JPH09274702A - Magnetic recording information reproducing device - Google Patents

Abstract

(57) Abstract: Thermal asperity noise and the like superimposed on a reproduction signal are removed by a relatively small-scale circuit increase. A variable gain amplifier 211, an analog equalizer circuit 212, an A / D converter 213, a digital equalizer 21.
4, maximum likelihood decoder 215, sync byte detection circuit 220,
A signal processing part including a demodulation circuit 216;
Gain amplifier control circuit 217, AD for controlling the gain of
In the reproduction circuit 201 including the voltage control oscillator control circuit 219 for controlling the C sample clock and the control circuit portion including the voltage control oscillator 218 for supplying the ADC sample clock, the input side of the maximum likelihood decoder 215 The subtraction circuit 221 is provided between the subtraction circuit 221 and the thermal asperity noise removal circuit 222 that detects thermal asperity noise from the output of the digital equalizer 214 and removes it by subtraction input in the subtraction circuit 221. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording information reproducing technique, and more particularly to a technique effectively applied to a reproducing circuit of a magnetic recording reproducing device using a magnetoresistive head (MR head) as a reproducing head.

[0002]

2. Description of the Related Art In a data recording device such as a magnetic disk device using a magnetic recording medium, in principle, the narrower the flying gap (spacing) of the head with respect to the medium, the higher the recording density can be achieved. It is going all the way. On the other hand, regarding the head, in the reproducing head, an MR head, which will be described later, which has various advantages over the conventional induction type head, has become mainstream.

FIG. 13 shows a structure of an interface portion between a magnetic head 1 and a magnetic disk 2 of a magnetic disk device (HDD). Here, an MR head having a relatively high sensitivity is used as the reproducing head 3. The MR head is a thin film head using a thin film element having a magnetoresistive effect as a sensor. When the MR head and the disk have a narrow spacing, due to a temperature change of the magnetoresistive effect element when the MR head is rubbed by the minute projection portion 4 of the magnetic disk 2,
Thermal asperity (TA: T as shown in FIG.
It is known that noise called "hermal asperity" occurs. The magnitude Ata of the thermal asperity may reach the same level as the signal amplitude Asig, which may have a fatal influence on the reproduction performance.

Referring to the structure of a possible conventional general reproducing circuit (RSPC) 201 illustrated in FIG. 15, the thermal asperity in the reproducing signal processing system associated with the MR head of the magnetic disk drive will be described below. Consider technical issues in more detail. Here, an example will be described in which a signal processing technique that combines partial response and maximum likelihood decoding (PRML) is applied. RSPC201
Is mainly a variable gain amplifier (VGA) 211, an analog equalization circuit (AEQ) 212, and an A / D converter (ADC) 21.
3, digital equalizer (DEQ) 214, maximum likelihood decoder (M
L) 215, sync byte detection circuit (SYNCDET)
220, a signal processing unit including a demodulation circuit (DEC) 216, a variable gain amplifier control circuit (VGAC) 217 for controlling the gain of VGA, a voltage control oscillator control circuit (VCOC) 219 for controlling the sample clock of the ADC,
And a control circuit portion including a voltage controlled oscillator (VCO) 218 that supplies a sample clock of the ADC.

The VGA 211 controls the amplitude of the input signal by the control circuit so as to approach the target amplitude by the ML input. AEQ
212 removes unnecessary band noise and performs pre-equalization. A
The DC 213 converts the analog output signal of the AEQ 212 into a digital signal. At this time, in the sample clock of the ADC 213, the control voltage of the voltage controlled oscillator is controlled by the control circuit so that the sample signal value sequence at the ML input does not deviate from the target amplitude. The DEQ 214 equalizes the waveform so that the ML 215 can easily identify it. S is a sync byte indicating the start of data from the serial data identified by the ML215.
When YNCDET 220 detects it, DEC 216 demodulates the user data after serial / parallel conversion of the data and thereafter.

In general, the signal amplitude input to the ADC 213 is usually set to 80% to 90% of full scale in order to sufficiently bring out the performance of the ADC 213. Therefore, when noise due to the thermal asperity as shown in FIG. 14 is applied to this reproduction circuit, the signal input to the ADC 213 greatly changes, and the ADC
The output of 213 is saturated, and as a result, equalization by DEQ 214 becomes impossible. For this reason, the discrimination result of the ML 215 is also erroneous. Further, the error detection result in the VGAC 217 or the VCOC 219 which is the control circuit of the VGA 211 or the ADC 213 may malfunction for a long period of time, and the control operation may become unstable.

