Magnetic recording and reproducing apparatus, and magnetic recording and reproducing signal processing circuit

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a magnetic recording / reproduction signal processing circuit for perpendicular magnetic recording.

【0002】

[Conventional technology]

Research on perpendicular magnetic recording is underway as a magnetic recording method suitable for high recording densities. In the perpendicular magnetic recording method, there are many recording methods in which a monopole head and a two-layer film structure medium composed of a soft magnetic backing layer and a recording magnetic layer are combined because of the strength and steepness of the recording magnetic field generated from the recording head. Used.

【0003】

When the magnetization information is reproduced by the reproduction head from the magnetization-recorded perpendicular magnetic recording medium, the reproduction signal from the head becomes a rectangular wavy signal waveform corresponding to the recording magnetization distribution on the medium.

【0004】

A signal processing method suitable for data demodulation of a perpendicular magnetic recording system reproduction signal has not been studied so much in the past, but a perpendicular magnetic recording system reproduction signal has a square wave shape and contains a large amount of DC signal components. Therefore, some techniques similar to partial response class I used in optical recording / playback devices, this extended method (Japanese Patent Laid-Open No. 11-66755), and integrated signal detection have been proposed.

【0005】

The signal equalization processing by partial-response is a signal processing method widely and generally used in the in-plane magnetic recording method, and performs signal processing in combination with the maximum-liklihood decoding method. This makes it possible to improve the SN quality of the reproduced signal and perform highly reliable data reproduction.

【0006】

[Problems to be Solved by the Invention]

As described above, the reproduced signal waveform in the perpendicular magnetic recording system contains a large amount of direct current and low frequency components. In a realistic reproduction signal processing circuit system, a reproduction amplifier and an automatic gain control circuit (AGC) are provided at the forefront of the circuit system, but the reproduction amplifier and AGC block low-frequency signals near DC due to circuit characteristics. Has the property of Therefore, distortion of the DC amplitude component and fluctuation of the signal baseline occur in the reproduced signal waveform.

【0007】

On the other hand, the direct current of the reproduced signal and the low frequency in the vicinity of the direct current include a lot of noise and distortion on the reproduced signal called medium noise. The power spectrum of this noise distortion has an energy distribution concentrated near direct current and low frequencies. Therefore, even if the reproduced signal is simply subjected to low frequency compensation, the noise component is also amplified and the signal quality is deteriorated. Since the partial response class I, its extended method (Japanese Patent Laid-Open No. 11-66755), and the integrated signal detection method are signal processing methods that leave the DC component as it is, noise contained in the DC component is not considered at all.

【0008】

It is an object of the present invention to provide a more suitable signal processing method for the reproduced signal waveform in the perpendicular magnetic recording method.

【0009】

[Means for solving problems]

As described above, the reproduced signal in the perpendicular magnetic recording method contains a large amount of DC signal components, but on the other hand, various noises from the recording medium and the reproduction system amplifier circuit are in the vicinity of this frequency component. Many disturbance factors such as distortion due to low frequency frequency loss of the signal transmission system are localized.

【0010】

In order to reduce this effect, waveform equalization processing is performed to give a frequency characteristic in which the low frequency signal component in the vicinity of the DC signal component of the reproduced signal is transmitted by the optimum amount. By performing such waveform equalization processing, the influence of medium noise and waveform distortion in the vicinity of low frequencies is appropriately suppressed, and the detection signal component of the perpendicular magnetic recording / reproduction signal contained more in the low frequency region in the vicinity of DC is eliminated. Optimal maintenance. At the same time, in order to suppress the emphasis of the high-frequency noise component of the white noise on the reproduced signal generated from the device, head, and circuit element, the equalization processing waveform is subjected to partial response waveform equalization to the most probable decoder. The input noise is whitened, and the most probable data demodulation is performed in the subsequent stage. By performing the waveform equalization processing of the reproduced signal in this way, the error rate characteristic of the demodulated data is improved.

【0011】

Specifically, the transfer characteristics for partial response waveform equalization that have the above-mentioned effects are polynomials. [0012]

[Number 1]

<img file="JP2002133604A_D0001.tif" />【0013】

It is described using the 1-bit signal delay operator D as in. The first term is p as the impulse response of the equalization process.₁, P₂, P_nIt means that the intersymbol interference response of the real value of is given as an n continuous bit signal value, and the high frequency noise component emphasis is suppressed by appropriately giving the intersymbol interference response to the impulse response waveform of the recording / reproduction system. Noise whitening waveform equalization can be realized.

