Abstract:
A magnetic recording apparatus has a magnetic head for writing data to a magnetic disk, a writing circuit for feeding a current to the magnetic head, a controller for controlling the operation of the writing circuit, and a temporary shutoff circuit for shutting off the current temporarily while the operation of the controller is in a transient period. The writing circuit has a first transistor, which is connected to the magnetic head. The temporary shutoff circuit has a second transistor so as to temporarily deactivate and thereafter activate the first transistor when electric power starts being supplied by pulling into the second transistor the transient current resulting from variation in the base voltage of the second transistor as a result of the parasitic capacitor present at the base of the second transistor being charged when electric power starts being supplied.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic recording apparatus such as a floppy disk drive or hard disk drive. 
     2. Description of the Prior Art 
     A conventional magnetic recording apparatus will be described. FIG. 4 is a circuit diagram of the writing circuit of a conventional magnetic recording apparatus. The writing circuit amplifies a write signal, by which data is written to a magnetic disk (not shown) such as a floppy disk or hard disk, so as to feed a write current I 7  or I 8  to a magnetic head  2 . In FIG. 4, the two ends of the magnetic head  2  are connected to output terminals  24  and  25  of the writing circuit. The magnetic head  2  has a center tap, which is connected to a supplied voltage Vcc. The write signal is fed in via two input terminals  40  and  41 . 
     The input terminal  40  is connected to the base of an npn-type transistor Q 11 . The input terminal  41  is connected to the base of an npn-type transistor Q 8 . The collector of the transistor Q 8  is connected to the supplied voltage Vcc. Between the base of the transistor Q 8  and the supplied voltage Vcc, a constant current source circuit  42  is connected. The constant current source circuit  42  outputs a current I 11  that flows from the supplied voltage Vcc to the base of the transistor Q 8 . Between the emitter of the transistor Q 8  and ground, a resistor R 6  is connected. Between the base of the transistor Q 8  and ground, a resistor R 5  is connected. 
     The collector of the transistor Q 11  is connected to the supplied voltage Vcc. Between the base of the transistor Q 11  and the supplied voltage Vcc, a constant current source circuit  43  is connected. The constant current source circuit  43  outputs a current I 12  that flows from the supplied voltage Vcc to the base of the transistor Q 11 . Between the base of the transistor Q 11  and ground, a resistor R 9  is connected. Between the emitter of the transistor Q 11  and ground, a resistor R 8  is connected. 
     The emitter of the transistor Q 8  is connected to the base of an npn-type transistor Q 9 . The emitter of the transistor Q 11  is connected to the base of an npn-type transistor Q 10 . The emitters of the transistors Q 9  and Q 10  are connected together, and, between this node and ground, a constant current source circuit  23  is connected. The constant current source circuit  23  outputs a constant current I 6 . The collector of the transistor Q 9  is connected to the output terminal  24 . The collector of the transistor Q 10  is connected to the output terminal  25 . 
     FIG. 5 is a circuit diagram showing the internal configuration of the constant current source circuit  42 . The emitter of a pnp-type transistor Q 30  is connected through a resistor R 20  to the supplied voltage Vcc. The collector of the transistor Q 30  is connected to a current source  50 . The current source  50  outputs a current I 20 . The base of the transistor Q 30  is connected to the collector of the transistor Q 30  and to the base of a pnp-type transistor Q 31 . Between the bases of the transistors Q 30  and Q 31  and ground, a parasitic capacitance  51  is present. The emitter of the transistor Q 31  is connected through a resistor R 21  to the supplied voltage Vcc. From the collector of the transistor Q 31 , the current I 11  is fed out. 
     This writing circuit is controlled by a controller  7  so as to be either in an active mode in which its data writing operation is permitted or in an inactive mode in which its data writing operation is inhibited. The controller  7  outputs a signal, which is fed to the gates of n-channel MOS transistors Q 13  and Q 14 . The sources of the MOS transistors Q 13  and Q 14  are each connected to ground. The drain of the MOS transistor Q 13  is connected to the input terminal  41 , and the drain of the MOS transistor Q 14  is connected to the input terminal  40 . 
     In the inactive mode, the controller  7  feeds a high-level signal to the writing circuit. This causes the MOS transistors Q 13  and Q 14  to be turned on. As a result, the ground voltage is fed to the bases of the transistors Q 8  and Q 11 , which are thus turned off. As a result, the ground voltage is fed to the bases of the transistors Q 9  and Q 10 , which are thus turned off. Consequently, the writing circuit does not operate as a whole, and thus does not feed the write current  17  nor I 8  to the magnetic head  2 . 