In a magnetic disk device, if a signal defect due to thermal asperity as shown in FIG. 14 occurs in a so-called sync byte that indicates the start of data, SYNCDET 220 cannot detect the start position of data, and therefore this sector All the user data recorded in will not be playable.

As a conventional technique for avoiding these problems, for example, as disclosed in US Pat. No. 4,914,398, noise due to thermal asperity is detected by an analog circuit method, and this noise is reproduced. First to remove noise by subtracting from signal
Method, and as disclosed in Japanese Unexamined Patent Publication No. 6-287785, the target amplitude of the DEQ 214 is reduced to reduce the ADC.
There is a second method, etc., in which the saturation of 213 is prevented and the low-frequency cutoff frequency of the reproducing circuit is increased to narrow the time region affected by noise due to thermal asperity.

[0009]

However, in the above-mentioned first method, the scale of the analog circuit becomes very large, and noise is generated by the removing circuit when the removing circuit is operated. There is performance degradation. Further, in the above-mentioned second method, the operations of the VGAC 217 and the VCOC 219 are stopped during the generation period of the thermal asperity noise. For this reason, when the position where the thermal asperity noise is generated is the sync byte or earlier, the deviation of the clock phase and the amplitude during the control stop period may become so large that the signal may not be reproduced.

In addition, H. Shafie et al.
Complexity Viterbi Detect
ion for a Family of Parti
alResponse Systems ”, IEEE
Trans. on Mag. , Vol. 28, N
o. 5, Sept. As shown in 1992, ML2
In order to reduce the increase in the circuit scale due to the increase in the number of states of 15, there has been proposed a combination of hard decision (hard decision). However, in this case, there is a technical problem that even a noise caused by a relatively small thermal asperity may not be adopted in a magnetic disk device in which an error may occur in a hard decision part and a thermal asperity noise may occur.

It is an object of the present invention to provide a magnetic recording information reproducing technique capable of removing the influence of such noise with a relatively small-scale circuit, even for a signal on which noise such as thermal asperity is superimposed. It is in.

Another object of the present invention is to provide a highly reliable magnetic recording information reproducing technique by providing a reproducing signal processing system capable of detecting noise due to a small thermal asperity which does not cause a reproducing error. is there.

Another object of the present invention is to provide a magnetic recording information reproducing technique capable of adopting various error-sensitive maximum likelihood decoding methods by detecting and correcting fine thermal asperity noise. is there.

Another object of the present invention is to provide a magnetic recording information reproducing technique capable of attaining a high recording density by narrowing the spacing without concern about mixing of thermal asperity noise into the reproduced signal. is there.

Another object of the present invention is a magnetic recording information reproducing technique capable of achieving a high throughput by reducing the overhead due to a retry of a data access operation due to the mixing of thermal asperity noise in a reproduced signal. To provide.

Another object of the present invention is to provide a high-performance magnetic recording information reproducing technique having a strong proof against the thermal asperity which becomes a problem at the time of narrow spacing.

[0017]

According to the present invention, for example, as shown in FIG. 14, the noise due to the thermal asperity has a relatively low frequency of about tens of samples after the noise is generated. Focusing on noise,
A method for removing thermal asperity using a feedback method is used. Specifically, in a signal processing circuit corresponding to an MR head having at least an equalizing means for equalizing a waveform and a maximum likelihood decoding means, and a magnetic recording information reproducing apparatus equipped with this signal processing circuit, the following first to first 1
Either of the means of 5 is used.

That is, first, a means for detecting thermal asperity noise having an amplitude equal to the reproduction signal amplitude and a means for removing it using a feedback method are provided.

Secondly, the input signal of the maximum likelihood decoding means is discriminated into three values, and the difference between this result and the output of the equalization means is taken to obtain a state in which thermal asperity and random noise are mixed. The error signal at is detected. Averaging means is used to average this signal to remove random noise. Further, a means for removing the detected thermal asperity from the output of the equalizing means is used.

Thirdly, by monitoring the amplitude level of the signal extracted by averaging by the second means, the output of the equalizing means is selected only when the thermal asperity is occurring. Remove from signal.

Fourthly, in the signal processing circuit according to the second and third means, the thermal circuit is provided with means for estimating the time series error amount of the thermal asperity noise from the error signal sequence input to the averaging means. An asperity noise removing means is provided.

Fifth, an error is detected from the input of the maximum likelihood decoding means, the error is successively accumulated, and the accumulated result is multiplied by a coefficient by the multiplying means to extract a signal corresponding to the thermal asperity. Subtract from the output of the digitizing means.

