JPH05182113A - Magnetic recording/reproducing device - Google Patents

Abstract

PURPOSE:To provide a high performance magnetic recording/reproducing device for gaining a reproduced output with little distortion by making a bias adjustment for deciding the operational center of a magnetic resistant element automatically. CONSTITUTION:The output of an MR head 1 is amplified at a head amplifier 5 and its output is inputted to a high adjustment wave detection circuit 10. The secondary high adjustment wave level of the reproduced output is measured at the high adjustment wave detection circuit 10 and the current value of a bias power source 3 is set so as to make its measured level minimum at a current setting circuit 11. Thus, the operational point of the MP head 1 is automatically set at an optimal point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus using a magnetoresistive effect element (hereinafter referred to as MR element).

[0002]

2. Description of the Related Art In recent years, devices for high-density digital magnetic recording such as DAT (Digital Audio Tape Recorder) have come into the market. In order to realize a device that performs such high density recording, the data transfer rate is also an important requirement. A method of transferring a large amount of data by moving the recording medium and the recording / reproducing head at high speed, and a method of simultaneously transmitting a large amount of data by using a plurality of recording / reproducing heads without increasing the relative speed of the recording medium and the head. Can be considered.

In the former high-speed transmission system, a head which is widely used as a reproducing head and which detects a change in magnetic flux leakage from a recording medium by using a coil is used.

When the latter parallel transmission system is adopted,
Since the relative velocity with respect to the recording medium is small, the amount of change in the leakage magnetic flux from the recording medium, which is proportional to the relative velocity, is small, and the magnetic flux change response type head has a small reproduction output and is difficult to use. Further, when using a plurality of channels, it is necessary to make a coil of several tens of turns for each head, which makes it difficult to make a head. Therefore, an MR reproducing head to which an integrated circuit technology is applied is used by using an MR element whose output changes in response to the magnetic flux itself rather than the change in magnetic flux.

FIG. 3 shows a block diagram of this conventional magnetic recording / reproducing apparatus. In FIG. 3, 1 is an MR head, 2 is a bias conductor, 3 is a bias current source, 4 is a sense current source,
Reference numeral 5 is a head amplifier, and 6 is an output terminal to the signal processing circuit section. The characteristic of the MR element is shown at 7 in FIG.
In FIG. 4, the horizontal axis represents the amount of magnetic flux and the vertical axis represents the amount of change in the resistance value of the MR element. 8 is the input signal waveform and 9 is the output signal waveform.

The operation will be described below with reference to FIGS. 3 and 4. Although only one channel is shown in FIG. 3, the operation is similar even if there are many reproduction channels.

The bias conductor 2 supplies a constant magnetic flux necessary for setting the operating point of the MR head 1 to the MR element. As shown in the operating characteristic 7 of FIG. 4, since the amount of change in the resistance value with respect to the magnetic flux of the MR element is not a linear characteristic,
Only the range that can be approximated to a narrow linear range is used. When an appropriate current is applied to the bias conductor 2 from the bias current source 3, the magnetic flux generated by this bias current is added to the MR element, and the operating point at the time of no signal input can be set.

In the MR head 1 whose operating point is set in this manner, a magnetic path is formed so that the magnetic flux reproduced from the recording medium passes through the MR element, and the reproduced magnetic flux has a resistance value of the MR element. Make a difference. The change in resistance value can be converted into a voltage by causing an appropriate current output from the sense current source 4 to flow through the MR element. This voltage change is amplified by the head amplifier 5 to obtain a signal output, and the signal is output from the output terminal 6 to a signal processing unit (not shown).

[0009]

However, in such a conventional structure, the output signal waveform is distorted unless the bias current is adjusted to select the most linear portion of the operating characteristic 7 of the MR element for operation. Therefore, there is a problem in that the reproduction characteristic is deteriorated when the operating point shifts due to element variations and changes in the surrounding environment. The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a magnetic recording / reproducing apparatus which does not require adjustment for each head and has stable operation characteristics.

[0010]

In order to achieve this object, a magnetic recording / reproducing apparatus of the present invention provides a magnetoresistive effect reproducing head for reading a signal from a digitally recorded recording medium and an operating point of the reproducing head. A bias current source that supplies a bias current to be set to a bias conductor, an amplifier that amplifies a reproduction signal from the reproduction head, a detection circuit that detects a double harmonic of the amplified reproduction signal, and a detection circuit of the detection circuit. And a current setting circuit that sets the bias current so that the output is minimized.

[0011]

According to the present invention, with the above-mentioned structure, the fluctuation of the operating point can be detected by measuring the second harmonic of the reproduced signal, and the level of the detected second harmonic can be minimized. By controlling the bias current source, the operating point can always be set to the center.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a magnetic recording / reproducing apparatus according to the first embodiment of the present invention. The same parts as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 1, the harmonic detection circuit 10 compares the output signal of the head amplifier 5 with a predetermined voltage to determine a binary value, and a band for selecting and outputting only twice the frequency of the input signal. The current setting circuit 11 is composed of a pass filter and a set value holding circuit having an appropriate time constant, and a set value updating circuit.

