JP3667494B2 - Magnetic disk unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk device, and more particularly to a magnetic disk device that amplifies a reproduction signal to a constant amplitude by ACG and outputs the amplified signal.
2. Description of the Related Art In recent years, information recording / reproducing devices such as magnetic disk devices are equipped with MR (Magneto-Resistive) magnetic heads that can be miniaturized with high sensitivity as the size and capacity increase.
[0002]
However, in the MR type magnetic head, a thermal response phenomenon (Thermal Asperity phenomenon) occurs due to contact with the magnetic disk. When the thermal response phenomenon occurs, DC (direct current) imbalance occurs in the information on the position on the magnetic disk where the thermal response phenomenon occurs, and the gain of the amplifier greatly fluctuates due to AGC (Automatic Gain Control). This affects the amplification of the reproduction signal at the position where the phenomenon ends, and the reproduction signal other than the portion where the thermal response phenomenon occurs becomes an error. The thermal response phenomenon is temporary, and when it occurs in a gap portion or the like, an error in the data portion is induced by AGC even though it has nothing to do with the data. It was necessary to reduce the occurrence of errors due to AGC.
[0003]
[Prior art]
FIG. 7 shows a block diagram of an example of a conventional magnetic disk device.
The conventional magnetic disk device 100 magnetically records information on the magnetic disk 101. The magnetic disk 101 is rotated in the direction of arrow A by the spindle motor 102.
[0004]
On the surface of the magnetic disk 101, an MR type magnetic head 103 that magnetically acts on the magnetic disk 101, records information on the magnetic disk 101, and reads out information recorded on the magnetic disk 101 is opposed to the magnetic disk 101. . The magnetic head 103 is fixed to the arm 104, and records and reproduces information on the magnetic disk 101 in a state where the magnetic head 103 slightly floats from the surface of the magnetic disk 101 by the rotation of the magnetic disk 101.
[0005]
The arm 104 is held so as to be rotatable about a rotation shaft 105, a magnetic head 103 is held at the tip, and a voice coil motor 106 is located on the opposite side across the rotation shaft 105. The arm 104 is rotated in the direction of arrow B about the rotation shaft 105 by the voice coil motor 106 to move the magnetic head 103 in the radial direction of the magnetic disk 101.
[0006]
The magnetic head 103 is connected to a head IC (Integrated Circuit) 108 via a connection line 107.
The head IC 108 amplifies the read signal read from the magnetic disk 101 by the magnetic head 103. The read signal amplified by the head IC 108 is supplied to an R / W (Read / Write) control circuit 109.
[0007]
The R / W control circuit 109 shapes the waveform of the read signal supplied from the head IC 108 and demodulates it. The signal demodulated by the R / W control circuit 109 is supplied to an HDC (Hard Disk Drive Controller) 112.
FIG. 8 is a block diagram of a read control circuit of an example of a conventional magnetic disk device.
[0008]
The R / W control circuit 109 includes a read control circuit (Read Channel; RDC) 120 and a write control circuit (not shown).
The read control circuit 120 includes an amplifier 121 that amplifies the read signal, a filter 122 that removes unnecessary components from the read signal amplified by the amplifier 121, an equalizer 123 that removes distortion of the read signal from which unnecessary components are removed by the filter 122, The read signal from which distortion has been removed by the equalizer 123 is sliced at a predetermined slice level and the waveform is shaped, a level detection circuit 124, a demodulator 125 that demodulates the original data from the waveform-shaped signal by the level detection circuit 124, A PLL (Phase Locked Loop) circuit 126 that generates a clock synchronized with the equalized read signal, and the gain of the amplifier 121 according to the level of the output read signal of the filter 122, the amplitude of the output read signal of the filter 122 becomes constant. AGC (Automatic Gain Control) control It is composed of a controller 127.
[0009]
The output reproduction signal of the head IC 108 supplied to the read control circuit 120 is first supplied to the amplifier 121. The amplifier 121 controls the gain according to the AGC control signal from the AGC controller 127 and performs amplification so that the amplitude of the reproduction signal supplied from the head IC 108 becomes constant. The output reproduction signal from the amplifier 121 is supplied to the filter 122.