Sixth, in the signal processing circuit according to the fifth means, a thermal asperity is generated by monitoring the amplitude level of the signal corresponding to the extracted thermal asperity. Only when it is removed from the output signal of the equalizer.

Seventh, in the signal processing circuit according to the sixth means, the output signal of the multiplication means is input to the offset amount correction means of the A / D conversion means.

Eighth, in the signal processing circuit according to the sixth means, an analog subtracting means is provided in the analog signal processing means before the maximum likelihood decoding means, and the output signal of the multiplying means is converted into the D / A converting means. From the analog signal via.

Ninth, in the signal processing circuit according to the fifth to eighth means, means for setting the coefficient value of the multiplying means is provided.

Tenth, in the signal processing circuit according to the third and fourth means and the sixth to ninth means, means for setting a level value for detecting thermal asperity noise is provided.

Eleventh, in the integrated circuit chip using the signal processing circuit according to the tenth means, the detection result of thermal asperity is output to a pin or a register of the integrated circuit chip.

Twelfth, in an integrated circuit chip using the signal processing circuit according to the eighth means, an external capacitor for integrating the output signal of the multiplication means at the connection point between the D / A conversion means and the analog subtraction means. To provide.

Thirteenth, in an integrated circuit chip for signal processing using extended partial response maximum likelihood decoding compatible with an MR head, means for removing at least thermal asperity, A / D conversion means, and hard decision combined type Is provided.

Fourteenth, the integrated circuit chip for signal processing described in the eleventh to thirteenth means is used in a magnetic recording / reproducing apparatus equipped with an MR head.

Fifteenth, in a magnetic recording / reproducing apparatus equipped with an MR head, a means for removing thermal asperity is provided, and a plurality of reproducing operations are performed for thermal asperity noise having an amplitude equal to the reproduced signal amplitude. Reproduction is possible without carrying out.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing an example of the structure of a reproducing circuit (RSPC) 201 provided in a magnetic disk apparatus which is a first embodiment of a magnetic recording information reproducing apparatus of the present invention. It is a figure. FIG. 12 is a conceptual diagram showing an example of the configuration of the magnetic disk device according to the present embodiment.

First, an example of the configuration of the magnetic disk device (HDD) 10 of the present embodiment will be described with reference to FIG. The HDD 10 of the present embodiment is roughly composed of a head disk assembly (HDA) 20 and a package substrate (PCB) 40.

The HDA 20 includes a magnetic disk 2 as a medium, a magnetic head 1 for recording / reproducing data on / from the magnetic disk 2, and a magnetic disk 2 of the magnetic head 1.
103 for performing positioning operation in the radial direction of the
And the R / WIC 104 mounted on the carriage
And a spindle motor 10 for rotating the magnetic disk 2.
Includes 5 etc.

The PCB 40 is a signal processing LSI (SPC)
21 and hard disk controller chip (HDC)
22, a servo controller (SVC) 23, a microprocessor (MP) 24, a SCSI chip 25, a ROM 26 in which a control program and the like are stored, and the like.

The magnetic head 1 is a decoding head having dedicated heads for recording and reproduction, and an MR head 3 for reproduction.

Here, the flow of the reproduction signal will be described. The reproduction signal of the MR head 3 is R on the carriage 103.
MR head preamplifier (MR_
Amplified by PREAMP, package board (PCB)
Input to 40. This signal is input to the reproduction circuit (RSPC) 201 in the signal processing LSI chip 21, and the reproduction circuit outputs the identification result to the interface circuit (INT) 2
Output to 02. Further, the identified signal sequence is sent to the hard disk controller chip (HDC) 22 and is further output from the HDD 10 to an external information processing device (not shown) or the like via the SCSI chip 25 or the like. here,
Only the reproducing circuit portion that receives a signal amplified to a certain amplitude will be described. Reference numeral 203 denotes a recording circuit including a modulation circuit and the like.

