JPH05266606A - Demodulator for magnetic recorder/reproducer - Google Patents

Abstract

PURPOSE:To make it possible to correct detection error due to peak shift, even if the peak shift due to interference between codes exceeds half period of recovered clock, by employing most likelihood decision in peak detection. CONSTITUTION:Peak position of a recovered signal is detected through a peak value detecting means 1 and an amount of peak is calculated through a peak shift amount calculating means 2 based on thus detected peak position and the calculated amount of peak shift is temporarily stored in a buffer means 3. An error between a previously calculated peak shift amount due to interference between codes and the peak shift amount stored in the buffer means 3 is detected through an error detecting means 4 and then a peak shift pattern having minimum error is determined. A most likely data series is then outputted from a most likelihood decoding means 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator for a magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus for correcting an error caused by a peak shift of a reproduced signal by maximum likelihood judgment to demodulate recorded data. Of the demodulator. Conventionally, in recent years, the recording density (BPI) on a recording medium has been improved year by year in order to advance the miniaturization and large capacity of magnetic recording devices. However, when the recording density is improved in this way, intersymbol interference in the recording medium is increased, and the peak shift is increased, resulting in a reproduction error. Therefore, there is a demand for a demodulator of a magnetic recording / reproducing device that can demodulate a reproduced signal without error even if the peak shift increases.

[0002]

2. Description of the Related Art FIG. 8 shows the structure of a peak detection demodulation circuit in a conventional magnetic disk device. A reproduction signal reproduced by a magnetic head (not shown) is amplified by a head amplifier 61 arranged near the magnetic head,
The peak value of the signal is detected in the peak detection circuit 62, and the shaping pulse is generated in the shaping pulse generation circuit 63. This shaped pulse is branched into two, one of which is input to the clock reproduction circuit 64 to become a reproduction clock, and the other of which is input to the flip-flop circuit (F / F) 65. The center pulse of the shaped pulse input to the flip-flop circuit 65 is sampled by this reproduced clock to be reproduced data.

[0003]

However, the conventional peak detection type demodulation circuit has a problem that the detected data becomes erroneous when the peak shift amount due to intersymbol interference exceeds a half cycle of the reproduction clock. Therefore, according to the present invention, even if the peak shift amount due to intersymbol interference exceeds a half cycle of the reproduction clock, the detection error caused by the peak shift can be corrected and the recording density can be improved. It is intended to provide a demodulator of.

[0004]

FIG. 1 shows the structure of a demodulator of a magnetic recording / reproducing apparatus of the present invention for achieving the above object. As shown in FIG. 1, the demodulator of the magnetic recording / reproducing apparatus of the present invention detects the peak of the reproduction signal from the magnetic recording medium D, and performs maximum likelihood determination to demodulate the recorded data. A demodulator, which is a peak value detecting means 1 for detecting a peak position of a reproduction signal, a peak shift amount calculating means 2 for calculating a shift amount of a detected peak value from a signal point, and a calculated peak shift amount Buffer means 3 that accumulates in advance, error detection means 4 that detects an error between the peak shift amount before and after the pre-calculated intersymbol interference and the peak shift amount accumulated in the buffer means 3.
And a maximum likelihood decoding means 5 for obtaining a peak shift pattern with a minimum error and outputting a most probable data string corresponding to the peak shift pattern.

[0005]

According to the demodulator of the magnetic recording / reproducing apparatus of the present invention,
The peak position of the reproduction signal is detected by the peak value detecting means 1, the shift amount of the detected peak value from the signal point is calculated by the peak shift amount calculating means 2, and the calculated peak shift amount is temporarily buffered. Stored in 3. The error between the peak shift amount before and after the pre-calculated intersymbol interference and the peak shift amount stored in the buffer unit 3 is detected by the error detection unit 4, and the peak shift pattern with the minimum error is obtained. Then, the most probable data sequence corresponding to it is output from the maximum likelihood decoding means 5.

[0006]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2A is a block circuit diagram showing the basic configuration of the demodulator of the magnetic recording / reproducing apparatus of the present invention. In the figure, 21 is a head amplifier for amplifying a reproduction signal read from a magnetic head (not shown), 22 is a peak detection circuit,
23 is a peak shift amount measuring circuit; 24 is a maximum likelihood decoder;
Reference numeral 5 is a clock recovery circuit. The peak signal detected by the peak detection circuit 22 is branched into two, one of which detects the peak shift amount by the peak shift amount measuring circuit 23, and the other of which is input to the clock reproduction circuit 25 to generate a clock signal. The peak shift amount measuring circuit 23 and the maximum likelihood decoder 24 operate with this clock signal, and reproduced data is obtained from the maximum likelihood decoder 24.

