JP2533077B2 - Waveform equalization circuit - Google Patents

Description

The present invention relates to a waveform equalization circuit that corrects distortion of a reproduction signal or the like due to a thin film head of a magnetic disk device.

In recent years, the technical progress of magnetic disk devices has been remarkable, and the development of thin film heads has led to a marked improvement in the direction of higher density. However, the thin-film head has a characteristic that a negative peak waveform peculiar to the isolated waveform is generated at the time of reproducing the isolated waveform, and this reduces the reliability of the signal reproducing system, and therefore a countermeasure is desired.

[Conventional technology]

As a conventional waveform equalizer circuit, there is a cosine type waveform equalizer circuit whose configuration is shown in FIG. In the figure,
The reproduced signal has a delay amount τ whose input is terminated by the termination resistor Re.
After being delayed by the time τ by the delay element 1 of, the signal is input to the adder 2 having an input impedance sufficiently larger than the terminating resistance Re. At this time, the signal is reflected due to the impedance mismatch, is again delayed by the time τ by the delay element 1, is attenuated by the attenuator 3 together with the input signal by a required amount, and is added to the adder with the polarity opposite to the reflection end of the delay element 1. Is entered.

FIG. 6 shows a waveform chart of each part in FIG. In the figure, when an isolated waveform A having a half-width Wi is applied to the input terminal, a waveform B delayed from the isolated waveform A by a time τ on the output side of the delay element 1 is largely reflected by the impedance mismatch. Appears. In addition, the waveform that has passed through the delay element 1 in the opposite direction due to the reflection action is further delayed from the waveform B by time τ.
Only by delaying and forming a composite waveform C together with the isolated waveform A,
The attenuator 3 attenuates a required amount to form a waveform D, which is input to the negative side input terminal of the adder 2. Therefore, the output of the adder 2 becomes the waveform E narrowed to the half width Wo by subtracting the waveform D from the waveform A.

Such a cosine type waveform equalizing circuit is used for correction of a solitary wave reproduction waveform by a conventional ferrite head, and is similar to the reproduction waveform of the thin film head shown in the waveform (a) of FIG. When waveform equalization is performed, a peculiar negative peak in the isolated wave reproduction waveform is not removed as shown in FIG. 6B, so that a peak waveform that does not correspond to the recorded data occurs in a portion with a wide bit interval. .

[Problems to be solved by the invention]

Therefore, in the error rate characteristic, there is a drawback that the amplitude margin is particularly reduced and the reliability of the signal reproducing system is remarkably lowered. In view of the above-mentioned conventional drawbacks, the present invention has a function of removing a negative peak peculiar to a thin film head, in addition to a conventional waveform equalizing means for narrowing a half value width in a solitary wave reproduced waveform, and thereby a reproduced signal of a thin film head. It is an object of the present invention to provide a waveform equalization circuit suitable for.

[Means for solving problems]

Further, according to the present invention, according to the present invention, in a waveform equalizing circuit composed of a delay element having an output terminal terminated, an attenuator, and an adder, the delay amount of each delay element is τ ₁ ,
a series of four delay elements τ ₂ , τ ₃ , and τ ₄ , and one positive peak point serving as an input signal of the series delay element,
For an isolated waveform having two negative peak points, the time intervals between the positive peak point and each of the two negative peak points are T ₁ and T ₄ , respectively. the half width as T ₂ + T ₃ the boundary of the positive peak point, the correction value alpha _1, alpha _2, respectively _{(T 2/2)> α} 1> (- T 2/2),
_{(T 3/2)> α} 2> (- T 3/2) and when said each delay equation _{τ 1 + τ 2 = T 1} -α 1 τ 2 = T 2 + α 1 τ 3 = T This is achieved by providing the waveform equalization circuit of the present invention, which is characterized in that ₃ + α ₂ τ ₃ + τ ₄ = T ₄ −α ₂ .

[Action]

That is, the present invention utilizes the reproduced signal waveform delayed by the delay element and appropriately selects the delay amount of the delay element to cancel the negative peak in the isolated wave reproduced waveform peculiar to the thin film head and narrow the half width. As a result, the quality of the reproduction signal of the thin film head is improved.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a block diagram of a waveform equalizing circuit according to the present invention. In addition, in order to facilitate understanding of the description of the configuration and operation, the same parts as those in the previous figure are denoted by the same reference numerals.

In FIG. ₁ , the delay amounts 5 to 8 are τ ₁ , τ ₂ and τ, respectively.
₃ and τ ₄ are delay elements, Re is a terminating resistor, 9 to 12 are attenuators with attenuation amounts of K ₁ , K ₂ , K ₃ , and K ₄ , 13 is an adder, and 14 is an adder.
Indicates an input terminal, and 15 indicates an output terminal. Further, F to K are output waveform diagrams of the respective parts of FIG. 1 as shown in FIG. The operation of FIG. 1 will be described below with reference to FIG.

In both figures, the input signal applied to the input terminal 14 (the solitary wave reproduction waveform A output by the thin film head) is the delay element 5
8 through 8 and are terminated by a terminating resistor Re. on the other hand,
Five types of signals with a time difference are obtained by these four types of delay elements 5-8. Of the five types of signals, the four types of signals F, G, I and J except for the output signal H of the delay element 6 are attenuation amounts K ₁ , K ₂ , K ₃ and K ₄ , respectively. Attenuated by 12. Both of these signals are guided to the adder 13.

In the adder 13, the output signals of the attenuators 9 and 12 are positive and the attenuators 10 and 11 are positive with respect to the polarity of the signal H which is not attenuated.
The output signal of is set negative and the addition processing is performed.

FIG. 3 is a solitary wave reproduction waveform output by the thin film head as described above, and corresponds to the signal A in FIG. This waveform A has one positive peak point P and two negative peak points Q and R, and the time difference between P point and Q point is T ₁ , P point and R point.
The time difference from the point is T ₄ . Further, the time width (half-value width) of 50% level of the point P is defined as T ₂ + T ₃ with the vertical axis of the point P as the boundary.

Alpha ₁ a correction value for correcting the delay amount of each delay element to the next, as _{α 2, (T 2/2} )> α 1> (- T 2/2) (T 3/2)> α 2> (-T _3/2) and when the respective amount of delay following equation _{τ 1 + τ 2 = T 1} -α 1 τ 2 = T 2 + α 1 τ 3 = T 3 + α 2 τ 3 + τ 4 = T 4 The negative peak in the solitary wave peculiar to the thin film head can be canceled and the half width can be narrowed by obtaining −α ₂ .

First, with reference to the output waveform chart of FIG. 2, the operation of narrowing the half-value width of the isolated waveform will be described. In this figure, there are shown a case where the correction is performed with reference to the waveform H that is input to the adder without passing through the attenuator, and a case where the correction is not performed (the waveform with the letter ‘A’). Therefore, the waveform H
Will be described as the same waveform regardless of the presence or absence of correction.

When correction is performed, the adder 13 adds (actually subtracts) the waveform G and the waveform I to the waveform H having the same level value as the waveform A of the input signal and delayed by the delay amount τ ₁ + τ ₂ .
A correction value α ₁ is added to the delay amount τ ₁ of the waveform G, and a correction value α ₂ is added to the delay amount τ ₁ + τ ₂ + τ ₃ of the waveform I. By this addition (waveform superposition), a waveform having a significantly narrow half width such as the waveform K shown by the solid line is obtained at the output of the adder 13.

On the other hand, when no correction is made, that is, when α ₁ = α ₂ = 0, the adder 13 adds the waveform G ′ to the waveform H ′ which has the same level value as the input signal waveform A ′ and is delayed by the delay amount τ ₁ + τ _2. And waveform I ′ are added (actually subtracted). By this addition (waveform superposition), a waveform having a peak level which is attenuated more than necessary, such as a waveform K'shown by a chain line, is obtained at the output of the adder 13, and therefore the half value width is narrowed to improve the resolution. Rather, the S / N deterioration due to the attenuation of the peak value becomes larger. That is, the waveform G'and the waveform I'in which the correction value is not added to the delay amount are the peaks of the waveforms G'and I'at the temporal position of the half-value width for the purpose of narrowing the half-value width of the isolated waveform (waveform H). Since the points are coincident with each other and superposition with the isolated waveform is performed, the same amount of subtraction is performed on the peak level side of the isolated waveform as on the zero level side. Therefore, the obtained waveform is like the waveform K ′ shown by the chain line. The peak level is a waveform that is attenuated more than necessary. In order to avoid this peak level attenuation, the correction amount α is added to the delay amount in the waveform G described above.
₁ is added so that the peak point of the waveform is shifted from the temporal position of the half width to the zero level side (left side of the paper) by α ₁ , and in waveform I, the correction value α ₂ is added to the delay amount. Correction is performed by shifting the peak point of the waveform by α ₂ from the temporal position of the half width to the zero level side (right side of the paper surface).