[0010]
The filter 122 is a filter for removing unnecessary components, and removes unnecessary components from the reproduction signal supplied from the amplifier 121. The filter 122 is supplied with a cutoff frequency control signal from the MPU 110.
In the filter 122, the cutoff frequency fc is controlled by the cutoff frequency control signal supplied from the MPU 110, and the pass band is controlled. The reproduction signal from which unnecessary components have been removed by the filter 122 is supplied to the equalizer 123 and the AGC controller 127.
[0011]
The AGC controller 127 detects the amplitude of the output reproduction signal of the filter 122. If the amplitude is larger than the predetermined amplitude, the gain of the amplifier 121 is small. If the amplitude is smaller than the predetermined amplitude, the gain of the amplifier 121 is large. AGC control signal is generated and supplied to the amplifier 121.
The amplifier 121 performs amplification so that the gain is controlled by the AGC control signal supplied from the AGC controller 127 and the amplitude of the reproduction signal supplied from the head IC 108 becomes constant.
[0012]
On the other hand, the equalizer 123 removes distortion from the reproduction signal supplied from the filter 122. The reproduction signal from which distortion has been removed by the equalizer 123 is supplied to the level detection circuit 124 and the PLL circuit 126.
The level detection circuit 124 shapes the reproduction signal into a pulse shape by slicing the reproduction signal from which distortion has been removed by the equalizer 123 at a predetermined slice level. The equalizer 123 is supplied with a slice level control signal from the MPU 110, and the slice level is varied according to the slice level control signal supplied from the MPU 110.
[0013]
The PLL circuit 126 generates a clock synchronized with the reproduction signal from the reproduction signal from which distortion has been removed by the equalizer 123. The clock generated by the PLL circuit 126 is supplied to the demodulator 125 and also supplied to the HDC 112 together with the data demodulated by the demodulator 125.
The reproduction signal pulsed by the level detection circuit 124 is supplied to the demodulator 125. The demodulator 125 demodulates the original data from the reproduction pulse signal from the level detection circuit 124 and the clock generated by the PLL circuit 126.
[0014]
The data demodulated by the demodulator 125 is supplied to the HDC 112 together with the clock of the PLL circuit 126.
The MPU 110 is connected to an R / W control circuit 109, a DSP (Digital Signal Processor) 111, and an HDC (Hard disk Drive Controller) 112. The MPU 110 processes information to be recorded / reproduced on the magnetic disk 101, and controls the rotation of the magnetic disk 101 and the positioning of the magnetic head 103 according to the information read from the magnetic disk 101 by the magnetic head 103.
[0015]
The DSP 111 generates digital data for controlling the rotation of the spindle motor 102 in accordance with the digital data for determining the rotation speed of the magnetic disk 101 supplied from the MPU 110. Further, the DSP 111 generates digital data for controlling the voice coil motor 106 according to the digital data for determining the position of the magnetic head 103 supplied from the MPU 110.
[0016]
Digital data for controlling the rotation of the spindle motor 102 generated by the DSP 111 and digital data for controlling the rotation position of the voice coil motor 106 are respectively supplied to a DAC (Digital Analog Converter) 114. The DAC 113 converts the digital data supplied from the DSP 111 for controlling the rotation of the spindle motor 102 and the digital data for controlling the rotation position of the voice coil motor 106 into analog signals.
[0017]
Digital data for controlling the rotation of the spindle motor 102 supplied from the DSP 113 to the DAC 113 is converted into an analog signal by the DAC 113 and then supplied to the spindle drive circuit 114. The spindle drive circuit 114 generates a drive signal for driving the spindle motor 102 according to the analog signal supplied from the DAC 113 and supplies the drive signal to the spindle motor 102. The spindle motor 102 is rotated by a drive signal supplied from the spindle motor drive circuit 114, and rotates the magnetic disk 101 in the arrow A direction at a constant rotation speed.
[0018]
Digital data for controlling the rotational position of the voice coil motor 106 supplied from the DSP 111 to the DAC 113 is converted into an analog signal by the DAC 113 and then supplied to the voice coil motor drive circuit 115. The voice coil motor drive circuit 115 generates a drive signal for driving the voice coil motor 106 according to the analog signal supplied from the DAC 113 and supplies the drive signal to the voice coil motor 106. The voice coil motor 106 positions the magnetic head 103 by controlling the rotational position of the arm 104 in the direction of arrow B by a drive signal supplied from the voice coil motor drive circuit 115.
