR-A-2443733 describes an integrated, multi-track, magnetic reading head which is produced by semiconductor integration processes. It comprises a system of magneto-electric transducers, each fulfilling the function of an elementary head and associated circuitry. DE-A-3150322 relates to a multiple magnetic head device suitable for recording video signals. The head unit is formed by masking and etching techniques resulting in a series of equally spaced ridges, each of which is provided with an electrical terminal. The invention aims to overcome, at least in part, see of the disadvantages outlined above in relation to the prior art. According to the invention there is provided a multi-track head assembly comprising; a shield casing; and a thin film magnetic head having a plurality of head elements mounted in the casing; characterised by a plurality of circuits disposed in the casing, one for each head element, wherein each circuit comprises a capacitance mounted on a first substrate and a resistance mounted on a second substrate, each said capacitance and its respective resistance being interconnected by an electrically conductive elastomer. In a preferred embodiment of the present invention a thin-film magnetic-head assembly is provided for a digital recording/reproducing device using multiple tracks. The preferred device is comprised of the following: various electronic-circuit components including a combined capacitor/resistor, a constant-current source, a reproduced-signal amplifier, and an analogue multiplex. All are located inside a casing surrounding the thin-film magnetic head(s), and respective components of each circuit on the upper and lower surfaces of said casing are connected to each other by means of an elastomer. These circuits are thereby integrally connected to said thin-film magnetic head(s). In order that the present invention may be better understood a detailed description will be given of an embodiment thereof, by way of example, and with reference to accompanying drawings wherein: Fig. 1 is a block diagram of a multi-track PCM-signal reproducing circuit representing an example of the prior art; Fig. 2 is a block diagram of a prior art magnetic head used for reproducing PCM-signals combined with peripheral circuits, a configuration suited for executing time-sharing process; Fig. 3 is a sectional view of another prior art PCM-signal reproducing head assembly; Fig. 4 is an enlarged sectional view of a multi-track head assembly according to the present invention; Fig. 5 is a perspective view of a multi-track head assembly shown in Fig. 4; Fig. 6 is a front view of the multi-track head assembly shown in Fig. 4; and Fig. 7 is an enlarged sectional view of a second multi-track head assembly according to the invention. As shown in Figure 4, the multi-track head assembly is installed in a position opposite magnetic tape 1. Upper and lower surfaces 18 and 19 of the metal casing and the yoke-type magnetic resistance element (YMR) protection glass 20 are mounted on the ferrite substrate 21. In addition, the thin-film magnetic-head assembly is also provided with: fine wire (e.g. wire bond) 22, substrates made of either ceramic or other hard material 24 and 26, capacitor 25, resistor 27, elastomer 28, flexible printed circuit board (FPC) 29, amplifier combined with an analogue-signal multiplexer IC circuit 30, constant current source, and the molded resin 32 which fills all remaining space in the metal. Upper and lower surfaces 18 and 19 of the metal casing are provided with either ceramic or hard material substrates 24 and 26, respectively. A number of monolithic capacitors (or thin-film capacitors) 25 are installed on the upper substrate 24, whereas a number of chip resistors (or thick-film resistors) 27 are installed on the lower substrate 26. Each capacitor 25 on substrate 24 and its respective resistance 27 on substrate 26 are electrically connected to each other via an elastomer 28. One end of the flexible printed circuit board 29 is connected to substrate 26, while the other end provides external connection through metal casing 19. To improve the S/N ratio, the circuit 30 comprising an amplifier and an analogue multiplexer IC is installed on flexible printed circuit board 29 inside the metal casing 19. Considering the complexity of wiring, the constant current source 31 is also installed on the flexible printed circuit board 29, and the inner space of said metal casing 19 is entirely filled with molded resin 32 to simplify the wiring. Fig. 5 is the external view of the thin-film magnetic-head assembly shown in Fig. 4. To ensure precise connection between elastomer 28 and each capacitor/resistor pair, the metal casings 18 and 19 are securely supported by holders 33. The flexible printed circuit board 29 is connected to the A/D converter of the external circuit and to the power source. Fig. 7 is an enlarged view of a thin-film magnetic-head assembly of a preferred embodiment of the present