JPH02278503A - Magnetoresistive element drive circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetoresistive element drive circuit, and particularly to a magnetoresistive element drive circuit that maintains an appropriate current density of a magnetoresistive element while simultaneously reducing external noise and noise of a sense current source circuit. The present invention relates to a magnetoresistive element drive circuit that enables.

[Conventional technology]

It is known to use a magnetoresistive element (hereinafter abbreviated as MR element) to reproduce data prerecorded on a magnetic recording medium of a predetermined length. The operating principle of this type of MR element utilizes the fact that the resistance change ΔR of the MR element changes as a function of the electromagnetic flux φ acting on the element.

Pre-recorded magnetic data is reproduced by using changes in the relationship between the increasing resistance and the electromagnetic flux.

Generally, the resistance change ΔR of the MR element is expressed as a nonlinear function (characteristic curve) of the strength of the magnetic field H acting on the element. In order to apply such an MR element as a read head for the above-mentioned magnetic recording medium, it is necessary to set it so that it operates mainly in the most linear region of the above-mentioned characteristic curve in order to ensure data reading reliability. is desirable.

Here, Japanese Patent Laid-Open No. 58-98826 discloses a prior art technique for applying a bias voltage to the MR element in order to reproduce data reserved for recording.

According to the technique described in the above-mentioned publication, one terminal of each terminal is connected to a DC voltage, and a current source as MR element biasing means is also connected to the other terminal from which the read head is taken out.

FIG. 3 shows a bias circuit for an MR resistance element in the prior art. In the figure, the range surrounded by the broken line 1 is the MR resistance element, 2 is the transistor as a sense current source of the MR resistance element, the range surrounded by the broken line 3 is the current source emitter resistance, and the range surrounded by the broken line 4 is the current source emitter resistance. A capacitor for removing an offset voltage, and 5 indicate a first stage amplifier (preamplifier).

In the figure, one end side of the MR element 1 is connected to a DC power supply VCC, and the other end side (output stage) on the MR element is connected to a sense current source by a transistor 2 and an offset removal capacitor 4, for example. It is connected to the input terminal of amplifier 5. The emitter side of the sense current source transistor 2 receives a direct current V E via the current source emitter resistor 3.
Connected to E.

[Problem to be solved by the invention]

The present inventor has revealed that the biasing method using a current source in the prior art has the following problems.

That is, at the input terminal to the circuit that processes the signal output from the MR element 1, an offset voltage is generated due to variations in the MR element resistance value.

The generation of such an offset voltage has a tendency to saturate preamplifiers commonly used in processing circuits, so it is necessary to remove the DC component, and for this purpose offset voltage removal as shown in Figure 3 4 capacitors were required. Since such a capacitor occupies a large area when mounted, there is a problem in that the entire circuit becomes large. In particular, in a multi-track magnetic tape device, the circuit configuration described above is required for each track, so increasing the size of the circuit has been a big problem.

Furthermore, there is a concern that the MR element sense current source generates an abnormal amount of noise and superimposes external noise, which may adversely affect the performance of the entire device. The current density cannot be maintained constant as the resistance value of the MR element increases, resulting in a decrease in output and an increase in heat generation in the MR element, resulting in phenomena such as wire breakage.

Since the MR element consumes a large amount of power due to its large current source, it also has the disadvantage that the integrated circuit scale is limited by the power consumption.

A main object of the present invention is to provide a magnetoresistive element drive circuit that suppresses the occurrence of offset voltage without increasing the size of the circuit and has high operational reliability.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

That is, two constant voltage fixed transistors detect the resistance change of the MR element as a current change, two fixed resistance elements convert it into the current change, and the voltage of the fixed resistance element is compared with a reference bias (ground potential) and the above Two arithmetic circuits are provided to control the voltage of the fixed resistance element to the installation voltage, and one capacitive element determines the pole of the frequency characteristic of the gain of the arithmetic circuit, making it infinite in direct current and 1 in alternating current. Two sense current source resistive elements are connected to the MR element so that the terminal voltage of the fixed resistive element becomes the DC ground voltage due to the output voltage of the inductive element circuit and the arithmetic circuit. By controlling the terminal voltage, the inductive element connected to two MR elements is simulated.

[Effect]

According to the above means, the input terminal voltage of the first stage amplifier is MR
Since the two inductive elements connected to each element are self-adjusted to a constant DC voltage, there is no need for a DC offset voltage removing capacitor compared to the case where a current source using a transistor is used. Furthermore, since the sense current source is a fixed resistance element that realizes the induction means connected to the two MR elements, it is possible to significantly reduce the power consumption of the integrated circuit by taking only the fixed resistance outside the integrated circuit. Therefore, high integration of circuits becomes possible.

In addition, since the sense current source is a resistive load that constitutes an induction means and does not include a transistor unlike the conventional technology, shot noise generated by a large current flowing through a transistor and Johnson noise generated by a resistance component are generated. reduced.

〔Example〕

FIG. 1 is a block diagram showing a differentially connected MR resistance element drive circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing details of the differentially connected MR resistance element drive circuit.

An embodiment of the present invention will be described below with reference to FIG.

The figure shows a stable drive circuit for a three-terminal MR element, in which a common-base transistor 6 for the preamplifier applies a constant voltage bias directly to the MR element 1 (RXRl and RMR2).
7, sense current source fixed resistance voltages E, F connected to the MR element 1 so that the output terminal voltages C, D (ground level in this embodiment) of the common base transistor 6.7 are constant values, A differentially connected gyrator 15 (operational amplifier 13.14) that controls the sense current source fixed resistance voltage E, F.
), and has an MR element 1 (RMRI
, RMR2) can operate in the linear part of its characteristic curve, a bias voltage is applied such that a unidirectional current flowing out from the ground potential flows through the MR element 1 (R)IRI, RMR2). .

In FIG. 1, the gyrator 75 includes a read signal preamplifier 5a, 5b and a bipolar operational amplifier 13.1.
4 and current source resistors R3 and R4, and contacts C and D.
In, MR element 1 (RXRI % R) 112
)It is connected to the. The common capacitor C1 is necessary for setting the value corresponding to the roll-off angular frequency of the gyrator by means of the active loads of the operational amplifiers 13, 14 and the common capacitor C1.

As is clear from the figure, the output stage of the MR element 1 is fixed at a constant voltage by the common base transistor 7.6. The sense current source (fixed resistance element 8.9) is connected to an operational amplifier 13.14 and a resistance element 10 realizing the inductive means.
．． 11 to the DC power supply V E H. The collector output of the common base transistor 6.7 is connected to a differentially connected gyrator 15 and an amplifier 16 as induction means. The differentially connected gyrator 15 operates to control the collector current 516 of the grounded base transistor 1 transistor 7 to a constant value and at the same time to AC couple the output signal of the MR element 1 to the preamplifier 16.

Therefore, according to the configuration shown in the figure, the magnitude of the sense current is 1. I2 is a common base transistor 7 of the MR element 1.
6 emitter potential C and MR element resistance element RMRI
determined by the resistance value of

Here, the sense current 11I2 is equal to the value obtained by dividing the emitter potential c1D by RMR.

The sense current is R)I with the emitter potentials C and D constant.
When the value of RI % RMR2 is changed, the values of the sense currents I and 12 are determined by the magnitude of the value of RIIRI 5R4R2, respectively. In this way, with this configuration, it is possible to self-adjust the current density with respect to the resistance values of R)IRI and RMR2 to maintain a constant state.

Furthermore, by adopting such a configuration, the MR element 1 (
The output impedance of RMRI, R)lR2) is extremely small within the range of the emitter resistance (10Ω) of the common-base transistor, so it is not affected by external noise. Therefore, there is an advantage that a shield is not required.

Further, the sense current source is a resistive load (fixed resistive elements 8, 9) that constitutes an induction means. Therefore, since no transistor is included, shot noise caused by a large current flowing through the transistor 2 and Johnson noise caused by a resistance component are reduced, as shown in FIG.

Furthermore, by placing only the fixed resistance elements 8 and 9 outside the integrated circuit, the power consumption of the integrated circuit can be significantly reduced, which has the advantage of allowing higher integration of the circuit. Also,
The first stage amplifier input terminal ASB voltage is self-adjusted to be a constant DC voltage by two inductive elements connected to each MR element, so DC offset voltage can be removed compared to one using a current source using a transistor. Since no additional capacitor (indicated by reference numeral 4 in FIG. 3) is required, the space required can be minimized.

FIG. 2 shows a more specific MR element drive circuit according to the present invention. This circuit configuration is symmetrical with respect to the broken line 60. The operational amplifiers 59 and 61 have an emitter-coupled amplification stage 62 (hereinafter referred to as including a symmetrical amplification stage 63) which is the first stage of a voltage amplifier. The emitter-coupled amplifier stage 62 includes a pair of emitter-coupled transistors 22,23. Current source transistor 24 is connected to voltage source V E H via bias resistor 26 . The reference voltage for the current source is connected to a fixed voltage VB.

The output terminal of the MR element RMRI is connected to the emitter of a common base type transistor 17.

The base of the transistor 17 has an MR element R)IRI.
A bias voltage V E I A S is supplied. In this embodiment, as explained below, the common base transistor 17 operates as a constant voltage bias circuit for the MR element RMRI, and also operates as a constant voltage bias circuit for the MR element R)IR.
The output terminal impedance of I is r a −k T / 9 I as the emitter resistance of transistor 17
It is expressed as e (where k is the Boltzmann constant, T is the temperature, and 1 is the emitter current).

Therefore, the impedance of the output terminal A of the MR element 1 (RxR+) can be made low, and the influence of external noise etc. can be made relatively small, so that a shield is not required. Furthermore, the transistor 17 operates as a preamplifier for the MR element 1 (R)IR) and performs triple operation.

Here, the gain (Ao
) is generally expressed as A o = R c / r e .

Further according to FIG. 2, the collector of transistor 17 is connected via resistor means 18 to voltage source V CC and to the base of transistor 19 . The collector of the transistor 19 is connected to the voltage source V. C, and the emitter is connected to one input stage of the emitter-coupled amplification stage 62 via two stages of level shift diodes 20 and 21, and the output signal of the preamplifier is sent to the next stage amplifier 1.
6. Transistor 23 on the other side of emitter-coupled amplification stage 62 is connected to the ground potential through three stages of level shift diodes 36, 35 and transistor 34, as described above.

Buffer stage 65 includes emitter-coupled amplification stage 62 and MR element 1
(RIRl) and the current source resistor R3. This buffer stage 65 is composed of transistors 32 and 33 and a bias resistor 66.
6 is connected to both emitters of transistors 32 and 33. The buffer stage 65 has a gain of about 1 and acts as a high impedance source that isolates the current source resistor R3 from the emitter-coupled amplifier stage 62.

The collectors of the pair of active load transistors 30.31 are respectively connected to the collectors of the aforementioned transistors 22.23. The emitters of the transistors 30.31 are also connected to the voltage source V via resistive means 28.29. connected to e.

A common capacitor C1 located between the operational amplifiers 59, 61 is connected to the collector of the transistor 22.

In the above description, the operational amplifier 59 located on the left side of the broken line 60 in the figure has been described, but the operational amplifier 61 located on the right side also has the same configuration as the operational amplifier 59. Since the operation at this time is the same, the explanation will be omitted here.

The above common capacitor C1 is connected to two emitter-coupled amplifier stages 6
2.63, and together with the transistor 30.31 constituting an active load, this is used to determine the pole corresponding to the roll-off angular frequency of the operational amplifier 59.61. Here the pole W of the operational amplifier 59.61. is Wo-1
It can be expressed as /(RX ・2C). In this equation, RX is the active load resistance, and C is the capacitance value of the common capacitor C1. DC gain A of this operational amplifier. Furthermore,
It is expressed as Ao = Rx / (2re).

The resistance value of □l, RMR2) increases, and the resistance value of MR element 1 (
When the voltage at the output terminal A of R)IRI) decreases, the collector current of the transistor 17 increases and the current discharge resistor 1
8, the voltage drop Δe increases. Here, operational amplifier 5
If the non-inverting input terminal E of the transistor 9 becomes larger than the inverting input terminal by Δe, the collector current 2 of the transistor 30.31 increases by Δi=gnΔe due to ΔC. The transistor 30 constitutes a current mirror with the transistor 31, and the collector current of the transistor 30 also increases by Δ1.

On the other hand, the emitter-coupled amplification stage 62 is connected to the current source transistor 2
Since the bias current due to 4 is a constant current, an increased current of △1 flows into the common capacitor C1, and due to the rise in the output terminal voltage F of the emitter-coupled amplifier stage 62, the buffer stage 65
The voltage at the output terminal B of the preamplifier increases, the current flowing to the collector of the transistor 17 of the preamplifier becomes smaller, and control is applied so that the potential at the output terminal C of the transistor 17 is always at the ground potential.

Similarly, in the opposite case, when the resistance value of MR element 1 (RMRI) decreases and the voltage at output terminal A of MR element 1 (RXRI) increases, the collector current of transistor 17 decreases, and the operational amplifier 59 increases. When the voltage at the non-inverting input terminal E becomes smaller than the inverting input terminal by Δe, the voltage at the output terminal B of the buffer stage 65 decreases, operating the output terminal C of the preamplifier transistor 17 to be equal to ground level.

For alternating current changes in data recorded on the medium, the preamplifier transistor 17 amplifies the data and the transistor 1
9 emitter followers and level soft diodes 2
0.21, it is connected in a straight line to the next stage amplifier 16 as an alternating current change around a constant DC level.

On the other hand, an emitter-coupled amplification stage 62 that functions as a differential amplifier.
is the operational amplifier 59 due to the action of the pole corresponding to the roll-off angular frequency due to the common capacitor C1 and the active load.
．． No feedback is applied to the overall amplification factor of 61.

As explained above, the present invention provides the MR element 1 (RMR
I, R) 112) is a common base transistor 17
．． 56, and the current density is maintained at the most linear region of the characteristic curve regardless of changes in the MR element resistance value. This effectively prevents wire breakage or demagnetization of information recorded on the medium.

In addition, the output terminal A of the MR element 1 is driven by low impedance, and the influence of external noise can be minimized.
No need for shield. Furthermore, the current source of the MR element is a fixed resistance load, and short circuit noise and Johnson noise due to the use of transistors can be made relatively small. Further, high integration can be achieved by attaching the current fixed resistors R3 and R4 through which a large current flows externally to the integrated circuit.

Since the preamplifier output voltage is always controlled to a constant DC voltage, direct connection between the preamplifier and the next stage amplifier is possible. Therefore, there is an effect that a capacitor for detecting a DC offset is not required and high integration is easy.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, according to the present invention, it is possible to achieve high integration of the circuit while saving space, and to obtain a highly reliable magnetoresistive element drive circuit by suppressing the influence of external noise.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a differentially connected MR resistance element drive circuit which is an embodiment of the present invention, Fig. 2 is a block diagram showing details of the differentially connected MR resistance element drive circuit, and Fig. 3 is a conventional technology. FIG. 2 is a block diagram showing an MR resistance element drive circuit in FIG. 1...MR (magnetoresistive) element, 2...Sense current source transistor, 3...Current source emitter resistance, 4...
Offset voltage removal capacitor, 5... Preamplifier, 5a, 5b... Read signal preamplifier, 6...
Base-grounded transistor, 7... Base-grounded transistor, 8-11... Fixed resistance element (R3-R6), 1
3.14... operational amplifier, 15... differential connection gyrator, 16... amplifier, 17... transistor,
18...Resistance means, 19...Transistor, 20.
... Level shift diode, 21... Level shift diode, 22... Transistor, 23... Transistor, 24... Current source transistor, 26...
Bias resistor, 25-29...resistance means, 30-34
...Transistor, 35...Level shift diode, 36...Level shift diode, 59...Operation amplifier, 6I...Operation amplifier, 62...Emitter coupled amplification stage, 63...Emitter coupled Amplification stage, 65...
- Buffer stage, 66...bias resistor, 75...gyrator, cl...common capacitor.

Claims (1)

[Claims] 1. Two constant voltage fixed transistors that detect the resistance change of the magnetoresistive element as a current change, two fixed resistance elements that convert the change in current, and compare the voltage of the fixed resistance element with a reference bias (ground potential). and two arithmetic circuits that control the voltage of the fixed resistance element to the set voltage, and one capacitive element that determines the pole of the frequency characteristic of the gain of the arithmetic circuit. An inductive element circuit having a double amplification factor, and two sense current source resistors connected to the magnetoresistive element so that the terminal voltage of the fixed resistance element becomes DC ground voltage due to the output voltage of the arithmetic circuit. A magnetoresistive element drive circuit having a magnetoresistive element.