JP3917130B2 - Magnetic disk unit - Google Patents

Description

  The present invention relates to a magnetic disk apparatus using a magnetoresistive effect (MR, GMR) type magnetic head, and more particularly to a magnetic disk apparatus having a signal reproducing amplifier circuit and a reproducing head abnormality detector.

  FIG. 7 shows a schematic configuration diagram of a conventional magnetic disk device. In FIG. 7, 2 is a current source, 4 is an amplifier, 6 is a voltage source, and 9 is a reproducing head. A current source 2 having one end connected to a power source for supplying a bias current to the reproducing head 9 is connected to the reproducing head terminal side, and one end of a capacitor C2 for DC cut is connected to the reproducing head terminal side. 9 is connected to one end of the capacitor C3 in consideration of the balance of the input of the amplifier 4, and a resistor R1 and a resistor R2 are connected in series between the capacitor C2 and the other end of the capacitor C3, and the resistor R1 and the resistor R2 are connected. A voltage source 6 for applying a bias voltage is connected to the point.

  The connection point between the capacitor C2 and the resistor R1 is connected to one input terminal of the amplifier 4, the other input terminal of the amplifier 4 is connected to the connection point between the capacitor C3 and the resistor R2, and the signal amplified by the amplifier 4 is amplified. Is output to the output terminal.

  The operation of the magnetic disk apparatus in the conventional configuration shown in FIG. 7 will be described below. A reproduction signal input from the reproducing head 9 is input to one input terminal of the amplifier 4 through a high-pass filter composed of a capacitor C2 and a resistor R1 on the reproducing head terminal side, and the DC level is a voltage given by the voltage source 6. As a reference level, the AC signal input from the reproducing head 9 is input to the amplifier 4. Further, in order to balance the ground side of the reproducing head 9, the same structure as that of the reproducing head terminal side is used, and the signal is inputted to the other input terminal of the amplifier 4 through a high-pass filter composed of a capacitor C3 and a resistor R2. Since it is a side input, it becomes a DC level and the bias voltage is determined by the voltage applied by the voltage source 6.

  However, in the magnetic disk drive having such a configuration, although there is an advantage that it does not depend on the DC level of the read head terminal voltage, the time constant that is the frequency characteristic of the high-pass filter including the capacitor C2 and the resistor R1 must be lowered. In other words, the value of the capacitor is very large, and the integrated circuit requires a very large area. In particular, the number of channels is the same as the number of channels, so that there is a problem that the chip area becomes very large.

  The present invention is directed to solving the problems of the prior art, and further provides a magnetic disk device capable of detecting an abnormality in the reproducing head and speeding up the operation recovery time by changing the mode. For the purpose.

To this end, a magnetic disk device according to claim 1 according to the present invention, first the order one end which gives a bias current to the read head is a magnetoresistive head is connected to a power source Of the current source, the first and second diodes connected in series for level shifting of the reproducing head terminal voltage between the reproducing head terminal and the current source, and one of the connection points between the current source and the first diode . An amplifier for amplifying an output signal from the reproducing head to which the input terminal is connected, one input terminal is connected between the current source and the first diode, and the voltage level of the other input terminal, output terminal and reproducing head terminal To connect the other input terminal of the amplifier, a capacitor having the other terminal connected to the output terminal of the gm amplifier grounded, and the other terminal grounded to determine the gm value connected to the gm amplifier. The second Current source, a third current source having the other end connected to the connection point between the gm amplifier and the second current source via the first switch, and the first current source and the first diode comprising a second switch for performing on / off control by the mode control signal, and a pulse generator for turning on / off controls the first switch to generate the mode switching pulse from the mode control signal between a reproducing head A pulse generator that shifts a DC level by a diode connected in series between a terminal and a current source for a bias current to secure an input dynamic range of the amplifier, and further changes the gm amplifier for a certain time when the mode is switched, and a gm amplifier The current source and the first switch are connected to each other to achieve a faster circuit recovery time when changing from standby mode to playback mode such as low power consumption. It can be obtained fast recovery time of the circuit operation during mode switching from the standby mode to reduce the Chikaraka.

