JPH0414404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording signal reproducing circuit that detects and reproduces signals recorded on a magnetic recording medium through a reproducing head using a magnetoresistive element.

(Prior art) Magnetoresistive elements (hereinafter referred to as MR elements) utilize the property that the electrical resistance of a ferromagnetic material is high when the magnetic direction is parallel to the current direction and low when the magnetic direction is perpendicular to the current direction. , which detects magnetic fields and converts them into electrical signals. As an example, the characteristics of an MR element with an axis of easy magnetization in the direction of current are shown in Figure 1. In Figure 1, the horizontal axis represents the strength of the applied magnetic field, and the vertical axis represents the resistance value. There is. The change in resistance value is usually several percent, but as shown in FIG. 1, the change in resistance value with respect to changes in the magnetic field is not linear. When trying to obtain a signal proportional to the strength of the input magnetic field from the MR element, by adding a bias magnetic field shown in B in Figure 1 in advance, the resistance can be approximated within a narrow range of the strength of the input magnetic field. The value change can be regarded as a straight line.

Figure 2 shows a magnetic head (hereinafter referred to as
1 is a block diagram of a conventional magnetic recording signal reproducing circuit using an MR head. In Figure 2,
1 is an MR head, which includes an MR element _1-1 and a winding 1 for applying a bias magnetic field.
_-2 . 2 is a constant current source that supplies a direct current to convert the resistance change of the MR element 1 into a voltage signal; 3 is a current source that provides a bias magnetic field; 4
is an AC amplifier that amplifies the reproduced output signal.

When using the conventional magnetic recording signal reproducing circuit shown in FIG. 2, the reproduced output signal is approximately proportional to the strength of the input magnetic field generated from the magnetic recording medium 5 such as a magnetic tape on which the signal to be reproduced is recorded. However, the linearity cannot be said to be good.

In order to obtain good linearity, the strength of the input magnetic field must be kept within a very small range, and as a result, the reproduced output signal is also weak, resulting in a loss of S/N.

(Object of the Invention) The present invention has been made in view of the above, and is capable of reproducing magnetic recording signals that eliminates the above-mentioned drawbacks and allows reproduction output signals with good linearity, no distortion, and a good S/N ratio to be obtained. The purpose is to provide circuits.

The present invention will be explained below using examples.

(Structure and operation of the invention) FIG. 3 is a block diagram showing a first embodiment of the invention.

In the first embodiment of the present invention, the same components as those of the conventional magnetic recording signal reproducing circuit shown in FIG. 2 are denoted by the same reference numerals, and the explanation thereof will be omitted.

6 is a current source that supplies an output to the winding _1-2 in place of the current source 3, and cooperates with the winding _1-2 to provide a bias magnetic field.The current source 6 has a triangular wave, sawtooth wave, trapezoidal wave, or Outputs a sine wave current, and the current value is
The value is set to such a value that a magnetic bias of a strength as shown in C in FIG. 1, for example, is applied until the resistance of the MR element 1 _-1 reaches saturation or near saturation.

The output of the AC amplifier 4 is supplied to a T flip-flop 7, and the Q output of the T flip-flop 7 is outputted via a low-pass filter 8.

In the first embodiment of the present invention configured as described above, the MR element 1 _-1 is magnetically biased by an alternating magnetic field generated by a triangular wave, sawtooth wave, trapezoidal wave, or sine wave bias current output from the current source 6. Ru.
Furthermore, the bias magnetic field generated by the current from the current source 6 causes the resistance of the MR element 1 _-1 to reach saturation or near saturation.

Furthermore, the frequency of the current output from the current source 6 is set to be sufficiently higher than the highest frequency of the signal to be reproduced, and at least twice the highest frequency.

The operation will be described below using an example in which the current waveform output from the current source 6 is a triangular wave.

As shown in FIG. 4a, the input magnetic field applied to the MR head 1 by the magnetic recording medium 5 has a magnetic field strength of "0" until time _t1 , and continues until time _t2 , where the magnetic field strength is "a positive predetermined value". It is assumed that the strength of the magnetic field is "a predetermined negative value" until time _t3 .

The waveform of the current supplied from the current source 6 is shown in Figure 4b.
As shown. Therefore, the strength of the bias alternating magnetic field applied to the MR element 1 _-1 is as shown in Fig. 4b.
It changes in a triangular wave shape as shown in the figure.

