JPH0757394A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the ability of a decoder against the lowering of the positioning accuracy of a head by changing over a Viterbi decoder and a level slicing decoder to each other in a magnetic recording device equalizing the waveform of partial response. CONSTITUTION:An original signal 7 from a reproducing head 1 is subjected to the waveform equalization by means of a partial response equalizer 2, inputted to a Viterbi decoder 3 and a level slicing decoder 4 and the outputs of binary signals 10, 11 are inputted to a selector 5. On the other hand, the error signal 12 of a track position from a head positioning controller 6 is inputted to the selector 5, compared with a predetermined threshold value, either of the signals 10, 11 is selected and a reproduced signal 13 is outputted from the selector 5. Consequently, the decoder of high ability is always available. It is also allowable that the output signal of the decoder is simultaneously inputted to the selector and an error detector, the presence or absence of an error is detected and two decoders are changed over to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing device such as a magnetic disk device.

[0002]

2. Description of the Related Art In a magnetic disk device, a digital VTR, etc., a digital recording method is used in which a binary digital signal is recorded on a recording medium as a magnetization reversal series. The reproduction signal obtained from the reproducing head during reproduction is a superposition series of isolated waveforms corresponding to the magnetization reversal position. The original binary data sequence is decoded depending on the presence or absence of the peak of the reproduced signal, but the signal amplitude decreases and the peak position varies due to the waveform interference of the solitary wave. To avoid this, waveform equalization to the Nyquist waveform is performed to eliminate waveform interference. However, as the linear recording density becomes higher, the sampling frequency becomes higher, which makes it difficult to correct the timing. Therefore, an equalization method called partial response is used. By intentionally adding a separable correlation to the signal, the cutoff characteristic becomes gentle, and the vibration of the tail of the pulse becomes small, so that there is a margin for timing correction and high density is possible.

A Viterbi algorithm is used for binarizing a signal obtained from the partial response equalizer. The Viterbi algorithm is a maximum-likelihood decoding method and uses signal correlation, and thus has a high decoding capability for noise that has no correlation. On the other hand, when the noise itself has the same correlation as the signal, the signal and the noise cannot be separated, and the decoding capability is deteriorated. In the magnetic recording device, thermal noise from the head, shot noise of the head amplifier, media noise, and the like become uncorrelated noise, and by using the Viterbi algorithm, decoding can be performed with high capability. However, the unerased component and the crosstalk noise from the adjacent track are in principle the same as the signal component and cannot be removed by the Viterbi algorithm. Therefore, when the head positioning error increases and the noise increases, the decoding capability of the Viterbi algorithm deteriorates sharply.

[0004]

As described above, in the magnetic recording apparatus using the partial response equalization and the Viterbi algorithm, the head positioning error becomes large and has the same property as the signal component such as the unerased component. Due to the increase in noise, the decoding capability deteriorates sharply and the throughput decreases. Therefore, it is necessary to develop a decoder that does not significantly reduce the decoding performance even if the positioning error is large and the correlated noise increases.

When a binarization circuit using the Viterbi algorithm is compared with a circuit which performs binarization by level slice for each sample, in the case of complete on-track reproduction, the binarization circuit using the Viterbi algorithm Has better decoding ability. However, when the off-track amount becomes large and the correlated noise such as the unerased component increases, the decoding capability of the binarization circuit using the Viterbi algorithm deteriorates sharply, and there is a positioning error above a certain off-track amount. And the binarization circuit using the level slice for each sample has higher decoding capability than the binarization circuit using the Viterbi algorithm. Therefore, the present invention solves the above-mentioned problems by incorporating two types of circuits as a decoding circuit of a magnetic recording device, that is, a binarization circuit using a Viterbi algorithm and a circuit that performs binarization by a level slice for each sample. The purpose is to do.

[0006]

According to the present invention, in a magnetic recording / reproducing apparatus for performing waveform equalization by using a partial response, a Viterbi decoder is provided according to the value of a head positioning error or the presence or absence of an error in a binarized sequence. This is a magnetic recording / reproducing apparatus in which the level slice decoder is switched.

[0007]

If the Viterbi decoder and the level slice decoder are switched and used according to the value of the head positioning error or the presence or absence of an error in the binarized sequence as in the present invention, the head positioning accuracy is reduced. , It is possible to reduce the deterioration of the capacity of the decoder.

[0008]

EXAMPLE A first example of the present invention will be described below. FIG. 1 is a graph showing the relationship between the on-track amount of the head and the error rate of the decoder. However, the on-track amount here is the off-track amount at the time of reproduction. The recorded data is recorded completely in the off-track state, and the off-track amount at the time of reproduction when another signal is written as the unerased component outside the recording track and the crosstalk noise of the adjacent track. And the error rate of the decoder. In the on-track state, the decoder using the Viterbi algorithm has a lower error rate than the decoder using the level slice for each sample. The capacity of the decoder using the Viterbi algorithm deteriorates sharply as the amount of off-track increases, and when the amount of off-track becomes Th or more, the capacity of the decoder using the level slice for each sample becomes higher.

