JPH0466045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for recording and reproducing digital signals at high density on a recording medium such as a magnetic tape or a magnetic disk.

2. Description of the Related Art Configurations of Conventional Examples and Their Problems Conventionally, there have been devices for recording digital signals on recording media such as magnetic tapes and magnetic disks.
In these devices, when recording, the digital signal is subjected to appropriate digital modulation (for example, FM :
requency Modulation , MFM: Modified F
Recording is performed on the magnetic recording medium via a recording element such that the inversion position of the digital signal coincides with the magnetization inversion position of the magnetic recording medium. Furthermore, during reproduction, the recorded signal is reproduced through the reproduction element, the magnetization reversal position is converted to correspond to the reversal position of the original digital signal, and the original digital signal is demodulated.

In this recording and reproducing process, generally depending on the characteristics of the recording element, recording medium, and reproducing element,
Frequency characteristic deterioration occurs, and the reproduced signal has frequency characteristics in which high frequency components are attenuated. As a result of this deterioration of frequency characteristics, interference occurs between the waveforms corresponding to each magnetization reversal, which causes the magnetization reversal position to shift (generally, since the magnetic regeneration process is a differential process, the magnetization reversal position is determined by the reproduction signal). (This corresponds to the peak position of When this peak shift occurs, it becomes impossible to correctly demodulate the digital signal from the reproduced signal. In particular, when digital signals are recorded at high density, the frequency characteristics of the digital signals necessarily extend well into the high frequency region, that is, have many high frequency components.

Therefore, the higher the recording density, the more
The peak shift due to the deterioration of the frequency characteristics of the reproduction element or medium increases, making it impossible to correctly demodulate the digital signal.

Conventionally, a method called equalization has been used as a means to suppress such peak shifts. Cosine equalization is known as a typical equalization method.
The purpose of cosine equalization is to compensate for the deterioration of the frequency characteristics of the signal amplitude by emphasizing high frequency components using cosine characteristics as shown in FIG.
An example of a configuration for realizing this cosine equalization is shown in Figure 2.
Let's explain its operation. Reference numeral 1 denotes a reproduction signal input terminal, into which a reproduction signal from a reproduction element is input. This reproduced signal is further input to the first delay circuit 2, attenuated by an attenuator 4-a, and input to the addition circuit 5. The first delay circuit 2 delays the input signal by τ (>0) and outputs the signal. This output signal is input to the second delay circuit 3, delayed by τ, further attenuated by an attenuator 4-b, and input to the adder circuit 5. The adder circuit 5 adds the reproduced signal from the reproduced signal input terminal 1, the signal delayed by 2τ by the first and second delay circuits 2 and 3, and the output signal of the first delay circuit 2, It is output to the playback signal output terminal 6.

Now, if a signal expressed as (t-τ) is input to the reproduced signal input terminal 1, the output signal of the first delay circuit 2 will be (t), and the output signal of the second delay circuit 3 will be (t+τ). ), and the attenuator 4-
If it is attenuated to K/2 (K>0) in a and 4-b, the output signal of the adder circuit 5 is reproduced as (t)-K/2{(t-τ)+(t+τ)} The signal is output to the signal output terminal 6. If this (t)-K/2{(t-.tau.) + (t+.tau.)} is expressed in terms of amplitude characteristics on the frequency axis, it becomes 1-cos2.pi..tau., which has the frequency characteristics shown in FIG. Therefore, by changing K and τ, the frequency characteristics can be changed.

Further, when a step pulse is recorded, the reproduced signal has a form as shown in a of FIG. 3 and is called an isolated reproduced signal. The width on the time axis where the isolated reproduction signal has an amplitude of 50% of the peak value is called the half-width (W ₅₀ ), and it is well known that the narrower the half-width, the better the frequency characteristics. . Therefore, by selecting appropriate values for the constants K and τ of the cosine equalization circuit in Fig. 2, the isolated reproduced signal in Fig. 3a has a half-width of W ₅₀ '(<W ₅₀ ) as shown in Fig. 3b. It can improve the frequency characteristics. In general, in the reproduction process, if the superposition theorem holds true, any signal pattern can be expressed by a superposition of isolated reproduced signals, and as mentioned above, narrowing the half-width improves the frequency characteristics and shifts the peak due to waveform interference. is suppressed.