Therefore, the resistance of MR element 1 _-1 exhibits high resistance at the time when the strength of the input magnetic field applied to MR element 1 _-1 becomes "0". As a result, the output voltage of _the MR head ₁ is as shown in FIG. The time and subsequent time when the strength of the composite magnetic field due to the magnetic field and the input magnetic field (positive predetermined value) becomes “0”
Until t ₃ , the strength of the composite magnetic field of the triangular wave-shaped bias alternating magnetic field and the input magnetic field (negative predetermined value) is “0”.
It becomes a pulse waveform at the point in time. In addition, Fig. 4c
, the voltage due to the steady-state component of the resistance of the MR element 1 _-1 is omitted, and only the varying component is shown. Figure 4c
As is clear from the above, when there is no input magnetic field, the pulses output from the MR head 1 are generated at equal intervals, but when an input magnetic field is applied, the pulse intervals become narrower and narrower alternately, and these narrower and denser intervals are caused by the input magnetic field. The order of density is proportional to the strength of the input magnetic field, and the order of density is reversed depending on the polarity of the strength of the input magnetic field.

The T flip-flop 7 receives the pulse output shown in FIG. 4c from the MR head 1, and the Q output is the fourth one.
As shown in Figure d, when there is no input magnetic field, an output pulse with a duty ratio of 50% is generated, and when an input magnetic field is applied, an output pulse with a duty ratio corresponding to the strength of the input magnetic field is generated.

The output of the T flip-flop 7 is supplied to a low-pass filter 8, which removes the frequency component of the strength of the bias alternating magnetic field.
Only the signal components are obtained as shown in FIG. 4e. This output corresponds to the input magnetic field.

In the above explanation, the current waveform from the current source 6 has been explained using a triangular wave as an example, but the same applies to sawtooth, trapezoidal, or sine waves. If it is sufficiently larger than the strength of , it is approximately the same as a triangular wave.

As explained above, according to the first embodiment of the present invention, the input magnetic field is converted into pulses with intervals corresponding to the strength and polarity, and the pulses are processed by the T flip-flop 7 and the low-pass filter 8, so that the reproduced output is The linearity of depends only on the linearity near the zero-crossing point of the current waveform of the current source 6 for applying the bias magnetic field, and does not depend on the resistance change characteristics of the MR element 1 _-1 . Therefore, the linearity of the reproduced output signal with respect to the strength of the input magnetic field can be made good, and the S/N ratio can also be improved.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a block diagram showing the configuration of a second embodiment of the present invention.

In the second embodiment of the present invention, an amplifier 4 is used instead of the T flip-flop 7 in the first embodiment of the present invention.
A multiplier 9 is connected to multiply the output of the current source 6 by a voltage obtained by converting the output current of the current source 6 into a voltage.

In the second embodiment of the present invention constructed as described above, the operation will be explained assuming that the input magnetic field is the same as in the first embodiment of the present invention and the output waveform of the current source 6 is a triangular wave.

The strength of the input magnetic field is shown in FIG. 6a, the output waveform of the current source 6 is shown in FIG. 6b, and the output voltage waveform of the MR head 1 is shown in FIG. 6c, which are the same as in FIGS. 4a to 4c.

The output voltage waveform of the multiplier 9, which is obtained by multiplying the output voltage of the MR head 1 by the voltage obtained by converting the output current of the current source 6, is as shown in FIG. 6d. That is, the multiplier 9 does not generate an output when there is no input magnetic field, but outputs a pulse voltage whose polarity and pulse interval vary depending on the strength and polarity of the input magnetic field. This output of multiplier 9 is passed through low pass filter 8
The output voltage waveform of the low-pass filter 8 is as shown in FIG. 6e.

The output voltage waveform of the low-pass filter 8 is shown in Figure 6a.
Although the shape is inverted, the polarity can be easily reversed by appropriate means, and a reproduced output signal having the same shape as that in FIG. 4e can be obtained.

In addition, an alternating voltage having the same cycle as the output current of the current source 6 is supplied to the multiplier 9 in place of the voltage obtained by converting the output current of the current source 6, and is multiplied by the output of the MR head 1 by the multiplier 9. The same is true even if In this case, the waveform of the alternating voltage needs to have a change in amplitude proportional to a change in time before and after the zero crossing point.

Alternatively, the output current of the current source 6 may be multiplied by a current obtained by converting the output voltage of the MR head 1 into a current.

In the second embodiment of the present invention, a reproduced output signal with excellent linearity and good S/N ratio can be obtained for the same reason as in the first embodiment.