【0014】

Further, the second term (1-αD) (α is a real value of 0 α 1) corresponds to the low frequency suppression process, and this process corresponds to the signal to be processed and α 1 bit time before this signal. It means to take the difference between the multiple signal values. Here, if α is set to 1, a frequency characteristic that completely blocks the DC signal is given, which corresponds to digital differential processing.

【0015】

In the present invention, the low frequency signal component is intentionally suppressed by taking the parameter α to an appropriate value, and the ratio of this suppression is arbitrarily adjusted by selecting the parameter α. In the present invention, partial response waveform equalization processing having these two functions is performed, and waveform equalization that simultaneously suppresses the influence of noise / distortion localized in the low frequency region and the increase in high frequency equalization noise. By carrying out the method and the most probable data demodulation processing according to the method, good data demodulation is realized for the reproduced signal of the perpendicular magnetic recording method.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) FIG. 1 shows a basic embodiment configuration of the magnetic recording / reproducing device provided by the present invention. In this embodiment, the information code data 1 {a input to the recording signal processing circuit 9a_k} (K; an integer indicating the bit time) is subjected to a predetermined code conversion process by the encoder 2, and the recording code data {b_kIs converted to }. Recording code data {b_k} Is an analog recording current signal {c via the recording current conversion processing circuit 3a and the recording amplifier 3b._kAfter being converted to }, the information is recorded by being supplied to the recording perpendicular magnetic recording head medium system 4.

【0017】

In the perpendicular magnetic recording head medium system 4, a bilayer film perpendicular magnetic recording medium having a recording magnetic layer 6a and a soft magnetic backing layer 6b on a substrate 6c is used as the recording medium 6, and a single magnetic pole head is used as the recording head 5. To use. The recording magnetic field of the recording head is induced by the recording current passing through the coil 5b wound around the main magnetic pole 5a. The recording magnetic field magnetizes the recording medium in the medium thickness direction. When the magnetization information is reproduced from the vertical magnetic recording medium recorded in this way by using the reproduction head 7 having the magnetoresistive (MR: Magneto Resistive) effect element 7a, the reproduction signal 8 from the head is as shown in FIG. Corresponding to the recording magnetization distribution on the medium, the voltage changes stepwise at the transition position in the recording magnetization direction, resulting in a rectangular wave shape with a blunt rise. Sign {d_k} Indicates the reproduction signal sequence.

【0018】

The width of the waveform rise or fall of the reproduced signal is determined by the structure and characteristics of the perpendicular magnetic recording head medium system 4, the recording / reproducing conditions, and the like, and both the output voltage of the signal are factors that hinder the high recording density. Further, noise due to various causes is superimposed on the waveform, and waveform distortion depending on the frequency transmission characteristics of the head medium system and other electronic components is superimposed. In the reproduction signal processing circuit 9b, the reproduction signal 8 is amplified by the reproduction amplifier 10, the reproduction signal amplitude is adjusted to a predetermined level by the automatic gain control amplifier 10a, and unnecessary high frequency noise and signal components are adjusted by the low frequency filter 11. After removing, the recording code data {b by the analog-to-digital (A / D) converter 12._kDiscrete playback signal sequence sampled to a digital value at the bit timing of} {e_kConvert to }. In the present invention, this discrete reproduction signal sequence {e_k}, In order to demodulate the data code with the highest efficiency and reliability, the equalizer 13 in the subsequent stage is used to equalize the partial response waveform suitable for the reproduced signal 8, and the output signal from this equalizer 13 is output. Demodulated data code string {g that seems to have the lowest error rate by the most likely decoder 14._kConvert to }. In partial response waveform equalization, by adding a known waveform interference value over a finite bit length on the output signal waveform, the increase in high frequency noise due to emphasis on high frequency signal components in waveform processing can be reduced as much as possible. , Performs waveform processing to avoid the influence of signal distortion and noise in the low frequency range including the DC (DC) component of the reproduced signal 8. The most likely decoder 14 performs data demodulation processing using a Viterbi algorithm. Demodulated data code string demodulated by the most likely decoder 14 {g_k} Is subjected to inverse conversion processing via the decoder 15, and the original information code data 1 {a_kReproduction code data 16 {a corresponding to}_kPlayback output as'}.