The magnetic disk device according to claim 2 is the magnetic disk device according to claim 1 , wherein the other input terminal and the output terminal of the gm amplifier are connected to the other input terminal of the amplifier. And a third switch for connecting a voltage source grounded at the other end for applying an arbitrary voltage assumed in advance in the standby mode, and performing on / off control of the third switch by the mode control signal, characterized by obtaining a fast recovery time of the circuit operation during mode switching from the standby mode to reduce power consumption, the third for fixing the stand-by mode the reference side input of the amplifier to a voltage level which is assumed after recovery A switch and a voltage source can be applied to the other input terminal (reference side) of the amplifier to reduce the amount of change on the reference side when the mode changes from the standby mode, thereby further increasing the recovery time of the circuit operation.

As described above, according to the present invention, the voltage (DC level) of the reproducing head terminal is fed back to the reference side (the other input terminal) of the amplifier using the gm amplifier and the capacitor, and further from the standby mode or the like. an effect that wear gm value of the gm amplifier when the mode switching in speeding recovery time of the circuit operation by changing just any time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a magnetic disk device according to Embodiment 1 of the present invention. In FIG. 1, 11 is a reproducing amplifier unit, 12 is a current source, 13 is an abnormality detector, 14 is a comparator, 15 is a diode, 16 is a voltage source, 17 is an amplifier, 18 is a gm amplifier, 19 is a reproducing head, and C1. Is a capacitor that is one of the factors that determine the response of the amplifier.

  In the magnetic disk apparatus shown in FIG. 1, a current source 12 having one end connected to a power source for applying a bias current to the reproducing head 19 is connected to a reproducing head terminal, and the reproducing head terminal includes a reproducing head abnormality detector 13; One input terminal of the amplifier 17 and one input terminal of the gm amplifier 18 intended to amplify the output signal from the reproducing head 19 are connected.

  The other input terminal of the amplifier 17 is connected to the other input terminal of the gm amplifier 18 and the output terminal of the gm amplifier 18 for the purpose of feeding back the voltage level of the reproducing head terminal to the other input terminal of the amplifier 17. The end of the capacitor C1 is connected to one end of the grounded capacitor C1.

  The operation of the reproducing amplifier unit in the magnetic disk apparatus of the first embodiment configured as described above will be described below. A bias current from the current source 12 flows to the reproducing head 19 and at the same time, a signal read by the reproducing head 19 is voltage-inputted to the reproducing head terminal. The reproduction signal is amplified by the amplifier 17, but the reference side voltage of the amplifier 17 is determined by a DC feedback circuit composed of the gm amplifier 18 and the capacitor C1, and feedback is automatically applied to match the DC level of the reproduction head voltage. The

  The gm amplifier 18 compares the voltage difference between the two input terminals of the amplifier 17 and charges and discharges the capacitor C1 according to the level, thereby realizing DC feedback, but the response is the gm value of the gm amplifier 18 and the capacitor. It is determined by the capacitance value of C1, and is a Low Pass Filter (hereinafter referred to as LPF) and an integrator. Thus, the reference side voltage of the amplifier 17 is determined according to the reproducing head terminal voltage, and the signal is amplified.

The operation of the abnormality detector for the reproducing head of the magnetic disk apparatus shown in FIG. 1 will be described below. As shown in FIG. 1, a reproducing head abnormality detector 13 connected to a reproducing head terminal to which a current source 12 for applying a bias current to the reproducing head 19 is connected includes a diode 15, a voltage source 16 and a comparator 14. Composed. The reproducing head terminal is connected to a diode 15 whose cathode is grounded and one input terminal of a comparator 14 , and a voltage source 16 having an arbitrary voltage level is connected to the other input terminal of the comparator 14 .

  The bias current Ibias from the current source 12 normally flows to the reproducing head 19 and the voltage Vhead at the reproducing head terminal becomes (Equation 1) when the resistance value of the reproducing head 19 is Rmr.

