A RECORDING/REPRODUCING SYSTEM FOR A MAGNETIC RECORDING MEDIUM

Abstract: A magnetic disk apparatus has a magnetic head (20) in contact with a flexible magnetic recording medium, for reading out data stored in the recording medium. The magnetic head is of the preceding-erase type. A converting circuit (25 to 27, 30) converts the output signal (SA) of the magnetic head (20) into digital read data (RD), and outputs it to the PLL circuit (32). The magnetic disk apparatus includes a preventing circuit for preventing the converting circuit from outputting to the PLL circuit the digital read data which is corre­ spond read out data from the DC erased areas in the tracks of said magnetic recording medium (21). The preventing circuit comprises an AFG amplifier (24) for amplifying the signal read out of the magnetic head (20), a circuit for obtaining an envelope of the output signal of the AGC amplifier (24), and a circuit for pre­ venting the converting circuit from outputting the read data when the signal level of the envelope is lower than a predetermined value.

Description: This invention relates to a recording/reproducing system used in conjunction with a magnetic disk apparatus which reproduces data. In the field of floppy disk apparatuses, a preceding-erase type magnetic head has recently been devised which is suitable for use with a high-density magnetic recording-medium (disk), cf. Published Unexamined Japanese Patent Application No. 61-39911. In the preceding-erase type magnetic head, an erase head is located in front of a read/write head in the rotational direction of the medium. Before new data are recorded in the medium by the read/write head, previously-recorded data are first erased by the erase head. When this type of magnetic head is employed, the erase head should preferably be turned on at a predetermined time before the recording of data on the medium, by the read/write head, begins, and turned off at a predetermined time before the recording of data ends. However, to be able to perform such a control procedure requires a controller, for turning the heads on and off, which is complicated in its construction. The conventional controller is incapable of performing such a control procedure, and for this reason, the erase head and the read/write head are turned on or off simultaneously. Normally, a track has a format shown in Fig. 1A, i.e. in which one sector comprises an ID field and a data field. The ID field comprises a synchronization area SYNC, an address mark area AM, an identification area ID, and a cyclic redundancy check area CRC. Information representative of the starting position and address of a sector are recorded in the ID field. The data field stores data, and comprises synchronization area SYNC, address mark area AM, data area DATA, and cyclic redundancy check area CRC. Synchronization areas SYNC of the ID field and the data field store synchronization data for a PLL circuit; address mark areas AM store address mark data indicative of the starting position of the ID field or the data field; ID area ID stores data such as the cylinder number, the side number, the sector number, and the length of the data field; data area DATA stores data read out or written in by a user; and cyclic redundancy check areas CRC store data for checking whether or not the data read out from the ID field or from data field contains an error. Gaps 1, 2, 3, and 4 are areas for absorbing a fluctuation of rotation and an error in a mechanical alignment. Read data reproduced from the recording medium by the magnetic head are supplied to a data separator which includes a PLL circuit and an external synchronization detecting circuit. The external synchronization detector detects the synchronization data in the read data, and upon detection of the synchronization data, the PLL circuit begins oscillating in synchronism with the read data and outputs data pulses and clock pulses. When the PLL circuit operates in synchronism with the read data, an internal synchronization detector detects the synchronization data, on the basis of the data pulse and the clock pulse, and a floppy disk controller checks whether or not the following data, other than synchronization data, are address mark data. When the address mark data are detected, the floppy disk controller reads out the data stored in the ID area ID or in data area DATA, on the basis of the data pulses and clock pulses. When data other than the address mark data are detected, the floppy disk controller stops operating for a predetermined time period, and then repeats the above-mentioned operation. Figs. 1B and 1C show the positions where the erase head and read/write head of the preceding-erase type magnetic head are turned on and off, during data are written in the medium. As is shown in Figs. 1A to 1C, DC erased areas are formed in Gap 3, where data are erased by the erase head and new data are not recorded. In such a system, when data identical to the synchronization data are recorded in the data areas, a problem arises in that the external synchronization detection circuit sometimes erroneously detects the synchronization area of the recording medium, with the result that the system may fail to read out the data from the data area. The PLL circuit oscillates at a frequency greatly different from the frequency of normal read data, due to irregular pulses derived from the DC erased area. Consequently, there is the possibility that the PLL circuit will be unable to read out even the normal data. Prior art document EP-A-0 