JPH0463442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic reproducing apparatus which uses a ring-shaped magnetic head to reproduce a magnetic recording medium on which digital signals are recorded with perpendicular magnetization.

Background technology and its problems The perpendicular magnetization recording method is a method of recording signals by magnetizing the magnetic layer of a magnetic recording medium in the thickness direction, and since high-density recording is possible, it has been applied to digital storage. is attracting attention.

Reproduction of a magnetic recording medium on which signals have been recorded using the perpendicular magnetization recording method is normally carried out using a ring-shaped magnetic head. This is because reproduction by a ring-shaped magnetic head is efficient.

Now, A and B in FIGS. 1 and 2 respectively show recording current waveforms and reproduction signal waveforms of a relatively low frequency digital signal and, for example, a 3-bit digital signal, respectively, by the perpendicular magnetization recording/reproducing method. . The waveform shown in FIG. 1B is referred to as an isolated reproduced waveform.

The BNC isolated reproduction waveform in FIG. 1 has a steep rise, but its half-width is relatively wide, and the symmetry of the waveform is not very good.

The frequency characteristics of the amplitude and group delay amount of the isolated reproduced waveform in FIG. 1B are the curves S _a1 and S _gd1 in FIG. 3, respectively.
As shown in , an increase in the amplitude and group delay amount in the low frequency range and an extension of the amplitude toward the high frequency side can be seen.

Furthermore, the reproduced waveform shown in FIG. 2B has the following waveform problem.

(a) Peak shift occurs due to mutual interference of adjacent pulses.

(b) When hardening reversal occurs three times in a row, the peak value corresponding to the central magnetization reversal decreases. That is, peak values become uneven.

(c) When the period without magnetization reversal is long, the amplitude gradually decreases.

Problems with the waveform of such reproduced waveforms include amplitude fluctuations due to time axis fluctuations, noise, and changes in the spacing between the reproducing magnetized head and the magnetic recording medium, as well as problems with the high precision of digital signals in the perpendicular magnetization recording/reproducing method. This has become an obstacle to high-density reproduction, detection, and recording.

Purpose of the Invention In view of the above, the present invention provides a magnetic reproducing apparatus that uses a ring-shaped magnetic head to reproduce a magnetic recording medium on which digital signals are perpendicularly magnetized. This paper attempts to propose a device that enables high-density detection and recording.

Summary of the Invention A magnetic reproducing apparatus according to the present invention includes a ring-shaped magnetic head for reproducing a magnetic recording medium on which digital signals are recorded with perpendicular magnetization, and a waveform equalizer to which the reproduction output from the ring-shaped magnetic head is supplied. This waveform equalizer has the following equation on the S plane: H(s)=s+a/s+b (where a<b and a, b
> 0).

According to the present invention, in a magnetic reproducing apparatus that uses a ring-shaped magnetic head to reproduce a magnetic recording medium on which digital signals are perpendicularly magnetized, high precision, reproduction, detection, and recording of digital signals can be achieved. A device that enables high density can be obtained.

Embodiment First, it is necessary to equalize the isolated reproduction waveform shown in FIG. 1B so that it becomes symmetrical and sharp. To do this, in the amplitude and group delay characteristics shown in Figure 3, it is necessary to remove low-frequency components of the amplitude that are not necessarily important for recording digital signals.
Moreover, it is necessary to keep the group delay amount as constant as possible.

Next, the relationship between the symmetry of the waveform and the constancy of the group delay amount will be explained. Generally, when the waveform of a signal is expressed as a Fourier series, it is expressed as shown in the following equation. However, ω is the angular frequency, t is time, and a _p , an, and b _o are coefficients.

E(t)=a _O /2+ _∞ 〓 ⁿ⁼¹ (a _o cos nωt＋b _o sin nωt)...
(1) Solitary wave E with a symmetrical shape as shown in Figure 4
Considering (t), since E(t)=E(-t), the following equation holds true.

a _O /2+ _∞ 〓 ⁿ⁼¹ {a _o cos nωt＋b _o sin nωt}=a _O /2+ _∞ 〓 ⁿ⁼¹ {a _o cos(−nωt)＋b _o sin(−nωt)} ……(2) This When rearranged, it can be expressed as the following formula. _∞ 〓 ⁿ⁼¹ a _o {cos(nωt)−cos(−nωt)}＋ _∞ 〓 ⁿ⁼¹ b _o {sin nωt−sin(−nωt)}=0 ……(3) Therefore, this (3 ) gives the following equation.