Next, a third embodiment of the present invention will be described.

FIG. 7 is a block diagram showing the configuration of a third embodiment of the present invention.

In the first and second embodiments of the present invention, MR
Although a constant current source 2 supplying a direct current is used to convert the resistance value of the element 1 _-1 into a voltage, the third embodiment of the present invention uses the output current of the current source 6.

In the third embodiment of the present invention, the constant current source 2 and the multiplier 9 in the second embodiment of the present invention are omitted, and the output current of the current source 6 is branched by a distributor 10 to the winding 1 _-2. At the same time, it is supplied to the MR element 1 _-1 , and the resistance value of the MR element 1 _-1 is converted into a voltage via the distributor 10. The output voltage from MR head 1 is supplied to amplifier 4 and amplified, and the output of amplifier 4 is
The signal is outputted via a low-pass filter 8 via a steady-state component removal circuit 11 that removes a voltage component resulting from the product of the steady-state resistance value of the MR element 1 _-1 and the current of the current source 6 .

In the third embodiment of the present invention, the voltage output from the MR head 1 is the product of the resistance value of the MR head 1 and the output current of the current source 6. Furthermore, excluding the constant resistance, the resistance of the MR element 1 _-1 changes as shown in FIG. 6c due to the input magnetic field. However, since the output current waveform of the current source 6 is as shown in FIG.
The output voltage waveform of is the same as that shown in FIG. 6d. Therefore, the reproduced output signal waveform after passing through the low-pass filter 8 is as shown in FIG. 6e.

Further, the same effect can be obtained even if an alternating current having the same cycle as the output current of the current source 6 is supplied to the MR element 1 _-1 instead of the output current of the current source 6.

The linearity and S/N of the reproduced output obtained by the third embodiment of the present invention with respect to the input magnetic field are the same as those of the first embodiment of the present invention.
And it is good as in the case of the second embodiment.
Further, the constant current source 2 can be omitted.

(Effects of the Invention) As explained above, according to the present invention, a bias magnetic field is generated by the output current from a bias current source, and pulse outputs are output at intervals corresponding to the strength and polarity of the input magnetic field to the magnetic head. This pulse output was obtained from Linearity with respect to the strength of the input magnetic field depends on the linearity near the zero-crossing point of the output current waveform of the current source for applying the bias magnetic field, and does not depend on the resistance change characteristics of the MR element. Even if the change in magnetic field is large, it is possible to obtain a reproduced output signal with excellent linearity that is proportional to the strength of the input magnetic field. Furthermore, the S/N ratio of the reproduced output signal is good and there is no distortion.

Furthermore, in order to further improve the linearity, it is easy and effective to feed a part of the reproduced output signal back to the winding for applying the bias magnetic field.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the resistance change characteristics of the MR element. FIG. 2 is a block diagram of a conventional magnetic recording signal reproducing circuit. FIG. 3 is a block diagram showing the configuration of a first embodiment of the present invention. FIG. 4 is a waveform diagram for explaining the operation of the first embodiment of the present invention. FIG. 5 shows the second embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of an embodiment. FIG. 6 is a waveform diagram for explaining the operation of the second embodiment of the present invention. 7th
The figure is a block diagram showing the configuration of a third embodiment of the present invention. 1...MR head, 1 _-1 ...MR element, 1 _-2 ...
...Winding, 2... Constant current source, 6... Current source, 7...
T flip-flop, 8...low pass filter,
9...multiplier, 10...divider.

Claims (1)

[Scope of Claims] 1. A magnetic recording signal reproducing circuit for reproducing signals recorded on a magnetic recording medium by a magnetic head comprising a magnetoresistive element and a winding for generating a bias magnetic field, wherein the magnetoresistive element is A bias current source that supplies the winding with an alternating current until the resistance reaches saturation or near saturation, and multiplication that multiplies the output of the magnetic head by a signal with a period matching the period of the output current of the current source. 1. A magnetic recording signal reproducing circuit comprising: a multiplier; and a low-pass filter to which the output of the multiplier is supplied. 2. The magnetic recording signal reproducing circuit according to claim 1, wherein the output current waveform of the current source is any one of a triangular waveform, a sawtooth waveform, a trapezoidal waveform, and a sine waveform. 3. The magnetic recording signal reproducing circuit according to claim 1, wherein the signal having the same period as the output current of the current source is a voltage obtained by converting the output current of the current source.