139 757 describes an apparatus for reproducing a data signal from a recording medium on which a digital data signal, which is processed according to run length limited code modulation, is recorded with a synchronizing signal portion. The apparatus is arranged so that the supply of a rectangular-wave reproduction signal from a waveform shaping unit to a reproduction signal processing unit is inhibited when the amplitude of a read signal detected by an amplitude detection unit is lower than a predetermined value, thereby preventing erroneous detection of the synchronizing signal. The apparatus is suitable for the reproduction of a data signal from a digital audio disc and prevents an erroneous detection of the synchronizing signal when there is a defective part on the recording surface of the recording medium. Prior art document EP-A-0 146 636 discloses a synchronizing circuit in which data signals are divided into groups of a predetermined number of bits, each having a synchronizing signal, any desired address signal and an error detection signal for detecting an error of the address signal. The groups of data signals are adapted to be written in a memory device in accordance with the address signals. The synchronizing circuit has means for detecting any error in the address signal, means for detecting the synchronizing signal, an internal synchronizing signal generating circuit and an internal address signal generating circuit. The internal synchronizing signal generating circuit is driven, when the error detecting means judges that the address signal is correct so that an internal synchronizing signal drives the internal address signal generating circuit. The address signal or the internal address signal is selectively supplied to the memory device depending on whether the address signal is correct or wrong. In this way, data blocks syncs are suppressed if a following block address cannot be detected, i.e. if data is misinterpreted as a sync pattern. It is an object of the present invention to provide a high reliability recording/reproducing system using a preceding-erase type magnetic head and in which a digital signal which is reproduced from DC erased areas in tracks of a magnetic recording medium is not output. To achieve the above object, the present invention provides a magnetic recording/reproducing system as stated in claim 1. In the system having the above configuration, the digital signal (RD) which is reproduced from the DC erased areas in the tracks (such as GAP3) is not output. This prevents the PLL circuit means (32) from oscillating at a frequency widely different from the original oscillating frequency, thereby ensuring normal oscillation. With the normal oscillation of the PLL circuit means (32), the data recorded in the magnetic recording medium (21) can be reliably read out. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1A to 1C show the format of the tracks, and the on/off timings of the read/write head and the erase head when data is recorded in data fields; Fig. 2 is a block diagram illustrating a configuration of a first embodiment of a floppy disk apparatus and a data separator circuit; Figs. 3A to 3E are timing charts useful in explaining an operation of the Fig. 1 configuration; Fig. 4 is a block diagram illustrating a configuration of a second embodiment of a floppy disk apparatus according to this invention; and Figs. 5A to 5G are timing charts explaining an operation of the Fig. 4 configuration. Some specific embodiments of a magnetic recording/reproducing system for a magnetic disk apparatus, according to this invention will be described, referring to the accompanying drawings. Fig. 2 is a block diagram illustrating a first embodiment of this invention. In the figure, magnetic head 20 is a magnetic head of the preceding-erase type, which has erase head 20A, read/write head 20B and separator 20C. Separator 20C magnetically separates erase head 20A from read/write head 20B. Erase head 20A is located in front of read/write head 20B with respect to the rotational direction of the medium 21. FDC 33 receives write data WD from a host computer (not shown), and supplies write data WD to write circuit 47. FDC 33 also supplies gate signal GS to write circuit 47 and selector 46. Gate signal GS functions as write gate signal WG, erase gate signal EG and select signal SS. Write gate signal WG and erase gate signal EG are supplied to write circuit 47. Select signal SS is supplied to selector 46. Selector 46 supplies write signal WS to read/write head 20B when select signal SS is H level. Selector 46 supplies output signal of read/write head 20B to preamplifier 22 when select signal SS is L level. The output signal of head 20 is supplied to preamplifier 22. Pre-amplifier 22 amplifies the output signal of magnetic head 20. The output signal of pre-amplifier 22 is supplied to AGC (automatic gain controlled) amplifier 24 via low-pass filter 23. Low-pass filter 23 removes the high-frequency noise of the output signal of pre-amplifier 22. AGC amplifier 24 keeps constant the amplitude of the output signal, and has a control terminal for gain adjustment. Output signal SA of AGC amplifier 24 is supplied to differential amplifier 25. Differential amplifier 25 detects peaks of output signal SA of AGC amplifier 24. The output signal of differential amplifier 25 is supplied to zero cross comparator 26. Zero cross comparator 26 outputs a pulse whose polarity is inverted at each zero cross point of output signal of differential amplifier 25, that