一般的にはダイオード電圧を超えるほどの電圧にはならない。再生ヘッド１９が何らかの異常で開放状態となったとき、電流Ｉbiasはダイオード１５に流れ再生ヘッド端子の電圧はダイオード電圧となる。もし再生ヘッド端子の電圧が通常時でもダイオード電圧を超えるようであればダイオード１５をもうひとつ直列接続する必要がある。この再生ヘッド端子の電圧を任意の電圧源１６の電圧Ｖthとコンパレータ１４により比較することで、再生ヘッド１９の異常である開放状態を検出することが可能であり異常という情報を伝達することができる。

In general, the voltage does not exceed the diode voltage. When the reproducing head 19 is opened due to some abnormality, the current Ibias flows to the diode 15 and the voltage at the reproducing head terminal becomes the diode voltage. If the voltage of the reproducing head terminal exceeds the diode voltage even at normal time, another diode 15 must be connected in series. By comparing the voltage of the reproducing head terminal with the voltage Vth of an arbitrary voltage source 16 by the comparator 14, it is possible to detect an open state which is an abnormality of the reproducing head 19, and to transmit information indicating abnormality. .

  FIG. 2 is a diagram showing a schematic configuration of the magnetic disk device according to the second embodiment of the present invention. In FIG. 2, 11 is a reproduction amplifier unit, 12 is a current source, 13 is an abnormality detector, 14 is a comparator, 15 is a diode, 16 is a voltage source, 17 is an amplifier, 18 is a gm amplifier, 19 is a reproduction head, and C1. Is a capacitor that is one of the factors that determine the response of the amplifier.

  The magnetic disk apparatus shown in FIG. 2 is a diode for the purpose of level shift of the voltage of the reproducing head terminal between the current source 12 having one end connected to a power source for supplying a bias current to the reproducing head 19 and the reproducing head terminal. 21 and a diode 22 are connected in series, and one input terminal of an amplifier 17 and one input terminal of a gm amplifier 18 for amplifying an output signal from the reproducing head 19 at a connection point between the current source 12 and the diode 21. Is connected, the other input terminal of the amplifier 17 is connected to the other input terminal and the output terminal of the gm amplifier 18, and is further connected to the capacitor C1.

  The operation of the reproducing amplifier section of the magnetic disk device according to the second embodiment configured as described above will be described below. A bias current from the current source 12 flows to the reproducing head 19 through two series-connected diodes 21 and 22, and at the same time, a signal read by the reproducing head 19 is voltage-inputted to the reproducing head terminal. Since this reproduced signal is a signal having a low DC level, it may be very difficult to configure a circuit as in the first embodiment from the viewpoint of circuit saturation.

  Therefore, the reproduction signal level-shifted by the two diodes 21 and 22 connected in series is input to the amplifier 17 and amplified for the purpose of shifting the DC level to a level that facilitates circuit design. The reference side voltage of the amplifier 17 is determined by a DC feedback circuit constituted by the gm amplifier 18 and the capacitor C1, and feedback is automatically adjusted so as to be equal to the DC level of the voltage of the reproducing head 19. The gm amplifier 18 compares the voltage difference between the two input terminals of the amplifier 17 and performs DC feedback by charging / discharging the capacitor C1 according to the level, but the responsiveness is the same as the gm value of the gm amplifier 18. This configuration is determined by the capacitance value of the capacitor C1, and this configuration is an LPF and an integrator.

  As described above, the two stages of diodes 21 and 22 connected in series are not intended for voltage clamping but are intended for level shifting. The signal is amplified depending on the voltage.

  FIG. 3 is a diagram showing a schematic configuration of the magnetic disk device according to the third embodiment of the present invention. In FIG. 3, 11 is a reproduction amplifier unit, 12, 23 and 24 are current sources, 13 is an anomaly detector, 14 is a comparator, 15 is a diode, 16 is a voltage source, 17 is an amplifier, 18 is a gm amplifier, and 19 is a reproduction. The head, 25 is a pulse generator at the time of mode switching, and C1 is a capacitor which is one of the factors that determine the response of the amplifier.

  The magnetic disk device shown in FIG. 3 is a magnetic disk device that requires low power consumption by mode switching, such as having a standby mode, and that requires high speed circuit recovery time during mode switching. A second switch (hereinafter referred to as SW2) for controlling on / off of the current source 12 depending on the mode is connected between the diodes 21, and the other end for determining the gm value is grounded to the gm amplifier 18. The current source 24 connected to the current source 23 is connected to the other end of the SW1 through the first switch (hereinafter referred to as SW1), and the other end of the SW1 is grounded. This is a configuration provided with a pulse generator 25 that generates a pulse when a mode is switched from a signal.