[0019]
On the other hand, the HDC 112 is connected with a memory 116 for temporarily storing read / write data and an interface (IF) 117 for connection with the outside. The HDC 112 controls data transmission / reception between the magnetic disk device 100 and an external device.
A host computer 130 is connected to the interface 117. The host computer 130 writes data to and reads data from the magnetic disk device 100 and processes the data.
[0020]
[Problems to be solved by the invention]
However, in the conventional magnetic disk device, the DC level of the reproduction signal temporarily increases due to the thermal response phenomenon caused by the collision between the MR type magnetic head and the protrusion of the magnetic disk. Control is performed to reduce the gain of the amplifier in an attempt to suppress the amplitude of the reproduction signal.
[0021]
FIG. 9 shows an operation waveform diagram at the time of data area reproduction of an example of a conventional magnetic disk device. 9A is a data format of the data area of the magnetic disk 101, FIG. 9B is a read gate signal, FIG. 9C is a reproduction signal, FIG. 9D is an AGC control signal, and FIG. Indicates an output reproduction signal of the amplifier.
The data area of the magnetic disk 101 includes a gap part GAP, a preamble part PREAMBLE, a training part TR, a sync byte part SB, a data part DATA, and an ECC (Error Checking and Correcting) part ECC.
[0022]
Here, when a thermal response phenomenon occurs in the gap portion GAP, the output DC level of the reproduction signal waveform supplied to the amplifier temporarily increases as shown in FIG. 9C. When the reproduction signal increases as shown in FIG. 9C, the AGC controller is controlled by this, and the AGC control signal supplied to the amplifier is increased as shown in FIG. 9D. The gain of the amplifier is reduced by increasing the AGC control signal. When the AGC control signal changes rapidly, the AGC controller delays the drop of the AGC control signal as shown in FIG. 9D, and even after the read gate signal shown in FIG. As shown in (E), sufficient amplitude cannot be obtained.
[0023]
As shown in FIG. 9E, if the reproduction signal does not have sufficient amplitude and the sync byte portion SB before the data portion DATA and the sync byte detection fails, the data portion DATA cannot be read. There was a problem that a read error occurred.
Further, when this phenomenon occurs in the gap portion of the servo region provided between the data regions, the servo mark portion SM provided in front of the servo portion as in the data region cannot be read, and a seek error occurs. There was a problem.
[0024]
  The present invention has been made in view of the above points, and even if there is a sudden increase or decrease in the DC level of the reproduction signal,Or laterData readingIncludedIt is an object of the present invention to provide a magnetic disk device that can reliably perform recording.
[0025]
[Means for Solving the Problems]
  According to a first aspect of the present invention, a gain is controlled based on a magnetic disk on which information is magnetically recorded, a magnetic head for reproducing a signal from the magnetic disk, and a gain control signal, and the gain is controlled according to the gain. An automatic gain control amplifying means for amplifying a reproduction signal reproduced from the magnetic disk by a magnetic head so that the amplitude thereof is constant; and a demodulation means for demodulating with an output reproduction signal of the automatic gain control amplification means In the magnetic disk device
  Holding means for holding the gain control signal;
  Error detection means for detecting an error in reading the demodulated signal output from the demodulation means;
  A gain control signal by the holding means at every rereadingAutomatic gain control hold setting information that controls on / off of the hold function ofSet table,
  When a reading error is detected by the error detecting means, the reading is performed again and the number of times of rereading is counted, and the number of times of rereading is determined.Automatic gain control hold setting informationRead from the table, read from the tableAutomatic gain control hold setting informationThe gain control signal by the holding means based onTo fixIt has a control means.
[0026]
  According to the first aspect, at the time of re-reading, the gain of the automatic gain control amplification means is kept constant and reproduction is performed, so that the reproduction signal rapidly increases or decreases due to the collision between the magnetic disk and the magnetic head. When a response phenomenon occurs, the gain of the automatic gain control amplification means is temporarily abruptly controlled by a sudden increase / decrease in the reproduction signal due to the thermal response phenomenon, and this gain fluctuation is a reproduction signal other than the part where the thermal response phenomenon occurs. Therefore, a reproduction signal other than the portion where the thermal response phenomenon occurs can be stably obtained. Also tableAutomatic gain control hold setting information set toDepending on the number of reloadsEvery timeControl signalTo fix.