is, each peak of the output signal SA of AGC amplifier 24. The output signal of zero cross comparator 26 is supplied to time domain filter 27. Time domain filter 27 removes pulses at abnormal intervals (erroneous pulses) caused by external noises and the like contained in the pulse signal from zero cross comparator 26. Filter 27 then outputs the pulse of normal intervals as the read data pulse. The output signal of time domain filter 27 is input to interface driver 30. Output signal SA of AGC amplifier 24 is also supplied to envelope detection circuit 28. Envelope detection circuit 28 detects signal SA to obtain the envelope of signal SA. Envelope detection circuit 28 outputs detect result SEN (a signal which corresponds to the detected envelope) to the terminal for gain adjustment of AGC amplifier 24. According to the signal level of signal SEN, the gain of AGC circuit 24 is controlled, so that an output signal of a constant amplitude is obtained. The output signal SEN of envelope detection circuit 28 is also supplied to the inverting input terminal of comparator 29. The reference voltage Vr is supplied to the non-inverting input terminal of comparator 29. Comparator 29 supplies signal E to the control terminal of interface driver 30. Signal E is high in level when the output voltage of envelope detection circuit 28 is below the reference voltage Vr. When signal E from comparator 29 is low, interface driver 30 is in an operable state, and supplies the output signal of time domain filter 27 to magnetic record/reproduction system 31 as read data RD. PLL circuit 32 internally includes a voltage controlled oscillator (not shown). PLL circuit 32 operates so that the phase of the output pulses are equal to that of the input pulses. PLL circuit 32 oscillates in synchronism with read data RD. It then separates read data RD into data pulses DP and clock pulses CP. Data pulses DP is a pulse signal which represents the data recorded on the tracks of magnetic recording medium 21. Clock pulses CP is a pulse signal which represents the timing for reading the data. FDC 33 is connected to a host computer (not shown), for example. In response to the command of the host computer, FDD 30 performs the data read-out on the basis of data pulses DP and clock pulses CP. The operation of the system of Fig. 2 will be described. First, the recording operation will be described. The host computer supplies a write command to FDC 33. In response to this command, FDC 33 causes gate signal GS to rise to H level. Gate signal GS functions as write gate signal WG, erase gate signal EG and select signal SS. Write circuit 47 receives signals WG and EG. When write gate signal WG and erase signal EG rise to H level, write circuit 47 generates write signal WS and erase signal ES on the bases of write data WD supplied from hose computer via FDC 33 to write circuit 47. Write circuit 47 supplies write signal WS to selector 46, and erase signal ES to erase head 20B. When select signal SS rises to H level, selector 46 supplied write signal WS, which has been supplied from write circuit, to read/write head 20A. By the above-mentioned operation, the data recorded on medium 21 is erased by erase head 20B, and new data is recorded on medium 21 by the read/write head 20A. Reproducing operation will now be described. FDC 33 causes gate signal GS fall to L level. When gate signal GS falls to L level, write circuit 47 stops generating erase signal ES and write signal WS. When write signal WS is not supplied to read/write head 20A, read/write head 20A reads the data recorded on medium 21, and outputs a signal corresponding to this data. When gate signal GS falls to L level, selector 46 supplies the output signal of read/write head 20A to preamplifier 22. Each track of magnetic recording medium 21 also has a format shown in Fig. 1A. The on/off timings of the erase head and the read/write head when the data is recorded, are same as Figs. 1B and 1C. When magnetic head 20 reads the data in the areas of the tracks on which data has been recorded, such as areas CRC, the output signal of magnetic head 20 is supplied to AGC amplifier 24 via pre-amplifier 22 and low-pass filter 23. AGC amplifier 24 outputs signal SA of a constant amplitude, as shown in Fig. 3B. The output signal of AGC amplifier 24 is differentiated by differential amplifier 25. The differential signal is input to zero cross comparator 26. Differential output signal SA of AGC amplifier 24 is converted into a pulse signal by zero cross comparator 26. The pulse signal is input to interface driver 30 as read data pulse signal, after its abnormal pulses are removed by time domain filter 27. Envelope detection circuit 28 detects the envelope of output signal SA of AGC amplifier 24, and output signal SEN (which corresponds to the envelope), as shown in Fig. 3C. On the basis of the signal level of signal SEN, the amplification of AGC amplifier 24 changes, so that output signal SA of a consant amplitude is obtained. Comparator 29 receives signal SEN, and outputs low-level signal E, because the voltage level of signal SEN is larger than the reference voltage Vr (Fig. 3D). Vr is set to such a level that, in the normal state, the voltage level of signal SEN is larger than the reference voltage. Upon receipt of low-level signal E, interface driver 30 supplies the read data pulse from time domain filter 27 to magnetic record/reproduction system 31. The PLL circuit 32 of magnetic record/reproduction system 31 oscillates in synchronism with read data RD, and separates read