【0019】

FIG. 3 illustrates the details of the partial response waveform processing in the equalizer 13 in the embodiment of FIG. In FIG. 3, the reproduction waveform 19 is an output waveform from the reproduction head 7 when the die-bit recording magnetization pattern 18 (pair of two adjacent recording magnetization inversions recorded at the shortest bit interval 18a) on the recording medium 6 is reproduced. is there. As described above, at the timing of the two magnetization transitions, the step response signals 19a having a blunt rise overlap depending on the frequency characteristics of the head medium system, so that an isolated pulse waveform is output. In a general perpendicular magnetic recording / reproduction system having the above-mentioned head medium system, it is known that each step response signal 19a can be approximated by a tanh type function, and the above-mentioned dibit reproduction waveform 19 has a signal amplitude Vpp. By the parameter K that determines the rising width, [0020]

[Number 2]

<img file="JP2002133604A_D0002.tif" />【0021】

It is approximated by the following equation. Here, K is a bit of the time width required for the change from 25% to 75% of the maximum amplitude at the rise or fall of the step response signal waveform obtained when the isolated recording magnetization reversal on the recording medium 6 is reproduced. It is a value standardized by the time interval Tb. This is the impulse response output waveform for the head medium system, that is, the recording code data {b._k} The signal response to the isolated bit 1 on}, and the individual bits b of the recorded code data._kThe power spectrum 20 (dotted curve) in the frequency domain of this dibit reproduction waveform 19 can be regarded as a detection response to, and as shown in FIG. 4, for bit detection in a lower region centering on the DC component. The signal energy is concentrated.

【0022】

However, since the reproduction signal 8 from the reproduction head 7 reproduces data via electronic components such as the reproduction amplifier 10 and signal transmission line characteristics, it is affected by waveform distortion due to deterioration of these frequency characteristics. In particular, the reproduction amplifier 10 has no choice but to allow low-frequency cutoff characteristics including a DC component in order to realize a wideband amplifier circuit for high-density and high-frequency recording / reproduction. Waveform distortion due to loss becomes remarkable. That is, the power spectrum 20 of the above-mentioned dibit reproduction waveform 19 is distorted and demodulated so as to have a frequency characteristic in which the frequency component near the direct current is missing as shown in 20b by passing through the reproduction amplifier. Become. In order to compensate for this low-frequency waveform distortion on waveform processing, an excessive compensation circuit is required, which causes excessive emphasis on the superimposed noise component and causes an adverse effect.

【0023】

Further, the spectrum of medium noise sensed by the reproduction head 7 from the recording medium 6 has a frequency composition localized in a low frequency region centered on a DC component, as shown in 20a of FIG. As described above, since the power spectrum 20 of the dibit reproduction waveform 19 to be detected and the spectrum 20a of the medium noise have the same frequency composition having a peak in the vicinity of the DC component, this and the low frequency component of the reproduction signal are combined. It is extremely difficult to separate and detect.

【0024】

With respect to this signal composition, in the present invention, the equalizer 13 waveform-processes the above-mentioned dibit reproduction waveform 19 into an equalized waveform 22 having the equalized waveform power spectrum 21 shape shown in FIG.

【0025】

Low-frequency compensation is performed so that the DC component has an appropriate magnitude for the reproduced waveform (the waveform obtained by viewing the power spectrum of 20b in FIG. 4 in the time domain) that has passed through the reproduction amplifier. By applying an appropriate low-frequency suppression in the equalization process, the medium noise component concentrated in the low frequency range such as 20a is appropriately suppressed / blocked, and it can be seen in the power spectrum 21 of the reproduced signal waveform actually observed. It is possible to set an optimum signal state that can realize data demodulation with a more suitable signal-to-noise ratio by effectively utilizing the low-frequency signal component obtained for data demodulation.