In FIG. 1, the RSPC 201 constitutes a signal processing LSI (SRC) 21, together with an interface circuit 202 and a recording circuit 203. In this embodiment, as in the conventional technique, a signal processing technique that combines partial response and maximum likelihood decoding (PRML) is applied. The reproduction circuit (RSPC) 201 mainly includes a variable gain amplifier (VGA) 211 and an analog equalization circuit (AE).
Q) 212, A / D converter (ADC) 213, digital equalizer (DEQ) 214, subtraction circuit (SUB) 221,
Maximum likelihood decoder (ML) 215, sync byte detection circuit (S
YNCDET) 220, demodulation circuit (DEC) 216, a signal processing part, a thermal asperity noise removal circuit (TAC) 222, a variable gain amplifier control circuit (VGAC) 217 for controlling the gain of VGA, and a sample clock of ADC. Voltage controlled oscillator control circuit (VC
OC) 219 and a voltage controlled oscillator (VCO) 218 that supplies the ADC sample clock. The subtraction circuit (SUB) 221 includes a digital equalizer (DEQ) 214 and a maximum likelihood decoder (ML) 215.
The inputs of the VGAC 217 and the VCOC 219, which are connected to each other, are the output of the SUB 221, that is, the input part of the ML 215. A scrambler may be inserted after the DEC 216.

When the noise due to the thermal asperity is input, the noise due to the thermal asperity at the DEQ 214 output is detected by the TAC 222 and the SUB 221 is detected.
This is a configuration for removing this.

An example of the basic configuration of the thermal asperity noise removing circuit (TAC) 222 in this embodiment is shown in FIG. 2 (a), and the process of removing the thermal asperity noise is shown in FIG. 2 (b). The description will be made using the waveforms of each part.

The TAC 222 receives the output waveform (DEQout) 51 of the DEQ 214 as an input. This input signal value sequence is a ternary waveform of partial response class 4 as shown in FIG. The signal DEQout51 including the thermal asperity noise is subtracted from the subtraction circuit (SUB) 31
Input to the addition side input of. On the other hand, the subtraction circuit (SUB) 2
21 output signal SUBout57 is used as a discriminator (DET) 3
Enter 0. The DET 30 is a bit-by-bit discriminator which outputs −-1, 0, +1 with −0.5 and +0.5 as threshold values. The subtraction circuit (SUB) 31 has a ternary waveform DEQ.
Subtract the signal value sequence 58 that is the identification result (-1, 0, +1) of the SUBout 57 in the DET 30 from out51,
The offset signal OFSout53 is calculated. This time,
When thermal asperity occurs at time t1, an error including thermal asperity and noise is output to OFSout53. This signal is the averaging circuit (A
When input to the VE) 32, the output waveform AVEout52 corresponding to the thermal asperity starts to be output at time t2 which is delayed from time t1 by the time Td required for averaging. Here, the averaging is for reducing the noise included in the error signal and more accurately extracting the change in the signal waveform due to the thermal asperity. This signal value sequence 52
Is subtracted from DEQout51 by SUB221, S
Large thermal asperities can be removed from DEQout 51 as shown in UBout 57.

FIG. 3 shows the configuration of a modification of FIG. 2 (a). The thick frame portion has the same structure as the TAC 222 in FIG. In this circuit, a subtraction circuit (SUB) 221 'corresponding to the SUB 221 of FIG. 2A is newly provided. Therefore, the output waveform of AVE32 AVEout52
Is the same as the circuit of FIG. In this circuit, a thermal asperity noise detection circuit (TACS) 33 and a switch (SW) 3 that further receive AVEout 52 are input.
4 are provided. The operation of this circuit will be described with reference to FIG.

A thermal asperity threshold value signal (TAT: TA threshold) 54 is set in the TACS 33 in advance. The TACS 33 closes the switch (SW) 34 by the signal SWgate 55 when the AVEout 52 exceeds the level set by the TAT 54 at time t3. As a result, the thermal asperity correction signal T
Output ACout56. This signal is DEQout5
By subtracting 1 from SUB221, the signal SUBout57 from which the thermal asperity noise is removed is obtained. When AVEout52 becomes TAT54 or less, SW34 opens at time t4 to stop the correction operation. That is, the output of the AVE 32 is used as the correction output of the thermal asperity noise only when the thermal asperity noise is generated. As a result, the above operation can be realized without affecting signals other than the thermal asperity generation period. SWgate 55 is a signal processing LSI as a signal indicating the occurrence of thermal asperity.
(SPC) 21 noise detection signal output pin 55a.

At this time, AVEout52 is added to AVE32.
If a circuit that predicts the thermal asperity from the slope of the rise time or the slope of the fall time of the error signal value sequence is applied, more accurate correction can be performed. Also, TAC
A hysteresis characteristic may be added to the comparison characteristic of S33. As a result, it is possible to avoid the occurrence of a phenomenon in which noise is increased due to the fact that the SWgate 55 frequently repeats on / off due to a slight change in the AVEout 52. The signal indicating the occurrence of thermal asperity (SWgate 55) may be recorded in a register (not shown), or may be output to the noise detection signal output pin 55a with different pulse widths. According to the present embodiment, the thermal asperity threshold signal (TA
By appropriately setting the threshold value of (T) 54, it is possible to avoid the performance deterioration due to the influence of the circuit noise of the TAC 222 which may occur even when the thermal asperity noise is not generated.

