JPH06139699A - Magnetic reproducing device - Google Patents

Abstract

PURPOSE:To suppress a useless noise component in a high band and to improve a signal versus noise ratio in a detection point by providing an equalizing filter means specifying an impulse response for a recording signal with one bit in a signal detection point. CONSTITUTION:A regenerative signal 3 is equalized by a low-pass filter 21 and the equalizing filter 22, and an ERP 4 equalized signal 7 is outputted. The signal 7 is maximum likelihood decoded by a viterbi decodeing method by using a restraining condition due to interference between codes occurring caused by the EPR4 equalization in a viterbi decoder 5, and the decoded signal 8 is obtained. At this time, the low-pass filter 21 is a cosine roll of filter with 1/(4T) a Niquist frequency and '1' of a roll off ratio when a bit period is defined as T, and its frequency characteristic L(W) is shown by relation I. Further, the frequency characteristic E(W) of the equalizing filter 22 is constituted so as to be shown by relation II when the frequency characteristic from recording to the reproducing signal 3 is defined as H(W).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk and a magnetic reproducing apparatus for reproducing digital information recorded on a magnetic recording medium such as a digital audio tape recorder and a digital VTR.

[0002]

2. Description of the Related Art In recent years, magnetic disks and digital VTRs
As a signal detection method in such cases, attempts have been actively made to improve the recording density by using a partial response method that equalizes predetermined intersymbol interference.

Among them, an extended partial response class 4 (hereinafter referred to as EPR4) in which a value obtained by sampling an impulse response at a detection point for recording 1 bit at a bit period is {1,1, -1, -1}. ) Is attracting attention (for example, “small HDD, recording density“ G bit era ”)
Bakushin ”, Nikkei Electronics, 1991 9-3
0 (No. 537), p. 77-106).

A conventional equalizing method for a magnetic reproducing apparatus using EPR4 will be described below. FIG. 4 is a block diagram of a signal detection unit of a conventional magnetic reproducing apparatus using EPR4.

In FIG. 4, a reproduction signal 3 reproduced from a magnetic medium is equalized by a low pass filter 1 and an equalization filter 2, and an EPR4 equalized signal 4 is obtained. The signal 4 is maximum-likelihood-decoded by the Viterbi decoder 5 by the Viterbi decoding method using a constraint condition due to intersymbol interference generated by EPR4 equalization, and a decoded signal 6 is obtained.

Here, the low-pass filter 1 is a cosine roll-off filter having a Nyquist frequency of 1 / (2T), where T is the bit period, and its frequency characteristic is represented by (Equation 4). To be done.

[0007]

[Equation 4]

The roll-off rate α is generally set to about 0.5. The frequency characteristic of the equalization filter 2 is
The frequency characteristic from recording to reproduction signal 3 is H (ω)
Is expressed by (Equation 5).

[0009]

[Equation 5]

As a result, the impulse response from recording to signal 4 is as shown in FIG. As shown in FIG. 5, when the impulse response is sampled for each bit period T, {1, 1, -1, -1} are obtained at the sampling points 10, 11, 12, and 13 in order, and EPR4 equalization is performed. Has been done.

[0011]

By the way, with the above-mentioned conventional configuration and the equalization characteristics shown in (Equation 4) and (Equation 5),
When the roll-off rate α is set to 0.5, the frequency characteristic from recording to the signal 4 is as shown in FIG.

In FIG. 6, frequencies 1 / (2T) to 3
A swell of the amplitude characteristic is seen up to / (4T).
In a magnetic recording / reproducing system, generally, the higher the frequency, the smaller the output, and the noise component relatively rises. As a result, the signal-to-noise ratio of the signal 4 input to the Viterbi decoder 5 is significantly deteriorated due to the rise of the amplitude characteristic from the frequency 1 / (2T) to 3 / (4T), and the decoded signal 6 There is a problem that the code error rate decreases.

By setting the characteristic of the low-pass filter 1 so that the roll-off rate α in (Equation 4) becomes 0, the frequency 1 / (2T) to 3 /
It is possible to eliminate the rise of the amplitude characteristic up to (4T). However, to construct a low-pass filter having a steep characteristic with a roll-off rate of 0 or close to
The circuit scale becomes enormous and practically impossible.

Therefore, the present invention is to solve the above-mentioned problems.
An object of the present invention is to provide an EPR4 equalization in which an unnecessary noise component in a high frequency band is suppressed to improve a signal-to-noise ratio at a detection point, and a magnetic reproducing device which is extremely easy to realize.

[0015]

In order to achieve the above object, the magnetic reproducing apparatus of the present invention is provided with an equalizing filter means for obtaining an impulse response (Equation 6) at a signal detection point for a 1-bit recording signal. It is characterized by that.

[0016]

[Equation 6]

More specifically, as the equalization filter means, a low-pass filter means having a frequency characteristic of (Equation 7) and a frequency characteristic from recording to reproduction when the frequency characteristic is H (ω) It is characterized in that the filter means of (Equation 8) is connected in cascade.

[0018]

[Equation 7]

[0019]

[Equation 8]

Further, an equalization filter means for obtaining an impulse response (Equation 6) at a signal detection point for a 1-bit recording signal, and a Viterbi decoding means for identifying reproduced data from the output signal of the equalization filter by a Viterbi decoding method. It is also possible to adopt a configuration including and.

[0021]

With the above-described structure, the present invention can perform EPR4 equalization in which an unnecessary noise component in a high frequency band is suppressed and the signal-to-noise ratio at the detection point is improved, and the circuit scale does not become large, which is extremely realized. Is easy.