[0027]
  In the second aspect of the present invention, servo information is recorded on the magnetic disk through a gap between data areas.
  The control means performs re-reading when an error occurs in the servo information, and from the gap portion immediately before the servo information in the reproduction signal.Control the holding meansIt is characterized by that.
[0028]
  According to the second aspect, when an error occurs in the servo information, it is re-read and from the gap portion immediately before the servo information in the reproduction signal.Control the holding meansTherefore, when servo information is reloaded,The gain of the automatic gain control amplification means can be kept constant from the gap portion,When a thermal response phenomenon occurs in a gap that is not related to servo information reproduction, the gain of the automatic gain control amplification means is temporarily abruptly controlled by a sudden increase / decrease in the reproduction signal due to the thermal response phenomenon. However, the servo information other than the portion where the thermal response phenomenon occurs is not affected, so that the servo information other than the portion where the thermal response phenomenon occurs can be obtained stably.
[0029]
  Claim 3 comprises level detection means for detecting a direct current level of the output reproduction signal of the amplifier,
  The control means is the error detection means.ReadWhen an error is detected, rereading is performed, and when the DC level detected by the level detection means is equal to or higher than a predetermined level,Counts the number of times of re-reading, reads the holding information corresponding to the number of times of re-reading from the table, and reads the holding information read from the table when the DC level detected by the level detecting means is equal to or higher than a predetermined level. Based on the information, the holding function of the gain control signal by the holding means is turned on / off.It is characterized by that.
[0030]
  According to claim 3, the error detection meansReadBy re-reading when an error is detected, and by controlling the gain holding means to maintain the gain just before the reproduction signal when the DC level detected by the level detecting means is equal to or higher than a predetermined level. Since the level detection means can detect a sudden increase / decrease in the reproduction signal due to the thermal response phenomenon and only the thermal response phenomenon occurrence part can be amplified with a constant gain, the automatic gain control amplification means can be used except for the thermal response phenomenon occurrence part. Therefore, the amplitude of the reproduction signal other than the portion where the thermal response phenomenon occurs can be made constant, and the reproduction signal can be demodulated with certainty.
[0031]
According to a fourth aspect of the present invention, the slice level is set so that the level detection means can detect a thermal response phenomenon caused by a collision between the magnetic head and the magnetic disk.
According to the fourth aspect of the present invention, the thermal response phenomenon can be reliably detected by setting the slice level of the level detection means to a level at which the thermal response phenomenon caused by the collision between the magnetic head and the magnetic disk can be detected. Can reduce errors.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of a magnetic disk apparatus according to the present invention. In the figure, the same components as those in FIG.
The magnetic disk device 1 of the present embodiment is different from the conventional magnetic disk device 100 shown in FIG. 7 in the configuration of the AGC controller 30 provided in the read control circuit 20 of the R / W control circuit 10 and the operation of the MPU 40. Is different.
[0033]
FIG. 2 shows a block diagram of a read control circuit of an embodiment of the magnetic disk apparatus of the present invention. In the figure, the same components as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted.
The AGC controller 30 of the read control circuit 20 of the present embodiment includes a full-wave rectifier 31 that converts the output reproduction signal of the filter 122 into a DC signal, and an AGC control signal according to the reproduction signal converted into a DC signal by the full-wave rectifier 31. An AGC charge pump 32 that generates a signal, a comparator 33 that detects the level of the output reproduction signal of the amplifier 121, an OR gate 34 that is supplied from the MPU 40 and outputs a logical sum of the AGC hold control signal and the output logic of the comparator 33, AGC A capacitor C1 connected to the connection point between the charge pump 32 and the amplifier 121 and holding the output AGC control signal of the AGC charge pump 32, provided between the AGC charge pump 32 and the amplifier 121, and the output logic of the OR gate 34 Switched according to the AGC controller And a switch SW1 for controlling the supply to the signal of the amplifier 121.
[0034]
The comparator 33 is supplied with a constant slice level SL10 from the MPU 40. When the output reproduction signal level of the amplifier 121 becomes equal to or higher than the slice level SL10, a high level is output, and the output reproduction signal level of the amplifier 121 is increased. When the slice level is less than SL10, a low level is output.