【0026】

In the high frequency region near the Nyquist frequency, the spectral intensity of the original power spectrum 20 of the reproduced waveform 19 and the spectral intensity of the equalized waveform match (ideally match) as in the conventional partial response equalization. By performing waveform equalization processing, high-frequency noise enhancement in equalization processing is suppressed. In the equalization process that moderately suppresses and retains the low frequency range, the spectral intensity of the power spectrum 20 originally possessed by the reproduced waveform 19 and the power spectrum of the equalized waveform 21 near the Nyquist frequency are compared with the equalization process that completely cuts off the direct current. Since the spectral intensities of the above can be brought closer to each other, the enhancement of high frequency noise in the equalization process can be further suppressed. Further, in order to prevent deterioration of the data decoding process in the subsequent stage, the noise component included in the reproduced signal waveform is whitened. As described above, by performing the equalization processing of the reproduced signal with the signal having the frequency characteristic as shown in FIG. 4 as the equalization target, it is possible to demodulate the data in a situation with less noise and distortion.

【0027】

In the conventional partial response equalization processing, the amount of waveform interference (a)₁, A₂, A₃, A_n) (Each interference value a_kIs a real number, k is an integer indicating the bit time, a₁, A_nReduces the emphasis of high frequency equalization noise by properly selecting non-zero) so that it faithfully matches the frequency composition of the reproduced waveform 19, that is, the power spectrum 20 (frequency composition with the DC signal component as the peak). ing. In this case, it is a condition that all the interference values have the same sign. In the present invention, in order to appropriately compensate the DC signal component for the reproduced waveform 19, a₁The same polarity (same sign) interference amount from the beginning starting from, and a_nCalculate the waveform interference amount of the equalization target so that the same polarity (same sign) interference amount at the end ending with is different polarity. The shape of the equalized waveform 22 with respect to the dibit reproduction waveform 19 at this time is observed as a dipulse signal waveform having an asymmetric inverse polarity amplitude, and as shown in FIG. 3, the main signal response (in 22 in FIG. 4, a₁, A₂, A₃Undershoot waveform with opposite polarity to the tail part (in 22 in Fig. 4, a)₄, A₅The waveform shape is as if the part) was added.

【0028】

On the other hand, in the case of completely blocking the DC component with respect to the interference amount of such an equalization target, (a)₁, A₂, A₃, A_n), Set the constraint condition as in Eq. (2).

【0029】

[Number 3]

<img file="JP2002133604A_D0003.tif" />【0030】

The constraint condition of Eq. (2) is the frequency representation H (f) (f is the frequency) of the equalized waveform 22. [0031]

[Number 4]

<img file="JP2002133604A_D0004.tif" />【0032】

However, it is easily derived from the condition that f = 0 and becomes 0.

【0033】

Also, [0034]

[Number 5]

<img file="JP2002133604A_D0005.tif" />【0035】

When | H (0) | = | a₁+ a₂+ a₃+ A_n| 0, so absolute value | a₁+ a₂+ a₃+ A_nBy constraining the magnitude of |, the DC component of the equalized waveform power spectrum 21 can be defined to a desired value.

【0036】

Under constraint condition (4), many classical filter theories are used to determine the noise whitening filter characteristics that minimize the output noise energy from the equalizer 13 for the reproduced waveform 19. By using many of the disclosed algorithms, such as the learning algorithm of the linear prediction filter, it can be easily implemented for the actual reproduced waveform.

【0037】

The target value of the partial response equalization waveform (interference amount) that intentionally suppresses such DC components is [0038]

[Number 6]

<img file="JP2002133604A_D0006.tif" />【0039】

It can be generally defined by the transfer polynomial F (D). Where p₁, P₂, ..., p_k, P_nIs a real number indicating the additional interference amount ratio, and when the transfer polynomial (4) is expressed as the partial response interference amount as described above, [0040]

[Number 7]

<img file="JP2002133604A_D0007.tif" />【0041】

Will be. That is, [0042]

[Number 8]

<img file="JP2002133604A_D0008.tif" />【0043】

Is.

【0044】

The first term (p) of the transfer polynomial F (D)₁+ p₂D + p₃D²+ P_nD^n-1) Is the waveform interference for matching the equalized waveform power spectrum 21 with the power spectrum 20 of the reproduced waveform 19, and can be determined based on the design of the noise whitening matching filter. In general, the additional interference amount ratios that match a signal having a frequency composition having a DC component as a peak, such as the power spectrum 20, all have the same sign.