Further, since the generation state of thermal asperity noise can be grasped from the outside by the signal output to the noise detection signal output pin 55a, for example, debugging at the development stage of the RSPC201,
It is possible to realize various controls by using the error monitoring and error recovery operation in the MP24.

(Embodiment 2) FIG. 5 is a block diagram showing an example of the structure of a reproducing circuit provided in a magnetic disk device which is a second embodiment of the magnetic recording information reproducing apparatus of the present invention. The configuration other than the TAC 222 is the same as that in FIG.

The TAC 222 according to the present embodiment is composed of a discriminator 30 and a subtraction circuit 31, and has an error detection section that receives the same signal as the input of the ML 215, an adder 35 that receives the output of the error detection section, and a memory. (M) 36 comprises an error accumulation circuit and a multiplication circuit 37 which receives the output of the error accumulation circuit as an input. DEQ the output of TAC222
A subtraction circuit (SUB) 221 that subtracts from the output of 214 is provided and input to the ML 215.

At this time, a switch (SW) 34 is provided at the output of the multiplication circuit 37, and the output of the error detector is used as an input to detect the occurrence of thermal asperity noise from this input value sequence. (TACS) 33 is provided, and the detection output of TACS 33
By opening and closing the switch 34, the output of the multiplication circuit 37 may be used as the correction output of the thermal asperity noise to the subtraction circuit 221 only when the thermal asperity noise is generated.

According to the present embodiment, as in the case of FIG. 3 of the first embodiment, the thermal asperity noise appearing at the output of the DEQ 214 is the SUBo illustrated in FIG.
It can be improved like ut57. The averaging circuit 32 in the first embodiment is replaced with an error accumulating circuit composed of an adder 35 and a memory (M) 36 and a multiplying circuit 37, and the circuit can be simplified. The coefficient value α of the multiplication circuit 37 determines the averaging accuracy. That is, the multiplication circuit 37
Since the coefficient value α of the multiplication of corresponds to the gain of the feedback system, if the coefficient value α is increased, the followability with respect to TA is improved but the accuracy is coarse, and if it is decreased, the followability is deteriorated but the accuracy is reduced. Will be improved. Also, TAC
By setting an appropriate threshold value in S33, it is possible to avoid performance deterioration when thermal asperity noise is not generated.

In the present embodiment, as shown in FIG.
The output of the AC 222 may be input to the A / D converter (ADC) 213 in the preceding stage of the DEQ 214. TAC at this time
A more detailed configuration near 222 is illustrated in FIG. ADC
Reference numeral 213 denotes an A / D conversion circuit 213-1 and a D / A conversion circuit (DAC) for varying the center level of the waveform of the analog signal input to the A / D conversion circuit 213-1.
It has a 213-2 and a subtraction circuit 213-3, and connects the output of the TAC 222 to the input of this DAC 213-2.

According to the present embodiment, the saturation of the ADC 213 due to the thermal asperity noise can be prevented, and the resistance to the thermal asperity noise can be improved as compared with the first embodiment.

(Third Embodiment) FIG. 8 is a block diagram showing an example of the structure of a reproducing circuit provided in a magnetic disk device which is a third embodiment of the magnetic recording information reproducing apparatus of the present invention. FIG. 9 is a block diagram showing the configuration of the detection portion and the correction portion of the thermal asperity noise.

As shown in FIG. 8, an offset amount correction circuit is provided in the analog signal processing circuit in the stage preceding the ML215,
Thermal asperity noise eliminator (TAC) 222
Is converted into an analog signal via a D / A converter (DAC) 224 and input. Further, as shown in FIG. 9, a DAC 224 for correcting the offset amount of the analog circuit, a capacitor 225 for holding the correction voltage, and the analog subtraction circuit 2
23, the error correction signal may be stored in the capacitor 225. Furthermore, the correction voltage holding capacitor 225 is a signal processing LSI (SP) shown in FIG.
C) 21 may be attached externally.

According to the present embodiment, since the DAC 224 and the capacitor 225 operate as a primary integrating circuit,
Smooth correction operation is possible. Further, the analog circuits after the analog subtraction circuit 223 do not need to additionally consider the input dynamic range. Therefore, the design of the analog circuit section is facilitated, and the power consumption and the high speed operation are facilitated.