The output logic of the comparator 33 is supplied to the OR gate 34. The OR gate 34 is supplied with an AGC hold control signal from the MPU 40 and takes a logical sum of the output logic of the comparator 11 and the AGC hold control signal from the MPU 40.
[0035]
  That is, the output logic of the OR gate 34 becomes high when one of the output logic of the comparator 33 and the AGC hold control signal from the MPU 40 is high, and the output logic of the comparator 33 and the output from the MPU 40 If both of the AGC hold control signals are low level, it becomes low level. The AGC hold control signal from the MPU 40 isReadWhen an error occurs, from the gap part GAPReadHigh during the data area where the error occurred. On the other hand, the output logic of the comparator 33 becomes a high level when the DC level of the output reproduction signal of the amplifier 121 increases due to a thermal response phenomenon or the like and becomes higher than a preset slice level SL10. That is, the AGC control signal isAbnormalIncrease todidSometimes it goes high.
[0036]
  Therefore,ReadOf the data area where an error has occurred, only the portion where the direct current level is equal to or higher than the slice level SL10 due to a thermal response phenomenon or the like becomes high level.
  The output logic of the OR gate 34 is supplied to the control terminal of the switch SW1. The switch SW1 is turned on when the control terminal is at a high level and turned off when the control terminal is at a low level.
[0037]
  When switch SW1 is on, the AGC charge pump32The gain of the amplifier 121 is controlled by the output signal. When the switch SW1 is off, the reproduction signal is amplified by the amplifier 121 in a state where the gain is fixed according to the state of the reproduction signal immediately before being held in the capacitor C1..
[0038]
FIG. 3 shows a data configuration diagram of a retry table of an embodiment of the magnetic disk apparatus of the present invention.
The retry table 21 includes retry number information N indicating the number of retries, cut-off frequency setting information Fc for setting the cut-off frequency fc of the filter 122, and slice level setting information for setting the slice level sl of the level detection circuit 124. SL and AGC hold information H for controlling ON / OFF of the AGC hold.
[0039]
  The retry count information N stores retry counts “1” to “n”. Information for setting the cutoff frequency fc of the filter 122, the slice level sl of the level detection circuit 124, and ON / OFF of the AGC hold are set for each retry count. The MPU 40 repeats the retry n times, and when the information cannot be read normally,Retry processingRecognize as an error.
[0040]
The cut-off frequency setting information Fc is information for setting the cut-off frequency fc of the filter 122, and stores increase / decrease information with respect to the reference cut-off frequency fc0. For example, when the number of retries N = 1, the cutoff frequency setting information Fc is “+ 10%”, and a cutoff frequency fc1 of “+ 10%” is set with respect to the reference cutoff frequency fc0. When the number of retries N = 2, the cutoff frequency setting information Fc is “−10%”, and a cutoff frequency fc2 of “−10%” is set with respect to the reference cutoff frequency fc0. . Further, when the number of retries N = n, the cutoff frequency setting information Fc is “−10%”, and a cutoff frequency fcn of “−10%” is set with respect to the reference cutoff frequency fc0. .
[0041]
The slice level setting information SL is information for setting the slice level sl of the level detection circuit 124, and stores slice levels sl1 to sln for each retry count. For example, when the number of retries N = 1, the slice level sl1 is set, when the number of retries N = 2, the slice level sl2 is set, and when the number of retries N = n, the slice level sln is set. .
[0042]
The AGC hold information H is information for setting ON / OFF of the switch SW1, and is set to ON or OFF for each retry count. For example, “ON” is set when the number of retries N = 1, “OFF” is set when the number of retries N = 2, and “OFF” is set when the number of retries is “n”.
FIG. 4 shows an operational flowchart of the retry process of one embodiment of the magnetic disk apparatus of the present invention.
[0043]
  The MPU 40 instructs reading of desired data (step S1).
  Data is demodulated by the read control circuit 120 of the R / W control circuit 109 in response to a data read instruction from the MPU 40 and supplied to the HDC 112. The HDC 112 receives the demodulated dataRead based onDetect the presence of errors. The HDC 112 converts the data supplied from the read control circuit 120 intoReadWhen an error is detected, the MPU 40ReadTo the data that gave instructionsReadNotify that an error has occurred.
[0044]
  MPU 40 starts from HDC 112ReadTo the data that gave instructionsReadWhen a notification that an error has occurred is received, first, a retry count indicating the number of retries is set to “1” (steps S2 and S3).
  Next, the MPU 40 refers to the retry table 21 set inside, reads the cutoff frequency setting information of the filter 122 corresponding to the retry count from the retry table 21, and generates cutoff frequency setting data to be supplied to the filter 122. The slice level setting information is read out, slice level setting data supplied to the level detection circuit 124 is generated, supplied to the level detection circuit 124, and the AGC hold setting information H is read out. An AGC hold control signal to be supplied to the OR gate 34 is generated and supplied to the OR gate 34 after the gap portion of the data area of the data to be read is detected until the data area is completed (step S4).
[0045]
The filter 122 of the read control circuit 20 has a cutoff frequency set by the cutoff frequency setting data set in step S3 of the MPU 40. Further, the level detection circuit 124 of the read control circuit 20 sets the slice level according to the slice level setting data set in step S3 of the MPU. Further, a high level signal is supplied to the OR gate 34 of the read control circuit 20 from the gap portion of the data area of the data to be read until the data area is completed.
[0046]
  Here, the MPU 40 instructs rereading of data (step S5).
  Data is demodulated by the read control circuit 20 of the R / W control circuit 109 in response to a data read instruction from the MPU 40 and supplied to the HDC 112. The HDC 112 receives the demodulated dataRead fromDetect the presence of errors. The HDC 112 converts the data supplied from the read control circuit 120 intoReadWhen an error is detected, the MPU 40 is instructed to read dataReadNotify that an error has occurred.
[0047]
  When the MPU 40 receives notification from the HDC 112 that an error has occurred in the data that has been instructed to read, the MPU 40 first increments the retry count indicating the number of retries by “+1” (steps S6 and S7).
  The MPU 40 determines whether or not the retry count incremented by “+1” in step S7 is “n + 1”, that is, the retry is over (step S8). If a retry over occurs in step S8, it can be determined that the read control circuit 20 cannot be read by the operation of the read control circuit 20.Retry processingAn error report is made (step S9).
[0048]
If the retry count is “n” or less in step S8, it can be determined that there is a condition to be set in the retry table 21. Therefore, the process returns to step S4, and the data is re-established under the condition corresponding to the retry count value. Read.
The case where the retry process is performed due to a thermal response phenomenon will be described with reference to FIGS.
[0049]
FIG. 5 shows an operation waveform diagram at the time of data area reproduction according to an embodiment of the present invention. 5A is a data area format, FIG. 5B is a read gate control signal, FIG. 5C is an output reproduction signal of the amplifier 121, FIG. 5D is an AGC hold control signal, and FIG. ) Is an output signal of the comparator 33, FIG. 5F is an AGC control signal supplied to the amplifier 121, and FIG. 5G is an operation waveform diagram of an output reproduction signal of the filter 122.
[0050]
If an increase in the DC level of the reproduction signal due to a thermal response phenomenon occurs in the gap portion GAP shown in FIG. 5A as shown in FIG. 5C, a retry is performed when the AGC hold setting information of the retry table 21 is turned on. At time t0, the AGC hold control signal is set to the high level.
As shown in FIG. 5C, when the DC level of the reproduction signal exceeds the slice level SL10 set in the comparator 33 due to the thermal response phenomenon at time t1, the output logic of the comparator 33 becomes high level, and the OR gate The output logic of 34 becomes high level.
[0051]
When the output logic of the OR gate 34 becomes high level at time t1, the switch SW1 is turned off, and the gain of the amplifier 121 is fixed to the gain corresponding to the charging voltage charged in the capacitor C1. That is, the gain of the amplifier 121 is set to the AGC control signal corresponding to the reproduction signal at time t0 immediately before the output logic of the comparator 33 becomes high level.
[0052]
  As shown in FIG. 5C, when the increase of the DC level of the reproduction signal due to the thermal response phenomenon is stopped at time t2, and becomes smaller than the slice level SL10 set in the comparator 33, the comparator as shown in FIG. The output logic of 33 becomes low level.At this time, if the AGC hold signal H is at a low level,Switch SW1 turns on and AGC charge pump32The gain of the amplifier 121 is determined in accordance with the AGC control signal supplied from. That is, AGC is applied to the reproduction signal, and control is performed so that the amplitude is constant.
[0053]
In this embodiment, a retry operation similar to that in the data area is also performed in the servo area.
FIG. 6 shows an operation waveform diagram at the time of servo area reproduction in one embodiment of the present invention. 6A is a servo area format, FIG. 6B is a servo gate control signal, FIG. 6C is an output reproduction signal of the amplifier 121, FIG. 6D is an AGC hold control signal, and FIG. ) Is an output signal of the comparator 33, FIG. 6F is an AGC control signal supplied to the amplifier 121, and FIG. 6G is an operation waveform diagram of an output reproduction signal of the filter 122.
[0054]
If an increase in the DC level of the reproduction signal due to the thermal response phenomenon occurs in the gap portion GAP shown in FIG. 6A as shown in FIG. 6C, during the retry when the AGC hold setting information of the retry table 21 is turned on. At time t10, the AGC hold control signal is set to the high level.
As shown in FIG. 6C, when the DC level of the reproduction signal exceeds the slice level SL10 set in the comparator 33 due to the thermal response phenomenon at time t11, the output logic of the comparator 33 becomes high level, and the OR gate The output logic of 34 becomes high level.
[0055]
When the output logic of the OR gate 34 becomes high level at time t11, the switch SW1 is turned off, and the gain of the amplifier 121 is fixed to the gain corresponding to the charging voltage charged in the capacitor C1. That is, the gain of the amplifier 121 is set to the AGC control signal corresponding to the reproduction signal at time t10 immediately before the output logic of the comparator 33 becomes high level.
[0056]
As shown in FIG. 6C, at time t12, when the increase in the DC level of the reproduction signal due to the thermal response phenomenon stops and becomes smaller than the slice level SL10 set in the comparator 33, the comparator as shown in FIG. The output logic of 33 becomes low level. When the output logic of the comparator 33 becomes low level, the switch SW1 is turned on, and the gain of the amplifier 121 is determined according to the AGC control signal supplied from the AGC charge pump. That is, AGC is applied to the reproduction signal, and control is performed so that the amplitude is constant.
[0057]
As described above, when the thermal response phenomenon occurs in the gap area GAP of the data area and the servo area, when the thermal response phenomenon occurs, the AGC control signal is fixed to the immediately preceding state, and the thermal response phenomenon occurs. Since the AGC control signal does not rise due to the DC level of the reproduction signal increased by the above, it is possible to quickly shift to the AGC state after the thermal response phenomenon. That is, if the data area, the preamble part PREAMBLE, the training part TR, the sync byte part SB, and if the servo area, the data immediately after the gap part GAP such as the AGC field part AGCFIELD, the servo mark part SM, the gray code part GLAYCODE. Reproduction is possible without affecting the thermal response phenomenon.
[0058]
At this time, in the present embodiment, AGC can be applied to portions other than the portion where the thermal response phenomenon occurs, so that data can be reliably reproduced.
[0059]
【The invention's effect】
As described above, according to the first aspect of the present invention, at the time of re-reading, the gain of the automatic gain control amplifying means is kept constant and reproduction is performed, so that the reproduction signal is suddenly caused by the collision between the magnetic disk and the magnetic head. When a so-called thermal response phenomenon occurs, the gain of the automatic gain control amplification means is temporarily abruptly controlled by a sudden increase / decrease in the reproduction signal due to the thermal response phenomenon. Since the reproduction signal other than the phenomenon occurrence portion is not affected, the reproduction signal other than the thermal response phenomenon occurrence portion can be stably obtained.
[0060]
According to claim 2, when an error occurs in the servo information, the read is performed again, and the gain is kept constant from the gap portion immediately before the servo information in the reproduction signal. Since the gain of the automatic gain control amplification means is kept constant from the gap portion and playback is performed, when a thermal response phenomenon occurs in the gap portion that is not related to servo information playback, the playback signal suddenly increases or decreases due to the thermal response phenomenon Thus, the gain of the automatic gain control amplifying means is temporarily and suddenly controlled, and the servo information other than the part where the thermal response phenomenon occurs is not affected by the fluctuation of this gain. It has the feature that it can be obtained stably.