【0045】

The first term (1-αD) of F (D) means an intersymbol interference addition operation for adding the characteristic of low frequency suppression, which is a feature of the present invention, and each signal in the time series of the reproduced signal. It means the process of subtracting the signal value obtained by multiplying the value by α with a delay of 1 bit. This parameter α is a parameter for suppressing the low frequency region of the target equalization waveform and adjusting the DC signal component. In particular, when α = 0 is set, it indicates that the DC component is not cut off, and when α = 1 is set, it indicates that the DC component is completely cut off. After determining the interference amount of the first term of F (D) with respect to the reproduced waveform, this parameter α is adjusted appropriately. Further, α is determined first, and the interference amount of the first term of F (D) is determined based on the above-mentioned design criteria of the noise whitening matching filter under the constraint condition of Eq. (4). You may.

【0046】

5 to 7 show the amplitude ratio of the optimum waveform interference amount to be set in the present invention for each parameter α with respect to the reproduced waveform 19 of the equation (1) having various parameters K. It is a thing.

【0047】

Further, FIG. 8 shows the relationship between the selected low-frequency suppression parameter α and the error rate of the data bit (reliability of data demodulation) for the reproduced signal having the parameter K of 1.5. As shown in this figure, α is in the range of 0.1 α 1, and α = 0, that is, an equalization method with a lower data bit error rate than the waveform equalization method that completely blocks the DC component. It turns out that it can be realized. For the reproduced signal of the actual perpendicular magnetic recording / reproduction system, the optimum α value is set according to the characteristics of the reproduced signal and the medium noise.

【0048】

As described above, in the partial response equalization method of the present invention, from the first condition of how much the DC component is compensated for the reproduced signal and the second condition of whitening the noise component and reducing the noise intensity as much as possible, The equalization target, that is, the amount of waveform interference is determined.

【0049】

Optimal waveform interference determined as above (a₁, A₂, A₃, A_n), It is extremely easy to set the circuit parameters of the equalizer 13 in relation to the input reproduced waveform 19 according to the known filter design theory. In many cases, the equalizer 13 has a shift register in which a storage delay element 23 for storing a 1-bit signal value is connected in series, and a predetermined tap coefficient (h), as shown in FIG.₁, h₂, h₃ H_L) (L is the tap length) is multiplied by each stored content to perform a product-sum operation. It is composed of a transversal filter composed of a multiplier 24, an adder 25a, and the like. 26 is an adaptive learning circuit that observes the signal output from the equalizer and the amount of waveform interference (a).₁, A₂, A₃, A_n) Is evaluated and the optimum tap coefficient is calculated.

【0050】

FIG. 10 shows an example of a general equalizer for effectively realizing the partial response equalization in the present invention with respect to an actual reproduced signal. In an actual recording / playback system, the equalizer 13 is realized by two delay addition arithmetic processing circuits in order to correspond to a vertical recording head medium system having various characteristics and to select and use a more optimum α. The above-mentioned partial response transmission characteristics [0051]

[Number 9]

<img file="JP2002133604A_D0009.tif" />【0052】

It is configured according to. The filter 27 in the previous stage is a noise-white matched filter, and has the same configuration as the transversal filter in FIG. 9, and has the first term (p).₁+ p₂D + p₃D² + P_n^n-1) Is used to equalize the partial response waveform that adds intersymbol interference. In order to realize the second term (1-αD) by using the variable parameter α, the low-frequency suppression filter 28 in the next stage has a storage delay element 23 that stores a 1-bit signal and an output from the storage delay element 23. It is composed of a multiplier 24 and a subtractor 25b that multiply the suppression parameter α. The (1-αD) processing by the low frequency suppression filter 28 in the subsequent stage may be preceded by the noise white matching filter 27. Further, referring to the output signal values of the noise white matched filter 27 and the equalizer 13, the adaptive learning circuit 26 provides the filter tap coefficient h of the transversal filter._fCan be easily calculated by using a known technique.

【0053】

The signal output from the equalizer 13 as in the above embodiment is demodulated by the most likely decoder 14 using a known Viterbi algorithm or the like. FIG. 11 shows an example (n = 4) of the state transition trellis diagram of this Viterbi decoding, and each arrow indicates the recording code data 3 {b assumed at the bit time k._k} And the corresponding output signal value from the equalizer 13 {f_kThe value of} is written. In all the state transitions indicated by the temporal transition of this trellis diagram, the code sequence indicated by the most probable transition is selected as the decoded data, and signal reproduction is performed.