The operation of the magnetic recording / reproducing apparatus of this embodiment constructed as described above will be described below. According to the reproduction characteristics of the MR head shown in FIG. 4, as the operating point of the MR head moves to the + side, the lower output level of the output signal waveform 9 lowers, and a vertically asymmetrical output waveform is obtained. .. On the contrary, as the operating point of the MR head moves to the-side, the upper output level of the output signal waveform 9 lowers and an up-down asymmetric output waveform is obtained. When this signal is Fourier-transformed, it is understood that such an asymmetrical waveform has a higher second-order harmonic level as the asymmetry increases. In order to measure the second harmonic more accurately, the harmonic detection circuit 10
First, it is converted to a binary rectangular wave and the "H" level time and "
Signals having different L "level times are obtained. The larger the difference in H / L time is, the larger the second-order harmonic level is. Therefore, a band in which only twice the frequency of the input signal is passed next. The second harmonic level can be measured by using a pass filter.

The second harmonic level thus measured is
By moving the operating point of the MR head so that the level becomes smaller, it is possible to obtain the optimum operating point that is not deviated to the + side or the-side.

In the current setting circuit 11, first, a standard bias current is set, the second harmonic level at that time is measured, and the measured value is stored. Next, change the bias current value to either + or-by a small amount and measure the second harmonic level again. If the measured value is smaller than the stored value, further change the bias current, and vice versa. If it is larger than the stored value, the operation of resetting the bias current in the opposite direction is performed. When this operation is repeatedly performed, the finally set value is set to an optimum bias current that does not deviate to either positive or negative, and the operating point of the MR head 1 is set to the central portion.

In the case of a recording medium for digital recording, the signal is recorded as a combination of signals of several frequencies, so a signal level twice the highest frequency is used as a signal for measurement. In this case, the bias can be set at the same time even during signal reproduction. Further, if a specific signal pattern included in the recording / reproducing signal is detected and the above-mentioned measurement is performed only at that portion, the second harmonic of another frequency band lower than the above-mentioned measurement frequency is generated. It is possible to perform the measurement, and it is possible to improve the measurement accuracy of the signal.

As described above, according to this embodiment, by providing the harmonic detection circuit 10 and the current setting circuit 11, the operating point of the MR head can be set to the optimum point without recording a special test signal. You can

FIG. 2 is a block diagram showing a second embodiment of the present invention. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 2, 12
Is a recording medium, 13 is a recording head, 14 is a recording amplifier, 1
5 is a test signal generator.

The operation of the magnetic recording / reproducing apparatus of this embodiment constructed as described above will be described below. When the recording / reproducing method is not the digital recording but the analog recording method, as in the case of the first embodiment,
A method of simply measuring the harmonic level twice the highest frequency to be reproduced and determining the optimum operating point from that level does not work well. This is because the recorded / reproduced signal has a very complicated spectrum.

Therefore, by adopting a method of recording a sine wave or a rectangular wave, which originally does not have a second-order harmonic wave, on a recording medium as a test signal, a harmonic level twice as high is measured. The operating point of the MR head can be set as in the first embodiment. Test signal generator 1
Create a sine wave or a rectangular wave with an appropriate frequency in 5,
The signal is written in the recording medium 13 through the recording amplifier 14.

Next, the recorded portion is reproduced to reproduce the first
The optimum operating point can be obtained by adjusting the bias current of the MR head in the same manner as in the above embodiment.

As described above, in the present embodiment, by adding the test signal recording circuit composed of the test signal generator 15 and the recording amplifier 14, even in the case of analog recording, M
The operating point of the R head can be set to the optimum point.

[0024]

As described above, according to the present invention, the operating point of the MR head can be optimally adjusted and kept stable, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a magnetic recording / reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a magnetic recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing the configuration of a conventional magnetic recording / reproducing apparatus.

FIG. 4 is a characteristic diagram showing reproduction characteristics of the MR head.

[Explanation of symbols]

 1 MR reproducing head 2 Bias conductor 3 Bias current source 4 Sense current source 5 Head amplifier 10 Harmonic wave detection circuit 11 Current setting circuit 12 Recording medium 13 Recording amplifier 14 Test signal generating circuit

Claims (2)

[Claims] 1. A magnetoresistive effect reproducing head for reading a signal from a digitally recorded recording medium, a bias current source for supplying a bias current to a bias conductor for setting an operating point of the reproducing head, and a reproducing current from the reproducing head. An amplifier for amplifying a reproduction signal, a detection circuit for detecting a double harmonic of the amplified reproduction signal, and a current setting circuit for setting the bias current so that the output of the detection circuit is minimized. Magnetic recording and reproducing device. 2. A test signal recording circuit for generating a test signal and recording it on a recording medium, a magnetoresistive reproducing head for reading the signal recorded by the test signal recording circuit from the recording medium, and an operation of the reproducing head. A bias current source that supplies a bias current for setting a point to a bias conductor; an amplifier that amplifies a reproduction signal from the reproduction head; a detection circuit that detects a doubled harmonic of the amplified reproduction signal; And a current setting circuit for setting the bias current so that the output of the circuit is minimized.