  The operation of the reproduction amplifier unit of the magnetic disk device of the third embodiment configured as described above will be described below. In the standby (low power consumption) mode controlled by the mode control signal input, all the reproduction amplifier units 11 are in a non-operating state, SW1 and SW2 are in an off state, and no current source current flows. At this time, the bias current of the reproducing head 19 is zero, the voltage of the reproducing head terminal is zero, and at the same time, the charge of the capacitor C1 is zero.

  Next, when the mode control signal input is switched to enter the operation mode, SW2 is turned on, a current is applied to the reproducing head, and the voltage at the reproducing head terminal and the potential at point B in FIG. The steady-state voltage Vb at point B is expressed by (Equation 2).

モード切り替えのパルス発生器２５は、モード変化後任意のパルス幅を持ったパルスを出力してＳＷ１を制御する。これにより一定時間ｇｍ値を変化させｇｍアンプ１８とコンデンサＣ１で決まるＬＰＦの時定数を変化させアンプ１７の基準側入力電圧の追従性を上げている。また、図３中Ａ点の電位の簡易的な応答性ｔｄは（数３）で表される。

The mode switching pulse generator 25 controls the SW1 by outputting a pulse having an arbitrary pulse width after the mode change. As a result, the gm value is changed for a certain period of time, and the time constant of the LPF determined by the gm amplifier 18 and the capacitor C1 is changed to improve the followability of the reference side input voltage of the amplifier 17. Also, a simple response td of the potential at point A in FIG. 3 is expressed by (Equation 3).

図３中Ａ点の電位がＢ点の電位に近づきアンプ１７の入力ダイナミックレンジ内に入れば通常アンプとして動作し再生信号が出力される。

In FIG. 3, when the potential at point A approaches the potential at point B and falls within the input dynamic range of the amplifier 17, it operates as a normal amplifier and a reproduction signal is output.

  FIG. 4 is a timing chart showing the waveform of each signal in the third embodiment. In FIG. 4, a waveform (a) is a mode control signal, and SW1 and SW2 change from an OFF state to an ON state, that is, a mode change from a certain mode to a reproduction mode. The waveform (b) is an output of the pulse generator 25 and represents the waveform at point C in FIG. 3, and generates a pulse for a time tr arbitrarily set when the mode switching signal of the waveform (a) is switched. And edge detection.

  Waveform (c) is the reproducing head bias current, which is switched immediately when the mode is switched. The waveform (d) is a current Igm for determining the gm value of the gm amplifier 18, and the waveform (b) is a high level section, that is, Igm becomes a current value of I2 + I3 during the time tr after the mode is switched, and the gm value is changed. By changing it, the response speed determined by the gm amplifier 18 and the capacitor C1 is increased, and the recovery time of the reproducing circuit is shortened. An input waveform of the amplifier 17 obtained by such control, that is, a waveform (e) at points A and B in FIG.

  The potential at point B is recovered immediately in the same manner as the reproduction head bias current response shown in waveform (c), and a reproduction signal is input. However, the reproduction signal in the timing chart of FIG. 4 is a sine wave for simplicity. As described above, the potential at the point A is determined by the gm amplifier 18 and the capacitor C1 and becomes a waveform as shown in the waveform (e), which has the characteristic of the recovery time td1 expressed by (Equation 4).

ここで仮にＩgmがＩ３のままで、Ｉ２の加算（ＳＷ１のオフ状態）が無いときのＡ点の応答波形の概念を波形（ｅ）の点線に示すとおり非常に回復が遅くなる。波形（ｆ）はＡ点及びＢ点の入力を受けてのアンプ１７の出力であり、Ａ点の電位がアンプ１７の入力ダイナミックレンジ内にまで回復すると信号は出力される。

Here, if Igm remains at I3 and there is no addition of I2 (the SW1 is in an OFF state), the concept of the response waveform at point A is very slow as shown by the dotted line in waveform (e). The waveform (f) is the output of the amplifier 17 receiving the input of the point A and the point B, and a signal is output when the potential at the point A is restored to within the input dynamic range of the amplifier 17.

  FIG. 5 is a diagram showing a schematic configuration of the magnetic disk device according to the fourth embodiment of the present invention. In FIG. 5, 11 is a reproduction amplifier unit, 12, 23 and 24 are current sources, 13 is an anomaly detector, 14 is a comparator, 15 is a diode, 16 is a voltage source, 17 is an amplifier, 18 is a gm amplifier, and 19 is a reproduction. The head, 25 is a pulse generator at the time of mode switching, and C1 is a capacitor which is one of the factors that determine the response of the amplifier.