【0054】

(Example 2) In the equalizer 13 of the present invention, the low frequency signal component including the DC component of the reproduced signal can be flexibly adjusted by changing the suppression parameter α. This helps to eliminate the effects of DC component offsets and low frequency fluctuations / distortions that often occur on actual playback signals. In particular, in a high-density recording / reproduction system, the magnetic resistance characteristic due to the temperature rise due to the contact between the magnetoresistive effect element 7a and the recording medium 6 due to the characteristic fluctuation of the reproduction head 7 and the narrowing of the distance between the reproduction head 7 and the recording medium 6. The TA (Thermal Asperity) phenomenon due to a large change in is remarkable. At this time, a large DC offset fluctuation that exceeds the normal maximum amplitude occurs in the reproduced signal. FIG. 12 is a diagram schematically explaining such a TA phenomenon.

【0055】

Normally, the normal signal waveform 30 is contained in the signal level between the normal maximum signal levels 29a by the automatic gain control amplifier 10a, and has a stable normal offset level 29b by a predetermined offset adjustment. When the above TA phenomenon occurs on the normal signal waveform 30, a waveform phenomenon such as the TA reproduction waveform 32 is typically observed, and the rapid maximum signal level 29a is exceeded from the TA occurrence time 32a. Signal offset fluctuation 32b occurs. This offset fluctuation continues for a relatively long period of time until the TA phenomenon is alleviated. The signal offset variation 32b often far exceeds the normal maximum signal level and has a duration typically ranging from tens to hundreds of bits. As can be seen from the figure, the signal offset fluctuation 32b due to the TA phenomenon is the partial response waveform equalization of the method in which the long-term offset signal fluctuation is superimposed on the regular reproduction waveform 30 and the DC component remains. Data demodulation by decoding makes it difficult to demodulate data. This effect can be eliminated by strengthening the DC cutoff characteristic of the equalizer.

【0056】

FIG. 13 shows an embodiment of the reproduction signal processing circuit 9b for this purpose. A TA detection circuit 33 for detecting the generation of the TA reproduction waveform 32 as shown in FIG. 12 is provided in the subsequent stage of the reproduction amplifier 10. There are various TA detection methods, and the automatic signal gain control amplifier 10a detects abrupt fluctuations in the detected input playback signal level, or the level of the playback communication waveform 32 detects a preset TA. Threshold 31a, 31b for a given time T_taThere are various methods such as catching this as a signal abnormality when the above is continuously exceeded. In this embodiment, data demodulation is usually performed using the parameter α that gives the optimum signal conditions to the normal reproduction signal waveform 30, or the partial response equalization processing that appropriately compensates for the low frequency range, and the TA reproduction waveform 32. When is detected, the DC cutoff is strengthened by setting the low frequency suppression parameter α in the equalizer 13 to 1, and its influence is eliminated. There are a plurality of suppression parameters α (α) in the register circuit 34 and the like.₁, Α₂, ...) is stored, and one of them is selected by the selection circuit 35 according to the abnormality detection signal (control signal) 33a that notifies the signal abnormality such as TA, and this is given to the equalizer 13. It has a structure.

【0057】

In this way, the equalizer 13 is operated by changing the values of a plurality of parameters α depending on whether a signal abnormality such as a TA waveform 28 or an offset fluctuation is detected and a normal case where it is not detected, in other words, it is different. By selectively using the partial response equalization processing having the DC component passing characteristic, the reliability of data demodulation can be further improved under the reproduction signal processing conditions more suitable for the state of the reproduction signal. Further, the tap coefficient (h) of the equalizer 13 for realizing the equalizer characteristic for partial response equalization having the DC component passing characteristic instead of the parameter α₁, h₂, h₃ H_L) Or, a plurality of equalizer parameters that specify other characteristics may be prepared and selected and set. The signal delay circuit 36 is a circuit that performs a process of delaying a signal abnormality portion in order to supplement the delay due to the signal abnormality detection process and the delay due to the parameter switching process. Since it is not involved, the explanation is omitted.

【0058】

(Example 3) As a concrete configuration for implementing a circuit in which equalization characteristics are used properly according to a reproduction signal, it is realized by one reproduction system signal processing circuit by making the equalizer parameter variable as shown in FIG. In addition to the configuration method, it is also possible to take an embodiment of the configuration as shown in FIG. 14 in which a plurality of sets of an equalizer 13 and a most probable decoder 16 having different DC low frequency component passing characteristics are prepared. By selectively inputting the reproduced signal to these plurality of systems based on the detection of the signal abnormality by the TA detection circuit 29 or the like described above, a more reliable data demodulation result can be obtained. Alternatively, when detecting a signal abnormality, the data demodulation result from a more appropriate signal system having a strong DC cutoff characteristic may be selected through the selector 35.

