JPH0125131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform equalization method when reproducing a signal, and in particular, when reproducing a digital signal recorded on a magnetic recording medium, the present invention can effectively reproduce a digital signal recorded on a magnetic recording medium without reducing the level of the reproduced signal. This is an attempt to correct the peak shift of the waveform.

2. Description of the Related Art In recent years, various attempts have been made to realize high-density recording in devices that record digital signals on magnetic recording media and reproduce the recorded signals. A major factor hindering this high-density recording is
There is a pattern peak shift of the reproduced signal when the magnetization reversal interval of the digital signal is shortened. That is, for a recorded magnetization 1 as shown in FIG. 1A, the reproduced signal is a rising reproduced wave 2 for the rising edge of the recorded magnetization 1 and a rising reproduced wave for the falling edge of the recorded magnetization 1, as shown in FIG. 1 B. The reproduced signal 4 obtained by superimposing with 3 is obtained, but by this superposition,
With respect to the magnetization reversal interval h during recording, the peak interval of the reproduced signal 4 is S, which is larger than the magnetization reversal interval h, and the peak position shifts, resulting in a so-called peak shift. In particular, the smaller the magnetization reversal interval h is made to achieve high-density recording, the larger the peak shift becomes, making it impossible to reproduce correct digital signals.

In order to reduce the peak shift, as can be understood from FIG. 1, it is sufficient to reduce the spread of the bases of the erect reproduction waves 2 and 3. Therefore, a cosine equalization method has been proposed in the past. The process of this signal processing is shown in FIG. 2A to O. Signal _i (t) in Figure 2 A, which is the amplified minute reproduction signal from the recording medium.
Signals K/2 _i (t+τ)6, K/2 _i (t-τ) with waveforms similar to this reproduced signal _i (t) are present at the leading and trailing edges of
7 and subtracting their sum K/2{ _i (t + τ) + _i (t - τ) 8 shown in Figure 2E from the reproduced signal _i (t), the base of the rising reproduced wave can be calculated. It is possible to obtain the waveform shown in FIG. 2E in which the spread is removed and the peak shift of the reproduced signal is reduced.

By the way, in this cosine equalization method, the correction signal 8 to be subtracted has the same polarity as the reproduced signal 5, so the output signal 9 _p (t) after cosine equalization has a waveform with less spread at the base, but the amplitude also decreases at the same time. . When multiple stages of cosine equalization are used to suppress peak shifts, the vibration decreases accordingly, the S/N ratio of the equalized signal worsens, and peak shifts due to noise become a problem.

The present invention eliminates the above-mentioned conventional drawbacks, and creates a differential signal of the reproduced signal a predetermined time before the reproduced signal and subtracts it from the reproduced signal, and creates a differential signal of the reproduced signal after a predetermined time of the reproduced signal. By adding this to the reproduced signal, the broadening of the base of the rising reproduced wave can be effectively removed and the peak shift can be reduced without reducing the amplitude of the reproduced signal.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram showing an example of an apparatus for realizing the waveform equalization method of the present invention, and FIG.

A reproduced signal 15 (for convenience, _i
+τ). ) is the constant delay circuit 1
0 and is delayed by a fixed time τ ₁ to become an output 16 ( _i (t)) shown in FIG. 4A. Further, this reproduced signal 15 is supplied to the differentiating circuit 11. The output 16 of the constant delay circuit 10 is supplied to the addition/subtraction circuit 14 and the constant delay circuit 12 at the next stage. The output 16 of the constant delay circuit 10 is the signal to be corrected.

The constant delay circuits 10 and 12 can be realized, for example, by all-pass constant delay circuits using operational amplifiers as shown in FIG. The value of each element may satisfy the relationship of equation (2) so as to realize the transfer function of equation (1).

H(S)=V ₂ /V ₁ =G・S ² −6ω _p S+12ω _p ² /S ² +6ω _p
S+12ω _p ² ...(1) However, R ₂ R ₃ = 4R ₁ R _4Here , G gives the amplification degree, and given the time delay amount T _d , T _d = 1/ω _p ... (3) From the relationship, the value of each element can be determined. The above-mentioned all-pass constant delay filter has a constant delay amount up to a signal with a frequency of approximately τω _p . Compared to the period T of the highest frequency ω of the signal to be corrected, the delay amount τ satisfies τ<T/2 (4), so ω<2ω _p (5) is satisfied. Therefore, this all-pass constant delay filter sufficiently operates as a constant delay circuit within the signal band. The amount of delay can be easily changed by changing the capacitance value of the capacitor shown in FIG. Further, the constant delay circuit 1 may be
0,12 can be configured.

Now, the signal supplied to the differentiating circuit 11 is differentiated and amplified by a factor of _K1 , and the differential signal 17 shown in FIG. 4C is obtained as its output. This differential signal 17 is expressed as K ₁ d/dt _i (t+τ ₁ ). The delay amount τ ₁ in the constant delay circuit 10 is, for example, the differential signal 1
The delay amount τ ₁ is set so that the peak point of opposite polarity to the signal 16 to be corrected among the two peak points of the signal 16 coincides with the peak point of the signal 16. The signal 16 is further delayed by a fixed time τ ₂ in the constant delay circuit 12, differentiated in the differentiating circuit 13, and amplified by a factor of K ₂ , and the differential signal 18 shown in FIG. 4E is obtained as an output. This differential signal 18 is expressed as K ₂ d/dt _i (t-τ ₂ ). The delay amount τ ₂ in the constant delay circuit 12 is, for example, the delay amount τ at which, among the two peak points of the differential wave 18, the peak point of the same polarity with respect to the signal 16 to be corrected coincides with the peak point 16. Set to ₂ .