There is also a transversal equalization circuit that further expands cosine equalization, but this consists of a delay circuit consisting of constant delay elements with several stages of taps, and each tap output is multiplied by an appropriate constant. It is the sum of the outputs.

As described above, in order to suppress the peak shift in both the cosine equalization circuit and the transversal type equalization circuit, it is necessary to find an optimal constant that can minimize the peak shift.

However, when recording and reproducing digital signals at higher density, waveform interference in magnetization reversal increases and peak shift increases, and the cosine equalization circuit described above either cannot suppress the peak shift or has almost no suppression effect. There are areas where this is not possible. For example, if the minimum magnetization reversal interval is T _nio
This is a case where W ₅₀ /T _nio exceeds 2. In such a region, even if the half width W ₅₀ can be reduced by simply changing the cosine equalization constant, the peak shift may not be suppressed, but may even worsen.

As described above, the cosine equalization circuit may not be able to suppress peak shifts when the recording density becomes high.
Furthermore, in a transversal type equalization circuit, the number of required taps increases, making it difficult to find optimal constants.

Purpose of the Invention The present invention provides a method for recording and reproducing digital signals on magnetic recording media such as magnetic tapes and magnetic disks in high recording density areas where deterioration in frequency characteristics of reproduced signals cannot be compensated for by cosine equalization.
It is an object of the present invention to provide a magnetic recording and reproducing device that compensates for frequency characteristic deterioration and records and reproduces digital signals at high density.

Composition of the Invention The present invention records and reproduces digital signals on a magnetic recording medium, and during reproduction, the frequency remains constant as the frequency increases up to the third harmonic frequency of half the highest recording frequency. This is a magnetic recording and reproducing device that has equalization means consisting of an amplifier circuit that emphasizes the output by a peak shift rate, and a low-pass filter whose cutoff frequency is twice the highest recording frequency and whose rolloff rate is constant around the cutoff frequency. A sufficient suppression effect can be obtained, and digital signals can be recorded and reproduced at high density.

DESCRIPTION OF EMBODIMENTS Before describing embodiments, the concept of the present invention will be explained.

FIG. 4 shows an example of an isolated reproduction signal waveform of a magnetic recording/reproduction device. The half width W ₅₀ of this isolated reproduction signal is approximately 220 nsec from the figure. Now, the minimum magnetization reversal interval
When recording and reproducing an FM-modulated digital signal with T _nio of 86.2 nsec and T _nax of 174.2 nsec, it is possible to create an arbitrary The peak shift of the pattern can be estimated. A pattern with a large peak shift due to waveform interference in the FM modulation method is a pattern shown in FIG. 5, in which the magnetization reversal of the maximum magnetization reversal interval T _nax narrows inward due to the peak shift. The state of the peak shift is shown in FIG. In this case, the peak shift amount is T ₀ around the bit of the digital signal before modulation.
Then, it becomes approximately 0.17T ₀ .

Taking the ratio of the half width W ₅₀ and T _nio in Figure 4 above,
W ₅₀ /T _nio ≈2.55, and cosine equalization could not compensate for frequency characteristic deterioration and suppress peak shift. Therefore, the seventh
As shown in the figure, (t)=
A/1 + (2t/W ₅₀ ) ² (sometimes called the Lorentz waveform. A is the maximum amplitude value) is an ideal waveform (sometimes called the Nyquist waveform) in which the amplitude becomes 0 with a period of T _b ) h(t)=sin(πt/T _b )/πt/T _b・cos(πβt/T _b
)/1−2βt/T _b ) An equalization transfer function that equalizes to ² was obtained. It becomes as follows.

F()=2/W ₅₀ πAl〓

Claims (1)

[Claims] 1 Record and reproduce digital signals on a magnetic recording medium, and during reproduction, emphasize the output at a constant rate as the frequency increases up to the third harmonic frequency, which is half the highest recording frequency. 1. A magnetic recording and reproducing apparatus comprising an equalizing means comprising an amplifier circuit and a low-pass filter having a cutoff frequency twice the highest recording frequency and a constant roll-off rate near the cutoff frequency.