[0061]
According to the third aspect, when an error is detected by the error detecting means, rereading is performed, and when the DC level detected by the level detecting means is equal to or higher than a predetermined level, the gain holding means is controlled. By maintaining the gain just before the playback signal, the level detection means can detect a sudden increase or decrease in the playback signal due to the thermal response phenomenon, and only the thermal response phenomenon occurrence part can be amplified with a constant gain. The automatic gain control amplifying means can be operated outside the phenomenon occurrence portion, and therefore, the amplitude of the reproduction signal other than the thermal response phenomenon occurrence portion can be made constant, and the reproduction signal can be reliably demodulated.
[0062]
According to the fourth aspect of the present invention, the thermal response phenomenon can be reliably detected by setting the slice level of the level detection means to a level at which the thermal response phenomenon caused by the collision between the magnetic head and the magnetic disk can be detected. It has features such as reducing errors caused by.
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of a magnetic disk device of the present invention.
FIG. 2 is a block diagram of a read control circuit of an embodiment of the magnetic disk device of the present invention.
FIG. 3 is a data configuration diagram of a retry table of an embodiment of the magnetic disk device of the present invention.
FIG. 4 is an operation flowchart of a retry process according to an embodiment of the magnetic disk device of the present invention.
FIG. 5 is an operation waveform diagram at the time of data area reproduction in one embodiment of the magnetic disk apparatus of the present invention.
FIG. 6 is an operation waveform diagram at the time of servo area reproduction in one embodiment of the magnetic disk device of the present invention.
FIG. 7 is a block diagram of an example of a conventional magnetic disk device.
FIG. 8 is a block diagram of a read control circuit of an example of a conventional magnetic disk device.
FIG. 9 is an operation waveform diagram at the time of data area reproduction of an example of a conventional magnetic disk device.
[Explanation of symbols]
1 Magnetic disk unit
10 R / W control circuit
40 MPU
21 Retry table
20 Read control circuit
30 AGC controller
33 Comparator
34 OR gate
101 magnetic disk
102 Spindle motor
103 Magnetic head
106 Voice coil motor
121 amplifier
122 Filter
123 equalizer
124 level detection circuit
125 demodulator
126 PLL circuit

Claims (4)

A magnetic disk on which information is magnetically recorded, a magnetic head that reproduces a signal from the magnetic disk, and a gain that is controlled based on a gain control signal, and is reproduced from the magnetic disk by the magnetic head according to the gain In a magnetic disk apparatus comprising: an automatic gain control amplifying means for amplifying the reproduced signal so that its amplitude is constant; and a demodulating means for demodulating with the output reproduction signal of the automatic gain control amplifying means,
Holding means for holding the gain control signal;
Error detection means for detecting an error in reading the demodulated signal output from the demodulation means;
A table in which automatic gain control hold setting information for controlling on / off of the holding function of the gain control signal by the holding means is set for each rereading;
When a read error is detected by the error detection means, rereading is performed, the number of times of rereading is counted, and the automatic gain control hold setting information corresponding to the number of times of rereading is read from the table, from the table An information reproducing apparatus comprising control means for fixing the gain control signal by the holding means based on the read automatic gain control hold setting information . Servo information is recorded on the magnetic disk through a gap between data areas.
2. The control unit according to claim 1, wherein when an error occurs in the servo information, the control unit re-reads and controls the holding unit from a gap portion immediately before the servo information in the reproduction signal. Magnetic disk unit. Level detecting means for detecting the DC level of the output reproduction signal of the amplifier;
The control means performs rereading when a reading error is detected by the error detecting means, and counts the number of times of rereading when the DC level detected by the level detecting means is equal to or higher than a predetermined level. The holding information corresponding to the number of rereads is read from the table, and the holding information is read based on the holding information read from the table when the DC level detected by the level detecting means is equal to or higher than a predetermined level. 3. The magnetic disk apparatus according to claim 1, wherein the holding function of the gain control signal by means is turned on / off.   4. The magnetic disk apparatus according to claim 3, wherein the level detecting means sets a slice level so that a thermal response phenomenon caused by a collision between the magnetic head and the magnetic disk can be detected.

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