  In the magnetic disk device described in the fourth embodiment, in the magnetic disk device that requires higher speed, the other input terminal of the gm amplifier 18, the output terminal of the gm amplifier 18, the other input terminal of the amplifier 17, and the like. A connection point of the capacitor C1 is connected to a third switch (hereinafter referred to as SW3) for the purpose of applying an arbitrary voltage assumed in advance in the standby mode, and the other end of SW3 is grounded. The voltage source 26 having an arbitrary voltage assumed in advance is connected, and the ON / OFF control of the SW3 is performed by a mode control signal.

  The following describes the operation of the reproduction amplifier section of the magnetic disk apparatus according to the fourth embodiment configured as described above. In the standby (low power consumption) mode controlled by the mode control signal input, all the reproduction amplifier units 11 are in a non-operating state, SW1 and SW2 are in an off state, and each current source current is not flowing. At this time, the bias current of the reproducing head 19 is zero and the voltage of the reproducing head terminal is also zero. SW3 is configured to be turned on in the standby mode, and the capacitor C1 is supplied with a voltage which is assumed in advance, that is, a voltage represented by (equation 5) having the same potential as the DC voltage level Vb at point B in the reproduction mode. 26 and is given.

次に、モードコントロール信号入力が切り替わり動作モードに入るとＳＷ２はオン状態になり、再生ヘッド１９に電流が印加され再生ヘッド端子の電圧および図５中のＢ点電位は（数５）で表される定常値に回復する。また、ＳＷ３はモードコントロール信号入力が切り替わり動作モードに入るとオフとなり、コンデンサＣ１とｇｍアンプ１８との接続点であるＡ点電圧は、電圧源２６で与えられた電圧であるほぼＶｂと同電位からスタートすることになる。モード切り替えのパルス発生器２５はモード変化後任意のパルス幅を持ったパルスを出力しＳＷ１を制御する。これにより一定時間ｇｍ値を変化させｇｍアンプ１８とコンデンサＣ１で決まるＬＰＦの時定数を変化させてアンプ１７の基準側入力電圧の追従性を上げている。

Next, when the mode control signal input is switched and the operation mode is entered, SW2 is turned on, a current is applied to the reproducing head 19, and the voltage at the reproducing head terminal and the point B potential in FIG. It recovers to a steady value. Further, SW3 is turned off when the mode control signal input is switched and the operation mode is entered, and the voltage at point A, which is a connection point between the capacitor C1 and the gm amplifier 18, is substantially equal to Vb which is a voltage given by the voltage source 26. Will start from. The mode switching pulse generator 25 controls the SW1 by outputting a pulse having an arbitrary pulse width after the mode is changed. As a result, the gm value is changed for a certain period of time, and the time constant of the LPF determined by the gm amplifier 18 and the capacitor C1 is changed to improve the followability of the reference side input voltage of the amplifier 17.

  The amplifier output recovery time td2 at the time of mode switching is expressed by (Equation 6).

前述の（数４）で表されるｔｄ１と同様になるがΔＶＡがゼロに近い値となり、逆に再生ヘッド端子の電圧の回復時間すなわちＢ点電圧の回復時間が支配的となることが起こり得る。図５中Ａ点の電位がＢ点の電位に近づきアンプ１７の入力ダイナミックレンジ内に入れば通常アンプとして動作し再生信号が出力される。

Although it is the same as td1 expressed by the above (Equation 4), ΔVA becomes a value close to zero, and conversely, the recovery time of the voltage of the reproducing head terminal, that is, the recovery time of the B point voltage may be dominant. . In FIG. 5, when the potential at point A approaches the potential at point B and falls within the input dynamic range of the amplifier 17, it operates as a normal amplifier and a reproduction signal is output.

  FIG. 6 is a timing chart showing the waveform of each signal in the fourth embodiment. A waveform (a) shown in FIG. 6 is a mode control signal input, and SW1 and SW2 change from an OFF state to an ON state, that is, a mode change from a certain mode to a reproduction mode. A waveform (b) is an output of the pulse generator 25 and represents the waveform at point C in FIG. 5, and generates a pulse for a time tr arbitrarily set when the mode switching signal of the waveform (a) is switched. And edge detection.