Next, the operation principle of the demodulator of the magnetic recording / reproducing apparatus configured as described above will be described. In the present invention, maximum likelihood decoding is performed by regarding the peak shift due to inter-code interference as a convolutional code. When the isolated reproduction waveform of the magnetic recording device is approximated by a Lorentz waveform, a can be expressed as follows, where a is a half-value width.

F (t) = 1 / (1+ (2t / a) ² ) ... (1) where T is the bit period, and the interference waveform from the magnetization reversal separated by n bits is expressed as follows. You can I (t) = f (t-nT / 2) -f (t + nT / 2) (2) Substituting equation (1) into equation (2) thus obtained,
The following equation (3) is obtained.

I (t) = (1 / A) + (1 / B) (3) where A = 1 + [(t-nT / 2) ² / (a / 2) ² ], B = 1 + [
(t + nT / 2) ² / (a / 2) ² ] To find the peak position, when dI / dt = 0 is set and expanded with respect to t, the following expression (4) is obtained. ^{3t 4 + (a 2 / 2-} (nT) 2/2) t 2 - (a 2/4 + (nT) 2/4) 2 = 0 ... (4) where the normalized linear density r = a / Assuming T, equation (4) can be transformed as follows.

[0010] ^{3t 4 + ((rT) 2} - (nT) 2) / 2t 2 - ((rT) 2 + (nT) 2) 2/16 = 0 ... (5) 3 (t / T) 4 + ( ^{r 2 -n 2) / 2 (} t / T) 2 - (r 2 + n 2) 2/16 = 0 ... (6) peak time | t / T | is expressed by equation (7). │t / T │ = (((n ² -r ² +2 (n ⁴ + r ² n ² + r ⁴ ) ^1/2 ) / 12) ¹ / ² … (7) Therefore, the normalized peak shift amount Is given by the following equation (8).

│Δ (t / T) │ = │t / T │-n / 2 = (((n ² -r ² +2 (n ⁴ + r ² n ² + r ⁴ ) ^1/2 ) / 12) / 12 ) ^1/2 -n / 2 (8) The following table shows the peak shift amount when the normalized linear density r = 4. [Table] Bit interval n Peak shift amount (%) 1 73 2 43 3 25 4 15 5 9 Here, if the peak shift amount is approximated only by the interference due to the adjacent magnetization reversal, the written data example becomes “0010
When it is 10010 ″, the peak shift amount of the read signal is as shown in FIG. 2 (b).

The maximum likelihood decoder 24 calculates the error between the peak shift amount due to the code interference and the peak shift of the reproduced signal as a metric, and finds the path with the smallest error among the path transitions shown in FIGS. Works like.
That is, FIGS. 5 and 6 show the process of the maximum likelihood signal in the case where noise occurs in FIG. 2 (b), where the first peak due to noise is shifted by 10% to the left and is erroneous. Is. For the metric of the maximum likelihood signal, The peak shift error shown by is used. In this case, FIGS.
The process indicated by the thick line is the maximum likelihood path, and the dotted line is the next most probable path. As can be seen from FIGS. 5 and 6, the maximum likelihood path and the next most probable path are branched at stage 2 and joined at stage 8. Then, the metric of the maximum likelihood path becomes 10 and the metric of the next most probable path becomes 40 at the connection point, and the path having the smaller metric value survives.

FIG. 3 shows an embodiment of the structure of the demodulator of the magnetic recording / reproducing apparatus which operates as described above. In this embodiment, the peak detecting circuit 22 includes a differentiating circuit 221, a zero clock detecting circuit 222, a shaping pulse generating circuit 223,
It is composed of a slice level determination circuit 224 and a gate 225. The reproduction signal is divided into two, one to the differentiation circuit 221 and the other to the level slice determination circuit 224.
Be led to. The signal differentiated by the differentiation circuit 221 is input to the zero-cross detection circuit 222, a zero-cross pulse corresponding to the zero-cross point of the differentiated waveform is generated, and the shaping pulse generation circuit 223 forms the shaping pulse. Then, the pulse from the shaping pulse generation circuit 223 is input to the gate 225. On the other hand, the signal input to the level slice determination circuit 224 is compared with a predetermined slice level voltage set in advance, and when the signal waveform exceeds the level slice voltage, the level slice gate is opened and the signal is level slice determined. Input from the circuit 224 to the gate 225. The gate 225 removes a pulse irrelevant to the peak of the reproduction signal by the zero cross pulse and the gate signal, and generates pulsed data corresponding to the peak point of the analog signal input to the peak detection circuit 22.