Further, the multiplication circuit 37 of the thermal asperity noise removal circuit (TAC) 222 may be provided with a register for setting the coefficient value β to be multiplied and a register for setting the maximum output current value of the DAC 224. By setting these register values, the time constant of the correction loop can be defined, and more detailed correction operation can be performed. Also,
As in the first embodiment, the thermal asperity noise detection circuit (TAC) 33 of the thermal asperity noise removal circuit (TAC) 222 may be provided with a register for setting a level for detecting thermal asperity noise. This makes it possible to avoid performance degradation when thermal asperity noise is not occurring.

Further, the detection result (SWgate55) of the thermal asperity noise detection circuit (TACS) 33 of the thermal asperity noise removal circuit (TAC) 222.
May be output to the noise detection signal output pin 55a of the signal processing LSI chip 21 or a register. By referring to the output of the noise detection signal output pin 55a and the register, it is possible to recognize that thermal asperity noise is generated in the reproduced signal even if an identification error due to ML does not occur during reproduction. Further, by referring to this signal, the accuracy for small thermal asperity noise is such that an error does not occur during normal reproduction, which is impossible with the conventional technology, and an error occurs when the spacing is narrowed for some reason. It becomes possible to detect a high value. Further, even if the thermal asperity noise having the same amplitude as the reproduced signal amplitude is input, it is possible to realize a reproducing circuit in which the reproduction performance is hardly deteriorated.

(Embodiment 4) In the present invention, as shown in FIG. 10, extended partial response and maximum likelihood decoding (EP
It is obvious that the same can be applied to a signal processing LSI and a magnetic disk device to which a signal processing technique combining RML) is applied.

Maximum likelihood decoder (ML ') 215' at this time
11 includes a branch metric generation circuit unit (BMU) 60, an add-compare-select unit (ACSU) 61, and a path memory unit (PM).
U) 62 and hard decision unit (HDU) 6
And 3. The HDU 63 reduces the calculation amount of the BMU 60 and the ACSU 61.
The circuit scale as a whole 5'can be reduced.

As described above, according to each of the embodiments of the present invention, even if a reproduced signal on which noise such as thermal asperity is superimposed, such noise can be generated by a relatively small increase in the number of circuit elements. It is possible to provide a signal processing circuit that removes the noise, and to detect a noise due to a small thermal asperity that does not cause an identification error, and to provide a magnetic disk device that does not deteriorate in performance even if a large noise occurs.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say, there is.

For example, in the above description of the first to fourth embodiments of the present invention, the magnetic disk device is taken as an example of the magnetic recording information reproducing apparatus, and the configuration and effects are explained. Obviously, the same can be applied to other magnetic recording / reproducing devices such as tape devices.

[0064]

According to the magnetic recording information reproducing apparatus of the present invention, even in the case of a signal on which noise such as thermal asperity is superimposed, the influence of such noise can be removed by a relatively small circuit. The effect is obtained.

According to the magnetic recording information reproducing apparatus of the present invention,
By providing a reproduction signal processing system capable of detecting noise due to a small thermal asperity that does not cause a reproduction error, it is possible to obtain the effect that the reliability of the operation can be improved.

According to the magnetic recording information reproducing apparatus of the present invention,
By detecting and correcting the minute thermal asperity noise, it is possible to adopt various error-sensitive maximum likelihood decoding methods.

According to the magnetic recording information reproducing apparatus of the present invention,
It is possible to achieve an effect that it is possible to realize a magnetic disk device capable of achieving a high recording density by narrowing the spacing without fearing that thermal asperity noise is mixed into a reproduction signal.

According to the magnetic recording information reproducing apparatus of the present invention,
It is possible to achieve an effect that it is possible to realize a magnetic disk device capable of achieving high throughput by avoiding an overhead due to a retry of a data access operation caused by mixing of thermal asperity noise in a reproduction signal.

According to the magnetic recording information reproducing apparatus of the present invention,
The effect that a high-performance magnetic disk device having a strong proof against the thermal asperity which becomes a problem at the time of narrow spacing can be realized is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a configuration of a reproducing circuit provided in a magnetic disk device which is a first embodiment of a magnetic recording information reproducing device of the present invention.

FIG. 2A is a block diagram showing an example of a basic configuration of a thermal asperity noise elimination circuit,
(B) is a diagram showing an example of the operation.

FIG. 3 is a block diagram showing a modified example of the thermal asperity noise elimination circuit of FIG. 2 (a).

