JPH1196509A - Magnetic disk device and semiconductor device used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a useless component from a regenerative signal mixed with a vertical component and the component proportionating to a magnetization amount by generating plural feedback signals from a decision output obtained from a decision feedback type equalizer and feeding it back to an addition circuit. SOLUTION: The regenerative signal from a head responses longer than a signal bit interval. A pre-filter 4 is constituted so that e.g. a delay element having a delay time of a bit interval is made an elemental element, and respective delay elements are synthesized while multiplying outputs of respective delay elements by a coefficient, and a prescribed filter characteristic is obtained. The number of pieces of the elemental elements are set more than a value dividing a time interval that at least a response waveform is provided with a significant value by the bit interval. The output signal of the pre-filter 4 is set so that the signal of a relevant bit is set to a prescribed value, and a response becomes zero at a bit time before then. A decision circuit 6 discriminates a bit position that magnetization reverse is performed from a zero value to detect the magnetization reverse.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing method for recording digital data on a recording medium for perpendicular recording at high density and reproducing the signal, a semiconductor device using the signal processing method, and further incorporating the semiconductor device. Related to magnetic disk drives.

[0002]

2. Description of the Related Art As the operation speed of computers increases, application software requiring a large-capacity memory is used, and the demand for high-density compact magnetic disks is increasing. For this reason, use of a perpendicular recording medium as a high-density magnetic recording medium has recently been studied. This recording medium is called a single-layer perpendicular recording medium, and a recording medium capable of recording in a direction perpendicular to the disk surface is formed on the magnetic disk surface. Using this perpendicular recording medium, a rectangular wave signal train is recorded by a recording head similar to the conventional one, that is, a wound ring head, and a magnetoresistive head having good reproduction sensitivity is used for reproduction. The properties have been measured and its high density has been confirmed.

[0003] In addition to the single-layer recording medium, a two-layer perpendicular recording medium (having an in-plane recording medium layer below the perpendicular recording medium) has been proposed as a perpendicular recording medium. If these proposed recording media provide ideal perpendicular recording, and if the magnetoresistive head also ideally has sensitivity only to the perpendicular component, the reproduced signal will be a single layer. In this case, the reproduction signal of the conventional in-plane recording is differentiated, and in the case of two layers, the reproduction signal is provided in an integrated form. Therefore, it is naturally conceivable to perform an integration or differentiation operation process to return to the same reproduction signal waveform as the conventional one, and to use the conventional signal processing.

However, an actual perpendicular recording medium is expected to include not only a vertical component but also a slight in-plane component. In addition, even in the head configuration of the magnetoresistive head, the magnetic shield interval sandwiching the magnetoresistive element is actually finite, and the magnetoresistive element itself requires a thickness. As a result, it should be considered that the magnetoresistive head has sensitivity to a perpendicular component, an in-plane component, and a component proportional to the amount of magnetization. In such a practical perpendicular recording / reproducing system, unnecessary signal components have an adverse effect on the simple signal processing as described above, and the probability of a decoded digital signal being erroneous is not necessarily low. Do not provide.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing method of a reproduced signal on a realistic perpendicular recording medium. Specifically, a perpendicular component and a component proportional to the amount of magnetization are mixed. It is an object of the present invention to provide a signal processing for removing unnecessary components from such a reproduced signal. It is another object of the present invention to provide a magnetic disk device utilizing the original high density of perpendicular recording by using this signal processing, and a semiconductor device used for the magnetic disk device.

[0006]

According to the present invention, a digital reproduction signal reproduced from a perpendicular recording medium by a magnetoresistive head is decoded and output by a decision feedback equalizer. However, the feedback signal generation means of the decision feedback equalizer has a plurality of generation means, based on the decision output, means for generating a feedback signal corresponding to the vertical component, and, based on the decision output, It comprises means for generating a feedback signal of an unnecessary component.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to embodiments. FIG. 1 shows a reproduced signal from a perpendicular recording medium in the embodiment. FIG. 1A shows a digital signal sequence recorded on a magnetic recording medium expressed by a binary signal. Tc indicates a bit interval of the digital signal. FIG.
(B) is a signal waveform shown in FIG.
(C) shows the magnetization state of the recording medium.
The thickness indicates the thickness of the magnetic layer of the recording medium, and is characterized in that it is magnetized in the thickness direction in perpendicular recording. Due to this feature, even if the bit interval of the signal sequence becomes narrow,
Since the magnetization directions that are mutually reversed act in a direction to increase the magnetization, a stable magnetization state is maintained even in a high-density recording state.