     By contrast, in the active mode, the controller  7  feeds a low-level signal to the writing circuit. This causes the MOS transistors Q 13  and Q 14  to be turned off. Consequently, the writing circuit can feed the write current I 7  or I 8  to the magnetic head  2  in synchronism with the signals fed in via the input terminals  40  and  41 . 
     However, in the circuit shown in FIG. 4, immediately after the supplied voltage Vcc starts being supplied in the magnetic recording apparatus, there is a possibility of a write current being unnecessarily fed to the magnetic head  2  before the entire apparatus becomes ready for writing operation. When electric power starts being supplied, the current source  50  is off, and thus does not output the current I 20 ; however, a current Ic that momentarily flows into the parasitic capacitance  51  induces the base currents of the pnp-type transistors Q 30  and Q 31 , which are thus turned on momentarily, causing the current I 11  to flow momentarily. At this moment, if the controller  7  has not yet been started up completely, it cannot feed a high-level signal to the n-channel MOS transistor Q 13 , and thus cannot make the MOS transistor Q 13  absorb the momentary current I 11  mentioned just above. This causes a momentary rise in the base voltage of the transistor Q 8 , which is thus turned on, causing an unnecessary write current to flow via the output terminal  24 . This is the reason that there is a possibility of the write current I 7  or I 8  being unnecessarily fed to the magnetic head  2 . Permitting such a flow of the write current I 7  or I 8  results in noise being written to the magnetic disk (not shown). Accordingly, in a magnetic recording apparatus, it is desirable in the first place that the flow of a write current such as I 7  or I 8  be inhibited in a transient period such as when electric power has just started being supplied. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a magnetic recording apparatus in which, when electric power has just started being supplied, generation of a write current is inhibited to prevent noise. 
     To achieve the above object, according to the present invention, a magnetic recording apparatus is provided with: a magnetic head for writing data to a magnetic disk; a writing circuit for feeding a write current to the magnetic head; and a temporary shutoff circuit for temporarily deactivating and thereafter activating the writing circuit when electric power starts being supplied. 
     According to this circuit configuration, when electric power starts being supplied, the temporary shutoff circuit suppresses, for example, the bias voltage output from the writing circuit. Thus, it is possible to prevent writing operation from being unnecessarily performed as a result of a transient current flowing through the magnetic head despite absence of data to be written. In this way, it is possible to prevent noise from being written to the magnetic disk before the bias voltage becomes stable after electric power starts being supplied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanying drawings in which: 
     FIG. 1 is a block diagram of the magnetic recording apparatus of a first embodiment of the invention; 
     FIG. 2 is a circuit diagram of the bias circuit and the writing circuit of the magnetic recording apparatus of the first embodiment; 
     FIG. 3 is a circuit diagram of the bias circuit and the writing circuit of the magnetic recording apparatus of a second embodiment of the invention; 
     FIG. 4 is a circuit diagram of the writing circuit of a conventional magnetic recording apparatus; and 
     FIG. 5 is a circuit diagram of the current source circuit employed in the conventional magnetic recording apparatus shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Hereinafter, a first embodiment of the present invention will be described. FIG. 1 is a block diagram of the magnetic recording apparatus of a first embodiment of the invention. A magnetic disk  1  is, for example, a floppy disk. A magnetic head  2  reads the data recorded on the magnetic disk  1 , and writes data to the magnetic disk  1 . 
     A spindle motor  3  is a motor for rotating the magnetic disk  1 . A voice control motor  4  is a motor for adjusting the tracking of the magnetic head  2 . A read/write preamplifier  5  is connected to the magnetic head  2 , and is composed of a reading circuit  11  for amplifying the signal reproduced by the magnetic head  2  and a writing circuit  12  for amplifying a write signal that is going to be fed to the magnetic head  2  to cause data to be written to the magnetic disk  1 . The read/write preamplifier  5  is provided with a bias circuit  26  (see FIG. 2) for feeding a bias current to the writing circuit  12 . 
     A read/write channel circuit  6  performs processing such as error correction on the reproduced signal fed from the read/write preamplifier  5 , and feeds a write signal to the read/write preamplifier  5 . In addition, the read/write channel circuit  6  performs PRML (partial response maximum likelihood) signal processing. 