【0059】

(Example 4) For many partial response waveform equalization circuits, the automatic gain control circuit 39a that controls the adjustment gain of the automatic control gain circuit 10a placed in the preceding stage and the reproduction by the analog-to-digital converter 12 A timing extraction circuit 39b that controls the signal sampling timing is placed. In this case, the control signal information 38 for control is returned and referred to from the output of the equalizer 13 or a portion after that. Further, the control information of the adaptive learning circuit 26 that adjusts the tap information of the equalizer 13 is also taken from the subsequent stage. In this case, DC offset or low-frequency waveform fluctuations such as the TA fluctuations described above have a large adverse effect on these control systems, and the effects stay in the feedback control system for a long period of time, so that the reproduced signal processing system operates normally. To prevent. In this embodiment, among the plurality of partial response signal processing systems prepared in the embodiment of FIG. 14, the equalizer 13 of the system having a characteristic of blocking the DC component or the regenerating system having a parameter of α = 1. The reference signal is obtained from the latter stage. The circuit configuration of this embodiment is shown in FIG. In this case, only for the purpose of obtaining the control information signal 38 as described above, only the equalizer 13 of the system having a characteristic of blocking the DC component or the equalizer 13 of the reproduction system having a parameter of α = 1 is provided. The signal processing system such as the maximum likelihood decoder 14 in the subsequent stage may be omitted. As a result, the input of DC / low frequency fluctuations that adversely affect the operation of the control system is eliminated, and the optimum DC cutoff characteristics by other systems and highly reliable data demodulation with the optimum parameter α are combined with the magnetic recording / playback apparatus of the present invention. It is possible to maintain high reproduction reliability.

【0060】

(Example 5) Since the magnetic recording / playback apparatus provided by the present invention uses partial response waveform processing that allows signal components in the low frequency region near DC and data demodulation by most likely decoding, it is as shown in FIG. The amount of medium noise concentrated in the low frequency range is a major factor in determining the reliability of data demodulation. According to the present invention, the influence thereof is optimally reduced from the viewpoint of efficient use of the low frequency signal component of the reproduced signal, but reducing the absolute amount of the medium noise is the data demodulation of the magnetic recording / reproducing apparatus. Needless to say, it has an advantage in increasing the level of noise. Therefore, as shown in FIG. 16, in order to suppress the localization of the influence of medium noise with low frequency fluctuations, the maximum continuous number m of magnetization reversal recorded on the medium with the shortest bit length is constant. After performing the code conversion processing on the recorded data in the encoder 2 so as to limit to the following, this is recorded on the recording medium 6.

【0061】

For example, when the constraint of m = 3 is set, the bit information recorded on the recording medium 6 can be realized by providing a redundancy of about 6 to 9% or less of the recorded information. With the m = 4 constraint, it can only be achieved with a redundancy of 3-5% or less, which reduces media noise and improves data demodulation reliability without compromising recording / playback efficiency. It leads to. By using such a code conversion process together with the partial response waveform process of the present invention, the influence of medium noise can be reduced.

【0062】

The signal processing circuit system, the recording signal processing circuit 9a, and the reproduction signal processing circuit 9b of the magnetic recording / reproducing device in the above embodiment can be easily realized as a high-speed, highly integrated, and compact semiconductor integrated circuit by the existing circuit technology. be able to. By mounting this semiconductor integrated circuit in a magnetic recording / playback device having a perpendicular magnetic recording head medium system 4, it is possible to improve the data demodulation reliability and realize recording / playback of information at a higher density. Become.