∴ _∞ 〓 ⁿ⁼¹ 2b _o sin nωt=0 ……(4) That is, the constant 2 can be taken outside of _∞ 〓 ⁿ⁼¹ , so _∞ 〓 ⁿ⁼¹ b _o sin nωt=0 ……(5) Therefore, E(t) is expressed only by the cos term as shown in the following equation.

E(t)=a _p /2+ _∞ 〓 ⁿ⁼¹ a _o cos nωt ...(6) From this result, the independent wave E'(t) delayed by τ with respect to the independent wave E(t) (Fig. 5 reference) is expressed as the following equation.

E′(t)=a _p /2+ _∞ 〓 ⁿ⁼¹ a _o cos nω(t−τ)……(7) Expressing this equation (7) as the following equation, E′(t)=a _p /2+ _∞ 〓 ⁿ⁼¹ a _o cos (nωt+φ _o )...(8) The phase φ _o is expressed as the following equation.

φ _o =−nωτ (9) As shown in FIG. 6, the phase φ _o is proportional to the angular frequency nω, and the proportionality coefficient is −τ. That is, it can be said that independent waves that are symmetric in the time domain have linear phase-frequency characteristics. Furthermore, since the amount of group delay is expressed as the gradient of the phase-frequency characteristic, it can be seen that independent waves that are symmetric in the time domain have a constant amount of group delay.

According to the present invention, as shown in FIG. The signal is supplied to the waveform equalizer 3 via the waveform equalizer 3, and the waveform-equalized reproduced signal is output to the output terminal 4. Note that this waveform equalizer 3 can also be incorporated into the amplifier 2.

This waveform equalizer 3 has the following formula: H(s)=s+a/s+b (however, a, b>0)...
(10) has a transfer function of As shown in FIG. 8, this transfer function H(s) is expressed by _{R e}
It has a zero point at =-a and a pole at R _e =-b.

Furthermore, a<b is selected.

Next, the reason why it is preferable to select a<b will be described.
It is known that for a waveform equalizer to be stable, the pole must be in the left plane of the s-plane.
Therefore, b>0. Furthermore, when looking at the group delay characteristics of the independent reproduction wave before equalization, it can be seen that the low range is delayed. Therefore, it is necessary to advance the low frequency range, and for this purpose, it is necessary to set -ba/ab<0. Therefore, a<b is obtained from a, b>0.

As a result of considering actual independent reproduction waves, a,
b is in the range of 10 ⁶ to 10 ⁸ rad/sec, respectively;
b is a value several times to several ten times larger than a. Note that the unit of a and b is radian/sec, which is the same as the angular frequency.

A specific example (monotonic decreasing equalizer) of the waveform equalizer 3 shown in FIG. 9 is shown. t ₁₁ , t ₁₂ are input terminals, t ₂₁ ,
t ₂₂ is an output terminal, and terminals t ₁₂ and t ₂₂ are directly connected as a common terminal. Between the input and output terminals _t11 and _t21 , there is a capacitor (capacitance is c)5, a resistor (resistance value is r)
A parallel circuit 9 is connected, which consists of a resistor 7, 8 (assuming the resistance value is 1<normalized>) connected in series. Furthermore, a series circuit consisting of a resistor (resistance value is r') 10 and an inductance (inductance is l) 11 is connected between the connection midpoint of the resistors 7 and ₈ and the common terminals t 12 and t ₂₂ . 12 are connected.

Next, various characteristics of the transfer function shown in equation (10) above will be explained. First, when the transfer function in equation (10) is shown by replacing s with jω, it is expressed as in the following equation.

H(jω)=jω+a/jω+b...(11) Also, the amplitude of this transfer function H(jω) |H(jω)|,
The phase φ(ω) and the group delay amount D(ω) are as shown in the following equations, respectively.

φ(ω)=tan ^-1 (b-a)ω/ ^ω2 .+ab...(13) D(ω)=(b-a)・ω2 ^- ab/( ^ω2 + ^a2 )( ^ω2
+b ² )... (14) Tenthly, the angular frequency characteristic of the amplitude |H(jω)| in equation (12) is expressed in a graph. In Figure 10, ω<
When a, the amplitude is a/b times the amplitude of ω>. This corresponds to reducing the low frequency components of the isolated reproduction wave and narrowing the pulse width.

FIG. 11 shows a graph of the angular frequency characteristic of the group delay amount D(ω) in equation (14). In Figure 11, ω
The difference in the delay amount when ω<√, which corresponds to the group delay amount when >√, is set to approximately −ba/ab. This means that the low frequency component of the isolated reproduction wave is advanced in time by b-a/ab.