The range of the correction values α ₁ and α ₂ is 50% of the full width at half maximum, and is set within this range. Positive positive side closer to the peak point of the concrete to the isolated waveform on the border of the temporal position of the half-value width, as a negative side away Conversely, the following correction value alpha ₁ of the formula described above (T _{2/2) > α 1> (- T 2} /2), the correction value alpha ₂ is _{(T 3/2)> α} 2> (- T 3/2) , respectively are set. The actual setting is selected so that the maximum value of the amplitude margin and the phase margin of the demodulation circuit that demodulates the reproduced waveform whose waveform is equalized is obtained.

Next, the action of canceling the negative peak of the isolated waveform will be described. In this case, the adder 13 adds the waveform F and the waveform J to the waveform H. Note that the correction values α ₁ and α ₂ are also added to the delay amounts in the waveforms F and J. This correction value is
Since the correction values α ₁ and α ₂ are added to the G and I waveforms and the peak points of these waveforms G and I are shifted by α ₁ and α ₂ from the time position of the half width of the isolated waveform H, these waveforms G and I ,
The signal level at the tail of I (near zero level) affects the negative peak of the isolated waveform, and the negative peak is completely canceled in the waveform (corresponding to waveforms F ′ and J ′) in which the correction value is not added. It is provided to correct the failure (waveform K'shown by the chain line).

More specifically, the waveform F has a peak point shifted by α _{1 to} the right side of the drawing from the negative peak point position of the isolated waveform H, and the waveform J has a peak point from the negative peak point position of the isolated waveform H. Is also shifted by α _{2 to} the left side of the page. Further, the waveform F is attenuated by the attenuator 9 so that its positive peak value Q ₁ becomes equal to one negative peak value Q ₀ of the isolated waveform H,
The waveform J is attenuated by the attenuator 12 so that its positive peak value R ₁ becomes equal to the other negative peak value R ₀ of the isolated waveform H. Therefore, by superimposing the waveforms F and J on the waveform H, a waveform in which the negative peak is removed, such as the waveform K shown by the solid line, is obtained.

As a result of the addition processing as described above, a waveform such as a waveform K shown by a solid line is obtained in which the peak level is not attenuated more than necessary, the half-value width is greatly narrowed, and there is no negative peak. In order to compare this waveform with the conventional example,
It is also shown in FIG.

〔The invention's effect〕

As described in detail above, according to the waveform equalizing circuit of the present invention, it is possible to remove the negative peak in the solitary wave reproduction waveform peculiar to the thin film head, and the half width can be narrowed. Therefore, the error rate characteristic is improved. It also has a great effect on improving the reliability of the thin film head signal reproducing system.

[Brief description of drawings]

FIG. 1 is a block diagram of a waveform equalizing circuit according to the present invention, FIG. 2 is an output waveform diagram of each part of FIG. 1, FIG. 3 is a solitary wave reproduction waveform diagram output from a thin film head, and FIG. 4 is a solitary wave reproduction. FIG. 5 is a diagram showing a comparative example of the equivalent waveform (b) of the conventional example with respect to the waveform (a) and the equalized waveform (c) of the present invention. FIG. 5 is a block diagram of a conventional cosine type waveform equalization circuit. FIG. 5 shows an output waveform diagram of each part. In the figure, the delay amounts 5 to 8 are τ ₁ , τ ₂ , τ ₃ and τ, respectively.
_The delay element is ₄ , 9 to 12 are attenuators, 13 is an adder, P is a positive peak point, and Q and R are negative peak points.

Claims (1)

(57) [Claims] 1. A waveform equalizer comprising a delay element having an output terminal terminated by a terminating resistor, an attenuator, and an adder, wherein the delay elements have delay amounts of τ ₁ , τ ₂ , τ ₃ , The positive peak is composed of four series delay elements of τ ₄ and has an isolated waveform having one positive peak point serving as an input signal of the series delay element and two negative peak points. Points and
The time intervals between the two negative peak points are T ₁ and T ₄ , respectively, and the half-value width of the positive waveform of the isolated waveform is T ₂ + T ₃ with the positive peak point as the boundary, and the correction value α ₁ , alpha _2, respectively _{(T 2/2)> α} 1> (- T 2/2), (T 3/2)> α 2> (- T 3
/ 2), the respective delay amounts are given by the following equations τ ₁ + τ ₂ = T ₁ −α ₁ τ ₂ = T ₂ + α ₁ τ ₃ = T ₃ + α ₂ τ ₃ + τ ₄ = T ₄ −α ₂ . Waveform equalization circuit characterized by being obtained by.