[0008] On the perpendicularly magnetized recording medium,
When a magnetoresistive head having a finite shield interval passes, a complex reproduced signal as shown in FIG. 1F is obtained as a head output. Examining the reproduced signal in FIG. 1 (f) in detail, it can be seen from FIG. 1 (d) that the component is proportional to the amount of change in the perpendicular magnetization by magnetically shielding the magnetoresistive element.
And the component diagram 1 (e) proportional to the amount of magnetization, which is a property inherent in the magnetoresistive element, was found to be added.
Generally, the component of FIG. 1 (d) is 70 to 80%, which is the main component, and therefore, the conventional signal processing focuses on only the component of FIG. 1 (d). However, it is indispensable to use a finite-length magnetoresistive element, and the component diagram (e) based on this cannot be ignored. Naturally, the error rate of the signal obtained by the reproduction signal processing when ignored is high.

FIG. 1D shows a response waveform depending on the location of the magnetization reversal. If there are two magnetization reversals, the response of each magnetization reversal is added. On the other hand, component diagram 1 (e) is a response waveform depending on how long the same signal continues, and component diagram 1 (d)
Is different in nature. Component diagram 1 for which addition is possible
(D) shows a conventional partial response (Partial
Response). However, since how long the same signal relating to the component diagram 1 (e) continues can be known from the decoded result, the conventional partial response cannot be used as it is.

In the present embodiment, a decision feedback equalizer is used to generate a feedback signal for the component diagram 1 (d), and the amount of feedback for the component diagram 1 (e) is determined using the signal sequence of the decision result. create. FIG. 2 shows a reproduction signal system diagram of the embodiment. 1 is a magnetic disk having a perpendicular magnetic recording medium, a head system, 2 is a variable amplifier for setting the amplitude of a reproduced signal to a constant value, 3 is a sampling circuit, 4 is a decision feedback based on the component (d) in FIG. Reference numeral 5 denotes an addition circuit, 6 denotes a determination circuit for determining a signal from which unnecessary components have been removed into a binary signal, and 7 denotes an output of a binary signal. Reference numeral 8 denotes a shift register for storing a judgment output, and 9 denotes an output of the shift register 8 as an input address.
A random access memory in which a feedback signal relating to (d) is created in advance, 10 is a D / A converter for returning an output signal of the random access memory 9 to an analog signal, and 11 is an output inverting according to a judgment output 7 Is a low-pass filter, and generates a pseudo feedback signal related to the response diagram 1 (e) by the flip-flop 11 and the low-pass filter 12.

FIG. 3 is an enlarged view of a signal waveform for explaining the embodiment in more detail. FIG. 3 (d1) shows a detailed waveform of a component diagram (d) corresponding to one magnetization reversal in FIG. The waveform example of FIG. 1 shows a case where the response of the disk and the head system is shorter than the signal bit interval Tc. FIG. 3 (d1) shows a waveform example in the case of high-density recording.
As shown in the figure, the reproduced signal from the head has a signal bit interval T
Responds longer than c. The pre-filter 4 includes, for example, a delay element having a delay time of a bit interval as an element element.
The output of each delay element is composed while multiplying it by a coefficient so as to have a predetermined filter characteristic. The number of element elements is set to be at least larger than a value obtained by dividing a time interval in which one response waveform has a significant value by a bit interval. As shown in FIG. 3 (g1), the output signal of the pre-filter 4 has a predetermined value (in FIG.
Indicated by ), And the response is set to zero at earlier bit times. Therefore, bits subsequent to the bit have a large interference value (indicated by ▲). The determination circuit 6 detects the magnetization reversal by distinguishing the bit position having the magnetization reversal from the above-mentioned predetermined value and the zero value.

When the magnetization reversal is detected, a first feedback signal having a different sign of the interference value indicated by the value 値 is supplied via the shift register 8, the random access memory 9, and the D / A converter 10. The output of the adder circuit 4 makes it possible to obtain a response waveform having no interference with bits other than the bit.
The same processing is performed for the response diagram 3 (g2) relating to the second magnetization reversal in FIG. The configuration of such a decision feedback equalizer has also been studied in conventional in-plane recording, and can be realized with almost the same design except for the difference in response waveforms. However, in the case of perpendicular recording, it is necessary to further return the component diagram (e) proportional to the amount of magnetization to eliminate the influence thereof. Therefore, the decision output 7 is input to the flip-flop 11, and the output FIG. 3 (h) is formed via the low-pass filter 12 to form the second feedback signal FIG. 3 (i), which is also input to the addition circuit 4. I do. With these two feedback signals, a response waveform diagram (j) without interference of bits other than the bit concerned is obtained.

Since two feedback loops are formed, a difference in delay time between them may occur. Therefore, although not shown in the circuit configuration diagram of FIG. Means may be provided. Since the low-pass filter 12 is a simple replacement of the pre-filter 4, the pre-filter 4 is used in place of the low-pass filter 12 in a magnetic disk device requiring particularly high reliability.