Next, a design example of the waveform equalizer 3 shown in FIG. 9 will be explained.

Assume that a=8.7702×10 ⁶ b=7.4924×10 ⁷ are obtained as the values of a and b. Thus, the transfer function H(s)
is expressed as the following equation.

H(s)s+8.7702×10 ⁶ /s+7.4924×10 ⁷ ……(
15) This transfer function H(s) can be realized by the circuit shown in FIG. The transfer function H'(s) of the circuit shown in FIG. 9 is expressed as follows.

H'(s)=s+(1-α)ω ₀ /s+(1+α)ω ₀
...(16) Thus, each of the constants c, r, r', and l in FIG. 9 can be expressed as the following equations.

c=1/2αω ₀ …(17) r=2α/1−α …(18) r′=1/r …(19) l=1/2αω ₀ …(20) (15)～( 20) From the formula, c, r, r', and l each take the following values.

c = 1.51 x 10 ^-8 , r = 7.54 r' = 0.133, l = 1.51 x 10 ^-8 Therefore, the resistance of resistors 7 and 8 with a resistance value of 1 in Fig. 9 should be set to a realistic value of 50Ω. If, c, r, r', l
have the following values:

c = 1.51 x 10 ^-8 /50 = 302 (pF) r = 7.54 x 50 = 377 (Ω) r' = 0.133 x 50 = 6.65 (Ω) l = 1.51 x 10 ^-8 x 50 = 0.755 (μH) Above When the isolated reproduced waveform shown in FIG. 1B is equalized by the waveform equalizer 3, it can be made symmetrical and thin as shown in FIG. In FIG. 12, P _a indicates an isolated reproduced waveform before equalization, and P _b indicates an isolated reproduced waveform after equalization.

Also, the amplitude, group delay amount, and frequency characteristics of the isolated reproduced waveform after equalization are shown by the curves S a2 and F _a2 in FIG. 13, respectively.
As shown in S _gd2 , the amplitude and group delay amount in the low frequency range are reduced.

Furthermore, by the waveform equalizer 3 described above, the waveform equalizer 3 shown in FIG.
When the reproduced waveform of the 3-bit digital signal is waveform-equalized, (a)' the amount of peak shift due to mutual interference of adjacent pulses is reduced.

(b)′ Even if magnetization reversals occur continuously, the peak values of the waveforms are equal to each other.

(c)′ During the period when magnetization does not reverse, the output becomes zero.
In other words, it remains constant.

Effects of the Invention According to the present invention described above, in a magnetic reproducing apparatus that uses a ring-shaped magnetic head to reproduce a magnetic recording medium on which digital signals are recorded with perpendicular magnetization, highly accurate reproduction and reproduction of digital signals can be achieved. A device that enables high-density detection and recording can be obtained.

Thus, according to the present invention, the amount of peak shift due to mutual interference of adjacent pulses is reduced, and even if magnetization reversal occurs continuously, the peak values of the waveforms become equal to each other, and the output during the period in which magnetization is not reversed is zero, i.e. A constant reproduced wave signal can be obtained.

[Brief explanation of drawings]

1 and 2 are waveform diagrams for explaining the conventional magnetic reproducing device, FIG. 3 is a characteristic curve diagram for explaining the conventional magnetic reproducing device, and FIG. 4 and 5 are for explaining the conventional magnetic reproducing device, respectively. FIG. 6 is a waveform diagram for explanation, FIG. 6 is a characteristic curve diagram for explanation of the present invention, FIG. 7 is a block diagram showing an embodiment of the magnetic reproducing device according to the present invention, and FIG. 8 is a magnetic reproduction diagram of FIG. 7. A graph for explaining the transfer function of the waveform equalizer of the device, FIG.
FIGS. 10 and 11 are characteristic curve diagrams for explaining the present invention, respectively. FIG. 12 is a waveform diagram for explaining the present invention, and FIG. FIG. 13 is a characteristic curve diagram for explaining the present invention, and FIG. 14 is a waveform diagram for explaining the present invention. 1 is a ring-shaped magnetic head, and 3 is a waveform equalizer.

Claims (1)

[Scope of Claims] 1. A ring-shaped magnetic head for reproducing a magnetic recording medium on which a digital signal is recorded with perpendicular magnetization, and a waveform equalizer to which the reproduction output from the ring-shaped magnetic head is supplied; The waveform equalizer has the following equation on the s plane: H(s)=s+a/s+b (where a<b and a, b
> 0) A magnetic reproducing device characterized in that it has a transfer function.