data RD into data pulse DP and clock pulse CP. On the basis of data pulses DP and clock pulses CP, FDC 33 performs the data read-out. When magnetic head 20 advances to the DC erased areas (GAP3) on the track of magnetic recording medium 21, the amplitude of the output signal of pre-amplifier 22 is substantially zero. The amplitude of output signal SA of AGC amplifier 24 is also substantially zero, as shown in Fig. 3B. The output of time domain filter 27 is instable. Signal SEN is at zero level, which is below the reference voltage level Vr, as shown in Fig. 3C. Comparator 29 outputs high-level signal E. Upon receipt of low-level signal E, interface driver 30 is in a high output impedance state, and does not input read data RD. PLL circuit 32 oscillates, while keeping the oscillating frequency up to this point. When magnetic head 20 moves out of the DC erased area, and reads the data recorded area (SYNC), again, AGC amplifier 24 outputs signal SA of a predetermined amplitude, as shown in Fig. 3B. Signal SEN exceeds the reference voltage level Vr, and the output signal of comparator 29 becomes low in level. Interface driver 30 transfers the read data pulse from time domain filter 27 to record/reproduction circuit 31 (Fig. 3E). In this embodiment, when magnetic head 20 reads the DC erased areas in the tracks, as shown in Fig, 3E, read data RD is not output from interface driver 30. This prevents the instable read data (whose period, amplitude and the like are irregular) from the data erased areas (a high frequency pulse, for example) from being supplied to PLL circuit and so on. Therefore, the sync frequency of PLL circuit 32 is not varied by the instable read data RD read out from the erased area, and PLL circuit 32 always operates in synchronism with the normal read data RD. This ensures the stable operation of PLL circuit 32 used in the data separator, even when the track contains the data erased areas. Next, a second embodiment of an FDP of this invention will be described, referring to Fig. 4. The most of portions of the Fig. 4 configuration are the same as those of the Fig. 2 configuration. Therefore, only the features of the second embodiment will be described. The structural features of the Fig. 4 FDP, as compared with the Fig. 2 FDP, are: (1) Selector 41 is provided instead of interface driver 30; (2) Oscillator 42 and frequency divider 43 are additionally used; (3) Buffer 44 is additionally used; and (4) The polarities of the input terminal of comparator 29 are opposite to those of the comparator 29 in the first embodiment. Selector 41 receives the output of time domain filter 27 at input terminal A, and the output signal of frequency divider 43, at input terminal B. Selector 41 receives the output signal E of comparator 29 at the select control terminal SEL. When supplied with high-level signal E from comparator 29, separator 29 selects read data pulse RP from time domain filter 27, and outputs the pulse RP to buffer 44. When signal E is low, selector 41 selects the clock signal from frequency divider 43, and outputs the clock signal to buffer 44. For oscillator 42, a system clock generating circuit used in the controller of a floppy disk apparatus may be used, for example. Frequency divider 44 frequency divides the clock signal from oscillator 42, and outputs a clock at a frequency corresponding to the transfer rate of the normal read data RD. The operation of the second embodiment of Fig. 4 will be described, referring to Figs. 5A to 5G. When magnetic head 20 reads the not DC erased area in the tracks, AGC amplifier 24 outputs signal SA of a predetermined amplitude (Fig. 5B). Signal SEN is in level above the reference level Vr (Fig. 5C), and output signal E of comparator 29 is high in level. Upon receipt of high-level signal E, selector 41 selects the output signal RP of time domain filter 27 (Fig. 5E) and outputs signal RD. Output data RD of selector 41 is supplied to magnetic record/reproduction system 31 via buffer 44. When magnetic head 20 starts reading the DC erased areas in the tracks, the amplitude of output signal SA of AGC amplifier 24 becomes small (Fig. 5B), and time domain filter 27 stops outputting pulses (Fig. 5E). Signal SEN is also below the reference level Vr (Fig. 5C), and signal E becomes low in level (Fig. 5D). Upon receipt of low-level signal E, selector 41 outputs clock SD from frequency divider 43 as read data RD. As shown in Fig. 5F, the clock SD from frequency divider 43 is a pulse signal at a frequency corresponding to the transfer rate of the normal read data RD. PLL circuit 32 (not shown in Fig. 4) in the data separator oscillates in synchronism with the input data, in the same manner as when normal read data RD is supplied. As seen from the foregoing, according to this invention, in a magnetic disk apparatus using a magnetic head of the preceding-erase type, the read data reproduced from the DC erased areas of the magnetic recording medium is prevented from being supplied to the magnetic record/reproduction system. This prevents the PLL circuit of the magnetic record/reproduction system from oscillating in synchronism with the signal with instable period that is reproduced from the data erased area, and therefore, from operating erroneously or instably. The read data with a high reliability can be obtained. Circuit configuration of this invention is not limited to those of Figs. 2 and 4. Other circuit configuration can be selected. And also, FDC 33 may be provided in a magnetic disk apparatus or outside of the apparatus.