【0063】

[Effect of the invention]

According to the present invention, for a perpendicular magnetic recording type reproduction signal using a double-layer film medium and a high-sensitivity MR reproduction head, the reliability of data demodulation in the most probable decoding is further improved and the SN is lower than that in the case of using the conventional technique. It is possible to provide a magnetic recording / reproducing device capable of tolerating signal quality and realizing higher-density information storage, and a magnetic recording / reproducing signal processing circuit using the magnetic recording / reproducing device. In the present invention, it is premised that the influence of noise from the recording medium can be reduced more effectively and that the reproduced waveform is subjected to low frequency frequency deterioration distortion due to the transmission characteristics of the pre-stage signal processing transmission system such as the reproduction system amplifier circuit. Since the waveform equalization processing that suppresses this can be performed, it is not necessary to increase the number of special compensation circuits, etc., and this effect is reduced to allow the deterioration of the characteristics of the pre-stage signal processing transmission system. Can be provided. In addition, a processing system that eliminates DC reproduction detection from the reproduction signal is provided, and by selecting and using this, the reproduction waveform generated by the contact (thermal asperity) between the recording medium and the MR reproduction element and the fluctuation of the head characteristics can be obtained. It is possible to provide a means for improving the reliability of the recording / playback system by eliminating the influence on the most probable decoding data demodulation such as DC offset and fluctuation.

[Simple explanation of drawings]

[Figure 1]

The figure which shows the basic embodiment of this invention.

[Figure 2]

The figure which shows the recording-reproduction process of the perpendicular magnetic recording system.

[Fig. 3]

The figure (time waveform) explaining the partial response waveform equalization processing of this invention.

[Fig. 4]

The figure (frequency spectrum) explaining the partial response waveform equalization processing of this invention.

[Fig. 5]

A table showing an example of the partial response waveform interference amount set in the present invention.

[Fig. 6]

A table showing an example of the partial response waveform interference amount set in the present invention.

[Fig. 7]

A table showing an example of the partial response waveform interference amount set in the present invention.

[Fig. 8]

The figure which shows the relationship between the low-pass suppression parameter α and the data bit error rate in this invention.

[Fig. 9]

The figure explaining the partial response equalizer configuration by a transversal filter.

[Fig. 10]

The figure explaining the Example of the partial response equalizer of this invention.

[Fig. 11]

The figure which shows an example of the state transition trellis diagram of the Viterbi decoding in this invention (n = 4).

[Fig. 12]

The figure explaining the thermal asperity phenomenon.

[Fig. 13]

A second embodiment of the reproduction signal processing circuit of the present invention.

[Fig. 14]

A third embodiment of the reproduction signal processing circuit of the present invention.

[Fig. 15]

A fourth embodiment of the reproduction signal processing circuit of the present invention.

[Fig. 16]

The figure explaining the recording code conversion process in this invention (example of m = 4).

[Explanation of symbols]

1: Information code data, 2: Coder, 3a: Recording current conversion processing circuit, 3b: Recording amplifier, 4: Vertical magnetic recording head medium system, 5: Recording head, 5a: Main magnetic pole, 5b: Coil, 5c: Auxiliary Magnetic pole, 6: Recording medium, 6a: Recording magnetic layer, 6b: Soft magnetic backing layer, 6c: Substrate, 7: Playback head, 7a: Magnetic resistance (MR) effect element, 7b: Shield film, 8: Playback signal, 9a : Recorded signal processing circuit, 9b: Reproduced signal processing circuit, 10: Reproduced amplifier, 10a: Automatic gain control amplifier, 11: Low frequency filter, 12: Analog / digital (A / D) converter, 13: Equalizer, 14: Most likely decoder, 15: Decoder, 16: Reproduction code data, 17: Recorded magnetization pattern, 18: Dybit recording magnetization pattern, 18a: Adjacent recording magnetization reversal pair, 19: Dybit reproduction waveform, 19a: Step response Signal, 20: Dibit reproduction waveform spectrum, 20a: Medium noise spectrum, 20b: Dibit reproduction waveform spectrum with low frequency distortion, 21: Equalized waveform spectrum, 22: Equalized waveform, 23: 1 bit storage delay Element, 24: Multiplier, 25a, Adder, 25b: Subtractor, 26: Adaptive Learning Circuit, 27: Noise White Matching Filter, 28: Low Frequency Suppression Filter, 29a: Normal Maximum Signal Level, 29b: Normal Offset Level, 30: Normal signal waveform, 31a, 31b: TA detection threshold level, 32: TA playback waveform, 32a: TA occurrence time, 32b: Signal offset fluctuation by TA, 33: TA detection circuit, 33a: Abnormality detection signal (control) Signal), 34: Register circuit, 35: Selection circuit, 36: Signal delay circuit, 38: Control signal information, 39a: Automatic gain control circuit, 39b: Timing extraction circuit.