The above embodiment has described the method of generating a feedback signal based on the response corresponding to the perpendicular magnetization reversal. In another embodiment, a decision feedback equalizer can be configured based on the response of a unit pulse. FIG. 4 is an explanatory diagram of a response waveform based on a unit pulse response. FIG. 5 is a circuit configuration diagram of a decision feedback equalizer based on a pulse response. The symbol p is added to indicate that the pulse response standard is used. FIG. 4 corresponds to FIG. In FIG. 4, the digital signal 1 indicates a positive unit pulse (bp). Although not shown in the drawing, the digital signal 0 is given a response waveform by a negative unit pulse. The magnetization state of the positive unit pulse is indicated by (cp). The response of only the vertical component is given by (dp). A signal proportional to the magnetization component is indicated by (ep). The response (dp) is divided into a response ○ of a predetermined value and a response 分 の of the interference by the pre-filter 4-p in the same manner as in FIG. However, since the response (dp) changes from a negative response to a positive response and then back to a negative response, in order not to lengthen the interference much, it is said that the polarity of the interference is one. It is necessary to break the conventional idea and reduce the number to two as shown in (gp) in FIG.

The circuit configuration based on the pulse response does not change much. Only the design of each element circuit is different. For this reason, the number of each element circuit is assigned a symbol p to correspond to each element circuit having a circuit configuration based on magnetization reversal. In the pulse response standard, a feedback signal having a component proportional to the amount of magnetization is generated from the determination result, and the determination result may be directly input to the low-pass filter 12-p.

The case where there is an unnecessary component proportional to the magnetization amount other than the perpendicular component has been described above. Further, the case where a reproduced signal that is not ideal for a perpendicular medium and includes an in-plane component can be obtained can be dealt with as is apparent from the above description. That is, a feedback signal for removing unnecessary in-plane components from the determination output may be created.

[0017]

According to the present invention, there is provided a signal processing method capable of putting a perpendicular recording medium suitable for high-density recording to practical use. In the in-plane recording, the recording bit is shortened, and the magnetizations facing in opposite directions act to weaken each other's magnetization, and it is said that the recording density is limited to about 10 gigabits per square inch. The practical use of perpendicular recording according to the present invention can provide a magnetic disk drive that exceeds this limit.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention using signal waveforms.

FIG. 2 is a circuit configuration diagram according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a signal waveform in the first embodiment in more detail;

FIG. 4 is a signal waveform diagram for explaining a second embodiment.

FIG. 5 is a circuit configuration diagram according to a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk with perpendicular magnetic recording medium, head system, 2 ... Variable amplifier, 3 ... Sampling circuit, 4 ... Pre-filter, 5 ... Addition circuit, 6 ... Judgment circuit, 8 ... Shift register, 9 ... Random access Memory, 10: D / A converter, 11: flip-flop, 12: low-pass filter.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichi Uehara 5-2-1, Josuihoncho, Kodaira-shi, Tokyo Inside Semiconductor Division, Hitachi, Ltd. Address: Central Research Laboratory, Hitachi, Ltd.

Claims (8)

[Claims] 1. A magnetic disk drive for obtaining a decoded output from a digital reproduction signal reproduced from a magnetic recording medium by a decision feedback equalizer having a pre-filter, an addition circuit, and a decision unit. A plurality of feedback signals are generated from the determined output and fed back to the adder circuit. 2. The magnetic disk drive according to claim 1, wherein said magnetic recording medium is a perpendicular recording medium in which a perpendicular component is dominant. 3. The magnetic disk drive according to claim 1, wherein a magnetoresistive head is used as said reproducing means. 4. The feedback signal generating means of the decision feedback equalizer includes means for generating a feedback signal based on a decision output, and means for generating a feedback signal based on a series of the decision outputs. 2. The magnetic disk drive according to claim 1, wherein: 5. A semiconductor device which obtains a decoded output of a digital reproduction signal reproduced from a magnetic recording medium by a decision feedback equalizer having a pre-filter, an addition circuit and a decision unit, is obtained from the equalizer. A semiconductor device, wherein a plurality of feedback signals are generated from a determination output and fed back to the addition circuit. 6. The semiconductor device according to claim 5, wherein said magnetic recording medium is a perpendicular recording medium in which a perpendicular component is dominant. 7. The semiconductor device according to claim 5, wherein a magnetoresistive head is used as said reproducing means. 8. The feedback signal generating means of the decision feedback equalizer includes means for generating a feedback signal based on a decision output, and means for generating a feedback signal based on a series of the decision outputs. The semiconductor device according to claim 5, wherein: