JP4144132B2 - MR head playback amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reproduction amplifier for an MR head. More particularly, the present invention relates to an MR head reproducing amplifier of a voltage bias voltage sense type.
[0002]
[Prior art]
An MR head is used for reproducing recorded data in a magnetic recording / reproducing apparatus such as an HDD (hard disk). This MR head has a characteristic that the resistance value changes according to the change of the magnetic field.
[0003]
As one of such MR head reproducing methods, a voltage bias voltage sensing method is used in which a predetermined voltage is applied to the MR head and a resistance change corresponding to recording data is taken out as a voltage.
[0004]
FIG. 2 is a circuit diagram of such a conventional MR head.
Feedback is applied by the voltage-current conversion circuit Gm2 so that the reference voltage V1 is generated in the MR head RMR. That is, the constant voltage application amplifier circuit AMP1 is connected to one node voltage terminal ND1 of the MR head, and the other terminal is grounded to GND. This constant voltage application amplifier circuit AMP1 includes a voltage / current conversion circuit Gm2 (feedback amplifier), one input terminal of which is connected to the power source of the reference voltage V1, and the other input terminal is connected by feeding back the output side. ing. A transistor Q4 is connected to the output side of the voltage-current conversion circuit Gm2 for passing the detection signal from the MR head RMR and extracting it. Thereby, the voltage of the node voltage terminal ND1 of the MR head RMR is fixed at V1, and the resistance change of the MR head RMR is transmitted as the collector current of the transistor Q4. The current flowing through the MR head RMR is called a bias current IB, and is represented by IB = V1 / RMR.
[0005]
The collector current corresponding to the resistance change of the MR head RMR taken out through the transistor Q4 cuts the signal component generated in R9 according to the frequency by the capacitor C5 and amplifies it by the differential amplifier A2 to reproduce the recorded data. To do. V3 is a reference voltage source for determining the bias point of the differential amplifier A2.
[0006]
[Problems to be solved by the invention]
However, in the conventional voltage bias type reproducing amplifier, since one end of the MR head is used while being grounded, when static electricity is applied due to external noise or the like, the voltage is determined by the resistance value of the MR head. The divided current flows through the MR head. Usually, since the resistance value of the MR head is about 30 to 80Ω, a large current flows due to static electricity, causing a problem that the MR head is broken and cannot be used.
[0007]
The signal extracted as the collector current of the transistor Q4 is converted into a voltage by the resistor R9 and input to the non-inverting input terminal of the differential amplifier A2. On the other hand, the inverting input terminal of the differential amplifier A2 is only DC biased by V3. That is, there is a circuit that converts the signal component extracted as a single signal through R9 and C5 into differential.
[0008]
In such a configuration, the input portion of the differential amplifier A2 is not completely symmetric. Therefore, the ripple component of the power supply line Vcc is input to the differential amplifier A2 from the two input terminals as a differential component. For this reason, the ripple component of the power supply line Vcc cannot be completely removed, leading to deterioration of high frequency characteristics in the HDD.
[0009]
The present invention is based on the above prior art, and prevents damage when a large current flows when static electricity is applied to the MR head, and when there is a ripple in the power supply line, etc. An object of the present invention is to provide an MR head reproducing amplifier that does not adversely affect the high frequency characteristics of the output.
[0010]
[Means for Solving the Problems]
To achieve the above object, according to the present invention, one node voltage terminal of the MR head is connected to a first power supply line via a first current source, and the other node voltage terminal of the MR head is connected to the first current source. A constant current is supplied to the MR head without grounding the node voltage terminal of the MR head through a second current source having the same current value as that of the MR head. A reproduction amplifier for an MR head that outputs a voltage change at a node voltage terminal after being amplified by a differential amplifier via a DC cut capacitor, wherein the first and second amplifiers are based on the voltage between the node voltage terminals of the MR head. A feedback amplifier for controlling the current value of the second current source, and having a frequency lower than the magnetoresistive change of the MR head by recorded data as a cutoff frequency; For frequencies below the frequency, the voltage between both node voltage terminals of the MR head is fixed, and for frequencies higher than the cut-off frequency, the same constant current is supplied from the two current sources to the MR. Provided is an MR head reproduction amplifier characterized in that a current change is taken out as a voltage change by energizing the head.
[0011]
According to this configuration, since the node voltage terminal of the MR head is connected between the two current sources, when static electricity is applied, one of the node voltage terminals is grounded as in the prior art, and a certain GND level is obtained. Unlike the configuration described above, no potential difference is generated between the node voltage terminals of the MR head, and the MR head can be prevented from being destroyed by a large current.
[0012]
Also, when ripples occur in the power supply line, the voltages at both node voltage terminals of the MR head change in phase, and when the output is taken out by connecting both node voltage terminals of the MR head to a differential amplifier. The amplifier input can be made symmetric, and the high frequency characteristics of the output are not degraded.
[0014]
In addition, by setting a frequency lower than the frequency of the magnetoresistive change due to the recording data as the cut-off frequency, the feedback amplifier acts on such a low frequency change of resistance and the node voltage terminal between the MR heads. Is maintained constant, so no regenerative action is performed. On the other hand, for a resistance change at a frequency higher than the cut-off frequency, the feedback amplifier for applying a constant voltage does not act, and the voltage between the MR head node voltage terminals is affected by the MR head resistance change and the current source. A voltage change based on the current value occurs between the node voltage terminals of the MR head. This voltage change is taken out as a reproduction output signal.
[0015]
In a further preferred configuration example, a resistance sufficiently larger than the resistance value of the MR head is connected to each node voltage terminal of the MR head , and the node voltage terminal of the MR head is grounded through the resistance. .
[0016]
According to this configuration, when an error component occurs in the direct current from the two current sources due to manufacturing variations or the like, the two same resistances that are sufficiently larger than the resistance value of the MR head are connected to each node voltage of the MR head. Since the node voltage terminal of the MR head is grounded through these resistors, the midpoint voltage of the MR head is determined by the product of the error amount of the two current sources and the parallel value of the two resistors. , It can always be kept at a substantially constant GND level.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit diagram of an MR head reproducing amplifier according to an embodiment of the present invention.
[0018]
In this embodiment, transistors P2 and Q2 serving as current sources are connected to node voltage terminals ND2 and ND3 at both ends of the MR head RMR, respectively, and a voltage-current conversion circuit Gm1 (feedback amplifier) for determining the voltages at both ends of the MR head RMR. ). The higher node voltage terminal ND2 of the MR head is connected to the inverting input of the voltage / current conversion circuit Gm1, and the lower node voltage terminal ND3 is connected to the non-inverting input of the voltage / current conversion circuit Gm1 via the reference voltage V1.
[0019]
Here, R1 = R2, R3 = R4, the emitter areas of the transistors Q1 and Q2 are made the same, and the areas of the transistors P1 and P2 are made the same. Thereby, the transistors P1 and P2 become a 1: 1 current mirror, and the collector current value of the transistor P2 is equal to the collector current value of P1. Therefore, the collector currents of both transistors P2 and Q2 are the same.
Further, the voltage / current conversion circuit Gm1 feeds back the voltage across the MR head (voltage between ND2 and ND3) to V1 in accordance with the set cutoff frequency of the predetermined feedback amplifier (voltage / current conversion circuit Gm1). It takes.
[0020]
In this case, the cutoff frequency fcl2 of the feedback amplifier (voltage-current conversion circuit Gm1) is
fcl2 = (1 / 2π) * (gm1 / C1) * (RMR / R2)
Determined by However, gm1 is the transfer conductance of the voltage-current conversion circuit Gm1.
[0021]
Since the feedback amplifier operates for frequencies below this cut-off frequency, the collector currents of the transistors P2 and Q2 change according to the resistance change of the MR head RMR, so the voltage across the MR head (between ND2 and ND3) Voltage) remains at V1 and no voltage fluctuation occurs.