     A controller  7  is composed of a digital signal processor  13 , a flash memory  14 , and a servo controller  15 . The digital signal processor  13  controls reading and writing operation of the magnetic recording apparatus. The flash memory  14 , which may be omitted in some magnetic recording apparatuses, is provided to allow storage of defective addresses of the magnetic disk  1  under the control of the digital signal processor  13  so as to prevent access to those addresses by the magnetic recording apparatus. 
     The servo controller  15 , by feeding a control signal to a driver  8 , controls the driver  8  automatically in accordance with the settings made in advance by the digital signal processor  13 . The driver  8  has a driver for driving the spindle motor  3  and a driver for driving the voice control motor  4 . The controller  7  is connected through an interface  9  to a personal computer  10 . 
     Next, with reference to FIG. 2, the internal configuration of the writing circuit  12  and the bias circuit  26  provided within the read/write preamplifier  5  will be described. The writing circuit  12  amplifies a signal that is fed in via input terminals  21  and  22 , and feeds a current I 7  or I 8  to the magnetic head  2 , which is connected to output terminals  24  and  25 , to write data to the magnetic disk  1  (see FIG.  1 ). The magnetic head  2  has a center tap, which is connected to a supplied voltage Vcc. To the input terminals  21  and  22 , a write signal is fed from the read/write channel circuit  6 . 
     The bias voltage V B  from the bias circuit  26  is fed to the bases of the npn-type transistors Q 7  and Q 12  provided in the writing circuit  12 . The collectors of the transistors Q 7  and Q 12  are both connected to the supplied voltage Vcc. Between the emitter of the transistor Q 7  and ground, a circuit having resistors R 4  and R 5  connected in series is connected. The node B between the resistors R 4  and R 5  is connected to the input terminal  21  and to the base of an npn-type transistor Q 8 . Between the emitter of the transistor Q 12  and ground, a circuit having resistors R 7  and R 9  connected in series is connected. The node C between the resistors R 7  and R 9  is connected to the input terminal  22  and to the base of an npn-type transistor Q 11 . 
     The collector of the transistor Q 8  is connected to the supplied voltage Vcc. Between the emitter of the transistor Q 8  and ground, a resistor R 6  is connected. The node D between the emitter of the transistor Q 8  and the resistor R 6  is connected to the base of an npn-type transistor Q 9 . The collector of the transistor Q 11  is connected to the supplied voltage Vcc. Between the emitter of the transistor Q 11  and ground, a resistor R 8  is connected. The node E between the emitter of the transistor Q 11  and the resistor R 8  is connected to the base of an npn type transistor Q 10 . 
     The collector of the transistor Q 9  is connected to the output terminal  24 . The collector of the transistor Q 10  is connected to the output terminal  25 . The emitters of the transistors Q 9  and Q 10  are connected together, and, between this node and ground, a constant current source circuit  23  is connected. The constant current source circuit  23  outputs a constant current I 6 . 
     A signal fed from the controller  7  is, within the writing circuit  12 , fed to the gates of two n-channel MOS transistors Q 13  and Q 14 . The drain of the MOS transistor Q 13  is connected to the input terminal  21 . The source of the MOS transistor Q 13  is connected to ground. The drain of the MOS transistor Q 14  is connected to the input terminal  22 . The source of the MOS transistor Q 14  is connected to ground. The transistors Q 9  and Q 10  and the constant current source circuit  23  together constitute a differential amplifier circuit, which amplifies, on a differential basis, the signal fed to the bases of the transistors Q 9  and Q 10 . As a result, the writing circuit  12  feeds the current I 7  or I 8  to the magnetic head  2  connected to the output terminals  24  and  25 . 
     The resistors R 4 , R 5 , and R 6  and the transistor Q 8  together constitute a buffer circuit. This buffer circuit, when activated by the bias voltage V B , amplifies the write signal fed in via the input terminal  21  and then feeds it to the base of the transistor Q 9 , which constitutes a part of the differential amplifier circuit. Similarly, the resistors R 7 , R 8 , and R 9  and the transistor Q 11  together constitute a buffer circuit. This buffer circuit, when activated by the bias voltage V B , amplifies the write signal fed in via the input terminal  22  and then feeds it to the base of the transistor Q 10 , which constitutes a part of the differential amplifier circuit. 
     The controller  7  controls the operation mode of the writing circuit  12 . To bring the writing circuit  12  into an active mode, the controller  7  outputs a low-level signal. As a result, the MOS transistors Q 13  and Q 14  are turned off, and thus the transistors Q 8  and Q 11  are activated. Consequently, the writing circuit  12  amplifies the write signal fed in via the input terminals  21  and  22  to write data to the magnetic disk (see FIG.  1 ). 