FIG. 4 is a diagram showing an example of the operation of the thermal asperity noise elimination circuit of FIG.

FIG. 5 is a block diagram showing an example of a configuration of a thermal asperity noise removing circuit in a reproducing circuit included in a magnetic disk device which is a second embodiment of a magnetic recording information reproducing device of the present invention.

FIG. 6 is a block diagram showing a modified example of a reproducing circuit provided in the magnetic disk device which is the second embodiment of the magnetic recording information reproducing device of the present invention.

FIG. 7 is a block diagram showing an example of a configuration of a thermal asperity noise elimination circuit in a modification of the reproduction circuit exemplified in FIG.

FIG. 8 is a block diagram showing an example of a configuration of a reproducing circuit provided in a magnetic disk device which is a third embodiment of a magnetic recording information reproducing device of the present invention.

9 is a block diagram showing a configuration of a detection portion and a correction portion of thermal asperity noise extracted in the reproducing circuit illustrated in FIG.

FIG. 10 is a block diagram showing an example of a configuration of a reproducing circuit provided in a magnetic disk device which is a fourth embodiment of a magnetic recording information reproducing device of the present invention.

11 is a block diagram showing an example of a configuration of a maximum likelihood decoding circuit in FIG.

FIG. 12 is a conceptual diagram showing an example of an overall configuration of a magnetic disk device which is a first embodiment of a magnetic recording information reproducing device of the present invention.

FIG. 13 is a conceptual diagram showing an example of a configuration of an interface portion between a magnetic head and a magnetic disk of a magnetic disk device.

FIG. 14 is a diagram showing an example of a reproduction signal waveform including thermal asperity noise.

FIG. 15 is a block diagram showing an example of a configuration of a conventional general reproduction circuit that can be considered.

[Explanation of symbols]

1 ... Magnetic head, 2 ... Magnetic disk (magnetic recording medium),
3 ... MR head (playback head), 4 ... minute projection portion, 1
0 ... Magnetic disk device, 20 ... Head disk assembly, 21 ... Signal processing LSI chip, 22 ... Hard disk controller chip, 23 ... Servo controller, 2
4 ... Microprocessor, 25 ... SCSI chip, 30
... discriminator, 31 ... subtraction circuit (second subtraction means), 32 ...
Averaging circuit, 33 ... Thermal asperity noise detection circuit (comparing means), 34 ... Switch (switching means), 3
5 ... Adder (adding means), 36 ... Memory (storage means),
37 ... Multiplier circuit (multiplier), 40 ... Package substrate,
54 ... Thermal asperity threshold signal, 55 ... Switch opening / closing control input, 55a ... Noise detection signal output pin, 6
0 ... Branch metric generation circuit unit, 61 ... Add-compare-select unit, 62 ... Path memory unit, 63 ... Hard decision unit, 103 ...
Carriage, 104 ... R / WIC, 105 ... Spindle motor, 201 ... Reproducing circuit (signal processing circuit), 202 ...
Interface circuit, 203 ... Recording circuit, 211 ... Variable gain amplifier, 212 ... Analog equalization circuit (first equalization means), 213 ... A / D converter, 213-1 ... A / D conversion circuit, 213-2 ... D / A conversion circuit, 213-3 ... Subtraction circuit, 214 ... Digital equalizer (second equalization means),
215, 215 '... Maximum likelihood decoder (maximum likelihood decoding means), 21
6 ... Demodulation circuit, 217 ... Variable gain amplifier control circuit, 21
8 ... Voltage controlled oscillator, 219 ... Voltage controlled oscillator control circuit, 220 ... Sync byte detection circuit, 221 ... Subtraction circuit (first subtraction means), 221 '... Subtraction circuit (third subtraction means) 222 ... Thermal aspe ..: noise reduction circuit, 223 ... analog subtraction circuit, 224 ... D / A converter, 225 ... capacitor.

Front page continuation (72) Inventor Akihiko Hirano 2880 Kozu, Odawara-shi, Kanagawa Hitachi Storage Systems Division (72) Inventor Naoya Kobayashi 1-280, Higashi Koigakubo, Kokubunji, Tokyo Hitachi Central Research Institute, Ltd. (72) Inventor Seiichi Mita 2880, Kozu, Odawara-shi, Kanagawa Hitachi Storage Systems Division (72) Inventor Masuo Umemoto 1-280, Higashi Koigakubo, Kokubunji, Tokyo Hitachi Research Laboratory, Hitachi Ltd.