[0022]
On the other hand, for a frequency higher than the cut-off frequency, the feedback loop including the voltage-current conversion circuit Gm1 for holding the voltage across the MR head at the constant value V1 becomes invalid. Therefore, the voltage across the MR head changes according to the resistance change of the MR head. At this time, as described above, the collector currents of the transistors P2 and Q2 are the same and do not change, and a constant bias current IB flows. The resistance change of the MR head is generated at both ends of the MR head as a voltage signal of the product of this resistance change amount and a constant bias current IB. This voltage signal is amplified by the differential amplifier A1 via the DC cut capacitors C2 and C3, and is taken out as a reproduction signal.
[0023]
The resistors R5 and R6 are intended to maintain the midpoint voltage of the MR head at approximately the GND level when an error component occurs in the DC current of the transistors P2 and Q2 due to variations in IC manufacturing. Therefore, the resistors R5 and R6 are set sufficiently large and equal to the resistance value of the MR head, and the terminals ND2 and ND3 at both ends of the MR head are grounded through the resistors R5 and R6. In this case, the product of the DC current error component of the transistors P2 and Q2 and the parallel resistance values of R5 and R6 is the midpoint voltage of the MR head.
[0024]
V2 is a reference voltage power source for determining the bias voltage of the differential amplifier A1 via the resistors R7 and R8.
The power supply lines Vcc and Vee are set to potentials of +3 V and −3 V, for example. The power source of the reference voltage V1 is connected to the non-inverting input side (+ side) of the voltage-current conversion circuit Gm1 in the example of the figure, but may be connected to the inverting input side (− side). In this case, the polarity is reversed and the + side of the power supply is connected to the terminal ND2 side and the-side is connected to the voltage-current conversion circuit Gm1 side.
[0025]
【The invention's effect】
As described above, in the present invention, since the MR head is connected between two current sources, both terminals are respectively connected to the current source, unlike the conventional example in which one terminal of the MR head is grounded. Therefore, when static electricity is applied, no differential voltage is generated between the two terminals of the MR head, so that a large current does not flow through the MR head and it is not destroyed.
[0026]
In addition, the power supply inside a personal computer or electronic device on which an HDD or the like is mounted is superimposed with noise such as a high-frequency clock component, but even when there is such a power supply ripple, the in-phase signal components are completely symmetrical. Therefore, this in-phase noise component is completely removed through the differential amplifier. Therefore, it does not adversely affect the high frequency characteristics of HDDs and the like that require high frequency recording.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an MR head reproducing amplifier according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of a conventional MR head reproducing amplifier.
[Explanation of symbols]
ND1, ND2, ND3: node voltage terminals P1, P2, Q1, Q2, Q4: transistors A1, A2: differential amplifiers Gm1, Gm2: voltage-current conversion circuits (feedback amplifiers)
RMR: MR head

Claims (2)

One node voltage terminal of the MR head is connected to the first power supply line via the first current source, and the other node voltage terminal of the MR head is connected via the second current source having the same current value as the first current source. To the second power supply line to supply a constant current to the MR head without grounding the node voltage terminal of the MR head, and to change the voltage at each node voltage terminal of the MR head for DC cutting. An MR head reproduction amplifier that outputs after amplification by a differential amplifier via a capacitor ,
A feedback amplifier that controls current values of the first and second current sources based on a voltage between node voltage terminals of the MR head;
The feedback amplifier has a cut-off frequency that is lower than the MR resistance change of the MR head due to recording data, and between the node voltage terminals of the MR head for frequencies below the cut-off frequency. In the MR head, the voltage is fixed and the MR head is supplied with the same constant current from the two current sources for a frequency higher than the cut-off frequency, and the resistance change of the MR head is taken out as a voltage change. Playback amplifier. 2. A resistance sufficiently larger than the resistance value of the MR head is connected to each node voltage terminal of the MR head, and the node voltage terminal of the MR head is grounded through the resistance. MR head playback amplifier.

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