     By contrast, to bring the writing circuit  12  into an inactive mode, the controller  7  outputs a high-level signal. As a result, the MOS transistors Q 13  and Q 14  are turned on, and thus the transistors Q 8  and Q 11  are turned off. Consequently, with the transistors Q 9  and Q 10  kept inactive, the writing circuit  12  does not output a write current to the magnetic head  2 . In this way, the controller  7  outputs a high-level signal to turn off the transistors Q 8  to Q 11  and thereby bring the writing circuit  12  into the inactive mode. 
     In the bias circuit  26 , between the emitter of a pnp-type transistor Q 1  and the supplied voltage Vcc, a resistor R 1  is connected. Between the collector of the transistor Q 1  and ground, a current source circuit  20  is connected. The base and collector of the transistor Q 1  are connected together. Between the emitter of a pnp-type transistor Q 2  and the supplied voltage Vcc, a resistor R 2  is connected. The collector of the transistor Q 2  is connected to the collector and base of an npn type transistor Q 4 . The emitter of the transistor Q 4  is connected to ground. The base of the transistor Q 4  is connected to the base of an npn-type transistor Q 5  and to the drain of an n-channel MOS transistor Q. The source of the MOS transistor Q is connected to the ground, and its gate is connected to the controller  7 . The transistors Q 4 , Q 5 , and Q together constitute a temporary shutoff circuit. 
     The bases of the transistors Q 1  and Q 2  and the base of a pnp-type transistor Q 3  are connected together. Between this node and ground, a parasitic capacitance  27  is present due to junction capacitance, wiring capacitance, and the like. Between the emitter of the transistor Q 3  and the supplied voltage Vcc, a resistor R 3  is connected. The collector of the transistor Q 3  is connected to the collector of the npn-type transistor Q 5 . The emitter of the transistor Q 5  is connected to ground. The collector of the transistor Q 3  is connected to the emitter of a pnp-type transistor Q 6 . The base of the transistor Q 6  is connected to a reference voltage V R . The collector of the transistor Q 6  is connected to ground. From the emitter A of the transistor Q 6 , the bias voltage V B  is fed out. 
     When electric power starts being supplied, a current source  20  is off. However, the charging current Ic that momentarily flows into the parasitic capacitance  27  present at the bases of the transistors Q 1 , Q 2 , and Q 3 , which constitute a first current mirror circuit, induces the base currents of these transistors, and thus the transistors Q 1 , Q 2 , and Q 3  are activated momentarily, causing a current I 3  to flow momentarily. However, at this moment, a current I 2  also flows, and thus the pnp-type transistors Q 4  and Q 5 , which constitute a second current mirror circuit, are also activated. As a result, the collector of the transistor Q 5  completely absorbs the current I 3 , and thereby keeps the voltage V B  stably at a low voltage (nearly equal to the ground voltage). Consequently, even if the current I 3  flows, the transistor Q 7  is not activated, nor is the transistor Q 12  activated. Accordingly, irrespective of whether the controller  7  has been started up completely or not, no unnecessary write current flows via the output terminals  24  and  25 . Thus, no noise is written to the magnetic disk  1 . 
     In a while, the current Ic that flows into the parasitic capacitance  27  increases the base voltages of the transistor Q 1  to Q 3 , and thereby decreases the current I 3 , decreasing similarly the current I 2  and also the current I 4 . This makes the transistor Q 5  less conducting, and thus increases the collector-emitter impedance thereof. As a result, the voltage V B  at the point A gradually rises. When this voltage becomes higher than the reference voltage V R  fed to the base of the transistor Q 6  by a voltage V BE  (the base-emitter conducting voltage of the transistor Q 6 ), the transistor Q 6  is turned on, and thus the bias voltage V B  is kept stably at a voltage V R  +V BE . Thereafter, when the controller  7  turns its output to a high level, the terminals  21  and  22  are fixed at a low level, bringing the writing circuit  12  into the inactive mode, and simultaneously the MOS transistor Q stops the operation of the temporary shutoff circuit. 
     In the magnetic recording apparatus of this embodiment, in a transient period as when electric power has just started being supplied, even if the bias circuit  26  starts operating earlier than the controller  7 , the bias voltage V B  is kept at a low voltage (ground voltage), and thus the transistors Q 7  and Q 12  are never turned on transiently. In this way, the bias circuit  26  is configured as a shutoff circuit that shuts off the currents I 7  and I 8  while the operation of the controller  7  is in a transient period, and accordingly no noise is ever written to the magnetic disk  1  in such a transient period. 