  Waveform (c) is the reproducing head bias current, which is switched immediately when the mode is switched. A waveform (d) is a current Igm for determining the gm value of the gm amplifier 18, and Igm becomes a current value of I2 + I3 during the time tr after the waveform (b) is in a high level section, that is, the mode is switched. By changing it, the response speed determined by the gm amplifier and the capacitor C1 is increased to shorten the recovery time of the reproducing circuit.

  The waveform of the input of the amplifier 17 obtained by such control, that is, the waveform (e) at points A and B in FIG. The potential at point B is recovered immediately in the same manner as the reproduction head bias current response shown in waveform (c), and a reproduction signal is input. However, the reproduction signal in this timing chart is a sine wave for simplification. The potential at point A is given a voltage close to the value of Ibias × Rmr + 2Vd assumed by SW3 and the voltage source 26 even when not operating, and recovery from this voltage is achieved. The recovery time is also the recovery time at point B It becomes dependent. Further, the waveform is determined by the gm amplifier 18 and the capacitor C1 and becomes a waveform as shown in the waveform (e), so that the recovery time can be further increased compared to the fourth embodiment. Waveform (f) is the amplifier output upon receiving the input at point A and point B, and a signal is output when the potential at point A is restored to within the input dynamic range of the amplifier.

  The magnetic disk device according to the present invention feeds back the voltage (DC level) of the reproducing head terminal to the reference side (the other input terminal) of the amplifier using a gm amplifier and a capacitor, and further switches the gm when switching the mode from the standby mode or the like. A signal reproduction amplifier circuit that can change the gm value of the amplifier for an arbitrary time to speed up the recovery time of the circuit operation, and when the reproduction head is in an abnormal state such as an open state, a bias current is supplied to the diode to fix the reproduction head terminal voltage. It has a reproducing head abnormality detector that detects an abnormality by comparing this voltage with a comparator, and is useful for a magnetic disk device using a magnetoresistive effect type magnetic head.

1 is a diagram showing a schematic configuration of a magnetic disk device according to a first embodiment of the present invention. The figure which shows schematic structure of the magnetic disc unit in Embodiment 2 of this invention. The figure which shows schematic structure of the magnetic disc unit in Embodiment 3 of this invention. Timing chart showing waveforms of signals in the third embodiment The figure which shows schematic structure of the magnetic disc unit in Embodiment 4 of this invention. Timing chart showing waveforms of signals in the fourth embodiment The figure which shows schematic structure of the conventional magnetic disc unit

Explanation of symbols

2, 12, 23, 24 Current source 4, 17 Amplifier 6, 16, 26 Voltage source 9.19 Playback head 11 Playback amplifier unit 13 Abnormality detector 14 Comparator 15, 21, 22 Diode 18 Gm amplifier 25 Pulse generator

Claims (2)

A first current source because one end which gives a bias current to the read head is a magnetoresistive head is connected to a power source, the reproducing head terminal voltage between the current source and the read head terminal An amplifier for amplifying an output signal from the reproduction head having one input terminal connected to a connection point between the current source and the first diode ; One input terminal is connected between the current source and the first diode, and the other input terminal, the output terminal, and the other input terminal of the amplifier are connected to feed back the voltage level of the reproducing head terminal. the conductance (hereinafter, referred to as gm) and amplifier, and the gm amplifier capacitor to ground the other end connected to the output terminal of the other end in order to determine the value gm connected to the gm amplifier is grounded A second current source, a third current source connected to a connection point between the gm amplifier and the second current source via a first switch, the other end grounded, and the first current source, A second switch for performing on / off control with a mode control signal between the first diode and a pulse generator for generating a mode switching pulse from the mode control signal to control on / off of the first switch; And a high-speed recovery time for circuit operation when switching from the standby mode to reduce power consumption . A voltage source having the other end to which an arbitrary voltage assumed in the standby mode is applied grounded is connected to a connection point where the other input end and output end of the gm amplifier are connected to the other input end of the amplifier. A third switch is provided, and the on / off control of the third switch is performed by a mode control signal to obtain a fast recovery time of the circuit operation at the time of mode switching from the standby mode for reducing power consumption. The magnetic disk apparatus according to claim 1.

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