[0022]

Embodiments of the magnetic reproducing apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a signal detector of the magnetic reproducing apparatus of the present invention. In the figure, blocks or signals having the same functions as those in the conventional example of FIG.

In FIG. 1, the reproduction signal 3 reproduced from the magnetic medium is a low-pass filter 21 and an equalization filter 2.
The signal 7 equalized by 2 and equalized by EPR4 is output. The signal 7 is sent to the Viterbi decoder 5 by the EPR4.
The decoded signal 8 is obtained by the maximum likelihood decoding by the Viterbi decoding method using the constraint condition due to the intersymbol interference generated by the equalization.

Here, when the present embodiment shown in FIG. 1 and the conventional example shown in FIG. 4 are compared, the configurations are completely equivalent. However, the low pass filter 1 of the conventional example and the low pass filter 21 of the present embodiment, and the equalization filter 2 of the conventional example and the equalization filter 22 of the present embodiment have different characteristics and configurations.

The low pass filter 21 in this embodiment.
Has a Nyquist frequency of 1 where T is the bit period.
It is a cosine roll-off filter having a roll-off rate of 1 at / (4T), and its frequency characteristic L (ω) is represented by (Equation 7). Further, the frequency characteristic E (ω) of the equalization filter 22 is configured to be expressed by (Equation 8) when the frequency characteristic from the recording to the reproduction signal 3 is H (ω). As a result, the impulse response g (t) from recording to the signal 7 is given by (Equation 6). This impulse response waveform is shown in FIG.

As shown in FIG. 2, the impulse response is sampled for each bit period T.
In 32 and 33, {1, 1, -1, -1} in order
Therefore, EPR4 equalization is performed.

By the way, when the configuration shown in FIG. 1 and the equalization characteristics of this embodiment shown in (Equation 7) and (Equation 8) are used, the frequency characteristic from recording to signal 7 is as shown in FIG. become. As is clear from comparison between FIG. 3 and FIG. 6 of the conventional example, in this embodiment, the frequency 1 / (2
There is no rise in the amplitude characteristics from T) to 3 / (4T). In a magnetic recording / reproducing system, generally, the higher the frequency, the smaller the output, and the noise component relatively rises. As a result, frequency 1 / (2T) to 3 / (4T)
Compared to the conventional example in which the amplitude characteristic rises over time,
In this embodiment, the signal-to-noise ratio of the signal 4 at the detection point can be greatly improved, and the code error rate of the decoded signal 8 can be improved.

The low-pass filter shown in FIG. 1 is a cosine roll-off filter having a Nyquist frequency of 1 / (4T) and a roll-off rate of 1, where T is the bit period, as described above. is there. Therefore, it has a frequency characteristic that changes gently, and can be realized very easily with a small circuit scale. Further, the frequency characteristic H (ω) from the recording to the reproduction signal 3 has a differential characteristic due to the nature of magnetic recording, and is a characteristic close to the numerator of (Equation 8). Therefore,
The equalization filter 22 whose frequency characteristic is expressed by (Equation 8) also has a frequency characteristic that changes gently, and can be easily realized with a relatively small circuit scale.

In the present embodiment, as shown in FIG. 1, the reproduction equalizer is constituted by a cascade connection of the low pass filter 21 and the equalization filter 22, but the present invention is not limited to this. . In other words, even with other configurations, it is sufficient to include equalization filter means that makes the impulse response at the signal detection point for the 1-bit recording signal equal to (Equation 6). As a result, the same effect as that of the present embodiment can be obtained.

Further, although the Viterbi decoder is used for decoding the EPR4 equalized signal in the present embodiment, a decoder using another decoding method such as a sequential decoding method may be used.

Further, the impulse response at the signal detection point for the 1-bit recording signal does not necessarily have to be (Equation 6) itself, but is a constant multiple of (Equation 6) or within a range that can be regarded as equivalent (Equation 6). It goes without saying that the present invention is also applicable to the ones that are close to those obtained by multiplying () to (Equation 6) by a constant number.

[0033]

As described above, the present invention can perform EPR4 equalization in which an unnecessary noise component in a high frequency band is suppressed to improve a signal-to-noise ratio at a detection point, and the circuit scale does not increase. Very easy to implement.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a signal detection unit in a first embodiment of a magnetic reproducing apparatus of the present invention.

FIG. 2 is an impulse response waveform diagram of a system from recording to signal 7 in the first embodiment.

FIG. 3 is a frequency characteristic diagram of a system from recording to signal 7 in the first embodiment.

FIG. 4 is a configuration diagram of a signal detection unit of a magnetic reproducing apparatus using conventional EPR4 equalization.

FIG. 5 is an impulse response waveform diagram of a system from recording to signal 4 in a conventional magnetic reproducing apparatus.

FIG. 6 is a frequency characteristic diagram of a system from recording to signal 4 in a conventional magnetic reproducing apparatus.

[Explanation of symbols]

 5 Viterbi Decoder 21 Low pass filter 22 Equalization filter

Claims (3)

[Claims] 1. An impulse response at a signal detection point for a 1-bit recording signal is expressed by the following equation: Magnetic reproducing apparatus provided with an equalizing filter means that becomes 2. The equalizing filter means has a frequency characteristic of When the frequency characteristic from recording to reproduction is H (ω), the frequency characteristic is as follows: 2. The magnetic reproducing apparatus according to claim 1, wherein the magnetic reproducing apparatus has a structure in which the filter means of FIG. 3. Equalization filter means for obtaining an impulse response (Equation 1) at a signal detection point for a 1-bit recording signal, and Viterbi decoding means for identifying reproduced data from an output signal of the equalization filter by a Viterbi decoding method. And a magnetic reproducing device having.