Therefore, the off-track amount during recording is set to Te
w, and the off-track amount during playback is Ter, dT = |
When Tew-Ter | <Th, a decoder using the Viterbi algorithm is used, and when dT ≧ Th, a decoder using a level slice for each sample is used to reduce the deterioration of the decoding capability due to the increase in the off-track amount. be able to.

At the time of reproduction, the off-track amount at the time of recording the data recorded on the track is unknown. However, if the head positioning controller is adjusted so that the bias of the off-track amount becomes 0, when Ter = Th, d
The probability of T> Th is almost 1/2. Therefore, when the off-track amount during reproduction is Ter <Th, a decoder based on the Viterbi algorithm is used, and when Ter ≧ Th, 1
A decoder with a level slice for each sample is used.

A servo system is used for head positioning control. Feedback control is performed so as to move to a target track based on servo information written in advance at a specific place on the medium. The track positioning error of the head can be known from the servo signal obtained at this time.

Next, a second embodiment of the present invention will be described. In a magnetic disk device, an error detection code is added to a data series, and an error detector detects the presence or absence of an error. Here, the output of the error detector is input to the selector, and when an error is detected in the output sequence of the binarization circuit using the Viterbi algorithm, the binarization circuit by the level slice is selected and obtained from this binarization circuit. The binary sequence that is used is the data sequence. Then, when an error is detected in the output sequence of the binarization circuit by level slice, retry is performed. If the cause of the error in the binarization circuit using the Viterbi algorithm is the deterioration of the head track positioning accuracy, it is likely that the level slice binarization circuit has correctly decoded and a retry is required. Is eliminated and throughput is improved. Also, if an error occurs due to an increase in system noise, etc., it is considered that the error is also detected in the output of the binarization circuit by the level slice. However, even in the conventional magnetic disk, the error is detected. Since it was compensated by performing the retry, the throughput does not decrease.

The above-described embodiment will be described below more specifically with reference to block diagrams. FIG. 2 is a block diagram showing the circuit of the first embodiment of the present invention described above. The original signal 7 obtained from the reproducing head 1 is subjected to waveform equalization by the partial response equalizer 2 and becomes input signals 8 and 9 to the Viterbi decoder 3 and the level slice decoder 4.
The binarized signals 10 and 11 output from the Viterbi decoder 3 and the level slice decoder 4 are input to the selector 5.
On the other hand, the head position controller 6 inputs an error signal 12 of the track position to the selector 5, compares it with a predetermined threshold value, selects either of the binarized signals 10 and 11, and outputs it from the selector. This signal becomes the reproduction signal 13 obtained from the present decoder.

FIG. 3 is a block diagram showing the circuit of the second embodiment of the present invention described above. Playhead 1
The original signal 21 obtained from 4 is subjected to waveform equalization by the partial response equalizer 15 and becomes input signals 22 and 23 to the Viterbi decoder 16 and the level slice decoder 17. The output signals 24 and 25 of the respective decoders are input to the selector 20 and at the same time the respective error detectors 18 and 25 are input.
Inputs 26 and 28 to 19. Error detectors 18, 19
The outputs 27 and 29 of the above are input to the selector 20, and either of the binarized signals 24 and 25 is selected according to the presence or absence of an error, and become the output 30 of the present decoder.

[0015]

According to the present invention, even if the track position accuracy is deteriorated and the off-track amount is increased in the decoder using the partial response equalization, it is possible to prevent the deterioration of the decoding capability and to improve the throughput. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing a decoding capability according to an off-track amount of a Viterbi decoder and a level slice decoder for explaining the present invention.

FIG. 2 is a block diagram showing a first embodiment of the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Playback head 2 ... Partial response equalizer 3 ... Decoder using Viterbi algorithm 4 ... Decoder by level slice for each sample 5 ... Selector 6 ... Head positioning controller 7 ... Original signal obtained from playback head 8 , 9 ... Partial response equalized signal 10 ... Binary signal obtained from Viterbi decoder 11 ... Binary signal obtained from level slice decoder 12 ... Track position error signal 13 ... Decoding sequence 14 ... Reproduction Head 15 ... Partial response equalizer 16 ... Decoder using Viterbi algorithm 17 ... Decoder by level slice for each sample 18 ... Error detector for output of Viterbi decoder 19 ... For output of level slice detector Error detector 20 ... Selector 21 ... Original signal 22, 23 obtained from reproducing head Partial response equalized signal 24, 26 ... Binary signal obtained from Viterbi decoder 25, 28 ... Binary signal obtained from level slice decoder 27 ... Error detection signal for output of Viterbi decoder 29 ... Error detection signal for output of level slice decoder 30 ... Decoding sequence

Claims (2)

[Claims] 1. A magnetic recording / reproducing apparatus for waveform equalization using a partial response, a binarizing means using a Viterbi decoder, a binarizing means by level slice, and a head for positioning the head. And a means for detecting the off-track amount, and the two binarizing means are switched and used according to the information obtained from the off-track amount detecting means. 2. Binarizing means using the Viterbi decoder,
It has a binarizing means by the level slice and a means for detecting an error in the binary sequence obtained from each of the binarizing means, and the two binarizing depending on the presence or absence of the error in the binary sequence. A magnetic recording / reproducing apparatus characterized in that means is switched and used.