Claims: A magnetic recording/reproducing system for a magnetic disk apparatus, comprising: head means (20, 22-24) having a preceding-erase type magnetic head (20) in contact with a flexible magnetic recording medium (21), for reading out data stored in said recording medium (21), and for outputting an analog signal corresponding to the read out data; and converting means (25-27) for converting the output signal of said head means (20, 22-24) to digital read data and outputting the digital read data; characterized by further comprising preventing means (28-30) for preventing said converting means (25-27) from outputting said digital read data which corresponds to read out data from DC erased areas in tracks of said magnetic recording medium (21). A system according to claim 1, wherein said preventing means (28-30) includes amplitude-detecting means (28) for detecting the amplitude of the output signal from said head means (20), means (29) for comparing the amplitude detected by said amplitude-detecting means (28) with a predetermined reference level, and means (30) for preventing the signal of said converting means (25-27) from being output when said amplitude is lower than said predetermined reference level. A system according to claim 2, wherein said magnetic head means (20, 22-24) includes an automatic gain control amplifier (24) for amplifying the output signal of said magnetic head (20), said amplitude-detecting means (28) includes means for obtaining the envelope of the output signal of said gain control amplifier (24), and said comparing means (29) includes means for comparing means for comparing said envelope and said reference signal. A system according to claim 1, wherein said preventing means (28-30) includes means (28) for detecting an envelope of the output signal of said head means (20, 22-24), means (29) for comparing the envelope detected by said envelope-detecting means (28) with a predetermined reference level and means (30) for preventing the signal of said converting means (25-27) from being output when the signal level of the detected envelope is lower than said predetermined reference level. A system according to claim 1, further comprising means (42, 43) for outputting a clock signal at a predetermined frequency, and in which said preventing means (28, 29, 41) selects and outputs said clock signal when said preventing means (28, 29, 41) prevents the output of said read data. A system according to claim 1, wherein said converting means (25-27) supplies said digital read data to a PLL circuit (32) of a data separator. A system according to claim 1, wherein the preventing means (28-30) includes DC-erased area detecting means (28, 29) for detecting a signal reproduced from the DC-erased areas, and preventing means (30) prevents said converting means (25-27) from outputting the digital read data in response to such detection by the DC-erased area detecting means (28, 29). A system according to claim 1, wherein said head means includes analog signal-outputting means (22, 23, 24) for outputting a read signal of analog type corresponding to recorded data read out by said magnetic head (20) from the magnetic recording medium (21). A system according to claim 1, wherein said preventing means (28-30) has amplitude-detecting means (28) for detecting the amplitude of output signal from said head means (20), means (29) for comparing the amplitude detected by the amplitude-detecting means (28) with a predetermined reference value, and means (30) for preventing said converting means (25-27) from outputting the digital read data to a PLL circuit (32) when the amplitude is less than the predetermined reference value. A system according to claim 1, wherein said preventing means (30) includes envelope-detecting means (28) for generating an envelope signal of the signal from said magnetic head means (20, 22-24), means (29) for comparing the envelope signal with a predetermined reference value, and means (30) for preventing said converting means (25-27) from outputting the digital read data to a PLL circuit when the amplitude of the envelope signal is less than the predetermined reference value.

Inventors: SUZUKI, HIROSHI C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1987
Main classification: G11B5
IPC codes: G11B20, G11B5