     Thereafter, when data is written to the magnetic disk  1 , the controller  7  outputs a low-level signal to bring the writing circuit  12  into the active mode in which its writing operation is permitted. Then, in accordance with the signal fed from the read/write channel circuit  6 , the writing circuit  12  feeds the write current I 7  or I 8  to the magnetic head  2  to write data to the magnetic disk  1 . 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described. FIG. 3 is a circuit diagram showing the internal configuration of the writing circuit  12 ′ of the magnetic recording apparatus of a second embodiment of the invention. In this embodiment, the magnetic recording apparatus as a whole has almost the same configuration as shown in the block diagram of FIG.  1 . Here, in place of the input terminals  21  and  22  shown in FIG. 2, input terminals  30  to  33  are provided. The input terminals  30  and  31  are connected to the bases of npn-type transistors Q 22  and Q 21 . The emitters of the transistors Q 21  and Q 22  are connected to output terminals  35  and  36  and to the collectors of transistors Q 17  and Q 20 , respectively. The collectors of the transistors Q 21  and Q 22  are connected to a supplied voltage Vcc. In this embodiment, the magnetic disk  1  is a hard disk. 
     Moreover, in the second embodiment, the input terminals  32  and  33  correspond to the input terminals  22  and  21 , respectively, of the first embodiment; the transistors Q 15  to Q 17  correspond to the transistors Q 7  to Q 9 , respectively, of the first embodiment; the transistors Q 18  to Q 20  correspond to the transistors Q 12  to Q 10 , respectively, of the first embodiment; the resistors R 10  to R 15  correspond to the resistors R 4  to R 9 , respectively, of the first embodiment. Moreover, the bias circuit  26  has the same configuration as the bias circuit  26  of the first embodiment. 
     In the inactive mode, the controller  7  outputs a high-level signal. This causes MOS transistors Q 13  and Q 14  to be turned on. As a result, the voltages at the bases of the transistors Q 16  and Q 19  turn to a low voltage, and thus the transistors Q 16  and Q 19  are turned off. As a result, the voltages at the bases of the transistors Q 17  and Q 20  turn to a low voltage, and thus the transistors Q 17  and Q 20  are turned off. Now that the transistors Q 17  and Q 20  are off, no current flows through the magnetic head  2 . In this way, when the controller  7  outputs a high-level signal, the writing circuit  12 ′ is brought into an inactive mode, and thus feeds no current to the magnetic head  2 . 
     By contrast, in the active mode, the controller  7  outputs a low-level signal. This causes the MOS transistors Q 13  and Q 14  to be turned off. As a result, the writing circuit  12 ′ feeds a write current I 9  or I 10  to the magnetic head  2  in accordance with the signals fed in via the input terminals  30  to  33 . The write signals fed in via the input terminals  30  and  32 , and the write signals fed in via the input terminals  31  and  33 , are switched in an interlocked and synchronized manner, so that the transistors Q 21  and Q 17  are not turned on simultaneously, nor are the transistors Q 22  and Q 20  turned on simultaneously. 
     In the magnetic recording apparatus of this embodiment, in a transient period as when electric power has just started being supplied, even if the bias circuit  26  starts operating earlier than the controller  7 , the bias circuit  26  keeps the bias voltage V B  at a low voltage until the operation of the controller  7  becomes stable. At this time, the transistors Q 15  and Q 18  are turned off, and thus the  15  voltage at the point B, which is connected to the base of the transistor Q 16 , turns to a low voltage. Similarly, the voltage at the point C, which is connected to the base of the transistor Q 19 , also turns to a low voltage. As a result, the transistors Q 16  and Q 19  are turned off, causing the voltages at both the points D and E at the emitters of the transistors Q 16  and Q 19  to turn to a low level. As a result, the transistors Q 17  and Q 20  are turned off. Thus, the write current I 9  or I 10  does not flow through the magnetic head  2 . 
     In this way, when electric power starts being supplied, even if the supplied voltage Vcc starts being fed to the bias circuit  26  before the controller  7  starts operating, no current flows into the magnetic head  2 , and thus no noise is written to the magnetic disk  1 . Thereafter, when the controller  7  starts operating stably, it outputs a low-level signal to bring the writing circuit  12 ′ into the active mode in which its writing operation is permitted. Then, the writing circuit  12 ′ feeds a current to the magnetic head  2  in accordance with the write signals fed from the read/write channel circuit  6 .