The differentiating circuits 11 and 13 can be constructed using operational amplifiers as shown in FIG. Amplification degree K ₁ , K ₂
can be adjusted by configuring the feedback resistance R with a variable resistor.

The differential signals 17 and 18 obtained in this way are sent to the addition/subtraction circuit 14 together with the signal 16 to be corrected.
is supplied to The addition/subtraction circuit 14 adds to the signal 16 a signal obtained by subtracting the differential signal 17 from the differential signal 18 . This is the composite signal 19 shown in Figure 1 O from the signal 16 (this composite signal is obtained when τ ₁ = τ ₂ = τ
K ₁ d/dt _i (t+τ)−K ₂ d/dt _i (t−τ). ) is equivalent to subtracting. As a result, the output of the adder/subtracter circuit 14 is a reproduced signal 20 with less width at the base. Note that this playback signal 2
0 is _p (t) = _i (t) - K ₁ d/dt _i (t + τ) - K
It is expressed as _2d /dt _i (t-τ).

The addition/subtraction circuit 14 can be constructed as shown in FIG. 7 using an operational amplifier. In the case of FIG. 7, the input/output relational expression is V ₂₀ =V ₁₆ −V ₁₇ +V ₁₈ (6). Here, the signal 16 to be corrected is V ₁₆ ,
By setting the differential signal 17 to V ₁₇ and the differential signal 18 to V ₁₈ , addition and subtraction necessary for correction can be realized.

In the above embodiment, the output signal 20 with a small width at the base is obtained because, as is clear from FIG. Since the polarity is opposite to that of the signal 16, and the peak of the reproduced signal 16 and the peak (reverse polarity) of the composite signal 19 match, by subtraction, the reproduced signal 16
The vicinity of the peak of is amplified, while the composite signal 19
has two peaks having the same polarity as the reproduced signal 16, which are located away from the peak of the reproduced signal 16, so the subtraction suppresses the spread of the base of the reproduced signal. In the conventional cosine equalization method, the polarity of the composite signal 8 to be subtracted at the peak position of the reproduced signal 5 is the same as the peak polarity, so the amplitude of the signal 9 after correction is smaller than before correction, Although the S/N ratio after correction deteriorates, in the present invention, as is clear from the above embodiments, the amplitude of the signal after correction increases. Furthermore, since it is possible to suppress the base portion of the reproduced signal and emphasize the vicinity of the peak, the effect of suppressing the width of the base is greater than that of the cosine equalization method. As a result, the required peak shift correction can be realized with fewer processing stages than the cosine equalization method.

Further, the delay amounts τ ₁ and τ ₂ are not limited to the values that align the peaks shown in the embodiment, but can be adjusted to values that can effectively suppress the width of the base, depending on the reproduced waveform. At this time, unless the values of τ ₁ and τ ₂ are selected within a range shorter than the values for aligning the peaks shown in the embodiment, suppression of the skirt broadening cannot be effectively realized. The amplification degrees K ₁ and K ₂ can also be adjusted in the same way as τ ₁ and τ ₂ . By making τ ₁ smaller than τ ₂ or making K ₁ larger than K ₂ , the leading edge of the reproduced signal can be suppressed, and τ ₁
The tail of the trailing edge of the reproduced signal can be suppressed by making τ ₂ smaller than τ ₂ or larger than K ₁ . Through such adjustment, it is possible to subtly correct the waveform of the reproduced signal.

Note that the constant delay circuits 10, 12, differentiating circuits 11, 13, and addition/subtraction circuits in the block diagram of FIG. 4 above are not limited to the circuits shown in FIGS. 5 to 7, but can be realized with other configurations. Needless to say.

As described above, according to the waveform equalization method of the present invention,
First and second differential signals of the reproduced signal of the digital signal are formed forward and backward by a predetermined time, the first differential signal is subtracted from the reproduced signal, and the second differential signal is subtracted from the reproduced signal. By adding differential signals, it is possible to suppress the spread of the waveform of the reproduced signal and reduce the peak shift, and to increase the amplitude of the peak point without lowering the level of the reproduced signal. This makes it possible to realize an excellent waveform equalization method that enables the following.

[Brief explanation of drawings]

Figures 1A and 1B are waveform diagrams showing the relationship between recording magnetization and reproduction signals, Figure 2A to O are waveform diagrams for explaining the conventional waveform equalization method, and Figure 3 is the waveform equalization method of the present invention. A block diagram showing an apparatus in one embodiment of the method, Figure 4A to 4A are waveform diagrams of signals in the main parts of the above block diagram, and Figures 5, 6, and 7 are
FIG. 2 is a circuit diagram showing an example of each circuit used in the figure. 10... Constant delay circuit, 11... Differential circuit, 12
... Constant delay circuit, 13 ... Differentiation circuit, 14 ... Addition and subtraction circuit.

Claims (1)

[Scope of Claims] 1. When reproducing a digital signal recorded on a magnetic recording medium, the first, first and second signals of the obtained reproduction signal are predetermined times before and after a predetermined time.
A waveform characterized in that a second differential signal is generated, the first differential signal located at the front is subtracted from the reproduced signal, and the second differential signal located at the rear is added to the reproduced signal. Equalization method. 2. The predetermined forward time is between the two peak points of the first differential signal located in front of the reproduced signal,
The predetermined backward time is set to be less than or equal to the time when the peak point of the opposite polarity to the reproduced signal matches the peak point of the reproduced signal, and the predetermined backward time is set within the two peak points of the second differential signal located after the reproduced signal. 2. The waveform equalization method according to claim 1, wherein the equalization time is set to be less than or equal to the time at which the peak point of the same polarity with respect to the reproduced signal and the peak point of the reproduced signal coincide.