Claims (3)

[Claims] 1. A magnetic recording information reproducing apparatus comprising a signal processing circuit for processing a reproduction signal of magnetic recording information read from a magnetic recording medium via a magnetoresistive head, wherein the signal processing circuit comprises: A magnetic recording information reproducing apparatus comprising: thermal asperity noise removing means including means for detecting thermal asperity noise included in a reproduction signal and means for removing the thermal asperity noise by feedback control. 2. The magnetic recording information reproducing apparatus according to claim 1, wherein the signal processing circuit includes at least equalizing means for equalizing the waveform of the reproduced signal and maximum likelihood decoding means, and the thermal asperity noise. The removing means identifies the input signal from the equalizing means to the maximum likelihood decoding means into three values and outputs it, an averaging means that averages and outputs the input signal, and first and second And subtraction means of
The addition input of the first subtraction means is connected to the output of the equalization means, the subtraction input is connected to the output of the averaging means, the output of the first subtraction means is the input of the identification means, and The output of the identification means is used as the subtraction input of the second subtraction means, the addition input of the second subtraction means is connected to the output of the equalization means, and the output of the second subtraction means is connected to the averaging means. A first configuration in which the input is connected to the output of the first subtraction means to the maximum likelihood decoding means, and in the first configuration, the thermal asperity noise removal means includes a third subtraction means and the averaging means Comparing means for comparing the output of the means with a desired threshold value, and switching means, the switching means being connected between the connection point of the output of the averaging means and the subtraction input of the first subtracting means. , Input of the output of the equalizer is added And the output of the third subtracting means, whose output is the subtraction input of the averaging means, is connected to the input of the identifying means, and the output of the comparing means, which receives the output of the averaging means, is the switch means. In the first and second configurations, when the thermal asperity noise removing means receives the thermal asperity noise from the error signal string input to the averaging means, A third configuration provided with means for estimating the amount of sequence error, the thermal asperity noise removing means, and an identifying means for identifying an input signal from the equalizing means to the maximum likelihood decoding means into three values and outputting the value. , First and second subtraction means,
An output of the second subtraction means, which includes an addition means, a storage means, and a multiplication means, has an output of the identification means as a subtraction input and an input to the maximum likelihood decoding means as an addition input of the addition means. The first addition input is used, and the output of the storage means is used as the second
The output of the adding means, which is the addition input to the storage means, is the input of the storage means, the output of the multiplication means is the input of the storage means, and the output of the equalization means is the addition input. A fourth configuration in which the output of the first subtraction means is the input of the maximum likelihood decoding means; in the fourth configuration, the thermal asperity noise removal means compares the output of the multiplication means with a desired threshold value. And a switch means for connecting the switch means to a connection point between the output of the multiplication means and the subtraction input of the first subtraction means, and the output of the storage means as an input. A fifth configuration in which an output of the comparison means is used as a switch opening / closing control input of the switch means, a sixth configuration in the fourth configuration, in which the multiplication means includes setting means for a coefficient value to be multiplied, Or in the fifth configuration, the comparison means,
Seventh, comprising setting means capable of arbitrarily setting the threshold value for determining the level for detecting the thermal asperity noise
In the second or fifth configuration, the comparison means is
Magnetic recording information, characterized in that it includes any one of an eighth structure having means for outputting a comparison result to at least one of an external input / output pin and a register of an integrated circuit element forming the signal processing circuit. Playback device. 3. The magnetic recording information reproducing apparatus according to claim 1, wherein the signal processing circuit includes a variable gain amplifier for controlling an amplitude of the reproduction signal, and a first waveform equalizing circuit for analog analog reproduction signal. The equalizing means, an A / D converting means for converting the reproduced signal into a reproduced digital signal, a second equalizing means for equalizing the waveform of the reproduced digital signal, and a maximum likelihood decoding means; The / D conversion means has at least an offset amount correction means, and the thermal asperity noise removal means extracts the component of the thermal asperity noise from the output signal from the second equalization means to the maximum likelihood decoding means. A first configuration for performing an operation of extracting and feeding back to the offset amount correcting means of the A / D converting means, an analog subtracting means is arranged in a stage before the first equalizing means, The thermal asperity noise removing means extracts a component of the thermal asperity noise from an output signal from the second equalizing means to the maximum likelihood decoding means, and D /
A second configuration in which an operation of feeding back to the analog subtraction unit via the A conversion unit is performed. In the first or second configuration, the maximum likelihood decoding unit is a maximum likelihood decoding unit of combined hard decision type. A magnetic recording information reproducing apparatus characterized by comprising any one of the following: