JPH08167102A - Data playback device - Google Patents

Abstract

(57) [Abstract] [Purpose] Low-frequency phase correction of the reproduction signal detected from the magnetic recording medium by the magnetic head is performed with a simple configuration at low cost.
Do better The phase correction circuit 26 includes N delay units (D) 40 (1) to 40 (N) connected in cascade to delay the sample series z _t supplied from the sampling quantization circuit by one sample time.
And N bits (N is n of 2) of each sample time delayed by the delay unit (D) 40 (i) (1 ≦ i ≦ N) of each stage.
BS 41 (1) to 41 (N) that bit-shifts the sample series z _t of (powers) to the m-bit (0 ≦ m ≦ n) LSB side
And an adder 42 for adding the outputs of BS 41 (1) to 41 (N), and an output of the adder 42 is (nm) -bit LSB.
BS44 that bit-shifts to the side, and delay device (D)
40 (k) (1 ≦ k ≦ N) and the subtractor 45 for subtracting the output of the BS 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data reproducing apparatus, and more particularly to a data reproducing apparatus which detects a reproduced signal from a magnetic recording medium such as a magnetic disk by a magnetic head and reproduces the data.

[0002]

2. Description of the Related Art A digital audio tape recorder (so-called D) for recording data on a magnetic recording medium such as a magnetic tape or a magnetic disk and reproducing the data therefrom.
In AT), magnetic disc devices, etc., a magnetic head (so-called ring head) is used as a recording head or a reproducing head. Then, for example, in a magnetic disk device, a reproduction signal is detected from a magnetic disk on which data is recorded by a magnetic head, and the reproduction signal is waveform-equalized using an equalizer (hereinafter referred to as an equalizer) to reproduce the data. It is supposed to do.

This equalizer usually includes an integrating circuit having an integrating characteristic in the low frequency band, a differentiating circuit having a differential characteristic in the high frequency band, and a phase equalizer for changing the phase without changing the amplitude. , Low-pass filter that passes only the signal in the required band (hereinafter referred to as LPF = Low pass fi1ter)
Composed of and. The integrator circuit is for correcting the differential characteristic of the magnetic head, and the differentiator circuit is for correcting the loss due to the gap of the magnetic head. The phase equalizer is used to correct the phase rotation by the LPF and the phase of the entire band.

In the DAT and the magnetic disk device,
The equalizer having such a circuit configuration is used to equalize the waveform of the reproduction signal and reproduce the data, but there are the following problems.

If the equalizer is composed of an analog circuit and an attempt is made to obtain sufficient integration characteristics in the low frequency range, the resistance value or the capacitance value of the capacitor forming the integration circuit becomes an unrealistic value, that is, the equalizer of the analog circuit. In, it was not possible to obtain sufficient integration characteristics from the low range.

Further, for example, respective circuits constituting a reproducing system such as a reproducing amplifier and an equalizer are connected to each other via a so-called coupling capacitor which cuts direct current (DC), and these coupling capacitors form a reproduced signal. High-pass filter (hereinafter referred to as HPF) that attenuates the low-frequency component of
= High pass fi1ter), this HPF
Around the phase due to has a bad influence on the waveform equalization.

Further, in a device using a rotary head composed of a magnetic head and a rotary transformer such as DAT, a rotary transformer for taking out a reproduced signal from the magnetic head causes a phase of a low frequency region of the reproduced signal to shift and a waveform to be reproduced. Had a bad effect on the change.

That is, for example, the first-order LPF having the transfer function H shown in the following equation 1 has the phase characteristic θ shown in the following equation 2, and as shown in FIG. 5, ω = 0 and θ = 0, ω = ω
₀ (= 2πf ₀ , f ₀ is the cutoff frequency) and θ = −π /
4, ω = ∞, θ = −π / 2, while the first-order HPF having the transfer function H shown in Equation 3 below has the phase characteristic θ shown in Equation 4 below, and As shown, ω = 0
At θ = π / 2, at ω = ω ₀ at θ = π / 4, at ω = ∞ at θ = 0
Therefore, in both cases of LPF and HPF, when the cutoff frequency f ₀ is used as a reference, the phase advances in the lower range than that.

H = ω ₀ / (s + ω ₀ ) Equation 1 θ = −tan ⁻¹ (ω / ω ₀ ) Equation 2 H = s / (s + ω ₀ ) Equation 3 θ = tan ⁻¹ (ω ₀ / ω) Equation 4 The phase characteristic that the phase advances in this low range is the same regardless of the order of a linear circuit, and as described above, the integration equalization failure and coupling HPF,
In a rotary transformer or the like, once the low frequency phase of the reproduced signal is advanced, an analog circuit generally has, for example, a transfer function H and a phase characteristic θ shown in the following equations 5 and 6, that is, ω = 0. At θ = 0, ω = ω ₀ at θ = −π /
2. Use a combination of multiple first-order phase equalizers (phase shifters) with ω = ∞ and θ = −π, or use higher-order phase shifters to further advance and correct the low-frequency phase. However, it was difficult to correct the phase.

H = (s−ω ₀ ) / (s + ω ₀ ) ... Formula 5 θ = tan ⁻¹ ((2ω × ω ₀ ) / (ω ² −ω ₀ ² )) Formula 6 Specifically, for example, In DAT, when the bit rate (frequency) of the data recorded on the magnetic recording medium is _fr Hz, the cutoff frequency f ₀ of the conventional integrating circuit is _fr / 1.
It had been the 28~f _r / 64. Further, about four coupling HPFs are used in, for example, a reproduction amplifier, an equalizer, etc., and their cutoff frequencies f ₀ are
It was _fr / 512. Further, the cut-off frequency f ₀ of the rotary transformer was f _r / 1024~f _r / 512.

Therefore, in the conventional DAT, for example,
As shown in FIG. 6, the phase of the reproduced signal is significantly advanced in the low range, and the conventional equalizer corrects the phase only for a predetermined frequency or higher, and does not perform the phase correction for the frequency equal to or lower than the predetermined frequency. In other words, in the conventional DAT, magnetic disk device, etc., low-frequency phase compensation is not sufficient, so that an error correction code having high error correction capability, that is, high redundancy, is required, or a magnetic recording medium such as a magnetic disk. It was difficult to increase the density.

Therefore, the present applicant has filed Japanese Patent Application No. 6-2370.
No. 41 proposes a data reproducing apparatus which corrects a low-frequency phase of a reproduced signal by using an FIR filter.

[0013]

However, the data reproducing apparatus of Japanese Patent Application No. 6-237041 can certainly correct the low-frequency phase of the reproduced signal, but it requires a plurality of multipliers. Therefore, there is a problem that the circuit scale becomes large and cannot be constructed at low cost.

The present invention has been made in view of the above circumstances, and it is possible to perform low-frequency phase correction of a reproduction signal detected from a magnetic recording medium by a magnetic head with a simple structure at low cost and better. An object of the present invention is to provide a data reproducing device capable of performing the above operation.

[0015]

A data reproducing apparatus of the present invention comprises a reproducing head 21 which is a magnetic head for detecting a reproducing signal from a magnetic tape 1 as a magnetic recording medium on which data is recorded, and a reproducing head 21. An equalizer 23 as an equalizer for equalizing the waveform of the reproduction signal, and a sampling quantum as a sampling quantizer for sampling the output of the equalizer 23 and outputting a plurality of sample values as bit string data. And a phase correction circuit 26 as a phase correction means for correcting the phase of the reproduction signal by bit-shifting and adding the bit string data which is a plurality of sample values from the sampling and quantization circuit 25. Demodulator 2 as data reproducing means for reproducing data based on the output of 26
It is configured with 8.

In the data reproducing apparatus of the present invention, the data recorded on the magnetic tape 1 is transferred to the partial response (1,
The data can be precoded corresponding to 1).

Further, in the data reproducing apparatus of the present invention, the data recorded on the magnetic tape 1 can be converted into data having no DC component.

[0018]

[Operation] In the data reproducing apparatus of the present invention, the reproducing head 2
1, a reproduction signal is detected from the magnetic tape 1 on which data is recorded, the reproduction signal is waveform-equalized by the equalizer 23, the reproduction signal from the equalizer 23 is sampled by the sampling / quantizing circuit 25, and the obtained signal is obtained. The bit string data, which is the sampled value, is bit-shifted and added by the phase correction circuit 26, and the phase of the reproduced signal is delayed substantially linearly below a predetermined frequency, thereby performing the correction of the low-frequency phase of the reproduced signal. It is possible to perform better at low cost with a simple configuration.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a data reproducing apparatus according to the present invention will be described in detail below with reference to the drawings. 1 to 4 relate to an embodiment of the present invention. FIG. 1 is a block diagram showing a configuration of an embodiment of a data recording / reproducing apparatus to which the present invention is applied.
1 is a block diagram showing the configuration of a phase correction circuit that constitutes the data recording / reproducing apparatus of FIG. 1, FIG. 3 is a graph showing the first frequency characteristic of the phase correction circuit of FIG. 2, and FIG. 4 is a graph of the phase correction circuit of FIG. It is a graph which shows the 2nd frequency characteristic.

In this embodiment, for example, a magnetic tape is used as a magnetic recording medium, data is recorded on the magnetic tape by a rotary head composed of a magnetic head, and the data is reproduced from the magnetic tape by the rotary head. The present invention is applied.

The data recording / reproducing apparatus to which the present invention is applied has a modulator 1 as its recording system, for example, as shown in FIG. 1, for modulating data suitable for recording on the magnetic tape 1.
1, a precoder 12 that precodes the modulation sequence x _t from the modulator 11, a recording amplifier 13 that amplifies the intermediate sequence y _t from the precoder 12, and an intermediate sequence amplified by the recording amplifier 13. A recording head 14 for recording y _t on the magnetic tape 1. In addition, the recording head 14
The rotary head includes a magnetic head and a rotary transformer.

The modulator 11 is a modulator suitable for recording on the magnetic tape 1, that is, a direct current (DC) component is cut in the rotary transformer of the recording head 14, so that, for example, so-called 8-10 conversion is performed. The modulator 11 is composed of a modulator that converts data into a code according to the DC-free coding rule. This modulator 11 converts data input as an information sequence (hereinafter, simply referred to as an information sequence) via a terminal 2 to a modulation sequence x.
Convert to _t (t = 0, 1, 2, ...).

The precoder 12 is, for example, a precoder for a partial response (1,1) (hereinafter, PR (1,1)), that is, for example, an exclusive OR circuit (hereinafter, EX0R circuit) and this EXOR circuit. Of the intermediate sequence y _t , which is the output of the delay circuit, and supplies it to the EXOR circuit. The precoder 12 uses the EXOR circuit to modulate the modulation sequence x _t supplied from the modulator 11 and the intermediate sequence y _t-1 delayed by the delay device.
Find the exclusive OR with. That is, the precoder 12
, By the addition of modulation series x _t of modulo 2, to produce a medium Q series y _t, and supplies the intermediate sequence y _t the recording amplifier 13.

The recording amplifier 13 amplifies the intermediate series y _t and drives the recording head 14. The recording head 14 is composed of the rotary head as described above, and records the recording signal based on the intermediate series y _t supplied from the recording amplifier 13 via the rotary transformer on the magnetic tape 1.

Thus, the data (information series) input through the terminal 2 is recorded on the magnetic tape 1.

On the other hand, this data recording / reproducing apparatus has, as its reproducing system, a reproducing head 21 for detecting a reproducing signal from the magnetic tape 1 and a reproducing signal from the reproducing head 21 as shown in FIG. Amplifier 2 for amplifying
2, an equalizer 23 as an equalizer for equalizing the waveform of the reproduction signal from the reproduction amplifier 22, and a phase-locked loop (hereinafter, PLL =) for extracting a clock component from the reproduction signal from the equalizer 23. Phase Locked Loop) 24
A sampling and quantizing circuit 25 as a sampling and quantizing means for sampling the reproduction signal from the equalizer 23 using the clock from the PLL 24 and outputting discrete sample values; A phase correction circuit 26 as a phase correction means for correcting the phase of the reproduction signal by weighted addition of the sample values from the quantization quantization circuit 25, and the phase correction circuit 26.
A Viterbi decoder 27 that performs Viterbi decoding by using the sample value whose phase has been corrected in (1) and a demodulator 28 as a data reproducing unit that demodulates the output of the Viterbi decoder 27 are provided.

The reproducing head 21 is composed of a rotary head, detects a reproducing signal from the magnetic tape 1, and reproduces the reproducing signal through a rotary transformer and a DC (DC) cutting coupling content amplifier. 22. The reproduction amplifier 22 amplifies this reproduction signal and supplies the amplified reproduction signal to an equalizer (hereinafter referred to as an equalizer) 23 via a coupling capacitor.

The equalizer 23 is composed of, for example, a general equalizer composed of a conventional analog circuit, that is, although not shown, for the low range for correcting the differential characteristic of the reproducing head 21 (magnetic head). An integrating circuit having an integrating characteristic, a differentiating circuit having a differentiating characteristic with respect to a high frequency band for compensating for a loss due to gearing of the reproducing head 21, and a low pass filter (hereinafter, LPF = Low pass fi1ter)
And a phase equalizer for changing the phase without changing the amplitude for correcting the phase around by the LPF.

Then, the equalizer 23 waveform-equalizes the reproduction signal supplied from the reproduction amplifier 22, and supplies the waveform-equalized reproduction signal to the PLL 24 and the sampling circuit 25 as the transmission line output Z. Therefore, the transmission line output Z, which is the output of the equalizer 23, is a signal having a large phase advance in the low frequency range, as shown in FIG.

The PLL 24 extracts a clock component from the output Z of the transmission path composed of the magnetic tape 1 or the like, that is, generates a clock synchronized with the reproduction signal, and the clock is sampled and quantized by the sampling / quantization circuit 25 and the phase correction circuit 26. Viterbi decoder 2
7. Supply to the demodulator 28.

The sampling / quantization circuit 25 samples the transmission line output Z by the clock supplied from the PLL 24, and supplies the obtained sample value (data) to the phase correction circuit 26 as a sample series z _t .

Then, the Viterbi decoder 27 performs Viterbi decoding on the sample sequence z _t , which has been subjected to the phase correction described later by the phase correction circuit 26, that is, based on the sample sequence z _t , for example, a so-called trellis line. By detecting the path with the highest likelihood in the diagram (Trellis diagram), the modulation sequence x _t corresponding to the output of the modulator 11 of the recording system is reproduced, and this modulation sequence x _t is supplied to the demodulator.

The demodulator 28 corresponds to the modulator 11 of the recording system, decodes the modulation sequence x _t , reproduces the original information sequence, and uses this information sequence as the demodulation sequence via the terminal 2. Output. Thus, the data is reproduced from the magnetic tape 1.

For example, as shown in FIG. 2, the phase correction circuit 26 includes N delay devices (D) connected in cascade for delaying the sample series z _t supplied from the sampling quantization circuit 25 by one sample time. ) 40 (1) -40 (N) and N delays (D) 40 (i) of each stage (i = 1, 2, ... N) at each sample time (N is 2). N-th power)
Shift register (hereinafter referred to as BS) 41 (1) to 41 (N) for bit-shifting the sample sequence z _t of m to the m-bit (0 ≦ m ≦ n; m, n: integer) LSB side;
Adder 42 for adding the outputs of 41 (1) to 41 (N)
And BS44 for bit-bit shifting the output of the adder 42 to the (nm) -bit LSB side, and the delay device (D) 40.
(K) (1 ≦ k ≦ N) and a subtractor 45 that subtracts the output of the BS 44.

The phase correction circuit 26 thus configured
Is to realize a desired frequency characteristic by taking an average of N sample sequences z _t and performing phase correction by subtracting the average value from a specific sample sequence.

The average may be obtained by dividing the total sum of N sample sequences by N. Here, since N is the nth power of 2, it is not necessary to use a multiplier, and bit data is bit-shifted to the LSB side. By truncating the lower n bits by dividing each bit data by N and then adding, the average can be easily obtained.

In FIG. 2, BS41 (1)-
41 (N) and BS44 are components that perform the above-mentioned bit operation, but this does not have to be configured by hardware, and it is also possible to take out the upper bits by removing the lower n bits. Needless to say.

BS41 (1) to 41 (N) and BS44
The reason why the bit shift is performed in two stages is to match both the calculation accuracy and the hardware scale.

That is, if N sample sequences are shifted by n bits in BS 41 (1) to 41 (N) and then addition is performed, the hardware scale is reduced, but the calculation accuracy is reduced. Conversely, when N sample sequences are added without using BS41 (1) to 41 (N) and then shifted by n bits by BS44, the calculation accuracy does not decrease, but addition with a large number of bits must be performed. Since it does not occur, the hardware scale becomes large.

That is, for example, N is "8" (that is,
When n = 3), the value of the sample series is constant at "36" (decimal number) (therefore, the average value is also "36"). Therefore, "36"
When expressed as a bit string (decimal number), "00100100"
Becomes In the former method, this is BS41 (1) -4
Since 1 (8) shifts 3 bits, each BS 41 (i)
Output is "00000100". When eight of these are added, the result becomes "00100000", and when expressed in decimal, the result becomes "32", which is deviated from the original value "36". In the latter case, if you don't even consider the size of the hardware, it will be "36" and you can get the correct average value.
As described above, the hardware scale becomes large.

In the case of the present embodiment in which the two are matched, for example, BS41 (1) to 41 (8) are shifted by 2 bits to BS.
If one bit is shifted by 44, each BS41
The output of (i) is "00001001". This 8
If you add them, it becomes "01001000" and BS44 gives 1
When bit-shifted, it becomes "00100100", resulting in "36" (decimal) and the correct average value.
It can be obtained accurately without increasing the hardware.

Specifically, in the phase correction circuit 26, the characteristic changes depending on the number of N and which sample series the average value is subtracted from. For example, N = 16, a delay device (which outputs the target sample series) ( D) i of 40 (i) is i = 15, 13, 1
When it is set to 1, the phase of the reproduction signal is delayed substantially linearly at a predetermined frequency or lower, for example, the frequency characteristic as shown in FIG. 3 is obtained. Further, for example, when N = 32 and i of the delay device (D) 40 (i) that outputs the target sample sequence is i = 31, 29, and 27, the phase of the reproduction signal is approximately below a predetermined frequency. It is delayed linearly, for example, has a frequency characteristic as shown in FIG.

Therefore, the phase correction circuit 26 shifts each of the N consecutive sample sequences z _t to the LSB side by m bits, then adds them, and shifts the addition output to the LSB side by (nm) bits. by, with cuts (attenuates) the f _r / 128 Hz or less of the components of the reproduction signal, delaying 8f _r / 128 Hz or less of the components of the phase of the reproduced signal substantially linearly, the above magnetic head, a rotary transformer, The phase lead (around) in the low range of the reproduced signal due to the coupling capacitor and the like is delayed and corrected. As a result, the phase characteristic from the reproducing head 21 to the phase correction circuit 26 is a characteristic obtained by combining the phase characteristic shown in FIG. 6 described in the conventional example and the phase characteristic shown in FIG. 3 or 4.

In other words, in this data recording / reproducing apparatus, by using the phase correction circuit 26, the low-frequency phase correction of the reproduced signal can be performed easily and inexpensively and better than the conventional apparatus.

It is needless to say that the present invention is not limited to the above-mentioned embodiments, but the present invention can be applied to, for example, a magnetic disk device which employs a magnetic disk as a recording medium.

[0046]

As described above, according to the data reproducing apparatus of the present invention, the reproducing signal from the magnetic recording medium on which the data is recorded is detected by the magnetic head, and the reproducing signal is waveform-equalized by the equalizing means. , The sampling and quantizing means samples the reproduction signal from the equalizing means, and bit sequence data, which is the obtained sample value, is bit-shifted and added by the phase correcting means, and the phase of the reproduction signal is substantially linear below a predetermined frequency. Since the correction is delayed, the low-frequency phase correction of the reproduction signal can be performed easily with a simple configuration at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a data recording / reproducing apparatus to which the present invention is applied.

FIG. 2 is a configuration diagram showing a configuration of a phase correction circuit that constitutes the data recording / reproducing apparatus of FIG.

3 is a graph showing a first frequency characteristic of the phase correction circuit of FIG.

FIG. 4 is a graph showing a second frequency characteristic of the phase correction circuit of FIG.

FIG. 5 is a graph showing phase characteristics of a conventional first-order LPF and HPF.

FIG. 6 is a graph showing a phase characteristic of a reproduction system such as a conventional DAT.

[Explanation of symbols]

 1 Magnetic Tape 2, 3 Terminal 11 Modulator 12 Precoder 13 Recording Amplifier 14 Recording Head 21 Reproducing Head 22 Reproducing Amplifier 23 Equalizer 24 PLL 25 Sampling Quantization Circuit 26 Phase Correction Circuit 40 (1) to 40 (N) Delay Device ( D) 41 (1) to 41 (N), 44 BS 42 adder 45 subtractor

Claims (4)

[Claims] 1. A magnetic head for detecting a reproduction signal from a magnetic recording medium on which data is recorded, an equalizer for equalizing waveforms of the reproduction signal from the magnetic head, and an output of the equalizer for sampling. A sampling and quantizing means for outputting a plurality of sample values as bit string data, and bit-shifting and adding the bit string data, which is the plurality of sample values from the sampling and quantizing means, and adding the phase of the reproduction signal. And a data reproducing means for reproducing the data based on the output of the phase correcting means. The phase characteristic of the phase correcting means has a substantially straight line when the phase of the reproduced signal is equal to or lower than a predetermined frequency. A data reproducing apparatus characterized by having a characteristic of delaying in time. 2. The sampling and quantizing means samples the output of the equalizing means to obtain N (N = 2).
ⁿ : n is an integer) sample value is output as bit string data, and the phase correction means shifts the N sample values to the LSB side by m bits (0 ≦ m ≦ n: m is an integer) N First bit shifting means, an adding means for adding the outputs of the N first bit shifting means, and a second bit for shifting the output of the adding means by (nm) bits to the LSB side. The data reproducing apparatus according to claim 1, further comprising shift means. 3. The data according to claim 1, wherein the data recorded on the magnetic recording medium is precoded data corresponding to a partial response (1, 1). Playback device. 4. The data reproduction according to claim 1, wherein the data recorded on the magnetic recording medium is data converted into a code having no DC component. apparatus.