invention. It shows an FPC of similar configuration to that shown in Fig. 4 but with the bottom surface 34 of the metal casing bent in an "L" shape. Flexible printed circuit board 29 exits the metal casing at the bottom on the metal casing. The IC circuit 30 covered by molded resin 32 and the constant current source 31 are located on FPC 29. Considering the movement of the thin-film magnetic head in the direction of the magnetic tape 1, the bent-and-extended bottom surface of the metal casing 34 has an advantageous depth, being shorter than that of the metal casing shown in Fig. 4. This provides a significant advantage in actual use. In addition, since the FPC 29 is in a position perpendicular to the magnetic head, it can be connected to external circuits very easily. The provision of various electronic-circuit components including a combined capacitor/resistor pair; a signal amplifier; an analogue-signal multiplexer; and a constant-current source, located either inside the metal casing as part of the thin-film magnetic-head or on the flexible printed circuit board of the metal casing, results in following advantages: 1. Since even a minimal signal output from the magnetic head can be fed to the amplifier over the shortest possible distance, a satisfactory S/N ratio is ensured, thus allowing the system to generate noise-free large-magnitude analogue signals before output. 2. Conventionally, use of multi-track tape requires a large number of wires which generate noise; in addition, wire distribution becomes difficult due to the greater sizes of wire bundles. A multi-track head assembly in accordance with the present invention provides easier wire handling since multi-tracks can be contained in a signal line, and the provision of an analog-signal multiplex in the signal line, and the provision of an analogue-signal multiplex in the signal processing system, ensures high signal-to-noise ratio. 3. The multi-track head assembly of the present invention uses multi-tracks in the casing, as shown in Fig. 5, yet a minimum number of wires exiting flexible printed circuit board 29 are required, still ensuring output of a large-magnitude signal. This allows the operator to easily handle the magnetic head. 4. Since part of the head assembly can be bent as shown in Fig. 7, operators can easily install the magnetic head assembly in the limited space available. Note that the A/D converter may also be installed on the head assembly if there is available space inside the head casing. If this method is applied, the FPC 29 outputs only digital signals. Application of alloy material featuring high magnetic permeability (e.g. "permalloy" (Ni-Fe 79% an alloy) in the metal casing effectively shields magnetism. As is clear from the above description, according to the preferred embodiments of the present invention, this digital-signal recording and reproducing device dealing with multi-track signals does not require a number of circuit-wires for distribution purposes. As a result, the signal quality can be satisfactorily maintained without any degradation, drastically minimizing data signal errors.

Claims: A multi-track head assembly comprising; a shield casing; (18,19) and a thin film magnetic head having a plurality of head elements (20,21) mounted in the casing; characterised by a plurality of circuits disposed in the casing, one for each head element, wherein each circuit comprises a capacitance (25) mounted on a first substrate (24) and a resistance (27) mounted on a second substrate (26), each said capacitance and its respective resistance being interconnected by an electrically conductive elastomer (28). An assembly according to claim 1 wherein a plurality of amplifiers (30) are disposed in the casing, one for each head element. An assembly according to claim 1 or 2 wherein a plurality of constant current regulators are provided in the casing, one for each head element. An assembly according to any preceding claim wherein a multiplexer is provided in the casing, common to all the head elements. An assembly according to claim 1 wherein the casing has an extended wall portion (34) on which are mounted a plurality of amplifiers (30), one for each head element. An assembly according to claim 5, wherein a multiplexer is provided on the extended wall portion, common to all the head elements. An assembly according to any preceding claim wherein the resistances and/or the capacitances and/or the amplifiers and/or the multiplexer are integrated. An assembly according to any of claims 5 to 7 wherein said extended wall portion is bent. An assembly according to any preceding claim wherein said shield casing is a metal casing. An assembly according to any preceding claim wherein said thin-film magnetic head includes a yoke-type magnetic resistance element.

Inventors: KOYANAGI, KATUBUMI, YAMAOKA, HIDEYOSHI, YASUDA, SYUHEI
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1985
Main classification: G11B5
IPC codes: G11B5, G11B20