The pulse thus obtained is input to the phase comparator 31. The output from the VCO 34 is input to the other input of the phase comparator 31, and the UP / DOWN counter 32 connected to the phase comparator 31 counts according to the phase difference between the two. The output of the UP / DOWN counter 32 is passed through the loop filter 33 to the VCO 34.
Be fed back to. The output of the UP / DOWN counter 32 becomes a beak shift amount and is input to the maximum likelihood decoder 25 to be reproduced data. As described above, in the embodiment of FIG. 3, the digital PLL is used for clock reproduction, the peak shift amount is detected from the tank circuit (UP / DOWN counter 32), and maximum likelihood decoding is performed.

FIG. 4 shows an embodiment of the maximum likelihood decoder 35 shown in FIG. 3. In this embodiment, the peak detection circuit 2 shown in FIG. 3 is used.
2 is shown by one block, and the phase comparator 31, UP / D
OWN counter 32, loop filter 33, VCO 34
Is shown as a peak shift amount measuring circuit 23. Then, the output of the peak shift amount measuring circuit 23 becomes reproduction data by the peak shift / metric conversion table 43, ACS 44, and path memory 45 via the input buffer 42.

The output indicating the peak shift amount from the peak shift amount measuring circuit 23 is temporarily stored in the input buffer 42, and the peak shift / metric conversion table 43 is used to convert the bit interval n and the beak shift amount as shown in the table. Is referred to according to the set normalized linear density, and the metric required for path determination is calculated.
FIG. 5 shows a circuit when the operation of the circuit shown in FIG. 4 is performed by using the microprocessor 52. In the figure, 22 is a peak detection circuit, 23 is a peak shift amount calculation circuit, and 51 is magnetization. An inversion detection circuit, 52 is a microprocessor. When the maximum likelihood decoding is performed using such a microprocessor 52, only when the magnetization reversal detection circuit 51 detects the magnetization reversal, the interrupt terminal of the microprocessor 52 is interrupted and the path to the magnetization reversal is passed. The transitions may be collectively processed by software to determine the maximum likelihood.

[0017]

As described above, according to the present invention,
By performing maximum likelihood determination for peak detection, even if the peak shift amount due to intersymbol interference exceeds the half cycle of the recovered clock,
It is possible to correct the detection error caused by the peak shift,
There is an effect that the recording density can be improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram showing a configuration of a demodulator of a magnetic recording / reproducing apparatus of the present invention.

FIG. 2A is a block circuit diagram showing a basic configuration of a demodulator of the magnetic recording / reproducing apparatus of the present invention, and FIG. 2B is a waveform diagram illustrating a change in beak shift amount.

FIG. 3 is a block circuit diagram showing the configuration of the first embodiment of the demodulator of the magnetic recording / reproducing apparatus of the present invention.

FIG. 4 is a block circuit diagram showing an embodiment of a maximum likelihood decoder used in the present invention.

FIG. 5 shows the left half of the trellis diagram in maximum likelihood decoding.

FIG. 6 shows the right half of the trellis diagram in maximum likelihood decoding.

FIG. 7 is a block circuit diagram showing another embodiment of the maximum likelihood decoder.

FIG. 8 is a block circuit diagram showing a configuration of a demodulator of a conventional peak detection type magnetic recording / reproducing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Peak detection means 2 ... Peak shift amount calculation means 3 ... Buffer means 4 ... Error detection means 5 ... Maximum likelihood decoding means 22 ... Peak detection circuit 23 ... Peak shift amount measuring circuit 24, 35 ... Maximum likelihood decoder 25 ... Clock Reproducing circuit 31 ... Phase comparator 32 ... UP / DOWN counter 33 ... Loop filter 34 ... VCO

Claims (1)

[Claims] 1. A demodulator of a magnetic recording / reproducing apparatus for detecting a peak of a reproduced signal from a magnetic recording medium (D) and performing maximum likelihood determination to demodulate recorded data, wherein a peak position of the reproduced signal is detected. Peak value detecting means (1) for detecting, peak shift amount calculating means (2) for calculating the shift amount of the detected peak value from the signal point, and buffer means (3) for temporarily storing the calculated peak shift amount. An error detection means (4) for detecting an error between the peak shift amount before and after the pre-calculated intersymbol interference and the peak shift amount stored in the buffer means (3); A demodulator for a magnetic recording / reproducing apparatus, comprising: a maximum likelihood decoding means (5) for obtaining a pattern and outputting a most probable data string corresponding to the pattern.